Editing Americium (section)

==History==
[[File:Berkeley 60-inch cyclotron.jpg|thumb|left|The 60-inch cyclotron at the Lawrence Radiation Laboratory, [[University of California, Berkeley]], in August 1939]]

Although americium was likely produced in previous nuclear experiments, it was [[discoveries of the chemical elements|first intentionally synthesized]], isolated and identified in late autumn 1944, at the [[University of California, Berkeley]], by [[Glenn T. Seaborg]], Leon O. Morgan, [[Ralph A. James]], and [[Albert Ghiorso]]. They used a 60-inch [[cyclotron]] at the University of California, Berkeley.<ref>[http://www.utexas.edu/faculty/council/2002-2003/memorials/Morgan/morgan.html Obituary of Dr. Leon Owen (Tom) Morgan (1919–2002)], Retrieved 28 November 2010</ref> The element was chemically identified at the Metallurgical Laboratory (now [[Argonne National Laboratory]]) of the [[University of Chicago]]. Following the lighter [[neptunium]], [[plutonium]], and heavier [[curium]], americium was the fourth [[transuranium element]] to be discovered. At the time, the [[periodic table]] had been restructured by Seaborg to its present layout, containing the actinide row below the [[lanthanide]] one. This led to americium being located right below its twin lanthanide element europium; it was thus by analogy named after the [[Americas]]: "The name americium (after the Americas) and the symbol Am are suggested for the element on the basis of its position as the sixth member of the actinide rare-earth series, analogous to europium, Eu, of the lanthanide series."<ref>Seaborg, G. T.; James, R.A. and Morgan, L. O.: "The New Element Americium (Atomic Number 95)", THIN PPR ''(National Nuclear Energy Series, Plutonium Project Record)'', ''Vol 14 B The Transuranium Elements: Research Papers'', Paper No. 22.1, McGraw-Hill Book Co., Inc., New York, 1949. [http://www.osti.gov/cgi-bin/rd_accomplishments/display_biblio.cgi?id=ACC0046&numPages=43&fp=N Abstract]; [http://www.osti.gov/accomplishments/documents/fullText/ACC0046.pdf Full text] (January 1948), Retrieved 28 November 2010</ref><ref>{{cite journal|last1=Street|first1=K.|last2=Ghiorso|first2=A.|last3=Seaborg|first3=G.|title=The Isotopes of Americium|doi=10.1103/PhysRev.79.530|date=1950|page=530|volume=79|journal=Physical Review|url=http://repositories.cdlib.org/cgi/viewcontent.cgi?article=7073&context=lbnl|issue=3|bibcode = 1950PhRv...79..530S |url-access=subscription}}</ref><ref name="g1252">Greenwood, p. 1252</ref>

The new element was isolated from its [[oxide]]s in a complex, multi-step process. First [[plutonium]]-239 nitrate (<sup>239</sup>PuNO<sub>3</sub>) solution was coated on a [[platinum]] foil of about 0.5&nbsp;cm<sup>2</sup> area, the solution was evaporated and the residue was converted into plutonium dioxide (PuO<sub>2</sub>) by [[calcining]]. After cyclotron irradiation, the coating was dissolved with [[nitric acid]], and then precipitated as the hydroxide using concentrated aqueous [[ammonia solution]]. The residue was dissolved in [[perchloric acid]]. Further separation was carried out by [[ion exchange]], yielding a certain isotope of curium. The separation of curium and americium was so painstaking that those elements were initially called by the Berkeley group as ''[[wikt:pandemonium|pandemonium]]''<ref>{{Cite web |title=Americium (Am) {{!}} AMERICAN ELEMENTS ® |url=https://www.americanelements.com/am.html |access-date=2024-05-09 |website=American Elements: The Materials Science Company |language=en}}</ref> (from Greek for ''all demons'' or ''hell'') and ''[[wikt:delirium|delirium]]'' (from Latin for ''madness'').<ref name="radio" /><ref>{{cite book| author = Robert E. Krebs| title = The History and Use of Our Earth's Chemical Elements: A Reference Guide| edition = Second| url = https://books.google.com/books?id=yb9xTj72vNAC&pg=PA322| date = 2006| publisher = Greenwood Publishing Group| isbn = 978-0-313-33438-2| page = 322 }}</ref>

Initial experiments yielded four americium isotopes: <sup>241</sup>Am, <sup>242</sup>Am, <sup>239</sup>Am and <sup>238</sup>Am. [[Americium-241]] was directly obtained from plutonium upon absorption of two neutrons. It decays by emission of a [[α-particle]] to <sup>237</sup>Np; the [[half-life]] of this decay was first determined as {{val|510|20}} years but then corrected to 432.2 years.<ref name="nubase">{{NUBASE 1997}}</ref>

:<math chem>\ce{^{239}_{94}Pu ->[\ce{(n,\gamma)}] ^{240}_{94}Pu ->[\ce{(n,\gamma)}] ^{241}_{94}Pu ->[\beta^-][14.35\ \ce{yr}] ^{241}_{95}Am}\ \left( \ce{->[\alpha][432.2\ \ce{yr}] ^{237}_{93}Np} \right)</math>

: <small> The times are [[half-lives]]</small>

The second isotope <sup>242</sup>Am was produced upon neutron bombardment of the already-created <sup>241</sup>Am. Upon rapid [[β-decay]], <sup>242</sup>Am converts into the isotope of curium <sup>242</sup>Cm (which had been discovered previously). The half-life of this decay was initially determined at 17 hours, which was close to the presently accepted value of 16.02 h.<ref name="nubase" />

: <math chem>\ce{^{241}_{95}Am ->[\ce{(n,\gamma)}] ^{242}_{95}Am}\ \left(\ce{->[\beta^-][16.02\ \ce{h}] ^{242}_{96}Cm} \right)</math>

The discovery of americium and curium in 1944 was closely related to the [[Manhattan Project]]; the results were confidential and declassified only in 1945. Seaborg leaked the synthesis of the elements 95 and 96 on the U.S. radio show for children ''[[Quiz Kids]]'' five days before the official presentation at an [[American Chemical Society]] meeting on 11 November 1945, when one of the listeners asked whether any new transuranium element besides plutonium and neptunium had been discovered during the war.<ref name="radio">{{cite web|url = http://pubs.acs.org/cen/80th/americium.html|title = Chemical & Engineering News: It's Elemental: The Periodic Table – Americium|access-date =7 July 2010| first = Rachel Sheremeta|last = Pepling|date = 2003}}</ref> After the discovery of americium isotopes <sup>241</sup>Am and <sup>242</sup>Am, their production and compounds were patented listing only Seaborg as the inventor.<ref>Seaborg, Glenn T. {{US patent|3156523}} "Element", Filing date: 23 August 1946, Issue date: 10 November 1964</ref> The initial americium samples weighed a few micrograms; they were barely visible and were identified by their radioactivity. The first substantial amounts of metallic americium weighing 40–200 micrograms were not prepared until 1951 by reduction of [[americium(III) fluoride]] with [[barium]] metal in high vacuum at 1100&nbsp;°C.<ref name="AM_METALL1">{{cite journal|title=The Preparation and Some Properties of Americium Metal|last1=Westrum|first1=Edgar F.|last2=Eyring|first2=Leroy|journal=Journal of the American Chemical Society|volume=73|page=3396|date=1951|doi=10.1021/ja01151a116|issue=7|bibcode=1951JAChS..73.3396W |hdl=2027/mdp.39015086480962|hdl-access=free}}</ref>