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Chemical Fact Sheet

Californium

Chemical Abstract Number (CAS #) 7440-71-3
Analytical Methods 200.8 - 6020
Atomic Symbol Cf

Synopsis from the CRC Handbook of Chemistry and Physics 92nd Edition 2011-2013

Californium — (State and University of California), Cf; at. wt. (251); m.p. 900 °C; sp. gr. 15.1; at. no. 98. Californium, the sixth transuranium element to be discovered, was produced by Thompson, Street, Ghioirso, and Seaborg in 1950 by bombarding microgram quantities of 242Cm with 35 MeV helium ions in the Berkeley 60-inch cyclotron. Californium (III) is the only ion stable in aqueous solutions, all attempts to reduce or oxidize californium (III) having failed. The isotope 249Cf results from the beta decay of 249Bk while the heavier isotopes are produced by intense neutron irradiation by the reactions: 249Bk(n,γ)→250 Bkβ→250 Cf and249Cf(n,γ)→250 Cf followed by 250Cf(n,γ)→251 Cf(n,γ)→252 Cf The existence of the isotopes 249Cf, 250Cf, 251Cf, and 252Cf makes it feasible to isolate californium in weighable amounts so that its properties can be investigated with macroscopic quantities. Californium-252 is a very strong neutron emitter. One microgram releases 170 million neutrons per minute, which presents biological hazards. Proper safeguards should be used in handling californium. Twenty isotopes of californium are now recognized. 249Cf and 252Cf have half-lives of 351 years and 900 years, respectively. In 1960 a few tenths of a microgram of californium trichloride, CfCl3, californium oxychloride, CfOCl, and californium oxide, Cf2O3, were first prepared. Reduction of californium to its metallic state has not yet been accomplished. Because californium is a very efficient source of neutrons, many new uses are expected for it. It has already found use in neutron moisture gages and in well-logging (the determination of water and oil-bearing layers). It is also being used as a portable neutron source for discovery of metals such as gold or silver by on-the-spot activation analysis. 252Cf is now being offered for sale by the Oak Ridge National Laboratory (O.R.N.L.) at a cost of $60/μg and 249Cf at a cost of $185/μg plus packing charges. It has been suggested that californium may be produced in certain stellar explosions, called supernovae, for the radioactive decay of 254Cf (55-day half-life) agrees with the characteristics of the light curves of such explosions observed through telescopes. This suggestion, however, is questioned. Californium is expected to have chemical properties similar to dysprosium.


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