Changes in atomic bomb survivors’ dosimetry with the new dosimetry system DS02

Cullings HM, Levenson ZB, Funamoto S, Teranishi S
Jpn J Health Phys 41(4):261-71, 2006

Summary

From 1987 through the late 1990s, thermal neutron activation measurements of materials exposed to the atomic bomb in Hiroshima appeared to show a different distance trend than estimates from dosimetry system DS86, calling into question the accuracy of DS86 and ultimately resulting in the formation of a joint US-Japan scientific working group to develop an improved system, DS02. DS02 recalculates both the source term and radiation transport using the newest methods and input data, with new estimates of explosive yield (15 kt → 16 kt) and height of detonation (580 m → 600 m) of the Hiroshima bomb, but no similar change in Nagasaki. DS02 developers evaluated new measurements in all previous categories and two new categories, made designed measurement inter-comparisons on split samples, and achieved a resolution of the apparent neutron discrepancy. DS02 free-in-air gamma kerma is about 10%>DS86 at distances>1 km where almost all survivors were located; neutron kerma ranges from about 10%>DS86 at 1 km to 15%<DS86 at 2.5 km in Hiroshima, but is <DS86 by 15% or more at all distances in Nagasaki. DS02 neutrons are less energetic than DS86 overall in both cities, resulting in slightly decreased transmission factors, particularly for body self-shielding of deeper organs. Shielding modules were also updated for DS02, resulting in fairly large changes in estimated shielding for some individuals but little change in averages except for the effect of Kompira-san on a large group at distances >2 km in Nagasaki. Average changes in shielded kerma and representative organ doses vs. distance are reviewed, concluding with a discussion of plans to improve dosimetry implementation at the Radiation Effects Research Foundation (RERF) by using tools such as the Geographical Information System (GIS).