Berkelium
. Berkelium, symbol Bk, artificially created radioactive metallic element. The atomic number of berkelium is 97; the element is one of the transuranium elements in the actinide series of the periodic table . Berkelium was discovered in 1949 by the American chemists Glenn T. Seaborg , Stanley G. Thompson, and Albert Ghiorso at the University of California laboratories in Berkeley, California, for which the element was named. An isotope of mass number 243 with a half-life of 4.6 hours was produced by bombarding americium-241 with alpha particles accelerated in a cyclotron (see Particle Accelerators ). Subsequently, nine more isotopes were produced, bringing the total range of mass numbers from 242 to 251. The most stable isotope of berkelium, with a half-life of about 1400 years, has a mass number of 247. See also Radioactivity .