On Earth , berkelium is mostly concentrated in certain areas , which were used for the atmospheric nuclear weapons tests between 1945 and 1980 , as well as at the sites of nuclear incidents , such as the Chernobyl disaster , Three Mile Island accident and 1968 Thule Air Base B-52 crash . Analysis of the debris at the testing site of the first U.S. hydrogen bomb , Ivy Mike , ( 1 November 1952 , Enewetak Atoll ) , revealed high concentrations of various actinides , including berkelium . For reasons of military secrecy , this result was published only in 1956
1968 Thule Air Base B-52 crash
1968 Thule Air Base B-52 crash
Berkelium