Californium

(State and University of California) Californium, the sixth transuranium element to bediscovered, was produced by Thompson, Street, Ghioirso, and Seaborg in 1950 by bombardingmicrogram 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 oroxidize californium (III) having failed. The isotope 249Cf results from the beta decay of249Bk while the heavier isotopes are produced by intense neutron irradiation by thereactions. The existence of the isotopes 249Cf, 250Cf, 251Cf, and 252Cf makes it feasibleto isolate californium in weighable amounts so that its properties can be investigatedwith macroscopic quantities. Californium-252 is a very strong neutron emitter. Onemicrogram releases 170 million neutrons per minute, which presents biological hazards.Proper safeguards should be used in handling californium. Reduction of californium to itsmetallic state has not yet been accomplished. Because californium is a very efficientsource of neutrons, many new uses are expected for it. It has already found use in neutronmoisture gauges 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 orsilver by on-the-spot activation analysis. 252-Cf is now being offered for sale by theO.R.N.L. at a cost of $10/mg. As of May, 1975, more than 63 mg have been produced andsold. It has been suggested that californium may be produced in certain stellarexplosions, called supernovae, for the radioactive decay of 254Cf (55-day half-life)agrees with the characteristics of the light curves of such explosions observed throughtelescopes. This suggestion, however, is questioned.