Design and performance of a hybrid fast and thermal neutron detector

Abstract

We report the performance and characterization of a custom-built hybrid detector consisting of BC501A liquid scintillator for fast neutrons and BC702 scintillator for thermal neutrons. The calibration and the resolution of the BC501A liquid scintillator detector are performed. The event identification via Pulse Shape Discrimination (PSD) technique is developed in order to distinguish gamma, fast and thermal neutrons. Monte Carlo simulation packages are developed in GEANT4 to obtain actual neutron energy spectrum from the measured recoil spectrum. The developed methods are tested by reconstruction of 241 AmBe(α, n) neutron spectrum.

Neutron background measurements with a hybrid neutron detector at the Kuo-Sheng Reactor Neutrino Laboratory

“…The measured ambient neutron flux is therefore the same as what the HPGe were exposed to in the physics data taking. Different particles produce different pulse shapes with the HND [9]. The normalized reference pulses of α, n fast , n thermal and γ are shown in Figure 4.…”

“…In Ref. [9], two independent PSD techniques were developed, which are based on the parameter of t P SD , derived from the ratio of partial (Q p ) to total (Q t ) integration of the pulses, and based on the B/A ratio of individual pulses given as…”

“…Simulated α energy spectra of 232 Th and 238 U parent isotopes convoluted with detector resolution and quenching effects are depicted in Figure 9. [9]. Normalization is fixed by the measured cascade sequences of Table I. roundings.…”

“…Once the HND spectra are measured, unfolding algorithms as discussed in Ref. [9], followed by a Friedman smoothing algorithm [23], are applied to produce the corresponding fast neutron spectra. The expected nuclear recoil background in HPGe detectors at the same location and shielding configurations are then evaluated with full GEANT simulation [24] and compared with 173.5kg-days of data taken under identical passive and active shielding configurations with an n-type point-contact germanium detector [25].…”

“…We report in this article in situ measurement of thermal (n thermal ) and fast (n fast ) neutron background at KSNL under identical shielding configurations as during the various physics data taking. A custom-built hybrid neutron detector (HND), whose characteristics and performances were reported earlier in our previous publication [9], are used for these measurements.…”