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


* the study 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 has an effect on living things at the molecular scale, to explain it another way the raidation alters the biochemicals within an organism, the alteration of the biomolecules then changes the chemistry which occurs within the organism, this change in [[biochemistry]] then can lead to a biological outcome. As a result nuclear chemistry greatly assists the understanding of medical treatments (such as [[cancer]] [[radiotherapy]]) and has enabled these treatments to improve.
* 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 study of the production and use of radioactive sources for a range of processes. These include [[radiotherapy]] in medical applications; 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] .
* 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] .


* 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]] and [[physical chemistry]] and for structural analysis in [[macromolecular chemistry]].
* 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]]. It was noticed in about 1901 that high doses of radiation could cause an injury in humans, Becquerel had carried a sample of radium in his pocket and as a result he suffered a high localised 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 [[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]].  


[[Ernest Rutherford]], working in [[Canada]] and [[England]], showed that radioactivity 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]] rays, 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.
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.


==Main areas==
[[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.
===Radiochemistry===
[[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'').  


====Activation analysis====
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>  
By [[neutron]] irradation of objects it is possible to induce radioactivity, this activation of stable isotopes to create radioisotopes is the basis of [[neutron activation analysis]]. One of the most interesting objects which has been studied in this way is the [[hair]] of [[Napoleon]]'s head, which have been examined for their [[arsenic]] content.<ref>H. SMITH, S. FORSHUFVUD & A. WASSÉN, ''Nature'', 1962, '''194'''(26 May), 725-726</ref>


A series of different experimental methods exist, these have been designed to enable the measurement of a range of different elements in different matrixs. To reduce the effect of the matrix it is common to use the chemical extraction of the wanted element ''and/or'' to allow the radioactivity due to the matrix elements to decay before the measurement of the radioactivity.
[[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.


[[Image:Neutronactivation.jpg|left|thumb|550px|In this diagram the matrix atoms are shown in black, the element of interest is in blue while the interfereing element is shown in green. The radioisotopes formed by the element of interest and the interfereing element are shown in magenta and red respectively. In the first picture a sample containing black (matrix), green and blue atoms is obtained, the sample is processed to extract only the blue and the green atoms, then the atoms are irradated with neutrons to render the atoms radioactive. After allowing the radioactivity due to the short lived isotopes to decay (magenta) the red radioisotope is counted]]
==Main areas==
 
===Radiochemistry===
The effects of a series of different cooling times can be seen if a hypothetical sample which contains sodium, uranium and cobalt in a 100:10:1 ratio is subjected to a very short pulse of [[thermal neutron]]s. In the following bar chart the radioactivity due to each of these three elements is shown, note that the uranium-239 decays very quickly to [[neptunium]]-239 which decays with a [[halflife]] of 2.36 days.
''see '''[[radiochemistry]]''' for fuller details.''
 
[[Image:Coollingtimeeffects2.jpg|center|thumb|550px|In this diagram the sodium activity (sodium-24) is on the left, the neptunium-239 activity in the centre and the cobalt-60 activity is on the right]]
 
====Biochemical uses====
One biological application is the study of [[DNA]] using radioactive [[phosphorus]]-32. In these experiments stable phosphorus is replaced by the chemical identical radioactive P-32, and the resulting radioactivity is used in analysis of the molecules and their behaviour.
 
Another example is the work which was done on the methylation of elements such as [[sulfur]], [[selenium]], [[tellurium]] and [[polonium]] by living organisms. It has been shown that [[bacteria]] can convert these elements into volatile compounds,<ref>N. Momoshima, Li-X. Song, S. Osaki and Y. Maeda, "Biologically induced Po emission from fresh water", ''Journal of Environmental Radioactivity'', 2002, '''63''', 187-197</ref> it is thought that [[methylcobalamin]] ([[vitamin]] [[B12]] alkylates these elements to create the dimethyls. It has been shown that a combination of [[Cobaloxime]] and inorganic polonium in [[sterile]] water forms a volatile polonium compound, while a control experiment which did not contain the [[cobalt]] compound did not form the volatile polonium compound.<ref>N. Momoshima, Li-X. Song, S. Osaki and Y. Maeda, "Formation and emission of volatile polonium compound by microbial activity and polonium methylation with methylcobalamin", ''Environmetal Science and Technology'', 2001, '''35''', 2956-2960</ref>. For the [[sulfur]] work the isotope <sup>35</sup>S was used, while for polonium <sup>207</sup>Po was used. In some related work by the addition of <sup>57</sup>Co to the bacterial culture, followed by isolation of the cobalamin from the bacteria (and the measurement of the radioactivity of the isolated cobalamin) it was shown that the bacteria convert avaiable cobalt into methylcobalamin.
 
[[Image:Posmissionbygerms.jpg|left|thumb|550px|In the first picture the polonium is added to the culture of the bacteria, by the time that the second picture is shown the bacteria have taken up some of the polonium. In the third picture the bacteria have converted some of the inorganic polonium into the dimethyl form]]
 
====Environmental====
Radiochemistry also includes the study of the behaviour of radioisotopes in the environment; for instance, a forest or grass fire can make radioisotopes become mobile again.<ref>Yoschenko VI ''et al'' (2006) Resuspension and redistribution of radionuclides during grassland and forest fires in the Chernobyl exclusion zone: part I. Fire experiments ''J Envir Radioact''  '''86''':143-63 PMID 16213067</ref> In these experiments, fires were started in the exclusion zone around [[Chernobyl]] and the radioactivity in the air downwind was measured.


It is important to note that a vast number of processes are able to release radioactivity into the environment, for example the action of [[cosmic ray]]s on the air is responsible for the formation of radioisotopes (such as <sup>14</sup>C and <sup>32</sup>P), the decay of <sup>226</sup>Ra forms <sup>222</sup>Rn which is a gas which can diffuse through rocks before entering buildings<ref>Janja Vaupotič and Ivan Kobal, "Effective doses in schools based on nanosize radon progeny aerosols", ''Atmospheric Environment'', 2006, '''40''', 7494-7507</ref><ref>Michael Durand, Building and Environment, "Indoor air pollution caused by geothermal gases", 2006, '''41''', 1607-1610</ref><ref>Paolo Boffetta, "Human cancer from environmental pollutants: The epidemiological evidence", ''Mutation Research/Genetic Toxicology and Environmental Mutagenesis'', 2006, '''608''', 157-162</ref> and dissolve in [[water]] and thus enter [[drinking water]]<ref>M. Forte, R. Rusconi, M.T. Cazzaniga and G. Sgorbati, "The measurement of radioactivity in Italian drinking waters", ''Microchemical Journal'', 2007, '''85''', 98-102</ref> in addition human activitys such as [[bomb test]]s, accidents(for example <ref>R. Pöllänen, M.E. Ketterer, S. Lehto, M. Hokkanen, T.K. Ikäheimonen, T. Siiskonen, M. Moring, M.P. Rubio Montero and A. Martín Sánchez, "Multi-technique characterization of a nuclearbomb particle from the Palomares accident", ''Journal of Environmental Radioactivity'', 2006, '''90''', 15-28</ref>) and normal releases from industry have resulted in the release of radioactivity.
[[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.
 
=====Chemical form of the actinides=====
The environmental chemistry of some radioactive elements such as plutonium is complicated by the fact that solutions of this element can undergo [[disproportionation]]<ref>Rabideau, S.W., ''Journal of the American Chemical Society'', 1957, '''79''', 6350-6353</ref>  and as a result many different oxidation states can coexist at once. Some work has been done on the identification of the oxidation state and coordination number of plutonium and the other actinides under different conditions has been done.[http://www.fas.org/sgp/othergov/doe/lanl/pubs/00818043.pdf] This includes work on both solutions of relativly simple complexes<ref>P. G. Allen, J. J. Bucher, D. K. Shuh, N. M. Edelstein, and T. Reich, "Investigation of Aquo and Chloro Complexes of UO22+, NpO2+, Np4+, and Pu3+ by X-ray Absorption Fine Structure Spectroscopy ", ''Inorganic Chemistry'', 1997, '''36''', 4676-4683</ref><ref>David L. Clark, Steven D. Conradson, D. Webster Keogh Phillip D. Palmer Brian L. Scott and C. Drew Tait, "Identification of the Limiting Species in the Plutonium(IV) Carbonate System. Solid State and Solution Molecular Structure of the [Pu(CO3)5]6- Ion", ''Inorganic Chemistry'', 1998, '''37''', 2893-2899</ref> and work on [[colloids]] <ref>Jörg Rothe, Clemens Walther, Melissa A. Denecke, and Th. Fanghänel, "XAFS and LIBD Investigation of the Formation and Structure of Colloidal Pu(IV) Hydrolysis Products ", ''Inorganic Chemistry'', 2004, '''43''', 4708-4718</ref> Two of the key matrixes are [[soil]]/[[rocks]] and [[concrete]], in these systems the chemical properties of plutonium have been studied using methods such as [[EXAFS]] and [[XANES]].<ref>M. C. Duff, D. B. Hunter, I. R. Triay, P. M. Bertsch, D. T. Reed, S. R. Sutton, G. Shea-McCarthy, J. Kitten, P. Eng, S. J. Chipera, and D. T. Vaniman, "Mineral Associations and Average Oxidation States of Sorbed Pu on Tuff", ''Environ. Sci. Technol'', 1999, '''33''', 2163-2169</ref>[http://www.wmsym.org/Abstracts/2002/Proceedings/6b/188.pdf][http://www.lanl.gov/orgs/nmt/nmtdo/AQarchive/02spring/synchrotron.html]
 
=====Movement of colloids=====
It is important to note that while binding of a metal to the surfaces of the soil particles can prevent its movement through a layer of soil, it is possible for the particles of soil which bear the radioactive metal can migrate as colloidal particles through soil. This has been shown to occur using soil particles labled with <sup>134</sup>Cs, these have been shown to be able to move through cracks in the soil.<ref>R.D. Whicker and S.A. Ibrahim, "Vertical migration of 134Cs bearing soil particles in arid soils: implications for plutonium redistribution", ''Journal of Environmental Radioactivity'', 2006, '''88''', 171-188.</ref>
 
=====Normal background=====
 
It is important to note that radioactivity is present everywhere (and has been since the formation of the earth). According to the [[IAEA]], one kilogram of soil typically contains the following amounts of the following three natural radioisotopes 370 Bq <sup>40</sup>K (typical range 100-700 Bq), 25 Bq <sup>226</sup>Ra (typical range 10-50 Bq), 25 Bq <sup>238</sup>U (typical range 10-50 Bq) and 25 Bq <sup>232</sup>Th (typical range 7-50 Bq).<ref>Generic Procedures for Assessment and Response during a Radiological Emergency, IAEA TECDOC Series number 1162, published in 2000 [http://www-pub.iaea.org/MTCD/publications/PubDetails.asp?pubId=5926]</ref>
 
=====Action of microorganisms=====
 
The action of microorganisms can fix uranium, it is interesting to note that [[Thermoanaerobacter]] can used [[chromium]](VI), [[iron]](III), [[cobalt]](III), [[manganese]](IV) and '''uranium(VI)''' as electron acceptors while [[acetate]], [[glucose]], [[hydrogen]], [[lactate]], [[pyruvate]], [[succinate]], and [[xylose]] can act as electron donors for the metabalism of the bacteria. In this way the metals can be reduced to form [[magnetite]] (Fe<sub>3</sub>O<sub>4</sub>), [[siderite]] (FeCO<sub>3</sub>), [[rhodochrosite]] (MnCO<sub>3</sub>), and '''[[uraninite]] (UO<sub>2</sub>)'''.<ref>Yul Roh, Shi V. Liu, Guangshan Li, Heshu Huang, Tommy J. Phelps, and Jizhong Zhou, "Isolation and Characterization of Metal-Reducing Thermoanaerobacter Strains from Deep Subsurface Environments of the Piceance Basin, Colorado", ''Applied and Environmental Microbiology'', 2002, '''68''', 6013-6020.</ref> Other researchers have also worked on the fixing of uranium using bacteria[http://www.physorg.com/news67270244.html][http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.0040282][http://www.pnl.gov/news/release.asp?id=175], Francis R. Livens ''et. al.'' (Working at [[Manchester]]) have suggested that the reason why ''Geobacter sulfurreducens'' can reduce UO<sub>2</sub><sup>2+</sup> carions to uranium dixoide is that the bacteria reduce the uranyl cations to UO<sub>2</sub><sup>+</sup> which then undergoes disproportionation to form UO<sub>2</sub><sup>2+</sup> and UO<sub>2</sub>. This reasoning was based (at least in part) on the observation that NpO<sub>2</sub><sup>+</sup> is not converted to an insoluble neptunium oxide by the bacteria.<ref>Joanna C. Renshaw, Laura J. C. Butchins, Francis R. Livens, Iain May, John M. Charnock, and Jonathan R. Lloyd, ''Environ. Sci. Technol.'', 2005, '''39'''(15), 5657-5660.</ref>


===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]].  
[[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]].
 
====Reduction of organics by solvated electrons====
A recent area of work has been the destruction of toxic organic compounds by irradiation <ref>Zhao C ''et al'' (2007) ''Radiation Physics and Chemistry'',  '''76''':37-45</ref>; after irradiation, "[[dioxin]]s" (polychlorodibenzo-''p''-dioxins) are dechloroinated in the same way as PCBs can be converted to [[biphenyl]] an inorganic chloride. This is because the [[solvated electron]]s react 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 irradiated 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. The base deprotonates the hydroxydimethylmethyl radical to be converted into acetone and a solvated electron, as the result the G value (yield for a given energy due to radiation deposited in the system) of chloride can be increased becuase the radiation now starts a chain reaction, each solvated electron formed by the action of the gamma rays can now convert more than one PCB molecule.<ref>Ajit Singh and Walter Kremers, ''Radiation Physics and Chemistry'', 2002, '''65'''(4-5), 467-472</ref><ref>Bruce J. Mincher, Richard R. Brey, René G. Rodriguez, Scott Pristupa and Aaron Ruhter, ''Radiation Physics and Chemistry'', 2002, '''65'''(4-5), 461-465</ref>If [[oxygen]], [[acetone]], [[nitrous oxide]], [[sulfur hexafluoride]] or [[nitrobenzene]]<ref>A. G. Bedekar, Z. Czerwik and J. Kroh, "Pulse radiolysis of ethylene glycol and 1,3-propanediol glasses—II. Kinetics of trapped electron decay", 1990, '''36''', 739-742</ref> is present in the mixture, then the reaction rate is reduced. This work has been done recently in the USA, 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]
 
[[Image:PCBdechloronation.jpg|left|thumb|550px|A diagram showing the mechanism by which PCBs are converted into biphenyl and inorganic chloride.]]
 
In addition to the work on the destruction of aryl chlorides it has been shown that [[aliphatic]] chlorine and [[bromine]] compounds such as perchloroethylene,<ref>V. Múka, *, R. Silber, M. Pospíil, V. Kliský and B. Bartoníek, ''Radiation Physics and Chemistry'', 1999, '''55'''(1), 93-97</ref> [[Freon]] (1,1,2-trichloro-1,2,2-trifluoroethane) and [[halon]]-2402 (1,2-dibromo-1,1,2,2-tetrafluoroethane) can be dehalogenated by the action of radiation on alkaline isopropanol solutions. Again a chain reaction has been reported.<ref>Seiko Nakagawa and Toshinari Shimokawa, ''Radiation Physics and Chemistry'', 2002, '''63'''(2), 151-156</ref>
 
In addition to the work on the reduction of organic compounds by irradation, some work on the radiation induced oxidation of organic compounds has been reported. For insatnce the use of radiogenic hydrogen peroxide (formed by irradation) to remove sulfur from [[coal]] has been reported. In this study it was found that the addition of [[manganese]] dioxide to the coal increased the rate of sulfur removal.<ref>P. S. M. Tripathi, K. K. Mishra, R. R. P. Roy and D. N. Tewari, "γ-Radiolytic desulphurisation of some high-sulphur Indian coals catalytically accelerated by MnO2", ''Fuel Processing Technology'', 2001, '''70''', 77-96</ref>
 
====Reduction of metal compounds====
 
In addition to the reduction of organic compounds by the solvated electrons it has been reported that upon irradation a [[pertechnetate]] solution, at pH 4.1 is converted to a [[colloid]] of [[technetium dioxide]]. Irradation of a solution at pH 1.8 soluble Tc(IV) complexes are formed. Irradation of a solution at 2.7 forms a mixture of the colloid and the soluble Tc(IV) compounds.<ref>T. Sekine, H. Narushima, T. Suzuki, T. Takayama, H. Kudo, M. Lin and Y. Katsumura, ''Colloids and Surfaces A: Physicochemical and Engineering Aspects'', 2004, '''249(1-3), 105-109</ref>
 
It has been shown that the irradation of aqueous solutions of [[lead]] compounds leads to the formation of elemental lead, when an inorganic solid such as [[bentonite]] and sodium formate are present then the lead is removed from the aqueous solution.<ref>M. Pospίšil, V. Čuba, V. Múčka and B. Drtinová, "Radiation removal of lead from aqueous solutions- effects of various sorbants and nitrous oxide", ''Radiation Physics and Chemistry'', 2006, '''75''', 403-407</ref>
 
====Polymer modifcation====
Another key area uses radiation chemistry to modify polymers. Using radiation, it is possible to convert [[monomer]]s to [[polymer]]s, to crosslink polymers, and to break polymer chains[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=7313004][http://mitr.p.lodz.pl/biomat/raport/3_5_radiation_hydrogels.html]. Both man-made and natural polymers (such as [[carbohydrate]]s [http://www-pub.iaea.org/MTCD/publications/PDF/te_1422_web.pdf]) can be processed in this way.
 
====Water chemistry====
Both the harmful effects of radiation upon biological systems (induction of [[cancer]] and [[radiation sickness|acute radiation injuries]]) and the useful effects of radiotherapy involve the radiation chemistry of water. The vast majority of biological molecules are present in an aqueous medium; when water is exposed to radiation, the water absorbs energy, and as a result forms chemically reactive species that can interact with dissolved substances ([[solute]]s). Water is ionized to form a [[solvated electron]] and H<sub>2</sub>O<sup>+</sup>, the H<sub>2</sub>O<sup>+</sup> cation can react with water to form a hydrated proton (H<sub>3</sub>O<sup>+</sup>) and a hydroxyl radical (HO<sup>.</sup>). Furthermore, the solvated electron can recombine with the H<sub>2</sub>O<sup>+</sup> cation to form an excited state of the water, this excited state then decomposes to species such as [[hydroxyl radical]]s (HO<sup>.</sup>), hydrogen atoms (H<sup>.</sup>) and oxygen atoms (O<sup>.</sup>). Finally, the solvated electron can react with solutes such as solvated protons or oxygen molecules to form respectively hydrogen atoms and dioxygen radical anions. The fact that oxygen changes the radiation chemistry might be one reason why oxygenated tissues are more sensitive to irradiation than the deoxygenated tissue at the centre of a tumor. The free radicals, such as the hydroxyl radical, chemically modify biomolecules such as [[DNA]], leading to damage such as breaks in the DNA strands. Some substances can protect again radiation-induced damage by reacting with the reactive species generated by the irradiation of the water.
 
[[Image:Aqueousradchem.jpg|left|thumb|550px|A scheme showing some of the different reactions which are possible when water is irradated.]]
 
It is important to note that the reactive species generated by the radiation can take part in ''following reactions'', this is similar to the idea of the non-electrochemical reactions which follow the electrochemical event which is observed in [[cyclic voltammetry]] when a non-reversable event occurs. For example the SF<sub>5</sub> radical formed by the reaction of solvated electrons and SF<sub>6</sub> undergo further reactions which lead to the formation of [[hydrogen flouride]] and [[sulfuric acid]].<ref>K.-D. Asmus and J.H. Fendler, "The reaction of sulfur hexaflouride with solvated electrons", ''The Journal of Physical Chemistry'', 1968, '''72''', 4285-4289</ref>
 
In water the dimerisation reaction of hydroxyl radicals can form [[hydrogen peroxide]], in saline systems the reaction of the hydroxyl radicals with [[chloride]] anions form [[hypochlorite]] anions.
 
It has been suggested that the action of radiation upon underground [[water]] is responsible for the formation of hydrogen which was converted by bacteria into [[methane]].[http://deepbio.princeton.edu/samp/papers/LinetalGCA69-893.pdf]<ref>LI-HUNG LIN, GREG F. SLATER, BARBARA SHERWOOD LOLLAR, GEORGES LACRAMPE-COULOUME and T. C. ONSTOTT, ''Geochimica et Cosmochimica Acta'', 2005, '''69''', 893-903.</ref>. A series of papers on the subject of bateria living under the surface of the earth which are fed by the hydrogen generated by the radiolysis of water can be read on line.[http://wetlands.ifas.ufl.edu/sickman/SOS%206932/Ocean%20vent%20papers.pdf]
 
====Equipment====
 
=====Industrial processing equipment=====
To process materials, either a gamma source or an electron beam can be used. The international type IV (''wet storage'') irradiator is a common design (the JS6300 and JS6500 gamma sterilizers (made by 'Nordion International'[http://www.mds.nordion.com/], which used to trade as 'Atomic Energy of Canada Ltd') are typical. <ref>Features of the design are discussed in the [[IAEA]] report on a [[human error]] accident in such an irradiation plant [http://www-pub.iaea.org/MTCD/publications/PDF/Pub847_web.pdf]</ref>. In these irradiation plants, the source is stored in a deep well filled with water when not in use. When the source is required, it is moved by a steel wire to the irradiation room where the products which are to be treated are present; these objects are placed inside boxes which are moved through the room by an automatic mechanism. By moving the boxes from one point to another, the contents are given a uniform dose. After treatment, the product is moved by the automatic mechanism out of the room. The irradiation room has very thick concrete walls (about 3m thick) to prevent gamma rays from escaping. The source consists of  <sup>60</sup>Co rods sealed within two layers of stainless steel, the rods are combined with inert dummy rods to form a rack with a total activity of about 12.6PBq (340kCi).
 
=====Research equipment=====
While it is possible to do some types of research using an irradiator much like that used for gamma sterilization, it is common in some areas of science to use a ''time resolved'' experiment where a material is subjected to a pulse of radiation (normally [[electron]]s from a [[LINAC]]. After the pulse of radiation, the concentration of different substances within the material are measured by [[emission spectroscopy]] or [[Absorption spectroscopy]], hence the rates of reactions can be determined. This allows the relative abilities of substances to react with the reactive species generated by the action of radiation on the solvent (commonly water) to be measured. This experiment is known as [[pulse radiolysis]][http://www.dur.ac.uk/oem.group/Research/radiolysis/Radiolysispage.htm] which is closely related to [[Flash photolysis]].
 
[[Image:Pulseradioysisequipment.jpg|left|thumb|450px|A diagram explaining the pulse radiolysis experiment, the sample is irradiated by a pulse of high energy electrons from the LINAC. The absorption of light is measured at different times after the pulse, and the results are often presented as a graph of absorption against time.]]
 
In the latter experiment the sample is excited by a pulse of light to examine the decay of the excited states by [[spectroscopy] [[http://www.chem.uic.edu/chem343/Flash-Photolysis.pdf]]; sometimes the formation of new compounds can be investigated.<ref>George Porter, Nobel lecture, 11 December 1967</ref>[http://nobelprize.org/nobel_prizes/chemistry/laureates/1967/porter-lecture.pdf] Flash photolysis experiments have led to a better understanding of the effects of [[halogen]]-containing compounds upon the [[ozone layer]].[http://www.bfrl.nist.gov/866/HOTWC/HOTWC2006/pubs/R0000232.pdf]


===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]] 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]].<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=====
* 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, and 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 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. 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.
 
* 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]]


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.


==== 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.


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.
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.  


In this way, aqueous solutions of the following isotopes can be made from parent isotopes (shown in brackets)
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.
 
 
*<sup>68</sup>Ga (<sup>68</sup>Ge)
*<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)
 
 
 
 
 
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)
 
*<sup>81m</sup>Kr (<sup>81</sup>Rb)
*<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]].
 
*<sup>241</sup>Am (<sup>241</sup>Pu)
 
=====Uses=====
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 make 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 a high enough density of cesium in any other compound.
*'''Sealed sources''' are used for radiotherapy treatment of many [[cancer]]s as well as for [[food irradiation]], [[industrial radiography]], [[nuclear gauges]] and many other applications. In medical radiotherapy, tumors can be treated either by focusing a beam of gamma rays on the area of the body that contains the tumor ([[teletherapy]]),, or by surgically placing a smaller radioactive source within or close to the tumor ([[brachytherapy]]). The aim is to confine the  radiation, as far as possible, to the tumor and to spare healthy tissues in other parts of the body from its effects.


<gallery>
<gallery>
Image:Diagramofpersonwithcancer.jpg|'''1''' A diagram showing a person with a tumor (in blue)
Image:Alphapu.jpg|Alpha plutonium (note that this is not a view of a unit cell)
Image:Diagramofpersonwithcancertele.jpg|'''2''' In teletherapy, gamma rays (yellow) are directed at the area of the body that contains the tumor.
Image:Betapu.jpg|Beta plutonium (note that this is not a view of a cell)
Image:Diagramofpersonwithcancerbracy.jpg|'''3''' In brachytherapy, the tumor is treated by gamma rays from a small source close to the tumor</gallery>
Image:Deltapu2.jpg|A unit cell of delta plutonium
 
Image:Deltaprimepu2.jpg|A unit cell of delta prime plutonium
*'''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]]. Because the iodine accumulates in the thyroid gland, the tissue of the thyroid gland (and the tummor) suffers a much higher dose of radiation than most of the body. As a result, the radioactive iodine can 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. <ref>Volkert WA, Hoffman TJ (1999) Therapeutic radiopharmaceuticals ''Chem Rev''
Image:gammapu.jpg|Gamma plutonium (note that this is not a view of a unit cell)
'''99''':2269-92 PMID 11749482</ref>
Image:Epipu.jpg|A unit cell of epsilon plutonium
 
Because cancer cells are more susceptible to being killed by radiation than normal, healthy cells, radiotherapy treatment can be very effective in reducing the bulk of tumors. Radiotherapy is usually accompanied by some form of [[chemotherapy]] designed to attack any remaining tumor cells.
 
<gallery>
Image:DiagramofpersonwithcancerfirststageofI131.jpg|'''4''' Treating a tumor with an open source. The patient is given a radioactive drug (orange) which spreads throughout the body
Image:DiagramofpersonwithcancersecondstageofI131.jpg|'''5''' In time, the radioactivity becomes concentrated in the part of the body that contains the tumor
</gallery>
</gallery>


Some radiopharmaceuticals are used for medical imaging, including many different [[technetium]] complexes <ref>Jurisson SS, Lydon JD (1999) Potential technetium small molecule radiopharmaceuticals ''Chem Rev'' '''99''':2205-18 PMID 11749479</ref>, 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]]. 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>
==== Solid state structures of actinide dioxides ====
Many of the actinide dioxides are similar to uranium dioxide, the structure of this is shown below.


=== The nuclear fuel cycle ===
{{Image|UO2lattice.jpg|right|250px|The solid state structure of uranium dioxide, the oxygen atoms are in red and the uranium atoms in green}}
[[Image:Nuclear Fuel Cycle.jpg|left|thumb|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).]]
 
The chemistry associated with any part of the [[nuclear fuel cycle]], including [[nuclear reprocessing]]. 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]].


==== Normal and abnormal conditions ====
==== 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.


The nuclear chemistry associated with the nuclear fuel cycle can be divided into two main areas, one area is concerned with operation under the intended conditions while the other area is concerned with maloperation conditions where some alteration from the normal operating conditions has occured or (''more rarely'') an accident is occuring.
====Reprocessing====
 
The releases of radioactivity from normal operations are the small planned releases from uranium ore processing, enrichment, power reactors, reporcessing plants and waste stores. These can be in a different chemical/physical form to the releases which could occur under accident conditions. In addition the isotope signature of a hypothetical accident may be very different to that of a planned normal operational discharge of radioactivity to the environment.
 
It is important to note that just becuase a radioisotope is released it does not mean it will enter a human and then cause harm. For instance the migration of radioactivity can altered by the binding of the radioisotope to the surfaces of soil particles. For example cesium binds tightly to clay minerals such as [[illite]] and [[montmorillonite]] hence it remains in the upper layers of soil where it can be accessed by plants with shallow roots (such as grass). Hence grass and mushrooms can carry a considerable amount of <sup>137</sup>Cs which can be transferred to humans through the food chain. But <sup>137</sup>Cs is not able to migrate quickly through most soils and thus is unlikely to contaminate [[well]] water. It is important to note that colloids of soil minterals can migrate through soil so simple binding of a metal to the surfaces of soil particles does not fix the metal totally.
 
According to Jiří Hála's [[text book]] the distribution coefficient K<sub>d</sub> is the ratio of the soil's radioactivity (Bq g<sup>-1</sup>) to that of the soil water (Bq ml<sup>-1</sup>). If the radioactivity is tightly bonded to by the minerals in the soil then less radioactivity can be absorbed by crops and [[grass]] growing on the soil.
 
* [[Cs-137]] K<sub>d</sub> = 1000
* [[plutonium|Pu-239]] K<sub>d</sub> = 10000 to 100000
* [[strontium|Sr-90]] K<sub>d</sub> = 80 to 150
* [[Iodine|I-131]] K<sub>d</sub> = 0.007 to 50
 
One of the best countermeasures in dairy farming against <sup>137</sup>Cs is to mix up the soil by deeply ploughing the soil. This has the effect of putting the <sup>137</sup>Cs out of reach of the shallow roots of the grass, hence the level of radioactivity in the grass will be lowered. Also after a nuclear war or serious accident the removal of top few cm of soil and its burial in a shallow trench will reduce the long term gamma dose to humans due to <sup>137</sup>Cs as the gamma photons will be attenuated by their passage through the soil.
 
Even after the radioactive element arrives at the roots of the plant, the metal may be rejected by the biochemistry of the plant. The details of the uptake of <sup>90</sup>Sr and <sup>137</sup>Cs into [[sunflower]]s grown under [[hydroponic]] conditions has been reported.<ref>P. Soudek, Š. Valenová, Z. Vavříková and T. Vaněk, ''Journal of Environmental Radioactivity'', 2006, '''88''', 236-250</ref> The cesium was found in the leaf veins, in the stem and in the [[apical]] leaves. It was found that 12% of the cesium entered the plant, and 20% of the strontium. This paper also reports details of the effect of [[potassium]], [[ammonium]] and [[calcium]] ions on the uptake of the radioisotopes.
 
In [[livestock]] farming an important countermeasure against <sup>137</sup>Cs is to feed to animals a little [[prussian blue]]. This [[iron]] [[potassium]] [[cyanide]] compound acts as a [[ion-exchanger]]. The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of prussian blue per day. The prussian blue reduces the [[biological half life]] (different from the [[half-life|nuclear half life]]) of the cesium. The physical or nuclear half life of <sup>137</sup>Cs is about 30 years.  This is a constant which can not be changed but the biological half life is not a constant.  It will change according to the nature and habits of the organism for which it is expressed. [[Cesium]] in humans normally has a biological half life of between one and four months. An added advantage of the prussian blue is that the cesium which is stripped from the animal in the [[feces|droppings]] is in a form which is not available to plants. Hence it prevents the cesium from being recycled. The form of prussian blue required for the treatment of humans or animals is a special grade.  Attempts to use the [[pigment]] grade used in [[paint]]s have not been successful. Note that a good source of data on the subject of [[cesium]] in [[chernobyl]] fallout exists at [http://www.uiar.org.ua/Eng/index.htm], this is the ''Ukrainian Research Institute for Agricultural Radiology''.
 
 
===== Release of radioactivity from fuel during normal use and accidents=====
 
The IAEA assume that under normal operation the coolant of a water cooled reactor will contain some radioactivity<ref>page 169 Generic Assessment Procedures for Determining Protective Actions During a Reactor Accident, IAEA-TECDOC-955, 1997</ref> but during a reactor accident the coolant radioactivity level may rise. The IAEA state that under a series of different conditions different amounts of the core inventory can be released from the fuel, the four conditions the IAEA consider are ''normal operation'', a spike in coolant activity due to a sudden shutdown/loss of preasure (core remains covered with water), a cladding failure resulting in the release of the activity in the fuel/cladding gap (this could be due to the fuel being uncovered by the loss of water for 15-30 minutes where the cladding reached a temperture of 650-1250 <sup>o</sup>C) or a melting of the core (the fuel will have to be uncovered for at least 30 minutes, and the cladding would reach a temperture in excess of 1650 <sup>o</sup>C).<ref>page 173 Generic Assessment Procedures for Determining Protective Actions During a Reactor Accident, IAEA-TECDOC-955, 1997</ref>
 
Based upon the assumption that a PWR contains 300 tons of [[water]], and that the activity of the fuel of a 1 GWe reactor is as the IAEA predict<ref>page 171 Generic Assessment Procedures for Determining Protective Actions During a Reactor Accident, IAEA-TECDOC-955, 1997</ref>, then the coolant activity after an accident such as the [[three mile island]] accident where a core is uncovered and then recovered with water then the resulting activity of the coolant can be predicted.
 
===== Releases from reprocessing under normal conditions =====
 
It is normal to allow used fuel to stand after the irradation to allow the shortlived and radiotoxic [[iodine]] isotopes to decay away, in one experiment in the USA fresh fuel which had not been allowed to decay was reporcessed (the [[Green run]][http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=7296321][http://www10.antenna.nl/wise/index.html?http://www10.antenna.nl/wise/381/3733.html][http://archive.tri-cityherald.com/thyroid/history.html]) to investigate the effects of a large iodine release from the reprocessing of short cooled fuel. It is normal in reprocessing plants to scrub the off gases from the dissolver to prevent the emission of iodine. In addition to the emission of iodine the [[noble gas]]es and [[tritium]] are released from the fuel when it is dissolved, it has been proposed that by voloxidation (heating the fuel in a furnace under oxidizing conditions) the majority of the tritium can be recovered from the fuel.[http://www.ornl.gov/~webworks/cppr/y2001/pres/123514.pdf]
 
A paper was been written on the radioactivity found in [[oyster]]s found in the [[Irish Sea]],<ref>A. Preston, J.W.R. Dutton and B.R. Harvey, ''Nature'', 1968, '''218''', 689-690.</ref> these were found by gamma spectrscopy to contain <sup>141</sup>Ce, <sup>144</sup>Ce, <sup>103</sup>Ru, <sup>106</sup>Ru, <sup>137</sup>Cs, <sup>95</sup>Zr and <sup>95</sup>Nb. In addition a zinc activation product (<sup>65</sup>Zn) was found, this is thought to be due to the corrosion of [[magnox]] fuel cladding in [[cooling pond]]s. It is likely that the modern releases of all these isotopes from Windscale is smaller.
 
==== The study of used fuel ====
Used nuclear fuel is studied in [[PIE (nuclear fuel)|post irradiation 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 <sup>o</sup>C. <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>).
 
[[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]]
 
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. 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.
 
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 tended 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>
 
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>.
 
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  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>
 
==== Fuel cladding interactions ====
The study of the nuclear fuel cycle includes 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 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.
 
[[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.]]


====Reprocessing====
=====Law=====
=====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 reporcessing was started in March [[1977]] for [[nuclear proliferation|nuclear weapons proliferation]] reasons. The President [[Jimmy Carter]] issued a [[Presidential directive]] which indefinitely suspended the commercial reprocessing and recycling of plutonium in the USA. This Presidential directive is likely to have been 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 goverment 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]]).
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=====
=====PUREX chemistry=====
The 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]]. This extraction is of the [[nitrate]] salts and is classed as being of a [[solvation]] mechanism. For example the extraction of plutonium by a extraction agent (S) in a nitrate medium occurs by the following reaction.
{{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]].
Pu<sup>4+</sup><sub>aq</sub> + 4NO<sub>3</sub><sup>-</sup><sub>aq</sub> + 2S<sub>organic</sub> --> [Pu(NO<sub>3</sub>)<sub>4</sub>S<sub>2</sub>]<sub>organic</sub>
 
A complex is formed between the metal cation, the nitrates and the tributyl phosphate, and a model compound of a dioxouranium(VI) complex with two nitrates and two triethyl phosphates has been characterised by X-ray crystalography.<ref>J.H. Burns,  "Solvent-extraction complexes of the uranyl ion. 2. Crystal and molecular structures of catena-bis(.mu.-di-n-butyl phosphato-O,O')dioxouranium(VI) and bis(.mu.-di-n-butyl phosphato-O,O')bis[(nitrato)(tri-n-butylphosphine oxide)dioxouranium(VI)]", ''Inorganic Chemistry'', 1983, '''22''', 1174-1178</ref>


When the nitric acid concentration is high the extraction into the organic phase is favoured, and when the nitric acid concentration is low the extraction is reversed (the organic phase is ''stripped'' of the metal). It is normal to dissolve the used fuel in nitric acid, after the removal of the insoluble matter the uranium and plutonium are extracted from the highly active liquor. It is normal to then back extract the loaded organic phase to create a ''medium active'' liquor which contains mostly uranium and plutonium with only small traces of fission products. This medium active aqueous mixture is then extracted again by tributyl phosphate/hydrocarbon to form a new organic phase, the metal bearing organic phase is then stripped of the metals to form an aqueous mixture of only uranium and plutonium. The two stages of extraction are used to improve the purity of the [[actinide]] product, the organic phase used for the first extraction will suffer a far greater dose of radiation. The radiation can degrade the tributyl phosphate into dibutyl hydrogen phosphate. The dibutyl hydrogen phosphate can act as an extraction agent for both the actinides and other metals such as [[ruthenium]]. The dibutyl hydrogen phosphate can make the system behave in a more complex manner as it tends to extract metals by an [[ion exchange]] mechanism (extraction favoured by low acid concentration), to reduce the effect of the dibutyl hydrogen phosphate it is common for the used organic phase to be washed with [[sodium carbonate]] solution to remove the acidic degradation products of the tributyl phosphate.
=====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)=====
=====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]] metal 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]] liquid (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]
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]
 
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 disadvantge 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 resonable 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]


The '''Butex, β,β'-dibutyoxydiethyl ether''' process is based on a solvation extraction process using the triether extractant named above. This process has the disadvantge 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 '''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]


[[Image:Butoxpicture.jpg|center|thumb|450px|The molecular strucutre of butex]]
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.


=====New methods being considered for future use=====
{{Image|Butoxpicture.jpg|center|450px|The molecular structure of butex}}


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]].
=====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.  


The UREX process is a PUREX process which has been modified to prevent the plutonium 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 (AHA) to the extraction and scrub sections of the process. The addition of AHA 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''' ('''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.


Adding a second extraction agent, octyl(phenyl)-N, N-dibutyl carbamoylmethyl phosphine oxide(CMPO) in combination with tributylphosphate, (TBP), the PUREX process can be turned into the '''TRUEX''' ('''TR'''ans'''U'''ranic '''EX'''traction) process this is a process which was invented in the USA by Argonne National Laboratory, and is designed to remove the transuranic metals (Am/Cm) from waste. The idea is that by lowering the alpha activity of the waste, the majority of the waste can then be disposed of with greater ease. In common with PUREX this process operates by a solvation mechanism.
{{Image|CMPOpicture.jpg|center|450px|The molecular structure of a typical CMPO}}


[[Image:CMPOpicture.jpg|center|thumb|450px|The molecular strucutre of a typical CMPO]]
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]


As an alternative to TRUEX, an extraction process using a malondiamide has been devised. The DIAMEX ('''DIAM'''ide'''EX'''traction) process has the advantage of avoiding the formation of organic waste which contains elements other than [[Carbon]], [[Hydrogen]], [[Nitrogen]], and [[Oxygen]]. Such an organic waste can be burned without the formation of 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. In common with PUREX this process operates by 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]
'''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.


'''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.
{{Image|BTPpicture.jpg|center|450px|The molecular structure of a BTP}}
 
[[Image:BTPpicture.jpg|center|thumb|450px|The molecular strucutre of a BTP]]


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


This is the '''''UN'''iversal'' '''EX'''traction process which was developed in [[Russia]] and the [[Czech Republic]], it is a process designed to remove all of the most troublesome (Sr, Cs and [[minor actinides]]) [[radioisotopes]] from the raffinates left after the extraction of 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 [[cesium]] and [[strontium]] with poly [[ethylene oxide]] (poly [[ethylene 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''-nitrobenzotri[[fluoride]] and phenyl trifluoromethyl [[sulfone]] [http://www.wmsym.org/Abstracts/2001/62/62-7.pdf]have been suggested as well.
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.


====Absorption of fission products on surfaces====
====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 (eg [[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]
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]


[[Image:TcO2layeronsteelsurface.jpg|center|thumb|450px|Formation of a TcO<sub>2</sub> layer on a steel surface.]]
{{Image|TcO2layeronsteelsurface.jpg|center|450px|Formation of a TcO<sub>2</sub> layer on a steel surface.}}


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]
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
 
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
* 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>
* 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>
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==== Kinetics (use within mechanistic 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 hydrogens ([[protons]]) by deuteriumwithin a [[chemical compound]] 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.
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 ====
==== 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).
''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 =====
===== 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.
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 a [[green plant]] uses 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 and not in the glucose formed in the [[chloroplasts]] within the plant cells.


For biochemical and physiological experiments and medical methods, a number of specific isotopes have important applications.
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, significant an excess of them in the organ or organisms might still interfere with its functioning, and the availability of sufficient amounts for whole-animal studies is limited for many isotopes. Measurement is also difficult, and ususally 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.   
*'''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.  
*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.  
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*<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.  
*<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.  


*<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.
*<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.


*<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.
*<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.


*<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 [[flourine]] (<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 specfic activity of the final product.
*<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.


=== Nuclear magnetic resonance (NMR) ===
=== Nuclear magnetic resonance (NMR) ===
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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.
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 ==
==References==
<references/>
{{reflist}}[[Category:Suggestion Bot Tag]]
 
==Text books==
;''Radiochemistry and Nuclear Chemistry'' :
Comprehensive textbook by Choppin, Liljenenzin and Rydberg. ISBN -0750674636, Butterworth-Heinemann, 2001 [http://www.abcte.org/exam_preparation/chemistry/nuclear_chemistry_3].
 
;''Radioactivity, Ionizing radiation and Nuclear Energy'' :
Basic textbook for undergraduates by Jiri Hála and James D Navratil. ISBN -807302053-X, Konvoj, Brno  2003 [http://www.litlit.com/Radioactivity.htm]
 
;''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)
 
{{Nuclear Technology}}
[[Category:Nuclear chemistry| ]]
[[Category:Chemistry Workgroup (Top)]]
[[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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