Cerium activated mixed lutetium/gadolinium- and aluminum/gallium-based garnets have great potential as host scintillators for medical imaging applications. (Gd,Lu)3(Al,Ga)5O12:Ce and denoted as GLuGAG feature high effective atomic number and good light yield, which make it particularly attractive for Positron Emission Tomography (PET) and other γ-ray detection applications. For PET application, rapid decay and good timing resolution are extremely important. Most Ce-doped mixed garnet materials such as GLuGAG:Ce, have their main decay component at around 80 ns. However, it has been reported that the decays of some single crystal scintillators (e.g., LSO and GGAG) can be effectively accelerated by codoping with selected additives such as Ca, Mg and B. In this study, transparent polycrystalline (Gd,Lu)3(Al,Ga)5O12:Ce ceramics codoped with Ca or Mg or additional Ce, were fabricated by the sinter-HIP approach. It was found the transmission of the ceramics are closely related to the microstructure of the ceramics. As the co-dopant levels increase, 2nd phase occurs in the ceramic and thus transparency of the ceramic decreases. Ca and Mg co-doping in GLuGAG:Ce ceramic effectively accelerate decays of GLuGAG:Ce ceramics at a cost of light output. However, additional Ce doping in the GLuGAG:Ce has no benefit on improving decay time but, on the other hand, reduces transmission, light output. The mechanism under the different scintillation behaviors with Mg, Ca and Ce dopants are discussed. The results suggest that decay time of GLuGAG:Ce ceramics can be effectively tailored by co-doping GLuGAG:Ce ceramic with Mg and Ca for applications with optimal timing resolution.
Numerous instruments have been developed for performing gamma-ray imaging and neutron imaging for research, nondestructive testing, medicine and national security. However, none are capable of imaging gamma-rays and neutrons simultaneously while also discriminating gamma-rays from the neutron. This paper will describe recent experimental results obtained using a gamma/neutron camera based on Cs2LiYCl6:Ce (CLYC) scintillation crystals, which can discriminate gamma-rays from neutrons. The ability to do this while also having good energy resolution provides a powerful capability for detecting and identifying shielded special nuclear materials for security applications. Also discussed are results obtained using a LaBr3 scintillation crystal.
He-3 tubes are the most popular thermal neutron detectors. They are easy to use, have good sensitivity for neutron
detection, and are insensitive to gamma radiation. Due to low stockpiles of the He-3 gas, alternatives are being sought to
replace these devices in many applications. One of the possible alternatives to these devices are scintillators
incorporating isotopes with high cross-section for neutron capture (e.g. Li-6 or B-10). Cs2LiYCl6:Ce (CLYC) is one of the scintillators that recently has been considered for neutron detection. This material offers good detection efficiency
(~80%), bright response (70,000 photons/neutron), high gamma ray equivalent energy of the neutron signal (>3MeV),
and excellent separation between gamma and neutron radiation with pulse shape discrimination. A He-3 tube alternative
based on a CLYC scintillator was constructed using a silicon photomultiplier (SiPM) for the optical readout. SiPMs are
very compact optical detectors that are an alternative to usually bulky photomultiplier tubes. Constructed detector was
characterized for its behavior across a temperature range of -20°C to 50°C.
Lanthanide gallium/aluminum-based garnets have a great potential as host structures for scintillation materials for
medical imaging. Particularly attractive features are their high density, chemical radiation stability and more importantly,
their cubic structure and isotropic optical properties, which allow them to be fabricated into fully transparent, highperformance
polycrystalline optical ceramics. Lutetium/gadolinium aluminum/gallium garnets (described by formulas
((Gd,Lu)3(Al,Ga)5O12:Ce, Gd3(Al,Ga)5O12:Ce and Lu3Al5O12:Pr)) feature high effective atomic number and good
scintillation properties, which make them particularly attractive for Positron Emission Tomography (PET) and other γ-
ray detection applications. The ceramic processing route offers an attractive alternative to single crystal growth for
obtaining scintillator materials at relatively low temperatures and at a reasonable cost, with flexibility in dimension
control as well as activator concentration adjustment.
In this study, optically transparent polycrystalline ceramics mentioned above were prepared by the sintering-HIP
approach, employing nano-sized starting powders. The properties and microstructures of the ceramics were controlled by
varying the processing parameters during consolidation. Single-phase, high-density, transparent specimens were
obtained after sintering followed by a pressure-assisted densification process, i.e. hot-isostatic-pressing. The transparent
ceramics displayed high contact and distance transparency as well as high light yield as high as 60,000-65,000 ph/MeV
under gamma-ray excitation, which is about 2 times that of a LSO:Ce single crystal. The excellent scintillation and
optical properties make these materials promising candidates for medical imaging and γ-ray detection applications.
Scintillator crystal detectors form the basis for many radiation detection devices. Therefore,
a search for high light yield single crystal scintillators with improved energy resolution, large
volume, and the potential for low cost, is an ongoing process that has increased in recent years due to
a large demand in the area of nuclear isotope identification. Alkaline earth halides, elpasolites and
rare earth halides are very interesting because many compositions from these crystal families
provide efficient Ce3+/ Eu2+ luminescence, good proportionality and good energy resolution. They
also have small band-gap leading to higher light yields. Ce3+and Eu2+ are efficient, and the emission
wavelengths in the 350-500 nm region matches well with PMTs and a new generation of Siphotodiodes.
In this presentation, we will the present progress made in the crystal growth of these
compositions, and scintillator properties of large diameter SrI2:Eu2+ single transparent crystals. The
crystals were grown successfully using the vertical Bridgeman technique. Crystals with different
diameters of 1”, 1.3”, and 1.5” will be discussed. SrI2:Eu was discovered a half century ago, and
was recently found to be an outstanding material for gamma ray-spectroscopy with high light yield,
very good non-proportionality, and excellent energy resolution.
We will also discuss growth and properties of larger Cs2LiYCl6 (CLYC) crystals. Recently,
it has been shown that crystals from the elpasolite family, including CLYC, can be successfully
employed for a dual gamma ray and neutron detection, which is possible with the help of pulse shape
discrimination (PSD). PSD allows for recognition of an incident particle’s nature based on the shape
of the corresponding scintillation pulse. CLYC has the potential to minimize the cost and
complexity of dual sensing gamma ray and neutron spectrometers. We also address progress in
growth of CLYC crystals with large diameters (1” and 2”) that are transparent and crack free.
For detecting neutrons, 3-He tubes provide sensitivity and a unique capability for detecting and discriminating
neutron signals from background gamma-ray signals. A solid-state scintillation-based detector provides an alternative to
3-He for neutron detection. A real-time, portable, and low cost thermal neutron detector has been constructed from a
6Li-enriched Cs2LiYCl6:Ce (CLYC) scintillator crystal coupled with a CMOS solid-state photomultiplier (SSPM).
These components are fully integrated with a miniaturized multi-channel analyzer (MCA) unit for calculation and
readout of the counts and count rates.
CLYC crystals and several other elpasolites including Cs2LiLaCl6:Ce (CLLC) and Cs2LiLaBr6:Ce (CLLB) have
been considered for their unique properties in detecting neutrons and discriminating gamma ray events along with
providing excellent energy resolution comparable to NaI(Tl) scintillators. CLYC's slower rise and decay time for
neutrons (70ns and 900ns respectively) relative to a faster rise and decay time for gamma ray events (6ns and 55ns
respectively) allows for pulse shape discrimination in mixed radiation fields.
Light emissions from CLYC crystals are detected using an array of avalanche photodiodes referred to as solid-state
photomultipliers. SSPMs are binary photon counting devices where the number of pixels activated is directly
proportional to the light output of the CLYC scintillator which is proportional to the energy deposited from the radiation
field. SSPMs can be fabricated using standard CMOS processes and inherently contain the low noise performance
associated with ordinary photomultiplier tubes (PMT) while providing a light and compact solution for portable neutron
We are working to perfect the growth of divalent Eu-doped strontium iodide single crystals and to optimize the design of
SrI2(Eu)-based gamma ray spectrometers. SrI2(Eu) offers a light yield in excess of 100,000 photons/MeV and light yield
proportionality surpassing that of Ce-doped lanthanum bromide. Thermal and x-ray diffraction analyses of SrI2 and EuI2
indicate an excellent match in melting and crystallographic parameters, and very modest thermal expansion anisotropy.
We have demonstrated energy resolution with SrI2(4-6%Eu) of 2.6% at 662 keV and 7.6% at 60 keV with small crystals,
while the resolution degrades somewhat for larger sizes. Our experiments suggest that digital techniques may be useful
in improving the energy resolution in large crystals impaired by light-trapping, in which scintillation light is re-absorbed
and re-emitted in large and/or highly Eu2+ -doped crystals. The light yield proportionality of SrI2(Eu) is found to be
superior to that of other known scintillator materials, such as LaBr3(Ce) and NaI(Tl).
Some applications, particularly in homeland security, require detection of both neutron and gamma radiation. Typically,
this is accomplished with a combination of two detectors registering neutrons and gammas separately. Recently, a new
scintillator, Ce doped Cs2LiLaCl6 (CLLC) that can provide detection of both has been investigated for gamma and
neutron detection. This material is capable of providing very high energy resolution, as good as 3.4% at 662 keV
(FWHM), which is better than that of NaI(Tl). Since it contains 6Li, it can also detect thermal neutrons. In the energy
spectra, the full energy thermal neutron peak appears near 3 GEE MeV. Thus very effective pulse height discrimination
can be achieved with this material. The CLLC emission consists of two main components: Core-to-Valence
Luminescence (CVL) spanning from 220 nm to 320 nm and Ce emission found in the range of 350 to 500 nm. The
former emission is of particular interest since it appears only under gamma excitation. It is also very fast, decaying with
a 2 ns time constant. This provides CLLC with different temporal responses under gamma and neutron excitation and it
can be used for effective pulse shape discrimination.
Lutetium oxyorthosilicate (Lu2SiO5:Ce3+, commonly known as LSO) is a scintillator of choice for medical imaging
applications such as Positron Emission Tomography (PET) because of its high light output, high gamma ray stopping
power and fast response. In the current study, phase-pure LSO ceramics were obtained with a high degree of optical
transparency and excellent scintillation properties. These LSO optical ceramics were prepared by combining
nanotechnology with a sinter-HIP approach. We found that the densities of the LSO ceramics increased with
increasing sintering temperature, which corresponds to a systematic decrease in porosity as found by SEM
examination. The residual pores were found to segregate at grain boundaries after sintering, and were essentially
removed by subsequent hot isostatic pressing (HIPing), which raised the density to essentially the value characteristic
of the single crystal and produced polycrystalline LSO ceramics with a high degree of transparency. Under
excitation a 22Na source such specimens displayed a light output as high as 30,100 ph/MeV. The LSO ceramics
showed an energy resolution of 15% (FWHM) at 662 keV (137Cs source) and a fast scintillation decay of 40 ns due to
the 5d → 4f transition of Ce3+. The excellent scintillation and optical properties make LSO ceramic a promising
candidate for future gamma-ray spectroscopy as well as medical imaging applications.
Recently SrI2, a scintillator patented by Hofstadter in 1968, has been rediscovered and shown to possess remarkable
scintillation properties. The light output of SrI2:Eu2+ has been measured to be even higher than previously observed and
exceeds 120,000 photons/MeV, making it one of the brightest scintillators in existence. The crystal also has excellent
energy resolution of less than 3% at 662 keV. The response is highly linear over a wide range of gamma ray energies.
The emission of SrI2:Eu2+ and SrI2:Ce3+/Na+ is well-matched to both photomultiplier tubes and blue-enhanced silicon
photodiodes. While SrI2:Eu2+ is relatively slow, SrI2:Ce3+/Na+ has a fast response. SrI2 crystals with many different
dopant concentrations have been grown and characterized. In this presentation, crystal growth techniques as well as the
effects of dopant concentration on the scintillation properties of SrI2, over the range 0.5% to 8% Eu2+ and 0.5% to 2%
Ce3+/Na+, will be discussed in detail.
Single crystals of LaBr3:1% Pr and CeBr3:1% Pr have been grown by the vertical Bridgman technique. Crystals of
these scintillators can be used in the fabrication of gamma-ray spectrometers. The LaBr3:1% Pr and CeBr3:1% Pr
crystals we have grown had light outputs of ~73,000 and ~50,000 photons/MeV, respectively, and principal decay
constants of 11μs and 26 ns, respectively. There were a number of emission peaks observed for these compounds. The
emission wavelength range for the LaBr3:1% Pr and CeBr3:1% Pr scintillators were from about 400 to 800 nm. The
CeBr3:1% Pr scintillator had a dominating emission peak due to CeBr3 at 390 nm. These two materials had energy
resolutions of 9 and 7% FWHM, respectively, for 662 keV photons at room temperature. In this paper, we will report on
our results to date for vertical Bridgman crystal growth and characterization of Pr-doped LaBr3 and Pr-doped CeBr3
crystals. We will also describe the special handling and processing procedures developed for these scintillator
Ceramic materials show significant promise for the production of reasonably priced, large-size scintillators. Ceramics
have recently received a great deal of attention in the field of materials for laser applications, and the technology for
fabricating high-optical-quality polycrystalline ceramics of cubic materials has been well developed. The formation of
transparent ceramics of non-cubic materials is, however, much more difficult as a result of birefringence effects in
differently oriented grains. Here, we will describe the performance of a few new ceramics developed for the detection of
gamma- and x-ray radiation. Results are presented for ceramic analogs of three crystalline materials - cubic Lu2O3, and
non-cubic LaBr3, and Lu2SiO5 or LSO (hexagonal, and monoclinic structures, respectively). The impact of various
sintering, hot-pressing and post-formation annealing procedures on the light yield, transparency, and other parameters,
will be discussed. The study of LaBr3:Ce shows that fairly translucent ceramics of rare-earth halides can be fabricated
and they can reach relatively high light yield values. Despite the fact that no evidence for texturing has been found in our
LSO:Ce ceramic microstructures, the material demonstrates a surprisingly high level of translucency or transparency.
While the scintillation of LSO:Ce ceramic reaches a light yield level of about 86 % of that of a good LSO:Ce single
crystal, its decay time is even faster, and the long term afterglow is lower than in LSO single crystals.
In this contribution we demonstrate the influence of shallow charge traps on emissions kinetics of LuAlO3:Ce3+ scintillator. Shallow traps through their interference with the recombination process not only introduce into the emission time profiles long components but also can change the rising and decaying parts of time profiles. The lifetime of excited Ce3+ ion in LuAP crystal is approximately 18 ns, while the excitation at 78 nm leads to the emission described by 21.5 and 1.22 ns decay and rise time constants, respectively. Furthermore, temperature dependence of time profile phase is observed. The analysis of emissions kinetics measured against temperature shows that observed features can be explained in terms of a trap described by the following parameters: E equals 0.142 eV and S equals 6.087 X 1010 s-1.