Ce Scintillation Crystals Research Articles

The crystal growth of ortho- and pyrosilicates from W and Mo crucibles

The feasibility to grow bulk La-GPS:Ce scintillation crystals by the Czochralski method using Mo crucibles has been reported.

Development and evaluation of a prototype detector for an intraoperative laparoscopic coincidence imaging system with PET tracers.

Conventional positron emission tomography can be used only preoperatively to identify lymph node metastases, and hence, these growths are difficult to locate intraoperatively. Previously, an intraoperative laparoscopic coincidence imaging system, with an external fixed detector array and a detector probe that can be moved and inserted into the stomach, was proposed to identify lymph node metastases during stomach cancer surgery. This paper proposes a prototype detector for this system. GAGG:Ce (Gd3Al2Ga3O12:Ce) scintillator crystals, one to one coupled with silicon photomultipliers (SiPMs), were used to identify 511keV photons. An optical tracking system followed the position and orientation of the movable detector. SiPM outputs were read out by time-over-threshold (TOT)-based application-specific integrated circuits, which converted the electrical charges into digital pulses. To identify the arrival time, channel number, and pulse width, which indicate the energy information of each TOT output, a data acquisition system was developed based on a field-programmable gate array. The spatial resolution of the reconstructed images in lateral direction was better than 7mm, but that of depth direction was limited, owing to inadequate projections. The prototype successfully reconstructed 44kBq 18F-fluorodeoxyglucose sources during a 2-min scan. We developed a prototype detector for an intraoperative laparoscopic coincidence imaging system. The prototype detector was evaluated successfully, and the produced images were similar to those obtained in the simulation results, thereby suggesting that this method offers a new possibility of imaging lymph node metastases intraoperatively.

Optical Properties of YAG:Ce and GGG:Ce Scintillation Crystals Irradiated with a High Fluence Proton Beam

In this paper, we report on the study of the optical properties of YAG:Ce and GGG:Ce garnet crystals after irradiation in a 660~MeV proton beam with a fluence up to 8.9$\times$10$^{14}$ protons/cm$^2$. We found that the transparency of both crystals fell by no more than 7\% in the region of their own luminescence. The light yield of a YAG:Ce sample, measured one year after irradiation, dropped by about 35\%.

Characterization of monolithic GAGG:Ce coupled to both PMT and SiPM array for gamma imaging in Nuclear Medicine

GaGG:Ce scintillation crystal is very useful for nuclear imaging purposes, thanks to its several advantages (high density, short decay time, high light yield and good energy resolution, no self-activity, no hygroscopic). However, only the recent improvements in the growth processes make it available with large size, in order to use it in monolithic configuration. The main drawbacks of pixelated crystals, as non-uniform response, high production costs and optical light loss, could be therefore overcome. In this work the characterization of this promising crystal coupled both to a single channel PMT (spectrometric purpose) and to a new technology SiPM (50% PDE and 74% geometrical fill factor) has been performed. The detection efficiency results good both for SPECT (87% at 122 keV) and for PET (18% at 356 keV) applications. However, the unexpected result arises from the energy resolution: at 356 keV 8.9% and 8.0% for single channel PMT and SiPM configuration, respectively. In other terms, the used SiPM allows to achieve higher energy resolution than single channel PMT. Moreover, a high imaging performance has been observed, with a millimeter intrinsic spatial resolution.

Convolutional Neural Network for Crystal Identification and Gamma Ray Localization in PET

Spatial resolution in positron emission tomography using traditional pixelated block detectors is inherently limited by the size of the detector array elements, namely, the scintillator crystals and readout pixels. Conventional centroiding algorithms based on Anger logic are widely used to localize individual events down to the scintillator level. However, these algorithms are associated with well-known performance degradation along the edges and corners of detector arrays. In this article, we explore the use of convolutional neural networks (CNNs) for 3D gamma ray localization as a computationally inexpensive alternative to classical centroiding. The method is successfully implemented on Monte Carlo simulated data from a single-ended readout depth-encoding detector array consisting of LYSO:Ce scintillator crystals coupled 4-to-1 to silicon photomultiplier (SiPM) pixels. The CNN demonstrated higher crystal identification accuracy at the edges and corners (99.0% versus 49.2%) and lower spatial error compared to classical centroiding (0.38 mm versus 0.76 mm). In addition, the CNN achieved 2.75 mm FWHM depth-of-interaction (DOI) resolution. Preliminary qualitative results for how our approach translates to experimental data after training on simulated data are also presented. Future work on the CNN-based approach with more experimental data could improve the performance of block detectors with multicrystal scintillators and possibly achieve subscintillator spatial resolution.

The use of scintillation crystals in nuclear medicine

Abstract Currently, several dozens of different types of scintillation crystals are known. Scintillation crystals are successfully used in nuclear medicine. When spectra of ionizing radiation are measured, one of the important problems is to ensure proportionality between the amplitude of a pulse at the output of the recording system and the energy of recorded particles. Investigation results of the dependence of the specific light yield on the energy of X-rays and γ-quanta in a range of 1.5–662 keV for NaI(Tl), CsI(Na), CsI(Tl), Bi4Ge3O12, CdWO4, ZnWO4, Y3Al5O12:Ce, CaF2(Eu), LSO, YAlO3:Ce scintillation crystals are presented. The obtained dependences are nonlinear with pronounced minima in a range of K- and L-absorption edges of scintillator-forming elements.

SIMULATION OF THE RESPONSE OF A LaBr3(Ce) DETECTOR IN AN ATMOSPHERE CONTAMINATED WITH RADIONUCLIDES AFTER A NUCLEAR POWER PLANT ACCIDENT.

The aim of this paper is to investigate the possibility of using detectors based on LaBr3(Ce) scintillation crystal as part of gamma spectrometry systems for field use and possibly as part of a monitoring network around nuclear power plants, i.e. whether LaBr3(Ce) detectors can follow the classical scintillation detectors based on NaI (Tl). For this purpose, the Monte Carlo simulation of the IPROL-1 probe response was performed in the simplified geometry of the radionuclides-contaminated atmosphere. A study shows that a LaBr3(Ce)-based probe is usable for this purpose and results are at least comparable to those with a conventional NaI (Tl)-based probe.

Study on High-Temperature Performance of LaBr3(Ce) Scintillators

In this paper, the relative light output, energy resolution and count rate of encapsulated LaBr3 (Ce) crystals were tested under the temperature from 25 °C to 175 °C using 137Cs γ radioactive source. The variation of high temperature scintillation performance of LaBr3 and NaI(Tl) crystal packages was measured and analyzed. The results show that the decline of light output of LaBr3(Ce) scintillation crystal is about 80% of that of NaI(Tl) at 175 °C. The energy resolution of LaBr3(Ce) at high temperature 175 °C is approximately 8%, which is better than the 9.9% energy resolution of NaI(Tl) scintillation crystals at room temperature 25 °C. The count rate of LaBr3(Ce) is about 5-6 times more than that of the NaI(Tl) crystal.

Improvement of response time in GAGG:Ce scintillation crystals by magnesium codoping

Dynamics of the population of the excited Ce states responsible for the luminescence response time in Gd3Al2Ga3O12:Ce scintillating crystals is studied by revealing the dynamics of nonequilibrium carriers in the picosecond domain. Optical pump and probe technique exploiting selective excitation of structural units of the crystal and probing the induced absorption as a function of time and spectral position is exploited. A fast response within a few picoseconds due to the absorption by holes at Gd ions and by electrons occupying the first excited state of Ce ions with the intracenter relaxation time of 500 fs are identified. Trapping of nonequilibrium electrons during their migration through the matrix to the emitting Ce ions are shown to be responsible for the slow component in the population of the excited Ce state. Elimination of the slow component is evidenced even at Mg codoping as low as 10 ppm. The elimination correlates with the acceleration of the response in coincidence time resolution experiments showing potential of GAGG:Ce, Mg in medical and high-energy physics applications.

Progresses of silicon photomultiplier technologies with epitaxial quenching resistors

During past years, Novel Device Laboratory (NDL) has developed silicon photomultiplier (SiPM) technologies with epitaxial quenching resistors (EQR). EQR-SiPMs feature a continuous low-resistance doping layer and integrated quenching resistors in the epitaxial silicon layer. This design allows small microcells to have a higher than usual fill-factor (FF), thus yielding a large dynamic range while retaining a useful photon detection efficiency (PDE). In this manuscript we report the new version of EQR-SiPM with p-on-n diode configuration and demonstrate its use in radiation detection. The 3 mm×3 mm device features a high cell density of 9381/mm2, a FF of 36.5%, and PDE of 27%. The SiPM was coupled to a 5 mm×5 mm×10 mm YSO(Ce) scintillation crystal and used to measure gamma-ray spectra from various isotopic sources. The detector exhibited an energy resolution of 7.6 ± 0.6% at 662 keV. The energy response was effectively linear between 32 and 1332 keV, owing to the large dynamic range of the SiPM. These characteristics make the SiPM-based detector well-suited to measure gamma ray spectra over a wide energy range.

Sub-3mm spatial resolution from a large monolithic LaBr3 (Ce) scintillator

Abstract A Compton camera prototype for ion beam range monitoring via prompt (< 1 ns) gamma detection in hadron therapy is being developed and characterized at the Medical Physics Department of LMU Munich. The system consists of a large (50x50x30 mm3) monolithic LaBr3(Ce) scintillation crystal as absorber component to detect the multi-MeV Compton scattered photons, together with a stack of 6 double-sided silicon strip detectors (DSSSD) acting as scatterer component. Key ingredient of the γ-source reconstruction is the determination of the γ-ray interaction position in the scintillator, which is read out by a 256-fold segmented multi-anode photomultiplier tube (PMT). From simulations an angular resolution of about 1.5o for the photon source reconstruction can be expected for the energy range around 3 – 5 MeV, provided that a spatial resolution of 3 mm can be reached in the absorbing scintillator [1]. Therefore, particular effort was dedicated to characterize this latter property as a function of the γ-ray energy. Intense, tightly collimated 137Cs and 60Co photon sources were used for 2D irradiation scans (step size 0.5 mm) as prerequisite for studying the performance of the “k-Nearest-Neighbors” algorithm developed at TU Delft [2] (together with its variant ”Categorical Average Pattern”, CAP) and extending its applicability into the energy range beyond the original 511 keV. In this paper we present our most recent interaction position analysis in the absorbing scintillator, leading to a considerably improved value for the spatial resolution: systematic studies were performed as a function of the k-NN parameters and the PMT segmentation. A trend of improving spatial resolution with increasing photon energy was confirmed, resulting in the realization of the presently optimum spatial resolution of 2.9(1) mm @1.3 MeV, thus reaching the design specifications of the Compton camera absorber. The specification goal was reached also for a reduced PMT segmentation of 8x8 anode segments (each with 6x6 mm2 active area), thus allowing to reduce the complexity of the signal processing while preserving the performance.

Integrated optical and nuclear simulation of a monolithic LYSO:Ce based PET detector module

In the recent years new digital photon counter devices (also known as silicon photomultipliers, SiPMs) were designed and manufactured to be used specifically in positron emission tomography (PET) scanners. Finely pixelated SiPM arrays have opened new opportunities in PET detector development, such as the utilization of monolithic scintillator crystals. We worked out a simulation tool (SCOPE2) to assist the optimization and characterization of such PET detector modules. In the present paper we report the first application of SCOPE2 on the performance evaluation of a prototype PET detector module. The PET detector is based on monolithic LYSO:Ce scintillator crystal and a fully digital, silicon photon-counter, SPADnet-I. A new interface has been developed for SCOPE2 to access GATE simulation results. A combination of GATE and SCOPE2 was used to simulate excitation of the prototype PET detector with an electronically collimated γ -beam. Measurement results from the collimated γ-beam experiment were compared with the combined simulation. A good agreement was observed in the tendencies of total count spectrum and point of interaction distribution. We used the performance evaluation to understand and explain the measurement results in detail.

Alpha spectroscopy by the Φ25 mm×0.1 mm YAlO3:Ce scintillation detector under atmospheric conditions

The YAlO3:Ce scintillation crystal has excellent mechanical properties and is not affected if used in chemically aggressive environments. The detector with the diameter of Φ25.4mm and thickness of 0.1mm was coupled with the PMT, associated electronics and the MCA in order to study its alpha spectroscopy properties. The measured alpha spectra of the surface calibration sources of 241Am and 230Th were compared with results of a Monte Carlo simulation. The experiment and the simulation were carried out for three distances between the detector and the surface alpha source in order to assess the effect of the distance on the detected energy of alpha radiation. Finally, the detector was used for the monitoring of radon (222Rn) decay products (radon daughters) in the air. It was concluded that the detector is suitable for the in-situ alpha spectroscopy monitoring under ambient atmospheric conditions. Nevertheless, in order to identify radionuclides and their activity from the measured alpha spectra a computer code would need to be developed.

Development of a Compton camera for prompt-gamma medical imaging

A Compton camera-based detector system for photon detection from nuclear reactions induced by proton (or heavier ion) beams is under development at LMU Munich, targeting the online range verification of the particle beam in hadron therapy via prompt-gamma imaging. The detector is designed to be capable to reconstruct the photon source origin not only from the Compton scattering kinematics of the primary photon, but also to allow for tracking of the secondary Compton-scattered electrons, thus enabling a γ-source reconstruction also from incompletely absorbed photon events. The Compton camera consists of a monolithic LaBr3:Ce scintillation crystal, read out by a multi-anode PMT acting as absorber, preceded by a stacked array of 6 double-sided silicon strip detectors as scatterers. The detector components have been characterized both under offline and online conditions. The LaBr3:Ce crystal exhibits an excellent time and energy resolution. Using intense collimated 137Cs and 60Co sources, the monolithic scintillator was scanned on a fine 2D grid to generate a reference library of light amplitude distributions that allows for reconstructing the photon interaction position using a k-Nearest Neighbour (k-NN) algorithm. Systematic studies were performed to investigate the performance of the reconstruction algorithm, revealing an improvement of the spatial resolution with increasing photon energy to an optimum value of 3.7(1)mm at 1.33MeV, achieved with the Categorical Average Pattern (CAP) modification of the k-NN algorithm.

Engineering of bulk and fiber-shaped YAGG:Ce scintillator crystals

Composition-property correlations have been systematically studied in the full concentration range of Y3Al5−xGaxO12:Ce (YAGG:Ce) scintillator crystals. The most promising compositions for new high energy physics experiments at colliders have been determined with the light output >200% relative to BGO and fast luminescence decay. Codoping with Ca2+ provides the decrease of phosphorescence intensity to 0.2% after 0.6 μs and shortening of the luminescence decay constant to 21 ns. Factors affecting the scintillation decay time in YAGG:Ce have been discussed. The crystals show weak transmission loss under γ-irradiation. The feasibility to produce YAGG:Ce fibers using the μ-PD method has been shown.

Investigation of radiation detection properties of CRY-018 and CRY-019 scintillators for medical imaging

During the last years the research for new scintillation crystals has been crucial for the improvement of imaging performance in nuclear medicine applications. Crytur company has recently released two new scintillators named CRY-018 and CRY-019 which are non hygroscopic, have short decay time and low refraction index. They represent the ideal candidates to substitute NaI:Tl and BGO crystals in future PET ad SPECT applications. The purpose of this work is to characterize this unknown crystals, look for possible applications in imaging for nuclear medicine. The results of this work were compared with the results obtained with a LaBr3:ce scintillation crystal. This particular crystal is used as a comparison benchmark because of its strong linear pulse height uniformity response and high energy resolution. Measurements have been performed with a high count rate which is typical for medical applications. Irradiation of the crystals have been performed in three different geometries and in a photon energy range suitable with SPECT and PET applications. The experimental results identify the CRY-018 as an Yttrium and Silicon mixture and the CRY-019 with as Lutetium and Silicon one. Moreover a light yield of about 45% of LaBr3 one, was obtained for both the CRY-018 and CRY-019. This is one of the higher light yield between most of the scintillation crystals usually used in nuclear medicine. Both crystals are characterized by a non-proportionality in the pulse height linearity response. Energy resolutions of 7.4% for CRY-018 and 8.4% for CRY-019 at 661 keV, have been measured. The intrinsic component of the energy resolution has been esteemed for all three scintillators. An intrinsic detection efficiency of about 45% at 122 keV for CRY-018 and 14% at 661 keV for CRY-019 has been measured. Compared with LaBr3:Ce efficiency, which is highly deteriorated by the coating required by the hygroscopicity, CRY-018 and CRY-019 are really interesting considering that these two samples are only 6 mm thick. Crytur's crystals seem to be suitable for nuclear medicine applications.

Medical gamma probe based on LaBr3:Ce scintillation crystal

The medical gamma probe for radionuclide diagnostics based on LaBr3:Ce scintillation crystal and a silicon photomultiplier is described. Spectrometric characteristics of the detector are studied. The energy resolution is measured to be 3.6%at 662 keV and 10% at 140.5 keV. Technical parameters of the developed gamma probe are described. It is shown that it matches the best world analogues in the set of characteristics.

LaBr3(Ce) gamma-ray detector for neutron capture therapy

Results of developing of a gamma-ray detector based on LaBr3(Ce) scintillation crystal for neutron capture therapy are presented. An energy resolution of the detector measured by photomultiplier tube Hamamatsu R6233-100 is showed. It was 2.93% for gamma line 662 keV from a source 137Cs. For radiative capture gamma line of isotope 10B (478 keV) and annihilation line (511 keV) the values were 3.33 and 3.24% respectively. Data analysis of gamma spectra for an estimation of energy resolution threshold required for visual identification gamma lines 478 and 511 keV was made.

Comparative Characterization Study of a LaBr3(Ce) Scintillation Crystal in Two Surface Wrapping Scenarios: Absorptive and Reflective.

The properties of a 50 mm × 50 mm × 30 mm monolithic LaBr3:Ce scintillator crystal coupled to a position-sensitive multi-anode photomultiplier (PMT, Hamamatsu H9500), representing the absorbing detector of a Compton camera under study for online ion (proton) beam range verification in hadron therapy, was evaluated in combination with either absorptive or reflective crystal surface coating. This study covered an assessment of the energy and position-dependent energy resolution, exhibiting a factor of 2.5–3.5 improvement for the reflectively wrapped crystal at 662 keV. The spatial dependency was investigated using a collimated 137Cs source, showing a steep degradation of the energy resolution at the edges and corners of the absorptively wrapped crystal. Furthermore, the time resolution was determined to be 273 ps (FWHM) and 536 ps (FWHM) with reflective and absorptive coating, respectively, using a 60Co source. In contrast, the light spread function (LSF) of the light amplitude distribution on the PMT segments improved for the absorptively wrapped detector. Both wrapping modalities showed almost no differences in the energy-dependent photopeak detection efficiency.

Determination of LaBr3(Ce) internal background using a HPGe detector and Monte Carlo simulations

The presence of 138La and 227Ac impurities in LaBr3(Ce) scintillator crystals is a drawback for their use in environmental radiation monitoring. A method is presented to evaluate the internal 138La activity. Firstly, an experimental set-up is prepared with the LaBr3(Ce) crystal acting as the radiation source and an HPGe detector that acquires the photon spectrum. Then, the internal background spectrum is simulated with a modified version of the PENELOPE/penEasy Monte Carlo code. The simulated spectra agree with measurements conducted at ultra-low-background facilities.