Experimental investigation of a neutron energy spectrometer in low-energy range using a position-sensitive proportional counter

This study investigated a novel spectrometer to measure the neutron energy spectrum in the epi-thermal range (0.5 eV to 10 keV) for Boron Neutron Capture Therapy (BNCT). A 3 He Position-Sensitive Proportional Counter (PSPC) was utilized to measure the depth-dependent distribution of neutron interactions within the detector (depth distribution). The energy spectrum was reconstructed using a spectrum unfolding technique based on Bayes' theorem. To demonstrate this approach, we conducted validation experiments using a custom-designed measurement system. A multi-parameter MCA was employed to detect two-dimensional reaction-depth distributions, from which the neutron spectrum was estimated. The results showed good agreement with the reference spectrum up to 1 keV, although side-neutron contributions were found to impact the estimation accuracy. This study serves as an important step to realize the feasibility of PSPC-based systems for low-energy neutron spectrometry and provides a foundation for further optimization to enhance estimation performance.