
Model of a cobalt-60 source
1985
1985
1932
1935-1945
1932
1932
1918-1925
1947; (1946-07-24)
1997
1945-1947
1938-1951
1911-1926
1947
1911-1926
1952
1964-1978
1962-1972
1973
1955-1960
1955-1960
1955-1961
1981
1988
1991
1980
1955
1955-1965
1942-1943
1969
1960-1965
1997
1995
circa 1990
1945-48
1950-78
1960-78
1946
1953-78
1945
1948-78
1949