Fabrication and characterization of a lithium-glass-based composite neutron detector

Abstract

A novel composite, scintillating material intended for neutron detection and composed of small (1.5 mm) cubes of KG2-type lithium glass embedded in a matrix of scintillating plastic has been developed in the form of a 2.2 in.diameter, 3.1 in.-tall cylindrical prototype loaded with (5.82 ± 0.02) % lithium glass by mass. The response of the material when exposed to 252 Cf fission neutrons and various γ-ray sources has been studied; using the charge-integration method for pulse shape discrimination, good separation between neutron and γ-ray events is observed and intrinsic efficiencies of (1.15 ± 0.16) × 10 −2 and (2.28 ± 0.21) × 10 −4 for 252 Cf fission neutrons and 60 Co γ rays are obtained; an upper limit for the sensitivity to 137 Cs γ rays is determined to be < 3.70 × 10 −8 . The neutron/γ discrimination capabilities are improved in circumstances when a neutron capture signal in the lithium glass can be detected in coincidence with a preceding elastic scattering event in the plastic scintillator; with this coincidence requirement, the intrinsic efficiency of the prototype detector for 60 Co γ rays is (2.42 ± 0.61) × 10 −6 while its intrinsic efficiency for unmoderated 252 Cf fission neutrons is (4.31 ± 0.59) × 10 −3 . Through use of subregion-integration ratios in addition to the coincidence requirement, the efficiency for γ rays from 60 Co is reduced to (7.15 ± 4.10) × 10 −7 while the 252 Cf fission neutron efficiency becomes (2.78 ± 0.38) × 10 −3 .

Neutron spectroscopy by thermalization light yield measurement in a composite heterogeneous scintillator

“…The capability to perform both thermal neutron detection and fast neutron spectroscopy in a single detector makes the capture-gated detection attractive in various applications. Here, we report on the neutron spectroscopic measurement of a recently developed heterogeneous composite scintillator that includes polyvinyl toluene (PVT)-based scintillator EJ-290 and 6 Li-doped scintillating glass (GS20) rods. The composite detector exhibits excellent gamma/neutron discrimination capabilities due to the large Q-value of the neutron capture reaction 6 Li(n,t) 4 He and has shown the advantage of low gamma misclassification rate for neutron detection in abundant gamma background, such as detection of delayed neutron emission from fissionable materials [5].…”

“…In this work, the neutron time-of-flight (TOF) was used to determine the neutron energy and, in conjunction with the capture-gated technique, the correlation between the light output of neutron thermalization pulse and the incident neutron energy was investigated. The scintillating polymer EJ-290 [6,7] and its equivalents BC-490 and NE-120 have already been used for constructing capture-gated detector prototypes and find their applications in radiation dosimetry [8] and nuclear safeguards [9]. However, the light yield nonproportionality of EJ-290 scintillator has not been measured.…”

“…However, the light yield nonproportionality of EJ-290 scintillator has not been measured. Here we describe the characterization of proton recoil light yield nonproportionality of the EJ-290 scintillator by use of spectroscopic capture-gated measurements in a composite heterogeneous detector based on EJ-290 scintillator and 6 Li-doped glass (GS20). Spectroscopic measurements are aided with Monte Carlo simulation of detector response, which allows the EJ-290 nonproportionality to be parametrized using the Birks model.…”

“…When a neutron is captured in the composite detector, two scintillation pulses are usually generated. Prior to the neutron capture reaction 6 Li(n,t) 4 He, the neutron is thermalized in the PVT component of the scintillator, where multiple neutron scatters typically take place in rapid succession.…”

“…Nevertheless, the strong correlation of the light output to incident neutron energy in capture-gated detectors is appealing for spectroscopic applications. Various types of 6 Li-doped plastic [14] and liquid scintillators [15,16] have been developed recently. This further motivates experimental studies that can improve the understanding of the spectroscopic characteristics of 6 Li-doped detectors, which will aid their optimization and use in applications.…”