Energy and Spatial Angular Distributions of Fast Neutrons Transmitted Through Polyethylene, Graphite and Iron Shields.

Integral experiments were performed to measure the transmitted angular and energy distributions of fast neutrons resulting from exposure of slab material of polyethylene, graphite and iron to a collimated beam of Californium-252 neutrons. The fast neutron spectra were measured by a neutron/gamma spectrometer with a stilbene scintillator. Discrimination against undesired pulses of gamma rays was achieved by a pulse shape discrimination technique based on the zero cross over method. A computer program NSPEC was used to analyze the measured data to obtain the corresponding neutron spectrum. The obtained results are represented in the form of displayed fast neutron fluxes and energy distributions for neutrons measured at different angles behind samples of different thickness. The given spectra were used to plot the attenuation relations for fast neutrons within the whole measured energy range and those of certain energy as a function of the transmitted angle. These attenuation relations were used to drive the total macroscopic cross sections Σ t for the investigated materials. In addition, an empirical formula was derived to calculate the transmitted integral neutron fluxes at different angles through the shield barrier under investigation. Comparison was made between the derived values of Σ t measured at zero angle and their counterparts measured by others using other neutron sources and those calculated by the derived empirical formula.