33
of radionuclides moving through the soil.
This is certainly
true for cst? and sx?°, which were abundant compared to other
radionuclides in the leachates.
It also wes demonstrated by
comparing the yamma-ray spectra of depth increments that there
is a more rapid movement of cs)3? than of other gamma-emitters
present.
It should be recalled that the exchange capacity of
these soils originates from the organic content, which, as is
obvious from the photographs of the core sections and Table III,
is far higher in the old than in the young soil.
There is thus
more opportunity for exchange and retention of radionuclides
in old soil.
Mechanical mixing, due mainly to the activity of
land crabs, plays an important role in redistribution in the
surface layers.
This effect is obvious in areas where there
has been active burrowing, and is probably occurring to a small
extent throughout densely vegetated areas as is indicated by
the presence of ce/44_p,144 and Eut?5 in the litter.
These
radionuclides could only have come directly from the soil by
upward mixing since they were not found in the vegetation which
contributed significantly to the litter.
CONCLUSIONS
Different plant and soil environments on single islets
have a different vertical distribution pattern of radionuclides
from the same fallout material.
The vertical distribution of
UY)