Reassessment of the RERF dosimetry system - overview of the new dosimetry system DS02

This paper describes a major reassessment of the system used at the Radiation Effects Research Foundation (RERF) to determine radiation doses for atomic-bomb survivors. This effort has resolved the neutron discrepancy in RERF dosimetry, and has defined the parameters for a replacement system for survivor dose calculation. A Joint US-Japan Working Group undertook a comprehensive evaluation of the calculations that comprise the RERF dosimetry system and the measurements used to verify those calculations. During the course of this reassessment, the working groups, with members from American, German and Japanese universities and national laboratories, have recomputed all of the Hiroshima and Nagasaki radiation calculations, made fast-neutron and low-background thermal-neutron measurements, upgraded the calculation of the radiation shielding provided by terrain and large buildings, and conducted a comprehensive reassessment of all radiation measurements. The new calculations produced during this reassessment agree with both gamma and neutron measurements out to distances from the detonations at which in-situ measurements become indistinguishable from background, effectively resolving the long-standing neutron dose discrepancy. The calculations that produce this agreement are the basis for the new DS02 dosimetry system. New calculations and measurements confirmed the yield and epicenter for the Nagasaki detonation while refining both these values for Hiroshima. Current measurements and calculations confirm a 21-kiloton-yield for the Nagasaki bomb and a burst point to within two meters of previous assessments. In Hiroshima, the estimated yield has been increased from 15 kt to 16 kt and the epicenter has been repositioned 20 meters higher and 15 meters to the west. While these refined parameters make the dosimetry system more accurate and users of the system more confident in the results, the calculated dose to survivors will change only about ten percent