Californium is one of the few transuranium elements with genuine, dedicated industrial uses; its star isotope is californium-252. It exhibits the unusual property of spontaneous fission: each microgram of californium-252 releases millions of neutrons per second, and when made into a compact neutron source it occupies no more than a grain of rice while delivering a strong, stable neutron beam. Such sources are widely used in the nuclear industry and in instrumentation. In oil-well logging, a californium-252 source is lowered into the borehole, and neutron activation analysis is used to determine formation porosity and oil-water content; nuclear reactors and fuel plants use it as a startup neutron source and for instrument calibration. In medicine, californium-252 neutron brachytherapy is used to treat certain inoperable brain and head-and-neck tumors. It is also used in neutron radiography, explosives detection, and materials activation analysis. Because worldwide annual production is only at the gram scale, californium-252 neutron sources are extremely expensive and are used only where a portable, strong neutron source is genuinely needed.
Californium compounds such as californium trichloride (CfCl3) and californium dioxide (CfO2) are obtained only by trace-scale separation from a small number of targets irradiated in high-flux reactors, where they are used to prepare californium metal targets and neutron sources. The commercial "californium-252 source" is in reality nothing more than an ultrathin piece of a californium compound sealed in a small metal capsule; no other consumer compound form exists.
