Measurement of Residual 60Co Activity Induced by Atomic-bomb Neutrons in Nagasaki and Background Contribution by Environmental Neutrons

60 Co / Specific activity / Atomic bomb / DS86 / Neutrons Residual 60 Co activity in five steel samples induced by neutrons from the Nagasaki atomic bomb has been measured within about 1000 m from the hypocenter. The chemical separation of cobalt and nickel from steel samples was performed, and cobalt-enriched samples were prepared for all samples. Gamma-ray measurements were carried out with a low-background well-type germanium detector. The gamma-ray spectra for five samples were compared with the spectrum of a control sample to ensure that the observed 60 Co was actually induced by A-bomb neutrons. The activation of cobalt by environmental neutrons was also investigated. It has been shown that the present 60 Co data are consistent with earlier Hashizume’s data.