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.