10.1117/2.1201009.003196
Transparent ceramic scintillators
for gamma-ray spectroscopy
and radiography
Nerine Cherepy, Joshua Kuntz, Zachary Seeley, Scott Fisher,
Owen Drury, Benjamin Sturm, Thomas Hurst, Jeffery Roberts,
and Stephen Payne
Advances in transparent ceramics fabrication could transform scintillator materials by offering performance similar to halide single crystals
with the ruggedness and processability of glass.
Transparent ceramics have become available in useful sizes
for a variety of applications within the past 15 years thanks
to improved understanding of sintering phenomena on the
nanoscale.1, 2 While traditional ceramics may comprise single
or multiple crystalline and amorphous mineral phases and
are typically translucent or opaque to light, modern optically
transparent ceramics are fully dense monoliths of micron-scale
(or smaller) crystallites, in most cases formed from pure-phase
cubic crystal structures. Fabrication of transparent ceramics
begins with high-purity ceramic nanopowders, which are
consolidated into a ‘green body’ by pressing or casting. The
green body is sintered to near-full density, and the residual
porosity is removed by processing the samples in a pressure
vessel with high-pressure argon gas (hot isostatic pressing).
A few commercial transparent ceramics are Lumicera lenses
(a barium-based oxide made by Murata Mfg.), laser gain
media—Nd:YAG (neodymium-doped yttrium aluminum garnet) is available from Konoshima—and transparent armor
(aluminum oxynitride and spinel are available from Surmet
and other vendors). As the manufacturing processes for transparent ceramics become better understood, industrial optical
uses for these transparent materials with excellent mechanical
robustness are likely to expand.
At Lawrence Livermore National Laboratory (LLNL), transparent ceramic oxide scintillators are being developed for
gamma ray spectrometers and for high-energy (MeV)
radiographic imaging devices.3–5 Scintillators are optical materials that emit pulses of visible photons when excited with
Figure 1. (left) GYGAG(Ce) ceramic gamma spectroscopy scintillator (3.2cm diameter 2cm high). (right) Lu2 O3 (Eu) radiography ceramic under UV illumination (2.5 diameter 0.2cm
thick). GYGAG(Ce): Cerium-doped gadolinium garnet. Lu2 O3 (Eu):
Europium-doped lutetium oxide.
high-energy radiation. These pulses may be read out with a photodetector and processed to provide gamma-ray spectroscopy.
Gamma-ray spectrometers providing high sensitivity and effective isotope identification require high energy resolution, high
effective atomic number, and scintillators that can be produced
in large volumes. The scintillators currently offering the best
energy resolution for gamma spectroscopy are cerium-doped
lanthanum bromide, LaBr3 (Ce), and europium-doped strontium
iodide, SrI2 (Eu). However, these materials are available only as
single crystals. In harsh environments, such as nuclear-fuel-rod
pools or for oil-well logging, a rugged material, such as a transparent ceramic, is desirable. Among the garnets, the density and
effective atomic number of YAG are too low, while lutetium
(Lu)-based garnets have excellent stopping power but possess
Continued on next page
10.1117/2.1201009.003196 Page 2/3
Figure 2. Gamma ray spectrum of GYGAG(Ce) reveals resolution
superior to thallium-doped iodide—NaI(Tl)—the most commonly
used scintillator for gamma spectroscopy. LaBr3 (Ce): Cerium-doped
lanthanum bromide. SrI2 (Eu): Europium-doped strontium iodide.
Ba-133: Barium-133.
intrinsic radioactivity due to the presence of Lu-176, resulting in
an undesirable background for low-rate counting.
We have developed a cerium-doped gadolinium yttrium
gallium aluminum garnet, with the chemical formula
(Gd,Y)3 (Ga,Al)5 O12 , referred to hereafter as GYGAG(Ce).
Figure 1 shows a 1in3 fully dense ceramic of GYGAG(Ce)
fabricated at LLNL. This material exhibits excellent light
yield proportionality, the intrinsic limit to scintillator energy
resolution.6 Gamma-ray spectra acquired with a barium (Ba)-133
source, using four different scintillators (see Figure 2), show that
GYGAG(Ce) resolves complex lines better than thallium-doped
sodium iodide—NaI(Tl)—though still not as well as SrI2 (Eu) or
LaBr3 (Ce). We are carefully engineering a GYGAG(Ce) gamma
spectrometer using a high-quantum-efficiency photodetector,
highly reflective cladding, and digital pulse readout to realize
its optimal performance.
For MeV radiography, moderate light yield terbium-doped
scintillating glass sheets, such as that produced by Industrial
Quality Inc. (IQI glass), may be coupled to imaging cameras.7
An alternative is the General Electric radiography scintillator ceramic, HiLight, a Eu-doped bixbyite—(Gd,Y)2 O3 —with
better light yield and stopping power about 2 that of
scintillating glass.8 We are developing fabrication methods for
extremely low optical scatter Lu2 O3 (Eu) ceramic sheets that offer 4 better stopping power and 3.5 higher light yield than
scintillating glass, thus potentially improving imaging throughput by more than 12. Figure 3 compares the light yields of
a IQI scintillating glass and a Lu2 O3 (Eu) ceramic scintillator
fabricated at LLNL, at 20,000 and 75,000 photons/MeV,
respectively.
Transparent ceramics are a promising class of materials
for scintillator and other optical materials applications where
Figure 3. Radioluminescence spectra obtained by excitation with a
Sr-90 beta source are shown along with the integrated spectra,
in photons/MeV. IQI Tb: Terbium-doped scintillating glass. Ph/MeV:
Photons/MeV.
single-crystal performance accompanied by robust mechanical
properties is desirable. Some challenges and limitations remain.
Unfortunately, relatively few cubic crystalline phases are thermodynamically and environmentally stable enough to achieve
the degree of phase purity required to form transparent ceramics, thus limiting candidate lists for new materials development
efforts. The preparation of sufficiently uniform green bodies for
sintering to the required transparency, especially for large or
unusual-sized optics, can be difficult. Polishing costs can become
a significant cost center when compared with glasses but are
typically less than for single-crystal optics.
For transparent ceramic scintillators, widespread use will depend on demonstrated performance enhancements such as high
light yields and uniformity of response, and on the economics
of industrial fabrication. In addition to gamma-ray spectroscopy
and MeV radiography, we are interested in extending our fabrication expertise to develop improved scintillators for medical
applications (keV imaging and positron-emission tomography),
particle physics (hadron calorimetry, rare-event detectors), and
well logging for oil and mineral exploration.
This work was supported by the Department of Homeland Security Domestic Nuclear Detection Office (Alan Janos) and the US Department
of Energy (DOE), Office of the National Nuclear Security Administration, Enhanced Surveillance Subprogram (Patrick Allen). This work
was performed under the auspices of DOE by LLNL under contract
DE-AC52-07NA27344.
Continued on next page
10.1117/2.1201009.003196 Page 3/3
Author Information
Nerine Cherepy, Joshua Kuntz, Zachary Seeley, Scott Fisher,
Owen Drury, Benjamin Sturm, Thomas Hurst, Jeffery Roberts,
and Stephen Payne
Lawrence Livermore National Laboratory
Livermore, CA
Nerine Cherepy works on scintillator materials and detector
development, including single-crystal SrI2 (Eu), transparent
ceramics for gamma spectroscopy and radiographic imaging,
and ‘high-Z’ polymer scintillators.
References
1. A. Ikesue and Y.-Lin Aung, Synthesis and performance of advanced ceramic lasers, J.
Am. Ceram. Soc. 89 (6), pp. 1936–1944, 2006.
2. J. W. McCauley, P. Patel, M. Chen, G. Gilde, E. Strassburger, B. Paliwal, K. T.
Ramesh, and D. P. Dandekar, AlON: a brief history of its emergence and evolution, J.
Eur. Ceram. Soc. 29, pp. 223–236, 2009.
3. N. J. Cherepy, S. A. Payne, S. J. Asztalos, G. Hull, J. D. Kuntz, T. Niedermayr,
S. Pimputkar, J. J. Roberts, R. D. Sanner, T. M. Tillotson, E. van Loef, C. M. Wilson,
K. S. Shah, U. N. Roy, R. Hawrami, A. Burger, L. A. Boatner, and W.-S. Choong,
Scintillators with potential to supersede lanthanum bromide, IEEE Trans. Nucl. Sci. 56,
pp. 873–880, 2009.
4. N. J. Cherepy, J. D. Kuntz, J. J. Roberts, T. A. Hurst, O. B. Drury, R. D. Sanner,
T. M. Tillotson, and S. A. Payne, Transparent ceramic scintillator fabrication, properties,
and applications, Proc. SPIE 7090, p. 707917, 2008.
5. N. J. Cherepy, J. D. Kuntz, Z. M. Seeley, S. E. Fisher, O. B. Drury, B. W. Sturm,
T. A. Hurst, R. D. Sanner, J. J. Roberts, and S. A. Payne, Transparent ceramic scintillators for gamma spectroscopy and radiography, Proc. SPIE 7805, p. 78050I, 2010.
6. S. A. Payne, N. J. Cherepy, G. Hull, J. D. Valentine, W. W. Moses, and W.-S.
Choong, Nonproportionality of scintillator detectors: theory and experiment, IEEE Trans.
Nucl. Sci. 56, pp. 2506–2512, 2009.
7. T. Martin and A. Koch, Recent developments in X-ray imaging with micrometer spatial resolution, J. Synchrotron Rad. 13, pp. 180–194, 2006.
8. C. Greskovich and S. Duclos, Ceramic scintillators, Annu. Rev. Mater. Sci. 27,
pp. 69–88, 1997.
c 2010 SPIE