A crack model of the Hiroshima atomic bomb: explanation of the contradiction of "Dosimetry system 1986"

Prospects and status of the dosimetry system for atomic bomb survivor cohort study conducted at Research Institute for Radiation Biology and Medicine of Hiroshima University

The Research Institute for Radiation Biology and Medicine (RIRBM) of Hiroshima University has been conducting a cohort study of atomic bomb survivors (ABS). Cohort members include those who were issued an Atomic Bomb Health Handbook from the Hiroshima local government. A series of dosimetry systems for the ABS were developed at RIRBM to evaluate the health effects associated with radiation exposure. The framework used to estimate individual doses in our dosimetry systems for ABS is mainly based on the Dosimetry System 86, and its revisions developed by the Radiation Effect Research Foundation. This article describes the design and computational principles for the dosimetry systems in RIRBM and the history of the revisions, from the first version of the system, ABS93D, to the most recent version, ABS16D. We then provide a perspective for further improvement and application of the dosimetry system.

Intercomparison study on (152)Eu gamma ray and (36)Cl AMS measurements for development of the new Hiroshima-Nagasaki Atomic Bomb Dosimetry System 2002 (DS02)

In the process of developing a new dosimetry system for atomic bomb survivors in Hiroshima and Nagasaki (DS02), an intercomparison study between (152)Eu and (36)Cl measurements was proposed, to reconcile the discrepancy previously observed in the Hiroshima data between measurements and calculations of thermal neutron activation products. Nine granite samples, exposed to the atomic-bomb radiation in Hiroshima within 1,200 m of the hypocenter, as well as mixed standard solutions containing known amounts of europium and chlorine that were neutron-activated by a (252)Cf source, were used for the intercomparison. Gamma-ray spectrometry for (152)Eu was carried out with ultra low-background Ge detectors at the Ogoya Underground Laboratory, Kanazawa University, while three laboratories participated in the (36)Cl measurement using accelerator mass spectrometry (AMS): The Technical University of Munich, Germany, the Lawrence Livermore National Laboratory, USA and the University of Tsukuba, Japan. Measured values for the mixed standard solutions showed good agreement among the participant laboratories. They also agreed well with activation calculations, using the neutron fluences monitored during the (252)Cf irradiation, and the corresponding activation cross-sections taken from the JENDL-3.3 library. The measured-to-calculated ratios obtained were 1.02 for (152)Eu and 0.91-1.02 for (36)Cl, respectively. Similarly, the results of the granite intercomparison indicated good agreement with the DS02 calculation for these samples. An average measured-to-calculated ratio of 0.98 was obtained for all granite intercomparison measurements. The so-called neutron discrepancy that was previously observed and that which included increasing measured-to-calculated ratios for thermal neutron activation products for increasing distances beyond 1,000 m from the hypocenter was not seen in the results of the intercomparison study. The previously claimed discrepancy could be explained by insufficient understanding of the measured data.

Reassessment of the cancer mortality risk among Hiroshima atomic-bomb survivors using a new dosimetry system, ABS2000D, compared with ABS93D

The aim of the present study was to examine the excess relative risk for leukemia mortality and all cancers, except leukemia, among Hiroshima atomic-bomb survivors by applying ABS93D and ABS2000D. Particular attention was given to any difference in the neutron-dose estimates between the two dosimetry systems. The study subjects were 51,532 atomic-bomb survivors registered in a database of the Research Institute for Radiation Biology and Medicine of Hiroshima University (RIRBM). The results obtained by both dosimetry systems are similar: the excess relative risk per Sv for leukemia mortality and all cancers except leukemia is significantly higher compared to the control group. In addition, the difference in the excess relative risks between the two systems is not significant. Therefore, it is indicated that a modification of the neutron-dose estimates would not markedly change the conclusions about the cancer mortality risk.