Computational evaluation of a two-source neutron irradiator
Abstract
The Philippine Nuclear Research Institute (PNRI) is currently establishing the Neutron Irradiation Facility (NIF) which features two legacy plutonium beryllium (239PuBe) neutron sources with source strengths of 3.6×106 n/s and 1.8×106 n/s. In this paper, a PHITS (Particle and Heavy Ion Transport Code System) computational model was developed based on the existing MCNP (Monte Carlo N-Particle) LUNIS file provided by PNRI. The PHITS model was then used to optimize a configuration for NAA applications by maximizing the total fluence and its thermal neutron component. It was determined that the optimal thickness for the HDPE was 5.4 cm, providing the highest distribution of thermal neutron flux with minimal absorption by the moderator. At this thickness, a significant thermal neutron flux of 6.4×103 n/cm2s is achieved, representing 58.24% of the total neutron flux. The configuration allows the maximum contribution of thermal neutrons while also maximizing the total number of neutrons in the irradiation location.
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