Identification of 63Ni and 60Co produced in a steel sample by thermal neutrons from the Hiroshima atomic bomb

Abstract Long-lived residual radioactivity 63 Ni produced by the (n, γ) reaction was detected for the first time from a steel plate sampled at near the hypocenter of the Hiroshima atomic bomb. Nickel and cobalt were chemically separated and enriched from the steel sample. Low energy beta rays of 63 Ni were measured with a low-background liquid scintillation counter and gamma-rays of 60 Co were measured with a low background Ge detector. Specific activities were determined as 0.0063±0.0004 Bq mg −1 for 63 Ni Ni and 8.70±0.46 Bq mg −1 for 60 Co Co at the time of the bomb explosion. Comparisons with the calculated yield based on the current dosimetry system DS86 neutrons were also given.