(<i>n</i>, γ)反応を利用した放射化分析に対するしきい反応の妨害

Abstract

In case of the activation analysis of trace amounts of sodium in magnesium or aluminium, of copper in zinc, and nickel in copper by (n, γ) reaction with thermal neutrons, such threshold reactions as (n, p) or (n, α) reaction on the major component elements with fast neutrons produce the radioisotopes of the same kinds as those produced by (n, γ) reaction on the minute component elements, and the results of the activation analysis of these minute components are affected more or less by the threshold reactions depending on the thermal and fast neutron flux distribution. In order to estimate the extent of the effect of the threshold reaction on the activation analysis, pure materials of the elements written above were irradiated in JRR-1 and -2 reactors together with sodium, copper and nickel. The amounts of the radioisotopes produced by the threshold reactions were determined and compared with those produced by the corresponding (n, γ) reactions. By the irradiation in No. 1 experimental hole of JRR-1, which had relatively high fast neutron flux, the threshold reaction on the major component elements produced the radioisotopes, of which amounts corresponded to several thousands ppm of the minute components elements. The apparent content of the minute component was still above 100 ppm even by the irradiation in No. 3 experimental hole of JRR-1, which had low fast neutron flux.