160 Health Physics Estimation of acute intake by adults of ‘I at Rongelap, Ailinginae, and Rongerik following the Bravo test. The estimation of '*'I intake by the highly exposed populationsin this work, as well as previously in Lessard et al. (1985) and NCI (2004), was based on bioassay measurements of urine samples collected within 19 d of the Bravo test originally reported by Harris (1954) and described more fully in Harris et al. (2010). The bioassay data provided direct empirical evidence of the internal contamination following the event to a subset of the Marshall Islands population. Becauseof the lack of detailed information on the pathways of the acute intakes, the bioassay data were used as the basis for estimating intakes to adults at all atolls. The basic calculation to estimate the average intake of '*'T amongthe adults from whom a 24-h urine sample wascollected, is shown in eqn (1): O — CRXKXV EF) X60" () where August 2010, Volume 99, Number 2 considered, and (3) a relationship between intake by adults and ground deposition density for any radionuclide following the Bravotest. (1) Time-of-intake (TOI). It is assumed in this work that the acute intake at Rongelap following the Bravo test took place during the period of time that the fallout was being deposited. As a general rule of thumb, based on Nevada Test Site (NTS) fallout data (Quinn 1990), the duration of fallout is approximately equal to the TOA (h). While intake might occur at various times within that period, we made the simplifying assumption that the entire acute intake occurred slightly before midway in the period of deposition, i.e., TO] = TOA + (0.4 X TOA) = 1.4 & TOA. Selection of a point in time less than halfway during the period of fallout is appropriate as a central estimate since the rate of fallout deposition generally decreases with time. The estimated TOA at Rongelap for Bravo was 6 h post-detonation (Beck et al. 2010); the corresponding TOI, rounded to one significant figure, is estimated to be 8 h. Q =acute intake of '*'] intake (Bq, group average); CR =background adjusted count rate of '*'I per mL of urine (c s ' mL’); K =correction factor corresponding to the ra- dioactive decay of ''I between time of sampling and time of counting; V =24-h urine volume (mL) averaged over sampled population; EF(t) = urinary excretion fraction for '*'I on day of sampling; and Ec = gammadetector counting efficiency (count per decay). The calculation of radionuclide intakes for this study via eqn (1) depends on having relevant data for the Marshallese population. The data usedin our calculations to determine the values of the acute intakes of '"'I are described in the Appendix. Estimation of acute intakes by adults of radionu- clides other than "I at Rongelap, Ailinginae, and Rongerik following the Bravo test. Our estimates of the acute intake of radionuclides other than '*'I by adults are based on: (1) an estimate of the time-of-intake (TOD, which is important for short-lived radionuclides due to the rapid change of their activity with time after the detonation, where TOIis derived from the corresponding value at the fallout time-of-arrival (TOA in h, provided in Beck et al. 2010), (2) the calculation of the ground deposition density (Bq m°) at TOI of the radionuclides (2) Ground deposition density at TOI. In this work, as in Beck et al. (2010), the model and data reported by Hicks (1982, 1984) to describe the variation of the relative ground deposition densities of all radio- nuclides deposited in the fallout with time, ¢, after the detonation, were used to estimate the ground deposition densities at Rongelap, Ailinginae, and Rongerik at the TOIs following the Bravo test. The data of Hicks, termed here as normalized deposition factors or ND factors, relate the ground deposition density of each radionuclide at time ¢ to the activity of a reference radionuclide at somereference time. In this work, we have chosen to use '"Cs activity at 12 h post-detonation as the reference radionuclide and reference time to be consistent with the deposition results discussed in Beck et al. (2010) where it is shown that using '’Cs as the reference allows comparisons of estimated deposition with contemporary soul analyses to validate the fallout estimates. Since the intakesof all radionuclides are based onthe intake of '*'1 at Rongelap, this requires use of the normalized deposi- tion of '*'I relative to '’Cs as indicated below in eqn(2). Hicks (1984) developed the nuclide-specific ND factors only at specific times post-detonation and for a limited set of fractionation ratios. For the purposes ofthis work,it was necessary to estimate the ND factors at times intermediate to the values Hicks provided (i.e., ~8 h for Rongelap, ~6 h for Ailinginae, and ~11 h for Rongerik). Using '°’Csas the reference radionuclide for ND simplifies the interpolation over ¢ since '*’Cs activity varieslittle with TOA,due to the long half-life of the radionuclide.