Californium

Author: Robert Husted, Mollie Boorman

History

(State and University of California) 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. 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. 

Properties

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. 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 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 or silver by on-the-spot activation analysis. ²⁵²Cf is now being offered for sale by the O.R.N.L. at a cost of $10/mg. As of May, 1975, more than 63 mg have been produced and sold. 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.