nuclear transmutation
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Nuclear transmutation is the conversion of one
chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nu ...
or an
isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom. The term ...
into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed. A transmutation can be achieved either by
nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a tr ...
s (in which an outside particle reacts with a nucleus) or by
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
, where no outside cause is needed. Natural transmutation by
stellar nucleosynthesis Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance cons ...
in the past created most of the heavier chemical elements in the known existing universe, and continues to take place to this day, creating the vast majority of the most common elements in the universe, including
helium Helium (from el, ἥλιος, Helios, lit=Sun) is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting ...

helium
,
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
and
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...
. Most stars carry out transmutation through fusion reactions involving
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
and helium, while much larger stars are also capable of fusing heavier elements up to
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...

iron
late in their evolution. Elements heavier than iron, such as
gold Gold is a chemical element with the Symbol (chemistry), symbol Au (from la, aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a brightness, bright, slightly reddish yel ...

gold
or
lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate h ...

lead
, are created through elemental transmutations that can only naturally occur in
supernova (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526 A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a powerful and luminous stellar explosion An explosion is a rapid expan ...

supernova
e. As stars begin to fuse heavier elements, substantially less energy is released from each fusion reaction. This continues until it reaches iron which is produced by an
endothermic An endothermic process is any process with an increase in the enthalpy Enthalpy is a property of a thermodynamic system A thermodynamic system is a body of matter and/or radiation, confined in space by walls, with defined permeabilities, whic ...
reaction consuming energy. No heavier element can be produced in such conditions. One type of natural transmutation observable in the present occurs when certain
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

radioactive
elements present in nature spontaneously decay by a process that causes transmutation, such as
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', modern pronunciation ''álfa'') is the first letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century ...

alpha
or
beta decay (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. Neither of these depictions shows the intermediate virtual boson. In nuclear physics, beta decay (''β''-decay) is a type of radioactive decay Rad ...
. An example is the natural decay of
potassium-40 Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.251 years. It makes up 0.012% (120 parts-per notation, ppm) of the total amount of potassium found in nature. Potassium-40 is a rare example of an isotope th ...

potassium-40
to
argon-40 Argon Argon is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the s ...
, which forms most of the
argon Argon is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same num ...
in the air. Also on Earth, natural transmutations from the different mechanisms of ''natural
nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a tr ...
s'' occur, due to
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approxi ...
bombardment of elements (for example, to form
carbon-14 Carbon-14 (14C), or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleag ...
), and also occasionally from natural neutron bombardment (for example, see
natural nuclear fission reactor A fossil natural nuclear fission reactor is a uranium mineral deposit, deposit where self-sustaining nuclear chain reactions have occurred. This can be examined by analysis of isotope ratios. The conditions under which a natural nuclear reactor cou ...
). Artificial transmutation may occur in machinery that has enough energy to cause changes in the nuclear structure of the elements. Such machines include
particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it was the most powerful particle accelerator in the world, accelerating protons to an en ...
s and
tokamak A tokamak (; russian: токамáк) is a device which uses a powerful magnetic field to confine plasma (physics), plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement fusion, magnetic confinement devices ...
reactors. Conventional fission power reactors also cause artificial transmutation, not from the power of the machine, but by exposing elements to
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

neutron
s produced by fission from an artificially produced
nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron">uranium-235.html" ;"title="nuclear fission chain reaction: 1) A uranium-235">nuclear fission chain reaction: 1) A uranium-235 atom absorbs a neutron, ...
. For instance, when a uranium atom is bombarded with slow neutrons, fission takes place. This releases, on average, 3 neutrons and a large amount of energy. The released neutrons then cause fission of other uranium atoms, until all of the available uranium is exhausted. This is called a
chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a pro ...
. Artificial nuclear transmutation has been considered as a possible mechanism for reducing the volume and hazard of
radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom An atom is the smallest unit of ordinary matter In classical physic ...
.


History


Alchemy

The term ''transmutation'' dates back to
alchemy Depiction of Ouroboros from the alchemical treatise ''Aurora consurgens'' (15th century), Zentralbibliothek Zürich, Switzerland Alchemy (from Arabic: ''al-kīmiyā''; from Ancient Greek: ''khumeía'') is an ancient branch of natural philosop ...
. Alchemists pursued the
philosopher's stone The philosopher's stone, more properly philosophers' stone or stone of the philosophers (Arabic Arabic (, ' or , ' or ) is a Semitic language that first emerged in the 1st to 4th centuries CE.Semitic languages: an international handbook ...

philosopher's stone
, capable of
chrysopoeia In alchemy File:Aurora consurgens zurich 044 f-21v-44 dragon-pot.jpg, Depiction of Ouroboros from the alchemical treatise ''Aurora consurgens'' (15th century), Zentralbibliothek Zürich, Switzerland Alchemy (from Arabic: ''al-kīmiyā''; from ...
– the transformation of
base metal A base metal is a common and inexpensive metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conduc ...
s into gold. While alchemists often understood chrysopoeia as a metaphor for a mystical, or religious process, some practitioners adopted a literal interpretation, and tried to make gold through physical experiment. The impossibility of the metallic transmutation had been debated amongst alchemists, philosophers and scientists since the Middle Ages. Pseudo-alchemical transmutation was outlawed and publicly mocked beginning in the fourteenth century. Alchemists like
Michael Maier Michael Maier ( la, Michael Maierus; 1568–1622) was a German physician and counsellor to Rudolf II Habsburg. He was a learned alchemist, epigramist and amateur composer. Early life Maier was born in Rendsburg, Duchy of Holstein, Holstein, ...

Michael Maier
and Heinrich Khunrath wrote tracts exposing fraudulent claims of gold making. By the 1720s, there were no longer any respectable figures pursuing the physical transmutation of substances into gold. Antoine Lavoisier, in the 18th century, replaced the Classical element#Elements in Medieval alchemy, alchemical theory of elements with the modern theory of chemical elements, and John Dalton further developed the notion of atoms (from the alchemical theory of Corpuscularianism, corpuscles) to explain various chemical processes. The disintegration of atoms is a distinct process involving much greater energies than could be achieved by alchemists.


Modern physics

It was first consciously applied to modern physics by Frederick Soddy when he, along with Ernest Rutherford in 1901, discovered that radioactive thorium was converting itself into radium. At the moment of realization, Soddy later recalled, he shouted out: "Rutherford, this is transmutation!" Rutherford snapped back, "For Christ's sake, Soddy, don't call it ''transmutation''. They'll have our heads off as alchemists." Rutherford and Soddy were observing natural transmutation as a part of
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
of the alpha decay type. The first artificial transmutation was accomplished in 1925 by Patrick Blackett, a research fellow working under Rutherford, with the transmutation of nitrogen into Oxygen-17, oxygen, using alpha particles directed at nitrogen 14N + α → Oxygen-17, 17O + p.  Rutherford had shown in 1919 that a proton (he called it a hydrogen atom) was emitted from alpha bombardment experiments but he had no information about the residual nucleus. Blackett's 1921-1924 experiments provided the first experimental evidence of an artificial nuclear transmutation reaction. Blackett correctly identified the underlying integration process and the identity of the residual nucleus. In 1932, a fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues John Cockcroft and Ernest Walton, who used artificially accelerated protons against lithium-7 to split the nucleus into two alpha particles. The feat was popularly known as "splitting the atom," although it was not the modern nuclear fission reaction discovered in 1938 by Otto Hahn, Lise Meitner and their assistant Fritz Strassmann in heavy elements. Later in the twentieth century the transmutation of elements within stars was elaborated, accounting for the relative abundance of heavier elements in the universe. Save for the first five elements, which were produced in the Big Bang and other
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approxi ...
processes, stellar nucleosynthesis accounted for the abundance of all elements heavier than boron. In their 1957 paper ''Synthesis of the Elements in Stars'', William Alfred Fowler, Margaret Burbidge, Geoffrey Burbidge, and Fred Hoyle explained how the abundances of essentially all but the lightest chemical elements could be explained by the process of nucleosynthesis in stars. Under true nuclear transmutation, it is far easier to turn gold into lead than the reverse reaction, which was the one the alchemists had ardently pursued. It would be easier to convert gold into lead via neutron capture and
beta decay (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. Neither of these depictions shows the intermediate virtual boson. In nuclear physics, beta decay (''β''-decay) is a type of radioactive decay Rad ...
by leaving gold in a nuclear reactor for a long period of time. Glenn T. Seaborg#Return to California, Glenn Seaborg produced several thousand atoms of gold from bismuth, but at a net loss. For more information on gold synthesis, see Synthesis of precious metals. (half-life 2.7 days) (half-life 47 days) (half-life 3.8 years) → Lead, 204Pb


Transmutation in the universe

The Big Bang is thought to be the origin of the hydrogen (including all deuterium) and helium in the universe. Hydrogen and helium together account for 98% of the mass of ordinary matter in the universe, while the other 2% makes up everything else. The Big Bang also produced small amounts of lithium, beryllium and perhaps boron. More lithium, beryllium and boron were produced later, in a natural nuclear reaction, cosmic ray spallation. Stellar nucleosynthesis is responsible for all of the other elements occurring naturally in the universe as stable isotopes and primordial nuclide, from
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...
to uranium. These occurred after the Big Bang, during star formation. Some lighter elements from carbon to iron were formed in stars and released into space by asymptotic giant branch (AGB) stars. These are a type of red giant that "puffs" off its outer atmosphere, containing some elements from carbon to nickel and iron. All elements with atomic weight greater than 64 atomic mass units are produced in
supernova (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526 A supernova ( plural: supernovae or supernovas, abbreviations: SN and SNe) is a powerful and luminous stellar explosion An explosion is a rapid expan ...

supernova
stars by means of neutron capture, which sub-divides into two processes: r-process and s-process. The Solar System is thought to have condensed approximately 4.6 billion years before the present, from a cloud of hydrogen and helium containing heavier elements in dust grains formed previously by a large number of such stars. These grains contained the heavier elements formed by transmutation earlier in the history of the universe. All of these natural processes of transmutation in stars are continuing today, in our own galaxy and in others. Stars fuse hydrogen and helium into heavier and heavier elements in order to produce energy. For example, the observed light curves of supernova stars such as SN 1987A show them blasting large amounts (comparable to the mass of Earth) of radioactive nickel and cobalt into space. However, little of this material reaches Earth. Most natural transmutation on the Earth today is mediated by cosmic rays (such as production of
carbon-14 Carbon-14 (14C), or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleag ...
) and by the radioactive decay of radioactive primordial nuclides left over from the initial formation of the solar system (such as
potassium-40 Potassium-40 (40K) is a radioactive isotope of potassium which has a long half-life of 1.251 years. It makes up 0.012% (120 parts-per notation, ppm) of the total amount of potassium found in nature. Potassium-40 is a rare example of an isotope th ...

potassium-40
, uranium and thorium), plus the radioactive decay of products of these nuclides (radium, radon, polonium, etc.). See decay chain.


Artificial transmutation of nuclear waste


Overview

Transmutation of transuranium elements (i.e. actinides minus actinium to uranium) such as the
isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom. The term ...
s of plutonium (about 1wt% in the light water reactors' used nuclear fuel or the minor actinides (MAs, i.e. neptunium, americium, and curium), about 0.1wt% each in light water reactors' used nuclear fuel) has the potential to help solve some problems posed by the management of
radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom An atom is the smallest unit of ordinary matter In classical physic ...
by reducing the proportion of long-lived isotopes it contains. (This does not rule out the need for a deep geological repository for High-level waste, high level radioactive waste.) When irradiated with fast neutrons in a nuclear reactor, these isotopes can undergo nuclear fission, destroying the original actinide isotope and producing a spectrum of radioactive and nonradioactive fission products. Ceramic targets containing actinides can be bombarded with neutrons to induce transmutation reactions to remove the most difficult long-lived species. These can consist of actinide-containing solid solutions such as , , , , or just actinide phases such as , , , mixed with some inert phases such as ,, , and . The role of non-radioactive inert phases is mainly to provide stable mechanical behaviour to the target under neutron irradiation. There are issues with this P&T (partitioning and transmutation) strategy however: * first, it is limited by the costly and cumbersome need to separate long-lived fission product isotopes before they can undergo transmutation. * also, some long-lived fission products, due to their small neutron capture cross sections, are unable to capture enough neutrons for effective transmutation to occur. The new study led by Satoshi Chiba at Tokyo Tech (called "Method to Reduce Long-lived Fission Products by Nuclear Transmutations with Fast Spectrum Reactors") shows that effective transmutation of long-lived fission products can be achieved in fast spectrum reactors without the need for isotope separation. This can be achieved by adding a yttrium deuteride moderator.


Reactor types

For instance, plutonium can be reprocessed into MOX fuel, mixed oxide fuels and transmuted in standard reactors. However, this is limited by the accumulation of Plutonium-240 in spent MOX fuel, which is neither particularly fertile (transmutation to fissile Plutonium-241 does occur, but at lower rates than production of more Plutonium-240 from neutron capture by Plutonium-239) nor fissile with thermal neutrons. Even countries like nuclear power in France, France which practice nuclear reprocessing extensively, usually do not reuse the Plutonium content of used MOX-fuel. The heavier elements could be transmuted in fast reactors, but probably more effectively in a subcritical reactor which is sometimes known as an energy amplifier and which was devised by Carlo Rubbia. Nuclear fusion, Fusion neutron sources have also been proposed as well suited.


Fuel types

There are several fuels that can incorporate plutonium in their initial composition at their beginning of cycle and have a smaller amount of this element at the end of cycle. During the cycle, plutonium can be burnt in a power reactor, generating electricity. This process is not only interesting from a power generation standpoint, but also due to its capability of consuming the surplus weapons grade plutonium from the weapons program and plutonium resulting of Nuclear reprocessing, reprocessing used nuclear fuel. Mixed oxide fuel is one of these. Its blend of oxides of plutonium and uranium constitutes an alternative to the low enriched uranium fuel predominantly used in light water reactors. Since uranium is present in mixed oxide, although plutonium will be burnt, second generation plutonium will be produced through the radiative capture of U-238 and the two subsequent beta minus decays. Fuels with plutonium and thorium are also an option. In these, the neutrons released in the fission of plutonium are captured by Th-232. After this radiative capture, Th-232 becomes Th-233, which undergoes two beta minus decays resulting in the production of the fissile isotope U-233. The radiative capture cross section for Th-232 is more than three times that of U-238, yielding a higher conversion to fissile fuel than that from U-238. Due to the absence of uranium in the fuel, there is no second generation plutonium produced, and the amount of plutonium burnt will be higher than in mixed oxide fuels. However, U-233, which is fissile, will be present in the used nuclear fuel. Weapons-grade and reactor-grade plutonium can be used in plutonium-thorium fuels, with weapons-grade plutonium being the one that shows a bigger reduction in the amount of Pu-239.


Long-lived fission products

Some radioactive fission products can be converted into shorter-lived radioisotopes by transmutation. Transmutation of all fission products with half-life greater than one year is studied in Grenoble, with varying results. Sr-90 and Cs-137, with half-lives of about 30 years, are the largest radiation (including heat) emitters in used nuclear fuel on a scale of decades to ~305 years (Sn-121m is insignificant because of the low yield), and are not easily transmuted because they have low neutron absorption Neutron cross-section, cross sections. Instead, they should simply be stored until they decay. Given that this length of storage is necessary, the fission products with shorter half-lives can also be stored until they decay. The next longer-lived fission product is Sm-151, which has a half-life of 90 years, and is such a good neutron absorber that most of it is transmuted while the nuclear fuel is still being used; however, effectively transmuting the remaining Sm-151 in nuclear waste would require separation from other isotopes of samarium. Given the smaller quantities and its low-energy radioactivity, Sm-151 is less dangerous than Sr-90 and Cs-137 and can also be left to decay for ~970 years. Finally, there are 7 long-lived fission products. They have much longer half-lives in the range 211,000 years to 15.7 million years. Two of them, Tc-99 and Iodine-129, I-129, are mobile enough in the environment to be potential dangers, are free (Technetium has no known stable isotopes) or mostly free of mixture with stable isotopes of the same element, and have neutron cross sections that are small but adequate to support transmutation. Also, Tc-99 can substitute for Uranium-238, U-238 in supplying Doppler broadening for negative feedback for reactor stability. Most studies of proposed transmutation schemes have assumed technetium, 99Tc, Iodine-129, 129I, and transuranium elements as the targets for transmutation, with other fission products, activation products, and possibly reprocessed uranium remaining as waste.The Nuclear Alchemy Gamble - Institute for Energy and Environmental Research
/ref> Technetium-99 is also produced as a waste product in nuclear medicine from Technetium-99m, a nuclear isomer that decays to its ground state which has no further use. Due to the decay product of (the result of capturing a neutron) decaying with a relatively short half life to a stable isotope of Ruthenium, a precious metal, there might also be some economic incentive to transmutation, if costs can be brought low enough. Of the remaining 5 long-lived fission products, Se-79, Sn-126 and Pd-107 are produced only in small quantities (at least in today's thermal neutron, Uranium-235, U-235-burning light water reactors) and the last two should be relatively inert. The other two, Zr-93 and Cs-135, are produced in larger quantities, but also not highly mobile in the environment. They are also mixed with larger quantities of other isotopes of the same element. Zirconium is used as cladding in fuel rods due to being virtually "transparent" to neutrons, but a small amount of is produced by neutron absorption from the regular zircalloy without much ill effect. Whether could be reused for new cladding material has not been subject of much study thus far.


See also

*Neutron activation *Nuclear power *List of nuclear waste treatment technologies *Synthesis of precious metals *Fertile material


References


External links

* "Radioactive change", Rutherford & Soddy article (1903), online and analyzed on
Bibnum
' [click 'à télécharger' for English version]. {{DEFAULTSORT:Nuclear Transmutation Nuclear physics Nuclear chemistry Radioactivity