A synthetic transuranic element having isotopes with mass numbers from 237 to 256 and half-lives varying from 21 milliseconds to 898 years. All isotopes are radioactive, chiefly by emission of alpha particles, and Cf-252 is a potent neutron emitter. Atomic number 98; melting point 900°C; specific gravity 15.1; valence 3. See Periodic Table.