Akihiro Fukabori

Development of Pr:LuAG Scintillator Array and Assembly for Positron Emission Mammography

Abstract-In order to detect the breast cancer at the early stage with high efficiency, we intend to develop positron emission mammography (PEM), using Pr:LuAG single crystal as a scintillator of this scanner. PEM has the same mechanism of PET, where two 511 keV annihilation gamma-rays are detected by two gamma cameras at opposite side, and reconstruction of the data shows the position of the cancer with malignancy grades. After cutting and polishing processes for each crystal to a physical dimensions of 2.1 × 2.1 × 15 mm3, Pr:LuAG array covered with BaSO4 reflector was used as a sensor head. The one camera unit consisted of 20 × 64 pixels optically coupled with three H8500-03 multi anode PMTs. Our PEM required four cameras at each side. Finally, eight cameras were installed in both sides of the prototype instrument and the spatial resolution was evaluated using the 18F in the breast phantom.

Scintillator-oriented combinatorial search in Ce-doped (Y,Gd)3(Ga,Al)5O12 multicomponent garnet compounds

Ce-doped (YyGd1−y)3(GaxAl1−x)5O12 (x = 0, 1, 2, 3, 4 and y = 1, 2, 3) single crystals are grown by the micro-pulling down method. X-ray diffraction and electron probe microanalysis techniques are employed to check their structure and chemical composition, respectively. Optical and photoluminescence characteristics are measured and radioluminescence spectra, light yield and scintillation decay measurements are further made to evaluate the scintillation performance. We show that balanced Gd and Ga admixture in the Y3Al5O12 structure can considerably increase the scintillation efficiency, and the spectrally corrected light yield value exceeds 44000photonMeV −1 . Scintillation decay times approach that of Ce 3+ photoluminescence decay and an additional less intense slower component is also observed. Physical aspects of energy transfer process and 5d1 excited state depopulation are discussed. The micro-pulling down technique is shown as an ideal tool for a directed combinatorial search for targeted single crystal compositions to reveal those with the highest figure-of-merit for a given application field. (Some figures may appear in colour only in the online journal)

Crystal Growth and Scintillation Properties of Ce Doped

Ce1%, 2% and 3% doped Gd3(Ga,Al)5O12 (GAGG) single crystals were grown by the Cz method. Luminescence and scintillation properties were measured. Light yield change along the growth direction and effects of Ce concentration on scintillation properties in Ce:GAGG were studied. Ce3+ 5d-4f emission within 520-530 nm was observed in the Ce:GAGG crystals. The Ce1%:GAGG sample with 3×3×1 mm size showed the highest light yield of 46000 photon/MeV. The energy resolution was 7.8%@662 keV. With increasing solidification fraction, the LY were decreased. It is proposed that the increase of Ga concentration along the growth direction is the main cause of the decrease of LY. The scintillation decay times were accelerated with increasing Ce concentration in the Ce:GAGG crystals. The scintillation decay times were 92.0 ns, 79.1 ns and 68.3 ns in the Ce1, 2 and 3% GAGG, respectively.

{\rm Gd}_{3}({\rm Ga},{\rm Al})_{5}{\rm O}_{12}

Various fundamental characteristics of Y2O3 ceramics, such as optical transmittance, reflectivity, absorption coefficient, refractive index, and dielectric constant, were investigated. Furthermore, in order to evaluate the possible application of this material as γ-ray scintillator, other radiation responses, like the α-ray excited emission spectrum, the γ-ray excited pulse height spectrum, the light yield, the nonproportionality, the energy resolution, and the γ-ray excited scintillation decay curves were obtained. The light yield of Y2O3 ceramics was evaluated in about 1.13 times higher than that of Bi4Ge3O12(BGO):Ce single crystals and was estimated in 9300 photon/MeV. The nonproportionality measurements showed a good proportionality. The scintillation decay curve could be fitted by an exponential function characterized by a fast component of about 34 ns.

Single Crystals

Pr:(Lu,Y)₃(Ga,Al)₅O₁₂ single crystals were grown by the micro-pulling down ( μ-PD) method. Luminescence and scintillation properties were measured. The substitution phenomenon in the Lu³⁺ sites with Y³⁺ and Al³⁺ sites with Ga³⁺ in garnet structure has been studied. Pr³⁺ 5d-4f emission within 300-400 nm accompanied by weak Pr³⁺ 4f-4f emission in 480-650 nm were observed in Ga 0-60 at.% substituted samples. Only Pr³⁺ 4f-4f emission was observed in Ga 80 at.% substituted sample. The light yield of Pr1%:Lu₂Y₁Ga₂Al₂O₁₂ sample was almost the same as that of Cz grown Pr:LuAG standard. Two-component scintillation decay of 17.9 ns (93%) and 68.0 ns (7%) were obtained using the PMT and digital oscilloscope TDS5032B. Slower decay components were reduced by Ga and Y substitution in LuAG structure.

Optical and scintillation characteristics of Y2O3 transparent ceramic

Detailed scintillation properties of Sc₂O₃, especially γ-ray response, are not well studied because of low density and low effective atomic number of this compound. They are reported in this paper. Sc₂O₃ single crystals grown by the micro-pulling-down method and Sc₂O₃ translucent ceramics produced by the spark plasma sintering are analyzed. Optical, luminescence, and scintillation properties of these single- and poly-crystalline solids are discussed and compared based on examination of their optical transmittance, radio-luminescence spectra, light yields under γ-ray excitation, non-proportionality, energy resolution, and scintillation decay profiles. Spectrally corrected light yields of the Sc₂O₃ single crystals and Sc₂O₃ ceramics were approximately 7,700 and 19,200 photons/MeV, respectively.

Improvement of Scintillation Properties in Pr Doped

Ce:(Lu,Y)₃(Ga,Al)₅ O₁₂ single crystals were grown by the μ -PD method with RF heating system. In these crystals, Ce³⁺ 4f-5d emission is observed within 500-530 nm wavelength. Emission peak shifts to shorter wavelength and the decay accelerates with increasing Ga concentration. In the case of Ce:Lu₂ Y₁ (Ga,Al)₅ O₁₂ series,the Ce0.2% Lu₂ Y₁Ga₃Al₂ O₁₂ crystal showed the highest emission intensity. In order to determine light yield, the energy spectra were measured under 662 keV ã-ray excitation (¹³⁷ Cs source) and detection by an APD S8664-55(Hamamatsu). The light yield was calibrated from <i>Fe</i>⁵⁵ direct irradiation peak to APD. The light yield of Ce0.2%: Lu₂ Y₁ Ga₃ Al₂ O₁₂ sample was of about 30,000 photon/MeV. Dominant scintillation decay time was of about 50 ns.

{\rm Lu}_{3}{\hbox {Al}}_{5}{\rm O}_{12}

Pr: (Lu,Y)<inf>3</inf>(Ga,Al)<inf>5</inf>O<inf>12</inf> single crystals were grown by the micro-pulling down (µ-PD) method. Luminescence and scintillation properties were measured. The substitution phenomenon in the Lu³⁺ sites with Y³⁺ and Al³⁺ sites with Ga³⁺ in garnet structure has been studied. Pr³⁺ 5d-4f emission within 300–400nm accompanied by weak Pr³⁺ 4f-4f emission in 480–650nm are observed in Ga 0–60 at.% substituted samples. Ga 80 at.% substituted sample shows only Pr³⁺ 4f-4f emission. The light output of Pr1%:Lu<inf>2</inf>Y<inf>1</inf>Ga<inf>2</inf>Al<inf>2</inf>O<inf>12</inf> sample was almost same as that of Cz grown Pr:LuAG standard. Two-component scintillation decay shows 17.9ns (93%) and 68.0ns (7%) using the PMT and digital oscilloscope TDS5032B. Slower decay components are reduced by Ga and Y substitution in LuAG structure.

Scintillator by Ga and Y Substitutions

In this report, the Ce: (Lu,Gd)<inf>3</inf>(Ga,Al)<inf>5</inf>O<inf>12</inf> single crystal were grown by the micro-pulling down (m-PD) method. Luminescence and scintillation properties were measured. The substitution at the Al<inf>3+</inf> sites by Ga³⁺ and at the Lu³⁺ sites by Gd³⁺ in garnet structure has been studied. In these crystals, Ce³⁺ 4f-5d emission is observed with 500–530nm wavelength. Emission peak shifts to shorter wavelength and the decay accelerates with increasing Ga concentration. In the case of Ce: Lu<inf>2</inf>Gd<inf>1</inf>(Ga,Al)<inf>5</inf>O<inf>12</inf> series, Ce: Lu<inf>2</inf>Gd<inf>1</inf>Ga<inf>3</inf>Al<inf>2</inf>O<inf>12</inf> shows highest emission intensity. The light yield of Ce: Lu<inf>2</inf>Gd<inf>1</inf>Ga<inf>3</inf>Al<inf>2</inf>O<inf>12</inf> sample with 3mmϕ×1mm size was around 30,000photon/MeV using calibration from ⁵⁵Fe direct irradiation peak to APD. Scintillation decay time was around 50ns. Density is theoretically 7.1g/cm³.

Scintillation Characteristics of Undoped

Pr:LuAG crystals possess interesting properties such as high density, high light yield, and very fast 5d-4f emission decay time. Recently, we developed a Pr:LuAG single crystal with a diameter of 92mm for scintillator applications such as medical imaging. In this study, Pr-doped Lu3Al5012 (Pr:LuAG) single crystals with a diameter of 92mm were grown by means of the Czochralski method; a body length of up to 100 mm was achieved. Scintillation light yield of Pr:LuAG was more than 2.8 times higher than the standard Bi4Ge3012(BGO) sample. Using 2.45mm ×5.1mm ×l5mm size sample coupled with photomultiplier (Hamamatsu H7195), energy resolution was 7.1% at 662 keV in average. The standard deviation of the light yield and the energy resolution was around 5.4 % and 9.5 % along the longitudinal direction of the grown crystal, respectively.