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