“el
by the leaves of plants and thus circumvent fixation on the soil.
Residual contamination from fallout a year or more old would have
an insignificant effect on rate of decline during the first 150
days if the total contamination from each detonation were of the
same order of magnitude or the first less than the second.
This
was the case following the Nectar test at Belle Island, which had
residual contamination from the Mike test (1.5 years previous to
Nectar).
After approximately 150 days following fallout,
the rate of
decline becomes less than the rate of decay of mixed fission
products, reflecting the
relative concentration by the island
organisms of the long-lived isotopes C3i37 and gr90 |
Other iso-
topes, both fission products and neutron induced products, are
involved, but C3137 and sr?° with their daughters account for 80
per cent or more of the total activity in land organisms two years
following the Nectar test.
This is true even though these isotopes
together contribute only 18 per cent of the total activity from
mixed fission products at that time.
Ona basis of fission yields,
Cal37 and gr9 would contribute no more than 35 per cent of the
total activity even if all of the activity at Belle Island were
from the Mike test.
Cet44 activity 1s low (1% in crabs) in the
island organisms because of its low rate of uptake by land plants
from g011.°*
On the other hand,
in marine organisms radiocerium
does enter into the food chain in significant amounts (26%--71%
of the totel B-activity).2°776
DOE ARCHIVES
It therefore appears that in so far as the long-lived radioactive fission products strontium,
cesium and cerium are concerned
27