Abstract

An elliptically shaped polythene phantom, filled with tissue-equivalent material, was exposed to collimated beams of fast neutrons from a Pu-Be source. Absorbed doses were measured at depth in the phantom for beams incident on both the major and minor axes. A Bragg-Gray type detector, made from plastic phosphor and polyvinyltoluene sheet, wasused to measure the proton recoil absorbed dose from the fast neutrons and a LiI(Eu) crystal to detect the thermal neutrons. Various correction factors to account for thermal neutron flux depression and self shielding from the crystal, neutron attenuation by the probe, etc., are discussed in detail. The absorbed dose at depth in tissue due to the 14N(n,p)14C, 1H(n,γ)2D reactions were derived from the corrected fluxes.The experimental doses are compared with the theoretical values of Snyder and Neufeld for broad beam irradiations, and with various other published results. Quality factors are determined and dose equivalents calculated.

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