A new method in beam shaping: Multi-Objective Genetic Algorithm method coupled with a Monte-Carlo based reactor physics code

In this study, a new technique which uses Multi-Objective Genetic Algorithm method (NSGA-II) coupled with a Monte-Carlo based reactor physics code (MCNP) was proposed to shape the beams of neutron sources. The method was applied for the beam of Piercing Beam Port of the Istanbul Technical University TRIGA Mark II Research and Training Reactor. The beam was shaped according to the requirements of the Boron Capture Neutron Therapy (BNCT) application as described by IAEA technical documents. A set of optimized patterns, consisting of the spectrum shifter, filtering, and collimator sub-patterns, were obtained. Epithermal neutrons were considered for BNCT. With the optimized pattern, the epithermal neutron flux at the port exit is calculated as 4.17 ± 0.14 × 10⁸ n·cm⁻²·s⁻¹ with a current-to-flux ratio of 0.87 ± 0.03. Thermal and fast neutron fluxes and photon flux are reduced by about 20, 3, and 200 times, respectively, when compared with the bare port values. As a result, BNCT is applicable in this port as the desired neutron fluxes at the port exit are obtained. The method suggested in this study provides promising results and is quite effective in shaping the beam.