64
6.
6.1
Discussion
Preliminary Surveys
6.11
Eniwetok,
1954-1955.
of fish collected at Belle
Welander's
Island,
(1957) analyses
Eniwetok Atoll in 1954
and 1955 provided gross beta radioactivity
measurements of
mixed fission-product and induced radioisotopes.
From these
data it is difficult to draw inferences as to the occurrence
and behavior of Zn 65
Since only 2.5 per cent of its radioac-
tivity is emitted as beta particles.
However,
radiochemical
analyses of fish collected several months after a shot showed
that by then,
the shorter-lived fission products contributed
little to the measurable radioactivity and that the induced
radioisotopes mn>4,
Fe?>,
Co? 758,60,
with Fe?> ana zn®5 predominating.
and gn©5 were present,
mn>4,
Fe>>,
and Co?’ are
not beta emitters, while co®8 with a 72 day half-life has 15
per cent beta emission and co0°? with a 5.2 year half-life has
but 0.01 per cent beta emission.
that zn°>
It is likely,
therefore,
(245 day half-life) could have contributed a sig-
nificant amount of the gross beta radioactivity in fish collected after an interval of several months after a shot when
much of the radioactivity from short-lived fission products
had decayed.