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Summary
1.
During July 1957, chemical separations by ion-exchange
resin columns were made on five grouped plankton samples taken
in and west of the #::we ok Proving Ground
in September 1956.
Also, radiochemical separations for Sr90-¥99 were made.
The
radioactive isotopes in the separated fractions were identi-
fied by decay rates, maximum beta energies and gamma energies.
2.
The distribution pattern of Co57 and zn65
samples
not subjected to
in plankton
ion-exchange separation was deter-
mined by analysis of gamma snectrum curves.
3.
The predominant fission product radiotsotopes found were
Zr95-Nb29, Celd4ppl44 ani in one sample,
Rul06_Ry106,
Fission products accounted for 22 to 44 per cent of the total
radioactivity at the collection date.
S$r90-y90 was not found
in the lon-exchange separations nor in fuming nitric acid pre-
cipitations made on duplicate aliquots.
4,
The non-fission radiotsotopes Fe25, Cool, CoS, and zn05
contributed 55 to 77 per cent of the total radioactivity, and
C069 and MnD4 accounted for a total of 0.8 to 1.6 per cent.
5.
Cod? and Co60 were present at Bikint Atoll in a l:l ratio
and at
Eniwetok ina
5.3:l ratio.
fThese
ratios
were re-
flected in plankton samples collected in the vicinity of the
two atolls.
The ratio of C057 /Co60 in an area 300 miles wide
r
north to south and 200 to 500 miles west of Eniwetok was