The following uses for californium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
Californium is radioactive and only available in very small amounts so its uses are somewhat specialist. Foils made from 252Cf are used as a source of fission fragments for research purposes. Californium is a good source of neutrons. It can be used as a portable neutron source for the detection of gold or silver by on-the-spot activation analysis. It is used in moisture gauges for the determination of water and oil-bearing layers in oil wells.