The californium is a chemical element of symbol cf and Atomic number 98. He was discovered in 1950 by Stanley G. Thompson, Glenn T. Seaborg, Kenneth Street, Jr., and Albert Ghiorso in Berkeley. This fissile element with the characteristic to have a very low Critical mass: a little more than 2 kg if reflectors neutrons as steel is used. It would be in theory possible to manufacture a very compact atomic bomb containing californium. In practice, there does not exist means economic to produce such a fuel mass, which returns the realization of such an impossible bomb.