63Cu(n,p)63Ni reaction and development of β-ray detector

Since the amount of 63Ni which is produced by neutron from atomic explosion is very slight, it is required for its measurement to develop a highly sensitive and low-background detector for low-energy β-ray. This report describes the development of a β-ray detector aiming at measurement of extremely weak 63Ni. Recently, the authors suggested that the data of fast neutron might be obtainable by measuring 63Ni produced from 63Cu(n,p)63Ni. Here, they estimated the detection probability and the counting rate of background for the reaction and expressed the detectable limit as follows: Q = 3√r/(ε√t)r: count rate of background, ε: efficiency of detection, t: time of measurement. When the measurement time is 1000 min, the detection limit was calculated as 2.1 x 10-3Bq, which nearly corresponds to 2.8x10-3Bq, the amount of 63Ni in 1 g of Hiroshima's sample. Thus, the measurement of 63Ni was found possible if several grams of sample is obtainable. (M.N.)