RETURN OF RONGELAPESE according to the external gamma dose rate and the amount of strontium—90. ht? co cz Ci The external gammadose rates at three feet above the ground on the Island of Rongelap are shown in Graph I. It would be expected that this curve would flatten out with time due to the dominance of the ceslum—-137 with its half-life of 27 years. The latest survey of the Rongelap Island at the end of July 1956 showed a range of valucs from 0.2-0.5 milliroentgen per hour, with an average of 0.4 mr/hr. However, the graph suggests an anticipated dose rate at the July 1956 survey of about 0.1 mrfhr. The higher value found is undoubtedly due to the small additional fallout that occurred during Operation Redwing. Since this was relatively fresh radioactive material, the decay should be more rapid so that the dose rates on Rongelap Island at the time of repatriation should be less than 30 muilliroentgens/week. The maximum permissible external gamma exposure to adult workers recommended by the National (U. 8.) Committee on Radiation Protection is 0.3 rems/week with an added restriction that the maximum permissible accumulated dose in rems, at any age is equal to five times the number of years beyond age 18, provided no annual increment exceeds 15 rem. (This applies to all critical organs except the skin, for which the value is double.) The maximum permissible exposure for the population as a whole from all sources of radiation, including medical and other man-made sources, and background shall not exceed 14 million rem per million of population over the period from conception up to age 30, and one-third that amount in each decade thereafter. It is difficult to extrapolate precisely far into the future, but the data suggest that the gamma doses on Rongelap Island would not greatly exceed (if at all) 0.5 roentgens for the first year of reoccupancy, with lesser doses in subsequent years, plus some additional whole body dose cn —— ge TE rere a 1. ExtrernaLt Gamma Doss RatTEs ON RonceLap ATOLL 49 from internally deposited cesium-137.* The gamma dose rates on other island of Rongelap Atoll have not been followed as closely as on Rongelap but the data suggest the relative dose rates now are the same as measured in thefirst part of March 1954; i. e., the highest activity on anyisland is about a factor of 12 higher than Rongelap. The Rongelapese go on fishing expeditions to otherislands, including those showing both higher and lower activity. However, these Rongelapese spend an appreciable part of their time in boats over water where the external gamma activity is near background values. Thus, the yearly average for these probably would not differ greatly from those on Rongelap Island. 2. STRONTIUM—90 a. Food Supply ‘The basic data on the normal food supply of the Rongelapese are contained in Table 48. There are wide variances in the data so that estimated average values are used. This is not an unreasonable approach since it would be expected that the food actually consumed would be about as variable as the individual samples collected for analysis. As will be seen below, these estimates could be in error by a factor of several without changing the conclusion. The isotope of principal concern in the food chain is strontium-90. For an adult worker the maintained maximum permissible body burden is 1,000 Sunshine Units (1,000 micromicrocuries of Sr® per gram of calcium). Values for maximum permissible exposures to the general population are 1/10 that for adult workers, or 100 Sunshine Units, maintained level in the body. The National (U. 5.) Academy of Sciences report stated, “. There seems no reason to hesitate to allow a universal human strontium—burden of 1/10 of the permissible . .” for adult workers. This corresponds to the 100 Sunshine Units. *Gamma dose rates at three feet above the ground on the Island of Rongelap in June 1957 were as follows: Highest reading 0.13 mrfhr Lowest reading 0.01 mr/hr Average reading 0.03 mrfhr