wy
410527
Long Term Activity Estimates
For The Northern Marshall Islands
This paper provides preliminary upper-bound estimates of the
residual gamma activity on the northern Marshal) Islands due to U.S.
atmospheric testing at Bikini.
These estimates are intended to be
indicative of the activity to be determined by up-comine deteiled
surveys.
Estimates are also provided for istands in the Enewetek ato?
and compared with the 1972 survey.
Finally, an analysis of wind pro-
files and fallout patterns is presented which serves to delineate those
northern Marshall islands which were uncontaminated by fallout froz
the Bikini tests.
1
"APPROACH
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.
After 20 years or so, the principal fission products of interest
are 5790 and csi3? whose characteristics are summarized belov.
Isotope
$790
e529?
Curies/kt of
Fraction of
Fission at H+l
Total Curies
110
2.1x1077
- 329
6.1x1077
kelf Life
_ Decay Mode
29y
B only
30y
(1005) and
¥ (932)
The fractional contribution of cs29? to the one-hour dose rate
fis not the same as the fraction of total Curies at one hour since the
cs}3? y energy is lower than that average energy for all fission products (.66 MeV vs. 2 MeV).
This results in a roentgen response for
cs}?? that is 0.4] times that for the inventory taken as a whole.
At
some time after burst, when cs9? is the only remaining fission product
Yoemitter, the dose rate is given by
DOE ARCHIVES
D(T) © B(1 mr) [6.1x20"7 x 0.42) (0.5)!/30
where T is in years.
Wote that beta activity is not being considered
here on the presumption that the survey techniques distinguish between
Enclosure
(2)
77