Berkelium

The element having the atomic number 97, the discovery of which was announced by Thompson, Ghiorso, and Seaborg in 1950. They produced an isotope of 4.5 h half-life, berkelium 243, by helium ion bombardment of americium 241. Symbol, Bk; valences, 3 and 4; and the mass number of the most stable isotope, 249. Handbook of Chemistry and Physics, 2

Source: Dictionary of Mining, Mineral, and Related Terms