-52- viduals of the same species taken within the contaminated region are being investigated at this Laboratory at the present time. Origin of the non-fission products A survey of the samples in which the non-fission product radioisotopes have been found reveals the following: (1) Snail liver samples collected prior to the Nectar shot and whole fish samples collected November 8, 1952,and examined an 1957 contained Co>’, 0°, and Mn>* ,» thus indicating that the Mike shot (Nov. 1, 1952) produced these isotopes. (2) Pish samples collected after the Nectar test (May 14, 1954) near the crater contained higher levels of radioactivity in comparison with the pre-Nectar levels, all of which were contributed by non-fission product isotopes, suggesting the production of these isotopes by the Nectar test, (3) Pish and clam samples collected at Bikini and Eniwetok Atolls in 1956 and examined early in 1957 contained the non-fisSion products mentioned previously, including the short lived isotope C08, thus indicating the production of these isotopes during the summer of 1956. The isotopes Mn?" , Pe, Fe”, Co?! 6078, Co, and zn? all belong to the so-called transition elements and are characterized chemically by variable valence, easy oxidation and reduetion, and marked tendency to form complexes. An examination of the interrelationship of these elements ina table of nuclides reveals that three, Mn, Fe, and Co, fall in one group with the elements Ni and Cu separating them from the remaining element, ay !