Demonstration of BSS Unfolding Method for BNCT Neutron Field and Development of New BSS using Li-glass Scintillators coupled with Current-mode-operated PMTs for Intense Neutron Field

摘要

Accelerator-based neutron sources for boron neutron capture therapy (BNCT) should be experimentally characterized to realize good quality treatments. Neutron spectral fluence measurements using a typical ^{3He-proportional-counter-based Bonner sphere spectrometer (BSS) were performed for weak neutron beams at an accelerator-based neutron source of the University of Tsukuba, and the applicability of the unfolding method was experimentally examined. New BSS using 6Li- and 7Li-glass scintillators coupled with current-mode-operated PMTs has been developed for direct measurements of the therapy-level intense neutron beam. The neutron-gamma discrimination is performed by simultaneous measurements of the 6Li- and 7Li-glass scintillators. Fundamental characteristics of the scintillator unit were investigated. Responses of each scintillator to neutrons were evaluated at the electron-linac-based pulsed neutron field of the Kyoto University. The linearity of the scintillator unit to neutron intensity was experimentally evaluated in thermal neutron fields of the National Institute of Advanced Industrial Science and Technology (AIST) and the Kyoto University. Responses of the new Bonner spheres with the Li-glass scintillators were evaluated under the current-mode and the pulse-mode operations for RI-emitted neutrons at AIST. Comparisons between the current-mode and the pulse-mode responses indicated that the new BSS worked as expected. Further characterization of the new BSS and the actual BSS measurement for the intense neutron beams at the BNCT facility will be performed in the near future.}