SECTION3 TECHNICAL APPROACH--EXTERNAL DOSE 3.1 DOSE CALCULATIONS. In order to calculate the radiation dose (i.e., dose equivalent) to personnel on Rongerik from the Shot Bravo fallout, the free-field radiation environment must be specified mathematically. Further, the calculated doses are dependent on any protection or shielding that was provided by buildings in which they stayed until they were evacuated. (1) Free-Field Radiation on Rongerik Based on the available data, the free-field radiation environment on Rongerik is estimated as follows: For times greater than 48 hours after burst, the radiation decay followed a ple decay rate. From the radiation intensity of 0.28 R/hr measured on Rongerik on 10 / March (about 216 hours after burst), the intensity at 48 hours after burst (1,9) is: Ig =7 Lope (216/48) 1.5 = 2.67 R/hr (1) Similarly, from Ing and the radiation decay according to t 0.315 between 10 and 48 hours after detonation, the intensity after cessation of fallout through the time of evacuation is: ¢ . During fallout deposition, this decay applies to landed fallout particles (the change in decay exponent at 10 hours is too early in the deposition to noticeably affect the calculations). Thus, it is necessary to determine the fraction of time-normalized activity (or mass, for constant specific activity) deposited with time. This deposition is assumed to occur as a Gaussian (normal) distribution in time, reflecting a similar Jt