The NCT-WES directional neutron spectrometer: validation of the response with monoenergetic neutron fields

A directional neutron spectrometer named NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was developed for quality assurance of the therapeutic neutron beam in Neutron Capture Therapy (NCT). NCT-WES operates as a "parallelized" Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a collimated cylindrical moderator. With the objective of validating the simulation model used to derive its response matrix, irradiations in reference monoenergetic fields were performed at National Physical Laboratory (UK). As the energy distributions of neutron beams in NCT extend from keV to a few MeV, monoenergetic fields in this domain were chosen, namely 71.5 keV, 144.2 keV, 565.1 keV, 841.9 keV and 1200.4 keV. The results of the experiment confirm the correctness of the NCT-WES simulation model, within an overall uncertainty lower than +/- 2%.