LuYAP Crystals Research Articles

Polarized spectroscopy and Judd-Ofelt analysis of Pr:LuYAP crystal

Pr 3+ ions doped Lu 0.7 Y 0 . 3 AlO 3 (LuYAP) crystal was successfully grown by the Czochralski method. Polarized absorption and polarized emission spectrum were recorded at room temperature. Using Judd-Ofelt theory, the intensity parameters Ω t, eff (t = 2, 4, 6) were calculated to be 3.52 × 10 −20 cm 2 , 1.43 × 10 −20 cm 2 , 15.88 × 10 −20 cm 2 , respectively. Based on F-L formula, the emission cross-sections peaking at 624 nm were calculated to be 1.67 × 10 −19 cm 2 , 8.71 × 10 −20 cm 2 and 8.00 × 10 −20 cm 2 for the a, b, and c polarization. The radiative lifetime and fluorescence lifetime was calculated to be 17.85 μs and 13.47 μs, respectively. All the results indicate that Pr:LuYAP is a potential material for visible laser operation. • Pr:LuYAP crystal was grown by Czochralski method. • Absorption and emission spectrum was recorded at room temperature. • Judd-Ofelt theory was used to analyze the spectroscopic properties of Pr:LuYAP. • Pr:LuYAP crystal is a potential laser material for visible laser output.

Pulse shape discrimination of LSO and LuYAP scintillators based on Discrete Fractional Fourier Transform

Parallax error decreases the accuracy of the Positron Emission Tomography (PET) scanner. One of suitable solutions to reduce this error is to gain the depth of interaction information in a PET which uses the phoswich detectors. The pulse shape of the scintillator material can identify the corresponding layer of interaction within the phoswich detector by using Pulse Shape Discrimination (PSD) methods. In this work, we propose the PSD based on a Discrete Fractional Fourier Transform (DFRFT) to extract the features of the scintillation pulses. Then, we use the Support Vector Machine (SVM) to classify these features. A data set consists of 100 000 scintillation pulses for LSO and LuYAP crystals are discriminated using the proposed method. Different fraction factors of the DFRFT are studied to select the optimum one. Also, the SVM is applied using linear, radial basis function, or quadratic kernel. The highest efficiency of the proposed PSD is 96.3% when the applied fraction factor is 0.8 and a quadratic SVM kernel is used.

Non-Proportionality Electron Response and Energy Resolution of LaBr3:Ce and LuYAP:Ce Scintillating Crystals

The present research work focuses on a comparative study of the non-proportionality of the electron response and the electron energy resolution for LaBr3:Ce and LuYAP:Ce scintillating crystals in the energy range from 97.8 keV to 437.0 keV by using the Compton coincidence technique (CCT). The results reveal that the LaBr3:Ce crystal shows the higher yield than the LuYAP:Ce crystal. Non-proportional electron responses at 97.8 keV were 6% higher and 2% lower for the LaBr3:Ce and the LuYAP crystals, respectively. The percentage proportionality of the electron response decreases with increasing electron energy. The proportionality of the electron response has higher values at energies beyond 374.5 keV for the LaBr3:Ce crystal and 260.4 keV for the LuYAP:Ce crystal. The electron energy resolution of the LaBr3:Ce crystal is better than that of the LuYAP:Ce crystal in the energy range from 97.8 keV to 437.0 keV. However, at low electron energy the resolutions of the electron responses for both scintillating crystal show similar values. Both the LaBr3:Ce and the LuYAP scintillating crystals show electron energy resolutions proportional to 1/√E.

Pulse shape discrimination based on Fractional Discrete Cosine Transform

One of the most serious errors in PET systems is the parallax error, which occurs due to spatial resolution limitation in PET. This error can be solved by using multilayer scintillation detector (phoswish detector) where each layer has a different decay constant. Each phoswish detector is optically coupled to a single PMT. Hence, by applying pulse shape discrimination (PSD) methods to identify the scintillated layer, the parallax error can be reduced. This paper proposes a PSD method relied on a Fractional Discrete Cosine Transform (FrDCT) and a Support Vector Machine (SVM) classifier. The proposed method can be used to differentiate between two arbitrary types of scintillation pulses where each type has a different decay constant. For demonstration of its performance, the proposed FrDCT-based method is applied to a data set of scintillation pulses of LSO and LuYAP crystals. Furthermore, FrDCT with different factors as well as different kernels of SVM; such as Linear, Quadratic, and Radial Basis Function (RBF) kernels, are used to study their effects on the discrimination efficiency. The highest achieved efficiency is equal to 95.9% for the 0.9 factor of FrDCT using a quadratic kernel SVM. On the other hand, the linear kernel consumes the lowest execution time at the expense of slightly reducing the discrimination efficiency.

Intrinsic and defect-related luminescence of YAlO3 and LuAlO3 single crystals and films

The work is dedicated to investigation of the luminescent properties of YAlO3 (YAP) and Lu0.95Y0.05AlO3 (LuYAP) crystals, grown from the melt by different crystallization methods. The intrinsic luminescent properties of YAP and LuYAP crystals were compared also with behavior of single crystalline films of these perovskites, grown using the liquid phase epitaxy method from the melt-solution based on the PbOB2O3 flux. The significant differences in the luminescent properties of YAP and LuYAP crystals were observed. These differences are explained by the various concentrations of the YAl and LuAl antisite defects (ADs) and oxygen vacancies formed during high-temperature crystallization of YAP and LuYAP crystals from the melt at the temperatures above 2000 °C. The ADs and oxygen vacancies form in YAP and LuYAP crystals the different types of emission centers in the UV and visible ranges. The luminescence of defect centers in the 4.1–6.2 eV range are related to the emission of exciton localized around and bound with the ADs as analogues of cations isoelectronic impurities. The emission centers of YAP and LuYAP crystals in the 2.75–4.1 eV range are formed by F+ and F centers. Apart from the intrinsic radiative transitions of F+ and F centers, the luminescence of excitons localized around F and F+ related centers in YAP and LuAP crystals is found as well. The emission bands of YAP and LuAP crystals in the visible range probably are caused by the aggregates of F+ and F centers.

Scintillation Properties of Ce-Doped LuYAP Crystal for Gamma Ray Detection

In the present day, inorganic scintillating crystals become a main part in detection and spectroscopy of nuclear particles and high energy photons, more spectively in X/g-ray imaging. The good properties for the scintillating crystals used in these applications require high photon yield, high stopping power, good energy resolution, good light yield proportionality, and minimal afterglow. The main useful of Ce-doped Lu0.7Y0.3AlO3 (LuYAP(Ce)) are high stopping power and non-hygroscopic which are expected to be key ingredients for medical imaging. In this work, we studied the light yield non-proportionality and energy resolution of LuYAP(Ce) crystal with the energy range from 31 to 1,274.5 keV using photomultiplier tube (PMT) readout. The intrinsic resolution of the LuYAP(Ce) crystal has been determined after correcting the measured PMT resolution. The results showed that the non-proportional response of the crystals was strongly correlated with the intrinsic resolution of the crystals.

A study of response of a LuYAP:Ce array with innovative assembling for PET

We propose the characterization of a first array of 10×10 Lutetium Yttrium Orthoaluminate Perovskite (LuYAP:Ce) crystals, 2mm×2mm×10mm pixel size, with an innovative assembling designed to enhance light output, uniformity and detection efficiency. The innovation consists of the use of 0.015mm thick dielectric coating as inter-pixel light-insulators, manufactured by Crytur (Czech Republic) intended to improve crystal insulation and then light collection. Respect to the traditional treatment with 0.2mm of white epoxy, a thinner pixel gap enhances packing fraction up to 98% with a consequent improvement of detection efficiency. Spectroscopic characterization of the array was performed by a Hamamatsu R6231 photomultiplier tube. A pixel-by-pixel scanning with a collimated 99mTc radioisotope (140keV photon energy) highlighted a deviation in pulse height close to 3.5% respect to the overall mean value. Meanwhile, in term of energy resolution a difference between the response of single pixel and the array of about 10% was measured. Results were also supported and validated by Monte Carlo simulations performed with GEANT4.Although the dielectric coating pixel insulator cannot overcome the inherent limitations of LuYAP crystal due to its self-absorption of light (still present), this study demonstrated that the new coating treatment allows better light collection (nearly close to the expected one) with in addition a very good uniformity between different pixels. These results confirm the high potentiality of this coating for any other crystal array suited for imaging application and new expectations for the use of LuYAP for PET systems.

Gamma induced atom displacements in LYSO and LuYAP crystals as used in medical imaging applications

The radiation damage, in terms of atom displacements, induced by gamma irradiation in LYSO and LuYAP crystals is presented. 44Sc, 22Na and 48V are used as gamma sources for this study. The energy of gammas from the electron–positron annihilation processes (511keV) is also included in the study. The atom displacements distributions inside each material are calculated following the Monte Carlo assisted Classical Method introduced by the authors. This procedure also allows to study the atom displacements in-depth distributions inside each crystal. The atom displacements damage in LYSO crystals is found to be higher than in LuYAP crystals, mainly provoked by the displacements of silicon and oxygen atoms. But the difference between atom displacements produced in LYSO and LuYAP decreases when more energetic sources are used. On the other hand, the correlation between the atom displacements and energy deposition in-depth distributions is excellent. The atom displacements to energy deposition ratio is found to increases with more energetic photon sources. LYSO crystals are then more liable to the atom displacements damage than LuYAP crystals.

TraPET: High performance small animal PET with trapezoidal phoswich detector

Abstract In recent years, small-animal PET scanners with depth of interaction (DOI) capability have been developed for molecular imaging research. The aim of this study is to perform simulations to design a high performance small-animal PET, called TraPET. TraPET has an inner diameter of 76.21 mm with 6 dual-layer phoswich detector modules. Each module is composed of a 5.0-mm-thick trapezoidal-monolithic-LSO crystal with a front face (surface facing toward the inside of the scanner) of 44.0×44.0 mm2 and a back face of 50.0×50.0 mm2 and a 25×25 array of LuYAP crystals with a 2.0×2.0 mm2 sensitive area with a 15.0 mm thickness. DOI information is extracted by a pulse shape discrimination method. The ability of event positioning in the trapezoidal-monolithic-LSO was evaluated by modeling the light distribution in the crystal using DETECT2000 and a 16×16 array of silicon photo-multipliers (SiPMs), with a 3.0 mm pixel size, selected as the photo-sensor. Also, the sensitivity and gap filling effect between modules were simulated using the Monte Carlo code, GATE. The new detector showed higher and more uniform sensitivity, as compared to scanners with rectangular-shaped detectors, because the trapezoidal-monolithic-LSO minimizes the dead space within the detector ring. In conclusion, our new detector proved to be a reliable design for small-animal PET with high spatial resolution by DOI information, and high sensitivity by high filling fraction.

Gamma-Ray Responses of Pr:LuYAP and Pr:YAP Scintillators

Pr3+ doped LuYAP crystal was grown by the Czochralski method with 1 inch diameter and 10 cm length. In order to compare scintillation characteristics, Pr3+ doped YAP crystal was also grown by the micro-pulling-down method. Absorption spectra of them were measured and Pr3+ 4f → 4f5d and 4f2 → 4f absorption lines were observed at 230,470, and 600 nm, respectively. In photoluminescence measurements, here excited by Xe lamp pulse of wavelength around 223,250 and 280 nm emission lines due to Pr3+ 4f5d → 4f transition were detected. When coupled with PMT R7600 and irradiated by gamma-rays, gamma-ray induced light yields were estimated as 1900 ph/MeV for Pr: LuYAP and 5600 ph/MeV for Pr: YAP. In both crystals, light yield non-proportionality and energy resolution were investigated by individual lines in the gamma-ray energy range from 59.5 keV to 1408 keV. The gamma-ray excited decay time constants turned out to be 9.8 ns for Pr:LuYAP and 9.0 ns for Pr:YAP.

Design and initial performance of PlanTIS: a high-resolution positron emission tomograph for plants

Positron emitters such as 11C, 13N and 18F and their labelled compounds are widely used in clinical diagnosis and animal studies, but can also be used to study metabolic and physiological functions in plants dynamically and in vivo. A very particular tracer molecule is 11CO2 since it can be applied to a leaf as a gas. We have developed a Plant Tomographic Imaging System (PlanTIS), a high-resolution PET scanner for plant studies. Detectors, front-end electronics and data acquisition architecture of the scanner are based on the ClearPET™ system. The detectors consist of LSO and LuYAP crystals in phoswich configuration which are coupled to position-sensitive photomultiplier tubes. Signals are continuously sampled by free running ADCs, and data are stored in a list mode format. The detectors are arranged in a horizontal plane to allow the plants to be measured in the natural upright position. Two groups of four detector modules stand face-to-face and rotate around the field-of-view. This special system geometry requires dedicated image reconstruction and normalization procedures. We present the initial performance of the detector system and first phantom and plant measurements.

Structural characterization of Lu0.7Y0.3AlO3 single crystal by Raman spectroscopy

AbstractLutetium yttrium orthoaluminate perovskite [Lu0.7Y0.3AlO3 (LuYAP)] crystals show great potential as fast response and high‐efficiency scintillators as an alternative to LuAlO3 (LuAP) crystals. This paper aims to offer a complete analysis of the vibrational modes of the LuYAP crystal by means of polarized Raman spectroscopy in the temperature range of 20–290 K and confronting the experimental results with numerical methods in order to characterize the crystal structure. Furthermore, an interpretation of the data in terms of vibrating molecular structures is suggested and the results are successfully confronted with the vibrational modes of similar perovskite crystals. Copyright © 2009 John Wiley & Sons, Ltd.

Development of scintillation materials for PET scanners

The growing demand on PET methodology for a variety of applications ranging from clinical use to fundamental studies triggers research and development of PET scanners providing better spatial resolution and sensitivity. These efforts are primarily focused on the development of advanced PET detector solutions and on the developments of new scintillation materials as well. However Lu containing scintillation materials introduced in the last century such as LSO, LYSO, LuAP, LuYAP crystals still remain the best PET species in spite of the recent developments of bright, fast but relatively low density lanthanum bromide scintillators. At the same time Lu based materials have several drawbacks which are high temperature of crystallization and relatively high cost compared to alkali-halide scintillation materials. Here we describe recent results in the development of new scintillation materials for PET application.

Image reconstruction for the ClearPET™ Neuro

ClearPET™ is a family of small-animal PET scanners which are currently under development within the Crystal Clear Collaboration (CERN). All scanners are based on the same detector block design using individual LSO and LuYAP crystals in phoswich configuration, coupled to multi-anode photomultiplier tubes. One of the scanners, the ClearPET™ Neuro is designed for applications in neuroscience. Four detector blocks with 64 2×2×10 mm LSO and LuYAP crystals, arranged in line, build a module. Twenty modules are arranged in a ring with a ring diameter of 13.8 cm and an axial size of 11.2 cm. An insensitive region at the border of the detector heads results in gaps between the detectors axially and tangentially. The detectors are rotating by 360° in step and shoot mode during data acquisition. Every second module is shifted axially to compensate partly for the gaps between the detector blocks in a module. This unconventional scanner geometry requires dedicated image reconstruction procedures. Data acquisition acquires single events that are stored with a time mark in a dedicated list mode format. Coincidences are associated off line by software. After sorting the data into 3D sinograms, image reconstruction is performed using the Ordered Subset Maximum A Posteriori One-Step Late (OSMAPOSL) iterative algorithm implemented in the Software for Tomographic Image Reconstruction (STIR) library. Due to the non-conventional scanner design, careful estimation of the sensitivity matrix is needed to obtain artifact-free images from the ClearPET™ Neuro.

Scintillation properties of LuAP and LuYAP crystals activated with Cerium and Molybdenum

Cerium and molybdenum-activated lutetium aluminum perovskite (LuAlO 3, LuAP) and mixed lutetium-yttrium aluminum perovskite (Lu x Y 1− x AlO 3, LuYAP) scintillator crystals have been grown by the Czochralski method at the Institute of Electronic Materials Technology (ITME, Warsaw). In this paper we report the measurements of scintillation light yields, absorption spectra, scintillation time profiles, low temperature thermoluminescence, and room temperature afterglow, performed on polished 2×2×10 mm 3 pixel samples cut from larger boules. We show that scintillation properties of the LuAP:Ce and LuAP:Ce,Mo crystals from ITME place them among the best crystals produced commercially.

Comparison of LuAP and LuYAP crystal properties from statistically significant batches produced with two different growth methods

Abstract Measurements of the light yield, decay time and transmission were carried out on LuAP:Ce and mixed LuYAP:Ce crystals, which are new scintillation materials considered for Positron Emission Tomography (PET) and are used in the ClearPET™ [Auffray et al., Nucl. Sci. Methods A 527 (2004) 171 [15] ], the small animal PET scanner developed by the Crystal Clear Collaboration at CERN [CR & D for the study of new fast and radiation hard scintillators for calorimetry at LHC, Crystal Clear Collaboration, project RD 18, CERN/DRDC/P27/91–15 [16] ]. The purpose was to compare the properties of these two crystal types and to evaluate LuAP and LuYAP crystals produced by one of the authors (A. Petrosyan) from the Institute for Physical Research (IPR), Armenia in comparison to the crystals commercially available from Photonics Materials Ltd. (PML), Glasgow, UK as well as from the Bogoroditsk Techno Chemical Plant (BTCP) in Russia. The influence of the Ce-concentration on the crystal properties was studied for crystals from IPR. The non-proportionality of the light output and the energy resolution at different energies for the best four crystals was compared to a LYSO crystal.

Characterization of pilot batch of LuYAP crystals to be used in prototypes of small animal positron emission tomograph ClearPET

Small animal positron emission tomograph ClearPET® is under development by Crystal Clear Collaboration, CERN. ClearPET® detector with Depth Of Interaction (DOI) determination capability is based on LSO and (Lu-Y)AlO3:Ce (LuYAP) scintillation crystals. Pilot batch of LuYAP crystals was grown at Bogoroditsk Techno Chemical Plant, and more than 9000 scintillation elements (pixels) with dimensions 2×2×8mm3 and 2×2×10mm3 were manufactured for small animal PET prototyping. During this effort, complete characterization of scintillation properties of grown crystal and selective control of scintillation pixels was performed. The aim of this work is to evaluate repeatability of LuYAP production technology and uniformity of scintillation pixel parameters. Methods and main results of characterization are presented.

First results on prototype production of new LuYAP crystals

A small animal positron emission tomograph, ClearPET, is under development by the Crystal Clear Collaboration at CERN. ClearPET, a detector with Depth Of Interaction (DOI) determination capability is based on LSO:Ce and (Lu0.7–Y0.3)AlO3:Ce ((Lu–Y)AP:Ce or LuYAP) scintillation crystals assembled in two-layer matrix with PMT readout. The key point of the ClearPET challenge was the development of the mass production technology of Lu-based scintillation crystals with perovskite structure. The LuYAP scintillation crystal has been proposed several years ago but its mass production technology could only be managed now, through tremendous efforts of the Crystal Clear Collaboration and of its industrial partners. Crystal ingots 18–25mm in diameter and 170–210mm in length are available now. In this paper, we discuss the results of the crystal mass production technology development and its application in detecting modules.

Scintillation properties of mixed LuYAP crystals in view of their use in a small animal PET scanner in phoswich configuration

Phoswich detectors are currently being considered by a number of investigators for depth-of-interaction (DOI) measurements in PET. In this work, the scintillation properties of several batches of Lu/sub 0.7/Y/sub 0.3/AlO/sub 3/ crystals doped with cerium were studied. The scintillators exhibited an excellent energy resolution and a light output comparable to BGO. The light pulse shape showed two components with 25 ns and around 250 ns. The light yield nonproportionality on photon energy was studied as well as the intrinsic energy resolution. Absorption, excitation and emission spectra were measured in a range extending from visible to ultraviolet. First results in the combination of these LuYAP crystals with LSO:Ce crystals in phoswich geometry for the final PET scanner are presented. The experimental results show that the new DOI detector is applicable for high-resolution PET systems.

Pulse shape discrimination of LSO and LuYAP scintillators for depth of interaction detection in PET

A feasible way to gain the depth of interaction information in a positron emission tomography scanner is the use of phoswich detectors. In general, the layer of interaction is identified from the pulse shape of the corresponding scintillator material. In this work, pulses from LSO and LuYAP crystals were investigated in order to find a practical method of distinguishing. It turned out that such a pulse processing could be kept simple because of an additional slow component in the light decay of the LuYAP pulse. At the same time, the short decay time guarantees that the major amount of the light output is still collected within a short pulse recording time.