Measurements of thermal-neutron spectra in plutonium nitrate solutions

Neutron spectrum measurements covering the range thermal to 3 keV have been made by time-of-flight in three solutions of plutonium nitrate. The concentrations and 240Pu composition of these solutions were 197.9 g/liter at 23 wt%, 193.4 g/liter at 5 wt%, and 355.0 g/liter at 5 wt%, respectively. Flux traverses and time-dependent measurements were also made in each solution. The measured spectra have been compared to theoretical calculations using the Haywood-II scattering kernel for H bound in H2O and the ENDF/B Version I cross sections for 239Pu. A good comparison is obtained for the two lowest concentrations. The disagreements for the highest concentration are ascribed to room return effects.