-7- 
Results 
The non-fission products C057, Co58, C062, zn©5 and 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(csl37) ana 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 plank- 
ton, 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 com- 
parison to radioactive cobalt, (Fig. 2, plankton stations 50, 
Saale -242) and in others the reverse relation 
gn©5 1.0 
isted (Fi 5 lankt tation 42 Corl = 5-5) 
Cxciesice ge 2, plankton ‘sita tion > on65 Teo) Mads 
Si See ee 
variation was related to the site of collection. A similar 
variation was observed in the levels of some other non-fission 
radioisotopes and will be discussed later. 
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. However, the gamma 
spectrum curves for plankton samples 50,51,52,53 and the sepa- 
réted fractions are shown in Figure 3 to illustrate the small 
