12
In contrast, the old soil has well-developed Ay and A,
—_
horizons and supports dense vegetation, which produces a heavy
litter fall during the dry season and which contributes to the
tedistribution of radionuclides in the system.
Sea birds nest in the vegetation and land crabs, predominantly Birgus latro and Coenobita perlatus, burrow in the soil.
Earthworms are seldom found and terrestrial isopods, although
found in old soils on some islets,
are few.
Ther>
few soil insects, which sce mainly tenebrionid and
beetles as well as ants.
are also
«rabid
“
Depth Gradient of Gamma Spectra
Old Soil
The gamma spectra, with background subtracted,
of the 0 to
l-inch, 1 to 2-inch, and 9 to 10-inch depth increments from old
50il collected in March 1959 are given in Fig. 5.
The spectra
of the increments between 2 inches and 9 inches have been
omitted from the figure for clarity but show a gradual change
from the condition at 1 to 2 inches to that at 9 to 10 inches.
The radionuclides corresponding to the photopeaks are indicated
in the figure.
and Eu
155
The photopeaks of co®?, zn°”, mn?*, Ce
137
4 py
144
show significant counts in the surface increments but
are not detectable in samples from greater depths.
of Cs
14
The amounts
$
137
125
and
decrease and the proportions of Cs
and Sb™"”
1c