The discoveries of americium, berkelium, and californium followed soon. In experiments during 1949-1950, they produced and identified elements 97 (berkelium) and 98 (californium). Similar conclusion was drawn for other actinides americium, berkelium and fermium. Americium, berkelium and livermorium were named after places that had been named for them. The second important berkelium isotope, berkelium-247, is an alpha-emitter, as are most actinide isotopes. Nuclear reactors produce mostly, among the berkelium isotopes, berkelium-249. A similar behavior is observed for the lanthanide analogue of berkelium, terbium. All berkelium isotopes have a half-life far too short to be primordial. There is currently no use for any isotope of berkelium outside basic scientific research. Berkelium and cerium are then separated with another round of ion-exchange treatment. Most available berkelium toxicity data originate from research on animals. Just over one gram of berkelium has been produced in the United States since 1967. Berkelium (Bk) is an artificial element, and thus a standard atomic weight cannot be given. The high radioactivity of berkelium gradually destroys the compound (within a period of weeks). Berkelium is a soft, silvery-white, radioactive metal.