Determination of the energy dependence of the 63Cu (n,2n)62Cu and 27Al (n,p)27Mg cross-sections, and their application to the measurement of 14-MeV neutron fluxes

Abstract

The variations in reaction cross-section of the 63Cu (n,2n)62Cu and the 27Al (n,p)27Mg reactions as a function of neutron energy have been measured in the 13·5 to 14·9-MeV range, which is commonly used for 14-MeV neutron activation.The cross-section of the 63Cu (n, 2n)62Cu reaction was found to increase approximately linearly with a gradient of 140 ± 10 mb MeV–1, and that of the 27Al (n, p)27Mg reaction to be approximately constant. It is, therefore, suggested that the 27Al (n, p)27Mg reaction is more suitable for measuring the numerical value of a 14-MeV neutron flux, in spite of its lower cross-section.It is also suggested that to obtain 14-MeV neutron-activation measurements that are independent of neutron energy, the energy dependence of the flux-measuring foil and irradiated specimen should be matched. The 27Al (n, p)27Mg reaction appears to be suitable for all (n, p) reactions, while the 63Cu (n, 2n)62Cu reaction may be more suitable for (n, 2n) reactions.