Retrospective Gamma Dosimetry in Hiroshima and Nagasaki
2006 Volume 32 Issue 3 Pages 168-182
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2006 Volume 32 Issue 3 Pages 168-182
The radiation doses of the atomic bomb survivors of Hiroshima and Nagasaki has been a subject of great importance for several decades, whose estimated dose depends on it, and second to all the peoples of the world, because estimates of radiation cancer risks are based mainly on the studies of the survivors. The T65D (tentative 1965 dose) was built using the BREN (Bared Reactor Experiment Nevada) reactor by the Oak Ridge National Laboratory. At that time, in Japan, the National Institute of Radiological Sciences (NIRS) group determined neutron doses using the 60Co activities induced in iron bars in some concrete buildings. the Nara University of Education (NEU) and the NIRS independently estimated gamma doses within about 1km from the hypocenter in both cities using a thermoluminescence (TL) dosimetry technique of quartz samples prepared from building materials (bricks, tiles etc.) exposed to the atomic bombs.
For neutrons and gamma rays, the Japanese data were considerably good agreement with the T65D. However, in 1980, Loewe and Mendelthsohn pointed out some differences between the T65D and their calculation data based on the recommended spectra by Preeg in the Los Alamos Scientific Laboratory. The US-Japan Joint Workshop for Reassessment of A-bomb Radiation Dosimetry in Hiroshima and Nagasaki, for shortly US-Japan Joint Workshop was established, and then the reassessment of the A-bomb radiation jointly conducted by Japan and the United States is fundamental issue of vital importance to many fields of science and has attracted much attention internationally.
Fortunately, since around 1975, the TL apparatuses became commercially available in the world. In the field of archaeology, the TL dosimetry of quartz was mostly developed for the dating of potteries and others. So that, since 1980, various TL techniques such as the quartz inclusion and the predose techniques were available for the DS86 and DS02. In the DS86, the intercomparison of TL dosimetry was carried out among two British groups, one US group and two Japanese groups. On the DS86 and DS02, gamma doses (up to about 2km from the hypocenter*) by the Japanese TL dosimetry were considerably good agreements with the calculated data by the US group.
*BG contribution mostly from natural radioactivity in brick and tile samples.
