ɪˈforniəm) is a metallic chemical elementwith the symbol Cf and atomic number98. A radioactive transuranic element, californium has very few uses. Uses include starting nuclear reactors (civilian and military); optimizing coal-fired power plants and concrete production facilities (via online analyzers); medical treatment of cancer; and oil exploration via down hole well logging. It was first produced by bombarding curiumwith alpha particles ( helium ions).
Weighable amounts of californium make it possible to determine some of its properties using macroscopic quantities.
half-life) is a very strong neutronemitter and is thus extremely radioactiveand harmful [cite web | url = https://narac.llnl.gov/uploads/Dillon2004_NARACEmergencyResponseGuide_202990_xchnw.pdf | title = The NARAC Emergency Response Guide to Initial Airborne Hazard Estimates | author = Michael B. Dillon, Ronald L. Baskett, Kevin T. Foster, and Connee S. Foster | date = 2004-03-18 | id = UCRL:UCRL-TM-202990 | publisher = National Atmospheric Release Advisory Center] (one microgramspontaneously emits 170 million neutrons per minute). 249Cf is formed from the beta decayof 249Bk and most other californium isotopes are made by subjecting berkelium to intense neutron radiation in a nuclear reactor.
Californium has no biological role and only a few californium compounds have been made and studied. Included among these are californium oxide (Cf2O3), californium trichloride (CfCl3) and californium oxychloride (CfOCl). The only californium
ionthat is stable in aqueous solutionis the californium(III) cation.
The element does have some specialist applications dealing with its radioactivity but otherwise is largely too difficult to produce to have widespread useful significance as a material. Some of its uses are:
*neutron startup source for some
nuclear reactors, calibrating instrumentation
*treatment of certain cervical and
brain cancers where other radiation therapyis ineffective
radiographyof aircraft to detect metal fatigue
*airport neutron-activation detectors of explosives
*portable metal detectors [cite web|url=http://www.pnl.gov/news/2000/00-43.htm|title=Will you be 'mine'? Physics key to detection|date=2000-10-25|publisher=
Pacific Northwest National Laboratory|accessdate=2007-03-21]
neutron moisture gaugesused to find waterand petroleumlayers in oil wells
*portable neutron source in
goldand silverprospecting for on-the-spot analysis
In October 2006 it was announced that on three occasions californium-249 atoms had been bombarded with
calcium-48 ions to produce ununoctium(element 118), [cite web | last = Sanderson | first = Katherine | title = Heaviest element made - again | work = firstname.lastname@example.org | publisher = Nature (journal)| date = 2006-10-17 | url = http://www.nature.com/news/2006/061016/full/061016-4.html | accessdate = 2006-10-19 ] [cite web | author = Phil Schewe and Ben Stein | title = Elements 116 and 118 Are Discovered | work = Physics News Update | publisher = American Institute of Physics| date = 2006-10-17 | url = http://www.aip.org/pnu/2006/797.html | accessdate = 2006-10-19 ] making this the heaviest element ever synthesized.
251Cf is famous for having a very small critical mass of 5 kg ( [http://europa.eu.int/comm/energy/nuclear/transport/doc/irsn_sect03_146.pdf] ), high lethality, and short period of toxic environmental irradiation relative to radioactive elements commonly used for radiation explosive weaponry, creating speculation about possible use in
pocket nukes. However, the costs of such a bomb would be extremely high (around US $100 billion [$27,000,000 per gram x 5,000 grams = $135,000,000,000 ] ). Other weaponry uses, such as showering an area with californium, are not impossible but are seen as inhumane and are subject to inclement weather conditions and porous terrain considerations. Nuclear fuel cycle
Californium is produced by
neutron captureon berkelium-249. Three californium isotopes with significant halflives are produced, requiring a total of 12 to 14 neutron captures on uranium-238without nuclear fissionor alpha decay. Their neutron cross sections are:
Thus 250Cf and 251Cf will be transmuted fairly quickly, with the majority fissioning at mass 251, but with a large fraction surviving to become 252Cf; the 252Cf however will not be transmuted or destroyed quickly in a well-thermalized reactor.
252Cf has a relatively high rate of
spontaneous fission. Although still much less likely than alpha decay, this makes californium a significant neutron radiationemitter. MOX fuelcontaining enough curiumwould likely contain enough californium after use to preclude manual handling of the spent fuelor its nuclear reprocessingproducts with a glove boxthat protects against alpha and beta radiationbut not against gamma radiationand especially neutron radiation.
Californium was first synthesized at the
University of California, Berkeleyby researchers Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorsoand Glenn T. Seaborgin 1950. It was the sixth transuranium elementto be discovered and the team announced their discovery on March 17, 1950. It was named after the U.S. state of Californiaand for the University of California, Berkeley, being that California is one of a few nicknames for the university.
To produce element 98, the team bombarded a microgram-sized target of 242Cm with 35 MeV
alpha particles in the 5-foot (1.52 m) Berkeley cyclotron, which produced atoms of 245Cf (half-life 44 minutes) and a free neutron.
Due to its $27 million per gram price tag, only 8 grams of 252Cf have been made in the western world since its discovery by Seaborg in 1950.Fact|date=March 2007 Plutonium supplied by the
United Kingdomto the U.S. under the 1958 US-UK Mutual Defence Agreementwas used for californium production. [cite web|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=2001-09-04|accessdate=2007-03-15]
radioisotopes of californium have been characterized, the most stable being 251Cf with a half-lifeof 898 years, 249Cf with a half-life of 351 years, and 250Cf with a half-life of 13 years. All of the remaining radioactiveisotopes have half-lives that are less than 2.7 years, and the majority of these have half-lives shorter than 20 minutes. The isotopes of californium range in atomic weightfrom 237.062 u (237Cf) to 256.093 u (256Cf).
Although californium does not occur naturally on Earth, the element and its decay products occur elsewhere in the universe. Their electromagnetic emissions are regularly observed in the spectra of
*"Guide to the Elements - Revised Edition", Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
* [http://www.webelements.com/webelements/elements/text/Cf/index.html WebElements.com - Californium]
* [http://www.nuclearweaponarchive.org/Nwfaq/Nfaq6.html#nfaq6.2 NuclearWeaponArchive.org - Californium]
* [http://periodic.lanl.gov/elements/98.html Los Alamos National Laboratory - Californium]
* [http://education.jlab.org/itselemental/ele098.html It's Elemental - Californium]
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rel+@na+californium,radioactive Hazardous Substances Databank – Californium, Radioactive]
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