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Title: Improved lithium iodide neutron scintillator with Eu 2+ activation: The elimination of Suzuki-Phase precipitates

Abstract

Monovalent alkali halides such as NaI, CsI, and LiI are widely used as inorganic scintillators for radiation detection due to their light yield, the capability for the growth of large single crystals, relatively low cost, and other favorable characteristics. These materials are frequently activated through the addition of small amounts (e.g., a few hundred ppm) of elements such as thallium - or sodium in the case of CsI. The monovalent alkali halide scintillators can also be activated with low concentrations of Eu 2+, however Eu activation has previously not been widely employed due to the non-uniform segregation of the divalent Eu dopant that leads to the formation of unwanted phases during Bridgman or other solidification crystal-growth methods. Specifically, for Eu concentrations near and above ~0.5%, Suzuki Phase precipitates form in the course of the melt-growth process, and these Suzuki Phase particles scatter the scintillation light. This adversely affects the scintillator performance via reduction in the optical transmission of the material, and depending on the crystal thickness and precipitated-particle concentration, this reduction can occur up to the point of opacity. Here we describe a post-growth process for the removal of Suzuki Phase precipitates from single crystals of the neutron scintillator LiImore » activated with Eu 2+ at concentrations up to and in excess of 3 wt.%, and we correlate the resulting neutron-detection performance with the thermal processing methods used to remove the Suzuki Phase particles. Furthermore, the resulting improved scintillator properties using increased Eu activator levels are applicable to neutron imaging and active interrogation systems, and pulse-height gamma-ray spectroscopy rather than pulse-shape discrimination can be used to discriminate between gamma ray and neutron interaction events.« less

Authors:
 [1];  [2];  [1];  [1];  [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1345003
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
Additional Journal Information:
Journal Volume: 854; Journal Issue: C; Journal ID: ISSN 0168-9002
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; neutron scintillator; lithium iodide; Suzuki phase; crystal growth; optical transparency

Citation Formats

Boatner, Lynn A., Comer, Eleanor P., Wright, Gomez W., Ramey, Joanne Oxendine, Riedel, Richard A., Jellison, Jr., Gerald Earle, and Kolopus, James A. Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates. United States: N. p., 2017. Web. doi:10.1016/j.nima.2017.02.059.
Boatner, Lynn A., Comer, Eleanor P., Wright, Gomez W., Ramey, Joanne Oxendine, Riedel, Richard A., Jellison, Jr., Gerald Earle, & Kolopus, James A. Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates. United States. doi:10.1016/j.nima.2017.02.059.
Boatner, Lynn A., Comer, Eleanor P., Wright, Gomez W., Ramey, Joanne Oxendine, Riedel, Richard A., Jellison, Jr., Gerald Earle, and Kolopus, James A. Tue . "Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates". United States. doi:10.1016/j.nima.2017.02.059. https://www.osti.gov/servlets/purl/1345003.
@article{osti_1345003,
title = {Improved lithium iodide neutron scintillator with Eu2+ activation: The elimination of Suzuki-Phase precipitates},
author = {Boatner, Lynn A. and Comer, Eleanor P. and Wright, Gomez W. and Ramey, Joanne Oxendine and Riedel, Richard A. and Jellison, Jr., Gerald Earle and Kolopus, James A.},
abstractNote = {Monovalent alkali halides such as NaI, CsI, and LiI are widely used as inorganic scintillators for radiation detection due to their light yield, the capability for the growth of large single crystals, relatively low cost, and other favorable characteristics. These materials are frequently activated through the addition of small amounts (e.g., a few hundred ppm) of elements such as thallium - or sodium in the case of CsI. The monovalent alkali halide scintillators can also be activated with low concentrations of Eu2+, however Eu activation has previously not been widely employed due to the non-uniform segregation of the divalent Eu dopant that leads to the formation of unwanted phases during Bridgman or other solidification crystal-growth methods. Specifically, for Eu concentrations near and above ~0.5%, Suzuki Phase precipitates form in the course of the melt-growth process, and these Suzuki Phase particles scatter the scintillation light. This adversely affects the scintillator performance via reduction in the optical transmission of the material, and depending on the crystal thickness and precipitated-particle concentration, this reduction can occur up to the point of opacity. Here we describe a post-growth process for the removal of Suzuki Phase precipitates from single crystals of the neutron scintillator LiI activated with Eu2+ at concentrations up to and in excess of 3 wt.%, and we correlate the resulting neutron-detection performance with the thermal processing methods used to remove the Suzuki Phase particles. Furthermore, the resulting improved scintillator properties using increased Eu activator levels are applicable to neutron imaging and active interrogation systems, and pulse-height gamma-ray spectroscopy rather than pulse-shape discrimination can be used to discriminate between gamma ray and neutron interaction events.},
doi = {10.1016/j.nima.2017.02.059},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = C,
volume = 854,
place = {United States},
year = {Tue Feb 21 00:00:00 EST 2017},
month = {Tue Feb 21 00:00:00 EST 2017}
}

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  • A glass-ceramic thermal neutron imaging plate material is reported. The material consists of a neutron sensitive 2B{sub 2}O{sub 3}-Li{sub 2}O glass matrix containing nanocrystallites of the storage phosphor BaCl{sub 2}:Eu{sup 2+}. When doped with 0.5 mol % Eu{sup 2+}, the neutron induced photostimulated luminescence (PSL) conversion efficiency of the {sup 10}B enriched glass-ceramic is around 60% of that a commercial neutron imaging plate, while the {gamma} sensitivity is an order of magnitude lower than that of the commercial plate. A Eu{sup 2+}-concentration series shows that the PSL efficiency for x rays is optimized at 0.01 mol % Eu{sup 2+}. Thermoluminescencemore » measurements indicate trap depths in BaCl{sub 2}:Eu{sup 2+} ranging from 0.55 to 2.7 eV.« less
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