Editing Californium (section)

== History ==
[[File:Berkeley 60-inch cyclotron.jpg|thumb|right|The {{convert|60|in|m|2|adj=mid|-diameter}} [[cyclotron]] used to first synthesize californium|alt=Large pieces of equipment with a man standing nearby.]]
Californium was [[timeline of chemical element discoveries|first made]] at [[University of California, Berkeley|University of California]] [[Lawrence Berkeley National Laboratory|Radiation Laboratory]], [[Berkeley, California|Berkeley]], by physics researchers [[Stanley Gerald Thompson]], [[Kenneth Street Jr.]], [[Albert Ghiorso]], and [[Glenn T. Seaborg]], about February 9, 1950.{{sfn|Cunningham|1968|p=103}} It was the sixth [[transuranium element]] to be discovered; the team announced its discovery on March 17, 1950.<ref name="CPoC1950">{{cite journal |last1 = Street | first1 = K. Jr. |last2 = Thompson |first2 = S. G. |last3 = Seaborg |first3 = Glenn T. |title = Chemical Properties of Californium |journal = Journal of the American Chemical Society |date = 1950 |volume = 72 |issue = 10 |page = 4832 |doi = 10.1021/ja01166a528 | bibcode = 1950JAChS..72R4832S |url = https://apps.dtic.mil/sti/pdfs/ADA319899.pdf |hdl = 2027/mdp.39015086449173 |access-date = February 20, 2011 |archive-date = January 19, 2012 |archive-url = https://web.archive.org/web/20120119092943/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA319899&Location=U2&doc=GetTRDoc.pdf |url-status = live }}</ref><ref>{{cite book |author=Glenn Theodore Seaborg |author-link=Glenn T. Seaborg bibliography |title=Journal of Glenn T. Seaborg, 1946–1958: January 1, 1950{{snd}} December 31, 1950 |url=https://books.google.com/books?id=pvpDAQAAIAAJ |year=1990 |publisher=Lawrence Berkeley Laboratory, University of California |page=80}}</ref>

To produce californium, a microgram-size target of curium-242 ({{nuclide|Cm|242}}) was bombarded with 35&nbsp;MeV [[alpha particle]]s ({{nuclide|He|4}}) in the {{convert|60|in|m|2|adj=mid|-diameter}} [[cyclotron]] at Berkeley, which produced californium-245 ({{nuclide|californium|245}}) plus one [[free neutron]] ({{SubatomicParticle|neutron}}).{{sfn|Cunningham|1968|p=103}}<ref name="CPoC1950" />
<!-- Weeks & Leichester 1968 p. 849 gives product as 98-244 -->
: {{nuclide|curium|242}} + {{nuclide|helium|4}} → {{nuclide|californium|245}} + {{su|b=0|p=1}}{{SubatomicParticle|neutron}}
To identify and separate out the element, [[ion exchange]] and adsorsion methods were undertaken.<ref name="CPoC1950" /><ref>{{cite journal |last1=Thompson |first1=S. G. | last2=Street | first2=K. Jr. |first3=Ghiorso |last3=A. |last4=Seaborg |first4=Glenn T.|title = Element 98 |journal = Physical Review |date=1950 |volume = 78 |issue = 3 |page = 298 |doi = 10.1103/PhysRev.78.298.2 |url=http://escholarship.org/uc/item/44g7z6hk |bibcode = 1950PhRv...78..298T|doi-access=free }}</ref> Only about 5,000 atoms of californium were produced in this experiment,{{sfn|Seaborg|1996|p=82}} and these atoms had a half-life of 44&nbsp;minutes.{{sfn|Cunningham|1968|p=103}}

The discoverers named the new element after the university and the state. This was a break from the convention used for elements 95 to 97, which drew inspiration from how the elements directly above them in the periodic table were named.{{sfn|Weeks|Leichester|1968|p=849}}{{efn|[[Europium]], in the sixth period directly above element 95, was named for the continent it was discovered on, so element 95 was named [[americium]]. Element 96 was named [[curium]] for [[Marie Curie]] and [[Pierre Curie]] as an analog to the naming of [[gadolinium]], which was named for the scientist and engineer [[Johan Gadolin]]. [[Terbium]] was named for the village it was discovered in, so element 97 was named [[berkelium]].{{sfn|Weeks|Leichester|1968|p=848}} }} However, the element directly above element 98 in the periodic table, [[dysprosium]], has a name that means "hard to get at", so the researchers decided to set aside the informal naming convention.{{sfn|Heiserman|1992|p=347}} They added that "the best we can do is to point out [that] ... searchers a century ago found it difficult to get to California".{{sfn|Weeks|Leichester|1968|p=848}}

Weighable amounts of californium were first produced by the<!-- long duration -HOW LONG? --> irradiation of plutonium targets at [[Materials Testing Reactor]] at [[Idaho National Laboratory|National Reactor Testing Station]], [[eastern Idaho]]; these findings were reported in 1954.<ref>{{cite journal |journal=[[Physical Review]] |volume=94 |issue=4 |pages=1083 |date=1954 |author=Diamond, H. |title=Identification of Californium Isotopes 249, 250, 251, and 252 from Pile-Irradiated Plutonium |doi = 10.1103/PhysRev.94.1083 |bibcode = 1954PhRv...94.1083D |last2=Magnusson |first2=L. |last3=Mech |first3=J. |last4=Stevens |first4=C. |last5=Friedman |first5=A. |last6=Studier |first6=M. |last7=Fields |first7=P. |last8=Huizenga |first8=J. }}</ref> The high spontaneous fission rate of californium-252 was observed in these samples. The first experiment with californium in concentrated form occurred in 1958.{{sfn|Cunningham|1968|p=103}} The isotopes {{sup|249}}Cf to {{sup|252}}Cf were isolated that same year from a sample of [[plutonium-239]] that had been irradiated with neutrons in a nuclear reactor for five years.{{sfn|Jakubke|1994|p=166}} Two years later, in 1960, Burris Cunningham and James Wallman of Lawrence Radiation Laboratory of the University of California created the first californium compounds—californium trichloride, [[californium(III) oxychloride]], and californium oxide—by treating californium with steam and [[hydrochloric acid]].<ref>{{cite journal |journal = Science News Letter |volume = 78 |issue = 26 |date=December 1960 |title = Element 98 Prepared }}</ref>

The [[High Flux Isotope Reactor]] (HFIR) at ORNL in [[Oak Ridge, Tennessee]], started producing small batches of californium in the 1960s.<ref>{{cite web |url=http://web.ornl.gov/sci/rrd/pages/hfir.html |title=The High Flux Isotope Reactor |publisher=Oak Ridge National Laboratory |access-date=August 22, 2010 |archive-url=https://web.archive.org/web/20100527164346/http://web.ornl.gov/sci/rrd/pages/hfir.html <!--Added by H3llBot--> |archive-date=May 27, 2010 }}</ref> By 1995, HFIR nominally produced {{convert|500|mg|oz}} of californium annually.{{sfn|Osborne-Lee|1995|p=11}} Plutonium supplied by the United Kingdom to the United States under the [[1958 US–UK Mutual Defence Agreement]] was used for making californium.<ref>{{cite web |archive-url=https://web.archive.org/web/20061213032416/http://www.mod.uk/NR/rdonlyres/B31B4EF0-A584-4CC6-9B14-B5E89E6848F8/0/plutoniumandaldermaston.pdf |archive-date=December 13, 2006 |url=http://www.mod.uk/NR/rdonlyres/B31B4EF0-A584-4CC6-9B14-B5E89E6848F8/0/plutoniumandaldermaston.pdf |title=Plutonium and Aldermaston – an Historical Account |publisher=UK Ministry of Defence |date=September 4, 2001 |access-date=March 15, 2007|page=30 }}</ref>

The [[United States Atomic Energy Commission|Atomic Energy Commission]] sold {{sup|252}}Cf to industrial and academic customers in the early 1970s for $10/microgram,<ref name="osti" /> and an average of {{convert|150|mg|oz|abbr=on}} of {{sup|252}}Cf were shipped each year from 1970 to 1990.{{sfn|Osborne-Lee|1995|p=6}}{{efn|The [[Nuclear Regulatory Commission]] replaced the Atomic Energy Commission when the [[Energy Reorganization Act of 1974]] was implemented. The price of californium-252 was increased by the NRC several times and was $60 per microgram by 1999; this price does not include the cost of encapsulation and transportation.<ref name="osti" /> }} Californium metal was first prepared in 1974 by Haire and Baybarz, who reduced californium(III) oxide with lanthanum metal to obtain microgram amounts of sub-micrometer thick films.{{sfn|Haire|2006|p=1519}}<ref>{{cite journal |last1=Haire |first1=R. G. |last2=Baybarz |first2=R. D. |title=Crystal Structure and Melting Point of Californium Metal |journal=Journal of Inorganic and Nuclear Chemistry |volume=36 |issue=6 |pages=1295 |date=1974 |doi=10.1016/0022-1902(74)80067-9 }}</ref>{{efn|In 1975, another paper stated that the californium metal prepared the year before was the hexagonal compound Cf{{sub|2}}O{{sub|2}}S and face-centered cubic compound CfS.<ref>{{cite journal |doi=10.1016/0022-1902(75)80787-1 |journal=Journal of Inorganic and Nuclear Chemistry |date=1975 |pages=1441–1442 |volume=37 |issue=6 |title=On Californium Metal |last=Zachariasen |first=W. }}</ref> The 1974 work was confirmed in 1976 and work on californium metal continued.{{sfn|Haire|2006|p=1519}} }}