IDENTIFICATION OF NI-63 AND CO-60 PRODUCED IN A STEEL SAMPLE BY THERMAL-NEUTRONS FROM THE HIROSHIMA ATOMIC-BOMB

Long-lived residual radioactivity Ni-63 produced by the (n, gamma) rea ction was detected for the first time from a steel plate sampled at ne ar the hypocenter of the Hiroshima atomic bomb. Nickel and cobalt were chemically separated and enriched from the steel sample. Low energy b eta rays of Ni-63 were measured with a low-background liquid scintilla tion counter and gamma-rays of Co-60 were measured with a low backgrou nd Ge detector. Specific activities were determined as 0.0063+/-0.0004 Bq mg(-1) for Ni-63/Ni and 8.70+/-0.46 Bq mg(-1) for Co-60/Co at the time of the bomb explosion. Comparisons with the calculated yield base d on the current dosimetry system DS86 neutrons were also given.