Residual 152Eu and 60Co Activities Induced by Neutrons from the Hiroshima Atomic Bomb

Abstract

Specific activities of 152Eu:Eu in stone samples exposed to the Hiroshima atomic bomb were determined for 70 samples up to a 1,500-m slant range from the epicenter. The specific activities of 60Co:Co were also determined for six samples near the Hiroshima hypocenter. First, the 152Eu data were investigated to find out the directional dependence of neutron activation. Directional anisotropy was not definite; however, there was an indication that the activation in the west-southwest was lower than in other directions. Second, measured 152Eu and 60Co radioactivity data were compared with activation calculations based on DS86 neutrons. It is clearly shown that the measured data are lower than the calculation near the hypocenter and vice versa at long distances beyond 1,000 m. The calculated-to-measured ratios of 152Eu are 1.6 at the hypocenter, 1.0 at approximately 900 m, and 0.05 at a 1,500-m slant range. Present results indicate that systematic errors exist in the DS86 neutrons concerning the source-term spectrum, neutron transport calculations in air, and/or activation measurements.

36Cl measurements in hiroshima granite samples as part of an international intercomparison study

“…This difference has been termed the "Hiroshima -~ 10.0 thermal neutron discrepancy". As indicated above, the o ~ radionuclides 152Eu and 6~ were assessed independently by Japanese teams, by means of gamma spectroscopy, and _-3 1.0 O9 the results were in apparent agreement with those obtained for 36C1, for large distances from the epicenter in Hiroshima [6,8,9,10,11,19,21,23,24,25,26,27] ( Fig. 1).…”

Mapping the Distribution of 90Sr in Teeth with a Photostimulable Phosphor Imaging Detector

“…(18)] at distances from the hypocenter where people could survive, and these results were in close agreement with calculated values in the investigated samples. In addition, new measurements of thermal-neutron-induced 36 Cl also showed a reasonable agreement with the DS02 calculations (19)(20)(21)(22)(23)(24), even at distances beyond 1,000 m from the hypocenter where previous studies found poor agreement with neutron transport calculations (25,26).…”

Measurements of 152Eu/Eu ratios in surfaces of rock samples near the hypocenter of the Hiroshima atomic bomb

“…Filled circles indicate the ratios measured by Komura, et al 3) . Filled and open squares indicate the ratios measured by Shizuma, et al 4,5) . Filled triangles indicate the ratios measured by Nakanishi et al 6) .…”

“…Because of the long life (13.537 y) 1) , the 152 Eu activities are still measurable. Many investigations have been performed for measuring the 152 Eu/Eu ratios in the rock samples exposed to the Hiroshima atomic bomb [2][3][4][5][6][7][8] . The data on the .…”