Internal Deposition of Iodine Isotopes Unfortunately, no direct measurement was possible on the radioactive iodine content of individuals from Roggelap. Urine samples were taken from which the average thyroid burden of I has been estimated. The Los Alamos Scientific Laboratony collected pooled 24-hour samples 15 days, gost detonation and estimated the l-day thyroid content as 11.2 uc of I USNRDL collected samples from each member of the exposed group 43 and 46 days post detonation, and, by an ingirest method, estimated the average thyroid content as 6.4 uc I at l,day.*’ The LASL estimate of 11.2 Lc was obtained by direct counting of I in the urine and should be more reliable than the NRDL estimate. The value of 11.2 uc will be used as a basis for all following considerations. This estimate was based on the assumption of 0.14% of the maximum thyroid burden being excreted in the urine on the 15th day. Variation in the biological half-life and other, factors indicate that a range of 0.05 - 0.2% should be placed on this number (see fol}towing section by Nz). We, therefore, take 5.6 - 22,4 uc as the range of adult I thyroid burden. The pooled samples represent all age groups. The number of individuals in these age groups ,ang the volume of urine from each age group is approximately as follows: *~’ Age Group <5 5 - 16 > 16 Number of Individuals Volume of Urine(ml) % of Total Volume 7 1155 4.8 11 31 4829 18011 20.1 75.0 The urine samples are typical of adults and the calculated thyroid burdens are presumably also those of adults. Associated with this 131, are the shorter lived isotopes 1320 1335 and I. If the iodine entered by way of inhalation, the time of intake was H + 6 to H+ 18. On the other hand, if water (and food) were the principal source, the time of ingestion would be extended from H + 6 to H + 5l. 135 Three items contribute to the differences in dose from the various todine isotopes. These are: (1) radioactive decay before inhalation, or oral ingestion, (2) differences in the fission yields of the chains, and (3) the average energy deposited in the, thyroid Pgs disintegration. These factors are presented in Table I for I d I. In the case of inhalation, uniform distribution in the cloud was assumed. For oral ingestion it was assumed that, on the average, 1/3 of the intake occurred at H + 10 and 2/3 at H + 30. 80