Neutron flux determination in a multi-channel Howitzer using foil activation and Monte Carlo simulations

In this study, the thermal, epithermal, and fast neutron fluxes produced in irradiation channels of a Howitzer neutron source system – featuring horizontal and vertical channels and housing a 74 GBq ²⁴¹Am–Be source – were determined through activation experiments and Monte Carlo simulations (MCNP) at different neutron source positions. The MCNP simulations were performed with precise modeling of the experimental setup, allowing comparison and alignment with measured data to accurately define the thermal and epithermal neutron energy boundaries. Experimentally, neutron flux determination was carried out using neutron activation analysis with gold and indium foils, combined with absolute measurement techniques. This approach enabled fast and reliable experimental data by correlating indium flux monitor values with those obtained from gold foils. The study identified the optimum irradiation conditions for neutron applications requiring various energy levels based on the source and foil positions within the system. Additionally, the effect of cadmium coating on epithermal and fast neutron fluxes was examined using MCNP results, demonstrating that depending on the flux density, approximately 4–6 % absorption occurred in epithermal neutrons, alongside a ±1 % change in fast neutron flux.