Radiation attenuation in light materials with spherical geometry

The spatial fluxes and energy distributions of fast neutrons and total gamma rays behind spherical shields of polyethylene and graphite have been carried out. A Pu-a-Be source has been used in spherical geometry. Measurements and calculations of the fast neutron spectra behind different thicknesses of polyethylene and graphite have been carried out. Also the total gamma ray spectra behind different thicknesses of polyethylene and graphite have been measured experimentally. A fast neutron and gamma ray spectrometer with a stilbene crystal was used in the present measurements. The undesired pulses of neutrons or gamma rays were prevented by a pulse shape discrimination technique based on the zero crossing method. The calculations of the fast neutron fluxes were performed by using the ANISN Westinghouse version (ANISN-W) code with the EUR LiB 15/5 cross section library. The obtained data were displayed in the form of spectra and flux distributions and attenuation curves. Comparison between the measured and calculated fast neutron spectra for polyethylene and graphite shows a reasonable agreement for all energies and for all investigated thicknesses. Also comparison between polyethylene, graphite and water from the radiation moderation and attenuation point of view have been carried out.