To apply this equation, not only must the time t of excretion relative to that of intake
be known, but also, for a radionuclide mixture, the time after detonation/release.
In
addition, the pathway may influence the body absorption fraction fy and Y(t) may be
influenced by the presence of parent radionuclides.
As mentioned above, the value of A. (D+17) is 4.0 nCi or 0.004 uCi for I-131.
For iodine, the biological parameters £, = 1.0 and F,, = -86 (References 14, 15), The
value of Y(t) is derived from Reference 16, which contains a recent retention model.
The value of Y(D+17) used is for an effectively instantaneous (relative to 17 days)
intake:
Y(D+17) = 2.87x107* uCi/day per pCi uptake.
I-131 that entered the body as I-131.
This value reflects excreted
However, at an early (shot-day) time of intake,
the parent radionuclide Te-131m (half-life of 30 hours) exists in modest abundance--
about 10 percent as much as I-131, by mass (Reference 11). Although tellurium is only
partially absorbed into the body, at least half of the Te-13lm decays prior to,
elimination from the body, and the iodine produced is fully absorbed. Therefore, up to”
about 7 percent of the excreted I-131 on D+17 could be from intake of Te-13im, With
this adjustment, Y (D+17) = 3.07x107*.
Using the values of A (D+17), fis Y(D+17), and F cited above, the amount of
the I-131 intake, Qp is 15 pCi. This value of Q is used to normalize the radionuclide
inventory.
Based on I-131 representing 0.2-0.3 percent of the total fission product
activity (Reference 11) at the estimated time of intake (discussed subsequently), the
total activity intake of fission products was about 5 to 7 mCi.
4.3.
PATHWAYS AND DOSE CONVERSION FACTORS
Researchers have arrived at various conclusions as to the dominant pathways for
exposure to the Bravo contamination.
The assumption of an inhalation pathway was
made by Cole based on a comparison of the internal and external radiation dose
estimates for the Americans on Rongerik and the natives on Rongelap (Reference 4).
Cole's basic logic was that since the ratio of the internal and external doses was
practically the same for both the Americans and the natives, the exposure pathways
must have been similar (i.e., inhalation) and not related to the personal hygiene or
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