The Epithermal Component in the Neutron Response of Various Self-Powered Detectors

The response of self-powered detectors are characterized by a sensitivity indicating the induced current per unit flux per unit length. However, a reactor neutron spectrum consists of a thermal and epithermal component and we show that the current produced by epithermal neutrons in Pt, Co and Rh detectors is a significant fraction of the total response. Since the ratio of the two spectral components varies with position within the core and with the age of the fuel a single sensitivity is not satisfactory for accurate flux measurements. A proper flux determination requires a knowledge of separate thermal and epithermal sensitivities as well as a means of measuring or calculating the ratio of the two neutron spectral components. In the paper we further discuss why the two sensitivities are required, provide values for Pt, Co and Rh detectors, describe how they were obtained and finally provide an interpretation of data in the literature in the light of the two sensitivities.