Monolithic Scintillator Research Articles

Feasibility Study of Simultaneous Measurement of Multiple Parameters from a Single Monolithic Scintillator Crystal Using the Geant4 Simulation Toolkit

Abstract A feasibility study for the construction of a minimal multi-parameter detector module from a single monolithic CeBr3 scintillator crystal and a SiPM matrix that is capable of simultaneously measuring deposited energy, position of particle interaction and time characteristics was performed by simulation and direct measurements. The results show that the detector module can operate successfully with characteristics that are close to the limits of the physical detector and that such minimal modules can potentially be used on micro- and nano-satellite platforms .

Impact Point Determination of Gamma Interaction in a Monolithic Scintillator Crystal Read Out by a SiPM Matrix

Abstract We construct a simulation framework which can determine simultaneously deposited energy, position and time resolution of interactions of gamma rays in a monolithic scintillator crystal read out by a matrix of photosensitive detectors. And we report and discuss the simulation results form three different methods to determine the impact position of a particle.

A novel proton-integrating radiography system design using a monolithic scintillator detector: Experimental studies

Research on proton-based imaging systems aims to improve treatment planning, internal anatomy visualization, and patient alignment for proton radiotherapy. The purpose of this study was to demonstrate a new proton radiography system design consisting of a monolithic plastic scintillator volume and two optical cameras for use with scanning proton pencil beams. Unlike the thin scintillating plates currently used for proton radiography, the plastic scintillator volume (20 × 20 × 20 cm 3) captures a wider distribution of proton beam energy depositions and avoids proton-beam modulation. The proton imaging system’s characteristics were tested using image uniformity (2.6% over a 5 × 5 cm 2 area), stability (0.37%), and linearity (R2=1) studies. We used the light distribution produced within the plastic scintillator to generate proton radiographs via two different approaches: (a) integrating light by using a camera placed along the beam axis, and (b) capturing changes to the proton Bragg peak positions with a camera placed perpendicularly to the beam axis. The latter method was used to plot and evaluate relative shifts in percentage depth light (PDL) profiles of proton beams with and without a phantom in the beam path. A curvelet minimization algorithm used differences in PDL profiles to reconstruct and refine the phantom water-equivalent thickness (WET) map. Gammex phantoms were used to compare the proton radiographs generated by these two methods. The relative accuracies in calculating WET of the phantoms using the calibration-based beam-integration (and the PDL) methods were -0.18 ± 0.35% (-0.29 ± 3.11%), -0.11 ± 0.51% (-0.15 ± 2.64%), -2.94 ± 1.20% (-0.75 ± 6.11%), and -1.65 ± 0.35% (0.36 ± 3.93%) for solid water, adipose, cortical bone, and PMMA, respectively. Further exploration of this unique multicamera-based imaging system is warranted and could lead to clinical applications that improve treatment planning and patient alignment for proton radiotherapy.

Development of a direction-sensitive gamma-ray monitoring system using a gamma camera with a dual-sided collimator: A Monte Carlo study

Nuclear explosions, sabotage, and dirty bomb materials are considered a security threat. This paper discusses the development of a gamma-ray monitoring system that enables the screening of nuclear materials moving simultaneously on both sides of the system at ports. This direction-sensitive gamma-ray monitoring (DSGM) system consists of a monolithic plastic scintillator surrounded by 28 photomultiplier tubes and dual-sided parallel-hole lead collimators. With Monte Carlo simulation, the monitoring performance of the DSGM system was assessed for static and moving sources. A multilayer perceptron model was employed to estimate the energy-deposited position of the gamma-rays emitted by nuclear materials in the scintillator.

Image quality evaluation of projection- and depth dose-based approaches to integrating proton radiography using a monolithic scintillator detector

The purpose of this study is to compare the image quality of an integrating proton radiography (PR) system, composed of a monolithic scintillator and two digital cameras, using integral lateral-dose and integral depth-dose image reconstruction techniques. Monte Carlo simulations were used to obtain the energy deposition in a 3D monolithic scintillator detector (30 × 30 × 30 cm3 poly vinyl toluene organic scintillator) to create radiographs of various phantoms—a slanted aluminum cube for spatial resolution analysis and a Las Vegas phantom for contrast analysis. The light emission of the scintillator was corrected using Birks scintillation model. We compared two integrating PR methods and the expected results from an idealized proton tracking radiography system. Four different image reconstruction methods were utilized in this study: integral scintillation light projected from the beams-eye view, depth-dose based reconstruction methods both with and without optimization, and single particle tracking PR was used for reference data. Results showed that heterogeneity artifact due to medium-interface mismatch was identified from the Las Vegas phantom simulated in air. Spatial resolution was found to be highest for single-event reconstruction. Contrast levels, ranked from best to worst, were found to correspond to particle tracking, optimized depth-dose, depth-dose, and projection-based image reconstructions. The image quality of a monolithic scintillator integrating PR system was sufficient to warrant further exploration. These results show promise for potential clinical use as radiographic techniques for visualizing internal patient anatomy during proton radiotherapy.

Sub-millimeter precise photon interaction position determination in large monolithic scintillators via convolutional neural network algorithms

In this work, we present the development and application of a convolutional neural network (CNN)-based algorithm to precisely determine the interaction position of γ-quanta in large monolithic scintillators. Those are used as an absorber component of a Compton camera (CC) system under development for ion beam range verification via prompt-gamma imaging. We examined two scintillation crystals: LaBr3:Ce and CeBr3. Each crystal had dimensions of 50.8 mm × 50.8 mm × 30 mm and was coupled to a 64-fold segmented multi-anode photomultiplier tube (PMT) with an 8 × 8 pixel arrangement. We determined the spatial resolution for three photon energies of 662, 1.17 and 1.33 MeV obtained from 2D detector scans with tightly collimated 137Cs and 60Co photon sources. With the new algorithm we achieved a spatial resolution for the CeBr3 crystal below 1.11(8) mm and below 0.98(7) mm for the LaBr3:Ce detector for all investigated energies between 662 keV and 1.33 MeV. We thereby improved the performance by more than a factor of 2.5 compared to the previously used categorical average pattern algorithm, which is a variation of the well-established k-nearest neighbor algorithm. The trained CNN has a low memory footprint and enables the reconstruction of up to 104 events per second with only one GPU. Those improvements are crucial on the way to future clinical in vivo applicability of the CC for ion beam range verification.

Optimization of CeBr[formula omitted] position-sensitive calorimeter module

For the next generation of MeV range gamma-ray telescopes, position sensitive calorimeters based on a monolithic scintillator coupled to a pixelated photodetector could be an important building block. In this paper, we present the optimization of the position reconstruction algorithms using machine learning, for a detector based on a 51×51×10mm3 CeBr3 crystal. For that purpose, we used an automated test bench and collimated radioactive sources to generate experimental data of known energy and position by irradiating the detector with gamma rays. We found in these data different gamma-ray interaction morphologies for which position reconstruction algorithms perform differently, and we developed an algorithm to automatically classify them. We also conducted an extensive optimization of the artificial neural networks that perform the 3D position reconstruction using the Keras Python library with Theano backend. We found that at 662keV, 90% of events have a morphology that facilitates position reconstruction. The optimized position reconstruction algorithms give for those events a rms error in the plane of the detector of 1.8mm on each axis. The rms error in the depth of the crystal is found to be 2mm.

A thick semi-monolithic scintillator detector for clinical PET scanners

Both monolithic and semi-monolithic scintillator positron emission tomography (PET) detectors can measure the depth of interaction with single-ended readout. Usually scintillators with a thickness of 10 mm or less are used since the position resolutions of the detectors degrade as the scintillator thickness increases. In this work, the performance of a 20 mm thick long rectangular semi-monolithic scintillator PET detector was measured by using both single-ended and dual-ended readouts with silicon photomultiplier (SiPM) arrays to provide a high detection efficiency. The semi-monolithic scintillator detector consists of nine lutetium–yttrium oxyorthosilicate slices measuring 1.37 × 51.2 × 20 mm3 with erythrocyte sedimentation rate foils of 0.065 mm thickness in between the slices. The SiPM array at each end of the scintillator detector consists of 16 × 4 SiPMs with a pixel size of 3.0 × 3.0 mm2 and a pitch of 3.2 mm. The 64 signals of each SiPM array are processed by using the TOFPET2 application-specific integrated circuit individually. All but the edge slices can be clearly resolved for the detectors with both single-ended and dual-ended readouts. The single-ended readout detector provides an average full width at half maximum (FWHM) Y (continuous direction) position resolution of 2.43 mm, Z (depth direction) position resolution of 4.77 mm, energy resolution of 25.7% and timing resolution of 779 ps. The dual-ended readout detector significantly improves the Y and Z position resolutions, slightly improves the energy and timing resolution at the cost of two photodetectors required for one detector module and provides an average FWHM Y position resolution of 1.97 mm, Z position resolution of 2.60 mm, energy resolution of 21.7% and timing resolution of 718 ps. The energy and timing resolution of the semi-monolithic scintillator detector in this work are worse than those of the segmented scintillator array detector and need to be further improved. The semi-monolithic scintillator detector described in this work reduces costs as compared to the traditional segmented scintillator array detector and reduces the edge effect as compared to the monolithic scintillator detector.

An approach to characterizing spatial aspects of image system blur

AbstractQuantitative X‐ray radiographic imaging systems that utilize a charged couple device (CCD) camera connected to a thick, monolithic scintillator can exhibit blur that varies spatially across the field of view, especially for thick scintillators used in pulse‐power radiography of dynamically compressed objects. A three‐point approach to estimating and accounting for this effect is demonstrated by (a) using a local estimation technique to measure the effect of blurring a calibration object at key locations across the field of view, (b) combining each of the local estimates into a spatially varying blurring function via partitions of unity interpolation, and (c) resolving the effects of that blur on the image by solving an ill‐posed inverse problem using a spatially varying regularization term. The technique is demonstrated on synthetic examples and actual radiographs collected at the Naval Research Laboratory's (NRL) Mercury pulsed power facility.

New probe for the improvement of the Spatial Resolution in total-body PET (PROScRiPT)

In recent decades, PET scanners have been widely used for diagnosis and treatment monitoring in nuclear medicine. The continuous effort of the scientific community has led to improvements in scanner performance. Total-body PET is one of the latest upgrades in PET scanners. These kinds of scanners are able to scan the whole body of the patient with a single bed position, since the scanner tube is long enough for the patient to fit inside. While these scanners show unprecedented efficiency and extended field-of-view, a drawback is their low spatial resolution compared to dedicated scanners. In order to improve the spatial resolution of specific areas when measuring with a total-body PET scanner, the IRIS group at IFIC-Valencia is developing a probe. The proposed setup of the probe contains a monolithic scintillation crystal and a SiPM. The signal of the probe is read out by a TOFPET2 ASIC from PETsys, which has shown good performance for PET in terms of spatial and time resolutions. Furthermore, the PETsys technology generates a trigger signal that will be used to time synchronise the probe and the scanner. The proof-of-concept of the probe will be tested in a Preclinical Super Argus PET/CT scanner for small animals located at IFIC. Preliminary simulations of the scanner and the probe under ideal conditions show a slight improvement in the position reconstruction compared to the data obtained with the scanner, therefore we expect a considerable improvement when using the probe in a total-body PET scanner. Characterisation tests of the probe have been performed with a 22Na point-like source, obtaining an energy resolution of 9.09% for the 511 keV energy peak and a temporal resolution of 619 ps after time walk correction. The next step of the project is to test the probe measuring in temporal coincidence with the scanner.

In-silico optimisation of tileable philips digital SiPM based thin monolithic scintillator detectors for SPECT applications

Over the last decade one of the most significant technological advances made in the field of radiation detectors for nuclear medicine was the development of Silicon Photomultipler (SiPM) sensors. At present only a small number of SiPM based radiation detectors for Single Photon Emission Computed Tomography (SPECT) applications have been explored, and even fewer experimental prototypes developed. An in-silico investigation into the optimal design of a Philips DPC3200 SiPM photosensor-based thin monolithic scintillator detector for SPECT applications was undertaken using the Monte Carlo radiation transport modelling toolkit Geant4 version 10.5. The performance of the 20 different SPECT radiation detector configurations, 4 scintillator materials (NaI(Tl), GAGG(Ce), CsI(Tl) and LaBr3(Ce)) and 5 thicknesses (1–5 mm), were determined through the use of seven figures of merit. It was found that a crystal thickness range of 4–5 mm was required for all four materials to ensure acceptable energy resolution, sensitivity and spatial resolution performance with the Philips DPC3200 SiPM. Any thinner than this and the performance of all four materials was found to degrade rapidly due to a high probability of material specific fluorescence x-ray escape after incident gamma/x-ray photoelectric absorption. When factoring in each material's magnetic resonance imaging compatibility, hygroscopy, and cost, it was found that CsI(Tl) represents the most promising material to construct tileable Philips digital SiPM based thin monolithic scintillator detectors for SPECT applications.

A Directional Gamma-Ray Spectrometer With Microcontroller-Embedded Machine Learning

The enhancement of a compact gamma-ray detection module for spectroscopy and imaging with machine learning for directional sensitivity is presented. In particular this development is targeted towards drone-based localization of radioactive sources in the environment. The unit is composed of a cylindrical monolithic scintillator crystal (3” <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3” LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> +Sr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> )), read by an array of 144 solid-state SiPM detectors whose signals are conditioned by an integrated front-end. In addition to state-of-the-art energy resolution (2.6% at 662keV) and sub-centimeter spatial resolution in the reconstruction of the photon interaction point projected on the base, this portable unit enables the 2D angular localization of gamma sources on a plane parallel to the detectors array as a function of the reconstructed interaction point distribution, thanks to a decision tree. The classifier is compared with other techniques (k-NN, PCA) and optimized with 1000 splits. It runs in a 32-bit ARM micro-controller for real-time operation with a processing time of 2.75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> per event, compatible with high gamma-ray counting rate (100kcps) operation. Despite the absence of a collimator, classification is correct within ±30° for a single photon. Angular resolution of 0.5° and accuracy better than 2° are experimentally demonstrated (along with 0.8W power consumption and 3kg weight), showing potential for identification of sources in the field.

Spatial Resolution Improvement of a Gamma Camera with a Diverging Collimator Using a Tapered Crystal Array

Diverging collimators are used to obtain reduced images of an object or detect a wide field-of-view (FOV) by using a small gamma camera. In gamma cameras equipped with diverging collimators, a monolithic scintillator, and a pixel scintillator array, gamma rays are obliquely incident on the scintillator surface when considering a source that is located near the periphery of the FOV. In such a situation, the spatial resolution is reduced due to oblique detection along the depth direction. In this study, we designed a novel system that improves the spatial resolution of the periphery of the FOV. A tapered crystal array is used to configure the scintillation pixels so that they coincide with the angle relative to the collator hole. This allows imaging of individual scintillation pixel locations, even if the events to be detected occur at different distances. That is, even if an event is detected at various points along the diagonal direction, the gamma rays interact with only a single crystal pixel, thus, the resolution is not degraded. The resolutions of the monolithic scintillator and the tapered crystal array were compared and evaluated using Geant4 Application for Tomographic Emission (GATE) simulations. The dimensions of the monolithic scintillator are 69.4 mm × 69.4 mm × 10.0 mm while those of the tapered crystal array are 49.4 mm × 49.4 mm at the small end and 69.4 mm × 69.4 mm at the large end, with a length of 20 mm. The tapered array contains 45 × 45 elements, and the pixel size is 1 mm × 1 mm at the small end and 1.4 mm × 1.4 mm at the large end. The diverging collimator has dimensions of 69.4 mm × 69.4 mm at the small end and 109.4 mm × 109.4 mm at the large end, with a length of 20 mm. The spatial resolutions of the obtained images were 3.22, 3.77, and 4.63 mm in the monolithic scintillator and 3.25, 3.29, and 3.12 mm in the tapered crystal array. A 16.8% spatial resolution improvement was seen with the tapered crystal array as compared to the monolithic scintillation crystal for all gamma source positions.

Deep learning based methods for gamma ray interaction location estimation in monolithic scintillation crystal detectors

In this work, we explore deep learning based techniques using the information from mean detector response functions (MDRFs) as a new method to estimate gamma ray interaction location in monolithic scintillation crystal detectors. Compared with searching based methods, deep learning techniques do not require recording all the MDRF information once the prediction networks are trained, which means the memory cost could be significantly reduced. In addition, the event positioning process using deep learning techniques only requires running through the network once, without the need to do searching in the reference dataset. This could greatly speed up the positioning process for each event. We have designed and trained four different neural networks to estimate the gamma ray interaction location given the MDRF data. We have studied network structures consisting only of fully connected (FC) layers, as well as Conv neural networks (CNNs). In addition, we tried to use both regression and classification to generate the final prediction of the gamma ray interaction position. We evaluated the estimation accuracy, testing speed and memory cost (numbers of parameters) of different network architectures, and also compared them with the exhaustive search method. Our results indicate that deep learning based estimation methods with a well designed network structure can achieve a relative positioning error with respect to the ground truth determined by the exhaustive search method of below 1 mm in both x and y directions (depth information is not considered in this work), which would imply a very high performance positioning algorithm for practical monolithic scintillation crystal detectors. The deep learning network also achieves a testing speed that is more than 400 times faster than the exhaustive search method. With proper design of the network structure, the deep learning based positioning methods have the potential to save memory cost by a factor of up to 100.

Characterization and Simulation of an Adaptable Fan-Beam Collimator for Fast Calibration of Radiation Detectors for PET

Monolithic scintillators for positron emission tomography systems perform best when calibrated individually. We present a fan-beam collimator with which a crystal can be calibrated within less than 1 h when suitable positioning algorithms are applied. The collimator is manufactured from lead, features an easily adaptable slit to tune the beam width and can be operated together with a coincidence detector to select a clean sample of 511-keV annihilation photons. We evaluated the performance of the collimator with a Geant4 simulation for slit widths of 0.25 mm, 0.4 mm, and 1mm and validated the shape of the beam profile experimentally by step-wisely moving a detector into the beam. This shows a clear narrow and box-shaped beam profile even if the collimator is operated without the coincidence set-up. In the latter configuration, the fraction of gammas in the beam region on a $50\times 50$ mm2 large detector is between 48% and 79% which is improved significantly to more than 94% by using only coincidence events. Analyzing the energy distribution shows that the fraction of 511-keV photons is increased from less than 50% to more than 96% by selecting coincidences. This demonstrates that our collimator produces a very defined and clean beam and provides optimal conditions for calibration.

Image restoration of high-energy X-ray radiography with a scintillator blur model

High-energy X-ray radiographic image restoration is performed using a simulated radiation point spread function and an experimentally derived optical point spread function. It is shown that a robust method for removal of thick monolithic scintillator blur can be determined through independent examination of the blur components. We show that the scintillator blur for a 20 MeV end-point X-ray beam and 20 mm thick LYSO scintillator contributes significantly to the system blur. It is also shown that the optical scatter in the monolithic crystal degrades the low-frequency response of the system. The use of a simulated point spread function for image restoration using deconvolution provides a simple method for image restoration, thereby enhancing feature identification and areal density reconstruction.

Novel preclinical PET geometrical concept using a monolithic scintillator crystal offering concurrent enhancement in spatial resolution and detection sensitivity: a simulation study

We propose a small-animal PET scanner design combining two sets of monolithic crystals with two different thicknesses. The detectors with thinner crystals serve for high resolution imaging while the thicker crystals retain the detection efficiency. Two small-animal PET models based on 10 and 12 detector blocks made of monolithic LYSO crystals were implemented in the GEANT4 Monte Carlo toolkit. In each of these models, half of the detector blocks consisted of a crystal thickness of 10 mm whereas the second half had a crystal thickness of 2 mm. The scintillator crystals were coupled to SiPM arrays. For the first model, the detector blocks were arranged in a full-ring polygonal geometry in such a way that detector blocks with the same thickness were sitting opposite to each other. For the second model, detector blocks with different crystal thicknesses were facing each other. The performance of the proposed PET models was assessed using standard parameters, including spatial resolution, sensitivity and noise equivalent count rate. Comparison was made with conventional PET models with crystal thicknesses of 2 mm, 6 mm and 10 mm. PET models with a crystal thickness of 2 mm led to the highest spatial resolution (up to 0.6 mm FWHM) at the cost of poor absolute sensitivity (2.5%). On the other hand, PET models with a crystal thickness of 10 mm led to good detection efficiency (4.4%), yet with substantial degradation of spatial resolution (1.2 mm FWHM). The proposed PET models with thick and thin crystals exhibited an optimal trade-off between spatial resolution and sensitivity outperforming the PET model with fixed 6 mm crystal by achieving a spatial resolution of 0.7 mm and absolute sensitivity of 3.7%. The novel proposed PET design concept achieved an optimal trade-off between the sensitivity and spatial resolution by combining two sets of monolithic crystals.

Optimisation of monolithic nanocomposite and transparent ceramic scintillation detectors for positron emission tomography

High-resolution arrays of discrete monocrystalline scintillators used for gamma photon coincidence detection in PET are costly and complex to fabricate, and exhibit intrinsically non-uniform sensitivity with respect to emission angle. Nanocomposites and transparent ceramics are two alternative classes of scintillator materials which can be formed into large monolithic structures, and which, when coupled to optical photodetector arrays, may offer a pathway to low cost, high-sensitivity, high-resolution PET. However, due to their high optical attenuation and scattering relative to monocrystalline scintillators, these materials exhibit an inherent trade-off between detection sensitivity and the number of scintillation photons which reach the optical photodetectors. In this work, a method for optimising scintillator thickness to maximise the probability of locating the point of interaction of 511 keV photons in a monolithic scintillator within a specified error bound is proposed and evaluated for five nanocomposite materials (LaBr3:Ce-polystyrene, Gd2O3-polyvinyl toluene, LaF3:Ce-polystyrene, LaF3:Ce-oleic acid and YAG:Ce-polystyrene) and four ceramics (GAGG:Ce, GLuGAG:Ce, GYGAG:Ce and LuAG:Pr). LaF3:Ce-polystyrene and GLuGAG:Ce were the best-performing nanocomposite and ceramic materials, respectively, with maximum sensitivities of 48.8% and 67.8% for 5 mm localisation accuracy with scintillator thicknesses of 42.6 mm and 27.5 mm, respectively.

Exploring TOF capabilities of PET detector blocks based on large monolithic crystals and analog SiPMs

Monolithic scintillators are more frequently used in PET instrumentation due to their advantages in terms of accurate position estimation of the impinging gamma rays both planar and depth of interaction, their increased efficiency, and expected timing capabilities. Such timing performance has been studied when those blocks are coupled to digital photosensors showing an excellent timing resolution.In this work we study the timing behaviour of detectors composed by monolithic crystals and analog SiPMs read out by an ASIC. The scintillation light spreads across the crystal towards the photosensors, resulting in a high number of SiPMs and ASIC channels fired. This has been studied in relation with the Coincidence Timing Resolution (CTR). We have used LYSO monolithic blocks with dimensions of 50 × 50 × 15 mm3 coupled to SiPM arrays (8 × 8 elements with 6 × 6 mm2 area) which compose detectors suitable for clinical applications.While a CTR as good as 186 ps FWHM was achieved for a pair of 3 × 3 × 5 mm3 LYSO crystals, when using the monolithic block and the SiPM arrays, a raw CTR over 1 ns was observed. An optimal timestamp assignment was studied as well as compensation methods for the time-skew and time-walk errors. This work describes all steps followed to improve the CTR. Eventually, an average detector time resolution of 497 ps FWHM was measured for the whole thick monolithic block. This improves to 380 ps FWHM for a central volume of interest near the photosensors. The timing dependency with the photon depth of interaction and planar position are also included.

Study of a small scale position-sensitive scintillator detector for γ-ray spectroscopy

Precision measurement of the energy and direction of gamma-rays plays a key role in many fields such as medical imaging, nuclear spectroscopy, and astrophysics. In astrophysics position sensitive gamma-ray detectors are used to study diffuse and point-like sources. These space-born gamma-ray telescopes, however, are mainly based on large arrays of detectors which are expensive, complex, and take long time to build. A different approach is the use of detector with similar energy and angular resolution, but small enough to be deployed on nanosatellites. We research a design based on monolithic scintillator and multi-pixel photo-sensor. At first we are focused on characterization of CeBr3 scintillator detectors. Bench test experiments were performed with CeBr3 crystal with square surfaces and thicknesses of 10 mm and 25 mm. The crystals were coupled to a single-anode PMT and the outcome compared to Geant4 simulation.