My’ DE ue bday Ue d cnn + LAOEE Se Cae. Rares LOSide Soe a ao in those areas where the amountof fallout was high, i.e., possi- bly over 75 roentgens whole body dose from the gamma radia- — tion with most of this exposure occurring in thefirst few days. Thus, the potential hazard of skin burns may be essentially eliminated by meeting the criteria of an acceptable whole body exposure. Of course, by evacuation from a highly contaminated area it is possible to reduce drastically whole body ex- posure, yet a relatively high skin dose could accumulate if the fallout materials were not removed early. D. IODINE 131 Background Information Approximately 0.15 million curie (a “curie” corresponds to 2.2 million million disintegrations of nuclei per minute) of iodine 131 are produced for each kiloton TNT equivalent of energy released by fission. For large yield airbursts most of the iodine 131 along with other radioactive materials will be swept into the upper atmosphere(stratosphere) and, since iodine 131 has a half-life of only eight days, a large part of its activity will decay before being deposited on the earth. On the other hand, iodine 131 that remains in the lower atmosphere, the troposphere, will be deposited relatively quickly and can enter the food chain. Milk is the principal route of entry of iodine 131 into the human body whereit is selectively deposited in the thyroid gland. The assumption is usually made that 30 percent of iodine 131 ingested by humans is deposited in the thyroid no matter whatthesize of this organ may be.’ Thus, an infant’s thyroid gland of about two grams weight would receive 10 times more radiation dose than the 20 gram adult’s thyroid for the same amount of iodine 131 ingested. For this reason calculations of radiation doses from iodine 131 for the general population are based on those for the infant rather than the adult. Direct measurements of iodine 131 in milk were not made around the Nevada Test Site during earlier times of testing since it was the consensus of scientists within and outside the AEC and Governmentat that time that the limiting factor was the potential external whole body exposure. It is now recog- nized that there can be situations where the iodine 181 exposure can be more limiting. An example of this was the Smallboy surface shot on July 14, 1962 at the Nevada Test Site. The detonation was large enough to producesignificant quantities of iodine 131 but due to its low energy yield the activity was not swept to high altitudes to be carried away, cr 7 Co a a, en ib “745-413 O-64—3 11