Californium (Cf) is a chemical element with atomic number 98. Just like berkelium, it was first discovered in Berkeley, California.

Unlike most synthetic elements, californium actually has some industrial uses. It is sometimes used as a neutron emitting startup source in nuclear reactors, and sometimes also in radiation therapy again certain cancers.

Notably, californium was also used, in combination with calcium, to synthesize oganesson which is the heaviest known chemical element.