Paper RESIDUAL 6oCo ACTIVITY IN STEEL SAMPLES EXPOSED TO THE HIROSHIMA ATOMIC-BOMB NEUTRONS

Residual 6oCo radioactivity produced by the neutrons from the Hiroshima atomic bomb has been measured by means of gamma-ray spectrometry for seven steel samples located up to 1,800 m slant range and one control sample obtained at 4.5 km from the hypocenter. After removing the main constituent of iron ions from the steel sample by the solvent extraction method, nickel and cobalt were chemically separated by the ion exchange process. Gamma-ray measurements were performed with a low background well-type germanium detector. Derived specific activities 6oCo:Co were compared with previous measurements and with the calculation based on the neutron fluence of current dosimetry system DS86. It has been shown that a systematic discrepancy exists between the measured and calculated activity. The calculatedto-measured ratios for 6oCo are consistent with those of lsZEu and 36CI activity. Health Phys. 75(3):278-284; 1998