( each year; additional shots may have caused additional contamination. Hence the true “upper limit” may ex- U.S. Census (1960 and 1950). The average birth time was taken as mid-year, followed by an average delay of or lower. My presumably less reliable estimates (see ginning at the start of the calendar year immediately following the year of birth. Only the dose during infancy has been computed. However, dose calculations activity, respectively). For 1955 and 1951, I only have my estimates of 2.0 and 0.4 rads from thefission yields of 84 and 18 kilotons during the growing season (see page 561, ref.5). Comparing my approximate fission yield estimates of dose with more reliable methods suggests that the fission estimates averaged over a year of testing might be accurate within a factor of ten. Therefore, I have assigned dose ranges of 0.2-20 rads for 1955 and 0.04-4 rads for 1951. It is not my intent to deceive the reader into believing that the true doses are well established for the years 1955, 1953, 1952 and 1951. More work is needed. Mybest estimates of the average yearly thyroid doses for Utah infants are summarized in Table 1 for each year of Nevada testing. Individual doses were, of course, much higher; Knapp estimated doses of 120-440 rads for infants in St. George, Utah, following the “Harry” shot of 19 May 1953.° The dose for our highest station in 1962 was 9-26 times greater than our average.® TABLE 2 INFANT EXPOSURES BY YEAR OF BIRTH YEAR OF BIRTH 1962 1961 1960 1959 1958 1957. 1956 1955 1954. 1953 1952 1951 1950 1949 BIRTHS DURING YEAR AV. THYROID DOSE (RADS) Age Age TOTAL 0.5to0 1.5 1.5t02.5 DOSE 26,000 25,000 0.6 — 0.8 24,000 23,000 22,000 22,000 21,000 21,000 20,000 20,000 19,000 0.2 1.3 TOTAL 243,000 0.2— 20 2 ~12 3-18 0.04—4 0.6 —0.8 0.2 1.3 0.2 ~ 20 2 ~12 3-18 0.04— 4 0.6 — 0.8 0.6-0.8 0.2 1.5 1.3 0.2 ~ 20 0.2 ~ 20 2 —12 5 ~30 3 ~22 0.04— 4 AVERAGE DOSE 1.3- 10 Next I tabulate the total number of exposed Utah infants, and compute the average dose for all of them (Table 2). The yearly births were derived from the August, 1966 can easily be extended throughout childhood using the method shown in Table 2 and correcting for the in- creasing mass of the thyroid with age.* Table 2 indicates that about a quarter of a million Utah infants were exposed to fallout iodine 131, with an indicated average thyroid dose of 1.3-10 rads.** The significance of these exposures is not the size of the average dose (which is small) but in the enormous number of irradiated children. THYROID CANCERS The natural occurrence of childhood thyroid cancer is extremely low. Values from Mustacchi and Cutler indicate that by age fifteen years only 25 thyroid can- cers are expected to appear per million children.* Thus only about six “natural” childhood thyroid cancers are anticipated in the 250 thousand exposed Utah children by age fifteen. The fraction of these so called “natural” cancers which were in fact induced by medical X-rays may be appreciable. In a series of childhood thyroid cancers collected by Winship and Rosvoll, about 80 per cent showed a history of prior irradiation.’ In the United Kingdom only about three children per million develop thyroid cancer by age fifteen." X-rays can induce thyroid cancer. About 20-30 years ago, it was common in some hospitals to X-irradiate infants in the neck region for benign conditions. Thyroid cancer has followed in an unpleasantly large number of these exposed children.? Beach and Dolphin" found reports of 132 post-irradiation thyroid malignancies in the published medical literature; the additional number of unpublished cases remains unknown. They analyzed the relation between incidence and dose in 4673 exposed children for whom the individual doses were obtainable. The incidence of thyroid cancer increased with dose to 1.7 per cent at 500 rads. Assuming incidence propor- tional to dose, they derived a cumulative lifetime incidence of 35 cancers per million infants each receiving *The enlargement of the thyroid gland with age reduces its iodine 131 concentration and the resuiting radiation dose from a given intake of jodine 13]. For example, the intake of one microcurie (1,000,000 picocures) of iodine 131 gives a seventeen-rad dose to the two-gram thyroid of a one-year old infant, a 6.8-rad dose to the eight-gram thyroid of an eight-year old child, and a 1.7-rad dose to the 20-gram thyroid of an adult. Furthermore, the weight of evidence indicates that the radiation resistance of the thyroid increases with age,7 although the exact sequence of changes in sensitivity has not yet been established precisels . **°My earlier crude methods (See Ref. 5) yielded an estimated thyroid dese averaging 4.4 agreement. rads to this population. I am pleased at the DOE ARCHIVES ts page 561, ref. 5) for these average yearly exposures were 6.3 rads for 1953 (from the fission yield) and 1.6 or 3.9 rads for 1952 (from the fission yield or air beta about six months before appreciable consumption of fresh cow’s milk. Thus, exposures were regarded as be- aS ceed myso-called “higher limit.” Second, the measurements were made in Salt Lake City, not in the pasture lands; pasture contamination could have been higher