Measurement and simulation of leakage spectra on polyethylene slab irradiated with D-T neutrons

The neutron leakage spectrum were measured at 40° by time-of-flight method for polyethylene slabs with the thicknesses of 4.5, 9, 18 and 27 cm, respectively. The experimental results were compared with the MCNP-4C simulations, which carefully considered many effects, such as the angle and energy distributions of the source neutrons, the width of the beam pulse, the detection efficiency and the effective measured area. The sample out and collimator-filled spectra were measured as the background, and the results showed that C/E values were larger than 1 when using the sample out background spectra, but smaller than 1 when using the collimator-filled background spectra. Combine these two different background spectra, a new method was used to calculate the background spectrum, and the results have a better agreement with the simulations. (authors)