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The contribution from the decay of each radioiodine nuclide to thy-
roid absorbed dose was dependent upon the time post-detonation and upon the
fractionation of the isobaric chains giving rise to the radioiodines. Both factors influenced our estimate of thyroid absorbed dose. James assumed theoretical fission yields and that one third the ingestion intake occurred at ten hours
and two thirds at 30 hours post-detonation. We assumed Bikini ash fractionation
and that one third the ingestion intake occurred at 5.5 hours (lunch) and two
thirds ac 12 hours (dinner) post-detonation. James considered only
ly, 1337,
and 1351 in the thyroid-dose estimate. We considered all likely iodine and
‘tellurium nuclides. Additionally, James adjusted the thyroid dose downward to
10.5 gray (1050 rad) for a 3.5-year-old to account for the possibility that part
of the intake was due to inhalation. We considered inhalation intake to be insignificant relative to ingestion intake and compared the James ingestion esti. Mate to our ingestion estimate.
c. Maximum Thyroid Absorbed Dose. We used several methods to estimate
a range of fallout material ingested. One was to ingest known quantities of pharmaceutical-grade CaCO3 with meals and subjectively arrive at descriptions of
taste similar to those given by the Rongelap people at the time of evacuation in
March 1954. A group of five adult white males at BNL reported that 200 mg of
CaC0O3 could not be sensed by taste when mixed with food. Another method was to
assume that the range of weights associated with the contents of the stomach in
cases of sudden death corresponded to the range of uctivity intake (Ev66}.
This
range - 0 to 380 g, mean 82 g - implies a maximum intake of about 5 times the
mean value. Another method was to examine the range of 137¢s daily activity intake estimated from 1957 to 1983 for Rongelap and Utirik people (Le84). The intake rate was estimated from whole-body counting results. The range of 137¢ intake rate was about 5 times the mean value. Another method was to examine the
range of !37cg body burden exhibited by the population inhabiting Bikini Island
me
from 1974 to 1978 (Mi83). The range was about 3.2 times che mean value. From
the above range values, we assumed a value of 4 times the intake and thus 4
times the mean thyroid absorbed dose for estimates made here (see Table 23).
d. External Sources of Thyroid
estimates were based on integrated. photon
justment for Living pattern in a variable
tail about the adjustment can be found in
Dose. External thyroid absorbed dose
exposure given previously and on an adexposure-rate environment. Further de(Na80) and (Le84).
Some questions about the external beta radiation penetrating to
the depth of the thyroid were expressed by Cronkite (Cr81). The thickness of
tissue overlying the thyroid ranges from 0.4 to 2.0 cm, average 0.82 cm, and
does not correlate well with age or body weight (ICRP74). A minimum beta energy
of 1.8 MeV was estimated by us for penetration of 0.82 cm of tissue. At
Rongelap Island, about 70% of the population had skin lesions on some part of
the neck.
The lesions appeared initially about 21 days post-exposure (Cr56).
br ———— —_______-
This would imply a skin surface dose of tens of gray (several thousand rad).
Only a small percent of the beta flux was above 1.8 MeV in kinetic energy. Of
this higher energy flux, only a small fraction would: penetrate 0.82 cm of tissue
and deposit energy in the thyroid. Thus, we considered thyroid dose from this
pathway to be insignificant.
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