Neutron Diffusion from a Fast Point Source in Aqueous Absorbing Solutions

Transport parameters (migration area, age to indium resonance) of fast neutrons from a plutonium -beryllium source have been measured in aqueous absorbing solutions at several temperatures (35, 40, 55, and 75°C), using boric acid as the 1/ absorber. For the measurements at 35 and 40°C, the saturation concentrations of boric acid were attained at 70 and 80 g/liter, respectively. For a 1/ absorber, a temperature-dependent power series representation of k² in terms of absorption cross section _∑ao was proposed, based on the concept of neutron temperature. The temperature range wherein such an expansion remains valid was experimentally determined. It was found that strong concentrations of a 1/ absorber caused much difficulty in experimentally resolving the thermal neutron spatial distributions, an observation which might have a direct relation to the (∑_t)_min limit of Corngold.