| Atomic Number: || 98|
| Atomic Radius: || ~186 pm|
| Atomic Symbol: || Cf|
| Melting Point: || 860 șC|
| Atomic Weight: || 251|
| Boiling Point: || --|
| Electron Configuration: || [Rn]7s25f10||
(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.
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.
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