Integral tests of neutron cross sections for iron, niobium, beryllium, and polyethylene

An NE-213 neutron spectrometry system was developed for measurements of neutron spectra in the range of 1.0 to 15 MeV. Pulse-shape discrimination against gamma-ray events was used. A photomultiplier bridge design which gave both good pulse-height linearity and good pulse-shape discrimination was developed for this spectrometry system. Neutron spectra were obtained by unfolding measured pulse-height spectra. Measurements of Pu--Be and D--T neutron sources were performed as tests of this spectrometry system. This spectrometry system was used to measure the neutron energy spectrum of a 252Cf spontaneous fission neutron source. Two measurements were fit with Maxwellian distributions for the energy range of 2.6 to 15.0 MeV. These fits yielded Maxwellian temperatures of 1.43 +- 0.05 MeV and 1.42 +- 0.03 MeV. Neutron leakage spectra were measured for the 252Cf source in spheres of iron, niobium, beryllium, and polyethylene. The neutron leakage spectrum for the D--T source in the iron sphere was also measured. These leakage spectrum measurements were integral experiments and were used to test neutron cross sections. The measurements were compared with discrete ordinates calculations using several different cross section sets. Calculations based on an ENDF/B-III data were in reasonably good agreement with the niobium, beryllium, and polyethylene measurements. Calculations for the 252Cf source in the iron sphere were made using cross section sets based on ENDF/B-III and DNA (Mat 4180, Mod 2) data. Calculations for the D--T source in the iron sphere were made using the same cross section sets as for the 252Cf source in iron