from July 8 meas- urement.) t = 27 days (May19June 15) Ay = 0.0866 day7! Ao-= 0.0204 day'* Thus 0.37 = feo fen'0.0868,27 gy itl.107)27 0.0204 Ro = 0.189 pe/gram/day. Now we determine the infinity [') dose using Eq. 2. EXAMPLE: Human Inhalation On May 19, 1953 the highest concentration of activity in the air due to fallout that has ever been recorded in the U. S., outside the Nevada Test Site, occurred at St. George, Utah. It amounted to about 1.3 yue/m?® averaged over 24 hours. The total radiation dose to the thyroids of the people at St. George from inhalation of the isotopes of I is estimated to be 0.302 rep as shown in the following tabular calculation. Estimate of Radiation Doses to Thyroid of Humans From Inhalation Din = K/XAe + Ap) where: A = 55 Rofl = 58(0.189)(0.2) = 2.08 Thus Di. = 224 reps is the infinity [! dose. To estimate the dose from shortlived isotopes of I enter Fig. 3 with these parameters: start of intake = 3.5 hr duration of intake = infinity. The graph indicates 2 ratio of approximately 0.45. But this is uncorrected for biological decay, 1.e., it is based on the assump- tion that the biological decay constant for the thyroid is significantly less than the physical decay constant. It is necessary to correct this ratio by Time Average Fissionproduct Fraction after defanahian far} fisstonproduct activity (uc; meter?) activity originally retained (ue) of fission product that tg [131b w% F131 aetivity reaching thyroid (malliuc) Infinity I31 dose to thyroid (rep) 2-7 7-10 10-14 14-18 18-30 4.0 2.9 0.62 0.043 0.014 12.4 4.3 1.56 0.104 0.105 0.16 0.35 0.47 0:7 1.1 5.00 O.t7 1.80 0.19 0.29 0.0304 0.0230 0.0110 0.0012 0.0018 Added dose fram shortlaved I Total tsolopest infinity dose (rep) (rep) 0.121 0.074 0.030 0.003 0.003 0.155 0.097 0.041 0.004 0.005 Tota 0.302 rep * Based on 0.83-meter?/hr air intake and assuming that 75% of the activity will be initially retained either in the lungs or find its way into the gastrointestinal tract. » Based on assumption that 75% of initial intake of both Te precursors of I?#! will remain within body until decayed to J™!. © Assuming 25% of initial retention of I'%! (either in lungs or gastrointestinal traet) reaches the thyroid. @ Tnitial dose rate (53) (0.2) (uc of I'! per gramof tissuc) in reps per day. Infinite dose = Initial dose rates (A, + Aa). é From Fig. 1. Multiply these ratios by (A, -+ An} /Ay for [8! in man. multiplying by the factort (A, $ An) Ap = 1.24. 0.45 & 1.24 = 0.557 The infinity cose to the thyroid from short-lived isotopes of iodine is this fraction of the [! slose 224 & 0.557 = 125 rep. Thus the total infinite dose is 22-4 — 125 350 rep. This is not considered dangerous. Experimental studies with sheep at Hanford Atomie Products Operation suggest that about 16.000 reps are required to produce minimal changes in the thyroid cellular structure and about 50,000 reps to produce definite ceil damage and hypothyroidism. BIBLIOGRAPHY 1. H. F. Hunter, N. E. Ballou, Necueonics 9, No. 5, C-2 (1951) 2. J. B. Stanbury, et al. “Endemie Goiter.” Harvard University Monograph in Medicine and Public Health No. 12 (Harvard University Press, 1954} 3. L. Van Middlesworth, NucLeonics 12, No. © (1954) 4. H. Kornberg, private communication (1953) * Biological half-life in sheep thyroids is about 34 days (4). {+ See footnote 6 Table 2. Vol. 14, No. 2 - February, 1956 TABLE 3—Sample Calculations for Figure 3 { Periods of antake (hours after delonation) B Cc Relatire mean (7) energy intake X Cumulative haurs tn pertud’ £13 energy intake D Mean of ratias of enerqies [Short Jisis E F G Relative energy [Short Cumulative [Short Ratio of total energies fFSeore 7131 for infinite thyroid dose intake fram ist hour to end of pervod BX D) intake (Column F + Cy (Columns energies indicated 1-11 11-21 21-31 31-41 41-51 31-61 61-71 160 158 150 146 140 135 130 160 318 168 614 jot 889 1,019 3.6 2.3 1.6 1.3 1.0 0,84 0.70 519 364 240 190 140 115 91 OTe 934 1,179 1,364 1,504 1,624 Lila 3.6 2.93 2.32 2.23 2.0 1.88 1.68 71-8] 125 1,144 0.55 69 1,784 1,56 81-91 “1-101 101-201 120 lla 920 1,264 1,879 2,209 Q.46 0,40 0.20 55 46 184 1,839 1,884 2,000 1,45 1.37 O.400 201-501 301 - 101 650 470 2.049 5,419 0.08 0.042 a2 14 2,121 2,140 O17 1S 0.626 601-801 280) 4,209 0.0005 3 2,155 0.500 401-601 $01 -1,001 600 140 4,019 4.489 0.02 0.005 12 1 2,152 2.13 0.980 0.484 ‘ Based on Fig. 2. >From Fig. 1. ¢ This is uncorrected for biological decay as described in footnote 4 Table 1. For cases where biological decay in the thyroid is significant for 1°3', multiply last column G by the factor (A, + A) /Ay. 41