Design and optimization of a source (reflector/shielding) performance test system based on (241Am-Be)-paraffin thermal neutron irradiation device

Laboratory measurements and Monte Carlo simulations were conducted to investigate the feasibility of employing a (reflector/shield) to improve the efficiency of a thermal neutron irradiator utilizing a paraffin-moderated single 241 Am-Be source with an activity of 1 Ci. A multi-parameter optimization was performed to evaluate the potential of natural lead (Pb) and 90 % enriched 208 Pb lead ( 208 Pb (90 %) ) in terms of increasing the neutron production while minimizing the total dose equivalent rate. The laboratory-derived optimal configuration for the (reflector/shield) assembly demonstrated that Pb significantly increased the neutron flux by approximately 58 % and reduced the total dose equivalent rate to 0.00443 mSv/h, thereby allowing for a workload of 4500 h within the annual permissible dose limit of 20 mSv. The MCNP simulations validated the potentials of Pb and confirmed the superiority of 208 Pb (90 %) in terms of increasing neutron flux to about 26 % compared to that measured for Pb, while also minimizing the total dose equivalent rate to 0.0037 mSv/h. Thus, enabling a workload of approximately 5400 h, which is higher by about 20 % compared to that permitted by Pb based on measurements. The geometrical configuration and results promoted the use of the proposed TNI device primarily for prompt gamma neutron activation analysis (PGNAA).