Monte Carlo simulation of neutron interaction in Mn bath used for primary standard neutron dosimetry

Ionizing Radiation Metrology Laboratory (IRML), National Institute of Standards (NIS), Egypt is developing its capabilities in neutron metrology to the primary standard level. Recently, a Mn-bath system was installed at IRML. MCNP6 was used to simulate physical processes, interactions, and calculations of the main parameters used in primary standard neutron dosimetry. MCNP6 was used to calculate Am-Be neutron flux considering its constitution mixture and capsule dimensions and neutron doses at different depths within the Mn bath. The effect of geometry, and composite material for various ratios of hydrogen to Manganese atoms (NH/NMn) within the solution of MnSo4 were considered in the simulation, in addition to the determination of neutron energy reduction within the Mn-bath. The variance of thermalized neutron energy due to their interaction with water and capture by MnSO4 solution was calculated. The induced gamma radiation from the 55 Mn (n, γ) 56 Mn interaction was calculated. It was found that neutron doses calculated using MCNP6 are incompatible with those measured by the standard neutron monitors. The average energy distribution decreases as depth increases. The induced gamma activity calculated from neutron interaction within the Mn bath agrees with the experimental results and literature. • MCNP6 was used to calculate neutron flux delivered by Americium-Beryllium (Am-Be) source. • MCNP6 was used to calculate main parameters used in primary standard neutron dosimetry. • MCNP6 was used to calculate neutron flux from the neutron source, neutron interactions with materials in the Mn-bath. • MCNP6 was used to calculate background radiation around the Mn bath and also the induced gamma activity.