Number of Individuals Age Group <5 Volume of Urine (m1) % of Total Volume 7 1,155 4.8 5 - 16 11 4,829 20.1 >16 34 18,011 75.0 The urine samples are typical of adults and the calculated thyroid burdens are presumably also those of adults. 133 Associated with this y}3} are the shorter-lived isotopes ps2 I 3 : and p39. If the iodine entered by wayof inhalation, the time of intake was H+6-+-0H+18, On the other hand, if water (and food) were the principal source, the time of ingestion would be extended from H+ 6toH +51. Three items contribute to the differences in dose from the various iodine 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 per disintegr ition. are presented in Table I for 1139 and p35. distribution in the cloud was assumed. These factors In the case of inhalation, uniform For oral ingestion it was assumed that, on the average, one-third of the intake occurred at H + 10 and twothirds at H + 30. Table I, Ratio of doses for the two modes of intake. Inhalation Oral Ingestion p33 77131 pi85 ;7131 Decay 0.68 0.31 0.487 0,148 Energy 2.00 1,50 2.00 1.50 1.85 0.57 1.35 0.27 Fission yield® Net Factor 1.38 p93 ),131 1.23 1.38 p99 ;131 1,23 The dose to the thyroid in rads from all three isotopes is thus 3.4 times the 31 131 dose due to v ingestion. alone for inhalation and 2.6 times the I dose for oral Delay in reaching the thyroid after inhalation or ingestion would lower these factors somewhat. However, the y)32 daughter of the 78-hour Tel 3? has been neglected and would approximately compensate for decay of § 2 133 ana 1) before reaching the thyroid. | We can now proceed to estimate the dose to the thyroids of 3- to 4- year-old girls assuming (1).inhalation as the mode of intake and (2) oral ingestion. “4 |