The effects of photoreactions on neutron dosimetry for reactor pressure vessel lifetime studies

A series of measurements and calculations was carried out to help quantify the effects of photoreactions on neutron dosimetry in the reactor pressure vessel surveillance program, with a 'photofraction gauge' which consisted of a 4.8 cm thick sintered metal disk (90% W, 6% Ni, 4% Cu, rho=16.9 g/cc) with a set of threshold foils fore and aft of the filter. The thickness was great enough to attenuate photofission gammas (> 5 MeV) by about a factor of 10 more than neutrons producing fission events in all foils except the non-threshold fission foils (235U and 239Pu). The threshold-foil spectrometry stack covers nearly all neutron dosimetry reactions. These include the reactions utilized in fission track recorders as well as fission chambers