The quest for the ideal inorganic scintillator

Advances in time-of-flight PET.

Innovations in Instrumentation for Positron Emission Tomography

We summarize the latest R&D state-of-art of Ce3+ and Pr3+-doped mixed (LuxY1-x)3Al5O12 (LuYAG) garnet scintillator crystals and compare their properties with those of Lu3Al5O12 (LuAG) and Y3Al5O12 (YAG) single crystal analogues. Light yield, energy resolution and proportionality were studied under radioisotope excitation within 8-1300 keV energy range. The highest light yield of about 27000 ph/MeV is obtained in the newest prepared Ce3+ -doped LuAG crystals while up to 17000 ph/MeV was measured in the Pr3+-doped ones. On the contrary, the energy resolution and proportionality are noticeably better in the Pr3+ -doped crystals. Mixed Ce3+- or Pr3+-doped LuxY1-xAG (x=0.9-1) crystals show comparable light yield and energy resolution compared to those doped pure LuAG, but the content of slow components in scintillation pulses lower.

Scintillation Properties of ${\rm Ce}^{3+}$ - and ${\rm Pr}^{3+}$ -Doped LuAG, YAG and Mixed ${\rm Lu}_{\rm x}{\rm Y}_{1-{\rm x}}{\rm AG}$ Garnet Crystals

Update on latest advances in time-of-flight PET

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.

Transparent garnet ceramic scintillators for gamma-ray detection

Phase-pure transparent LSO ceramic was obtained, with its scintillation properties rivaling those of single crystalline LSO. The transparent LSO ceramic was prepared by a nano-technology approach. The densities of the LSO ceramic increased with increasing sintering temperature. Further SEM examination confirmed the decrease of the porosity during densification of the ceramic. Pores were segregated at grain boundaries after sintering. Hot isostatic pressing (HIPing) was employed to further densify the ceramic and eliminate porosity after sintering. Transparent polycrystalline LSO ceramics were obtained after the final HIP. XRD examination confirms single monoclinic LSO phase. A light output as high as 30,100 ph/MeV was obtained using a 22Na excitation source. LSO ceramic showed an energy resolution of 15% (FWHM) at 662 keV (137Cs source) and a fast scintillation decay of 40 ns due to the 5d \ura 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.

${\rm Lu}_{2}{\rm SiO}_{5}:{\rm Ce}$ Optical Ceramic Scintillator for PET

Effect of Microstructure on the Radioluminescence and Transparency of Ce-Doped Strontium Hafnate Ceramics.

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) 5 O 12 :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) 5 O 12 :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, 2 nd 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.

Properties of transparent (Gd,Lu)3(Al,Ga)5O12:Ce ceramic with Mg, Ca and Ce co-dopants

Scintillator materials based on mixed garnet compositions, as well as corresponding methods and systems, are described.

Gary Baldoni

Papers

Transparent garnet ceramic scintillators for gamma-ray detection

${\rm Lu}_{2}{\rm SiO}_{5}:{\rm Ce}$ Optical Ceramic Scintillator for PET

Effect of Microstructure on the Radioluminescence and Transparency of Ce-Doped Strontium Hafnate Ceramics.

Properties of transparent (Gd,Lu)3(Al,Ga)5O12:Ce ceramic with Mg, Ca and Ce co-dopants

Mixed garnet oxide scintillators and corrsponding systems and methods