Berkelium, a radioactive, metallic chemical element. Berkelium does not occur in nature; it is artificially created. Its most easily manufactured isotope, berkelium 249, is produced in nuclear reactors by bombarding isotopes of plutonium, americium, or curium with neutrons. The most stable isotope is berkelium 247, with a half-life period of about 1,400 years. Berkelium has no commercial uses, but it is important as a radioactive tracer in nuclear research.

Berkelium was first produced in 1949 by Stanley G. Thompson, Albert Ghiorso, and Glenn T. Seaborg at the University of California, Berkeley. The element was discovered in a sample that had been prepared by bombarding americium 241 with helium ions in a cyclotron. It was named for the city of Berkeley.

Symbol: Bk. Atomic number: 97. Atomic weight of most stable isotope: 247. Berkelium has nine isotopes: Bk-243 to Bk-251. Berkelium is a transuranium element belonging to the actinide series of the Periodic Table and may have a valence of 3 or 4.