Novel Materials for Radiation Detection: Transparent Ceramics and Glass Scintillators

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Novel Materials for Radiation DetectionTranspare
nt Ceramics and Glass Scintillators
Lynn A. Boatner Oak Ridge National
Laboratory Center for Radiation Detection
Materials Systems 2008 AAAS Annual
Meeting February 16, 2008
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Scintillators A Little History
Wilhelm Conrad Röntgen
Barium Platinocyanide purchased in the late
1800s by Sidney Rowland, Kings College, London

• Barium platinocyanide is considered to be the
  first radiation detector. The scintillation from
  a screen of platinocyanide alerted Wilhelm
  Röntgen to the presence of some strange radiation
  emanating from a gas discharge tube he was using
  to study cathode rays. Since Röntgen did not
  know what these rays were, he named them x-rays.

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Scintillators A Little History

• This radiographic image was formed by placing the
  barium platinocyanide on a photographic film. The
  reason for this effect is that the state of
  separations chemistry in the 1800s was poor and
  the barium platinocyanide was contaminated by
  radium.
• G. Brandes found that sufficiently energetic
  x-rays produced a uniform blue-grey glow that
  seemed to originate within the eye itself.
• Friedrich Giesel (Curie) saw radiation from
  radium to obtain this effect, one places the box
  containing the radium in front of the closed eye
  or against the temple" and "one can attribute
  this phenomenon to a phosphorescence in the
  middle of the eye under the action of the
  invisible rays of radium" (Curie 1900, 1903). In
  the United States, the Colorado physician George
  Stover5 was among the first investigate radiation
  phosphenes (the proper name for visual sensations
  induced by radiation within the eye) "Sitting in
  a perfectly dark room and closing the eyes, if
  the tube of radium is brought close to the
  eyelids a sensation of light is distinctly
  perceived, which disappears on removal of the
  tube...

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State of the Art Scintillators
Material Light Yield (photons/MeV) Resolution _at_ 662keV ()
NaI(Tl) 38,000 5.5
BGO 8,200 9.0
LaBr3(Ce) 70,000 2.8
LSO(Ce) 39,000 7.9
BC-408 Plastic 10,600 -
GS-20 Li Glass (2930 for 1-inch round, 2mm thick/ 4,739 for 6.2-inch square, 2mm thick plate) 4,100 17
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Transparent Polycrystalline Ceramic
ScintillatorsGlass Scintillators

• Why would we want these?
• Single crystal growth is a time-consuming,
  expensive, and rate-limiting process.
• Transparent polycrystalline ceramic scintillators
  and glass scintillators offer an alternative
  approach to scintillator synthesis that
  eliminates single crystal growth.

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• Oak Ridge National Laboratory-Transparent
  Polycrystalline Scintillators

• Conceptual Overview
• The Realization of an Entirely New Paradigm for
  the Fabrication of Inorganic Scintillators
  Specifically, an approach that is applicable to
  non-cubic as well as cubic materials
• Through the development of versatile methods for
  producing large, optically transparent,
  high-performance (resolution, light yield, decay
  time,) inorganic scintillators without the
  necessity of growing large single crystals.
• Accomplish this goal by applying the concept of
  developing highly crystallographically oriented
  (highly textured) ceramic microstructures1,2
• So that the material looks like a single crystal
  from the crystallographic point of view, and
  therefore, light scattering due to the effects of
  birefringence of the randomly oriented grains in
  a conventional ceramic is obviated.

• L. A. Boatner, J. L. Boldú, and M. M. Abraham,
  Characterization of Textured Ceramics by
  Electron Paramagnetic Resonance Spectroscopy I,
  Concepts and Theory, J. Am. Ceram. Soc. 73, (8)
  23332344 (1990).
• J. L. Boldú, L. A. Boatner, and M. M. Abraham,
  Characterization of Textured Ceramics by
  Electron Paramagnetic Resonance Spectroscopy II,
  Formation and Properties of Textured MgO, J. Am.
  Ceram. Soc. 73, (8) 23452359 (1990)

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Oak Ridge National Laboratory-Transparent
Polycrystalline Scintillators

• Why is it important to develop methods for
  forming transparent ceramic scintillators of
  non-cubic materials?
• The current scintillators with the highest energy
  resolution (LaBr3Ce at 2.6) or very high light
  yield (LuI3Ce at 100,00 photons/Mev) are not
  cubic materials.
• There are a lot more non-cubic materials than
  there are cubic materials.
• The technology for forming transparent ceramics
  of cubic materials is already well developed for
  a number of materials (e.g. YAG and related
  materials) as a result of Japanese research on
  polycrystalline laser rods.
• The claims that transparent ceramics can only be
  made with cubic materials is WRONG!

Transparent HAp sintered body fabricated by PECS.
(2.0 cm O.D., 1 mm thick) Ca10(PO4)6(OH)2 A
hexagonal (NOT CUBIC) crystal
XRD patterns of the sintered HAp body measured on
the sections parallel (a) and perpendicular (b)
to the pressure direction.
Transparent polycrystalline ceramic prepared by
developing a high degree of texturing.
Y. Watanabe, et all, J. Am. Ceram. Soc., 88 1
243-5 (2005)
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Project Objectives and Key Research

• Project Objectives
• Develop New Densification Techniques for
  Producing Optically Transparent, Highly Textured
  Inorganic Scintillatorsof both non-cubic and
  cubic materials
• At reduced cost
• At increased production rates
• Eliminate single crystal growth
• Minimize fabrication steps near-net shape
  ceramics
• Maintain scintillator performance
• Key Research
• Hot pressing and annealing
• Vacuum sintering
• Precursor Development
• Post Sintering Processing
• Scintillator Characterization

Lu2O3 5Eu2O3 Transparent Ceramics Hot pressed
at 1520 ºC, 321 kg/cm2 for 2 hrs

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• Lu2O3Eu
• Synthesis and Post Synthesis Treatment
• Lu2O3 and Eu2O3 (5 wt. ) powders combined
  physically
• Powder heated in vacuum to dry
• Hot pressed at 1530C with 262 kg/cm2 of pressure
• Annealed with flowing oxygen for 72 hours at
  1050C

Photograph of a Lu2O3Eu ceramic before (right)
and after (left) annealing in an oxygen
atmosphere. Hot pressing technique tends to draw
oxygen out of the host lattice, creating a dark
color in the densified body. This coloration can
be removed by annealing in an O2.
Photographs of a transparent Lu2O3Eu ceramic
(1mm thick)
Photograph of a Lu2O3Eu ceramic excited by a
30kV continuous X-ray source.
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• LSOCe
• Synthesis and Post-synthesis Treatment
• High quality LSOCe powder produced by Nichia
  Corporation (Japan) used
• Powder heated in vacuum to dry
• Hot pressed at 1400C with 337 kg/cm2 of pressure
  for 2 hours
• Annealed in vacuum at 1050C/108h
• Annealed in water vapor at 1050C/32h
• Annealed in air at 1150C/32h

Photograph of a LSOCe ceramic before (left) and
after (right) annealing in vacuum
Photograph of an LSOCe ceramic (0.6 mm thick).
Note that no back-light is used in this
photograph.
Scanning electron microscopy (SEM) image of
LSOCe powder from Nichia Corporation.
Transmission electron microscopy (TEM) image of
LSOCe powder from Nichia Corporation
Particle size distribution of the Nichia LSOCe
powder used to make the LSO ceramic.
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X-ray pole figure for LSOCe ceramic showing no
evidence for texturing in the ceramic
microstructure.
X-ray diffraction T-2T scan for the LSOCe
ceramic with the standard powder diffraction
pattern.
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Scintillating pulse shape of a LSOCe
polycrystalline ceramic excited by 662 KeV gamma
photons. The solid line represents single- and
three-exponential ( noise) fits to the
experimental data . The decay time constants and
contribution of faster components in comparison
to the decay time of about 42 ns generally
accepted for single crystal LSO.
Energy spectra (for 662 keV excitation photons)
of the LSOCe refernce crystal (the light yield
for this crystal was 30,000 photons/MeV) and the
LSOCe ceramic at various post-sintering
annealing stages. Symbol A denotes a ceramic
with a 2 mm thickness after annealing in vacuum,
A1 denotes a 0.7 mm thick piece of the former
ceramic after additional annealing in water
vapor, and A1a the same after additional
annealing in air.
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• LaBr3Ce
• Synthesis and Post-synthesis Treatment
• LaBr3 and CeBr3 (2 wt. ) powders combined
  manually
• Powder heated at 350C/24 in vacuum to dry
• Hot pressed under vacuum at 780C with
  388kg/cm2 of pressure for 3 hours.
• Annealed in vacuum at 650C/24h

Photograph of a translucent LaBr3Ce ceramic
scintillator (-0.7 mm thick). Illumination
circle is about 2.5 cm in diameter.
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Energy spectra of a BGO reference crystal and the
LaBr3Ce (2) ceramic for several excitation
energies.
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Novel Cerium-Activated Phosphate Glass
Scintillators
IR Phosphors Linda Lewis
Modeling David Singh
Phosphate Glass
Gamma, X-Ray, and Neutron Scintillators Lynn
Boatner and John Neal
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Research Goals Objectives

• Research Goals To exploit the chemical
  flexibility, optical properties, and the unusual
  structural features and variability of the ORNL
  phosphate glasses and other glass systems in
  order to develop a new glass scintillator with
  significantly improved radiation-detection (i.e.,
  light yield) characteristics.
• Applications Glass scintillators can be easily
  and economically fabricated in the form of large
  structures (e.g., as large area plates, tubes,
  rods, or bars) or pulled into optical fiber
  structures with wave-guiding properties.
• As a result of their thermal, mechanical and
  chemical durability, glass scintillators are
  ideal for use as radiation detectors in devices
  that have to operate in the field under a variety
  of frequently adverse conditions.

High Durability Lead Scandium Phosphate Glasses

• Nd-doped phosphate glasses known to be effective
  phosphors when excited by IR

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Glass Scintillators How Can We Improve Their
Performance?Glass Scintillator Parameter Space
Composition (Glass-forming space) Cladding
Phosphate Lead Phosphate Silicate Germanate Arsen
ate
Activation Ce,Pr,Nd,Eu,Tb,Yb Co-doping
Structure Phosphate glass only Phosphate chain
length
Post-synthesis Treatment Time Temperature Atmosphe
re
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Phosphate Glass - Gamma and X-ray Scintillators
Ce3 valence can be a challenging problem -
partially solved for silicate glasses, needs to
be solved for phosphate and other glasses.
Retort for variations of synthesis routes for
introducing Ce3 and maintaining it in the
trivalent state.
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Energy Spectra of Ce Doped Ca-Na Phosphate Glasses
137Cs 1µCi ? source 662 keV ? photons 0.5 µs
shaping time
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Variation Of Compton Edge Position as a
Functionof Ce Concentration in Ca-Na Phosphate
Glass
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Comparison of Energy Spectra
137Cs 1µCi ? source 662 keV ? photons 0.5 µs
shaping time
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Effects of Na Substitution By Li AndGd Co-doping
in Li-Ca Glass
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• Key General Objectives and Goals
• Develop new glass scintillator systems through
  the exploration of compositional variations in
  phosphate, silicate, germanate, arsenate and
  other glass-forming systems.
• Explore the effects of post-synthesis treatments
  (i.e., thermochemical processing) on glass
  scintillator properties.
• Investigate the performance of activators other
  than cerium in various glass host systems.
• Investigate energy transfer processes in glasses
  as a function of the materials structure
  (amorphous versus crystalline materials) and
  electronic properties.
• Variable temperature studies
• Identification of luminescence centers,
  impurities, defects, etc
• Relative position of luminescence center levels
  in the bandgap of the host
• Idendtify mechanisms that delay the transfer of
  energy to luminescence centers
• Apply this increased understanding to the
  synthesis of glass scintillators with improved
  performance characteristics.