Reevaluation of the Dosimetry System 1986 (DS86) -collection and measurements-

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The aim of this study was (1) to collect A-bomb exposed speciments, (2) to measure ^<15i>Eu and (3) to discuss the DS86 contradiction of neutron induced radioactivites ( ^<152>Eu and ^<60>Co) between the measured data and the calculation based on DS86. The collection of the A-bomb exposed materials was performed successfully. We collected 15 specimens (14 from Hiroshima and 1 from Nagasaki) within 2 km ground range. The samples within 1000 m were powdered 122 keV and 344 keV gamma rays from ^<152>Eu were measured. Those more than 1000 m were chemically concentrated and measured at Faculty of Engineering, Hiroshima University.Analysis of these data was begun by so called "benchmark test" of the MCNP code. We utilized ^<252>Cf fission neutrons at our institution and they were degraded in four materials (granite, polyethylene with B, water and ammonium chloride). In these materials thermal and fast neutrons were measured. The yield of the corresponding thermal and fast neutrons were calculated by the MCNP code and compared with the experimental results. We found good fit within 15% until 1/1000 degradation, which correspond to 1500 m ground range in Hiroshima. We are performing the transport calculation in Hiroshma using the MCNP and are almost finding the cause of DS86 contradiction. We will discuss our solution at the US-Japan joint meeting, which will be held in near future.