Nuclear transmutation 194030 226136113 2008-07-16T23:52:33Z 71.199.16.166 /* Reasoning behind transmutation */ '''Nuclear transmutation''' is the conversion of one [[chemical element]] or [[isotope]] into another, which occurs through [[nuclear reaction]]s. Natural transmutation occurs when [[radioactive]] [[chemical elements|elements]] spontaneously decay over a long period of time and transform into other more stable elements. Artificial transmutation occurs in machinery that has enough energy to cause changes in the nuclear structure of the elements. Machines that can cause artificial transmutation include [[particle accelerator]]s and [[tokamak]] reactors as well as conventional fission power reactors. Nuclear transmutation is considered as a possible mechanism for reducing the volume and hazard of [[radioactive waste]]. ==History== The term ''transmutation'' dates back to the search for the [[philosopher's stone]]. In [[alchemy]], it was believed that the transformation of base metals into gold could be accomplished in table-top experiments. The alchemical belief in transmutation was based on a thoroughly wrong understanding of the underlying processes. The realisation that such simple transformations would not be possible began when [[Antoine Lavoisier|Lavoisier]] first identified the chemical elements and [[John Dalton|Dalton]] restored the Greek notion of [[atoms]] to explain chemical processes. The disintegration of atoms is a distinct process involving much greater energies than could be achieved by alchemists. It was first consciously applied to modern physics by [[Frederick Soddy]] when he, along with [[Ernest Rutherford]], discovered that radioactive [[thorium]] was converting itself into [[radium]] in [[1901]]. At the moment of realization, Soddy later recalled, he shouted out: "Rutherford, this is transmutation!" Rutherford snapped back, "For Christ's sake, Soddy, don't call it ''transmutation''. They'll have our heads off as alchemists."{{Fact|date=January 2008}} Later in the twentieth century the transmutation of elements within stars was elaborated, accounting for the relative abundance of elements in the universe. In their 1957 paper ''Synthesis of the Elements in Stars'',<ref>William Alfred Fowler, Margaret Burbidge, Geoffrey Burbidge, and Fred Hoyle, 'Synthesis of the Elements in Stars', ''Reviews of Modern Physics'', vol. 29, Issue 4, pp. 547–650</ref> [[William Alfred Fowler]], [[Margaret Burbidge]], [[Geoffrey Burbidge]], and [[Fred Hoyle]] explained how the abundances of essentially all but the lightest chemical elements could be explained by the process of [[nucleosynthesis]] in stars. Author [[Ken Croswell]] summarised their discoveries thus: {{Quote|Burbidge, Burbidge, Fowler, Hoyle<br/> Took the stars and made them toil:<br/> Carbon, copper, gold, and lead<br/> Formed in stars, is what they said<ref>Ken Croswell, ''[[The Alchemy of the Heavens]]''</ref> }} Ironically, it transpired that, under true nuclear transmutation, it is far easier to turn gold into lead than the reverse reaction, which was the one the alchemists had ardently pursued. Nuclear experiments have successfully transmuted lead into gold, but the expense far exceeds any gain.<ref>Anne Marie Helmenstine, [http://chemistry.about.com/cs/generalchemistry/a/aa050601a.htm Turning Lead into Gold: Is Alchemy Real?], About.com:Chemistry, retrieved January 2008</ref> It would be easier to convert gold into lead via [[neutron capture]] and [[beta decay]] by leaving gold in a nuclear reactor for a long period of time. <sup>197</sup>{{gold}} + [[neutron capture|n]] → <sup>198</sup>Au ([[halflife]] 2.7 days) → <sup>198</sup>{{mercury}} + n → <sup>199</sup>Hg + n → <sup>200</sup>Hg + n → <sup>201</sup>Hg + n → <sup>202</sup>Hg + n → <sup>203</sup>Hg (halflife 47 days) → <sup>203</sup>{{thallium}} + n → <sup>204</sup>Tl (halflife 3.8 years) → <sup>204</sup>{{lead}} (halflife 1.4x10<sup>17</sup> years) == Transmutation of nuclear wastes == ===Overview=== Transmutation of [[transuranium elements]] ([[actinides]]) such as the [[isotope]]s of [[plutonium]], [[neptunium]], [[americium]], and [[curium]] has the potential to help solve the problems posed by the management of [[radioactive waste]], by reducing the proportion of long-lived isotopes it contains. When irradiated with [[fast neutrons]] in a [[nuclear reactor]], these isotopes can be made to undergo [[nuclear fission]], destroying the original [[actinide]] isotope and producing a spectrum of radioactive and nonradioactive [[fission products]]. ===Reactor types=== For instance, plutonium can be reprocessed into [[MOX]] fuels and transmuted in standard reactors. The heavier elements could be transmuted in [[fast reactor]]s, but probably more effectively in a [[subcritical reactor]][http://einstein.unh.edu/FWHersman/energy_amplifier.html] which is sometimes known as an [[energy amplifier]] and which was devised by [[Carlo Rubbia]]. [[Nuclear fusion|Fusion]] [[neutron source]]s have also been proposed as well suited.<ref>Rita Plukiene, ''[http://www-dapnia.cea.fr/Phocea/file.php?class=std&file=Doc/Publications/Archives/dapnia-03-12-T.pdf Evolution Of Transuranium Isotopic Composition In Power Reactors And Innovative Nuclear Systems For Transmutation]'', PhD Thesis, Vytautas Magnus University, 2003, retrieved January 2008</ref><ref>Takibayev A., Saito M., Artisyuk V., and Sagara H., '[http://cat.inist.fr/?aModele=afficheN&cpsidt=17035603 Fusion-driven transmutation of selected long-lived fission products]', ''Progress in nuclear energy'', Vol. 47, 2005, retrieved January 2008.</ref> ===Reasoning behind transmutation=== Isotopes of plutonium and other actinides tend to be long-lived with [[half-life|half-lives]] of many thousands of years, whereas radioactive fission products tend to be shorter-lived (most with half-lives of 30 years or less). From a waste management viewpoint, transmutation of actinides eliminates a very long-term radioactive hazard and replaces it with a much shorter-term one. It is important to understand that the threat posed by a radioisotope is influenced by many factors including the [[chemical]] and [[biology|biological]] properties of the element. For instance [[caesium]] has a relatively short [[biological halflife]] (1 to 4 months) while [[strontium]] and [[radium]] both have very long biological half-lives. As a result [[strontium-90]] and radium are much more able to cause harm than [[caesium-137]] when a given activity is ingested. Many of the actinides are very radiotoxic because they have long biological half-lives and are [[alpha particle|alpha]] emitters. In transmutation the intention is to convert the actinides into [[fission products]]. The fission products are very radioactive, but the majority of the activity will decay away within a short time. The most worrying shortlived fission products are those that accumulate in the body, such as [[iodine]]-131 which accumulates in the thyroid gland, but it is hoped that by good design of the [[nuclear fuel]] and transmutation plant that such fission products can be isolated from humans and their environment and allowed to decay. In the medium term the fission products of highest concern are strontium-90 and caesium-137; both have a half life of about 30 years. The caesium-137 is responsible for the majority of the external [[gamma radiation|gamma]] dose experienced by workers in [[nuclear reprocessing]] plants and at this time (2005) to workers at the [[Chernobyl]] site. When these medium-lived isotopes have decayed the remaining isotopes will pose a much smaller threat. ===Long-lived fission products=== {{Medium-lived fission products}} {{Long-lived fission products}} Some radioactive fission products can be converted into shorter-lived radioisotopes by transmutation. Transmutation of all fission products with halflife greater than one year is studied in [http://www.patentstorm.us/patents/4721596-description.html], with varying results. [[Sr-90]] and [[Cs-137]], with halflives of about 30 years, are the largest radiation emitters in used nuclear fuel on a scale of decades to a few hundreds of years, and are not easily transmuted because they have low [[neutron absorption]] [[cross section]]s. Instead, they should simply be stored until they decay. Given that this length of storage is necessary, the fission products with shorter halflives can also be stored until they decay. The next longer-lived fission product is [[Sm-151]], which has a halflife of 90 years, and is such a good neutron absorber that most of it is transmuted while the nuclear fuel is still being used; however effectively transmuting the remaining Sm-151 in nuclear waste would require separation from other isotopes of [[samarium]]. Given the smaller quantities and its low-energy radioactivity, Sm-151 is less dangerous than Sr-90 and Cs-137 and can also be left to decay. Finally, there are 7 [[long-lived fission product]]s. They have much longer halflives in the range 211,000 years to 16 million years. Two of them, [[Tc-99]] and [[Iodine-129|I-129]], are mobile enough in the environment to be potential dangers, are free or mostly free of mixture with stable isotopes of the same element, and have neutron cross sections that are small but adequate to support transmutation. Also, Tc-99 can substitute for [[U-238]] in supplying [[Doppler broadening]] for negative feedback for reactor stability. <ref>http://www.osti.gov/bridge/servlets/purl/10180577-PCAEyE/10180577.PDF Transmutation of Selected Fission Products in a Fast Reactor </ref> Most studies of proposed transmutation schemes have assumed transuranics, [[technetium|<sup>99</sup>Tc]], and [[Iodine-129|<sup>129</sup>I]] as the targets for transmutation, with other fission products, [[activation products]], and possibly [[reprocessed uranium]] remaining as waste. [http://www.ieer.org/reports/transm/report.pdf] Of the remaining 5 long-lived fission products, [[Se-79]], [[Sn-126]] and [[Pd-107]] are produced only in small quantities (at least in today's [[thermal neutron]], [[U-235]]-burning [[light water reactors]]) and the last two should be relatively inert. The other two, [[Zr-93]] and [[Cs-135]], are produced in larger quantities, but also not highly mobile in the environment. They are also mixed with larger quantities of other isotopes of the same element. ==References== <references/> [[Category:Nuclear chemistry]] [[Category:Radioactivity]] [[de:Transmutation]] [[el:Μεταστοιχείωση]] [[es:Transmutación]] [[fr:Transmutation]] [[id:Transmutasi]] [[it:Trasmutazione]] [[la:Fabricatio auri]] [[hu:Transzmutáció]] [[ml:ന്യൂക്ലിയര്‍ ട്രാന്‍സ്‌മ്യൂട്ടേഷന്‍]] [[nl:Transmutatie]] [[no:Transmutasjon]] [[pl:Transmutacja]] [[pt:Transmutação]] [[ru:Трансмутация]] [[sv:Transmutation]] [[uk:Трансмутація]]