Californium

Californium is a radioactive metal made in nuclear reactors. Stanley Thompson, Kenneth Street Jr., Albert Ghiorso and Glenn Seaborg first created it in 1950 at Berkeley by bombarding curium with alpha particles, and named it after the state and university of California.

Its best-known form, californium-252, splits apart on its own and showers out neutrons: about 2.3 million per second from a single microgram. That makes it a handy portable neutron source. It is used to start up nuclear reactors, to find oil and water layers around boreholes, to scan for explosives and to measure moisture in soil. Californium-249 was also the target used to create oganesson, the heaviest known element.