History(Berkeley, home of the University of California) Berkelium, the eighth member of the actinide transition series, was discovered in December 1949 by Thompson, Ghiorso, and Seaborg, and was the fifth transuranium element synthesized. It was produced by cyclotron bombardment of milligram amounts of 241Am with helium ions at Berkeley, California. The first isotope produced had a mass of 243 and decayed with a half-life of 4.5 hours. Fourteen isotopes are now known ranging in mass from 238 to 251. The discovery of 249Bk with a half-life of 330 days made it feasible to isolate berkelium in weighable amounts so that its physicochemical properties could be thoroughly investigated. The first visible amounts of a pure berkelium compound, berkelium chloride, was produced in 1962. It weighed 1 billionth of a gram. Berkelium was first prepared in elemental form in 1968 and weighed 1.7 micrograms. The metal is silver colored, quite soluble in dilute mineral acids, and readily oxidized in air or oxygen to form the oxide. Since its discovery in 1949, a total of approximately 1.1 grams of berkelium-249 has been produced in the U.S. by neutron bombardment of lighter actinides in nuclear reactors. Berkelium is known to exist in oxidation states 0, III, and IV in solution and the solid state. X-ray diffraction and other methods have been used to identify about forty known berkelium compounds. As with other actinide elements, berkelium tends to accumulate in the skeletal system. There are no practical or commercial applications for any known berkelium isotopes. However, the longer lived and more readily available isotope, berkelium-249, has been used extensively as a target material for the production of still-heavier actinide and transactinide elements. Bk-249 has been used extensively as a žcowÓ for žmilkingÓ isotopically pure californium-249 daughter product. Berkelium is in a unique position as the first member of the second half of the actinide series. Knowledge of the properties of berkelium enable more accurate extrapolations to the behavior of heavier elements for which experimental studies are severely limited by lack of material, short half-lives, and intense radiation.
Sources: Los Alamos National Laboratory
David E. Hobart, Ph.D.