A New Low-Energy Neutron Spectrometer Based on Position-Sensitive Proportional Counter for Accelerator-Based Neutron Source

Accelerator-based neutron sources are being developed worldwide. In a neutron source, it is essential to know the characteristics of the field including neutrons and gamma rays. However, for the neutron, it is still difficult to measure the energy spectrum below 10 keV. In the present study, a low-energy neutron spectrometer has been designed and developed to examine the accelerator-based neutron source performance. The proposed spectrometer will finally cover neutron energy from the thermal-to-kilo-electron-volt region and is based on a ³He proportional counter. It is positioned in parallel with the incident neutron beam, and the reaction depth distribution is measured. Since the reaction depth distribution varies depending on the incident neutron energy, it can be converted to the neutron energy spectrum. The spectrometer is 50 cm long × 5 cm in diameter with a gas pressure of 0.5 MPa. Recently, a prototype detector was completed, and the signal test is now in progress. The preliminary test result has described the present spectrometer availability as a low-energy neutron spectrometer for an accelerator-based neutron source. Because this kind of spectrometer did not exist heretofore, the spectrometer can be applied to neutron source facilities, e.g., proton accelerators like the Japan Proton Accelerator Research Complex (J-PARC) and nuclear reactors as well as accelerator-based neutron sources for boron neutron capture therapy like the fixed field alternating gradient-emittance-energy recovery internal target (FFAG-ERIT).