Nuclear chemistry: Difference between revisions

From Citizendium
Jump to navigation Jump to search
imported>Mark Rust
imported>Hillary Hildegard IlI
No edit summary
Line 1: Line 1:
'''Nuclear chemistry''' is a subfield of [[chemistry]] dealing with [[radioactivity]], nuclear processes and nuclear properties. It includes:


* the chemistry of [[radioactive]] elements such as the [[actinides]], [[radium]] and [[radon]] together with the chemistry associated with equipment (such as [[nuclear reactor]]s) which are designed to perform nuclear processes. [[Nuclear reactors]] can be distinghuished in two categories, the [[high flux]] reactor, primarily used for the creation of radio-active isotopes for [[medicinal]] or [[scientific]] use, and the [[low flux]] reactor, primarily used for power generation. [[Flux]] in this content meaning 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 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 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]].
==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.
[[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.
During the inital attempts to make the ''transuranium'' elements natural uranium was bombarded with [[neutrons]], the idea was that by the creation of a neutron rich uranium isotope that the next element would be formed by beta decay. Instead in these early studys the [[fissile]] <sup>235</sup>U underwent fission to generate the highly radioactive [[fission products]]. Due to their high activity these fission products (such as some of the shortlived [[barium]] isotopes) dominated the radiochemical anaylsis of the irradated uranium. At first it was thought that the uranium had been converted into [[radium]] (many of the early radiochemical methods have difficulty in distingishing between baroum and radium). But with time it was understood that the majority of the radioactivity was due to the products of breaking uranium nuclei into two fragements.<ref>Lise Meitner and Otto Robert Frisch, "Disintegration of Uranium by Neutrons: a New Type of Nuclear Reaction", ''Nature'', 1939, '''143''', 239-240 (doi = 10.1038/224466a0) [http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Meitner-Fission-1939.html]</ref>
[[Edwin McMillan]] attempted to measure the range of the fission products using cigarette paper, during this work he isolated a beta active isotope with a half life of 2.3 days (<sup>239</sup>Np). A short time later in 1940 plutinium was discovered
==Main areas==
===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'').
For further details please see the page on [[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 [[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]].
=== The nuclear fuel cycle ===
[[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 ====
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====
=====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]]).
=====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.
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 [[PWR]] could be used in place of naturial uranium in a ''heavy water'' moderated CANDU. The term DUPIC means '''D'''irect '''U'''se of spent '''P'''reasureised 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 duiscussion of the DUPIC idea.<ref>W.I. Ko and H.D. Kim, ''Journal of Nuclear Science and Technology'', 2001, '''38'''(9), 757 [http://wwwsoc.nii.ac.jp/aesj/publication/JNST2001/No.9/38_757-765.pdf]</ref.
=====Old methods (no longer used)=====
The '''bismuth phosphate''' process is a very old process which adds lots of material to the final highly active [[waste]], and which was replaced by solvent extraction processes. The process was designed to extract [[plutonium]] from [[aluminium]]-clad [[uranium]] 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 '''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.
[[Image:Butoxpicture.jpg|center|thumb|450px|The molecular strucutre of butex]]
=====New 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 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, (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|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 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.
[[Image:BTPpicture.jpg|center|thumb|450px|The molecular strucutre of a BTP]]
'''References:'''
*[http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-26.pdf SANEX-BTP Process Studies]
*[http://www.nea.fr/html/pt/docs/iem/jeju02/session2/Session%20II-19.pdf SANEX-BTP Process Development]
*[http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-24.pdf Modelling and achievement of a SANEX process]
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.
====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]
[[Image:TcO2layeronsteelsurface.jpg|center|thumb|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]
Similarly, the release of '''iodine-131''' in a serious power reactor accident could be retarded by absorption on [[metal]] surfaces within the nuclear plant. <ref>Glänneskog H (2004) Interactions of [[Iodine|I]]<sub>2</sub> and [[Methyl iodide|CH]]<sub>3</sub>I with reactive metals under BWR severe-accident conditions ''Nuclear Engineering and Design'' '''227''':323-9
* Glänneskog H (2005) Iodine chemistry under severe accident conditions in a nuclear power reactor, PhD thesis, Chalmers University of Technology, Sweden
* For other work on the iodine chemistry which would occur during a bad accident, see[http://www.sbf.admin.ch/htm/services/publikationen/international/frp/eu-abstracts/html/fp/fp5/5eu99.0423.html][http://www.nea.fr/html/nsd/docs/2000/csni-r2000-12.pdf][http://www.ing.unipi.it/~dimnp/CD/supporto/pdf/paci03.pdf]</ref>
==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 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.
==== 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).
===== 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 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.
*'''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. 
*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 <sup>11</sup>C, very rapid synthetic methods have been developed to permit the rapid addition of the radioactive isotope to the molecule. For instance a [[palladium]] catalysed [[carbonylation]] reaction in a [[microfluidic]] device has been used to rapidly form amides<ref>Miller PW ''et al'' (2006) ''Chemical Communications'' 546-548</ref> and it might be possible to use this method to form radioactive imaging agents for [[PET]] imaging.[http://www.rsc.org/Publishing/Journals/CC/article.asp?d.oi=b515410b]
*<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>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.
=== Nuclear magnetic resonance (NMR) ===
[[Nuclear magnetic resonance |NMR spectroscopy]] uses the net spin of nuclei in a substances upon energy absorption to identify molecules. This has now become a standard spectroscopic tool within [[synthetic chemistry]]. One major use of NMR is to determine the [[chemical bond|bond]] connectivity within an organic molecule.
NMR imaging also uses the net spin of nuclei (commonly protons) for imaging. This is widely used 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/>
==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]]

Revision as of 03:48, 7 February 2007

Retrieved from "https://citizendium.org/wiki/index.php?title=Nuclear_chemistry&oldid=80826"