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'''Nuclear chemistry''' is a subfield of [[chemistry]] dealing with [[radioactivity]], nuclear processes and nuclear properties.  
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'''Nuclear chemistry''' is a subfield of [[chemistry]] dealing with [[radioactivity]], nuclear processes and nuclear properties. It includes the study of:


* It includes the chemistry of [[radioactive]] elements such as the [[actinides]], [[radium]] and [[radon]] together with the chemistry associated with equipment (such as [[nuclear reactor]]s) which are designed to perform nuclear processes. This includes the [[corrosion]] of surfaces and the behaviour under conditions of both normal and abnormal operation (such as during an [[nuclear accidents|accident]]). An important area is the behaviour of objects and materials after being placed into a [[waste]] store or otherwise disposed of.  
* the chemistry of [[radioactive]] elements such as the [[actinides]], [[radium]] and [[radon]] together with the chemistry associated with equipment (such as [[nuclear reactor]]s) which are designed to perform nuclear processes. Nuclear reactors can be "high-flux" reactors, mainly used to make radio-active isotopes for medical or scientific use, or "low-flux" reactors, mainly used for power generation. (''Flux'' in this content means the density of neutrons per unit of volume.) These processes include the [[corrosion]] of surfaces and the behaviour under conditions of both normal and abnormal operation (such as during an [[nuclear accidents|accident]]). An important area is the behaviour of objects and materials after being placed into a waste store or otherwise disposed of.  


* Nuclear chemistry also includes the study of the production and use of radioactive sources for a range of processes which include [[radiotherapy]]; The use of tracers within [[industry]], [[science]] and the [[environment]]; The use of radiation to modify materials such as [[polymer]]s[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6050016][http://www.ebeamservices.com/cross-li.htm] and polychlorobiphenyls.
* the chemical effects resulting from the absorption of radiation within living animals, plants, and other materials. The [[radiation chemistry]] controls much of [[radiation biology]] as radiation affects living things at the molecular scale. In particular, radiation alters the biochemicals within an organism, this changes the chemistry within the organism, and this can lead to a biological outcome. Nuclear chemistry is important in the development of some medical treatments (such as [[cancer]] [[radiotherapy]]).


* Nuclear chemistry also involves the study and use of nuclear processes in ''non-radioactive'' areas of human activity. For instance, nuclear magnetic resonance ([[NMR]]) spectroscopy is commonly used in synthetic [[organic]] chemistry.
* the production and use of radioactive sources for many different processes. These include the sources used for radiotherapy; the use of radioactive tracers within industry, science and the environment; and the use of radiation to modify materials such as [[polymer]]s[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6050016][http://www.ebeamservices.com/cross-li.htm] .
 
* nuclear processes in ''non-radioactive'' areas of human activity. For instance, nuclear magnetic resonance ([[NMR spectroscopy]]) spectroscopy is commonly used in synthetic [[organic chemistry]] and [[physical chemistry]] and for structural analysis in [[macromolecular chemistry]].


==Early history==
==Early history==
After the discovery of [[X-ray|X-rays]] by [[Wilhelm Röntgen]], many scientists began to work on ionizing radiation. One of these was [[Henri Becquerel]], who investigated the relationship between [[phosphorescence]] and the blackening of [[photographic plates]]. When Becquerel (working in France) discovered that, with no external source of energy, the uranium generated rays which could blacken (or ''fog'') the photographic plate, radioactivity was discovered. [[Marie Curie]] (working in [[Paris]]) and her husband [[Pierre Curie]] isolated two new radioactive elements from uranium ore. They used [[radiometric]] methods to identify which stream the radioactivity was in after each each chemical separation; they separated the uranium ore into each of the different chemical elements that were known at the time, and measured the radioactivity of each fraction. They then attempted to separate these radioactive fractions further, to isolate a smaller fraction with a higher specific activity (radioactivity divided by mass). In this way, they isolated [[polonium]] and [[radium]]. Their daughter [[Irène Joliot-Curie]] and her husband were the first to 'create' radioactivity: they bombarded [[boron]] with alpha particles to make a proton-rich isotope of [[nitrogen]]; this isotope emitted [[positron]]s.[http://www.sciencemuseum.org.uk/collections/treasures/artrad2.asp] In addition, they bombarded [[aluminium]] and [[magnesium]] with [[neutrons]] to make new radioisotopes.
After the discovery of [[X-ray|X-rays]] by Wilhelm Röntgen, many scientists began to investigate ionizing radiation. In France, Henri Becquerel investigated the relationship between phosphorescence and the blackening of photographic plates, and he discovered that, with no external source of energy, uranium generated "rays" that could blacken (or ''fog'') a photographic plate. This observation marks the discovery of radioactivity. Subsequently, [[Marie Curie]] (working in Paris) and her husband Pierre Curie isolated two new radioactive elements from uranium ore. They used radiometric methods to identify which stream the radioactivity was in after each each chemical separation; they separated the uranium ore into each of the different chemical elements that were known at the time, and measured the radioactivity of each fraction. They then attempted to separate these radioactive fractions further, to isolate a smaller fraction with a higher specific activity (radioactivity per unit mass). In this way, they isolated [[polonium]] and [[radium]].  
 
By 1901 it was noticed that high doses of radiation could injure humans. Becquerel had carried a sample of radium in his pocket, and as a result he suffered a high localized dose which resulted in a radiation burn [http://www.britannica.com/nobel/micro/59_13.html] This injury resulted in the biological properties of radiation being investigated, which in time resulted in the development of medical treatments. Marie Curie's daughter (Irène Joliot-Curie) and her husband were the first to create radioactivity: they bombarded [[boron]] with alpha particles to make a proton-rich isotope of [[nitrogen]]; this isotope emitted positrons. [http://www.sciencemuseum.org.uk/collections/treasures/artrad2.asp] In addition, they bombarded [[aluminium]] and [[magnesium]] with [[neutrons]] to make new radioisotopes.
 
[[Ernest Rutherford]], working in Canada and England, showed that radioactive decay can be described by a simple equation (a linear first-degree derivative equation, now called first-order kinetics), implying that a given radioactive substance has a characteristic "[[half life]]" (the time taken for the amount of radioactivity present in a source to diminish by half). He also coined the terms alpha, beta, and gamma radiation, he converted [[nitrogen]] into [[oxygen]], and most importantly he supervised the students who did the Geiger-Marsden experiment (gold leaf experiment) which showed that the "plum pudding model" of the [[atom]] was wrong. In the plum pudding model, proposed by [[J. J. Thomson]] in 1904, the atom is composed of electrons surrounded by a cloud of positive charge to balance the electrons' negative charge. To Rutherford, the gold foil experiment implied that the positive charge was confined to a very small nucleus, leading first to the Rutherford model and eventually to the Bohr model of the atom, where the positive nucleus is surrounded by the negative electrons.


[[Ernest Rutherford]], working in [[Canada]] and [[England]], discovered that radioactivity decays according to [[first order kinetics]] ([[half life]]); he coined the terms [[alpha]], [[beta]] and [[gamma]] rays. He also converted [[nitrogen]] into [[oxygen]], and most importantly he supervised the students who did the [[Geiger-Marsden experiment]] (gold leaf experiment) which showed that the '[[plum pudding model]]' of the [[atom]] was wrong. In the plum pudding model, proposed by [[J. J. Thomson]] in 1904, the atom is composed of electrons surrounded by a 'cloud' of positive charge to balance the electrons' negative charge. To Rutherford, the gold foil experiment implied that the positive charge was confined to a very small nucleus leading first to the [[Rutherford model]], and eventually to the [[Bohr model]] of the atom.
In initial attempts to make the ''transuranium'' elements, uranium was bombarded with neutrons; the idea was that, by creating a neutron-rich uranium isotope, the next element would be formed by beta decay. Instead, in these early studies the [[fissile]] <sup>235</sup>U underwent fission to generate highly radioactive [[fission products]]. Because of their high activity, these fission products (such as short-lived [[barium]] isotopes) dominated the radiochemical analysis of the irradiated uranium. At first, it was thought that the uranium had been converted into radium, as many of the early radiochemical methods had difficulty in distinguishing between barium and radium. But gradually it was recognized that most of the radioactivity was due to the products of breaking uranium nuclei into two fragments.<ref>Meitner L, Frisch OR (1939) Disintegration of uranium by neutrons: a new type of nuclear reaction. ''Nature'' 143:239-40 (doi = 10.1038/224466a0) [http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Meitner-Fission-1939.html]</ref>
 
[[Edwin McMillan]] attempted to measure the range of the fission products using cigarette paper; during this work he isolated a beta active isotope with a half life of 2.3 days (<sup>239</sup>Np). A short time later in 1940 plutonium was discovered.


==Main areas==
==Main areas==
===Radiochemistry===
===Radiochemistry===
[[Radiochemistry]] is the chemistry of radioactive materials. In radiochemistry, radioactive [[isotope]]s of elements are used to study the properties and [[chemical reaction]]s of ordinary non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being ''inactive'' as the isotopes are ''stable''). An example of a biological use of radiochemistry is the study of [[DNA]] using radioactive [[phosphorus]]-32.
''see '''[[radiochemistry]]''' for fuller details.''


Radiochemistry also includes the study of the behaviour of radioisotopes within the environment, for instance V.I. Yoschenko ''et. al.'' in ''Journal of Environmental Radioactivity'', 2006, '''86''', 143-163 report how a forest or grass fire can make radioisotopes become mobile again. As an experiment, fires were set within the exclusion zone around [[chernobyl]] and the levels of the radioactivity in the air down wind of these fires was measured.
[[Radiochemistry]] is the chemistry of radioactive materials, where radioactive [[isotope]]s of elements are used to study the properties and [[chemical reaction]]s of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being ''inactive'' as the isotopes are ''stable''). Both the behaviour of man made<ref>Imanaka T ''et al.'' (2006) ''J Radiation Research'' '''47''' Suppl A121-A127</ref> and natural radioisotopes are part of radiochemistry.


===Radiation chemistry===
===Radiation chemistry===
[[Radiation chemistry]] is the study of the chemical effects of radiation on matter; this is very different to [[radiochemistry]] as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into [[hydrogen]] gas and [[hydrogen peroxide]]. A recent area of work has been the destruction of toxic organic compounds by irradation, C. Zhao, K. Hirota, M. Taguchi, M. Takigami and T. Kojima, ''Radiation Physics and Chemistry'', 2007, '''76''', 37-45 reported that irradation of "[[dioxin]]" (polychlorodibenzo-''p''-dioxins) that the dioxin is dechloroinated in the same way as PCBs can be converted to [[biphenyl]] an inorganic chloride. This is due to the reaction of the [[solvated electron]] with the organic compound to form a [[radical]] anion which decomposes by the loss of a [[chloride]] anion. If a deoxygenated mixture of PCBs in [[isopropanol]] or [[mineral oil]] is subject to irradation with [[gamma rays]] then the PCBs will be dechlorinated to form inorganic [[chloride]] and [[biphenyl]]. The reaction works best in isopropanol if [[potassium hydroxide]] (''[[caustic potash]]'') is added. [[Solvated electron]]s have been shown to be responsible for the reaction. If [[oxygen]], [[nitrous oxide]], [[sulfur hexafluoride]] or [[nitrobenzene]] is present in the mixture then the reaction rate is reduced. This work has been done recently in the US often with used [[nuclear fuel]] as the radiation source[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=10116942][http://www.patentstorm.us/patents/6132561.html].
[[Radiation chemistry]] is the study of the chemical effects of radiation on matter.This is very different to radiochemistry, as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into [[hydrogen]] gas and [[hydrogen peroxide]].
 
Another key area within radiation chemistry is the modification of polymers,[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=7313004][http://mitr.p.lodz.pl/biomat/raport/3_5_radiation_hydrogels.html] it is possible to convert [[monomer]]s to [[polymer]]s with radiation, to crosslink polymers and to break polymer chains using irradation. Both manmade and natural polymers (such as [[carbohydrate]]s)[http://www-pub.iaea.org/MTCD/publications/PDF/te_1422_web.pdf] can be processed using these methods.


===Study of nuclear reactions===
===Study of nuclear reactions===
''see also [[nuclear physics]]''
''see also '''[[nuclear physics]]''''' and '''''[[nuclear reactions]]''''' for further details.


A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as [[nuclear fission|fission]] and [[nuclear fusion|fusion]]. Some early evidence for nuclear fission was the formation of a shortlived radioisotope of [[barium]] which was isolated from [[neutron]] irradated [[uranium]] ( <sup>139</sup>Ba, with a half-life of 83 minutes and <sup>140</sup>Ba, with a half-life of 12.8 days, are major [[fission product]]s of uranium). At the time, it was thought that this was a new radium isotope, as it was then standard radiochemical practise to use a barium sulphate carrier precipitate to assist in the isolation of [[radium]].[http://chemcases.com/nuclear/nc-03.htm]. More recently, a combination of radiochemical methods and nuclear physics has been used to try to make new 'superheavy' elements; it is thought that islands of relative stability exist where the nuclides have half-lives of years, thus enabling weighable amounts of the new elements to be isolated. For more details of the original discovery of nuclear fission see the work of [[Otto Hahn]].<ref>Meitner L, Frisch OR (1939) Disintegration of uranium by neutrons: a new type of nuclear reaction ''Nature'' '''143''':239-240 [http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Meitner-Fission-1939.html]</ref>.
A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as [[nuclear fission|fission]] and [[nuclear fusion|fusion]]. Some early evidence for nuclear fission was the formation of a shortlived radioisotope of barium which was isolated from neutron-irradiated uranium ( <sup>139</sup>Ba, with a half-life of 83 minutes and <sup>140</sup>Ba, with a half-life of 12.8 days, are major [[fission product]]s of uranium). At the time, it was thought that this was a new radium isotope, as it was then standard radiochemical practice to use a barium sulphate carrier precipitate to assist in the isolation of radium.[http://chemcases.com/nuclear/nc-03.htm]. More recently, a combination of radiochemical methods and nuclear physics has been used to try to make new 'superheavy' elements; it is thought that islands of relative stability exist where the nuclides have half-lives of years, thus enabling weighable amounts of the new elements to be isolated. For more details of the original discovery of nuclear fission see the work of [[Otto Hahn]].


====Radioisotope production====
=== The nuclear fuel cycle ===
The processes forming new isotopes (often radioactive) involve several areas of nuclear chemistry.  
{{Image|Nuclear Fuel Cycle.jpg|left|300px|In the nuclear fuel cycle, uranium is mined, enriched and manufactured to nuclear fuel (1) which is delivered to a nuclear power plant. After use, the spent fuel is delivered to a reprocessing plant (2) or for permanent storage (3) in a safe place, such as inside rock. In reprocessing, 95% of spent fuel can be recycled to be returned to use in a power plant (4).}}


=====Processes=====
The fuel cycle includes all the operations involved in producing fuel, from mining, ore processing and enrichment to fuel production (''Front end of the cycle''). It also includes the 'in-pile' behaviour (use of the fuel in a reactor) before the ''back end'' of the cycle. The ''back end'' includes the management of the [[used nuclear fuel]] in either a [[cooling pond]] or dry storage, before it is disposed of into an underground waste store or [[nuclear reprocessing|reprocessed]]. The chemistry associated with any part of the nuclear fuel cycle, including [[nuclear reprocessing]] is studied in this part of nuclear chemistry. One of the key topics is the materials used for fuels.  
* By irradiation with '''slow neutrons''', it is possible to form neutron-rich isotopes which tends to decay by beta decay (i.e. by electron emission from the nuclei). For instance, irradiating <sup>59</sup>Co with neutrons forms an excited state of <sup>60</sup>Co (best written as <sup>60m</sup>Co) which decays by emitting a [[gamma ray]] to the ground state of <sup>60</sup>Co, which in turn decays by emitting an [[electron]] to form <sup>60m</sup>Ni. The excited state of the <sup>60m</sup>Ni then decays with the emission of two gamma photons to the ground state of <sup>60</sup>Ni. As the neutron energy increases, the simple capture reactions become less important, while other reactions such as the (n,p) reaction become more important. An example is the production of [[phosphorus]]-32 by neutron irradiation of <sup>32</sup>S. The [[sulphur]] nucleus captures a neutron and emits a [[proton]] to form the radioactive phosphorus isotope ( <sup>32</sup>P). Carbon-14 is obtained in a similar manner by irradiating <sup>14</sup>N with neutrons.


*A beam of '''fast moving positive particles''' can be obtained by using a [[cyclotron]] or a [[linear accelerator]] (linac); up to 30MeV protons and deuterons can be obtained this way. The energies of these particles are so high that they can overcome the [[electrostatic]] barrier which opposes the entry of positive particles into the nucleus. An example of the use of the (p,n) reaction is the conversion of <sup>103</sup>Rh into <sup>103</sup>Pd, this can be done by irradiating [[rhodium]] foil with protons to form the radioactive [[palladium]] isotope. The reaction of [[beryllium]] with alpha particles is another example of this type of reaction. While the reaction of <sup>9</sup>Be with <sup>4</sup>He<sup>2+</sup> generates <sup>12</sup>C, its most important aspect is that it generates [[neutron]]s.
==== Solid state forms of actinide metals ====
Most power reactors use dioxide fuel, but some reactor designs do use actinide metal fuel. One of the disadvantages of metal fuel is that the melting point of the fuel is lower than that of either the oxide, nitride or carbide. But for some special applications metal fuel is used, because of this can form general interest a discussion of the crystalography of plutonium metal is provided below. Of the actinides plutonium is the metal which has the most crystal forms, and hence we will restrict our discussion to plutonium.


* Many isotopes can be made from a '''parent isotope''' which decays to form the desired isotope. If the parent and the product element can be chemically separated, then it is possible to create an "isotope cow". The classic isotope cow is the [[technetium cow]], many others work by the same principle. The technetium cow uses [[molybdum]]-99 absorbed on alumina, and it is "milked" by passing saline solution through it to give a solution of technetium. [[Image:Growthoftcinacow.jpg|left|thumb|450px|A diagram explaining the operation of a technetium cow, the technetium, represented in red, is milked off the alumina column and then builds up again]]
Many different crystal forms of different actinide metals exist. Plutonium can exist in many different forms, alpha,<ref>Zachariasen WH, Ellinger FH (1957) ''J Chem Physics'',27:811-2</ref> beta,<ref> Zachariasen WH, Ellinger FH (1963) ''Acta Crystallographica'' 16:369-75</ref> gamma, delta (ρ = 16.0),<ref>Ellinger FH (1956) ''J Metals'', 1956, 8:1256-125</ref> delta' (ρ = 16.0),<ref>Ellinger FH (1956) ''J Metals'' 8:1256-125</ref> gamma<ref>Ellinger FH (1955) ''Acta Crystallographica'' 8:431-3</ref>  and epsilon <ref>Ball JB ''et al.'' (1960) ''Memoires Scientifiques de la Revue de Metallurgie'' 57:49-56</ref> forms are known.  


The alpha form has a monoclinic cell (a = 6.184, b = 4.824, c = 10.973, alpha = 90<sup>o</sup>, beta = 101.80<sup>o</sup> and gamma 90<sup>o</sup>) with many atoms inside the unit cell, the resulting solid can be thought of consisting of many face sharing distorted tetrahedra. The beta form has a monoclinic cell with many atoms inside the cell, the resulting solid contains tetrahedra and other polyhedra linked together in a face sharing manner. The delta form is a face centred cubic type solid where the cell dimension is 4.632 A. The delta prime form is a tetragonally distorted body centred cubic solid in which the cell dimensions are a = b = 3.339 A and c = 4.446 A.


<gallery>
Image:Alphapu.jpg|Alpha plutonium (note that this is not a view of a unit cell)
Image:Betapu.jpg|Beta plutonium (note that this is not a view of a cell)
Image:Deltapu2.jpg|A unit cell of delta plutonium
Image:Deltaprimepu2.jpg|A unit cell of delta prime plutonium
Image:gammapu.jpg|Gamma plutonium (note that this is not a view of a unit cell)
Image:Epipu.jpg|A unit cell of epsilon plutonium
</gallery>


In the diagram, the technetium is represented in red, in picture two the cow is milked to make a product solution. The technetium then builds up again to allow the cow to return to the technetium loaded state where it can be milked again.
==== Solid state structures of actinide dioxides ====
Many of the actinide dioxides are similar to uranium dioxide, the structure of this is shown below.


In this way, aqueous solutions of the following isotopes can be made from parent isotopes (shown in brackets)
{{Image|UO2lattice.jpg|right|250px|The solid state structure of uranium dioxide, the oxygen atoms are in red and the uranium atoms in green}}


==== Normal and abnormal conditions ====
The nuclear chemistry associated with the nuclear fuel cycle can be divided into two main areas. One area concerns operation under the intended conditions; the other area concerns maloperation conditions, where some alteration from the normal operating conditions has occurred or (''more rarely'') during an accident.


*<sup>68</sup>Ga (<sup>68</sup>Ge)
====Reprocessing====
*<sup>82</sup>Rb (<sup>82</sup>Sr)
*<sup>99m</sup>Tc (<sup>99</sup>Mo)
*<sup>113m</sup>In (<sup>113</sup>Sn)
*<sup>188</sup>Re (<sup>188</sup>W)
*<sup>62</sup>Cu (<sup>62</sup>Zn)


=====Law=====
In the USA, it is normal to use fuel once in a power reactor before placing it in a waste store. The long term plan is currently to place the civil used power reactor fuel in a deep store. This policy of not reprocessing was started in March 1977 for [[nuclear proliferation|nuclear weapons proliferation]] reasons. President [[Jimmy Carter]] issued a [[Presidential directive]] which indefinitely suspended the commercial reprocessing and recycling of plutonium in the USA. This directive was probably an attempt by the USA to lead other countries by example, but many other nations continue to reprocess spent nuclear fuels. It is noteworthy that the government under [[Putin]] (President of Russia) repealed a law which had banned the inport of used nuclear fuel into Russia, this change in Russian law now permits the Russians to offer a reprocessing service for clients outside Russia (In a similar way to that offered by [[BNFL]]).


=====PUREX chemistry=====
{{main | PUREX}}
To separate useful isotopes from fission byproducts, current method of choice is to use the [[PUREX]] [[liquid-liquid extraction]] process which uses a [[tributyl phosphate]]/[[hydrocarbon]] mixture to extract both uranium and plutonium from [[nitric acid]].


=====DUPIC (an alternative)=====
As an alternative to the use of normal uranium in a [[CANDU]] it has been suggested that the spent fuel from a Pressurised Water Reactor could be used in place of natural uranium in a ''heavy water'' moderated CANDU. The term DUPIC means '''D'''irect '''U'''se of spent '''P'''ressurized water reactor fuel '''I'''n '''C'''ANDU.[http://www.niof.org/campaigns/dupic.htm][http://www.intlsecconf.sandia.gov/yang_05isc.pdf] A discussion of different fuel cycles has been published, this includes a discussion of the DUPIC idea.<ref>Ko WI, Kim HD (2001) ''J Nuclear Sci Technol'' 38:757-65 [http://wwwsoc.nii.ac.jp/aesj/publication/JNST2001/No.9/38_757-765.pdf]</ref>


=====Old methods (no longer used)=====
The '''bismuth phosphate''' process is a very old process which adds lots of material to the final highly active waste, and which was replaced by solvent extraction processes. The process was designed to extract plutonium from aluminium-clad uranium fuel. The fuel was declad by boiling it in [[caustic soda]]. After decladding, the uranium metal was dissolved in [[nitric acid]]. The plutonium at this point is in the +4 oxidation state. It was then precipitated by the addition of [[bismuth]] nitrate and [[phosphoric acid]] to form the bismuth phosphate. The plutonium was co-precipitated with this. The [[supernatant]] (containing many of the fission products) was separated from the solid. The precipitate was then dissolved in nitric acid before the addition of an [[oxidant]] such as [[potassium permanganate]] which converted the plutonium to PuO<sub>2</sub><sup>2+</sup> (Pu VI), then a [[dichromate]] salt was added to maintain the plutonium in the +6 oxidation state. The bismuth phosphate was then re-precipitated leaving the plutonium in solution. Then, an iron (II) salt such as ''ferrous sulfate'' was added and the plutonium re-precipitated again using a bismuth phosphate carrier precipitate. Then [[lanthanum]] salts and [[fluoride]] were added to create solid lanthanum fluoride which acted as a carrier for the Pu. This was converted to the oxide by the action of a base. The lanthanum plutonium oxide was then collected and extracted with nitric acid to form plutonium nitrate. [http://www.bonestamp.com/sgt/process.htm]


When the product isotope is a gas, the cow can be milked by allowing the product to diffuse out of a solid. An early way of making [[radiography]] sources was to milk [[radon]] from a [[radium]] source; this method was used by [[Marie Curie]] during the first World War ([[WWI]]), and was used in the USA to make [[Brachytherapy]] sources. By this method, the following isotopes can be obtained from parent isotopes (shown in brackets)
The '''Hexone or Redox'''process is a liquid-liquid extraction process which uses methyl isobutyl ketone as the extractant. The extraction is by a ''solvation'' mechanism. This process has the disadvantage of requiring a salting-out reagent (aluminium [[nitrate]]) to increase the nitrate concentration in the aqueous phase to obtain a reasonable distribution ratio (D value). Also hexone is degraded by concentrated nitric acid. This process has been replaced by PUREX.[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=4134289][http://www.llnl.gov/tid/lof/documents/pdf/235702.pdf]


*<sup>81m</sup>Kr (<sup>81</sup>Rb)
The '''Butex, β,β'-dibutyoxydiethyl ether''' process is based on a solvation extraction process using the triether extractant named above. This process has the disadvantage of requiring the use of a salting out reagent (aluminium nitrate) is required to increase the nitrate concentration in the aqueous phase to obtain a reasonable distribution ratio. This process was used at [[Windscale]] many years ago, and has since been replaced by PUREX.
*<sup>222</sup>Rn (<sup>226</sup>Ra)


In some nuclear materials, new isotopes are formed by the decay of a parent isotope. For instance, the beta decay of <sup>241</sup>Pu will form <sup>241</sup>Am, so if a sample of [[plutonium]] which has been standing for several years is subjected to a new chemical purification, then it is possible to harvest the [[americium]].
{{Image|Butoxpicture.jpg|center|450px|The molecular structure of butex}}


*<sup>241</sup>Am (<sup>241</sup>Pu)
=====Methods being considered for future use=====
The PUREX process can be modified to make a '''UREX''' ('''UR'''anium '''EX'''traction) process which could be used to save space inside high-level nuclear waste disposal sites, such as [[Yucca Mountain]], by removing the uranium which makes up the vast majority of the mass and volume of used fuel, and recycling it as reprocessed uranium. The UREX process is a PUREX process which has been modified to prevent the plutonium from being extracted. This can be done by adding a plutonium reductant before the first metal extraction step. In the UREX process, ~99.9% of the uranium and >95% of [[technetium]] are separated from each other and the other fission products and actinides. The key is the addition of acetohydroxamic acid to the extraction and scrub sections of the process; this greatly diminishes the extractability of plutonium and [[neptunium]], providing greater proliferation resistance than with the plutonium extraction stage of the PUREX process.


=====Uses=====
Adding a second extraction agent, octyl(phenyl)-N, N-dibutyl carbamoylmethyl phosphine oxide(CMPO) in combination with tributylphosphate, the PUREX process can be turned into the '''TRUEX''' ('''TR'''ans'''U'''ranic '''EX'''traction) process, a process invented in the USA by Argonne National Laboratory, and designed to remove the transuranic metals (Am/Cm) from waste. The idea is that, by lowering the alpha activity of the waste, most of the waste can be disposed of easily. Like PUREX, this process uses a solvation mechanism.
Radioactive sources have many different uses <ref>A short review of [http://www.world-nuclear.org/info/printable_information_papers/inf56print.htm the use of radioactivity in industry]</ref>. A ''sealed source'' is sealed within a container so that, in normal use, no radioactive material is lost from the source. In many sealed sources, the radioactive filling is surrounded by one or more layers of a [[corrosion]]-resistant material (such as [[stainless steel]] or [[gold]]). Alternatively, it is possible to form a source using material which holds the radioactivity in a chemically resistant and strong form without needing a metal cover. In designing sealed sources, it is common to choose a chemically stable form of the radioactive element, but for [[cesium]] [[radiotherapy]] sources it is common to use the water soluble [[chloride]], because it is impossible to obtain the required density of cesium in another compound.


{{Image|CMPOpicture.jpg|center|450px|The molecular structure of a typical CMPO}}


*'''Sealed sources''' are used for radiotherapy treatment of many [[cancer]]s (both [[brachytherapy]] and [[teletherapy]]), as well as for [[food irradiation]], [[industrial radiography]], [[nuclear gauges]] and many other applications.
As an alternative to TRUEX, an extraction process using a malondiamide has been devised. The DIAMEX ('''DIAM'''ide'''EX'''traction) process avoids the formation of organic waste which contains elements other than carbon, hydrogen, nitrogen and oxygen. Such an organic waste can be burned without forming acidic gases which could contribute to [[acid rain]]. The DIAMEX process is being worked on in Europe by the French [[CEA]]. The process is sufficiently mature that an industrial plant could be constructed with the existing knowledge of the process. Like PUREX, this process uses a solvation mechanism.[http://www.nea.fr/html/trw/docs/mol98/session2/SIIpaper5.pdf][http://www.nea.fr/html/trw/docs/mol98/session2/SIIpaper2.pdf]


To explain the use of radioactive sources in cancer treatment we will consider a hypothetical person with a tumor (shown in blue).
'''S'''elective '''A'''cti'''N'''ide '''EX'''traction. As part of the management of minor actinides it has been proposed that the lanthanides and trivalent minor actinides should be removed from the PUREX raffinate by a process such as DIAMEX or TRUEX. In order to allow the actinides such as americium to be either reused in industrial sources or used as fuel the lanthanides must be removed. The lanthanides has large neutron cross sections and hence they would poison a neutron driven nuclear reaction. To date the extraction system for the SANEX process has not been defined, but currently several different research groups are working towards a process. For instance, the French CEA is working on a bis-triaiznyl pyridine (BTP) based process.


<gallery>
{{Image|BTPpicture.jpg|center|450px|The molecular structure of a BTP}}
Image:Diagramofpersonwithcancer.jpg|'''1''' A diagram showing a person with a tumor (in blue)
Image:Diagramofpersonwithcancertele.jpg|'''2''' A diagram showing a person with a tumor (in blue) which is being treated with teletherapy (gamma rays shown in yellow)
Image:Diagramofpersonwithcancerbracy.jpg|'''3''' A diagram showing a person with a tumor (in blue) which is being treated with brachytherapy (the source shown in red and the gamma rays are shown in yellow)
gallery>


As an alternative the person might be treated with a smaller radioactive source which is placed within or close to the tumor (brachytherapy). Here the source is shown as the red dot while the gamma rays from the source are shown in yellow. One of the advantages of this type of treatment is that the radiation is confined to the part of the person where the disease is, the healthy tissues in other parts of the person are not subjected to irradation.
'''References:'''


*'''Open sources''' are used for a range of applications which include the use of tracers to study the physical operation of industrial processes, to trace the chemical mechanism by which a product forms.  For instance, [[krypton]] has been used to study the underground combustion of fuels such as oil and coal.[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=7335434][http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5253963]. They are also used for some forms of radiotherapy. For example, in the treatment of thyroid [[cancer]] the patient is given a large dose of <sup>131</sup>[[iodine|I]] becuase the iodine accumulates in the thyroid gland, the tissue of the thyroid gland (and the tummor) suffers a large radiation dose when compaired with the majority of the body. As a result the radioactive iodine is able to selectively destroy the thyroid gland and the tumor which is derived from it. Also in terminal care <sup>89</sup>Sr is used to destroy bone tumors. (See W.A. Volkert and T.J. Hoffman, ''Chemical Reviews'', 1999, 2269-2292 for further details on open source radiotherapy).
*[http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-26.pdf SANEX-BTP Process Studies]
*[http://www.nea.fr/html/pt/docs/iem/jeju02/session2/Session%20II-19.pdf SANEX-BTP Process Development]
*[http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-24.pdf Modelling and achievement of a SANEX process]


The use of an open source in either cancer treatment or imaging can be explained using the following two diagrams, in the first diagram the person has been recently given the radioactive drug. The drug is spread throughout the whole body. Then with time the radioactivity will concentrate (according to its chemical properties) within a target organ or tumor.  
Other systems such as the dithiophosphinic acids are being worked on by some other workers.


<gallery>
This is the '''''UN'''iversal'' '''EX'''traction process which was developed in [[Russia]] and the Czech Republic; it is designed to remove all of the most troublesome (Sr, Cs and [[minor actinides]]) radioisotopes from the raffinates left after extracting uranium and plutonium from used nuclear fuel. [http://www.usembassy.it/file2001_12/alia/a1121910.htm][http://www.osti.gov/bridge/product.biblio.jsp?osti_id=765723] The chemistry is based upon the interaction of [[caesium]] and [[strontium]] with polyethylene oxide (polyethylene glycol) [http://www.osti.gov/em52/2003projsum/81895.pdf] and a [[cobalt]] [[carborane]] anion (known as chlorinated cobalt dicarbollide). The actinides are extracted by CMPO, and the diluent is a polar [[aromatic]] such as [[nitrobenzene]]. Other dilents such as ''meta''-nitrobenzotrifluoride and phenyl trifluoromethyl sulfone [http://www.wmsym.org/Abstracts/2001/62/62-7.pdf]have been suggested as well.
Image:DiagramofpersonwithcancerfirststageofI131.jpg|'''4''' A diagram showing a person with a tumor (in blue) which is being treated with an open source, the radioactivity has yet to localise(the radioactivity shown in orange)
Image:DiagramofpersonwithcancersecondstageofI131.jpg|'''5''' A diagram showing a person with a tumor (in blue) which is being treated with an open source after the radioactivity has localised in one part of the body(the radioactivity shown in orange)</
</gallery>


Some radiopharmaceuticals are used for medical imaging, for instance a great array of different [[technetium]] complexes are used medically (See S.S. Jurisson and J.D. Lydon, ''Chemical Reviews'', 1999, 2205-2218 for further detail) while [[radioactive]] <sup>201</sup>Tl (half-life of 73 hours) is used for diagnostic purposes in [[nuclear medicine]], particularly in stress tests used for risk stratification in patients with [[coronary artery disease]] (CAD).<ref>[http://www.wramc.amedd.army.mil/departments/nuclear/PatientInfo/Thallium.htm Thallium Test] from [[Walter Reed Army Medical Center]]</ref><ref>[http://www.americanheart.org/presenter.jhtml?identifier=4743 Thallium Stress Test] from the [[American Heart Association]]</ref> This isotope of thallium can be generated using a transportable generator which is similar to the [[technetium cow]].<ref>[http://www.medscape.com/medline/abstract/7169272 Abstract]<!-- dead link --></ref> The generator contains [[lead]]-201 (half life 9.33 hours) which decays by [[electron capture]] to the <sup>201</sup>Tl. The <sup>201</sup>Pb can be produced in a [[cyclotron]] by the bombardment of thallium with [[proton]]s or [[deuteron]]s by the (p,3n) and (d,4n) reactions.<ref>[http://www.med.harvard.edu/JPNM/physics/isotopes/Tl/Tl201/prod.html Thallium-201 production] from [[Harvard Medical School]]'s Joint Program in Nuclear Medicine</ref>
====Absorption of fission products on surfaces====
Another important area of nuclear chemistry is the study of how fission products interact with surfaces; this is thought to control the rate of release and migration of fission products both from waste containers under normal conditions and from power reactors under accident conditions. It is interesting to note that, like [[chromate]] and [[molybdate]], the '''<sup>99</sup>TcO<sub>4</sub>''' anion can react with steel surfaces to form a [[corrosion]]-resistant layer. In this way, these metaloxo anions act as [[anode|anodic]] [[corrosion inhibitor]]s. The formation of <sup>99</sup>TcO<sub>2</sub> on steel surfaces is one effect which will retard the release of <sup>99</sup>Tc from nuclear waste drums and nuclear equipment which has been lost before decontamination (e.g. [[submarine]] reactors  lost at sea). This <sup>99</sup>TcO<sub>2</sub> layer renders the steel surface passive, inhibiting the anodic corrosion reaction. The radioactive nature of technetium makes this corrosion protection impractical in almost all situations. It has also been shown that <sup>99</sup>TcO<sub>4</sub> anions react to form a layer on the surface of activated carbon ([[charcoal]]) or [[aluminium]].<ref>Decontamination of surfaces, George H. Goodalland Barry.E. Gillespie, United States Patent 4839100</ref>[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=885448]. A short review of the biochemical properties of a series of key long lived radioisotopes can be read on line.[http://web.em.doe.gov/lowlevel/llw_apxc.html]


=== The nuclear fuel cycle ===
{{Image|TcO2layeronsteelsurface.jpg|center|450px|Formation of a TcO<sub>2</sub> layer on a steel surface.}}
[[Image:Nuclear Fuel Cycle.jpg|left|thumb|300px|This diagram demonstrates the nuclear fuel cycle. Uranium is mined, enriched and manufactured to nuclear fuel (1) which is delivered to a nuclear power plant. After usage in the power plant the spent fuel is delivered to a reprocessing plant (2) or to final repository (3) for permanent storage in a safe place, such as inside rock. In reprocessing 95% of spent fuel can be recycled to be returned to usage in a power plant (4).]]


The chemistry associated with any part of the [[nuclear fuel cycle]] which includes [[nuclear reprocessing]]. The fuel cycle includes all the operations involved in producing fuel, from mining, ore processing, enrichment and fuel production (''Front end of the cycle''). It also includes the 'in-pile' behaviour (use of the fuel in a reactor) before the ''back end'' of the cycle. The back end includes the management of the [[used nuclear fuel]] in either a [[cooling pond]] or dry storage, before it is either disposed of into an underground waste store or [[nuclear reprocessing|reprocessed]].
It is important to note that <sup>99</sup>Tc in nuclear waste may exist in chemical forms other than the <sup>99</sup>TcO<sub>4</sub> anion, these other forms have different chemical properties.[http://www.osti.gov/Reference_Linking/817638.pdf] Similarly, the release of '''iodine-131''' in a serious power reactor accident could be retarded by absorption on [[metal]] surfaces within the nuclear plant. <ref>Glänneskog H (2004) Interactions of [[Iodine|I]]<sub>2</sub> and [[Methyl iodide|CH]]<sub>3</sub>I with reactive metals under BWR severe-accident conditions ''Nuclear Engineering and Design'' 227:323-9
* Glänneskog H (2005) Iodine chemistry under severe accident conditions in a nuclear power reactor, PhD thesis, Chalmers University of Technology, Sweden
* For other work on the iodine chemistry which would occur during a bad accident, see[http://www.sbf.admin.ch/htm/services/publikationen/international/frp/eu-abstracts/html/fp/fp5/5eu99.0423.html][http://www.nea.fr/html/nsd/docs/2000/csni-r2000-12.pdf][http://www.ing.unipi.it/~dimnp/CD/supporto/pdf/paci03.pdf]</ref>


==== The study of used fuel ====
==Spinout areas==
Used nuclear fuel is studied in [[PIE (nuclear fuel)|post irradation examination]], where used fuel is examined to know more about the processes that occur in fuel during use, and how these  might alter the outcome of an accident. For example, during normal use, the fuel expands due to thermal expansion. This causes cracking, and in extreme cases, such as during the [[power]] surge which destroyed the [[Chernobyl]] nuclear reactor in April, 1986, the fuel can shatter into very small fragments. Most [[nuclear fuel]] is uranium dioxide, which is a [[cubic]] solid which has a structure similar to that of [[calcium fluoride]], in used fuel the solid state structure of most of the solid remains the same as that of pure cubic uranium dioxide. SIMFUEL is the name given to the simulated spent fuel which is made by mixing finely ground metal oxides, grinding as a slurry, spray drying it before heating in hydrogen/argon to 1700 oC. <ref>A good report on the microstructure of used fuel is Lucuta PG ''et al'' (1991) ''J Nuclear Materials'' '''178''':48-60</ref> In SIMFUEL, 4.1% of the volume of the solid was in the form of metal [[nanoparticle]]s which are made of [[molybdenum]], [[ruthenium]], [[rhodium]] and [[palladium]]. Most of these metal particles are of the ε phase ([[hexagonal]]) of Mo-Ru-Rh-Pd alloy, while smaller amounts of the α ([[cubic]]) and σ ([[tetragonal]]) phases of these metals were found in the SIMFUEL. Also present within the SIMFUEL was a cubic [[perovskite]] phase which is a [[barium]] [[strontium]] [[zirconium|zirconate]] (Ba<sub>x</sub>Sr<sub>1-x</sub>ZrO<sub>3</sub>).
Some methods first developed within nuclear chemistry and physics have become so widely used within chemistry and other physical sciences that they may be best thought of as separate from ''normal'' nuclear chemistry. For example, the isotope effect is used so extensively to investigate chemical mechanisms and the use of cosmogenic isotopes and long-lived unstable isotopes in [[geology]] that it is best to consider much of isotopic chemistry as separate from nuclear chemistry.


[[Image:UO2lattice.jpg|right|thumb|250px|The solid state structure of uranium dioxide, the oxygen atoms are in red and the uranium atoms in green]]
==== Kinetics (use within mechanistic chemistry) ====
The mechanisms of chemical reactions can be investigated by observing how the kinetics of a reaction are changed by making an isotopic modification of a substrate. This is now a standard method in [[organic chemistry]]. Briefly, replacing normal hydrogen (protons) by deuterium within a chemical compound causes the rate of molecular vibration (C-H, N-H and O-H bonds show this) to decrease. This can lead to a decrease in the reaction rate, if the rate-determining step involves breaking a bond between hydrogen and another atom. Thus, if the reaction changes in rate when protons are replaced by deuteriums, it is reasonable to assume that the breaking of the bond to hydrogen is part of the step which determines the rate.


Uranium dioxide is very insoluble in water, but after oxidation it can be converted to uranium trioxide or another uranium(VI) compound which is much more soluble in water. It is important to understand that uranium dioxide (UO<sub>2</sub>) can be oxidised to an oxygen rich hyperstoichiometric oxide (UO<sub>2+x</sub>) which can be further oxidised to U<sub>4</sub>O<sub>9</sub>, U<sub>3</sub>O<sub>7</sub>, U<sub>3</sub>O<sub>8</sub> and UO<sub>3</sub>.2H<sub>2</sub>O.
==== Uses within geology, biology and forensic science ====
''See [[Isotope geochemistry]] and [[Isotopic signature]] for further details


Because used fuel contains alpha emitters (plutonium and the [[minor actinides]]), the effect of adding an alpha emitter (<sup>238</sup>Pu) to uranium dioxide on the leaching rate of the oxide has been investigated. For the crushed oxide, adding <sup>238</sup>Pu did tend to increase the rate of leaching, but the difference in the leaching rate between between 0.1 and 10% <sup>238</sup>Pu was very small. <ref>V.V. Rondinella VV ''et al'' (2000) ''Radiochimica Acta'' '''88''':527-531</ref>
[[Cosmogenic isotopes]] are formed by the interaction of [[cosmic rays]] with the nucleus of an atom. These can be used for dating purposes and for use as natural tracers. In addition, by careful measurement of some ratios of stable isotopes it is possible to obtain new insights into the origin of bullets, ages of ice samples, ages of rocks, and the diet of a person can be identified from a hair or other tissue sample.
===== Biology =====
Within living things, isotopic labels (both radioactive and nonradioactive) can be used to probe how the complex web of reactions which makes up the [[metabolism]] of an organism converts one substance to another. For instance, green plants use light energy to convert water and carbon dioxide into glucose by [[photosynthesis]]. If the oxygen in the water is labeled, then the label appears in the oxygen gas formed by the plant.


The concentration of [[carbonate]] in the water which is in contact with the used fuel has a considerable effect on the rate of corrosion, because [[uranium]](VI) forms soluble anionic carbonate complexes such as [UO<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>]<sup>2-</sup> and [UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>]<sup>4-</sup>. When carbonate ions are absent, and the water is not strongly acidic, the hexavalent uranium compounds which form on oxidation of [[uranium dioxide]] often form insoluble hydrated [[uranium trioxide]] phases. <ref>for a review of the corrosion of uranium dioxide in a waste store which explains much of the chemistry, see  Shoesmith DW (2000) ''J Nuclear Materials'' '''282''':1-31</ref>.
For biochemical and physiological experiments and medical methods, a number of specific isotopes have important applications.


By ‘[[sputtering]]’, using uranium metal and an [[argon]]/[[oxygen]] gas mixture, thin films of uranium dioxide can be deposited upon gold surfaces. These gold surfaces which are modified with uranium dioxide have been used for both [[cyclic voltammetry]] and [[AC impedance]] experiments, and these offer an insight into the likely leaching behaviour of uranium dioxide. <ref>Miserque F ''et al'' (2001) ''J Nuclear Materials'' '''298''':280-90</ref>
*'''Stable isotopes''' have the advantage of not delivering a radiation dose to the system being studied; however, an excess of them might still interfere with the system's functioning, and the availability of sufficient amounts for whole-animal studies is limited for many isotopes. Measurement is also difficult, and usually requires [[mass spectroscopy]] to determine how much of the isotope is present in particular compounds, and there is no means of localizing measurements within the cell.


==== Fuel cladding interactions ====
*H-2 (deuterium), the stable isotope of hydrogen, is a stable tracer, the concentration of which can be measured by mass spectroscopy or NMR. It is incorporated into all cellular structures. Specific deuterated compound can also be produced.  
The study of the nuclear fuel cycle includes both the study of the behaviour of nuclear materials both under normal conditions and under accident conditions. For example, there has been much work on how [[uranium dioxide]] based fuel interacts with the [[zirconium]] alloy tubing used to cover it. During use, the fuel swells due to [[thermal expansion]] and then starts to react with the surface of the zirconium alloy, forming a new layer which contains both fuel and zirconium (from the cladding). Then, on the fuel side of this mixed layer, there is a layer of fuel which has a higher [[cesium]] to [[uranium]] ratio than most of the fuel. This is because [[xenon]] isotopes are formed as [[fission products]] that diffuse out of the lattice of the fuel into voids such as the narrow gap between the fuel and the cladding. After diffusing into these voids it decays to cesium isotopes. Because of the thermal gradient which exists in the fuel during use, the volatile fission products tend to be driven from the centre of the pellet to the rim area.<ref>Further reading on fuel cladding interactions: Tanaka K ''et al'' (2006) ''J Nuclear Materials'' '''357''':58-68</ref>. Below is a graph of the temperature of uranium metal, uranium nitride and [[uranium dioxide]] as a function of the distance from the centre of a 20 mm diameter pellet with a rim temperature of 200 <sup>o</sup>C. It is important to note that the uranium dioxide (because of its poor thermal conductivity) will overheat at the centre of the pellet, while the more thermally conductive other forms of uranium remain below their melting points.
*N-15  the stable isotope of nitrogen, has also been used. It is incorporated mainly into proteins.  


[[Image:Rim200pd1000rad1000fueltemp.jpg|center|thumb|450px|Temperature profile for a 20 mm diameter fuel pellet with a power density of 1000 W per cubic meter. The fuels other than uranium dioxide are not compromised.]]
*'''Radioactive isotopes''' have the advantages of being detectable in very low quantities, in being easily measured by [[scintillation counting]] or other radiochemical methods, and in being localizable to particular regions of a cell, and quantifiable by [[autoradiography]]. Many compounds with the radioactive atoms in specific positions can be prepared, and are widely available commercially. In high quantities they require precautions to guard the workers from the effects of radiation--and they can easily contaminate laboratory glassware and other equipment. For some isotopes the half-life is so short that preparation and measurement is difficult.  


====Absorption of fission products on surfaces====
By organic synthesis it is possible to create a complex molecule with a radioactive label that can be confined to a small area of the molecule. For short-lived isotopes such as <sup>11</sup>C, very rapid synthetic methods have been developed to permit the rapid addition of the radioactive isotope to the molecule. For instance a [[palladium]] catalysed [[carbonylation]] reaction in a [[microfluidic]] device has been used to rapidly form amides<ref>Miller PW ''et al'' (2006) ''Chemical Communications'' 546-548</ref> and it might be possible to use this method to form radioactive imaging agents for [[PET]] imaging.[http://www.rsc.org/Publishing/Journals/CC/article.asp?d.oi=b515410b]
Another important area of nuclear chemistry is the study of the interaction of fission products with surfaces. This is thought to control the rate of release and migration of fission products both from waste containers under normal conditions and from power reactors under accident conditions. It is interesting to note that, like [[chromate]] and [[molybdate]], the '''<sup>99</sup>TcO<sub>4</sub>''' anion can react with steel surfaces to form a [[corrosion]] resistant layer. In this way, these metaloxo anions act as [[anode|anodic]] [[corrosion inhibitor]]s. The formation of <sup>99</sup>TcO<sub>2</sub> on steel surfaces is one effect which will retard the release of <sup>99</sup>Tc from nuclear waste drums and nuclear equipment which has been lost before decontamination (eg [[submarine]] reactors  lost at sea). This <sup>99</sup>TcO<sub>2</sub> layer renders the steel surface passive, it inhibits the [[anodic]] [[corrosion]] reaction. It has also been shown that <sup>99</sup>TcO<sub>4</sub> anions react to form a layer on the surface of activated carbon ([[charcoal]]).


[[Image:TcO2layeronsteelsurface.jpg|center|thumb|450px|Formation of a TcO2 layer on a steel surface.]]
*<sup>3</sup>H, Tritium, the radioisotope of hydrogen, it available at very high specific activities, and compounds with this isotope in particular positions are easily prepared by standard chemical reactions such as hydrogenation of unsaturated precursors. The isotope emits very soft beta radiation, and can be detected by scintillation counting.  


In a similar way, the release of '''iodine-131''' in a serious power reactor accident could be retarded by absorption on [[metal]] surfaces within the nuclear plant. <ref>* Glänneskog H (2004) Interactions of [[Iodine|I]]<sub>2</sub> and [[Methyl iodide|CH]]<sub>3</sub>I with reactive metals under BWR severe-accident conditions ''Nuclear Engineering and Design'' '''227''':323-9
*<sup>11</sup>C, Carbon-11 can be made using a [[cyclotron]], [[boron]] in the form of [[boric oxide]] is reacted with protons in a (p,n) reaction. An alternative route is to react <sup>10</sup>B with deuterons. By rapid organic synthesis, the <sup>11</sup>C compound formed in the cyclotron is converted into the imaging agent which is then used for PET.
* Glänneskog H (2005) Iodine chemistry under severe accident conditions in a nuclear power reactor, PhD thesis, Chalmers University of Technology, Sweden
* A lot of other work on the iodine chemistry which would occur during a bad accident has been done.[http://www.sbf.admin.ch/htm/services/publikationen/international/frp/eu-abstracts/html/fp/fp5/5eu99.0423.html][http://www.nea.fr/html/nsd/docs/2000/csni-r2000-12.pdf][http://www.ing.unipi.it/~dimnp/CD/supporto/pdf/paci03.pdf]</ref>


==Spinout areas==
*<sup>14</sup>C, Carbon-14 can be made (as above), and it is possible to convert the target material into simple inorganic and organic compounds. In most [[organic synthesis]] work it is normal to try to create a product out of two approximately equal sized fragments and to use a convergent route, but when a radioactive label is added, it is normal to try to add the label late in the synthesis in the form of a very small fragment to the molecule to enable the radioactivity to be localised in a single group. Late addition of the label also reduces the number of synthetic stages where radioactive material is used.
Some methods first developed within nuclear chemistry and physics have become so widely used within chemistry and other physical sciences that they may be best thought of as not being part of ''normal'' nuclear chemistry. For example, [[Isotopic chemistry]] could be included in this subtopic, but due to the use of the isotope effect to investigate chemical mechanisms and the use of cosmogenic isotopes and long-lived unstable isotopes in [[geology]] it is best to consider much of isotopic chemistry as separate from nuclear chemistry.


==== Kinetics (use within mechanistic chemistry) ====
*<sup>18</sup>F, fluorine-18 can be made by the reaction of [[neon]] with deuterons, <sup>20</sup>Ne reacts in a (d,<sup>4</sup>He) reaction. It is normal to use neon gas with a trace of stable [[fluorine]] (<sup>19</sup>F<sub>2</sub>). The <sup>19</sup>F<sub>2</sub> acts as a carrier which increases the yield of radioactivity from the cyclotron target by reducing the amount of radioactivity lost by absorption on surfaces. However, this reduction in loss is at the cost of the specific activity of the final product.
The mechanisms of chemical reactions can be investigated by observing the effect upon the kinetics of making an isotopic modification of a substrate in a reaction. This is now a standard method in [[organic chemistry]]. Briefly, replacing normal hydrogens ([[protons]]) within a [[chemical compound]] with deuterium causes the rate of molecular vibration (C-H, N-H and O-H bonds show this) to decrease, this then can lead to a decrease in the reaction rate if the rate-determining step involves breaking a bond between hydrogen and another atom. Thus, if the reaction changes in rate when protons are replaced by deuteriums, it is reasonable to assume that the breaking of the bond to hydrogen is part of the step which determines the rate.


==== Uses within geology, biology and forensic science ====
[[Cosmogenic isotopes]] are formed by the interaction of [[cosmic rays]] with the nucleus of an atom. These can be used for dating purposes and for use as natural tracers. In addition, by careful measurement of some ratios of stable isotopes it is possible to obtain new insights into the origin of bullets, ages of ice samples, ages of rocks, and the diet of a person can be identified from a hair or other tissue sample. (See [[Isotope geochemistry]] and [[Isotopic signature]] for further details).
=== Nuclear magnetic resonance (NMR) ===
=== Nuclear magnetic resonance (NMR) ===
[[Nuclear magnetic resonance |NMR spectroscopy]] uses the net spin of nuclei in a substances upon energy absorption, and is used to identify molecules. This has now become a standard spectrscopic tool within [[synthetic chemistry]] One of the main uses of NMR is to determine the [[chemical bond|bond]] connectivity within an organic molecule.
[[Nuclear magnetic resonance |NMR spectroscopy]] uses the net spin of nuclei in a substances upon energy absorption to identify molecules. This has now become a standard spectroscopic tool within [[synthetic chemistry]]. One major use of NMR is to determine the [[chemical bond|bond]] connectivity within an organic molecule.
 
NMR imaging also uses the net spin of nuclei (commonly protons) for imaging. This is widely used in medicine, and can provide detailed images of the inside of a person without inflicting any radiation upon them. In a medical setting, NMR is often known simply as "Magnetic resonance" imaging, as the word 'nuclear' has negative connotations for many people.
 
== References ==
<references/>
 
==Text books==
;''Radiochemistry and Nuclear Chemistry'' :
Comprehensive textbook by Choppin, Liljenenzin and Rydberg. ISBN -0750674636, Butterworth-Heinemann, 2002.
 
;''Radioactivity, Ionizing radiation and Nuclear Energy'' :
Basic textbook for undergraduates by Hála and Navratil. ISBN -807302053-X, Konvoj, 2003
 
;''The Radiochemical Manual'' :
Overview of the production and uses of both open and sealed sources. Edited by BJ Wilson and written by RJ Bayly, JR Catch, JC Charlton, CC Evans, TT Gorsuch, JC Maynard, LC Myerscough, GR Newbery, H Sheard, CBG Taylor and BJ Wilson. The radiochemical centre (Amersham) was sold via [[HMSO]], 1966 (second edition)


NMR imaging also uses the net spin of nuclei (commonly protons) for imaging. This is widely used for diagnostic purposes in medicine, and can provide detailed images of the inside of a person without inflicting any radiation upon them. In a medical setting, NMR is often known simply as "magnetic resonance" imaging, as the word 'nuclear' has negative connotations for many people.


[[Category:Nuclear chemistry| ]]
==References==
[[Category:Chemistry Workgroup (Top)]]
{{reflist}}[[Category:Suggestion Bot Tag]]
[[Category:CZ Live]]

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Nuclear chemistry is a subfield of chemistry dealing with radioactivity, nuclear processes and nuclear properties. It includes the study of:

  • the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. Nuclear reactors can be "high-flux" reactors, mainly used to make radio-active isotopes for medical or scientific use, or "low-flux" reactors, mainly used for power generation. (Flux in this content means the density of neutrons per unit of volume.) These processes include the corrosion of surfaces and the behaviour under conditions of both normal and abnormal operation (such as during an accident). An important area is the behaviour of objects and materials after being placed into a waste store or otherwise disposed of.
  • the chemical effects resulting from the absorption of radiation within living animals, plants, and other materials. The radiation chemistry controls much of radiation biology as radiation affects living things at the molecular scale. In particular, radiation alters the biochemicals within an organism, this changes the chemistry within the organism, and this can lead to a biological outcome. Nuclear chemistry is important in the development of some medical treatments (such as cancer radiotherapy).
  • the production and use of radioactive sources for many different processes. These include the sources used for radiotherapy; the use of radioactive tracers within industry, science and the environment; and the use of radiation to modify materials such as polymers[6][7] .

Early history

After the discovery of X-rays by Wilhelm Röntgen, many scientists began to investigate ionizing radiation. In France, Henri Becquerel investigated the relationship between phosphorescence and the blackening of photographic plates, and he discovered that, with no external source of energy, uranium generated "rays" that could blacken (or fog) a photographic plate. This observation marks the discovery of radioactivity. Subsequently, Marie Curie (working in Paris) and her husband Pierre Curie isolated two new radioactive elements from uranium ore. They used radiometric methods to identify which stream the radioactivity was in after each each chemical separation; they separated the uranium ore into each of the different chemical elements that were known at the time, and measured the radioactivity of each fraction. They then attempted to separate these radioactive fractions further, to isolate a smaller fraction with a higher specific activity (radioactivity per unit mass). In this way, they isolated polonium and radium.

By 1901 it was noticed that high doses of radiation could injure humans. Becquerel had carried a sample of radium in his pocket, and as a result he suffered a high localized dose which resulted in a radiation burn [8] This injury resulted in the biological properties of radiation being investigated, which in time resulted in the development of medical treatments. Marie Curie's daughter (Irène Joliot-Curie) and her husband were the first to create radioactivity: they bombarded boron with alpha particles to make a proton-rich isotope of nitrogen; this isotope emitted positrons. [9] In addition, they bombarded aluminium and magnesium with neutrons to make new radioisotopes.

Ernest Rutherford, working in Canada and England, showed that radioactive decay can be described by a simple equation (a linear first-degree derivative equation, now called first-order kinetics), implying that a given radioactive substance has a characteristic "half life" (the time taken for the amount of radioactivity present in a source to diminish by half). He also coined the terms alpha, beta, and gamma radiation, he converted nitrogen into oxygen, and most importantly he supervised the students who did the Geiger-Marsden experiment (gold leaf experiment) which showed that the "plum pudding model" of the atom was wrong. In the plum pudding model, proposed by J. J. Thomson in 1904, the atom is composed of electrons surrounded by a cloud of positive charge to balance the electrons' negative charge. To Rutherford, the gold foil experiment implied that the positive charge was confined to a very small nucleus, leading first to the Rutherford model and eventually to the Bohr model of the atom, where the positive nucleus is surrounded by the negative electrons.

In initial attempts to make the transuranium elements, uranium was bombarded with neutrons; the idea was that, by creating a neutron-rich uranium isotope, the next element would be formed by beta decay. Instead, in these early studies the fissile 235U underwent fission to generate highly radioactive fission products. Because of their high activity, these fission products (such as short-lived barium isotopes) dominated the radiochemical analysis of the irradiated uranium. At first, it was thought that the uranium had been converted into radium, as many of the early radiochemical methods had difficulty in distinguishing between barium and radium. But gradually it was recognized that most of the radioactivity was due to the products of breaking uranium nuclei into two fragments.[1]

Edwin McMillan attempted to measure the range of the fission products using cigarette paper; during this work he isolated a beta active isotope with a half life of 2.3 days (239Np). A short time later in 1940 plutonium was discovered.

Main areas

Radiochemistry

see radiochemistry for fuller details.

Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being inactive as the isotopes are stable). Both the behaviour of man made[2] and natural radioisotopes are part of radiochemistry.

Radiation chemistry

Radiation chemistry is the study of the chemical effects of radiation on matter.This is very different to radiochemistry, as no radioactivity needs to be present in the material which is being chemically changed by the radiation. An example is the conversion of water into hydrogen gas and hydrogen peroxide.

Study of nuclear reactions

see also nuclear physics and nuclear reactions for further details.

A combination of radiochemistry and radiation chemistry is used to study nuclear reactions such as fission and fusion. Some early evidence for nuclear fission was the formation of a shortlived radioisotope of barium which was isolated from neutron-irradiated uranium ( 139Ba, with a half-life of 83 minutes and 140Ba, with a half-life of 12.8 days, are major fission products of uranium). At the time, it was thought that this was a new radium isotope, as it was then standard radiochemical practice to use a barium sulphate carrier precipitate to assist in the isolation of radium.[10]. More recently, a combination of radiochemical methods and nuclear physics has been used to try to make new 'superheavy' elements; it is thought that islands of relative stability exist where the nuclides have half-lives of years, thus enabling weighable amounts of the new elements to be isolated. For more details of the original discovery of nuclear fission see the work of Otto Hahn.

The nuclear fuel cycle

In the nuclear fuel cycle, uranium is mined, enriched and manufactured to nuclear fuel (1) which is delivered to a nuclear power plant. After use, the spent fuel is delivered to a reprocessing plant (2) or for permanent storage (3) in a safe place, such as inside rock. In reprocessing, 95% of spent fuel can be recycled to be returned to use in a power plant (4).

The fuel cycle includes all the operations involved in producing fuel, from mining, ore processing and enrichment to fuel production (Front end of the cycle). It also includes the 'in-pile' behaviour (use of the fuel in a reactor) before the back end of the cycle. The back end includes the management of the used nuclear fuel in either a cooling pond or dry storage, before it is disposed of into an underground waste store or reprocessed. The chemistry associated with any part of the nuclear fuel cycle, including nuclear reprocessing is studied in this part of nuclear chemistry. One of the key topics is the materials used for fuels.

Solid state forms of actinide metals

Most power reactors use dioxide fuel, but some reactor designs do use actinide metal fuel. One of the disadvantages of metal fuel is that the melting point of the fuel is lower than that of either the oxide, nitride or carbide. But for some special applications metal fuel is used, because of this can form general interest a discussion of the crystalography of plutonium metal is provided below. Of the actinides plutonium is the metal which has the most crystal forms, and hence we will restrict our discussion to plutonium.

Many different crystal forms of different actinide metals exist. Plutonium can exist in many different forms, alpha,[3] beta,[4] gamma, delta (ρ = 16.0),[5] delta' (ρ = 16.0),[6] gamma[7] and epsilon [8] forms are known.

The alpha form has a monoclinic cell (a = 6.184, b = 4.824, c = 10.973, alpha = 90o, beta = 101.80o and gamma 90o) with many atoms inside the unit cell, the resulting solid can be thought of consisting of many face sharing distorted tetrahedra. The beta form has a monoclinic cell with many atoms inside the cell, the resulting solid contains tetrahedra and other polyhedra linked together in a face sharing manner. The delta form is a face centred cubic type solid where the cell dimension is 4.632 A. The delta prime form is a tetragonally distorted body centred cubic solid in which the cell dimensions are a = b = 3.339 A and c = 4.446 A.

  • Alpha plutonium (note that this is not a view of a unit cell)

    Alpha plutonium (note that this is not a view of a unit cell)

  • Beta plutonium (note that this is not a view of a cell)

    Beta plutonium (note that this is not a view of a cell)

  • A unit cell of delta plutonium

    A unit cell of delta plutonium

  • A unit cell of delta prime plutonium

    A unit cell of delta prime plutonium

  • Gamma plutonium (note that this is not a view of a unit cell)

    Gamma plutonium (note that this is not a view of a unit cell)

  • A unit cell of epsilon plutonium

    A unit cell of epsilon plutonium

Solid state structures of actinide dioxides

Many of the actinide dioxides are similar to uranium dioxide, the structure of this is shown below.

The solid state structure of uranium dioxide, the oxygen atoms are in red and the uranium atoms in green

Normal and abnormal conditions

The nuclear chemistry associated with the nuclear fuel cycle can be divided into two main areas. One area concerns operation under the intended conditions; the other area concerns maloperation conditions, where some alteration from the normal operating conditions has occurred or (more rarely) during an accident.

Reprocessing

Law

In the USA, it is normal to use fuel once in a power reactor before placing it in a waste store. The long term plan is currently to place the civil used power reactor fuel in a deep store. This policy of not reprocessing was started in March 1977 for nuclear weapons proliferation reasons. President Jimmy Carter issued a Presidential directive which indefinitely suspended the commercial reprocessing and recycling of plutonium in the USA. This directive was probably an attempt by the USA to lead other countries by example, but many other nations continue to reprocess spent nuclear fuels. It is noteworthy that the government under Putin (President of Russia) repealed a law which had banned the inport of used nuclear fuel into Russia, this change in Russian law now permits the Russians to offer a reprocessing service for clients outside Russia (In a similar way to that offered by BNFL).

PUREX chemistry
For more information, see: PUREX.

To separate useful isotopes from fission byproducts, current method of choice is to use the PUREX liquid-liquid extraction process which uses a tributyl phosphate/hydrocarbon mixture to extract both uranium and plutonium from nitric acid.

DUPIC (an alternative)

As an alternative to the use of normal uranium in a CANDU it has been suggested that the spent fuel from a Pressurised Water Reactor could be used in place of natural uranium in a heavy water moderated CANDU. The term DUPIC means Direct Use of spent Pressurized water reactor fuel In CANDU.[11][12] A discussion of different fuel cycles has been published, this includes a discussion of the DUPIC idea.[9]

Old methods (no longer used)

The bismuth phosphate process is a very old process which adds lots of material to the final highly active waste, and which was replaced by solvent extraction processes. The process was designed to extract plutonium from aluminium-clad uranium fuel. The fuel was declad by boiling it in caustic soda. After decladding, the uranium metal was dissolved in nitric acid. The plutonium at this point is in the +4 oxidation state. It was then precipitated by the addition of bismuth nitrate and phosphoric acid to form the bismuth phosphate. The plutonium was co-precipitated with this. The supernatant (containing many of the fission products) was separated from the solid. The precipitate was then dissolved in nitric acid before the addition of an oxidant such as potassium permanganate which converted the plutonium to PuO22+ (Pu VI), then a dichromate salt was added to maintain the plutonium in the +6 oxidation state. The bismuth phosphate was then re-precipitated leaving the plutonium in solution. Then, an iron (II) salt such as ferrous sulfate was added and the plutonium re-precipitated again using a bismuth phosphate carrier precipitate. Then lanthanum salts and fluoride were added to create solid lanthanum fluoride which acted as a carrier for the Pu. This was converted to the oxide by the action of a base. The lanthanum plutonium oxide was then collected and extracted with nitric acid to form plutonium nitrate. [13]

The Hexone or Redoxprocess is a liquid-liquid extraction process which uses methyl isobutyl ketone as the extractant. The extraction is by a solvation mechanism. This process has the disadvantage of requiring a salting-out reagent (aluminium nitrate) to increase the nitrate concentration in the aqueous phase to obtain a reasonable distribution ratio (D value). Also hexone is degraded by concentrated nitric acid. This process has been replaced by PUREX.[14][15]

The Butex, β,β'-dibutyoxydiethyl ether process is based on a solvation extraction process using the triether extractant named above. This process has the disadvantage of requiring the use of a salting out reagent (aluminium nitrate) is required to increase the nitrate concentration in the aqueous phase to obtain a reasonable distribution ratio. This process was used at Windscale many years ago, and has since been replaced by PUREX.

The molecular structure of butex
Methods being considered for future use

The PUREX process can be modified to make a UREX (URanium EXtraction) process which could be used to save space inside high-level nuclear waste disposal sites, such as Yucca Mountain, by removing the uranium which makes up the vast majority of the mass and volume of used fuel, and recycling it as reprocessed uranium. The UREX process is a PUREX process which has been modified to prevent the plutonium from being extracted. This can be done by adding a plutonium reductant before the first metal extraction step. In the UREX process, ~99.9% of the uranium and >95% of technetium are separated from each other and the other fission products and actinides. The key is the addition of acetohydroxamic acid to the extraction and scrub sections of the process; this greatly diminishes the extractability of plutonium and neptunium, providing greater proliferation resistance than with the plutonium extraction stage of the PUREX process.

Adding a second extraction agent, octyl(phenyl)-N, N-dibutyl carbamoylmethyl phosphine oxide(CMPO) in combination with tributylphosphate, the PUREX process can be turned into the TRUEX (TRansUranic EXtraction) process, a process invented in the USA by Argonne National Laboratory, and designed to remove the transuranic metals (Am/Cm) from waste. The idea is that, by lowering the alpha activity of the waste, most of the waste can be disposed of easily. Like PUREX, this process uses a solvation mechanism.

The molecular structure of a typical CMPO

As an alternative to TRUEX, an extraction process using a malondiamide has been devised. The DIAMEX (DIAMideEXtraction) process avoids the formation of organic waste which contains elements other than carbon, hydrogen, nitrogen and oxygen. Such an organic waste can be burned without forming acidic gases which could contribute to acid rain. The DIAMEX process is being worked on in Europe by the French CEA. The process is sufficiently mature that an industrial plant could be constructed with the existing knowledge of the process. Like PUREX, this process uses a solvation mechanism.[16][17]

Selective ActiNide EXtraction. As part of the management of minor actinides it has been proposed that the lanthanides and trivalent minor actinides should be removed from the PUREX raffinate by a process such as DIAMEX or TRUEX. In order to allow the actinides such as americium to be either reused in industrial sources or used as fuel the lanthanides must be removed. The lanthanides has large neutron cross sections and hence they would poison a neutron driven nuclear reaction. To date the extraction system for the SANEX process has not been defined, but currently several different research groups are working towards a process. For instance, the French CEA is working on a bis-triaiznyl pyridine (BTP) based process.

The molecular structure of a BTP

References:

Other systems such as the dithiophosphinic acids are being worked on by some other workers.

This is the UNiversal EXtraction process which was developed in Russia and the Czech Republic; it is designed to remove all of the most troublesome (Sr, Cs and minor actinides) radioisotopes from the raffinates left after extracting uranium and plutonium from used nuclear fuel. [18][19] The chemistry is based upon the interaction of caesium and strontium with polyethylene oxide (polyethylene glycol) [20] and a cobalt carborane anion (known as chlorinated cobalt dicarbollide). The actinides are extracted by CMPO, and the diluent is a polar aromatic such as nitrobenzene. Other dilents such as meta-nitrobenzotrifluoride and phenyl trifluoromethyl sulfone [21]have been suggested as well.

Absorption of fission products on surfaces

Another important area of nuclear chemistry is the study of how fission products interact with surfaces; this is thought to control the rate of release and migration of fission products both from waste containers under normal conditions and from power reactors under accident conditions. It is interesting to note that, like chromate and molybdate, the 99TcO4 anion can react with steel surfaces to form a corrosion-resistant layer. In this way, these metaloxo anions act as anodic corrosion inhibitors. The formation of 99TcO2 on steel surfaces is one effect which will retard the release of 99Tc from nuclear waste drums and nuclear equipment which has been lost before decontamination (e.g. submarine reactors lost at sea). This 99TcO2 layer renders the steel surface passive, inhibiting the anodic corrosion reaction. The radioactive nature of technetium makes this corrosion protection impractical in almost all situations. It has also been shown that 99TcO4 anions react to form a layer on the surface of activated carbon (charcoal) or aluminium.[10][22]. A short review of the biochemical properties of a series of key long lived radioisotopes can be read on line.[23]

Formation of a TcO2 layer on a steel surface.

It is important to note that 99Tc in nuclear waste may exist in chemical forms other than the 99TcO4 anion, these other forms have different chemical properties.[24] Similarly, the release of iodine-131 in a serious power reactor accident could be retarded by absorption on metal surfaces within the nuclear plant. [11]

Spinout areas

Some methods first developed within nuclear chemistry and physics have become so widely used within chemistry and other physical sciences that they may be best thought of as separate from normal nuclear chemistry. For example, the isotope effect is used so extensively to investigate chemical mechanisms and the use of cosmogenic isotopes and long-lived unstable isotopes in geology that it is best to consider much of isotopic chemistry as separate from nuclear chemistry.

Kinetics (use within mechanistic chemistry)

The mechanisms of chemical reactions can be investigated by observing how the kinetics of a reaction are changed by making an isotopic modification of a substrate. This is now a standard method in organic chemistry. Briefly, replacing normal hydrogen (protons) by deuterium within a chemical compound causes the rate of molecular vibration (C-H, N-H and O-H bonds show this) to decrease. This can lead to a decrease in the reaction rate, if the rate-determining step involves breaking a bond between hydrogen and another atom. Thus, if the reaction changes in rate when protons are replaced by deuteriums, it is reasonable to assume that the breaking of the bond to hydrogen is part of the step which determines the rate.

Uses within geology, biology and forensic science

See Isotope geochemistry and Isotopic signature for further details

Cosmogenic isotopes are formed by the interaction of cosmic rays with the nucleus of an atom. These can be used for dating purposes and for use as natural tracers. In addition, by careful measurement of some ratios of stable isotopes it is possible to obtain new insights into the origin of bullets, ages of ice samples, ages of rocks, and the diet of a person can be identified from a hair or other tissue sample.

Biology

Within living things, isotopic labels (both radioactive and nonradioactive) can be used to probe how the complex web of reactions which makes up the metabolism of an organism converts one substance to another. For instance, green plants use light energy to convert water and carbon dioxide into glucose by photosynthesis. If the oxygen in the water is labeled, then the label appears in the oxygen gas formed by the plant.

For biochemical and physiological experiments and medical methods, a number of specific isotopes have important applications.

  • Stable isotopes have the advantage of not delivering a radiation dose to the system being studied; however, an excess of them might still interfere with the system's functioning, and the availability of sufficient amounts for whole-animal studies is limited for many isotopes. Measurement is also difficult, and usually requires mass spectroscopy to determine how much of the isotope is present in particular compounds, and there is no means of localizing measurements within the cell.
  • H-2 (deuterium), the stable isotope of hydrogen, is a stable tracer, the concentration of which can be measured by mass spectroscopy or NMR. It is incorporated into all cellular structures. Specific deuterated compound can also be produced.
  • N-15 the stable isotope of nitrogen, has also been used. It is incorporated mainly into proteins.
  • Radioactive isotopes have the advantages of being detectable in very low quantities, in being easily measured by scintillation counting or other radiochemical methods, and in being localizable to particular regions of a cell, and quantifiable by autoradiography. Many compounds with the radioactive atoms in specific positions can be prepared, and are widely available commercially. In high quantities they require precautions to guard the workers from the effects of radiation--and they can easily contaminate laboratory glassware and other equipment. For some isotopes the half-life is so short that preparation and measurement is difficult.

By organic synthesis it is possible to create a complex molecule with a radioactive label that can be confined to a small area of the molecule. For short-lived isotopes such as 11C, very rapid synthetic methods have been developed to permit the rapid addition of the radioactive isotope to the molecule. For instance a palladium catalysed carbonylation reaction in a microfluidic device has been used to rapidly form amides[12] and it might be possible to use this method to form radioactive imaging agents for PET imaging.[25]

  • 3H, Tritium, the radioisotope of hydrogen, it available at very high specific activities, and compounds with this isotope in particular positions are easily prepared by standard chemical reactions such as hydrogenation of unsaturated precursors. The isotope emits very soft beta radiation, and can be detected by scintillation counting.
  • 11C, Carbon-11 can be made using a cyclotron, boron in the form of boric oxide is reacted with protons in a (p,n) reaction. An alternative route is to react 10B with deuterons. By rapid organic synthesis, the 11C compound formed in the cyclotron is converted into the imaging agent which is then used for PET.
  • 14C, Carbon-14 can be made (as above), and it is possible to convert the target material into simple inorganic and organic compounds. In most organic synthesis work it is normal to try to create a product out of two approximately equal sized fragments and to use a convergent route, but when a radioactive label is added, it is normal to try to add the label late in the synthesis in the form of a very small fragment to the molecule to enable the radioactivity to be localised in a single group. Late addition of the label also reduces the number of synthetic stages where radioactive material is used.
  • 18F, fluorine-18 can be made by the reaction of neon with deuterons, 20Ne reacts in a (d,4He) reaction. It is normal to use neon gas with a trace of stable fluorine (19F2). The 19F2 acts as a carrier which increases the yield of radioactivity from the cyclotron target by reducing the amount of radioactivity lost by absorption on surfaces. However, this reduction in loss is at the cost of the specific activity of the final product.

Nuclear magnetic resonance (NMR)

NMR spectroscopy uses the net spin of nuclei in a substances upon energy absorption to identify molecules. This has now become a standard spectroscopic tool within synthetic chemistry. One major use of NMR is to determine the bond connectivity within an organic molecule.

NMR imaging also uses the net spin of nuclei (commonly protons) for imaging. This is widely used for diagnostic purposes in medicine, and can provide detailed images of the inside of a person without inflicting any radiation upon them. In a medical setting, NMR is often known simply as "magnetic resonance" imaging, as the word 'nuclear' has negative connotations for many people.

References

  1. ↑ Meitner L, Frisch OR (1939) Disintegration of uranium by neutrons: a new type of nuclear reaction. Nature 143:239-40 (doi = 10.1038/224466a0) [1]
  2. ↑ Imanaka T et al. (2006) J Radiation Research 47 Suppl A121-A127
  3. ↑ Zachariasen WH, Ellinger FH (1957) J Chem Physics,27:811-2
  4. ↑ Zachariasen WH, Ellinger FH (1963) Acta Crystallographica 16:369-75
  5. ↑ Ellinger FH (1956) J Metals, 1956, 8:1256-125
  6. ↑ Ellinger FH (1956) J Metals 8:1256-125
  7. ↑ Ellinger FH (1955) Acta Crystallographica 8:431-3
  8. ↑ Ball JB et al. (1960) Memoires Scientifiques de la Revue de Metallurgie 57:49-56
  9. ↑ Ko WI, Kim HD (2001) J Nuclear Sci Technol 38:757-65 [2]
  10. ↑ Decontamination of surfaces, George H. Goodalland Barry.E. Gillespie, United States Patent 4839100
  11. ↑ Glänneskog H (2004) Interactions of I2 and CH3I with reactive metals under BWR severe-accident conditions Nuclear Engineering and Design 227:323-9
    • Glänneskog H (2005) Iodine chemistry under severe accident conditions in a nuclear power reactor, PhD thesis, Chalmers University of Technology, Sweden
    • For other work on the iodine chemistry which would occur during a bad accident, see[3][4][5]
  12. ↑ Miller PW et al (2006) Chemical Communications 546-548
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