the gamma ratios of cesium-137 to potassium-40 in place of the cesium
unit.
Cesium units for Birgus muscle are given in Table 1 for compari-
son with other published data on fallout given in the same units.
However,
since the potassium and cesium levels are both highly variable in Birgus
muscle, there is some doubt as to the usefulness of the unit in this case.
For example, the comparatively high value for cesium units of samples
from Rongelap Island is due to the exceptionally low potassium
of one of the samples
content
On the other hand, the high value for the March
1959 collection at Kabelle Island is due to high levels of cesium-137,
while the potassium levels are about average.
These differences are not surprising when the following facts are
considered.
Gross (1959) has
reported that
Coenobita, which has habits
similar to those of Birgus, obtains blood salts from its food.
From work
in progress at this Laboratory it is known that Pandanus fruit, which form
apart
of the diet of Birgus,
vary by as much asa factor of five in
cesium-137 content and a factor of four in potassium content and that the
range in potassium levels in soils on which Pandanus grows at Rongelap
is 0.1 to 1.5 milliequivalents per 100 grams.
Also, the extremes in the
range of gross beta activity in the top inch of soil at a single island
differ by
more than a factor of ten
Ona basis of
the
variability in
cesium-137 and potassium levels found in the environment alone,
might expect the high degree of variability found in Birgus.
can
one
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