of the analog.
Estimates of the_potential dose to the thyroid from ingestion of I-131
contaminated cow's milk are made utilizing an empirical relationship
between gamma fallout ficld intensities and T-131 peak concentration in
cow's milk developed by Knapp (6),
Knapp found that after a sincle dry
deposition of radioactive fallout on pastureland the level of I-131 in
the fresh milk of dairy cattle reached a maximum value within 4 days and
thereafter decreased exponentially with a half reduction time of about
5 days.
The maximum level of I-131 in the fresh milk, L,,, was related
to the external gamma radiation level by the relation
Trax = (26,000%) to (96,000%) pei/2
where Y% is the open field, external gamna dose rate at 3 feet above the
' ground surface, 24 hours following detonation, expressed in mr/hr.
Further,
child consumes 1 liter of contaminated cow's milk per day, the fraction
of ingested I-131 reaching the thyroid is 0.3, and the half reduction
time of I-131 in fresh milk is 5 days, Knapp provides the following relation
between the maximum I-131 level in the milk and the dose to the thyroid
we ee
ad
wre eR eh oh BRALtt
by assuming the mass of the thyroid to be 2 grams (1 year old child), the
D = (1.71 x 1074) Inax rads
Thus, if Tix lies in the range of (26,000 %) to (96,0007) then
D = (4.4%) to (16.4 99) rade
|
Since the gamma exposure rate at H+1 hour, rather than at H+24 hours, is
normally obtained in the scaling technique, the above equations have been
’
modified, assuming a t71-2 decay dependence, to the following