from the leaves of the vegetation and perhaps also to some ©
shielding effect by additional moisture in the soil.
It was
certainly not due to rapid vertical movement of material in
the soil.
Analysis of soil leachates and soil cores shows that
vertical movement of radionuclides in atoll soils is very slow.
For example, cores taken in immature soils in 1963 still contained 90 per cent of the activity in the top centimeter.
However, the reduction of gamma-dose rates to approximately
half the predicted levels in 1959-63 probably reflects the
.
.
1
downward movement of the long-lived gamma~emitter Cs 37 in the
-Soil.,
Cesium-137 and Sb
125
are very slowly leached in the atoll
soils while other gamma-emitters, cel44_pyt44 pul?>, zn®>,
co°?, and mn? tend to remain at the surface (11647) |
Although
the gamma-dose rate values at Rongelap islet in 1959-63 fall
on the theoretical curve, it appears that the levels due to
the 1954 fallout have fallen below values predicted by the theoretical curve here also.
Since the theoretical curve had reached
background levels by 1959 it would be expected that the
sum of
gamma-dose rates due to the fallout and due to background would
be approximately twice background.
CONCHUS TONS
ergy
Department of En
Historian’s Office
ARCHIVES
The Rongelap experience has shown that the decline of
|
gamma dose rates can be approximated from the decay curve for
9