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 geometr y. Measurements and calculations of the fast neutron spectra behind di fferent thicknesses of polyethylene and graphite have been carried out . Also the total gamma ray spectra behind different thicknesses of pol yethylene and graphite have been measured experimentally. A fast neutr on and gamma ray spectrometer with a stilbene crystal was used in the present measurements. The undesired pulses of neutrons or gamma rays w ere prevented by a pulse shape discrimination technique based on the z ero 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 display ed in the form of spectra and flux distributions and attenuation curve s. Comparison between the measured and calculated fast neutron spectra for polyethylene and graphite shows a reasonable agreement for all en ergies and for all investigated thicknesses. Also comparison between p olyethylene, graphite and water from the radiation moderation and atte nuation point of view have been carried out.