Evaluation of the neutron field uniformity from a plutonium-beryllium howitzer using PHITS
The neutron fluence rate and energy spectrum of a 239PuBe neutron howitzer source were simulated at different distances using PHITS to investigate the uniformity of the neutron field around the source. Equivalent dose rates for neutrons were also mapped near the howitzer which indicated a dose of approximately 100 μSv/hr and 10 μSv/hr at 10 cm and 50 cm, respectively, from the tank. Percentage differences between the maximum and the minimum total fluence rates at different distances were calculated. The quantitative results in supplement to the energy spectrum were used as the basis for the neutron field uniformity. The findings are useful in the positioning of neutron detectors (e.g., multi-shelled polyethylene spheres, TLDs) for experiments to produce optimum data, and determining the zones inside the room with minimum radiation exposure during these experiments.