Californium

Californium is a synthetic, radioactive, silvery-white metal. It is made in nuclear reactors by irradiating heavier elements with neutrons; it does not occur naturally in significant amounts. Californium-252 emits neutrons as it undergoes radioactive decay, making it useful as a compact neutron source for starting some reactors, analyzing materials, and research. Because californium is highly radioactive, it must be handled with specialized shielding and care.