GSO Crystals Research Articles

A comparative study on the scintillation characteristics of Gd2SiO5:Ce and Lu1.2Gd0.8SiO5:Ce scintillators

In the present day, inorganic scintillators have been developed to detect high-energy photons such as x-rays and γ-rays. They have been applied in many works, such as astronomy, materials inspection, high energy physics, industrial application, and natural resources exploration. Especially in the medical field, they are used as radiation detectors in diagnostic equipment such as PET scanner, x-ray CT scanner, SPECT scanner, etc. This research studied the scintillation characteristics of Ce:GSO and Ce:LGSO single crystals. We found that at 662 keV gamma-ray energy, Ce:LGSO crystal has about 2.3 times more light yield than Ce:GSO crystal, but the energy resolution of both crystals is not different. For the degree of non-proportionality of both crystals, Ce:LGSO scintillator shows 0.08, which is better than the 0.19 obtained from Ce:GSO scintillator. This work also discusses the two scintillators’ peak-to-total ratio, loss parameter, and intrinsic light yield.

Monte Carlo Simulation to Test the Effectiveness of Crystal Detector Length for PHITS-Based PET Modality

PET (Positron-emission tomography) is used to determine physiological and metabolic functions in the body. Monte Carlo simulation is an important part of PET imaging, and the Particle Heavy Ion Transport code System (PHITS) is a simulation platform that can be used to perform Monte Carlo simulations. This study uses a Monte Carlo simulation based on PHITS to determine the range of gamma absorption with an energy of 511 keV in a scintillation detector crystal material. The gamma absorption range determines the effective crystal length in the PET modality. The simulation process is carried out by shooting Gamma at various types of materials, which are the materials used in PET scintillation crystals. The materials used in this simulation are NaI (Sodium Iodide), BaF2 (Barium Florida), BGO (Bismuth Germanate), and GSO (Gadolinium Oxyorthosilicate), considering their atomic number and crystal density. The crystal material is capable of absorbing gamma radiation with an energy of 511 keV with detailed crystal lengths for each NaI crystal of 0.26 cm; 0.25 cm BaF2 crystals; 0.1cm BGO crystals; and 0.18 cm GSO crystals. The crystal length from this simulation is smaller than the commercially available crystal length (range 1-3 cm). Based on the crystal length data, the most effective crystal for absorbing gamma radiation is the BGO crystal.

The coordinate sensitive detector with high space and time resolution based on the MA-20 multianode PMT

The work is dedicated to the discussion of the possibility of creating a position-sensitive detector with high coordinate reconstruction. The paper presents the simulation results and the experimentally obtained data for a prototype detector based on the MA-20 multianode PMT [1] and a linear stack of scintillating crystal or plastic strips. The multianode position-sensitive PMT MA-20 has a semitransparent bi-alkaline photocathode with the size of the sensitive area of 10 × 200 mm2, 10 evaporated type bi-alkaline type dynodes of the same length, and 20 separated anodes. This PM is the invention of the authors. The maximum gain of the dynode system is 106. The stack of scintillating strips made of GSO (gadolinium orthosilicate) crystals with an element size of 3 × 10 × 50 mm3, of BGO (bismuth germanate) crystals with an element size of 5 × 15 × 40 mm3, and finally stack of strips made of a plastic scintillator with an element size of 5 × 10 × 200 mm3 were used for experimental measurement of a spatial resolution of the detector prototype. Space resolution was determined by the position of the center of gravity of charges of neighboring anodes [2]. As a source of radiation, the collimated 137Cs (γ 0.662 MeV) and 90Sr (β− 2.283 MeV) were used, the measured number of photoelectrons is 10–20 of one element of the stack, depending on the scintillating strip type. The use of a multi-anode photomultiplier in combination with the stack of crystal or plastic scintillators allows one to get a simple linear detector with high performance in spatial resolution and also with a low level of intrinsic noise in comparison, for example, with silicon PMT. A resolution simulation was performed for a system consisting of a one-dimensional stack of scintillation strips placed on the photocathode of a multi-anode PMT for different values of the strips width and the number of photoelectrons of one strip. The experimental dependences of the signal value versus position of optical fiber with a diameter of 1 mm on the photocathode of the 20 anodes PMT were also measured that allowed to specify the coordinate resolution for the described detector. As a result of processing the collected data, spatial resolution was obtained at the level of 1 mm. The obtained results are in good agreement with the simulation results.

First prototyping of a dedicated PET system with the hemisphere detector arrangement

A strong demand is expected for high-sensitivity, high-resolution and low-cost brain positron emission tomography (PET) imaging for early diagnosis of dementia, as well as for general neuroscience studies. Therefore, we have proposed novel geometries of a hemisphere detector arrangement for high-sensitivity brain imaging, in which an add-on detector at the chin position or neck position helps in sensitivity uniformity improvement. In this study, we developed the first prototype system for proof-of-concept using four-layer depth-of-interaction detectors, each of which consisted of 16 × 16 × 4 Zr-doped GSO crystals with dimensions of 2.8 × 2.8 × 7.5 mm3 and a high-sensitivity 64-channel flat-panel photomultiplier tube. We used 47 detectors to form a hemisphere detector with a hemisphere shape of 25 cm inner diameter and 50 cm outer diameter, and we used seven detectors for each of the add-on detectors. The total detector number of 54 was about one-fourth that of a typical whole-body PET scanner. The hemisphere detector for the prototype system was realized by multiple rings having different numbers of detectors and a cross-shaped top detector unit covering the top. Performance evaluation showed uniform spatial resolutions of 3–4 mm by the filtered back-projection method. Imaging tests of a hot-rod phantom done with an iterative method were able to resolve 2.2 mm rods. Peak sensitivity was measured as more than 10% at a region near the top of the head, which was achieved with the help of the top detector unit. In addition, using the prototype system, we performed the first FDG clinical test with a healthy volunteer. The results showed that the proposed geometries had high potential for realizing high-sensitivity, high-resolution, and low-cost brain PET imaging. As for the add-on detector position, it was shown that the neck position resulted in higher sensitivity and wider field of view (FOV) than the chin position because the add-on detector at the neck position can be placed continuously to the hemisphere detector and close to the FOV.

Research of long GSO and LYSO crystals used in the calorimeter developed for the COMET experiment

Research of long GSO and LYSO crystals used in the calorimeter developed for the COMET experiment

Investigation of LYSO and GSO crystals and simulation of the calorimeter for comet experiment

The research results of parameters of LYSO and GSO crystals—candidates for being used in an electronic calorimeter for the COMET experiment—are described. The research has been made at the specially created high precision measuring setup. Measurements of uniformity of LYSO and GSO crystals along the crystal length were made. The energy resolution of crystals, their light output and processing speed were measured. The energy calibration of crystals was also performed. The research results were used for GEANT4 simulation of the calorimeter for COMET experiment. As a result of simulation of the calorimeter on the collimated 105 MeV electrons source with use of real optical parameters, the energy resolution of 5.0% was obtained for a calorimeter on GSO crystals and 2.5% for a calorimeter on LYSO crystals.

Performance evaluation of a depth-of-interaction detector by use of position-sensitive PMT with a super-bialkali photocathode

Our purpose in this work was to evaluate the performance of a 4-layer depth-of-interaction (DOI) detector composed of GSO crystals by use of a position-sensitive photomultiplier tube (PMT) with a super-bialkali photocathode (SBA) by comparing it with a standard bialkali photocathode (BA) regarding the ability to identify the scintillating crystals, energy resolution, and timing resolution. The 4-layer DOI detector was composed of a 16 × 16 array of 2.9 × 2.9 × 7.5 mm(3) GSO crystals for each layer and an 8 × 8 multi-anode array type position-sensitive PMT. The DOI was achieved by a reflector control method, and the Anger method was used for calculating interacting points. The energy resolution in full width at half-maximum (FWHM) at 511 keV energy for the top layer (the farthest from the PMT) was improved and was 12.0% for the SBA compared with the energy resolution of 12.7% for the BA. As indicators of crystal identification ability, the peak-to-valley ratio and distance-to-width ratio were calculated; the latter was defined as the average of the distance between peaks per the average of the peak width. For both metrics, improvement of several percent was obtained; for example, the peak-to-valley ratio was increased from 1.78 (BA) to 1.86 (SBA), and the distance-to-width ratio was increased from 1.47 (BA) to 1.57 (SBA). The timing resolution (FWHM) in the bottom layer was improved slightly and was 2.4 ns (SBA) compared with 2.5 ns (BA). Better performance of the DOI detector is expected by use of a super bialkali photocathode.

Comparison of modeled and measured performance of a GSO crystal as gamma detector

We have modeled, tested, and installed a large, cerium-activated Gd2SiO5 crystal scintillator for use as a detector of gamma rays. We present the measured detector response to two types of incident photons: nearly monochromatic photons up to 40MeV, and photons from a continuous Compton backscattering spectrum up to 200MeV. Our GEANT4 simulations, developed to determine the analyzing power of the Compton polarimeter in Hall A of Jefferson Lab, reproduce the measured spectra well.

Performance measurements of a depth-encoding TraPET detector module

The new method to correct a parallax error and the loss of coincidence counts caused by the gap between modules was developed for a small animal PET scanner. We proposed the TraPET scanner composed of 6 dual-layer phoswich detector modules. Each detector module consists of a 5.0 mm-thick trapezoidal-shaped monolithic LSO crystal and a 23 x 23 array of GSO crystal. The layer of interaction is identified by the pulse shape discrimination method. One detector module was built and the algorithm for layer identification was optimized. The dual-layer crystals were optically coupled to a Hamamatsu H8500 position-sensitive PMT and a resistive charge divider was used to multiplex 64-channel anode outputs into 4-channel position signals. The 4 signals have been sampled continuously by 14-bit ADC at a sampling rate of 105 MHz and the pulse shape discrimination algorithm was achieved through FPGA programming. The detector module was irradiated with a Na-22 point source from the side of the crystals to obtain flood images of each layer and two layers were clearly identified, thus verifying the DOI capability. The TraPET detector proved to be a reliable design for correcting the parallax error and improving the sensitivity simultaneously in the small animal PET.

Preliminary Results from Integrating Compton Photon Polarimetry in Hall A of Jefferson Lab

A wide range of nucleon and nuclear structure experiments in Jefferson Lab's Hall A require precise, continuous measurements of the polarization of the electron beam. In our Compton polarimeter, electrons are scattered off photons in a Fabry-Perot cavity; by measuring an asymmetry in the integrated signal of the scattered photons detected in a GSO crystal, we can make non-invasive, continuous measurements of the beam polarization. Our goal is to achieve 1% statistical error within two hours of running. We discuss the design and commissioning of an upgrade to this apparatus, and report preliminary results for experiments conducted at beam energies from 3.5 to 5.9 GeV and photon rates from 5 to 100 kHz.

Scintillation Efficiency of Inorganic Scintillators for Intermediate-Energy Charged Particles

We carried out experiments to investigate the light output response of NaI(Tl), CsI(Tl), GSO(Ce) and LYSO(Ce) crystals for intermediate-energy 4 He, 12 C and 40 Ar beams from HIMAC at National Institute of Radiological Sciences. And we investigate the light output of these crystals for several-energy gamma-ray for comparison. From these light output responses, we obtained the relationships between the scintillation efficiency (dL/dx) and the specific energy loss (dE/dx) for each crystal. The scintillation efficiency curves of NaI(Tl) and CsI(Tl) crystal have the peak in a particular dE/dx. On the other hand, the scintillation efficiency curves of GSO(Ce) and LYSO(Ce) crystal decrease with increasing dE/dx. The light output curves of these crystals were systematically reproduced using obtained scintillation efficiencies.

A Large Field of View Coincidence Imaging System Based on One-Dimensional Sharing Block Detectors

For such as breast cancer imaging, dedicated coincidence imaging detector will be promising for new instrumentation of nuclear medicine. For this purpose, a large field of view (FOV) coincidence imaging system was developed and tested. The imaging system consists of four sets of one-dimensional sharing block detectors and a single gamma probe and measures coincidence between these two detectors. The one-dimensional sharing detector uses 5 GSO blocks optically coupled to 6 dual photomultiplier tubes (PMT). The size of a single GSO is 2.9 mm times 2.9 mm times 15 mm. The signals from four one-dimensional sharing detectors are fed to weighted summing circuits. They are digitized by 100 MHz free running analog to digital (A-D) converters and are used to calculate the position of gamma interaction. Coincidence was measured between this gamma imaging detector (panel detector) and a hand-held single gamma probe. Acquired data was transferred to a personal computer and displayed. Most spots corresponding to GSO crystals were resolved in the position histogram. Spatial resolution was around 4 to 6 mm FWHM when the detector is greater than 25 mm. The sensitivity was 0.1-0.2% when the single probe was 25 mm away from the imager surface. Images of phantoms were successfully obtained. We conclude developed coincidence imaging system has large FOV and easy to handle, reasonable spatial resolution and may have potential to be a new instrument for nuclear medicine.

Preliminary study on potential of the jPET-D4 human brain scanner for small animal imaging

One trend in positron emission tomography (PET) instrumentation over the last decade has been the development of scanners dedicated to small animals such as rats and mice. Thicker crystals, which are necessary to obtain higher sensitivity, result in degraded spatial resolution in the peripheral field-of-view (FOV) owing to the parallax error. On the other hand, we are developing the jPET-D4, which is a dedicated human brain PET scanner that has a capability for depth-of-interaction (DOI) measurement. Although its crystal width is about twice that of commercially available small animal PET scanners, we expect the jPET-D4 to have a potential for small animal imaging by making full use of the DOI information. In this article, we investigate the jPET-D4's potential for small animal imaging by comparing it with the microPET Focus220, a state-of-the-art PET scanner dedicated to small animals. The jPET-D4 uses four-layered GSO crystals measuring 2.9 mm x 2.9 mm x 7.5 mm, whereas the microPET Focus220 uses a single layer of LSO crystals measuring 1.5 mm x 1.5 mm x 10.0 mm. First, the absolute sensitivity, counting rate performance and spatial resolution of both scanners were measured. Next a small hot-rod phantom was used to compare their imaging performance. Finally, a rat model with breast tumors was imaged using the jPET-D4. Thanks to the thicker crystals and the longer axial FOV, the jPET-D4 had more than four times higher sensitivity than the microPET Focus220. The noise equivalent counting-rate performance of the jPETD4 reached 1,024 kcps for a rat-size phantom, whereas that of the microPET Focus220 reached only 165 kcps. At the center of the FOV, the resolution was 1.7 mm for the microPET Focus220, whereas it was 3.2 mm for the jPET-D4. On the other hand, the difference of resolution became smaller at the off-center position because the radial resolution degraded faster for the microPET Focus220. The results of phantom imaging showed that the jPET-D4 was comparable to the microPET Focus220 at the off-center position even as the microPET Focus220 outperformed the jPET-D4 except for the peripheral FOV. The jPET-D4 human brain PET scanner, which was designed to achieve not only high resolution but also high sensitivity by measuring DOI information, was proven to have a potential for small animal imaging.

SU-GG-I-144: Validation of a Monte Carlo Model of the PET Component of the Gemini GXL PET/CT

Purpose: To validate a Monte Carlomodel of the PET component of the Gemini GXL PET/CT scanner (Philips Medical Systems) developed using the GATE simulation toolkit. Method and Materials: The precise PET geometry was reproduced with the GATE toolkit, including the 17 864 GSO(Zr) crystals with dimensions of 4 mm × 6 mm × 30 mm. A series of standard tests from the NEMA NU 2‐2001 protocol were simulated with the Monte Carlomodel and compared to experimental data: sensitivity, spatial resolution, scatter fraction, and noise equivalent count rate. The sensitivity is evaluated through an extrapolation technique both in the middle and at a 10 cm radial offset of a uniform line source surrounded by known absorbers. The spatial resolution is given by the full width at half‐maximum amplitude of the point spread function in the transverse and axial directions for compact radioactive sources in a glass capillary. The scatter fraction and noise equivalent count (NEC) rate are evaluated in a cylindrical phantom with variable radioactivity in a line source. Results: For the sensitivity test, the simulations for both central and offset positions overestimate the measured sensitivity values by 4%. For the resolution test, the difference between experimental and simulated data is between 0.4 mm (radial resolution at 10 cm radius) and 1.3 mm (transverse resolution at 1 cm radius). For the scatter fraction, the simulated results are within 0.5% of the experimental data. For the count rate tests, the peak NEC rate is at (62.8+/−0.5) kcps in the simulation, which is 4% lower than the measurements. Globally, the agreement for the count rate is always better than 5% for all activities less than 17 kBq/cc. Conclusion: The PETMonte Carlomodel reproduces experimental validation data within acceptable limits. It is suitable for PETtesting without experimental use of FDG.

Light Output Characteristic of Inorganic Scintillators to Intermediate-energy Charged Particles

In order to convert the light output of an inorganic scintillator to the deposited energy, the study of light output curves is very important due to its non linearity. We carried out experiments to investigate the light output response of Nal(Tl), CsI(Tl), GSO(Ce) and LYSO(Ce) crystals to intermediate-energy 4He and 12C beams from HIMAC at National Institute of Radiological Sciences. Scintillation efficiency was obtained in the wide energy range. It was found that a light output curve is represented using the peculiar scintillation efficiency despite it greatly changes its shape with different particles. In addition, it was found that scintillation efficiency was a function of the stopping power. Using the measured scintillation efficiency, the light output curves of the crystals were systematically reproduced

(Lu-Y)AlO$_{3}$:Ce Scintillator for Well Logging

Lutetium Yttrium Perovskite - (Lux - Y1-x)AlO3: Ce, LuYAP:Ce - is a cerium doped scintillation crystal that offers high light yield and high density. LuYAP:Ce with 70% lutetium content in (Lu-Y) system has been applied for medical imaging. Recently volume crystals with good transparency in the spectral range of scintillation have been obtained. It made possible detailed test of the material for well logging application. A unique combination of the parameters: high stopping power, fast and bright scintillation, light yield increase at high temperature makes them attractive for gamma-ray detection in a wide range of temperatures. Evaluation performance test of (Lu0.7 -Y0.3)AIO3: Ce scintillation crystal detector and widely used Nal(Tl), BGO and GSO crystal based detectors of the same size thetas 18 times 60 mm3 has been performed. All crystals were assembled in aluminium case with light reflective material and attached to a high temperature PMTs. It was found that (Lu0.7-Y0.3)AlO3:Ce based detector exhibits the most impressive set of operational characteristics: highest detection efficiency in integral and spectrometric gamma- and n-gamma well logging, excellent stability of the detector response with clear tendency to increase with temperature raise, stable signal-to-noise ratio in the temperature range 25 degC - 175 degC and high resistance to neutron activation. Shock and vibration tests also showed good mechanical stability of the material. Details of the tests and forthcoming application of the scintillator in well-logging are discussed.

Performance of the gamma-ray camera based on GSO(Ce) scintillator array and PSPMT with the ASIC readout system

We have studied the performance of a readout system with ASIC chips for a gamma-ray camera based on a 64-channel multi-anode PSPMT (Hamamatsu flat-panel H8500) coupled to a GSO(Ce) scintillator array. The GSO array consists of 8×8 pixels of 6×6×13 mm 3 with the same pixel pitch as the anode of the H8500. This camera is intended to serve as an absorber of an electron tracking Compton gamma-ray camera that measures gamma rays up to ∼1 MeV. Because we need a readout system with low power consumption for a balloon-borne experiment, we adopted a 32-channel ASIC chip, IDEAS VA32_HDR11, which has one of the widest dynamic range among commercial chips. However, in the case of using a GSO(Ce) crystal and the H8500, the dynamic range of VA32_HDR11 is narrow, and therefore the H8500 has to be operated with a low gain of about 10 5. If the H8500 is operated with a low gain, the camera has a narrow incident-energy dynamic range from 100 to 700 keV, and a bad energy resolution of 13.0% (FWHM) at 662 keV. We have therefore developed an attenuator board in order to operate the H8500 with the typical gain of 10 6, which can measure up to ∼1 MeV gamma ray. The board makes the variation of the anode gain uniform and widens the dynamic range of the H8500. The system using the new attenuator board has a good uniformity of min:max∼1:1.6, an incident-energy dynamic range from 30 to 900 keV, a position resolution of less than 6 mm, and a typical energy resolution of 10.6% (FWHM) at 662 keV with a low power consumption of about 1.7 W/64ch.

New 9$\,\times\,$9 and 10$\,\times\,$10 BGO Block Detector for Human PET Using PMT Quadrant Sharing Design

Our objectives were to develop two 9times9 and 10times10 array high resolution position sensitive block detectors using low cost photomultiplier-quadrant-sharing (PQS) technology. These two blocks can decode 4.3 mm or 3.9 mm BGO crystals with 39 mm size regular round PMT. By using ESR film as reflector between crystals, we achieved 96% packing fractions for these two blocks. Compared with conventional block design using 19 mm or 26 mm PMT, Phi39 mm size PMT can reduce the number of PMT in a camera by 55%-75%. Use of BGO crystal can reduce crystal cost by more than 70% compared to LSO or GSO crystals that are used in some of the newest PET cameras. The BGO crystal sizes-4.3 mm or 3.9 mm-in these two PQS blocks were similar to or smaller than BGO, LSO, or GSO crystals (4-6.3 mm) in commercial human PET cameras. The spatial resolution of the PQS blocks was expected to be similar or better. List mode data of these two blocks were acquired with Na- 22 source. Crystal-decoding map of blocks and individual crystal spectra were derived. All 9times9 and 10times10 crystals were clearly decoded on the block decoding map. These two PQS detectors decoded 81 or 100 BGO crystals per PMT. The average peak to valley ratio of decoding map was 3.4 and 1.8 respectively. The light collection efficiency for all crystals in the blocks were 71%-100% and 66%-100% respectively. The average energy resolutions of all crystals were 16.8% and 17.2% respectively. Our data suggest that even at lower cost the new PQS PET camera may outperform recent conventional PET cameras.

Performance evaluation for 120 four-layer DOI block detectors of the jPET-D4

The jPET-D4 is a brain positron emission tomography (PET) scanner that we have developed to meet user demands for high sensitivity and high spatial resolution. For this scanner, we developed a four-layer depth-of-interaction (DOI) detector. The four-layer DOI detector is a key component for the jPET-D4, its performance has great influence on the overall system performance. Previously, we reported the original technique for encoding four-layer DOI. Here, we introduce the final design of the jPET-D4 detector and present the results of an investigation on uniformity in performance of the detector. The performance evaluation was done over the 120 DOI crystal blocks for the detectors, which are to be assembled into the jPET-D4 scanner. We also introduce the crystal assembly method, which is simple enough, even though each DOI crystal block is composed of 1,024 crystal elements. The jPET-D4 detector consists of four layers of 16 x 16 Gd(2)SiO(5) (GSO) crystals and a 256-channel flat-panel position-sensitive photomultiplier tube (256ch FP-PMT). To identify scintillated crystals in the four-layer DOI detector, we use pulse shape discrimination and position discrimination on the two-dimensional (2D) position histogram. For pulse shape discrimination, two kinds of GSO crystals that show different scintillation decay time constants are used in the upper two and lower two layers, respectively. Proper reflector arrangement in the crystal block then allows the scintillated crystals to be identified in these two-layer groupings with two 2D position histograms. We produced the 120 DOI crystal blocks for the jPET-D4 system, and measured their characteristics such as the accuracy of pulse shape discrimination, energy resolution, and the pulse height of the full energy peak. The results show a satisfactory and uniform performance of the four-layer DOI crystal blocks; for example, misidentification rate in each GSO layer is <5% based on pulse shape discrimination, the averaged energy resolutions for the central four crystals of the first (farthest from the FP-PMT), second, third, and 4th layers are 15.7 +/- 1.0, 15.8 +/- 0.6, 17.7 +/- 1.2, and 17.3 +/- 1.4%, respectively, and variation in pulse height of the full energy peak among the four layers is <5% on average.

Growth and spectral properties of Er:Gd 2SiO 5 crystal

Er 3+-doped Gd 2SiO 5 (Er:GSO) single crystal with dimensions of ∅ 35×40 mm 3 has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd–Ofelt theory, and the intensity parameters Ω 2, Ω 4 and Ω 6 are obtained to be 6.168×10 −20, 1.878×10 −20, and 1.255×10 −20 cm 2, respectively. The emission cross-section has been calculated by Fuechtbauer–Ladenbury formula.