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Long Term Activity Estimates
For The Northern Marshall Islands
This paper provides preliminary upper-bound estimates of the
residual gamma activity on the northern Marsha}] Islends due to U.S.
atmospheric testing at Bikini.
These estimates are intended to be
indicative of the activity to be determined by up-comino detziled
surveys.
Estimates are also provided for islands in the Enewetak atol}
and compared with the 1972 survey.
Finally, an analysis of wind pro-
files and fallout patterns is presented which serves to delineate those
northern Harshal] islands which were uncontaminated by fallout fron
the Bikini tests.
4.
_ APPROACH
%
After 20 years or so, the principal fission procucts of interest
are 5720 and cls? whose characteristics are summarized belov.
Isotope
sree
csi3/
Curies/kt of
Fission at H+]
Fraction of
Total Curies
110
320
2.1x107?
61x10"?
Half Life
Decay Mode
20y
30y
3 only
(100%) and
y (93%)
_ the fractional contribution of Cs 137 to the one-hour dose rate
is not the same as the fraction of total Curies at one hour since the
cs}? y energy 1s lower than that average energy for all fission products (.66 MeV vs. 2 MeV).
This results in a roentgen response for
e513? that is 0.4] times that for the inventory taken as a whole.
At
some time after burst, when cst3? is the only remaining fission product
y-emitter, the dose rate is given by
D(T) = D(1 hr) [6.1x107 7 x 0.41} (0.5)'/3°
where T is in years.
Note that beta activity is not being considered
here on the presumption that the survey techniques distinguish between
Enclosure
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