Pa OFFICIAL |US ~le ONL , | UCRL-12273 ESTIMATE OF RADIATION DOSE TO THYROIDS OF THE RONGELAP CHILDREN FOLLOWING THE BRAVO EVENT Ralph A. James Lawrence Radiation Laboratory, University of California Livermore, California December 16, 1964 General Information The cloud arrival time is given(?) as H + 4 to 6 hours. The duration of the cloud passage is less-well known but probably lies in the range of 8 ~ 16 hours. In ‘all calculations we will assume that cloud passage was in the interval H + 6 to H + 18. The residents of Rongelap were evacuated at H + 51 hours. Reliable dose rate measurements were not obtained at that time but the gamma dose rate 43 feet above the ground was measured as 375 mr/hr seven days after the deto- nation. Assuming t_ “2 decay the H + 24 hour dose rate was then ~3.8 R/hr. The sources of exposure to the thyroid which met be considered are: (1) Whole body gamma dose. | (2) Internal deposition of iodine isotopes. Whole Body Gamma Dose. The whole body dose was estimatea(?? to be 175 R. The exact method of making this estimate is not given, so an independent estimate is made below In particular, it appears that this estimate does not include the dose from the cloud but only from fallout. If we assume a linear puildup of fallout from H + 6 to KH + 18, + an Fanent -1.2 decay during this interval and usé the reading of 575 mr/hr at seven days, the estimated dose from fallout during cloud passage is 47 R. the fallout from H + 130 to evacuation at H+ 51 46 114 R. The dose from Experience from Sedan indicates that the dose from the cloud, itself, is approximately equal irl Al pion OLY wu