Neutron detector based on Particles of 6Li glass scintillator dispersed in organic lightguide matrix

Abstract

Q3detectors 6 Li glass Neutron/gamma separation 3 He replacement Nuclear safeguards Neutron coincidence counters Active interrogation a b s t r a c t Most 3 He replacement neutron detector technologies today have overlapping neutron-gamma pulseheight distributions, which limits their usefulness and performance. Different techniques are used to mitigate this shortcoming, including Pulse Shape Discrimination (PSD) or threshold settings that suppress all gammas as well as much of the neutrons. As a result, count rates are limited and dead times are high when PSD is used, and the detection efficiency for neutron events is reduced due to the high threshold. This is a problem in most applications where the neutron-gamma separation of 3 He detectors had been essential. This challenge is especially severe for neutron coincidence and multiplicity measurements that have numerous conflicting requirements such as high detection efficiency, short dieaway time, short dead time, and high stability. 6 Li-glass scintillators have excellent light output and a single peak distribution, but they are difficult to implement because of their gamma sensitivity. The idea of reducing the gamma sensitivity of 6 Li-glass scintillators by embedding small glass particles in an organic light-guide medium was first presented by L.M. Bollinger in the early 60s but, to the best of our knowledge, has never been reduced to practice. We present a proof of principle detector design and experimental data that develop this concept to a large-area neutron detector. This is achieved by using a multi-component optical medium ( 6 Li glass particles attached to a glass supporting structure and a mineral oil light guide) which matches the indices of refraction and minimizes the absorption of the 395 nm scintillator light. The detector design comprises a 10 in. long tube with dual end readout with about 3% volume density of 6 Li glass particles installed. The presented experimental data with various neutron and gamma sources show the desired wide gap between the neutron and gamma pulse height distributions, resulting in a true plateau in the counting characteristics similar to that of 3 He detectors.

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

“…[7]). Alternative matrices, such as nonscintillating acrylic, may also yield composite, lithium-glass-based detectors with very effective neutron/γ discrimination: Ianakiev et al have shown promising initial results for high neutron/γ discrimination efficacy with composites based on GS20-type lithium glass and poly(methyl methacrylate) (PMMA) or mineral oil matrices [29].…”

Current Status of Helium-3 Alternative Technologies for Nuclear Safeguards

“…A new detector concept for 3 He replacement based on GS20 6 Li scintillator glass particles uniformly distributed in mineral oil that serves as both light transport and neutron moderation medium has recently been developed at LANL. The technology provides good neutron/gamma-ray separation by selection of a scintillator particle size that limits the energy deposited by gamma-rays to below the peak of the 6 Li reaction products [Ianakiev 2014a]. A prototype detector with an active volume of 7.6 cm diameter by 25.4 cm length containing ~2.7 vol% of GS20 glass scintillator was developed and is shown in Figure 3.25.…”

A Monte Carlo Model of the Neutron Detector Based on Lithium-Glass Scintillator

“…The neutron detection technique is one of the key issues in neutron research. The widespread 3 He-based detectors are becoming less available due to constraints in gas supply. Alternative types of detectors are required that can provide reasonable detection efficiency for neutrons in a wide energy range, a limited sensitivity to γ rays or ability to discriminate them, and a short dead time.…”

“…Works on reducing the γ-ray sensitivity of glass scintillators are underway in two main directions. The first direction is to create heterogeneous scintillators based on lithium glasses with various geometries and optical characteristics, in particular, for problems of control over nuclear-material handling [3][4][5]. The second direction is to search for methods of digital signal processing to discriminate between pulses from neutrons and γ rays [6,7].…”