The new design and validation of an epithermal neutron flux detector using ⁷¹Ga(n,γ)⁷²Ga reaction for BNCT

Abstract

The epithermal neutron (0.5 eV-10 keV) flux is an essential characteristic for the boron neutron capture therapy (BNCT) neutron beam. The epithermal neutron flux measurement of a BNCT neutron beam is always a critical issue to its quality assessment and radiation dose evaluation. In this work, a cylindrical activation detector using 71 Ga(n, γ) 72 Ga reaction is designed by Monte Carlo simulations to determine the epithermal neutron flux of the BNCT neutron beam. In the detector, the activation material, i.e., gallium nitride (GaN) wafer, is positioned in the geometrical center of a high-density polyethylene (HDPE) cylinder covered with cadmium (Cd) foil. On completion of the design, the performance of the detector is validated by Monte Carlo simulations using reactor-and accelerator-based BNCT neutron beams. It is concluded from the performance validation results that the detector can accurately determine the epithermal neutron flux of the BNCT neutron beam. The designed epithermal neutron flux detector will be efficiently applicable to characterize the field of the BNCT neutron beam. K: Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors); Instrumentation for neutron sources; Neutron detectors (cold, thermal, fast neutrons); Solid state detectors 1Corresponding author.

Validation and optimization of the epithermal neutron flux detector using the 71Ga(n,γ)72Ga reaction

“…The detector is made similar to the original one [5]. The dimensions of the detector are 63.2 mm in height and 65.2 mm in diameter.…”

“…It can be seen that in the epithermal energy range there are a number of resonances with a high value of the reaction cross section, which ensures the selective efficiency of the detector to epithermal neutrons. The use of HDPE as a moderator makes it possible, as shown in [5], to achieve a flat sensitivity curve in the epithermal neutron energy range, while its sensitivities to thermal and fast neutrons are low. Detector sensitivity for a range of neutron energies is simulated by the Monte Carlo method using the NMC code [7] and ENDF-VII library of evaluated incident-neutron data.…”

“…Part of this discrepancy is explained by the difference in the used values of the 71 Ga(n,𝛾) 72 Ga reaction cross section. We used the ENDF-VII library in simulations, and the authors of [5] used the JENDL-4.0 library. In figure 2 shows that if in the resonance region the reaction cross sections are practically the same, then in the region of energies below the resonances, the cross section in ENDF-VII library approximately 1.3 times larger than in JENDL-4.0 library.…”

“…So the high value of the thermal neutron detection efficiency of the original detector seems strange. It is possible that the authors of [5] did not take into account the absorption of neutrons by hydrogen and cadmium, or did not set the temperature of the detector, or both.…”

Comparison of Neutron Detection Performance of Four Thin-Film Semiconductor Neutron Detectors Based on Geant4

“…In 2020, a GaN neutron detector with LiF was fabricated with a neutron detection efficiency of approximately 1.9% under a 0 V bias [ 23 ]. There are also studies using GaN for fast neutron detectors [ 24 ] and boron neutron capture therapy monitors [ 25 , 26 ]. Besides the layered structure, ion-implanted GaN detectors have also been studied [ 27 ].…”