Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth

L. A. Boatner; J. O. Ramey; J. A. Kolopus; John S. Neal

doi:10.1016/j.nima.2015.02.031

Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth

L. A. Boatner, J. O. Ramey, J. A. Kolopus, John S. Neal

Research output: Contribution to journal › Article › peer-review

17 Scopus citations

Abstract

The alkaline-earth scintillator, CaI₂:Eu²⁺, was initially discovered around 1964 by Hofstadter, Odell, and Schmidt. Serious practical problems quickly arose, however, that were associated with the growth of large monolithic single crystals of this material due to its lamellar, mica-like structure. As a result of its theoretically higher light yield, CaI₂:Eu²⁺ has the potential to exceed the excellent scintillation performance of SrI₂:Eu²⁺. In fact, theoretical predictions for the light yield of CaI₂:Eu²⁺ scintillators suggested that an energy resolution approaching 2% at 662 keV could be achievable. As in the case of the early SrI₂:Eu²⁺ scintillator, the performance of CaI₂:Eu²⁺ scintillators has traditionally suffered due, at least in part, to outdated materials synthesis, component stoichiometry/purity, and single-crystal-growth techniques. Based on our recent work on SrI₂:Eu²⁺ scintillators in single-crystal form, we have developed new techniques that are applied here to CaI₂:Eu²⁺ and pure CaI₂ with the goal of growing large un-cracked crystals and, potentially, realizing the theoretically predicted performance of the CaI₂:Eu²⁺ form of this material. Calcium iodide does not adhere to modern glassy carbon Bridgman crucibles - so there should be no differential thermal-contraction-induced crystal/crucible stresses on cooling that would result in crystal cracking of the lamellar structure of CaI₂. Here we apply glassy carbon crucible Bridgman growth, high-purity growth-charge compounds, our molten salt processing/filtration technique, and extended vacuum-melt-pumping methods to the growth of both CaI₂:Eu²⁺ and un-doped CaI₂. Large scintillating single crystals were obtained, and detailed characterization studies of the scintillation properties of CaI₂:Eu²⁺ and pure CaI₂ single crystals are presented that include studies of the effects of plastic deformation of the crystals on the scintillator performance.

Original language	English
Pages (from-to)	23-31
Number of pages	9
Journal	Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume	786
DOIs	https://doi.org/10.1016/j.nima.2015.02.031
State	Published - Jun 21 2015

Funding

This research was sponsored in part by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory , managed by UT-Battelle for the U.S. Department of Energy and in part by the Nuclear Non-proliferation Program ( NA-22 ) of the National Nuclear Security Administration , U.S. Department of Energy . Contributions by Alexandra E. Vandegrift and Jason Craig who fabricated the quartz growth-charge preparation apparatus described here are gratefully acknowledged as are the technical contributions of Shelby Stooksbury, the graphic-arts contributions of Sandra L. Salmen, and the preparation of the CaI 2 crystal structure figure by Bryan Chakoumakos. The authors are indebted to Prof. Arnold Burger and the members of his research group at Fisk University in Nashville, Tennessee for carrying out the purification of EuI 2 by zone refining.

Funders	Funder number
UT-Battelle
U.S. Department of Energy	NA-22
National Nuclear Security Administration
Oak Ridge National Laboratory

Keywords

Bridgman growth
CaI:Eu Plastic deformation
Crystal growth
Scintillator

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10.1016/j.nima.2015.02.031

Cite this

Boatner, L. A., Ramey, J. O., Kolopus, J. A., & Neal, J. S. (2015). Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 786, 23-31. https://doi.org/10.1016/j.nima.2015.02.031

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title = "Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth",

abstract = "The alkaline-earth scintillator, CaI2:Eu2+, was initially discovered around 1964 by Hofstadter, Odell, and Schmidt. Serious practical problems quickly arose, however, that were associated with the growth of large monolithic single crystals of this material due to its lamellar, mica-like structure. As a result of its theoretically higher light yield, CaI2:Eu2+ has the potential to exceed the excellent scintillation performance of SrI2:Eu2+. In fact, theoretical predictions for the light yield of CaI2:Eu2+ scintillators suggested that an energy resolution approaching 2% at 662 keV could be achievable. As in the case of the early SrI2:Eu2+ scintillator, the performance of CaI2:Eu2+ scintillators has traditionally suffered due, at least in part, to outdated materials synthesis, component stoichiometry/purity, and single-crystal-growth techniques. Based on our recent work on SrI2:Eu2+ scintillators in single-crystal form, we have developed new techniques that are applied here to CaI2:Eu2+ and pure CaI2 with the goal of growing large un-cracked crystals and, potentially, realizing the theoretically predicted performance of the CaI2:Eu2+ form of this material. Calcium iodide does not adhere to modern glassy carbon Bridgman crucibles - so there should be no differential thermal-contraction-induced crystal/crucible stresses on cooling that would result in crystal cracking of the lamellar structure of CaI2. Here we apply glassy carbon crucible Bridgman growth, high-purity growth-charge compounds, our molten salt processing/filtration technique, and extended vacuum-melt-pumping methods to the growth of both CaI2:Eu2+ and un-doped CaI2. Large scintillating single crystals were obtained, and detailed characterization studies of the scintillation properties of CaI2:Eu2+ and pure CaI2 single crystals are presented that include studies of the effects of plastic deformation of the crystals on the scintillator performance.",

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Boatner, LA, Ramey, JO, Kolopus, JA & Neal, JS 2015, 'Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth', Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 786, pp. 23-31. https://doi.org/10.1016/j.nima.2015.02.031

Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth. / Boatner, L. A.; Ramey, J. O.; Kolopus, J. A. et al.
In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 786, 21.06.2015, p. 23-31.

Research output: Contribution to journal › Article › peer-review

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T1 - Divalent europium doped and un-doped calcium iodide scintillators

T2 - Scintillator characterization and single crystal growth

AU - Boatner, L. A.

AU - Ramey, J. O.

AU - Kolopus, J. A.

AU - Neal, John S.

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AB - The alkaline-earth scintillator, CaI2:Eu2+, was initially discovered around 1964 by Hofstadter, Odell, and Schmidt. Serious practical problems quickly arose, however, that were associated with the growth of large monolithic single crystals of this material due to its lamellar, mica-like structure. As a result of its theoretically higher light yield, CaI2:Eu2+ has the potential to exceed the excellent scintillation performance of SrI2:Eu2+. In fact, theoretical predictions for the light yield of CaI2:Eu2+ scintillators suggested that an energy resolution approaching 2% at 662 keV could be achievable. As in the case of the early SrI2:Eu2+ scintillator, the performance of CaI2:Eu2+ scintillators has traditionally suffered due, at least in part, to outdated materials synthesis, component stoichiometry/purity, and single-crystal-growth techniques. Based on our recent work on SrI2:Eu2+ scintillators in single-crystal form, we have developed new techniques that are applied here to CaI2:Eu2+ and pure CaI2 with the goal of growing large un-cracked crystals and, potentially, realizing the theoretically predicted performance of the CaI2:Eu2+ form of this material. Calcium iodide does not adhere to modern glassy carbon Bridgman crucibles - so there should be no differential thermal-contraction-induced crystal/crucible stresses on cooling that would result in crystal cracking of the lamellar structure of CaI2. Here we apply glassy carbon crucible Bridgman growth, high-purity growth-charge compounds, our molten salt processing/filtration technique, and extended vacuum-melt-pumping methods to the growth of both CaI2:Eu2+ and un-doped CaI2. Large scintillating single crystals were obtained, and detailed characterization studies of the scintillation properties of CaI2:Eu2+ and pure CaI2 single crystals are presented that include studies of the effects of plastic deformation of the crystals on the scintillator performance.

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Divalent europium doped and un-doped calcium iodide scintillators: Scintillator characterization and single crystal growth

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