Leakage neutron spectra from spherical samples with a Pu–Be source

Leakage neutron spectra from a Pu–Be source placed in the center of a 30 cm diameter sphere filled with water, paraffin oil, SiO2 and river sand were measured using a pulse height response spectrometer (PHRS) in the 1.4–12.0 MeV energy range. The measured leakage neutron spectra have been compared with the calculated results obtained by the three dimensional Monte Carlo code MCNP-4A and point-wise cross sections from the FENDL data file. A comparison of the measured and calculated data has shown that the MCNP-4A code with appropriate data library can approximate reasonably the measured leakage spectra of neutrons. The observed linear dependence of the integrated spectral yield as a function of water content in SiO2 rendered possible the determination of the moisture content in river sand.