~10-
amount of cross-contamination between the radioactive elements separated by a combination of the Dowex 50 cation-
exchange method and the Dowex 1 chloride complexing tecmidque.
The results of the radioisotopic separations are summa-
rized in Tables 1 end 2.
In these samples the predominant
figsion-product radioisotopes were the relatively short-
lived Zr95-nb?5 (65 a), Cel44-prl44 (285 4), and in one
sample,
RuLOE_ Ry] 6 (1 yr).
The fission products accounted
for 22 to 37 per cent of the total radioactivity in the three
analyses from which cerium determinations were made.
In the
other two samples fission products contributed at least 5.7
per cent (stations 57,58,59) and 44 per cent (stations 13,14,
15) of the total radioactivity.
gr90-y90 were not detected in the lon-exchange separations nor were
they found in fuming nitric acid precipi-
tations made on duplicate aliquots from both the five samples
and their filtrates.
Of the non-fission radioisotopes, Fe55, Cod’, Co>S and
zn©5 contributed almost all of the activity.
Although C0?
was present at an average level of only about one per cent,
it has the longest half life
(5.3 yrs) of the reported non-
fission radioisotopes and is
therefore important.
The variability,
mentioned previously,
between the
retios of Co>’ to zn©5 also was evident between Co57 and Co0©°,
and between Co°5? and Fe>>.
In Figure 4a, the ratios
of
Co57/C06° in the five plankton samples are shown; also,
these