-~30—
later, contained the lowest levels of gamma radioactivity.
levels
The low
in the plankton from this location indicated that the
south-
western perimeter of the contaminated water mass at this time was
only afew miles away.
The low level of radioactivity also suggests
that the radioactive water had travelled primarily ina westward
rather than a southwestward direction.
The radioisotopic composition of the plankton samples
before and after the Wahoo detonationis givenin Table 3.
collected
Np239
was the major contributor in all of the samples, but the relative
amounts of Mo99-Tc99m,
Tel32_7132
and U237
differed,
Mo28-
Tc99M was:much higher and Te!32-1132 was much lower in the pre-
Wahoo sample. Ru!05-Rn105 was detected in one post-Wahoo sample
and Rul06-Rn196 was detected
in one pre- Wahoo sample.
These differences in radioisotopic content may be used to establish the origin of the radioactive material in the samples
during the survey.
collected
As seen in Table 3, the radioisotopes in samples
P-25 and P-26, collected at the western periphery,
were similar to
the radioisotopes in earlier samples; therefore, it was assumed that
the origin of the radioactive material was
the same for all samples
collected after the Wahoo detonation.
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Results of radiochemical separations and gamma spectrum analyses
revealed that the percentages of Bal40-1,a140 and U237 were
higher in