Fesults The non-fission products Co57, C058, C062, zn®5 ana mn54 contributed almost all of the activity in gamma spectrum curves made from filtered plankton samples eleven months after collection, masking the weaker peaks from the fission products Zr95-Nb95, Rhl06, Bal37m(cs137) and Cel44 (Fig. 2). The gamma peaks of the latter isotopes were detected only in the frac- tions eluted from the ion-exchange columns (Fig. 3). Although the non-fission products, in each instance, contributed the major part of the gamma activity in the plankton, they were not always present at a constant ratio to each other in the different samples. Thus in some samples the amount of zn65, based on the gamma spectra, was high in comoarison to radioactive cobalt, 51, 52, 53, (Fig. 2, plankton stations 50, Coo’ = 0.19 6 ) and in others the reverse relation zn°> 1,0 existed (Fig. 2, plankton station 42, Coll = zn65 5-5) 1.0). variation was related to the site of collection. This A similar variation was observed in the levels of some other non-fission radioisotopes and will be discussed later. DOE ARCHIVES Detailed descriptions of the elution patterns from ion- exchange resin columns and the identification of the separated fission and non-fission radioisotopes appear in an earlier paper (16) and are not repeated here. the gamma However, spectrum curves for plankton samples 50,51,52,53 and the separated fractions are shown in Figure 3 to illustrate the small iw