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Title: Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix

Abstract

Composite materials consisting of 6Li scintillator particles in an organic matrix can enable thermal neutron detectors with excellent rejection of gamma-ray backgrounds. The efficiency of transporting scintillation light through such a composite is critical to the detector performance. This optical raytracing study of a composite thermal neutron detector quantifies the various sources of scintillation light loss and identifies favorable photomultiplier tube (PMT) readout schemes. The composite material consisted of scintillator cubes within an organic matrix shaped as a right cylinder. The cylinder surface was surrounded by an optical reflector, and the light was detected by PMTs attached to the cylinder end faces. A reflector in direct contact with the composite caused 53% loss of scintillation light. This loss was reduced 8-fold by creating an air gap between the composite and the reflector to allow a fraction of the scintillation light to propagate by total internal reflection. Replacing a liquid mineral oil matrix with a solid acrylic matrix decreased the light transport efficiency by only ~10% for the benefit of creating an all-solid-state device. The light propagation loss was found to scale exponentially with the distance between the scintillation event and the PMT along the cylinder main axis. This enabled amore » PMT readout scheme that corrects for light propagation loss on an event-by-event basis and achieved a 4.0% energy resolution that approached Poisson-limited performance. These results demonstrate that composite materials can enable practical thermal neutron detectors for a wide range of nuclear non-proliferation and safeguard applications.« less

Authors:
ORCiD logo [1];  [1];  [1];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
OSTI Identifier:
1477701
Alternate Identifier(s):
OSTI ID: 1474776
Report Number(s):
LA-UR-18-25954
Journal ID: ISSN 0021-8979
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 124; Journal Issue: 12; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; photocathodes; gamma rays; optical reflectors; photomultipliers; scintillators; neutron detectors; composite materials; luminescence; solid-state devices

Citation Formats

Hehlen, Markus P., Wiggins, Brenden W., Favalli, Andrea, Iliev, Metodi, and Ianakiev, Kiril D. Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix. United States: N. p., 2018. Web. doi:10.1063/1.5047433.
Hehlen, Markus P., Wiggins, Brenden W., Favalli, Andrea, Iliev, Metodi, & Ianakiev, Kiril D. Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix. United States. doi:10.1063/1.5047433.
Hehlen, Markus P., Wiggins, Brenden W., Favalli, Andrea, Iliev, Metodi, and Ianakiev, Kiril D. Fri . "Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix". United States. doi:10.1063/1.5047433. https://www.osti.gov/servlets/purl/1477701.
@article{osti_1477701,
title = {Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix},
author = {Hehlen, Markus P. and Wiggins, Brenden W. and Favalli, Andrea and Iliev, Metodi and Ianakiev, Kiril D.},
abstractNote = {Composite materials consisting of 6Li scintillator particles in an organic matrix can enable thermal neutron detectors with excellent rejection of gamma-ray backgrounds. The efficiency of transporting scintillation light through such a composite is critical to the detector performance. This optical raytracing study of a composite thermal neutron detector quantifies the various sources of scintillation light loss and identifies favorable photomultiplier tube (PMT) readout schemes. The composite material consisted of scintillator cubes within an organic matrix shaped as a right cylinder. The cylinder surface was surrounded by an optical reflector, and the light was detected by PMTs attached to the cylinder end faces. A reflector in direct contact with the composite caused 53% loss of scintillation light. This loss was reduced 8-fold by creating an air gap between the composite and the reflector to allow a fraction of the scintillation light to propagate by total internal reflection. Replacing a liquid mineral oil matrix with a solid acrylic matrix decreased the light transport efficiency by only ~10% for the benefit of creating an all-solid-state device. The light propagation loss was found to scale exponentially with the distance between the scintillation event and the PMT along the cylinder main axis. This enabled a PMT readout scheme that corrects for light propagation loss on an event-by-event basis and achieved a 4.0% energy resolution that approached Poisson-limited performance. These results demonstrate that composite materials can enable practical thermal neutron detectors for a wide range of nuclear non-proliferation and safeguard applications.},
doi = {10.1063/1.5047433},
journal = {Journal of Applied Physics},
issn = {0021-8979},
number = 12,
volume = 124,
place = {United States},
year = {2018},
month = {9}
}

Journal Article:
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Figures / Tables:

Table 1 Table 1: Wavelength dependence of the refractive index ($n$) and the absorption coefficient ($α$) of the materials used in the detector. The refractive-index dispersion is modeled using the Sellmeier equation $n$2 = 1 ∑$N\atop{K=1}$ $B$$k$ $λ$2 / ($λ$2 - $C$$k$). The $B$$k$ and $C$$k$ parameters for GS20 glass were obtainedmore » by fitting this equation to the dispersion curve for aluminosilicate glass (Corning 1723) [13, 14] shifted to match the GS20 refractive index of 1.55 at 404.7 nm [15], those for Drakeol 9 LT mineral oil were obtained by fitting the equation to data reported for Markol 7 mineral oil [16] shifted to match the Drakeol 9 LT refractive index of 1.4667 at 589.6 nm [17], those for SUVT acrylic were obtained from a fit of the equation to data reported for acrylic [18], and those for fused silica were taken from Ref. [19]. The refractive index at the GS20 peak scintillation wavelength, $n$(0.397 $μ$m), calculated from the $B$$k$ and $C$$k$ parameters is also shown for reference. The absorption coefficient is modeled using the functional form $α$($λ$) = A0 + A1 exp(-($λ$-$λ$0)/$l$1) + A2exp(-$λ$-$λ$0)/($l$2) obtained from a fit to the measured data (Figure 2) over the 0.32–0.50 $μ$m wavelength range.« less

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