Hydrogen is a chemical element with atomic number 1 which means there are 1 protons and 1 electrons in the atomic structure. The chemical symbol for Hydrogen is H.
With a standard atomic weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.
Discoverer: Ramsey, Sir William and Cleve, Per Teodor
Element Category: Noble gas
Helium is a chemical element with atomic number 2 which means there are 2 protons and 2 electrons in the atomic structure. The chemical symbol for Helium is He.
It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements.
Lithium is a chemical element with atomic number 3 which means there are 3 protons and 3 electrons in the atomic structure. The chemical symbol for Lithium is Li.
It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element. Like all alkali metals, lithium is highly reactive and flammable, and is stored in mineral oil.
Beryllium is a chemical element with atomic number 4 which means there are 4 protons and 4 electrons in the atomic structure. The chemical symbol for Beryllium is Be.
Beryllium is a hard, grayish metal naturally found in mineral rocks, coal, soil, and volcanic dust. The commercial use of beryllium requires the use of appropriate dust control equipment and industrial controls at all times because of the toxicity of inhaled beryllium-containing dusts that can cause a chronic life-threatening allergic disease in some people called berylliosis.
Discoverer: Davy, Sir H. and Thénard, L.-J. and Gay-Lussac, L.-J.
Element Category: Metalloids
Boron is a chemical element with atomic number 5 which means there are 5 protons and 5 electrons in the atomic structure. The chemical symbol for Boron is B.
Significant concentrations of boron occur on the Earth in compounds known as the borate minerals. There are over 100 different borate minerals, but the most common are: borax, kernite, ulexite etc. Natural boron consists primarily of two stable isotopes, 11B (80.1%) and 10B (19.9%). In nuclear industry boron is commonly used as a neutron absorber due to the high neutron cross-section of isotope 10B.
Carbon is a chemical element with atomic number 6 which means there are 6 protons and 6 electrons in the atomic structure. The chemical symbol for Carbon is C.
It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in the Earth’s crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen.
Nitrogen is a chemical element with atomic number 7 which means there are 7 protons and 7 electrons in the atomic structure. The chemical symbol for Nitrogen is N.
Nitrogen is a colourless, odourless unreactive gas that forms about 78% of the earth’s atmosphere. Liquid nitrogen (made by distilling liquid air) boils at 77.4 kelvins (−195.8°C) and is used as a coolant.
Discoverer: Priestley, Joseph and Scheele, Carl Wilhelm
Element Category: Nonmetals
Oxygen is a chemical element with atomic number 8 which means there are 8 protons and 8 electrons in the atomic structure. The chemical symbol for Oxygen is O.
Oxygen is a colourless, odourless reactive gas, the chemical element of atomic number 8 and the life-supporting component of the air. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.
Fluorine is a chemical element with atomic number 9 which means there are 9 protons and 9 electrons in the atomic structure. The chemical symbol for Fluorine is F.
Fluorine is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. As the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.
Neon is a chemical element with atomic number 10 which means there are 10 protons and 10 electrons in the atomic structure. The chemical symbol for Neon is Ne.
Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air.
Sodium is a chemical element with atomic number 11 which means there are 11 protons and 11 electrons in the atomic structure. The chemical symbol for Sodium is Na.
Sodium is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell that it readily donates, creating a positively charged atom—the Na+ cation.
Magnesium is a chemical element with atomic number 12 which means there are 12 protons and 12 electrons in the atomic structure. The chemical symbol for Magnesium is Mg.
Magnesium is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column (group 2, or alkaline earth metals) of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.
Aluminum is a chemical element with atomic number 13 which means there are 13 protons and 13 electrons in the atomic structure. The chemical symbol for Aluminum is Al.
Aluminium is a silvery-white, soft, nonmagnetic, ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth’s crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below.
Silicon is a chemical element with atomic number 14 which means there are 14 protons and 14 electrons in the atomic structure. The chemical symbol for Silicon is Si.
Silicon is a hard and brittle crystalline solid with a blue-grey metallic lustre, it is a tetravalent metalloid and semiconductor.
Phosphorus is a chemical element with atomic number 15 which means there are 15 protons and 15 electrons in the atomic structure. The chemical symbol for Phosphorus is P.
As an element, phosphorus exists in two major forms—white phosphorus and red phosphorus—but because it is highly reactive, phosphorus is never found as a free element on Earth. At 0.099%, phosphorus is the most abundant pnictogen in the Earth’s crust.
Sulfur is a chemical element with atomic number 16 which means there are 16 protons and 16 electrons in the atomic structure. The chemical symbol for Sulfur is S.
Sulfur is abundant, multivalent, and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula S8. Elemental sulfur is a bright yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for gold, platinum, iridium, tellurium, and the noble gases.
Chlorine is a chemical element with atomic number 17 which means there are 17 protons and 17 electrons in the atomic structure. The chemical symbol for Chlorine is Cl.
Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity, behind only oxygen and fluorine.
Discoverer: Ramsay, Sir William and Strutt, John (Lord Rayleigh)
Element Category: Noble gas
Argon is a chemical element with atomic number 18 which means there are 18 protons and 18 electrons in the atomic structure. The chemical symbol for Argon is Ar.
Argon is the third-most abundant gas in the Earth’s atmosphere, at 0.934% (9340 ppmv). Argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning.
Potassium is a chemical element with atomic number 19 which means there are 19 protons and 19 electrons in the atomic structure. The chemical symbol for Potassium is K.
Potassium was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Naturally occurring potassium is composed of three isotopes, of which 40K is radioactive.
Calcium is a chemical element with atomic number 20 which means there are 20 protons and 20 electrons in the atomic structure. The chemical symbol for Calcium is Ca.
Calcium is an alkaline earth metal, it is a reactive pale yellow metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth’s crust and the third most abundant metal, after iron and aluminium.
Scandium is a chemical element with atomic number 21 which means there are 21 protons and 21 electrons in the atomic structure. The chemical symbol for Scandium is Sc.
Scandium is a silvery-white metallic d-block element, it has historically been sometimes classified as a rare-earth element, together with yttrium and the lanthanides.
Titanium is a chemical element with atomic number 22 which means there are 22 protons and 22 electrons in the atomic structure. The chemical symbol for Titanium is Ti. Titanium is a lustrous transition metal with a silver color, low density, and high strength. Titanium is resistant to corrosion in sea water, aqua regia, and chlorine. Titanium can be used in surface condensers. These condensers use tubes that are usually made of stainless steel, copper alloys, or titanium depending on several selection criteria (such as thermal conductivity or corrosion resistance). Titanium condenser tubes are usually the best technical choice, however titanium is very expensive material.
Discoverer: Del Rio, Andrés Manuel (1801) and Sefström, Nils Gabriel (1830)
Element Category: Transition metals
Vanadium is a chemical element with atomic number 23 which means there are 23 protons and 23 electrons in the atomic structure. The chemical symbol for Vanadium is V.
Vanadium is a hard, silvery grey, ductile, and malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer (passivation) stabilizes the free metal somewhat against further oxidation.
Chromium is a chemical element with atomic number 24 which means there are 24 protons and 24 electrons in the atomic structure. The chemical symbol for Chromium is Cr.
Chromium is a steely-grey, lustrous, hard and brittle metal4 which takes a high polish, resists tarnishing, and has a high melting point. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel.
Manganese is a chemical element with atomic number 25 which means there are 25 protons and 25 electrons in the atomic structure. The chemical symbol for Manganese is Mn.
Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.
Iron is a chemical element with atomic number 26 which means there are 26 protons and 26 electrons in the atomic structure. The chemical symbol for Iron is Fe.
Iron is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth’s outer and inner core. It is the fourth most common element in the Earth’s crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars.
Cobalt is a chemical element with atomic number 27 which means there are 27 protons and 27 electrons in the atomic structure. The chemical symbol for Cobalt is Co.
Cobalt is found in the Earth’s crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
Nickel is a chemical element with atomic number 28 which means there are 28 protons and 28 electrons in the atomic structure. The chemical symbol for Nickel is Ni.
Nickel is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile.
Copper is a chemical element with atomic number 29 which means there are 29 protons and 29 electrons in the atomic structure. The chemical symbol for Copper is Cu.
Copper is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a reddish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins.
Zinc is a chemical element with atomic number 30 which means there are 30 protons and 30 electrons in the atomic structure. The chemical symbol for Zinc is Zn.
In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state (+2), and the Zn2+ and Mg2+ ions are of similar size.
Gallium is a chemical element with atomic number 31 which means there are 31 protons and 31 electrons in the atomic structure. The chemical symbol for Gallium is Ga.
Gallium has similarities to the other metals of the group, aluminium, indium, and thallium. Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in zinc ores and in bauxite.
Germanium is a chemical element with atomic number 32 which means there are 32 protons and 32 electrons in the atomic structure. The chemical symbol for Germanium is Ge.
Germanium is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Pure germanium is a semiconductor with an appearance similar to elemental silicon.
Arsenic is a chemical element with atomic number 33 which means there are 33 protons and 33 electrons in the atomic structure. The chemical symbol for Arsenic is As.
Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid.
Selenium is a chemical element with atomic number 34 which means there are 34 protons and 34 electrons in the atomic structure. The chemical symbol for Selenium is Se.
Selenium is a nonmetal with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth’s crust.
Bromine is a chemical element with atomic number 35 which means there are 35 protons and 35 electrons in the atomic structure. The chemical symbol for Bromine is Br.
Bromine is the third-lightest halogen, and is a fuming red-brown liquid at room temperature that evaporates readily to form a similarly coloured gas. Its properties are thus intermediate between those of chlorine and iodine.
Discoverer: Ramsay, Sir William and Travers, Morris
Element Category: Noble gas
Krypton is a chemical element with atomic number 36 which means there are 36 protons and 36 electrons in the atomic structure. The chemical symbol for Krypton is Kr.
Krypton is a member of group 18 (noble gases) elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps.
Discoverer: Bunsen, Robert Wilhelm and Kirchhoff, Gustav Robert
Element Category: Alkali metals
Rubidium is a chemical element with atomic number 37 which means there are 37 protons and 37 electrons in the atomic structure. The chemical symbol for Rubidium is Rb.
Rubidium is a soft, silvery-white metallic element of the alkali metal group, with an atomic mass of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air.
Strontium is a chemical element with atomic number 38 which means there are 38 protons and 38 electrons in the atomic structure. The chemical symbol for Strontium is Sr.
Strontium is an alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly reactive chemically.
Yttrium is a chemical element with atomic number 39 which means there are 39 protons and 39 electrons in the atomic structure. The chemical symbol for Yttrium is Y.
Yttrium is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a “rare-earth element”.
Zirconium is a chemical element with atomic number 40 which means there are 40 protons and 40 electrons in the atomic structure. The chemical symbol for Zirconium is Zr. Zirconium is a lustrous, grey-white, strong transition metal that resembles hafnium and, to a lesser extent, titanium. Zirconium is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. Zirconium is widely used as a cladding for nuclear reactor fuels.
Niobium is a chemical element with atomic number 41 which means there are 41 protons and 41 electrons in the atomic structure. The chemical symbol for Niobium is Nb.
Niobium is a soft, grey, ductile transition metal, often found in the minerals pyrochlore (the main commercial source for niobium) and columbite.
Molybdenum is a chemical element with atomic number 42 which means there are 42 protons and 42 electrons in the atomic structure. The chemical symbol for Molybdenum is Mo.
Molybdenum a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is used in steel alloys, including high-strength alloys and superalloys.
Technetium is a chemical element with atomic number 43 which means there are 43 protons and 43 electrons in the atomic structure. The chemical symbol for Technetium is Tc.
Technetium is the lightest element whose isotopes are all radioactive; none are stable. Nearly all technetium is produced synthetically, and only minute amounts are found in the Earth’s crust. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.
Ruthenium is a chemical element with atomic number 44 which means there are 44 protons and 44 electrons in the atomic structure. The chemical symbol for Ruthenium is Ru.
Ruthenium is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemicals.
Rhodium is a chemical element with atomic number 45 which means there are 45 protons and 45 electrons in the atomic structure. The chemical symbol for Rhodium is Rh.
Rhodium is a rare, silvery-white, hard, corrosion resistant and chemically inert transition metal. It is a noble metal and a member of the platinum group.
Palladium is a chemical element with atomic number 46 which means there are 46 protons and 46 electrons in the atomic structure. The chemical symbol for Palladium is Pd.
Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.
Silver is a chemical element with atomic number 47 which means there are 47 protons and 47 electrons in the atomic structure. The chemical symbol for Silver is Ag.
Silver is a soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is found in the Earth’s crust in the pure, free elemental form (“native silver”), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite.
Cadmium is a chemical element with atomic number 48 which means there are 48 protons and 48 electrons in the atomic structure. The chemical symbol for Cadmium is Cd.
Cadmium is a soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. In nuclear industry cadmium is commonly used as a thermal neutron absorber due to very high neutron absorption cross-section of 113Cd. 113Cd has specific absorption cross-section.
Discoverer: Reich, Ferdinand and Richter, Hieronymus
Element Category: Post-transition metals
Indium is a chemical element with atomic number49 which means there are 49 protons and 49 electrons in the atomic structure. The chemical symbol for Indium is In.
Indium is a post-transition metal that makes up 0.21 parts per million of the Earth’s crust. Very soft and malleable, indium has a melting point higher than sodium and gallium, but lower than lithium and tin. Chemically, indium is similar to gallium and thallium.
Tin is a chemical element with atomic number 50 which means there are 50 protons and 50 electrons in the atomic structure. The chemical symbol for Tin is Sn.
Tin is a post-transition metal in group 14 of the periodic table. It is obtained chiefly from the mineral cassiterite, which contains tin dioxide. The first alloy used on a large scale was bronze, made of tin and copper, from as early as 3000 BC.
Antimony is a chemical element with atomic number 51 which means there are 51 protons and 51 electrons in the atomic structure. The chemical symbol for Antimony is Sb.
Antimony is a lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite. Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name, kohl.
Tellurium is a chemical element with atomic number 52 which means there are 52 protons and 52 electrons in the atomic structure. The chemical symbol for Tellurium is Te.
Tellurium is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur. It is occasionally found in native form as elemental crystals. Tellurium is far more common in the universe as a whole than on Earth. Its extreme rarity in the Earth’s crust, comparable to that of platinum.
Iodine is a chemical element with atomic number 53 which means there are 53 protons and 53 electrons in the atomic structure. The chemical symbol for Iodine is I.
Iodine is the heaviest of the stable halogens, it exists as a lustrous, purple-black metallic solid at standard conditions that sublimes readily to form a violet gas. Iodine is the least abundant of the stable halogens, being the sixty-first most abundant element. It is even less abundant than the so-called rare earths. It is the heaviest essential mineral nutrient.
Discoverer: Ramsay, William and Travers, Morris William
Element Category: Noble gas
Xenon is a chemical element with atomic number 54 which means there are 54 protons and 54 electrons in the atomic structure. The chemical symbol for Xenon is Xe.
Xenon is a colorless, dense, odorless noble gas found in the Earth’s atmosphere in trace amounts. The name xenon for this gas comes from the Greek word ξένον [xenon], neuter singular form of ξένος [xenos], meaning ‘foreign(er)’, ‘strange(r)’, or ‘guest’. In nuclear industry, especially artificial xenon 135 has a tremendous impact on the operation of a nuclear reactor.
Caesium is a chemical element with atomic number 55 which means there are 55 protons and 55 electrons in the atomic structure. The chemical symbol for Caesium is Cs.
Caesium is a soft, silvery-gold alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium.
Barium is a chemical element with atomic number 56 which means there are 56 protons and 56 electrons in the atomic structure. The chemical symbol for Barium is Ba.
Barium is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. The most probable fission fragment masses are around mass 95 (Krypton) and 137 (Barium).
137.33 amu
57-71
Lanthanoids
Lanthanoids
Discoverer: —
Element Category:
Lanthanoids comprise the 15 metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.
Discoverer: Coster, Dirk and De Hevesy, George Charles
Element Category: Transition metals
Hafnium is a chemical element with atomic number 72 which means there are 72 protons and 72 electrons in the atomic structure. The chemical symbol for Hafnium is Hf. Hafnium is a lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Hafnium’s large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.
Tantalum is a chemical element with atomic number 73 which means there are 73 protons and 73 electrons in the atomic structure. The chemical symbol for Tantalum is Ta.
Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion-resistant.
Discoverer: Elhuyar, Juan José and Elhuyar, Fausto
Element Category: Transition metals
Tungsten is a chemical element with atomic number 74 which means there are 74 protons and 74 electrons in the atomic structure. The chemical symbol for Tungsten is W.
Tungsten is a rare metal found naturally on Earth almost exclusively in chemical compounds. Tungsten is an intrinsically brittle and hard material, making it difficult to work.
Discoverer: Noddack, Walter and Berg, Otto Carl and Tacke, Ida
Element Category: Transition metals
Rhenium is a chemical element with atomic number 75 which means there are 75 protons and 75 electrons in the atomic structure. The chemical symbol for Rhenium is Re.
Rhenium is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table.
Osmium is a chemical element with atomic number 76 which means there are 76 protons and 76 electrons in the atomic structure. The chemical symbol for Osmium is Os. Osmium is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with a density of 22.59 g/cm3. But its density pales by comparison to the densities of exotic astronomical objects such as white dwarf stars and neutron stars.
Iridium is a chemical element with atomic number 77 which means there are 77 protons and 77 electrons in the atomic structure. The chemical symbol for Iridium is Ir.
Iridium is a very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium). It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C.
Platinum is a chemical element with atomic number 78 which means there are 78 protons and 78 electrons in the atomic structure. The chemical symbol for Platinum is Pt. Platinum is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Platinum is one of the least reactive metals. It has remarkable resistance to corrosion, even at high temperatures, and is therefore considered a noble metal. Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry.
Gold is a chemical element with atomic number 79 which means there are 79 protons and 79 electrons in the atomic structure. The chemical symbol for Gold is Au.
Gold is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold is thought to have been produced in supernova nucleosynthesis, from the collision of neutron stars.
Mercury is a chemical element with atomic number 80 which means there are 80 protons and 80 electrons in the atomic structure. The chemical symbol for Mercury is Hg.
Mercury is commonly known as quicksilver and was formerly named hydrargyrum. Mercury is a heavy, silvery d-block element, mercury is the only metallic element that is liquid at standard conditions for temperature and pressure.
Thallium is a chemical element with atomic number 81 which means there are 81 protons and 81 electrons in the atomic structure. The chemical symbol for Thallium is Tl.
Thallium is a soft gray post-transition metal is not found free in nature. Commercially, thallium is produced as a byproduct from refining of heavy metal sulfide ores. Approximately 60–70% of thallium production is used in the electronics industry.
Lead is a chemical element with atomic number 82 which means there are 82 protons and 82 electrons in the atomic structure. The chemical symbol for Lead is Pb.
Lead is a heavy metal that is denser than most common materials. Lead is soft and malleable, and has a relatively low melting point. Lead is widely used as a gamma shield. Major advantage of lead shield is in its compactness due to its higher density. Lead has the highest atomic number of any stable element and concludes three major decay chains of heavier elements.
Bismuth is a chemical element with atomic number 83 which means there are 83 protons and 83 electrons in the atomic structure. The chemical symbol for Bismuth is Bi.
Bismuth is a brittle metal with a silvery white color when freshly produced, but surface oxidation can give it a pink tinge. Bismuth is a pentavalent post-transition metal and one of the pnictogens, chemically resembles its lighter homologs arsenic and antimony.
Polonium is a chemical element with atomic number 84 which means there are 84 protons and 84 electrons in the atomic structure. The chemical symbol for Polonium is Po.
Polonium is a rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth.
Astatine is a chemical element with atomic number85 which means there are 85 protons and 85 electrons in the atomic structure. The chemical symbol for Astatine is At.
Astatine is the rarest naturally occurring element on the Earth’s crust. It occurs on Earth as the decay product of various heavier elements. The bulk properties of astatine are not known with any certainty.
Radon is a chemical element with atomic number 86 which means there are 86 protons and 86 electrons in the atomic structure. The chemical symbol for Radon is Rn.
Radon is a radioactive, colorless, odorless, tasteless noble gas. Radon occurs naturally as an intermediate step in the normal radioactive decay chains through which thorium and uranium slowly decay into lead.
Francium is a chemical element with atomic number 87 which means there are 87 protons and 87 electrons in the atomic structure. The chemical symbol for Francium is Fr.
Francium is an alkali metal, that has one valence electron. Francium is the second-least electronegative element, behind only caesium, and is the second rarest naturally occurring element (after astatine). Francium is a highly radioactive metal that decays into astatine, radium, and radon.
Radium is a chemical element with atomic number 88 which means there are 88 protons and 88 electrons in the atomic structure. The chemical symbol for Radium is Ra.
Pure radium is silvery-white alkaline earth metal. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226.
226 amu
89-103
Actinoids
Actinoids
Discoverer: —
Element Category:
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.
Discoverer: Scientists at Dubna, Russia (1964)/Albert Ghiorso et. al. (1969)
Element Category: Transition metal
Rutherfordium is a chemical element with atomic number 104 which means there are 104 protons and 104 electrons in the atomic structure. The chemical symbol for Rutherfordium is Rf.
Discoverer: Scientists at Dubna, Russia (1967)/Lawrence Berkeley Laboratory (1970)
Element Category: Transition metal
Dubnium is a chemical element with atomic number 105 which means there are 105 protons and 105 electrons in the atomic structure. The chemical symbol for Dubnium is Db.
Seaborgium is a chemical element with atomic number 106 which means there are 106 protons and 106 electrons in the atomic structure. The chemical symbol for Seaborgium is Sg.
Bohrium is a chemical element with atomic number 107 which means there are 107 protons and 107 electrons in the atomic structure. The chemical symbol for Bohrium is Bh.
Discoverer: Armbruster, Paula and Muenzenberg, Dr. Gottfried
Element Category: Transition metal
Hassium is a chemical element with atomic number 108 which means there are 108 protons and 108 electrons in the atomic structure. The chemical symbol for Hassium is Hs. It is a synthetic element (first synthesised at Hasse in Germany) and radioactive. The most stable known isotope, 269Hs, has a half-life of approximately 9.7 seconds. It has an estimated density of 40.7 x 103 kg/m3. The density of Hassium results from its high atomic weight and from the significant decrease in ionic radii of the elements in the lanthanide series, known as lanthanide and actinide contraction.
Discoverer: Armbruster, Paula and Muenzenberg, Dr. Gottfried
Element Category: unknown, probably a transition metal
Meitnerium is a chemical element with atomic number 109 which means there are 109 protons and 109 electrons in the atomic structure. The chemical symbol for Meitnerium is Mt.
Discoverer: Armbruster, Paula and Muenzenberg, Dr. Gottfried
Element Category: unknown, probably a transition metal
Darmstadtium is a chemical element with atomic number110 which means there are 110 protons and 110 electrons in the atomic structure. The chemical symbol for Darmstadtium is Ds.
Discoverer: David Anderson, Ruhani Rabin, Team Updraft
Element Category: unknown, probably a transition metal
Roentgenium is a chemical element with atomic number 111 which means there are 111 protons and 111 electrons in the atomic structure. The chemical symbol for Roentgenium is Rg.
Discoverer: Armbruster, Paula and Muenzenberg, Dr. Gottfried
Element Category: unknown, probably a transition metal
Copernicium is a chemical element with atomic number 112 which means there are 112 protons and 112 electrons in the atomic structure. The chemical symbol for Copernicium is Cn.
Element Category: unknown, probably a transition metal
Nihonium is a chemical element with atomic number 113 which means there are 113 protons and 113 electrons in the atomic structure. The chemical symbol for Nihonium is Nh.
Element Category: unknown, probably a post-transition metal
Flerovium is a chemical element with atomic number 114 which means there are 114 protons and 114 electrons in the atomic structure. The chemical symbol for Flerovium is Fl.
Moscovium is a chemical element with atomic number 115 which means there are 115 protons and 115 electrons in the atomic structure. The chemical symbol for Moscovium is Mc.
Livermorium is a chemical element with atomic number 116 which means there are 116 protons and 116 electrons in the atomic structure. The chemical symbol for Livermorium is Lv.
Tennessine is a chemical element with atomic number 117 which means there are 117 protons and 117 electrons in the atomic structure. The chemical symbol for Tennessine is Ts.
Oganesson is a chemical element with atomic number 118 which means there are 118 protons and 118 electrons in the atomic structure. The chemical symbol for Oganesson is Og.
Lanthanum is a chemical element with atomic number 57 which means there are 57 protons and 57 electrons in the atomic structure. The chemical symbol for Lanthanum is La.
Lanthanum is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals and is traditionally counted among the rare earth elements.
Discoverer: Hisinger, Wilhelm and Berzelius, Jöns Jacob/Klaproth, Martin Heinrich
Element Category: Lanthanoids
Cerium is a chemical element with atomic number 58 which means there are 58 protons and 58 electrons in the atomic structure. The chemical symbol for Cerium is Ce.
Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series. Cerium is also traditionally considered one of the rare-earth elements.
Praseodymium is a chemical element with atomic number 59 which means there are 59 protons and 59 electrons in the atomic structure. The chemical symbol for Praseodymium is Pr.
Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. Praseodymium is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals.
Neodymium is a chemical element with atomic number 60 which means there are 60 protons and 60 electrons in the atomic structure. The chemical symbol for Neodymium is Nd.
Neodymium is a soft silvery metal that tarnishes in air. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a rare earth, it is a fairly common element.
Discoverer: Marinsky, Jacob A. and Coryell, Charles D. and Glendenin, Lawerence. E.
Element Category: Lanthanoids
Promethium is a chemical element with atomic number 61 which means there are 61 protons and 61 electrons in the atomic structure. The chemical symbol for Promethium is Pm.
Promethium is one of only two such elements that are followed in the periodic table by elements with stable forms. All of its isotopes are radioactive. In nuclear reactors, promethium equilibrium exists in power operation. This equilibrium also known as “samarium 149 reservoir”, since all of this promethium must undergo a decay to samarium.
Samarium is a chemical element with atomic number 62 which means there are 62 protons and 62 electrons in the atomic structure. The chemical symbol for Samarium is Sm. Samarium is a typical member of the lanthanide series, it is a moderately hard silvery metal that readily oxidizes in air. The name samarium is after the mineral samarskite from which it was isolated. Although classified as a rare earth element, samarium is the 40th most abundant element in the Earth’s crust and is more common than such metals as tin. In nuclear industry, especially natural and artificial samarium 149 has an important impact on the operation of a nuclear reactor.
Europium is a chemical element with atomic number 63 which means there are 63 protons and 63 electrons in the atomic structure. The chemical symbol for Europium is Eu.
Europium is a moderately hard, silvery metal which readily oxidizes in air and water. Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3. Europium is one of the least abundant elements in the universe. Only about 5×10−8% of all matter in the universe is europium.
Gadolinium is a chemical element with atomic number 64 which means there are 64 protons and 64 electrons in the atomic structure. The chemical symbol for Gadolinium is Gd.
Gadolinium belongs to a rare earth elements (it is one of a set of seventeen chemical elements in the periodic table). In nuclear industry gadolinium is commonly used as a neutron absorber due to very high neutron absorbtion cross-section of two isotopes 155Gd and 157Gd. In fact their absorption cross-sections are the highest among all stable isotopes.
Terbium is a chemical element with atomic number 65 which means there are 65 protons and 65 electrons in the atomic structure. The chemical symbol for Terbium is Tb.
Terbium is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas.
Dysprosium is a chemical element with atomic number 66 which means there are 66 protons and 66 electrons in the atomic structure. The chemical symbol for Dysprosium is Dy.
is a rare earth element with a metallic silver luster. Dysprosium is used for its high thermal neutron absorption cross-section in making control rods in nuclear reactors, for its high magnetic susceptibility in data storage applications.
Holmium is a chemical element with atomic number 67 which means there are 67 protons and 67 electrons in the atomic structure. The chemical symbol for Holmium is Ho.
Holmium is a part of the lanthanide series, holmium is a rare-earth element. Holmium is a relatively soft and malleable silvery-white metal.
Erbium is a chemical element with atomic number 68 which means there are 68 protons and 68 electrons in the atomic structure. The chemical symbol for Erbium is Er.
Erbium is a silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare earth element, originally found in the gadolinite mine in Ytterby in Sweden.
Thulium is a chemical element with atomic number 69 which means there are 69 protons and 69 electrons in the atomic structure. The chemical symbol for Thulium is Tm.
Thulium is an easily workable metal with a bright silvery-gray luster. It is fairly soft and slowly tarnishes in air. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices. Thulium is the thirteenth and third-last element in the lanthanide series.
Ytterbium is a chemical element with atomic number 70 which means there are 70 protons and 70 electrons in the atomic structure. The chemical symbol for Ytterbium is Yb.
Because of its closed-shell electron configuration, its density and melting and boiling points differ significantly from those of most other lanthanides.
Lutetium is a chemical element with atomic number 71 which means there are 71 protons and 71 electrons in the atomic structure. The chemical symbol for Lutetium is Lu.
Lutetium is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted among the rare earths.
Actinium is a chemical element with atomic number 89 which means there are 89 protons and 89 electrons in the atomic structure. The chemical symbol for Actinium is Ac.
Actinium is a soft, silvery-white radioactive metal. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table.
Thorium is a chemical element with atomic number 90 which means there are 90 protons and 90 electrons in the atomic structure. The chemical symbol for Thorium is Th.
Thorium metal is silvery and tarnishes black when exposed to air, forming the dioxide. Thorium is moderately hard, malleable, and has a high melting point. Thorium is a naturally-occurring element and it is estimated to be about three times more abundant than uranium. Thorium is commonly found in monazite sands (rare earth metals containing phosphate mineral).
Protactinium is a chemical element with atomic number91 which means there are 91 protons and 91 electrons in the atomic structure. The chemical symbol for Protactinium is Pa.
Protactinium is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids.
Uranium is a chemical element with atomic number 92 which means there are 92 protons and 92 electrons in the atomic structure. The chemical symbol for Uranium is U.
Uranium is a silvery-white metal in the actinide series of the periodic table. Uranium is weakly radioactive because all isotopes of uranium are unstable, with half-lives varying between 159,200 years and 4.5 billion years. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and slightly lower than that of gold or tungsten.
Discoverer: McMillan, Edwin M. and Abelson, Philip H.
Element Category: Actinoids
Neptunium is a chemical element with atomic number 93 which means there are 93 protons and 93 electrons in the atomic structure. The chemical symbol for Neptunium is Np.
Neptunium metal is silvery and tarnishes when exposed to air. Neptunium is the first transuranic element.
Discoverer: Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan, Arthur C. Wohl
Element Category: Actinoids
Plutonium is a chemical element with atomic number 94 which means there are 94 protons and 94 electrons in the atomic structure. The chemical symbol for Plutonium is Pu.
Plutonium is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized.
Discoverer: Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso
Element Category: Actinoids
Americium is a chemical element with atomic number 95 which means there are 95 protons and 95 electrons in the atomic structure. The chemical symbol for Americium is Am.
Americium is a transuranic member of the actinide series, in the periodic table located under the lanthanide element europium, and thus by analogy was named after the Americas.
Discoverer: Glenn T. Seaborg, Ralph A. James, Albert Ghiorso
Element Category: Actinoids
Curium is a chemical element with atomic number 96 which means there are 96 protons and 96 electrons in the atomic structure. The chemical symbol for Curium is Cm.
Curium is a hard, dense, silvery metal with a relatively high melting point and boiling point for an actinide.
Discoverer: Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street, Jr., Albert Ghiorso
Element Category: Actinoids
Berkelium is a chemical element with atomic number97 which means there are 97 protons and 97 electrons in the atomic structure. The chemical symbol for Berkelium is Bk.
Berkelium is a member of the actinide and transuranium element series.
Discoverer: Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street, Jr., Albert Ghiorso
Element Category: Actinoids
Californium is a chemical element with atomic number 98 which means there are 98 protons and 98 electrons in the atomic structure. The chemical symbol for Californium is Cf.
Californium is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all the elements that have been produced in amounts large enough to see with the unaided eye (after einsteinium). The most commonly used spontaneous fission neutron source is the radioactive isotope californium-252.
Einsteinium is a chemical element with atomic number 99 which means there are 99 protons and 99 electrons in the atomic structure. The chemical symbol for Einsteinium is Es.
Einsteinium is the seventh transuranic element, and an actinide.
Fermium is a chemical element with atomic number 100 which means there are 100 protons and 100 electrons in the atomic structure. The chemical symbol for Fermium is Fm.
Fermium is a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities.
Discoverer: Stanley G. Thompson, Glenn T. Seaborg, Bernard G. Harvey, Gregory R. Choppin, Albert Ghiorso
Element Category: Actinoids
Mendelevium is a chemical element with atomic number 101 which means there are 101 protons and 101 electrons in the atomic structure. The chemical symbol for Mendelevium is Md.
Mendelevium is a metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities.
Discoverer: Albert Ghiorso, Glenn T. Seaborg, Torbørn Sikkeland, John R. Walton
Element Category: Actinoids
Nobelium is a chemical element with atomic number 102 which means there are 102 protons and 102 electrons in the atomic structure. The chemical symbol for Nobelium is No.
Nobelium is the tenth transuranic element and is the penultimate member of the actinide series. Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles.
Discoverer: Albert Ghiorso, Torbjørn Sikkeland, Almon E. Larsh, Robert M. Latimer
Element Category: Actinoids
Lawrencium is a chemical element with atomic number 103 which means there are 103 protons and 103 electrons in the atomic structure. The chemical symbol for Lawrencium is Lr.
Lawrencium is the final member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles.
262 amu
Atomic Mass of Copernicium
Atomic mass of Copernicium is 285 u.
The atomic mass is the mass of an atom. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element. The atomic mass is carried by the atomic nucleus, which occupies only about 10-12 of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance.
The size and mass of atoms are so small that the use of normal measuring units, while possible, is often inconvenient. Units of measure have been defined for mass and energy on the atomic scale to make measurements more convenient to express. The unit of measure for mass is the atomic mass unit (amu). One atomic mass unit is equal to 1.66 x 10-24 grams. One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.
For 12C the atomic mass is exactly 12u, since the atomic mass unit is defined from it. For other isotopes, the isotopic mass usually differs and is usually within 0.1 u of the mass number. For example, 63Cu (29 protons and 34 neutrons) has a mass number of 63 and an isotopic mass in its nuclear ground state is 62.91367 u.
There are two reasons for the difference between mass number and isotopic mass, known as the mass defect:
The neutron is slightly heavier than the proton. This increases the mass of nuclei with more neutrons than protons relative to the atomic mass unit scale based on 12C with equal numbers of protons and neutrons.
The nuclear binding energy varies between nuclei. A nucleus with greater binding energy has a lower total energy, and therefore a lower mass according to Einstein’s mass-energy equivalence relation E = mc2. For 63Cu the atomic mass is less than 63 so this must be the dominant factor.
Note that, it was found the rest mass of an atomic nucleus is measurably smaller than the sum of the rest masses of its constituent protons, neutrons and electrons. Mass was no longer considered unchangeable in the closed system. The difference is a measure of the nuclear binding energy which holds the nucleus together. According to the Einstein relationship (E=mc2), this binding energy is proportional to this mass difference and it is known as the mass defect.
Mass numbers of typical isotopes of Copernicium are XY.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
Neutron number is rarely written explicitly in nuclide symbol notation, but appears as a subscript to the right of the element symbol. Nuclides that have the same neutron number but a different proton number are called isotones. The various species of atoms whose nuclei contain particular numbers of protons and neutrons are called nuclides. Each nuclide is denoted by chemical symbol of the element (this specifies Z) with tha atomic mass number as supescript. Therefore, we cannot determine the neutron number of uranium, for example. We can determine the neutron number of certain isotope. For example, the neutron number of uranium-238 is 238-92=146.
Density of Copernicium
Density of Copernicium is –g/cm3.
Typical densities of various substances are at atmospheric pressure.
Density is defined as the mass per unit volume. It is an intensive property, which is mathematically defined as mass divided by volume:
ρ = m/V
In words, the density (ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance. The standard SI unit is kilograms per cubic meter (kg/m3). The Standard English unit is pounds mass per cubic foot (lbm/ft3).
Density – Atomic Mass and Atomic Number Density
Since the density (ρ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance, it is obvious, the density of a substance strongly depends on its atomic mass and also on the atomic number density (N; atoms/cm3),
Atomic Weight. The atomic mass is carried by the atomic nucleus, which occupies only about 10-12 of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Therefore it is determined by the mass number (number of protons and neutrons).
Atomic Number Density. The atomic number density (N; atoms/cm3), which is associated with atomic radii, is the number of atoms of a given type per unit volume (V; cm3) of the material. The atomic number density (N; atoms/cm3) of a pure material having atomic or molecular weight (M; grams/mol) and the material density (⍴; gram/cm3) is easily computed from the following equation using Avogadro’s number (NA = 6.022×1023 atoms or molecules per mole):
Since nucleons (protons and neutrons) make up most of the mass of ordinary atoms, the density of normal matter tends to be limited by how closely we can pack these nucleons and depends on the internal atomic structure of a substance. The densest material found on earth is the metal osmium, but its density pales by comparison to the densities of exotic astronomical objects such as white dwarf stars and neutron stars.
If we include man made elements, the densest so far is Hassium. Hassium is a chemical element with symbol Hs and atomic number 108. It is a synthetic element (first synthesised at Hasse in Germany) and radioactive. The most stable known isotope, 269Hs, has a half-life of approximately 9.7 seconds. It has an estimated density of 40.7 x 103 kg/m3. The density of Hassium results from its high atomic weight and from the significant decrease in ionic radii of the elements in the lanthanide series, known as lanthanide and actinide contraction.
Nuclear binding energy curve. Source: hyperphysics.phy-astr.gsu.edu
If the splitting releases energy and the fusion releases the energy, so where is the breaking point? For understanding this issue it is better to relate the binding energy to one nucleon, to obtain nuclear binding curve. The binding energy per one nucleon is not linear. There is a peak in the binding energy curve in the region of stability near iron and this means that either the breakup of heavier nuclei than iron or the combining of lighter nuclei than iron will yield energy.
The reason the trend reverses after iron peak is the growing positive charge of the nuclei. The electric force has greater range than strong nuclear force. While the strong nuclear force binds only close neighbors the electric force of each proton repels the other protons.
A neutron is one of the subatomic particles that make up matter. In the universe, neutrons are abundant, making up more than half of all visible matter. It has no electric charge and a rest mass equal to 1.67493 × 10−27 kg—marginally greater than that of the proton but nearly 1839 times greater than that of the electron. The neutron has a mean square radius of about 0.8×10−15 m, or 0.8 fm, and it is a spin-½ fermion.
The neutrons exist in the nuclei of typical atoms, along with their positively charged counterparts, the protons. Neutrons and protons, commonly called nucleons, are bound together in the atomic nucleus, where they account for 99.9 percent of the atom’s mass. Research in high-energy particle physics in the 20th century revealed that neither the neutron nor the proton is not the smallest building block of matter. Protons and neutrons have also their structure. Inside the protons and neutrons, we find true elementary particles called quarks. Within the nucleus, protons and neutrons are bound together through the strong force, a fundamental interaction that governs the behaviour of the quarks that make up the individual protons and neutrons.
A nuclear stability is determined by the competition between two fundamental interactions. Protons and neutrons are attracted each other via strong force. On the other hand protons repel each other via the electric force due to their positive charge. Therefore neutrons within the nucleus act somewhat like nuclear glue, neutrons attract each other and protons , which helps offset the electrical repulsion between protons. There are only certain combinations of neutrons and protons, which forms stable nuclei. For example, the most common nuclide of the common chemical element lead (Pb) has 82 protons and 126 neutrons.
Nuclear binding energy curve. Source: hyperphysics.phy-astr.gsu.edu
Because of the strength of the nuclear force at short distances, the nuclear binding energy (the energy required to disassemble a nucleus of an atom into its component parts) of nucleons is more than seven orders of magnitude larger than the electromagnetic energy binding electrons in atoms. Nuclear reactions (such as nuclear fission or nuclear fusion) therefore have an energy density that is more than 10 000 000x that of chemical reactions.
Knowledge of the behaviour and properties of neutrons is essential to the production of nuclear power. Shortly after the neutron was discovered in 1932, it was quickly realized that neutrons might act to form a nuclear chain reaction. When nuclear fission was discovered in 1938, it became clear that, if a fission reaction produced free neutrons, each of these neutrons might cause further fission reaction in a cascade known as a chain reaction. Knowledge of cross-sections (the key parameter representing probability of interaction between a neutron and a nucleus) became crutial for design of reactor cores and the first nuclear weapon (Trinity, 1945).
Discovery of the Neutron
The story of the discovery of the neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century. The neutron was discovered in 1932 by the English physicist James Chadwick, but since the time of Ernest Rutherford it had been known that the atomic mass number A of nuclei is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus. The Rutherford’s model for the atom in 1911 claims that atoms have their mass and positive charge concentrated in a very small nucleus.
The alpha particles emitted from polonium fell on certain light elements, specifically beryllium, an unusually penetrating radiation is produced. Source: dev.physicslab.orgChadwick’s neutron chamber containing parallel disks of radioactive polonium and beryllium. Radiation is emitted from an aluminium window at the chamber’s end. Source: imgkid.com
An experimental breakthrough came in 1930 with the observation by Bothe and Becker. They found that if the very energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. Since this radiation was not influenced by an electric field (neutrons have no charge), they presumed it was gamma rays (but much more penetrating). It was shown (Curie and Joliot) that when a paraffin target with this radiation is bombarded, it ejected protons with energy about 5.3 MeV. Paraffin is high in hydrogen content, hence offers a target dense with protons (since neutrons and protons have almost equal mass, protons scatter energetically from neutrons).These experimental results were difficult to interpret. James Chadwick was able to prove that the neutral particle could not be a photon by bombarding targets other than hydrogen, including nitrogen, oxygen, helium and argon. Not only were these inconsistent with photon emission on energy grounds, the cross-section for the interactions was orders of magnitude greater than that for Compton scattering by photons. In Rome, the young physicist Ettore Majorana suggested that the manner in which the new radiation interacted with protons required a new neutral particle.
The task was that of determining the mass of this neutral particle. James Chadwick chose to bombard boron with alpha particles and analyze the interaction of the neutral particles with nitrogen. These particlular targets were chosen partly because the masses of boron and nitrogen were well known. Using kinematics, Chadwick was able to determine the velocity of the protons. Then through conservation of momentum techniques, he was able to determine that the mass of the neutral radiation was almost exactly the same as that of a proton. In 1932, Chadwick proposed that the neutral particle was Rutherford’s neutron. In 1935, he was awarded the Nobel Prize for his discovery.
The quark structure of the neutron. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons.
Neutrons and protons are classified as hadrons, subatomic particles that are subject to the strong force and as baryons since they are composed of three quarks. The neutron is a composite particle made of two down quarks with charge −⅓ e and one up quark with charge +⅔ e. Since the neutron has no net electric charge, it is not affected by eletric forces, but the neutron does have a slight distribution of electric charge within it. This results in non-zero magnetic moment (dipole moment) of the neutron. Therefore the neutron interacts also via electromagnetic interaction, but much weaker than the proton.
The mass of the neutron is 939.565 MeV/c2, whereas the mass of the three quarks is only about 12 MeV/c2 (only about 1% of the mass-energy of the neutron). Like the proton, most of mass (energy) of the neutron is in the form of the strong nuclear force energy (gluons). The quarks of the neutron are held together by gluons, the exchange particles for the strong nuclear force. Gluons carry the color charge of the strong nuclear force.
Mean square radius of a neutron is ~ 0.8 x 10-15m (0.8 fermi)
The mass of the neutron is 939.565 MeV/c2
Neutrons are ½ spin particles – fermionic statistics
Neutrons are neutral particles – no net electric charge.
Neutrons have non-zero magnetic moment.
Free neutrons (outside a nucleus) are unstable and decay via beta decay. The decay of the neutron involves the weak interaction and is associated with a quark transformation (a down quark is converted to an up quark).
Mean lifetime of a free neutron is 882 seconds (i.e. half-life is 611 seconds ).
A natural neutron background of free neutrons exists everywhere on Earth and it is caused by muons produced in the atmosphere, where high energy cosmic rays collide with particles of Earth’s atmosphere.
Neutrons cannot directly cause ionization. Neutrons ionize matter only indirectly.
Neutrons can travel hundreds of feet in air without any interaction. Neutron radiation is highly penetrating.
The fission process produces free neutrons (2 or 3).
Thermal or cold neutrons have the wavelengths similar to atomic spacings. They can be used in neutron diffraction experiments to determine the atomic and/or magnetic structure of a material.
Free neutrons can be classified according to their kinetic energy. This energy is usually given in electron volts (eV). The term temperature can also describe this energy representing thermal equilibrium between a neutron and a medium with a certain temperature.
Classification of free neutrons according kinetic energies
Cold Neutrons (0 eV; 0.025 eV). Neutrons in thermal equilibrium with very cold surroundings such as liquid deuterium. This spectrum is used for neutron scattering experiments.
Thermal Neutrons. Neutrons in thermal equilibrium with a surrounding medium. Most probable energy at 20°C (68°F) for Maxwellian distribution is 0.025 eV (~2 km/s). This part of neutron’s energy spectrum constitutes most important part of spectrum in thermal reactors.
Epithermal Neutrons (0.025 eV; 0.4 eV). Neutrons of kinetic energy greater than thermal. Some of reactor designs operates with epithermal neutron’s spectrum. This design allows to reach higher fuel breeding ratio than in thermal reactors.
Neutrons of kinetic energy below the cadmium cut-off energy (~0.5 eV) are strongly absorbed by 113-Cd. Source: JANIS (Java-based nuclear information software) www.oecd-nea.org/janis/
Cadmium Neutrons (0.4 eV; 0.5 eV). Neutrons of kinetic energy below the cadmium cut-off energy. One cadmium isotope, 113Cd, absorbs neutrons strongly only if they are below ~0.5 eV (cadmium cut-off energy).
Epicadmium Neutrons (0.5 eV; 1 eV). Neutrons of kinetic energy above the cadmium cut-off energy. These neutrons are not absorbed by cadmium.
Slow Neutrons (1 eV; 10 eV).
Resonance Neutrons (10 eV; 300 eV). The resonance neutrons are called resonance for their special bahavior. At resonance energies the cross-sections can reach peaks more than 100x higher as the base value of cross-section. At this energies the neutron capture significantly exceeds a probability of fission. Therefore it is very important (for thermal reactors) to quickly overcome this range of energy and operate the reactor with thermal neutrons resulting in increase of probability of fission.
Intermediate Neutrons (300 eV; 1 MeV).
Fast Neutrons (1 MeV; 20 MeV). Neutrons of kinetic energy greater than 1 MeV (~15 000 km/s) are usually named fission neutrons. These neutrons are produced by nuclear processes such as nuclear fission or (ɑ,n) reactions. The fission neutrons have a Maxwell-Boltzmann distribution of energy with a mean energy (for 235U fission) 2 MeV. Inside a nuclear reactor the fast neutrons are slowed down to the thermal energies via a process called neutron moderation.
Relativistic Neutrons (20 MeV; ->)
Distribution of kinetic energies of neutrons in the thermal reactor. The fission neutrons (fast flux) are immediately slowed down to the thermal energies via a process called neutron moderation. Source: serc.carleton.edu
The reactor physics does not need this fine division of neutron energies. The neutrons can be roughly (for purposes of reactor physics) divided into three energy ranges:
Thermal neutrons (0.025 eV – 1 eV).
Resonance neutrons (1 eV – 1 keV).
Fast neutrons (1 keV – 10 MeV).
Even most of reactor computing codes use only two neutron energy groups:
Neutrons are neutral particles, therefore they travel in straight lines, deviating from their path only when they actually collide with a nucleus to be scattered into a new direction or absorbed. Neither the electrons surrounding (atomic electron cloud) a nucleus nor the electric field caused by a positively charged nucleus affect a neutron’s flight. In short, neutrons collide with nuclei, not with atoms. A very descriptive feature of the transmission of neutrons through bulk matter is the mean free path length (λ – lambda), which is the mean distance a neutron travels between interactions. It can be calculated from following equation:
λ=1/Σ
Neutrons may interact with nuclei in one of following ways:
Neutron Cross-section
Typical cross-sections of fission material. Slowing down neutrons results in increase of probability of interaction (e.g. fission reaction).
The extent to which neutrons interact with nuclei is described in terms of quantities known as cross-sections. Cross-sections are used to express the likelihood of particular interaction between an incident neutron and a target nucleus. It must be noted this likelihood do not depend on real target dimensions. In conjunction with the neutron flux, it enables the calculation of the reaction rate, for example to derive the thermal power of a nuclear power plant. The standard unit for measuring the microscopic cross-section (σ-sigma) is the barn, which is equal to 10-28 m2. This unit is very small, therefore barns (abbreviated as “b”) are commonly used. The microscopic cross-section can be interpreted as the effective ‘target area’ that a nucleus interacts with an incident neutron.
A macroscopic cross-section is derived from microscopic and the material density:
Σ=σ.N
Here σ, which has units of m2, is referred to as the microscopic cross-section. Since the units of N (nuclei density) are nuclei/m3, the macroscopic cross-sectionΣ have units of m-1, thus in fact is an incorrect name, because it is not a correct unit of cross-sections.
Neutron cross-sections constitute a key parameters of nuclear fuel. Neutron cross-sections must be calculated for fresh fuel assemblies usually in two-Dimensional models of the fuel lattice.
The neutron cross-section is variable and depends on:
Target nucleus (hydrogen, boron, uranium, etc.) Each isotop has its own set of cross-sections.
Type of the reaction (capture, fission, etc.). Cross-sections are different for each nuclear reaction.
Neutron energy (thermal neutron, resonance neutron, fast neutron). For a given target and reaction type, the cross-section is strongly dependent on the neutron energy. In the common case, the cross section is usually much larger at low energies than at high energies. This is why most nuclear reactors use a neutron moderator to reduce the energy of the neutron and thus increase the probability of fission, essential to produce energy and sustain the chain reaction.
Target energy (temperature of target material – Doppler broadening) This dependency is not so significant, but the target energy strongly influences inherent safety of nuclear reactors due to a Doppler broadening of resonances.
For thermal neutrons (in 1/v region), absorption cross sections increases as the velocity (kinetic energy) of the neutron decreases. Source: JANIS 4.0
For thermal neutrons (in 1/v region), absorption cross-sections increases as the velocity (kinetic energy) of the neutron decreases. Therefore the 1/v Law can be used to determine shift in absorbtion cross-section, if the neutron is in equilibrium with a surrounding medium. This phenomenon is due to the fact the nuclear force between the target nucleus and the neutron has a longer time to interact.
This law is aplicable only for absorbtion cross-section and only in the 1/v region.
Example of cross- sections in 1/v region:
The absorbtion cross-section for 238U at 20°C = 293K (~0.0253 eV) is:
.
The absorbtion cross-section for 238U at 1000°C = 1273K is equal to:
This cross-section reduction is caused only due to the shift of temperature of surrounding medium.
Resonance neutron capture
Resonance peaks for radiative capture of U238. At resonance energies the probability of capture can be more than 100x higher as the base value. Source: JANIS program
Absorption cross section is often highly dependent on neutron energy. Note that the nuclear fission produces neutrons with a mean energy of 2 MeV (200 TJ/kg, i.e. 20,000 km/s). The neutron can be roughly divided into three energy ranges:
Fast neutron. (10MeV – 1keV)
Resonance neutron (1keV – 1eV)
Thermal neutron. (1eV – 0.025eV)
The resonance neutrons are called resonance for their special bahavior. At resonance energies the cross-section can reach peaks more than 100x higher as the base value of cross-section. At this energies the neutron capture significantly exceeds a probability of fission. Therefore it is very important (for thermal reactors) to quicklyovercome this range of energy and operate the reactor with thermal neutrons resulting in increase of probability of fission.
Doppler broadening
Doppler effect improves reactor stability. Broadened resonance (heating of a fuel) results in a higher probability of absorbtion, thus causes negative reactivity insertion (reduction of reactor power).
A Doppler broadening of resonances is very important phanomenon, which improves reactor stability. The prompt temperature coefficient of most thermal reactors is negative, owing to an nuclear Doppler effect. Although the absorbtion cross-section depends significantly on incident neutron energy, the shape of the cross-section curve depends also on target temperature.
Nuclei are located in atoms which are themselves in continual motion owing to their thermal energy. As a result of these thermal motions neutrons impinging on a target appears to the nuclei in the target to have a continuous spread in energy. This, in turn, has an effect on the observed shape of resonance. The resonance becomes shorter and wider than when the nuclei are at rest.
Although the shape of a resonance changes with temperature, the total area under the resonance remains essentially constant. But this does not implyconstant neutron absorbtion. Despite the constant area under resonance, a resonance integral, which determines the absorbtion, increases with increasing target temperature. This, of course, decreases coefficient k (negative reactivity is inserted).
Typical cross-sections of materials in the reactor
Following table shows neutron cross-sections of the most common isotopes of reactor core.
Table of cross-sections
Types of neutron-nuclear reactions
Elastic Scattering Reaction
Generally, a neutron scattering reaction occurs when a target nucleus emits a single neutron after a neutron-nucleus interaction. In an elastic scattering reaction between a neutron and a target nucleus, there is no energy transferred into nuclear excitation.
Inelastic Scattering Reaction
In an inelastic scattering reaction between a neutron and a target nucleus some energy of the incident neutron is absorbed to the recoiling nucleus and the nucleus remains in the excited state. Thus while momentum is conserved in an inelastic collision, kinetic energy of the “system” is not conserved.
Neutron Absorption
The neutron absorption reaction is the most important type of reactions that take place in a nuclear reactor. The absorption reactions are reactions, where the neutron is completely absorbed and compound nucleus is formed. This is the very important feature, because the mode of decay of such compound nucleus does not depend on the way the compound nucleus was formed. Therefore a variety of emissions or decays may follow. The most important absorption reactions are divided by the exit channel into two following reactions:
Radiative Capture. Most absorption reactions result in the loss of a neutron coupled with the production of one or more gamma rays. This is referred to as a capture reaction, and it is denoted by σγ.
Neutron-induced Fission Reaction. Some nuclei (fissionable nuclei) may undergo a fission event, leading to two or more fission fragments (nuclei of intermediate atomic weight) and a few neutrons. In a fissionable material, the neutron may simply be captured, or it may cause nuclear fission. For fissionable materials we thus divide the absorption cross section as σa = σγ + σf.
Radiative Capture
The neutron capture is one of the possible absorption reactions that may occur. In fact, for non-fissionable nuclei it is the only possible absorption reaction. Capture reactions result in the loss of a neutron coupled with the production of one or more gamma rays. This capture reaction is also referred to as a radiative capture or (n, γ) reaction, and its cross-section is denoted by σγ.
The radiative capture is a reaction, in which the incident neutron is completely absorbed and compound nucleus is formed. The compound nucleus then decays to its ground state by gamma emission. This process can occur at all incident neutron energies, but the probability of the interaction strongly depends on the incident neutron energy and also on the target energy (temperature). In fact the energy in the center-of-mass system determines this probability.
Nuclear Fission
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei). The fission process often produces free neutrons and photons (in the form of gamma rays), and releases a large amount of energy. In nuclear physics, nuclear fission is either a nuclear reactionor a radioactive decay process. The case of decay process is called spontaneous fission and it is very rare process.
Neutron Emission
Although the neutron emission is usually associated with nuclear decay, it must be also mentioned in connection with neutron nuclear reactions. Some neutrons interacts with a target nucleus via a compound nucleus. Among these compound nucleus reactions are also reactions, in which a neutron is ejected from nucleus and they may be referred to as neutron emission reactions. The point is that compound nuclei lose its excitation energy in a way, which is identical to the radioactive decay. Very important feature is the fact the mode of decay of compound nucleus does not depend on the way the compound nucleus was formed.
Charged Particle Ejection
Charged particle reactions are usually associated with formation of a compound nucleus, which is excited to a high energy level, that such compound nucleus can eject a new charged particle while the incident neutron remains in the nucleus. After the new particle is ejected, the remaining nucleus is completely changed, but may or may not exist in an excited state depending upon the mass-energy balance of the reaction. This type of reaction is more common for charged particles as incident particles (such as alpha particles, protons, and so on).
The case of neutron-induced charged particle reactions is not so common, but there are some neutron-induced charged particle reactions, that are of importance in the reactivity control and also in the detection of neutrons.
Detection of Neutrons
Since the neutrons are electrically neutral particles, they are mainly subject to strong nuclear forces but not to electric forces. Therefore neutrons are not directly ionizing and they have usually to be converted into charged particles before they can be detected. Generally every type of neutron detector must be equipped with converter (to convert neutron radiation to common detectable radiation) and one of the conventional radiation detectors (scintillation detector, gaseous detector, semiconductor detector, etc.).
Neutron converters
Two basic types of neutron interactions with matter are for this purpose available:
Elastic scattering. The free neutron can be scattered by a nucleus, transferring some of its kinetic energy to the nucleus. If the neutron has enough energy to scatter off nuclei the recoiling nucleus ionizes the material surrounding the converter. In fact, only hydrogen and helium nuclei are light enough for practical application. Charge produced in this way can be collected by the conventional detector to produce a detected signal. Neutrons can transfer more energy to light nuclei. This method is appropriate for detecting fast neutrons (fast neutrons do not have high cross-section for absorption) allowing detection of fast neutrons without a moderator.
Neutron absorption. This is a common method allowing detection of neutrons of entire energy spectrum. This method is is based on variety of absorption reactions (radiative capture, nuclear fission, rearrangement reactions, etc.). The neutron is here absorbed by target material (converter) emitting secondary particles such as protons, alpha particles, beta particles, photons (gamma rays) or fission fragments. Some reactions are threshold reactions (requiring a minimum energy of neutrons), but most of reactions occurs at epithermal and thermal energies. That means the moderation of fast neutrons is required leading in poor energy information of the neutrons. Most common nuclei for the neutron converter material are:
10B(n,α). Where the neutron capture cross-section for thermal neutrons is σ = 3820 barns and the natural boron has abundance of 10B 19,8%.
3He(n,p). Where the neutron capture cross-section for thermal neutrons is σ = 5350 barns and the natural helium has abundance of 3He 0.014%.
6Li(n,α). Where the neutron capture cross-section for thermal neutrons is σ = 925 barns and the natural lithium has abundance of 6Li 7,4%.
113Cd(n,ɣ). Where the neutron capture cross-section for thermal neutrons is σ = 20820 barns and the natural cadmium has abundance of 113Cd 12,2%.
235U(n,fission). Where the fission cross-section for thermal neutrons is σ = 585 barns and the natural uranium has abundance of 235U 0.711%. Uranium as a converter produces fission fragments which are heavy charged particles. This have significant advantage. The heavy charged particles (fission fragments) create a high output signal, because the fragments deposit a large amount of energy in a detector sensitive volume. This allows an easy discrimination of the background radiation (e.i. gamma radiation). This important feature can be used for example in a nuclear reactor power measurement, where the neutron field is accompanied by a significant gamma background.
The free neutron decays into a proton, an electron, and an antineutrino with a half-life of about 611 seconds (10.3 minutes). Source: scienceblogs.com
A free neutron is a neutron that is not bounded in a nucleus. The free neutron is, unlike a bounded neutron, subject to radioactive beta decay.
It decays into a proton, an electron, and an antineutrino (the antimatter counterpart of the neutrino, a particle with no charge and little or no mass). A free neutron will decay with a half-life of about 611 seconds (10.3 minutes). This decay involves the weak interaction and is associated with a quark transformation (a down quark is converted to an up quark). The decay of the neutron is a good example of the observations which led to the discovery of the neutrino. Because it decays in this manner, the neutron does not exist in nature in its free state, except among other highly energetic particles in cosmic rays. Since free neutrons are electrically neutral, they pass through the electrical fields within atoms without any interaction and they are interacting with matter almost exclusively through relatively rare collisions with atomic nuclei.
In radiation protection there are three ways how to protect people from identified radiation sources:
Limiting Time. The amount of radiation exposure depends directly (linearly) on the time people spend near the source of radiation. The dose can be reduced by limiting exposure time.
Distance. The amount of radiation exposure depends on the distance from the source of radiation. Similarly to a heat from a fire, if you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from nuclear sources.
Shielding. Finally, if the source is too intensive and time or distance do not provide sufficient radiation protection the shielding must be used. Radiation shielding usually consist of barriers of lead, concrete or water. Even depleted uranium can be used as a good protection from gamma radiation, but on the other hand uranium is absolutely inappropriate shielding of neutron radiation. In short, it depends on type of radiation to be shielded, which shielding will be effective or not.
Shielding of Neutrons
Water as a neutron shield
There are three main features of neutrons, which are crucial in the shielding of neutrons.
Neutrons have no net electric charge, therefore they cannot be affected or stopped by electric forces. Neutrons ionize matter only indirectly, which makes neutrons highly penetrating type of radiation.
Neutrons scatter with heavy nuclei very elastically. Heavy nuclei very hard slow down a neutron let alone absorb a fast neutron.
An absorption of neutron (one would say shielding) causes initiation of certain nuclear reaction (e.g. radiative capture or even fission), which is accompanied by a number of other types of radiation. In short, neutrons make matter radioactive, therefore with neutrons we have to shield also the other types of radiation.
The best materials for shielding neutrons must be able to:
Slow down neutrons (the same principle as the neutron moderation). First point can be fulfilled only by material containing light atoms (e.g. hydrogen atoms), such as water, polyethylene, and concrete. The nucleus of a hydrogen nucleus contains only a proton. Since a proton and a neutron have almost identical masses, a neutron scattering on a hydrogen nucleus can give up a great amount of its energy (even entire kinetic energy of a neutron can be transferred to a proton after one collision). This is similar to a billiard. Since a cue ball and another billiard ball have identical masses, the cue ball hitting another ball can be made to stop and the other ball will start moving with the same velocity. On the other hand, if a ping pong ball is thrown against a bowling ball (neutron vs. heavy nucleus), the ping pong ball will bounce off with very little change in velocity, only a change in direction. Therefore lead is quite ineffective for blocking neutron radiation, as neutrons are uncharged and can simply pass through dense materials.
Table of cross-sections
Absorb this slow neutron.Thermal neutrons can be easily absorbed by capture in materials with high neutron capture cross sections (thousands of barns) like boron, lithium or cadmium. Generally, only a thin layer of such absorbator is sufficient to shield thermal neutrons. Hydrogen (in the form of water), which can be used to slow down neutrons, have absorbtion cross-section 0.3 barns. This is not enough, but this insufficiency can be offset by sufficient thickness of water shield.
Shield the accompanying radiation. In the case of cadmium shield the absorption of neutrons is accompanied by strong emission of gamma rays. Therefore additional shield is necessary to attenuate the gamma rays. This phenomenon practically does not exist for lithium and is much less important for boron as a neutron absorption material. For this reason, materials containing boron are used often in neutron shields. In addition, boron (in the form of boric acid) is well soluble in water making this combination very efective neutron shield.
Water as a neutron shield
Water due to the high hydrogen content and the availability is efective and common neutron shielding. However, due to the low atomic number of hydrogen and oxygen, water is not acceptable shield against the gamma rays. On the other hand in some cases this disadvantage (low density) can be compensated by high thickness of the water shield. In case of neutrons, water perfectly moderates neutrons, but with absorption of neutrons by hydrogen nucleus secondary gamma rays with the high energy are produced. These gamma rays highly penetrates matter and therefore it can increase requirements on the thickness of the water shield. Adding a boric acid can help with this problem (neutron absorbtion on boron nuclei without strong gamma emission), but results in another problems with corrosion of construction materials.
Concrete as a neutron shield
Most commonly used neutron shielding in many sectors of the nuclear science and engineering is shield of concrete. Concrete is also hydrogen-containing material, but unlike water concrete have higher density (suitable for secondary gamma shielding) and does not need any maintenance. Because concrete is a mixture of several different materials its composition is not constant. So when referring to concrete as a neutron shielding material, the material used in its composition should be told correctly. Generally concrete are divided to “ordinary “ concrete and “heavy” concrete. Heavy concrete uses heavy natural aggregates such as barites (barium sulfate) or magnetite or manufactured aggregates such as iron, steel balls, steel punch or other additives. As a result of these additives, heavy concrete have higher density than ordinary concrete (~2300 kg/m3). Very heavy concrete can achieve density up to 5,900 kg/m3 with iron additives or up to 8900 kg/m3 with lead additives. Heavy concrete provide very effective protection against neutrons.
A neutron source is any device that emits neutrons. Neutron sources have many applications, they can be used in research, engineering, medicine, petroleum exploration, biology, chemistry and nuclear power. A neutron source is characterized by a number of factors:
Significance of the source
Intensity. The rate of neutrons emitted by the source.
Energy distribution of emitted neutrons.
Angular distribution of emitted neutrons.
Mode of emission. Continuous or pulsed operation.
Classification by significance of the source
Large (Significant) neutron sources
Nuclear Reactors. There are nuclei that can undergo fission on their own spontaneously, but only certain nuclei, like uranium-235, uranium-233 and plutonium-239, can sustain a fission chain reaction. This is because these nuclei release neutrons when they break apart, and these neutrons can induce fission of other nuclei. Uranium-235 which exists as 0.7% of naturally occurring uranium undergoes nuclear fission with thermal neutrons with the production of, on average, 2.4 fast neutrons and the release of ~ 180 MeV of energy per fission. Free neutrons released by each fission play very important role as a trigger of the reaction, but they can be also used fo another purpose. For example: One neutron is required to trigger a further fission. Part of free neutrons (let say 0.5 neutrons/fission) is absorbed in other material, but an excess of neutrons (0.9 neutrons/fission) is able to leave the surface of the reactor core and can be used as a neutron source.
Fusion Systems. Nuclear fusion is a nuclear reaction in which two or more atomic nuclei (e.g. D+T) collide at a very high energy and fuse together. Thy byproduct of DT fusion is a free neutron (see picture), therefore also nuclear fusion reaction has the potential to produces large quantities of neutrons.
Spallation Sources. A spallation source is a high-flux neutron source in which protons that have been accelerated to high energies hit a heavy target material, causing the emission of neutrons. The reaction occurs above a certain energy threshold for the incident particle, which is typically 5 – 15 MeV.
Medium neutron sources
Bremssstrahlung from Electron Accelerators / Photofission. Energetic electrons when slowed down rapidly in a heavy target emit intense gamma radiation during the deceleration process. This is known as Bremsstrahlung or braking radiation. The interaction of the gamma radiation with the target produces neutrons via the (γ,n) reaction, or the (γ,fission) reaction when a fissile target is used. e-→Pb → γ→ Pb →(γ,n) and (γ,fission). The Bremsstrahlung γ energy exceeds the binding energy of the “last” neutron in the target. A source strength of 1013 neutrons/second produced in short (i.e. < 5 μs) pulses can be readily realised.
Dense plasme focus. The dense plasma focus (DPF) is a device that is known as an efficient source of neutrons from fusion reactions. Mechanism of dense plasma focus (DPF) is based on nuclear fusion of short-lived plasma of deuterium and/or tritium. This device produces a short-lived plasma by electromagnetic compression and acceleration that is called a pinch. This plasma is during the pinch hot and dense enough to cause nuclear fusion and the emission of neutrons.
Light ion accelerators. Neutrons can be also produced by particle accelerators using targets of deuterium, tritium, lithium, beryllium, and other low-Z materials. In this case the target must be bombarded with accelerated hydrogen (H), deuterium (D), or tritium (T) nuclei.
Small neutron sources
Neutron Generators. Neutrons are produced in the fusion of deuterium and tritium in the following exothermic reaction. 2D + 3T → 4He + n + 17.6 MeV. The neutron is produced with a kinetic energy of 14.1 MeV. This can be achieved on a small scale in the laboratory with a modest 100 kV accelerator for deuterium atoms bombarding a tritium target. Continuous neutron sources of ~1011 neutrons/second can be achieved relatively simply.
Radioisotope source – (α,n) reactions. In certain light isotopes the ‘last’ neutron in the nucleus is weakly bound and is released when the compound nucleus formed following α-particle bombardment decays. The bombardment of beryllium by α-particles leads to the production of neutrons by the following exothermic reaction: 4He + 9Be→12C + n + 5.7 MeV. This reaction yields a weak source of neutrons with an energy spectrum resembling that from a fission source and is used nowadays in portable neutron sources. Radium, plutonium or americium can be used as an α-emitter.
Radioisotope source – (γ,n) reactions. (γ,n) reactions can also be used for the same purpose. In this type of source, because of the greater range of the γ-ray, the two physical components of the source can be separated making it possible to ‘switch off’ the reaction if so required by removing the radioactive source from the beryllium. (γ,n) sources produce a monoenergetic neutrons unlike (α,n) sources. The (γ,n) source uses antimony-124 as the gamma emitter in the following endothermic reaction.
124Sb→124Te + β− + γ
γ + 9Be→8Be + n – 1.66 MeV
Radioisotope source – spontaneous fission. Certain isotopes undergo spontaneous fission with emission of neutrons. The most commonly used spontaneous fission source is the radioactive isotope californium-252. Cf-252 and all other spontaneous fission neutron sources are produced by irradiating uranium or another transuranic element in a nuclear reactor, where neutrons are absorbed in the starting material and its subsequent reaction products, transmuting the starting material into the SF isotope.
Since their discovery in 1932 neutrons play an important role in many fields of modern science. The discovery of the neutron immediately gave scientists a new tool for probing the properties of atomic nuclei. In particular, discovery of neutrons and their properties has been important in the development of nuclear reactors and nuclear weapons. Main branches where the neutrons play key role are summarized below:
Nuclear Reactors
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei). Source: chemwiki.ucdavis.edu
A nuclear reactor is a key device of nuclear power plants, nuclear research facilities or nuclear propelled ships. Main purpose of the nuclear reactor is to initiate and control a sustained nuclear chain reaction. The nuclear chain reaction is initiated, sustained and controlled just via the free neutrons. The term chain means that one single nuclear reaction (neutron induced fission) causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The “one or more” is the key parameter of reactor physics. To raise or lower the power, the amount of reactions, respectively the amount of the free neutrons in the nuclear core must be changed (using the control rods).
Neutron diffraction
Simple scheme of neutron diffraction experiment. Source: www.psi.ch
Neutron diffraction experiments use an elastic neutron scattering to determine the atomic (or magnetic) structure of a material. The neutron diffraction is based the fact that thermal or cold neutrons have the wavelengths similar to atomic spacings. An examined sample (crystalline solids, gasses, liquids or amorphous materials) must be placed in a neutron beam of thermal (0.025 eV) or cold (neutrons in thermal equilibrium with very cold surroundings such as liquid deuterium) neutrons to obtain a diffraction pattern that provides information about the structure of the examined material. The neutron diffraction experiments are similar to X-ray diffraction experiments, but neutrons interact with matter differently. Photons (X-rays) interact primarily with the electrons surrounding (atomic electron cloud) a nucleus, but neutrons interact only with nuclei. Neither the electrons surrounding (atomic electron cloud) a nucleus nor the electric field caused by a positively charged nucleus affect a neutron’s flight. Due to their different properties, both methods together (neutron diffraction and X-ray diffraction) can provide complementary information about the structure of the material.
Applications in Medicine
Medical applications of neutrons began soon after the discovery of this particle in 1932. Neutrons are highly penetrating matter and ionizing, so they can be used in medical therapies such as radiation therapy or boron capture therapy. Unfortunately neutrons, when they are absorbed in matter, active the matter and leave the matter (target area) radioactive.
Neutron activation analysis
An analyzed sample is first irradiated with neutrons to produce specific radionuclides. The radioactive decay of these produced radionuclides is specific for each element (nuclide). Source: www.naa-online.net
Neutron activation analysis is a method for determining the composition of examined material. This method was discovered in 1936 and stands at the forefront of methods used for quantitative material analysis of major, minor, trace, and rare elements. This method is based on neutron activation, where an analyzed sample is first irradiated with neutrons to produce specific radionuclides. The radioactive decay of these produced radionuclides is specific for each element (nuclide). Each nuclide emits the characterictic gamma rays which are measured using gamma spectroscopy, where gamma rays detected at a particular energy are indicative of a specific radionuclide and determine concentrations of the elements. Main advantage of this method is that neutrons does not destroy the sample. This method can be also used for determine an enrichment of nuclear material.
It is known the fission neutrons are of importance in any chain-reacting system. Neutrons trigger the nuclear fission of some nuclei (235U, 238U or even 232Th). What is crucial the fission of such nuclei produces 2, 3 or morefree neutrons.
But not all neutrons are released at the same time following fission. Even the nature of creation of these neutrons is different. From this point of view we usually divide the fission neutrons into two following groups:
Prompt Neutrons. Prompt neutrons are emitted directly from fission and they are emitted within very short time of about 10-14 second.
Delayed Neutrons. Delayed neutrons are emitted by neutron rich fission fragments that are called the delayed neutron precursors. These precursors usually undergo beta decay but a small fraction of them are excited enough to undergo neutron emission. The fact the neutron is produced via this type of decay and this happens orders of magnitude later compared to the emission of the prompt neutrons, plays an extremely important role in the control of the reactor.
A chemical element is a species of atom having the same number of protons in their atomic nuclei (that is, the same atomic number, or Z). For example, the atomic number of carbon is 6, so the element carbon consists of all atoms which have exactly 6 protons. Periodic Table
A chemical element is a species of atom having the same number of protons in their atomic nuclei (that is, the same atomic number, or Z). For example, the atomic number of carbon is 6, so the element carbon consists of all atoms which have exactly 6 protons.
The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Periodic Table
The periodic table is a tabular arrangement of the chemical elements. It is organized in order of increasing atomic number. There is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. Generally, within one row (period) the elements are metals to the left, and non-metals to the right, with the elements having similar chemical behaviours placed in the same column.
Chemical Properties of Elements
Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
The total number of protons in the nucleus of an atom is called the atomic number (or the proton number) of the atom and is given the symbol Z. The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19coulombs. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
It is the Pauli exclusion principle that requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. The ordering of the electrons in the ground state of multielectron atoms, starts with the lowest energy state (ground state) and moves progressively from there up the energy scale until each of the atom’s electrons has been assigned a unique set of quantum numbers. This fact has key implications for the building up of the periodic table of elements.
Electron Affinity
In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as:
the change in energy (in kJ/mole) of a neutral atom or molecule (in the gaseous phase) when an electron is added to the atom to form a negative ion.
X + e– → X– + energy Affinity = – ∆H
In other words, it can be expressed as the neutral atom’s likelihood of gaining an electron. Note that, ionization energies measure the tendency of a neutral atom to resist the loss of electrons. Electron affinities are more difficult to measure than ionization energies.
A fluorine atom in the gas phase, for example, gives off energy when it gains an electron to form a fluoride ion.
F + e– → F– – ∆H = Affinity = 328 kJ/mol
To use electron affinities properly, it is essential to keep track of sign. When an electron is added to a neutral atom, energy is released. This affinity is known as the first electron affinity and these energies are negative. By convention, the negative sign shows a release of energy. However, more energy is required to add an electron to a negative ion which overwhelms any the release of energy from the electron attachment process. This affinity is known as the second electron affinity and these energies are positive.
Affinities of Non metals vs. Affinities of Metals
Metals: Metals like to lose valence electrons to form cations to have a fully stable shell. The electron affinity of metals is lower than that of nonmetals. Mercury most weakly attracts an extra electron.
Nonmetals: Generally, nonmetals have more positive electron affinity than metals. Nonmetals like to gain electrons to form anions to have a fully stable electron shell. Chlorine most strongly attracts extra electrons. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.
Electronegativity
Electronegativity, symbol χ, is a chemical property that describes the tendency of an atom to attract electrons towards this atom. For this purposes, a dimensionless quantity the Pauling scale, symbol χ, is the most commonly used.
The electronegativity of fluorine is:
χ = 4.0
In general, an atom’s electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an element or compound attracts electrons towards it.
The most electronegative atom, fluorine, is assigned a value of 4.0, and values range down to cesium and francium which are the least electronegative at 0.7.
Ionization Energy
Ionization energy, also called ionization potential, is the energy necessary to remove an electron from the neutral atom.
X + energy → X+ + e−
where X is any atom or molecule capable of being ionized, X+ is that atom or molecule with an electron removed (positive ion), and e− is the removed electron.
A nitrogen atom, for example, requires the following ionization energy to remove the outermost electron.
N + IE → N+ + e− IE = 14.5 eV
The ionization energy associated with removal of the first electron is most commonly used. The nth ionization energy refers to the amount of energy required to remove an electron from the species with a charge of (n-1).
1st ionization energy
X → X+ + e−
2nd ionization energy
X+ → X2+ + e−
3rd ionization energy
X2+ → X3+ + e−
Ionization Energy for different Elements
There is an ionization energy for each successive electron removed. The electrons that circle the nucleus move in fairly well-defined orbits. Some of these electrons are more tightly bound in the atom than others. For example, only 7.38 eV is required to remove the outermost electron from a lead atom, while 88,000 eV is required to remove the innermost electron. Helps to understand reactivity of elements (especially metals, which lose electrons).
In general, the ionization energy increases moving up a group and moving left to right across a period. Moreover:
Ionization energy is lowest for the alkali metals which have a single electron outside a closed shell.
Ionization energy increases across a row on the periodic maximum for the noble gases which have closed shells
For example, sodium requires only 496 kJ/mol or 5.14 eV/atom to ionize it. On the other hand neon, the noble gas, immediately preceding it in the periodic table, requires 2081 kJ/mol or 21.56 eV/atom.
Source: wikipedia.org License: CC BY-SA 3.0
References:
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Atom
We hope, this article, Chemical Elements, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The strong force and the electromagnetic force are two the four fundamental forces. They are very different. This article summarizes these differences.
Strong Interaction – Strong Force
The strong interaction or strong force is one of the four fundamental forces and involves the exchange of the vector gauge bosons known as gluons. In general, the strong interaction is very complicated interaction, because it significantly varies with distance. The strong nuclear force holds most ordinary matter together because it confines quarks into hadron particles such as the proton and neutron. Moreover, the strong force is the force which can hold a nucleus together against the enormous forces of repulsion (electromagnetic force) of the protons is strong indeed. From this point of view, we have to distinguish between:
Fundamental Strong Force. The fundamental strong force, or the strong force, is a very short range (less than about 0.8 fm, the radius of a nucleon) force, that acts directly between quarks. This force holds quarks together to form protons, neutrons, and other hadron particles. The strong interaction is mediated by the exchange of massless particles called gluons that act between quarks, antiquarks, and other gluons.
Residual Strong Force. The residual strong force, also known as the nuclear force, is a very short range (about 1 to 3 fm) force, which acts to hold neutrons and protons together in nuclei. In nuclei, this force acts against the enormous repulsive electromagnetic force of the protons. The term residual is associated with the fact, it is the residuum of the fundamental strong interaction between the quarks that make up the protons and neutrons. The residual strong force acts indirectly through the virtual π and ρ mesons, which transmit the force between nucleons that holds the nucleus together.
Electromagnetic Interaction – Electromagnetic Force
The electromagnetic force is the force responsible for all electromagnetic processes. It acts between electrically charged particles. It is infinite-ranged force, much stronger than gravitational force, obeys the inverse square law, but neither electricity nor magnetism adds up in the way that gravitational force does. Since there are positive and negative charges (poles), these charges tend to cancel each other out. Electromagnetism includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other.
The photon, the quantum of electromagnetic radiation, is an elementary particle, which is the force carrier of the electromagnetic force. Photons are gauge bosons having no electric charge or rest mass and one unit of spin. Common to all photons is the speed of light, the universal constant of physics. In empty space, the photon moves at c (the speed of light – 299 792 458 metres per second).
Forces between static electrically charged particles are governed by the Coulomb’s law. Coulomb’s Law can be used to calculate the force between charged particles (e.g. two protons). The electrostatic force is directly proportional to the electrical charges of the two particles and inversely proportional to the square of the distance between the particles. Coulomb’s Law is stated as the following equation.
Both, the Coulomb’s law and the magnetic force, are summarized in the Lorentz force law. Fundamentally, both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons.
The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The chemical properties of atoms and molecules are determined by the number of protons, in fact, by number and arrangement of electrons.
Strong Force vs Electromagnetic Force
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Strong Force
We hope, this article, Strong Force vs Electromagnetic Force, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The strong force and the gravitational force are two the four fundamental forces. They are very different. This article summarizes these differences.
Strong Interaction – Strong Force
The strong interaction or strong force is one of the four fundamental forces and involves the exchange of the vector gauge bosons known as gluons. In general, the strong interaction is very complicated interaction, because it significantly varies with distance. The strong nuclear force holds most ordinary matter together because it confines quarks into hadron particles such as the proton and neutron. Moreover, the strong force is the force which can hold a nucleus together against the enormous forces of repulsion (electromagnetic force) of the protons is strong indeed. From this point of view, we have to distinguish between:
Fundamental Strong Force. The fundamental strong force, or the strong force, is a very short range (less than about 0.8 fm, the radius of a nucleon) force, that acts directly between quarks. This force holds quarks together to form protons, neutrons, and other hadron particles. The strong interaction is mediated by the exchange of massless particles called gluons that act between quarks, antiquarks, and other gluons.
Residual Strong Force. The residual strong force, also known as the nuclear force, is a very short range (about 1 to 3 fm) force, which acts to hold neutrons and protons together in nuclei. In nuclei, this force acts against the enormous repulsive electromagnetic force of the protons. The term residual is associated with the fact, it is the residuum of the fundamental strong interaction between the quarks that make up the protons and neutrons. The residual strong force acts indirectly through the virtual π and ρ mesons, which transmit the force between nucleons that holds the nucleus together.
Gravitational Interaction – Gravitational Force
Gravity was the first force to be investigated scientifically. The gravitational force was described systematically by Isaac Newton in the 17th century. Newton stated that the gravitational force acts between all objects having mass (including objects ranging from atoms and photons, to planets and stars) and is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between the bodies. Since energy and mass are equivalent, all forms of energy (including light) cause gravitation and are under the influence of it. The range of this force is ∞ and it is weaker than the other forces. This relationship is shown in the equation below.
The equation illustrates that the larger the masses of the objects or the smaller the distance between the objects, the greater the gravitational force. So even though the masses of nucleons are very small, the fact that the distance between nucleons is extremely short may make the gravitational force significant. The gravitational force between two protons that are separated by a distance of 10-20 meters is about 10-24 newtons. Gravity is the weakest of the four fundamental forces of physics, approximately 1038 times weaker than the strong force. On the other hand, gravity is additive. Every speck of matter that you put into a lump contributes to the overall overall gravity of the lump. Since it is also a very long range force, it is dominant force at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Strong Force vs Gravitational Force
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Strong Force
We hope, this article, Strong Force vs Gravitational Force, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The electromagnetic force and the gravitational force are two the four fundamental forces. They are very different. This article summarizes these differences.
Electromagnetic Interaction – Electromagnetic Force
The electromagnetic force is the force responsible for all electromagnetic processes. It acts between electrically charged particles. It is infinite-ranged force, much stronger than gravitational force, obeys the inverse square law, but neither electricity nor magnetism adds up in the way that gravitational force does. Since there are positive and negative charges (poles), these charges tend to cancel each other out. Electromagnetism includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other.
The photon, the quantum of electromagnetic radiation, is an elementary particle, which is the force carrier of the electromagnetic force. Photons are gauge bosons having no electric charge or rest mass and one unit of spin. Common to all photons is the speed of light, the universal constant of physics. In empty space, the photon moves at c (the speed of light – 299 792 458 metres per second).
Forces between static electrically charged particles are governed by the Coulomb’s law. Coulomb’s Law can be used to calculate the force between charged particles (e.g. two protons). The electrostatic force is directly proportional to the electrical charges of the two particles and inversely proportional to the square of the distance between the particles. Coulomb’s Law is stated as the following equation.
Both, the Coulomb’s law and the magnetic force, are summarized in the Lorentz force law. Fundamentally, both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons.
The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The chemical properties of atoms and molecules are determined by the number of protons, in fact, by number and arrangement of electrons.
Gravitational Interaction – Gravitational Force
Gravity was the first force to be investigated scientifically. The gravitational force was described systematically by Isaac Newton in the 17th century. Newton stated that the gravitational force acts between all objects having mass (including objects ranging from atoms and photons, to planets and stars) and is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between the bodies. Since energy and mass are equivalent, all forms of energy (including light) cause gravitation and are under the influence of it. The range of this force is ∞ and it is weaker than the other forces. This relationship is shown in the equation below.
The equation illustrates that the larger the masses of the objects or the smaller the distance between the objects, the greater the gravitational force. So even though the masses of nucleons are very small, the fact that the distance between nucleons is extremely short may make the gravitational force significant. The gravitational force between two protons that are separated by a distance of 10-20 meters is about 10-24 newtons. Gravity is the weakest of the four fundamental forces of physics, approximately 1038 times weaker than the strong force. On the other hand, gravity is additive. Every speck of matter that you put into a lump contributes to the overall overall gravity of the lump. Since it is also a very long range force, it is dominant force at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Electromagnetic Force vs Gravitational Force
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Electromagnetic Force
We hope, this article, Electromagnetic Force vs Gravitational Force, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The weak force and the electromagnetic force are two the four fundamental forces. They are very different. This article summarizes these differences.
Weak Interaction – Weak Force
The weak interaction or weak force is one of the four fundamental forces and involves the exchange of the intermediate vector bosons, the W and the Z. Since these bosons are very massive (on the order of 80 GeV, the uncertainty principle dictates a range of about 10-18meters which is less than the diameter of a proton. As a result, the weak interaction takes place only at very small, sub-atomic distances.
The weak interaction responsible for some nuclear phenomena such as beta decay, which can be understood in terms of the weak force operating on the quarks within the neutron. One of two down quarks changes into an up quark by emitting a W– boson (carries away a negative charge). The W– boson then decays into a beta particle and an antineutrino. This process is equivalent to the process, in which a neutrino interacts with a neutron.
Electromagnetic Interaction – Electromagnetic Force
The electromagnetic force is the force responsible for all electromagnetic processes. It acts between electrically charged particles. It is infinite-ranged force, much stronger than gravitational force, obeys the inverse square law, but neither electricity nor magnetism adds up in the way that gravitational force does. Since there are positive and negative charges (poles), these charges tend to cancel each other out. Electromagnetism includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other.
The photon, the quantum of electromagnetic radiation, is an elementary particle, which is the force carrier of the electromagnetic force. Photons are gauge bosons having no electric charge or rest mass and one unit of spin. Common to all photons is the speed of light, the universal constant of physics. In empty space, the photon moves at c (the speed of light – 299 792 458 metres per second).
Forces between static electrically charged particles are governed by the Coulomb’s law. Coulomb’s Law can be used to calculate the force between charged particles (e.g. two protons). The electrostatic force is directly proportional to the electrical charges of the two particles and inversely proportional to the square of the distance between the particles. Coulomb’s Law is stated as the following equation.
Both, the Coulomb’s law and the magnetic force, are summarized in the Lorentz force law. Fundamentally, both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons.
The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The chemical properties of atoms and molecules are determined by the number of protons, in fact, by number and arrangement of electrons.
Weak Force vs Electromagnetic Force
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Weak Force
We hope, this article, Weak Force vs Electromagnetic Force, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The weak force and the gravitational force are two the four fundamental forces. They are very different. This article summarizes these differences.
Weak Interaction – Weak Force
The weak interaction or weak force is one of the four fundamental forces and involves the exchange of the intermediate vector bosons, the W and the Z. Since these bosons are very massive (on the order of 80 GeV, the uncertainty principle dictates a range of about 10-18meters which is less than the diameter of a proton. As a result, the weak interaction takes place only at very small, sub-atomic distances.
The weak interaction responsible for some nuclear phenomena such as beta decay, which can be understood in terms of the weak force operating on the quarks within the neutron. One of two down quarks changes into an up quark by emitting a W– boson (carries away a negative charge). The W– boson then decays into a beta particle and an antineutrino. This process is equivalent to the process, in which a neutrino interacts with a neutron.
Gravitational Interaction – Gravitational Force
Gravity was the first force to be investigated scientifically. The gravitational force was described systematically by Isaac Newton in the 17th century. Newton stated that the gravitational force acts between all objects having mass (including objects ranging from atoms and photons, to planets and stars) and is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between the bodies. Since energy and mass are equivalent, all forms of energy (including light) cause gravitation and are under the influence of it. The range of this force is ∞ and it is weaker than the other forces. This relationship is shown in the equation below.
The equation illustrates that the larger the masses of the objects or the smaller the distance between the objects, the greater the gravitational force. So even though the masses of nucleons are very small, the fact that the distance between nucleons is extremely short may make the gravitational force significant. The gravitational force between two protons that are separated by a distance of 10-20 meters is about 10-24 newtons. Gravity is the weakest of the four fundamental forces of physics, approximately 1038 times weaker than the strong force. On the other hand, gravity is additive. Every speck of matter that you put into a lump contributes to the overall overall gravity of the lump. Since it is also a very long range force, it is dominant force at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Weak Force vs Gravitational Force
References:
Nuclear and Reactor Physics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
Advanced Reactor Physics:
K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.
E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.
See also:
Weak Force
We hope, this article, Weak Force vs Gravitational Force, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.
The danger of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, yet it deposits energy to the molecules of material. Periodic Table
Executive Summary
Radiation is all around us. We are continually exposed to natural background radiation and it seems to be without any problem. Yes, high doses of ionizing radiation is harmful and potentially lethal to living beings, but these doses must be really high. Moreover, what is not harmful in high doses? Even high amount of water can be lethal to living beings.
The truth about low-dose radiation health effects still needs to be found. It is not exactly known, whether these low doses of radiation are detrimental or beneficial (and where is the threshold). There are studies, that claim, that small doses of radiation given at a low dose rate stimulate the defense mechanisms. Moreover, ionizing radiation can have health benefits in medicine, for example, in diagnostics where X-rays are used to produce pictures of the inside of the body. We do not claim, everything is OK. It also depends on the type of radiation and tissue, which was exposed.
But finally, if you compare risks, which arise from existence of radiation, natural or artificial, with risks, which arise from everyday life, then you must conclude that fear of radiation is irrational. Humans are often inconsistent in our treatment of perceived risks. Even though two situations may have similar risks, people will find one situation permissible and another unjustifiably dangerous.
The problem of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, and therefore they feel fear of this invisible threat.
Ionizing radiation – hazard symbol
How Dangerous is Radiation
Radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. All living creatures, from the beginning of time, have been, and are still being, exposed to ionizing radiation.
For example, potassium-40 is one of isotopes which contributes to internal exposure of human. Traces of potassium-40 are found in all potassium, and it is the most common radioisotope in the human body. Higher amounts can be also found in bananas. Does it mean, eating bananas must be dangerous? Of course not.
Explanation - Banana Equivalent Dose
In all cases, intensity of radiation matters. Banana equivalent dose is intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. One BED is often correlated to 10-7 Sievert (0.1 µSv). The radiation exposure from consuming a banana is approximately 1% of the average daily exposure to radiation, which is 100 banana equivalent doses (BED). A chest CT scan delivers 58,000 BED (5.8 mSv). A lethal dose, the dose that kills a human with a 50% risk within 30 days (LD50/30) of radiation, is approximately 50,000,000 BED (5000 mSv). However, in practice, this dose is not cumulative, as the principal radioactive component is excreted to maintain metabolic equilibrium. Moreover, there is also a problem with the collective dose.
The BED is only meant to inform the public about the existence of very low levels of natural radioactivity within a natural food and is not a formally adopted dose measurement.
Whether the source of radiation is natural or man-made, whether it is a large dose of radiation or a small dose, there will be some biological effects. In general, ionizing radiation is harmful and potentially lethal to living beings but can have health benefits in medicine, for example, in radiation therapy for the treatment of cancer and thyrotoxicosis.
But where is the threshold between positive and negative effects of radiation?
What does danger mean?
In the following thoughts, we try to summarize facts and hypothesis, which can help you understand the problem. It is all about the risks arising from exposure to ionizing radiation and about the consistency in all risks of everyday life. But first we have to summarize key facts about ionizing radiation.
Intensity of Radiation – Dose and Dose Rate
Principles of Radiation Protection – Time, Distance, Shielding
Intensity of ionizing radiation is a key factor, which determines health effects from being exposed to any radiation. It is similar as being exposed to heat radiation from a fire (in fact, it is also transferred by photons). If you are too close to a fire, the intensity of thermal radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from ionizing radiation sources.
In short, to get burned (deterministic effects and demonstrable stochastic effects) by ionizing radiation, you must be exposed to really high amount of radiation. But almost everytime, we are talking about so called low doses. As was written, today the protection system is based on the LNT-hypothesis, which is a conservative model used in radiation protection to estimate the health effects from small radiation doses. This model is excellent for setting up a protection system for all use of ionizing radiation. This model assumes, that there is no threshold point and risk increases linearly with a dose, i.e. the LNT model implies that there is no safe dose of ionizing radiation. If this linear model is correct, then natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second. It must be added, the research during the last two decades is very interesting and show that small doses of radiation given at a low dose rate stimulate the defense mechanisms. Therefore the LNT model is not universally accepted with some proposing an adaptive dose–response relationship where low doses are protective and high doses are detrimental. Many studies have contradicted the LNT model and many of these have shown adaptive response to low dose radiation resulting in reduced mutations and cancers. On the other hand, it is very important, to what type of radiation is a person exposed.
Natural Background Radiation
Natural background radiation is ionizing radiation, that originates from a variety of natural sources. All living creatures, from the beginning of time, have been, and are still being, exposed to ionizing radiation. This radiation is not associated with any human activity. There are radioactive isotopes in our bodies, houses, air, water and in the soil. We all are also exposed to radiation from outer space.
Sources of Natural Background Radiation
We divide all these natural radiation sources into three groups:
Alternative assumptions for the extrapolation of the cancer risk vs. radiation dose to low-dose levels, given a known risk at a high dose: LNT model, and hormesis model.
You can not go through life without radiation. The danger of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, yet it deposits energy to the molecules of the body.
But don’t worry, the doses from background radiation are usually very small (except radon exposure). Low dose here means additional small doses comparable to the normal background radiation (10 µSv = average daily dose received from natural background). The problem is that, at very low doses, it is practically impossible to correlate any irradiation with certain biological effects. This is because the baseline cancer rate is already very high and the risk of developing cancer fluctuates 40% because of individual life style and environmental effects, obscuring the subtle effects of low-level radiation.
Intensity - Acute and Chronic Doses
Biological effects of radiation and their consequences depends strongly on the level of dose rate obtained. Dose rate is a measure of radiation dose intensity (or strength). Low-level doses are common for everyday life. In the following points there are a few examples of radiation exposure, which can be obtained from various sources.
05 µSv – Sleeping next to someone
09 µSv – Living within 30 miles of a nuclear power plant for a year
1 µSv – Eating one banana
3 µSv – Living within 50 miles of a coal power plant for a year
10 µSv – Average daily dose received from natural background
20 µSv – Chest X-ray
From biological consequences point of view, it is very important to distinguish between doses received over short and extended periods. Therefore, biological effects of radiation are typically divided into two categories.
Acute Doses. An “acute dose” (short-term high-level dose) is one that occurs over a short and finite period of time, i.e., within a day.
Chronic Doses. A “chronic dose” (long-term low-level dose) is a dose that continues for an extended period of time, i.e., weeks and months, so that it is better described by a dose rate.
High doses tend to kill cells, while low doses tend to damage or change them. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Acute doses below 250 mGy are unlikely to have any observable effects. Acute doses of about 3 to 5 Gy have a 50% chance of killing a person some weeks after the exposure, if a person receives no medical treatment.
Low doses spread out over long periods of time don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years. Moreover, some studies demonstrate, most of human tissues exhibit a more pronounced tolerance to the effects of low-LET radiation in case of a prolonged exposure compared to a one-time exposure to a similar dose.
In radiation protection, most adverse health effects of radiation exposure are usually divided into two broad classes:
Deterministic effects are threshold health effects, that are related directly to the absorbed radiation dose and the severity of the effect increases as the dose increases.
Stochastic effects occur by chance, generally occurring without a threshold level of dose. Probability of occurrence of stochastic effects is proportional to the dose but the severity of the effect is independent of the dose received.
Deterministic Effects
Deterministic effects (or non-stochastic health effects) are health effects, that are related directly to the absorbed radiation dose and the severity of the effect increases as the dose increases. Deterministic effects have a threshold below which no detectable clinical effects do occur. The threshold may be very low (of the order of magnitude of 0.1 Gy or higher) and may vary from person to person. For doses between 0.25 Gy and 0.5 Gy slight blood changes may be detected by medical evaluations and for doses between 0.5 Gy and 1.5 Gy blood changes will be noted and symptoms of nausea, fatigue, vomiting occur.
Once the threshold has been exceeded, the severity of an effect increases with dose. The reason for the presence of this threshold dose is that radiation damage (serious malfunction or death) of a critical population of cells (high doses tend to kill cells) in a given tissue needs to be sustained before injury is expressed in a clinically relevant form. Therefore, deterministic effects are also termed tissue reaction. They are also called non-stochastic effects to contrast with chance-like stochastic effects (e.g. cancer induction).
Deterministic effects are not necessarily more or less serious than stochastic effects. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Acute doses below 250 mGy are unlikely to have any observable effects. Acute doses of about 3 to 5 Gy have a 50% chance of killing a person some weeks after the exposure, if a person receives no medical treatment. Deterministic effects can ultimately lead to a temporary nuisance or also to a fatality. Examples of deterministic effects:
Examples of deterministic effects are:
Acute radiation syndrome, by acute whole-body radiation
Radiation burns, from radiation to a particular body surface
Radiation-induced thyroiditis, a potential side effect from radiation treatment against hyperthyroidism
Chronic radiation syndrome, from long-term radiation.
Radiation-induced lung injury, from for example radiation therapy to the lungs
Stochastic Effects
Stochastic effectsof ionizing radiation occur by chance, generally occurring without a threshold level of dose. Probability of occurrence of stochastic effects is proportional to the dose but the severity of the effect is independent of the dose received. The biological effects of radiation on people can be grouped into somatic and hereditary effects. Somatic effects are those suffered by the exposed person. Hereditary effects are those suffered by the offspring of the individual exposed. Cancer risk is usually mentioned as the main stochastic effect of ionizing radiation, but also hereditary disorders are stochastic effects.
According to ICRP:
(83) On the basis of these calculations the Commission proposes nominal probability coefficients for detriment-adjusted cancer risk as 5.5 x 10-2 Sv-1 for the whole population and 4.1 x 10-2 Sv-1 for adult workers. For heritable effects, the detriment-adjusted nominal risk in the whole population is estimated as 0.2 x 10-2 Sv-1 and in adult workers as 0.1 x 10-2 Sv-1 .
Special Reference: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).
The SI unit for effective dose, the sievert, represents the equivalent biological effect of the deposit of a joule of gamma rays energy in a kilogram of human tissue. As a result, one sievert represents a 5.5% chance of developing cancer. Note that, the effective dose is not intended as a measure of deterministic health effects, which is the severity of acute tissue damage that is certain to happen, that is measured by the quantity absorbed dose.
Biological Effects and Dose Limits
In radiation protection, dose limits are set to limit stochastic effects to an acceptable level, and to prevent deterministic effects completely. Note that, stochastic effects are those arising from chance: the greater the dose, the more likely the effect. Deterministic effects are those which normally have a threshold: above this, the severity of the effect increases with the dose. Dose limits are a fundamental component of radiation protection, and breaching these limits is against radiation regulation in most countries. Note that, the dose limits described in this article apply to routine operations. They do not apply to an emergency situation when human life is endangered. They do not apply in emergency exposure situations where an individual is attempting to prevent a catastrophic situation.
The limits are split into two groups, the public, and occupationally exposed workers. According to ICRP, occupational exposure refers to all exposure incurred by workers in the course of their work, with the exception of
excluded exposures and exposures from exempt activities involving radiation or exempt sources
any medical exposure
the normal local natural background radiation.
The following table summarizes dose limits for occupationally exposed workers and for the public:
Table of dose limits for occupationally exposed workers and for the public. Source of data: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).
Source of data: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).
According to the recommendation of the ICRP in its statement on tissue reactions of 21. April 2011, the equivalent dose limit for the lens of the eye for occupational exposure in planned exposure situations was reduced from 150 mSv/year to 20 mSv/year, averaged over defined periods of 5 years, with no annual dose in a single year exceeding 50 mSv.
Limits on effective dose are for the sum of the relevant effective doses from external exposure in the specified time period and the committed effective dose from intakes of radionuclides in the same period. For adults, the committed effective dose is computed for a 50-year period after intake, whereas for children it is computed for the period up to age 70 years. The effective whole-body dose limit of 20 mSv is an average value over five years. The real limit is 100 mSv in 5 years, with not more than 50 mSv in any one year.
Controversy of LNT Model
As was written previously (LNT model), today the protection system is based on the LNT-hypothesis, which is a conservative model used in radiation protection to estimate the health effects from small radiation doses. This model is excellent for setting up a protection system for all use of ionizing radiation. In comparison to the hormesis model, the LNT model assumes, that there is no threshold point and risk increases linearly with a dose, i.e. the LNT model implies that there is no safe dose of ionizing radiation. If this linear model is correct, then natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second.
The LNT model is primarily based on the life span study (LSS) of atomic bomb survivors in Japan. However, while this pattern is undisputed at high doses, this linear extrapolation of risk to low doses is challenged by many recent experiments involving cell mechanisms and there is also high uncertainty involved in estimating risk using only epidemiological studies. The problem is that, at very low doses, it is practically impossible to correlate any irradiation with certain biological effects. This is because the baseline cancer rate is already very high and the risk of developing cancer fluctuates 40% because of individual life style and environmental effects, obscuring the subtle effects of low-level radiation. Government and regulatory bodies assume a LNT model instead of a threshold or hormesis not because it is the more scientifically convincing, but because it is the more conservative estimate.
In case of low doses, its conservativeness (linearity) has enormous consequences and the model is sometimes wrongly (perhaps intentionally) used to quantify the cancerous effect of collective doses of low-level radioactive contamination. A linear dose-effect curve makes it possible to use collective doses to calculate the detrimental effects to an irradiated population. It is also argued that LNT model had caused an irrational fear of radiation, since every microsievert can be converted to the probability of cancer induction, however small this probability is. For example, if ten million people receives an effective dose of 0.1 µSv (an equivalent of eating one banana), then the collective dose will be S = 1 Sv. Does it mean there is 5.5% chance of developing cancer for one person due to eating banana? Note that, for high doses one sievert represents a 5.5% chance of developing cancer.
Problem of this model is that it neglects a number of defence biological processes that may be crucial at low doses. The research during the last two decades is very interesting and show that small doses of radiation given at a low dose rate stimulate the defense mechanisms. Therefore the LNT model is not universally accepted with some proposing an adaptive dose–response relationship where low doses are protective and high doses are detrimental. Many studies have contradicted the LNT model and many of these have shown adaptive response to low dose radiation resulting in reduced mutations and cancers.
Type of Radiation – High-LET x Low-LET
Source: ICRP Publ. 103: The 2007 Recommendations of the International Commission on Radiological Protection
This section is about the fact, that there are several types of ionizing radiation and each type of radiation interacts with matter in a different way. When discussing the intensity of radiation, we have to take into account to which type of radiation are you exposed. For example, alpha radiation tend to travel only a short distance and do not penetrate very far into tissue if at all. Therefore, alpha radiation is sometimes treated as non-hazardous, since it cannot penetrate surface layers of human skin. This is naturally true, but this is not valid for internal exposure by alpha radionuclides. When inhaled or ingested, alpha radiation is much more dangerous than other types of radiation. Note that, the radiation weighting factor for alpha radiation is equal to 20. It was discovered, biological effects of any radiation increases with the linear energy transfer (LET). In short, the biological damage from high-LET radiation (alpha particles, protons or neutrons) is much greater than that from low-LET radiation (gamma rays).
Ionizing radiation is categorized by the nature of the particles or electromagnetic waves that create the ionizing effect. These particles/waves have different ionization mechanisms, and may be grouped as:
Directly ionizing. Charged particles (atomic nuclei, electrons, positrons, protons, muons, etc.) can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. These particles must be moving at relativistic speeds to reach the required kinetic energy. Even photons (gamma rays and X-rays) can ionize atoms directly (despite they are electrically neutral) through the Photoelectric effect and the Compton effect, but secondary (indirect) ionization is much more significant.
Indirectly ionizing. Indirect ionizing radiation is electrically neutral particles and therefore does not interact strongly with matter. The bulk of the ionization effects are due to secondary ionizations.
As was written, it is crucial, whether we are exposed to radiation from external sources or from internal sources. This is similar as for another dangerous substances. Internal exposure is more dangerous than external exposure, since we are carrying the source of radiation inside our bodies and we cannot use any of radiation protection principles (time, distance, shielding). The intake of radioactive material can occur through various pathways such as ingestion of radioactive contamination in food or liquids, inhalation of radioactive gases, or through intact or wounded skin. On this place, we have to distinguish between radiation and contamination. Radioactive contamination consist of radioactive material, that generate ionizing radiation. It is the source of radiation, not radiation itself. Anytime that radioactive material is not in a sealed radioactive source container and might be spread onto other objects, radioactive contamination is a possibility. For example, radioiodine, iodine-131, is an important radioisotope of iodine. Radioiodine plays a major role as a radioactive isotope present in nuclear fission products, and it is a major contributor to the health hazards when released into the atmosphere during an accident. Iodine-131 has a half-life of 8.02 days. The target tissue for radioiodine exposure is the thyroid gland. The external beta and gamma dose from radioiodine present in the air is quite negligible when compared to the committed dose to the thyroid that would result from breathing this air.
Internal Dose Uptake
If the source of radiation is inside our body, we say, it is internal exposure. The intake of radioactive material can occur through various pathways such as ingestion of radioactive contamination in food or liquids, inhalation of radioactive gases, or through intact or wounded skin. Most radionuclides will give you much more radiation dose if they can somehow enter your body, than they would if they remained outside. For internal doses, we first should distinguish between intake and uptake. Intake means what a person takes in. Uptake means what a person keeps.
When a radioactive compound enters the body, the activity will decrease with time, due both to radioactive decay and to biological clearance. The decrease varies from one radioactive compound to another. For this purpose, the biological half-life is defined in radiation protection.
The biological half-life is the time taken for the amount of a particular element in the body to decrease to half of its initial value due to elimination by biological processes alone, when the rate of removal is roughly exponential. The biological half-life depends on the rate at which the body normally uses a particular compound of an element. Radioactive isotopes that were ingested or taken in through other pathways will gradually be removed from the body via bowels, kidneys, respiration and perspiration. This means that a radioactive substance can be expelled before it has had the chance to decay.
As a result, the biological half-life significantly influences the effective half-life and the overall dose from internal contamination. If a radioactive compound with radioactive half-life (t1/2) is cleared from the body with a biological half-life tb, the effective half-life (te) is given by the expression:
As can be seen, the biological mechanisms always decreases the overall dose from internal contamination. Moreover, if t1/2 is large in comparison to tb, the effective half-life is approximately the same as tb.
For example, tritium has the biological half-life about 10 days, while the radioactive half-life is about 12 years. On the other hand, radionuclides with very short radioactive half-lives have also very short effective half-lives. These radionuclides will deliver, for all practical purposes, the total radiation dose within the first few days or weeks after intake.
For tritium, the annual limit intake (ALI) is 1 x 109 Bq. If you take in 1 x 109 Bq of tritium, you will receive a whole-body dose of 20 mSv. The committed effective dose, E(t), is therefore 20 mSv. It does not depend whether a person intakes this amount of activity in a short time or in a long time. In every case, this person gets the same whole-body dose of 20 mSv.
Contamination versus Radiation
Radioactive contamination consist of radioactive material, that generate ionizing radiation. It is the source of radiation, not radiation itself. Anytime that radioactive material is not in a sealed radioactive source container and might be spread onto other objects, radioactive contamination is a possibility. Radioactive contamination may be characterized by following points:
Radioactive contamination consist of radioactive material (contaminants), that may be solid, liquid or gaseous. Large contaminants can be even visible, but you cannot see radiation produced.
When released, contaminants can be spread by air, water or just by mechanical contact.
We cannot shield contamination.
We can mitigate contamination by protecting integrity of barriers (source container, fuel cladding, reactor vessel, containment building)
Since contaminants interact chemically, they may be contained within objects such as the human body.
We can rid of contamination by many mechanical, chemical (decontaminate surfaces), or biological processes (biological half-life).
It is of the highest importance, which material is the radioactive contaminant (half-life, mode of decay, energy).
Ionizing radiation is formed by high-energy particles (photons, electrons, etc.), that can penetrate matter and ionize (to form ion by losing electrons) target atoms to form ions. Radiation exposure is the consequence of the presence nearby the source of radiation. Radiation exposure as a quantity is defined as a measure of the ionization of material due to ionizing radiation. The danger of ionizing radiation lies in the fact that the radiation is invisible and not directly detectable by human senses. People can neither see nor feel radiation, yet it deposits energy to the molecules of the body. The energy is transferred in small quantities for each interaction between radiation and a molecule and there are usually many such interactions. Unlike radioactive contamination, radiation may be characterized by following points:
Radiation consist consist of high-energy particles that can penetrate matter and ionize (to form ion by losing electrons) target atoms. Radiation is invisible, and not directly detectable by human senses. It must be noted, beta radiation is indirectly visible due to cherenkov radiation.
Unlike contamination, radiation cannot be spread by any medium. It travels through materials until it loses its energy. We can shield radiation (e.g. by standing around the corner).
Exposure to ionizing does not necessary mean, that the object becomes radioactive (except very rare neutron radiation).
Radiation can penetrate barriers, but sufficiently thick barrier can minimize all effects.
Unlike contaminants, radiation cannot interact chemically with matter and cannot be bound inside body.
It is not important, which material is the source of certain radiation. Only type of radiation and energy matters.
Airborne Contamination
Airborne contamination is of particular importance in nuclear power plants, where it must be monitored. Contaminants can become airborne especially during reactor top head remove, reactor refueling, and during manipulations within spent fuel pool. The air can be contaminated with radioactive isotopes especially in particulate form, which poses a particular inhalation hazard. This contamination consists of various fission and activation products that enter the air in gaseous, vapour or particulate form. There are four types of airborne contamination in nuclear power plants, namely:
Particulates. Particulate activity is an internal hazard, because it can be inhaled. Transportable particulate material taken into the respiratory system will enter the blood stream and be carried to all parts of the body. Non-transportable particulates will stay in the lungs with a certain biological half-life. For example, Sr-90, Ra-226 and Pu-239 are radionuclides known as bone-seeking radionuclides. These radionuclides have long biological half-lives and are serious internal hazards. Once deposited in bone, they remain there essentially unchanged in amount during the lifetime of the individual. The continued action of the emitted alpha particles can cause significant injury: over many years they deposit all their energy in a tiny volume of tissue, because the range of the alpha particles is very short.
Noble gases. Radioactive noble gases, such as xenon-133, xenon-135 and krypton-85 are present in reactor coolant especially when fuel leakages are present. As they appear in coolant, they become airborne and they can be inhaled. They are exhaled right after they are inhaled, because the body does not react chemically with them. If workers are working in a noble gas cloud, the external dose they will receive is about 1000 times greater than the internal dose. Because of this, we are only concerned about the external beta and gamma dose rates.
Radioiodine. Radioiodine, iodine-131, is an important radioisotope of iodine. Radioiodine plays a major role as a radioactive isotope present in nuclear fission products, and it is a major contributor to the health hazards when released into the atmosphere during an accident. Iodine-131 has a half-life of 8.02 days. The target tissue for radioiodine exposure is the thyroid gland. The external beta and gamma dose from radioiodine present in the air is quite negligible when compared to the committed dose to the thyroid that would result from breathing this air. The biological half-life for iodine inside the human body is about 80 days (according to ICRP). Iodine in food is absorbed by the body and preferentially concentrated in the thyroid where it is needed for the functioning of that gland. When 131I is present in high levels in the environment from radioactive fallout, it can be absorbed through contaminated food, and will also accumulate in the thyroid. 131I decays with a half-life of 8.02 days with beta particle and gamma emissions. As it decays, it may cause damage to the thyroid. The primary risk from exposure to high levels of 131I is the chance occurrence of radiogenic thyroid cancer in later life. For 131I, ICRP has calculated that if you inhale 1 x 106 Bq, you will receive a thyroid dose of HT = 400 mSv (and weighted whole-body dose of 20 mSv).
Tritium.Tritium is a byproduct in nuclear reactors. Most important source (due to releases of tritiated water) of tritium in nuclear power plants stems from the boric acid, which is commonly used as a chemical shim to compensate an excess of initial reactivity. Note that, tritium emits low-energy beta particles with a short range in body tissues and, therefore, poses a risk to health as a result of internal exposure only following ingestion in drinking water or food, or inhalation or absorption through the skin. The tritium taken into the body is uniformly distributed among all soft tissues. According to the ICRP, a biological half-time of tritium is 10 days for HTO and 40 days for OBT (organically bound tritium) formed from HTO in the body of adults. As a result, for an intake of 1 x 109 Bq of tritium (HTO), an individual will get a whole-body dose of 20 mSv (equal to the intake of 1 x 106 Bq of 131I). While for PWRs tritium poses a minor risk to health, for heavy water reactors, it contributes significantly to collective dose of plant workers. Note that, “Air that is saturated with moderator water at 35°C can give 3 000 mSv/h of tritium to an unprotected worker (See also: J.U.Burnham. Radiation Protection). The best protection from tritium can be achieved using an air-supplied respirator. Tritium cartridge respirators protects workers only by a factor of 3. The only way to reduce the skin absorption is by wearing plastics. In PHWR power plants, workers must wear plastics for work in atmospheres containing more than 500 μSv/h.
Consistency in all Risks
Finally, it is all about the risks arising from exposure to ionizing radiation and about the consistency in all risks of everyday life. In general, danger (also risk or peril) is the possibility of something bad happening. A situation in which there is a risk of something bad happening, is called dangerous, risky or perilous. Yes, the term ionizing radiation sounds very dangerous, but how exactly dangerous radiation is?
Humans are often inconsistent in our treatment of perceived risks. Even though two situations may have similar risks, people will find one situation permissible and another unjustifiably dangerous. For radiation risks, doses to the public must be kept under 1 mSv/year. Even for very conservative case of linear non-threshold assumption, one millisievert represents a 0.0055% chance of some detrimental health effects. Two points:
In our opinion, this is an acceptable risk. Note that, annual doses from natural background radiation in on average about 3.7 mSv/year (10 µSv = average daily dose received from natural background).
Moreover, problem of this model is that it neglects a number of defence biological processes that may be crucial at low doses. The research during the last two decades is very interesting and shows that small doses of radiation given at a low dose rate stimulate the defense mechanisms.
Annually received dose of 1 mSv causes very conservatively about 0.0055% chance of some detrimental health effects. In April 2012, a year after the Fukushima accident, cleanup efforts are supposed to be happening wherever the radiation dose exceeds government regulations. Entire towns are still off limits because the annual dose from the ground is projected to be greater than 50 mSv or even 20 mSv, leaving many people in the area homeless and jobless. But did anyone take into account health effects of this evacuation. The consequences of low-level radiation are often more psychological than radiological. Forced evacuation from a radiological or nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in Ukraine. A comprehensive 2005 study concluded that “the mental health impact of Chernobyl is the largest public health problem unleashed by the accident to date”. But what if the threshold model is true, and doses of up to 100 mSv/yr actually result in no detectable health risks? This would mean that people are being unnecessarily kept away and prevented from working on their farms for negligible health effects. Recall that the annual dose in some parts of Araxa, Brazil is higher than 20 mSv while the average dose examined in the three-country nuclear worker studies was 30-40 mSv/yr, and that these studies found no significant increase in solid cancers or leukemias from those doses.
Another point of view can be obtained when we will consider all risks of everyday life. What about risks, which arise from transportation. Nearly 1.25 million people die in road crashes each year, on average 3,287 deaths a day. Road crashes are the leading cause of death among young people ages 15-29, and the second leading cause of death worldwide among young people ages 5-14. On a road, people don’t realize the kinetic energy of a car. So why we do not stop driving cars? Yes, transportation is today essential, but so are the peaceful uses of radiation. And what about smoking cigarettes? Cigarettes contain also polonium-210, originating from the decay products of radon, which stick to tobacco leaves. Polonium-210 emits a 5.3 MeV alpha particle, which provides most of equivalent dose. Heavy smoking results in a dose of 160 mSv/year to localized spots at the bifurcations of segmental bronchi in the lungs from the decay of polonium-210. This dose is not readily comparable to the radiation protection limits, since the latter deal with whole body doses, while the dose from smoking is delivered to a very small portion of the body.
Finally, we would like to discuss a very interesting fact. It is generally known, the increasing use of nuclear power and electricity generation using nuclear reactors will lead to a small but increasing radiation dose to the general public. But it is not generally known, power generation from coal also creates additional exposures, and, what is more interesting, while exposure levels are very low, the coal cycle contributes more than half of the total radiation dose to the global population from electricity generation. The nuclear fuel cycle contributes less than one-fifth of this. The collective dose, which are defined as the sum of all individual effective doses in a group of people over the time period or during the operation being considered due to ionizing radiation, is:
670-1400 manSv for coal cycle, depending on the age of the power plant,
130 man Sv for nuclear fuel cycle,
5-160 man Sv for geothermal power,
55 man Sv for natural gas
03 man Sv for oil
Yes, these results should be seen from the perspective of the share of each technology in worldwide electricity production. Since 40 per cent of the world’s energy was produced by the coal cycle in 2010, and 13 per cent by nuclear, the normalized collective dose will be about the same:
7 – 1.4 man Sv/GW.a (man sievert per gigawatt year) for coal cycle
43 man Sv/GW.a (man sievert per gigawatt year) for nuclear fuel cycle
Special Reference: Sources and effects of ionizing radiation, UNSCEAR 2016 – Annex B. New York, 2017. ISBN: 978-92-1-142316-7.
Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.
See also:
Radiation
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