Talk #73, 7/11/12

“Fallout Deposition in Hiroshima”
Where Gamma-Ray TLD Measurements Exceed the Dosimetry System (DS02)

Stephen Egbert

Senior Scientist – SAIC

In certain Hiroshima neighborhoods, radiation measurements using thermoluminescence dosimetry (TLD) exceed what can be explained by the initial gamma-ray doses and uncertainties from the Dosimetry System 2002 (DS02). The ratio between TLD measurements and DS02 dose calculations for gamma rays grows slowly larger than unity with increasing ground range, but closer examination shows the excess TLD dose (0.1, 0.2, or possibly up to 0.8 gray) is correlated with certain neighborhoods, possibly due to radioactive fallout. At Nagasaki, the TLD measurements do not show this same excess. If the excess TLD doses at Hiroshima are an indication of fallout, it may be possible for TLD studies to make better estimates of the locations and radiation doses to survivors from the fallout after the bombings at both cities. In the future more proximal and distal TLD measurements may help locate and confirm neighborhoods having significant residual radiation. The excess TLD dose locations and magnitudes can be compared with other physical or biological indicators of fallout. Identification of materials containing contributing radioisotopes is important. Mechanisms for fallout dispersal can explain this observation. The effect of adding residual dose to the DS02 dosimetry will be discussed, specifically for the cancer risk factors and acute effect thresholds used throughout the world. DS02 is the current dosimetry system for the atomic-bomb survivors at the Radiation Effects Research Foundation (RERF) in Hiroshima and Nagasaki. A previous Lyncean Group presentation about the development of DS02 by SAIC can be found on “Japanese A-Bomb Dosimetry Project: Personal Recollections” by Dean Kaul given on May 14, 2008 in a_bomb_dosimetry.ppt. This new presentation begins with a closer examination of the “apparent” agreement in gamma-ray dose that was shown on slide #48. A distinct geographic pattern of residual radiation over Hiroshima will be shown.This topic will also be discussed at the DOE-sponsored special session and an all-day workshop, during the week of July 24 and 25, 2012, at the annual Health Physics Society meeting in Sacramento, CA.


The following is a link to the PowerPoint presentation