A composite fast neutron detector module based on the 6Li(n,α) 3H reaction in 6Li-enriched GS20® scintillating glass has been engineered to be compact, robust, and tunable. The solid scintillating composite consists of only three components, all commercially sourced, and can be optically coupled to silicon photomultipliers (SiPMs) to create a highly capable and portable neutron detector module. The composite provides moderation of incident fast neutrons through an optically transparent organic matrix and achieves high gamma rejection by the use of small scintillating particles. The performance of the module was assessed by measurements of the die-away time and the sensitivity to both gammas and neutrons. Controlled scintillation light losses enable determination of the neutron capture location along the length of the cylindrical composite. Optical raytracing was used to predict the light-transport efficiencies and the longitudinal position dependency of scintillation events within the module. These assessments indicate that this module can be effective in the detection of nuclear material for nonproliferation, safeguards and security applications, and in fundamental and applied science.
Radiographic imaging represents a vital capability within non-destructive assessment, quality control and fundamental science. This study focuses on Gd2O2S:Tb3+ based scintillating composites incorporated into pixelated-metallic aperture screens, attached to amorphous silicon-based flat panels. Performance metrics are explored through coupled MCNP6- FRED simulations; here, scintillation light transport is investigated as a function of pixelated screen geometry and optical characteristics. For the first time, we demonstrate image acquisition with a 100 micron thick pixelated metallic aperture screen. The results demonstrate promising improvements to x-ray interaction rates while maintaining image quality.
Garnet based scintillators have been shown to have high light yield with fast scintillation decay constants. The availability of high refractive index resin enables the fabrication of translucent garnet based scintillating composites; here, this study investigates optical transport improvements through reducing the refractive index difference between composite constituents. The results of this study will demonstrate radiation response characteristics of garnet based scintillating composites, support hard-radiation imaging applications, basic science and explore optical transport limitations in composite technology.
The technological advances introduced by additive manufacturing techniques have significantly improved the ability to generate functional composites with a wide variety of mechanical and optical properties. Progress in the additive manufacturing of scintillating particle composites could enable new capabilities that span applications in nuclear nonproliferation, nuclear energy and basic science. The present work focuses on developing capabilities for additively manufacturing scintillating particle composites where successful implementation could enable cost-effective highperformance detectors for a wide range of applications. The results demonstrate the optical and response characteristics of arranged scintillating glass particle composites that are optically transparent, mechanically robust and respond to incident fast neutrons.
Neutron detectors are used for illicit material detection, neutron radiography, stellar investigations of chemical content including biological compounds in planetary terrain and to monitor nuclear power plant fuel products and radioactive waste. Li-containing chalcogenide materials are promising alternative thermal neutron detection materials due to the incorporation of the 6Li isotope at high density. 6LiInSe2 is limited in its effective thermal neutron efficiency by 115In neutron capture which results in gamma decay rather than charge creation. This study includes investigations of mixed crystalline material 6LiIn1-xGaxSe2 where the indium concentration is reduced by Ga substitution. The optical properties have been tuned by gallium substitution and radiation response has been observed.
Eric Lukosi, Elan Herrera, Ashley Stowe, Robert Milburn, Dylan Richardson, Brenden Wiggins, Arnold Burger, Ondrej Chvala, Louis Santodonato, Hassina Bilheux
The development of a thermal neutron imaging sensor constructed with semiconducting lithium indium diselenide is presented. Both a computational and experimental investigation were conducted. In the computational investigation, it is shown that the imaging potential of Lithium Indium Diselenid (LISe) is excellent, even when using a large pixel pitch through the use of super sampling. In the experimental investigation, it was found that a single pixel LISe detector using detector super sampling shows a spatial variation in the count rate, which is a clear sign of imaging capability. However, a good image was not obtained in the first experiment and may be caused by a variety of experimental conditions. Finally, a search is still underway to find a suitable contact metal with good mechanical adhesion for wedge bonding.
Chalcopyrite crystals of 6LiInSe2 have recently been shown to respond to gamma and thermal neutron radiation. Thus far, large crystals have been prepared although the charge collection efficiency has not been sufficient for high energy resolution. In an effort to improve energy resolution needed for gamma spectroscopy as well as pulse shape discrimination for mixed gamma neutron fluxes, the precipitate concentration within the 6LiInSe2 crystal have been studied. The precipitate volume greatly affects the energy resolution in the pulse height spectrum. Further, the charge mobility varies greatly with holes being preferentially trapped by these precipitates or some other defect site within the crystal.
Impurity analysis and compositional distribution studies have been conducted on a crystal of
LiInSe2, a compound semiconductor which recently has been shown to respond to ionizing radiation.
IR microscopy and laser induced breakdown spectroscopy (LIBS) revealed the presence of
inclusions within the crystal lattice. These precipitates were revealed to be alkali and alkaline earth
elemental impurities with non-uniform spatial distribution in the crystal. LIBS compositional maps
correlate the presence of these impurities with visual color differences in the crystal as well as a
significant shift of the band gap. Further, LIBS revealed variation in the ratio of I-III-VI2 elemental
constituents throughout the crystal. Analysis of compositional variation and impurities will aid in
discerning optimal synthesis and crystal growth parameters to maximize the mobility-lifetime
product and charge collection efficiency in the LiInSe2 crystal. Preliminary charge trapping
calculations have also been conducted with the Monte Carlo N-particle eXtended (MCNPx) package
indicating preferential trapping of holes during irradiation with thermal neutrons.
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