154 Health Physics primarily from cosmic radiation, since the concentrations of *8U, “K, and *’Th in the coral soils is very low (Robison et al. 1997). This can be compared to the highest annual dose received in Majuro from fallout of 8 mGy in 1954 and annual doses on the order of 3-5 pGy after testing in the Marshall Islands ended (Fig. 5). External doses from atmospheric tests conducted at the NTS from 1951-1958 that were received by Americans (in this example, outdoor workers who lived in towns in Nevada and SW Utah) ranged from about 0.03 to 40 mGy (Henderson and Smale 1990). Because of shielding when indoors, the NTS doses were smaller for persons who spent much oftheir time indoors. uncertainties, that the exposure was delivered only during the year of the test. During that year: : X/E12 _ 10 a ny (AnXTOA) 5 |e n=1 | __ 10 a ne LAn(EOY — HD] 5 |e } n=1 (5) where a, and A,, with n varying from 1 to 10, are the parameters of the fit to Hicks’ calculated exposurerates vs. time (Hicks 1981, 1984), TOA, in hours, is the estimated time of arrival of fallout counted from the time of the test, H, and (EOY—H) is the time elapsed between the time of the test and the end of the year (EOY). As previously indicated, the exposure, X, is very Uncertainty Uncertainties in the total dose received by each population group in each year from all tests in that year were derived relying, primarily, on the uncertainty of available measurements of exposure rates and of deposition densities of long-lived radionuclides. For a given test 7 and a givenatoll j, the external dose to permanent residents of age a, D, in mGy, can be expressed as: soy August 2010, Volume 99, Number 2 12; DA, j) =E . X(i, j) wax aae| * (F2 X x [> , where E12(i, j) =the exposure rate at H+12 (mR h')following test 7 at atoll j; X(i, j) =the lifetime exposure (mR) duetotest i at atoll 7; and D,,/X =the conversion factor from exposure to dose for adults (mGy mR'). The uncertainties were assessed to be as follows: e £12: as discussed in Beck et al. (2010), an uncer- tainty estimate was assigned to each estimate of E12 as inferred from the available measurement data. These uncertainties, expressed in terms of geometric standard deviations (GSDs), range from 1.3 to 3.0, depending on the availability, quality, and number of measurements of exposure rates and long-lived radionuclides at the atoll for the test under consid- eration; and e X/E12: because the exposure, X, is delivered over a number of years, at a rate that is relatively high during the year of the test and much smaller during the following years, the simplifying assumption was made, for the purposes of the evaluation of the sensitive to TOA (Table 2), while the uncertainty in the values of a, and A, is assumed to berelatively minor compared to the uncertainty due to TOA. Also, as shown in Fig. 1, regression fit parameters vary little from one test to another. For that reason, we assumed that TOA is the parameter in eqn (5), which is uncertain to any significant degree. In our simulations, the uncertainty distribution for TOA forall atolls and all tests was taken to be uniform between 0.8 and 1.2 times the nominal values given in Table 6 of Beck et al. (2010): e D,,/X: its nominal value of 6.6 X 10° mGy mR|! is based on the calculations of Jacob et al. (1990) and on the recommendations of ICRP (1996). The value of D,,/X depends on the geometry of irradiation, on the energy spectrum of the incident y-rays, and on the tissue or organ that is considered. In our analysis, the same nominal value is taken to apply to all organs and tissues of the body. The uncertainty distribution of D,,/X 1s taken to be uniform between 0.9 and 1.1 times the nominal value and to mainly reflect differences between the doses to various organsandtissues of the body for exposures to y-rays of a few hundred keV characteristic of fallout; and e D,/D,, 18 the ratio of the external dose to children of age a to adults. Its nominal value is 1.3 for young children (less than 3 y of age) and 1.2 for older children. Here, the uncertainty distribution, which is assumed to be uniform between 0.9 and 1.1 times the nominal value, reflects the relatively large range of ages to which the nominal value applies. The uncertainty estimates for individual tests were derived via Monte Carlo simulation to obtain an estimate of uncertainty for the total external dose received in each calendar year from all tests in that year. Results are presented in Table 7 in terms of GSD for representative persons (both adults and children) of four communities (Kwajalein residents, Majuro residents, the Rongelap Island