Improved Lithium Iodide neutron scintillator with Eu activation II: Activator zoning and concentration effects in Bridgman-grown crystals
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology Division
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science & Technology; Univ. of Tennessee, Knoxville, TN (United States). Nuclear Engineering Department and Scintillation Materials Research Center
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Nuclear Security and Isotope Technology Division
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Instrument and Source Division, Neutron Sciences Directorate
We have previously reported on the formation of Suzuki Phase precipitate particles as a result of the addition of the divalent activator ion Eu2+ to the monovalent alkali halide host LiI. [Boatner et al. (2017)]. These precipitates form during Bridgman or other melt-growth processes, even at low Eu2+ concentrations (e.g., 0.1% EuI2 doping), and scatter the scintillation light reducing the optical transparency of the scintillator and adversely affecting its radiation-detection performance. In our prior work, we developed a two-stage thermal-treatment method for the post-growth removal of the Suzuki Phase particles and the realization of a significant improvement in the optical transparency and associated neutron-detection of LiI:Eu2+ scintillators. These improvements resulted in neutron-detection performance that is superior to GS-20 glass and that allows for the application of pulse height gamma-ray discrimination over a wide range of gamma ray energies as opposed to pulse shape discrimination. Here in this paper, we apply the two-stage thermal-processing method for the removal of Suzuki phase precipitates and carry out an in-depth study, first, of the neutron scintillator performance versus the Eu2+ activator-ion-concentration spatial variation as a result of zoning effects during the Bridgman growth of LiI:Eu and, second, of the effects of varying the initial Eu2+ activator ion concentration prior to crystal growth. The Eu2+ zoning variation results allow one to identify and select the most efficient location of the scintillation performance in a directionally solidified single-crystal boule. The present study of the initial activator concentration levels shows that there are, in fact, two distinct types of luminescence centers with varying performance properties — one that occurs only at low EuI2 addition levels (e.g., 0.01 to 0.06 %EuI2) and that is quickly replaced by a second luminescing center with increasing Eu content (e.g., at 0.1% EuI2). The light yield for the luminescing center formed using a Eu activator in LiI is a critical function of the Eu concentration in the range of 0.01 to 0.1 % EuI2, and a high light yield of 100,000 photons/neutron is observed at the 0.06 %EuIadditive level prior to thermal processing.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1470866
- Alternate ID(s):
- OSTI ID: 1495637
- Journal Information:
- Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 903, Issue C; ISSN 0168-9002
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Defect chemistry of Eu dopants in NaI scintillators studied by atomically resolved force microscopy
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journal | July 2019 |
Critical Review of Scintillating Crystals for Neutron Detection
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journal | September 2019 |
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