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Scintillation characteristics of Y0.8Gd2.2 (Al5– x Ga x )O12:Ce,Mg ( $x = 2.6$ and 3) single crystals are presented. At 662-keV $\gamma $ -rays, the light yield of 35 600 photons/MeV obtained for Y0.8Gd2.2Al2Ga3O12:Ce,Mg is higher than that of 32 600 photons/MeV for Y0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. Scintillation decay components of 32.3 ns (52.4%) + 104 ns (47.6%) obtained for Y0.8Gd2.2Al2Ga3O12:Ce,Mg are faster than those of 11.5 ns (5%) + 51.2 ns (69%) + 302 ns (26%) obtained for Y0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. The coincidence time resolution of 336 and 389 ps was obtained, respectively, for Y0.8Gd2.2Al2Ga3O12:Ce,Mg-photomultiplier (PMT) and Y0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg-PMT, in coincidence experiment with a BaF2-PMT detector. The radioluminescence yield at room temperature (RT) is comparable for both crystals while the yield below 130 K is about 20% higher for Y0.8Gd2.2Al2Ga3O12:Ce,Mg. Afterglow and thermally stimulated luminescence (TSL) below RT are also measured.

In the first part of this paper the various characteristics of SiPMs that affect the use of SiPMs in gamma spectroscopy using scintillators , are reviewed. It covers SiPM gain, photon detection efficiency (PDE), after-pulses and cross-talk (which are responsible for the excess noise factor), dark noise, and linearity of response. In this respect the influence of the SiPMs’ effective dead time on the linearity of the response is discussed. In the second part, the optimization of SiPM operation for the best energy resolution and linearity of response is presented. Finally, a number of tests on combinations of SiPM arrays of different sizes that are coupled to different scintillators used in gamma spectroscopy are reported (such as NaI(Tl), BGO, LaBr 3 , and LYSO are reviewed, including 3x3 inch NaI(Tl) and BGO tests. Besides the characterization of the different SiPMs used in scintillation detection and spectroscopy, a discussion is carried out concerning their present and future application in various fields of use — covering instrumentation for homeland security, environmental study, plasma physics and others.

A custom design cryostat was constructed to study the temperature dependence of relative light yield and non-proportionality trends of scintillators between −182 °C and ＋152 °C. CsI:Tl crystal response to γ -rays and X-rays was investigated between 14 keV and 662 keV. Scintillation light was detected by a SiPM device, which was installed on a copper frame separated from the crystal and the cooling rod to enable operating the device at room temperature. The scintillation efficiency of CsI:Tl is peaked at about room temperature. The light yield of CsI:Tl at temperature close to liquid nitrogen boiling point is reduced by a factor of 15 in comparison to room temperature conditions. The non-proportionality of CsI:Tl scintillation response is high at low temperatures and is getting more proportional with increasing temperature.

Relative changes of light yield were investigated for LuAG:Pr, LuAG:Pr,Mo and LuYAG:Pr as a function of sample temperature. The measurements were performed using a dedicated cryostat filled with liquid nitrogen allowing for controlling the temperature of the samples between 90 K and 425 K. Scintillation light was detected by an MPPC photodetector, which was installed on a copper frame separated from the crystal and the cooling rod. Light yields as a function of temperature were investigated by irradiation of the crystals with 662 keV gamma-rays from a 137 Cs source. The temperature dependences were recorded using a short ( 1 μ s ) and long ( 10 μ s ) shaping time constants in the spectroscopy amplifier to study the changes in the intensity of fast and slow scintillation components. In addition, the ratio of light yield measured with short and long shaping time was calculated, providing some information on the balance between fast and slow decay modes in the tested scintillators.

The paper presents a study of n ∕ γ discrimination with 4x4 ch and 8x8 ch Multi Pixel Photon Counter (MPPC) arrays in neutron detectors based on Stilbene and EJ299-33 plastic scintillators. The n ∕ γ discrimination showed an excellent capability of the MPPC arrays, comparable to that observed earlier with the classical PMTs. Particularly, an application of a zero-crossing method of n − γ discrimination prevented deterioration of the discrimination by the slow response of the Silicon Photomultiplier (SiPM, or MPPC interchangeably) array related to its large capacitance. It was confirmed by a good agreement of the Figure of Merit normalized to the number of photoelectrons determined for the MPPC arrays and XP5500 PMT.

This report presents a concept of constructing a detector dedicated for detection of muons observed during measurements carried out at the MPD (Multi-Purpose Detector) detector that is currently under construction at the NICA facility, Russia, Dubna. It has been proposed to design and build an additional detector that will complement the current MPD set and increase its measurement capabilities. The main goal of this project is to provide information from cosmic muons that pass the MPD detector in both in-beam and off-beam experiments. Hence, the detector is called the MPD COsmic Ray Detector (MCORD).The conceptual design of MCORD is proposed by a Polish consortium NICA-PL comprising several Polish scientific institutions. The data from cosmic ray muons could be used as a trigger for calibration of other detection systems comprising the MPD detector. Large surface covered by the MCORD offers also possibility for efficient registration of muons generated in expanding atmospheric showers induced by distant sources. Moreover, beyond some energy threshold, observation of muons originating from decays of collision products will also be possible. In this report examples of the MCORD functionality as a part of the MPD detector are presented. The MCORD is designed as a universal, fast triggering system built as a modular reconfigurable construction. The detection system will be based on plastic scintillators equipped with wavelength shifting fibers, and silicon photomultipliers (SiPM) will be used for scintillation readout. The online analysis of received signals will be performed using digital FPGA modules. Due to the modular design, the same system (its small part) can be used for both laboratory testing of other MPD sub-detectors, and the calibration of these detectors after placing them inside the MPD in off-beam mode. The full detector will support these systems as an additional trigger, calibrator, and muon identifier during the normal operation of the MPD detector with the beam. Thanks to its unique construction, it will expand the possibilities of collecting scientific data of the MPD detector with astrophysical observations. The publication will show the assumptions of the mechanical structure and electronic systems of the planned detector. The installation site of the detector as part of the MPD detector will be described in detail. In the following, the results of simulations made in preparation for this project will be presented. In particular, simulations with the CORSIKA code present angular distributions of particles in cosmic showers in the Dubna city region. Since muons dominate the cosmic ray showers, the MPD detector response to expected cosmic muon flux was also simulated. The results provide information about the muon cut-off thresholds depending on the MPD detector composition during the installation campaign. Simulations of muon events that could be used for MPD subsystems calibration were also performed. The results shown for various configuration of MCORD detector modules will enable the estimation of the time necessary to perform such tests in the future. Simulations with UrQMD model shows the muon abundances due to beam-beam collisions. Approximately 90% of muons are created from pions, whereas the number of muons that reach the MCORD detector is 10 times greater than the number of pions. The MPD detector response was also simulated under the influence of a stream of various particles, especially muons. It shows energy dependence of muon transmission coefficient for MPD with and without ECal assembled. Assuming requirement for muon transmission above 95%, the muon cut-off thresholds are 1.6 GeV and 2.0 GeV, respectively. MCORD detector performance evaluation is also reported. In the case when we used scintillators with one fiber with a diameter of 1 mm, the time resolution of about 1.0 ns was recorded, which corresponds to the positional accuracy (σx) of 7.1 cm. The results of laboratory tests show that application of a 2 mm diameter WLS fiber instead of the previously used 1 mm diameter fiber improves the time resolution to 0.80 ns.

Majority of papers concerning scintillation detectors with light readout by means of silicon photomultipliers refer to nuclear medicine or radiation monitoring devices where energy of detected gamma rays do not exceed 2 MeV. Detection of gamma radiation with higher energies is of interest to e.g. high energy physics and plasma diagnostics . The aim of this paper is to study applicability (usefulness) of SiPM light readout in detection of gamma rays up to 6.1 MeV in combination with various scintillators . The reported measurements were made with 3 samples of one type of Hamamatsu TSV (Through-Silicon Via technology) MPPC arrays. These 4x4 channel arrays have a 50 × 50 μ m2 cell size and 12 × 12 mm2 effective active area. The following scintillators were used: CeBr3 , NaI:Tl, CsI:Tl. During all the tests detectors were located in a climatic chamber. The studies are focused on optimization of the MPPC performance for practical use in detection of high energy gamma rays. The optimization includes selection of the optimum operating voltage in respect to the required energy resolution, dynamic range, linearity and pulse amplitude. The presented temperature tests show breakdown voltage dependence on the temperature change and define requirements for a power supply and gain stabilization method. The energy spectra for energies between 511 keV and 6.1 MeV are also presented and compared with data acquired with a classic photomultiplier XP5212B readout. Such a comparison allowed study of nonlinearity of the tested MPPCs, correction of the energy spectra and proper analysis of the energy resolution.

The main objective of this work was to characterize the new multi-pixel photon counter (MPPC) arrays with a 12 × 12 mm 2 and a 24 × 24 mm 2 active area, made using through-silicon via (TSV) technology and with trenches introduced between the cells, in gamma-ray spectrometry with five different scintillators: CsI:Tl, NaI:Tl, LSO/LYSO, BGO, and LaBr 3 . The results of the study are compared to those obtained previously with the older sample of the 12 × 12 mm 2 MPPC array made as a monolithic device. TSV MPPC array with the size of 24 × 24 mm 2 is one of the first commercially available SiPM with such a large active area and with the dead space between channels minimized to only 0.2 mm. Moreover, in these devices, Hamamatsu introduced trenches between cells to reduce cross-talk. Hence excess noise factor (ENF) was also reduced from a value of 1.7 to 1.2 in comparison to the “old” monolithic sample (data for the same overvoltage of 1.3V). Whereby for the new MPPCs, the optimum operating voltage is higher by about 0.6V. In consequence, this higher optimal overvoltage means a higher photon detection efficiency (PDE) and number of photoelectrons, and leads to improved energy resolution. Energy resolution measured for the 662keV full energy peak in a 137 Cs γ -source spectrum recorded with 12 × 12 mm 2 TSV MPPC and two CsI:Tl scintillators ( 12 × 12 × 12 mm 3 and 1 × 1 in ) equals to 5.8% and 6.8%, respectively. For the “old” MPPC with the same CsI:Tl scintillators energy resolution is equal to 6.4% and 7.1%, respectively. These improved TSV MPPC arrays can be commercially used for scintillation light readout of “large” crystals with a diameter of 1 × 1 in or 2 × 2 in , suitable for gamma spectrometry in a wide range of applications. The combination of new 8 × 8 ch ( 24 × 24 mm 2 ) TSV MPPC and 2 × 2 in NaI:Tl gives an excellent energy resolution below 8%, despite the incomplete match of the scintillator surface to the active area of MPPC and loss of the part of the light.

The market of Silicon Photomultipliers (SiPMs) consists of many manufacturers that produce their detectors in different technology. Hamamatsu (Japan) and SensL (Ireland) seems to be the most popular companies that produce large SiPM arrays. The aim of this work is characterization and comparison of 4×4 channel SiPM arrays produced by these two producers. Both of the tested SiPMs are made in through-silicon via (TSV) technology, consist of 16, 3×3 mm avalanche photodiode (APD) cells and have fill factor slightly above 60%. The largest difference is a single APD cell size and hence total number of APD cells (55,424 for Hamamatsu, 76,640 for SensL). In the case of SensL SiPM, its spectral response characteristics is shifted slightly toward shorter wavelengths with maximum at 420 nm (450 nm for Hamamatsu). The presented measurements cover selection of the SiPM optimum operating voltage (in respect to energy resolution), verification of the excess noise factor and check of the linearity characteristics. Moreover, the gamma spectrometry with LSO, BGO and CsI:Tl scintillators together with pulse characteristics for these crystals (rise time and fall time) is reported, as well as temperature dependence. The presented measurements show better performance of the SensL array comparing to the Hamamatsu detector.

In spite of the excellent performance of SiPMs in the application of time-of-flight PET detectors, the development of better photomultipliers for PET detectors is still worth considering. Fast timing with detectors based on the PMT light readout depends mainly on the time jitter and the quantum efficiency of the PMTs. Several studies in the past showed that a screening grid at the anode significantly improves the time resolution when measured with scintillation detectors. ADIT Co. has started a development of a 1” diameter fast PMT with the screening grid at the anode to be applied in the block detectors in TOF PET scanners. In the presented studies, we report the first comparative study of the L25, a classical PMT, with one that is equipped with a screening grid. Adding the screening grid yielded a large improvement in the time resolution, up to a factor of 1.2.

The main detector system at the Nuclotron-based Ion Collider fAcility (NICA) located in Dubna, Russia is the Multi-Purpose Detector (MPD). For better calibration reason, the MPD needs an additional trigger system for an off-beam calibration of MPD sub-detectors and for rejection (veto) of cosmic muons. The system should also be useful for practical astrophysics observations of cosmic showers. The consortium NICA-PL group defines goals and basic assumptions for the MPD Cosmic Ray Detector (MCORD). This article describes the conceptual design and simulation plans of the MCORD detector based on plastic scintillators with SiPM photodetectors and electronic digital system based on the MicroTCA crate.

Multi-Purpose Detector (MPD) is a part of Nuclotron-based Ion Collider fAcility (NICA) located in Dubna, Russia. For full functionality, the MPD needs an additional trigger system for off-beam calibration of MPD subdetectors and for rejection of cosmic ray particles (mainly muons). The system could also be useful for astrophysics observations of cosmic showers initiated by high energy primary particles. The consortium NICA-PL comprised of several Polish scientific institutions has been formed to define goals and basic assumptions for MPD Cosmic Ray Detector (MCORD). This article describes the early stage design of the MCORD detector based on plastic scintillators with silicon photomultiplier photodetectors for scintillation readout and electronic system based on MicroTCA crate. Plans for simulations of MCORD detector performance are also presented.

The timing characteristics of scintillation response of Czochralski-grown Gd 3 Al 2 Ga 3 O 12 :Ce and Gd 3 Al 2.6 Ga 2.4 O 12 :Ce single crystals were compared. The photoelectron yield, scintillation decay times, and coincidence time resolution were measured. At 662 keV γ-rays, the photoelectron yield of 6200 phe MeV −1 obtained for Gd 3 Al 2 Ga 3 O 12 :Ce is higher than that of 4970 phe MeV −1 obtained for Gd 3 Al 2.6 Ga 2.4 O 12 :Ce, while an inferior energy resolution of the former (7.2% vs. 5.6%) is observed. Scintillation decays are approximated by sum of exponentials with the dominant fast component decay time and its relative intensity of 89 ns (73%) for Gd 3 Al 2 Ga 3 O 12 :Ce and 136 ns (69%) for Gd 3 Al 2.6 Ga 2.4 O 12 :Ce. The coincidence time resolution obtained for Gd 3 Al 2 Ga 3 O 12 :Ce is superior than that of Gd 3 Al 2.6 Ga 2.4 O 12 :Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay characteristics of the light pulse.

According to the present knowledge, the non-proportionality of the light yield of scintillators appears to be the fundamental limitation of energy resolution. However, several observations collected in the last 15 years on the influence of slow components of the light pulses on energy resolution suggest more complex processes in the scintillators. The presented study of undoped CsI crystals shows a large deterioration of the intrinsic resolution of the crystal, when most of the light, including slow component was integrated. Moreover, it was confirmed by a large difference of the non-proportionality characteristics measured at short peaking time, corresponding to the integration of the fast intrinsic emission of the CsI, and that observed with a long peaking time, when the slow component was integrated.

According to current knowledge, the non-proportionality of the light yield of scintillators appears to be a fundamental limitation of energy resolution. A good energy resolution is of great importance for most applications of scintillation detectors. Thus, its limitations are discussed below; which arise from the non-proportional response of scintillators to gamma rays and electrons, being of crucial importance to the intrinsic energy resolution of crystals. The important influence of Landau fluctuations and the scattering of secondary electrons (δ-rays) on intrinsic resolution is pointed out here. The study on undoped NaI and CsI at liquid nitrogen temperature with a light readout by avalanche photodiodes strongly suggests that the non-proportionality of many crystals is not their intrinsic property and may be improved by selective co-doping. Finally, several observations that have been collected in the last 15 years on the influence of the slow components of light pulses on energy resolution suggest that more complex processes are taking place in the scintillators. This was observed with CsI(Tl), CsI(Na), ZnSe(Te), and undoped NaI at liquid nitrogen temperature and, finally, for NaI(Tl) at temperatures reduced below 0 °C. A common conclusion of these observations is that the highest energy resolution, and particularly intrinsic resolution measured with the scintillators, characterized by two or more components of the light pulse decay, is obtainable when the spectrometry equipment integrates the whole light of the components. In contrast, the slow components observed in many other crystals degrade the intrinsic resolution. In the limiting case, afterglow could also be considered as a very slow component that spoils the energy resolution. The aim of this work is to summarize all of the above observations by looking for their origin.

This paper presents the results of the proton irradiation of silicon photomulipliers (SiPMs) by mono-energetic 170 MeV protons with fluence up to 4.6$\times$10$^{9}$ particles/cm$^2$. In our work, three types of silicon photodetectors from Hamamatsu with areas 3$\times$3 mm$^2$ and different subpixel sizes of 25$\times$25 $\mu$m$^2$, 50$\times$50 $\mu$m$^2$, and 75$\times$75 $\mu$m$^2$ were used. The changes in the SiPM dark count rate (DCR) spectrum before and after irradiation in temperatures in the range of 20 $^\circ$C to -65 $^\circ$C are presented. The influence of the DCR changes on the energy resolution of the 662 keV gamma line from the $^{137}$Cs for a non-irradiated GAGG:Ce (1$\%$) scintillator is investigated. The time period of usability of the SiPM detector irradiated by protons in cosmic space was estimated.

Multi-Purpose Detector (MPD) is a main part of a new Ion Collider fAcility (NICA) located in Dubna, Russia. To increase MPD functionality, it was proposed to add an additional muon trigger system for off-beam calibration of the MPD sub-detectors and for rejection of cosmic ray background during experiments. The system could also be very useful for astrophysical observations of cosmic showers initiated by high energy primary particles. This article describes the main goals of MCORD detector and the early stage of MCORD design, based on plastic scintillators with silicon photomultiplier photodetectors (SiPM) for scintillation readout and electronic system based on MicroTCA standard.

A custom designed cryostat was constructed to measure the response of a CsI:Tl scintillator in temperature range from $- 183 ^{circ}\mathrm {C}$ up to $+90 ^{circ}\mathrm {C}$. The light readout was realized using a SiPM developed by FBK in near ultraviolet high density (NUV-HD) technology. The crystal and the SiPM were installed on separated copper frames. The crystal was cooled down by liquid nitrogen, while the SiPM was kept at temperature close to room temperature. A separation of 1 mm was kept between the crystal and the photodetector to ensure thermal isolation. The temperature of the crystal could be varied by heaters on the scintillator frame and was continuously monitored using a coil shaped resistance thermometer. The CsI:Tl scintillation decay profiles were recorded in the entire temperature range provided by the cryostat.

Spectroscopic performance of 4 types of large detectors consisting of 3 different scintillators (LaBr3, NaI(Tl) and BGO) coupled to large MPPC array are presented. The measurements are made with S12642–1616PB-50(X) Hamamatsu TSV MPPC array having a 50x50 µm2 cell size and effective active area of 48x48 mm2 (16x16 channels). In all measurements the common readout of all channels is used. The results obtained with MPPC, such as energy resolution and linearity, are compared with measurements of the same crystals on classic photomultiplier. Also the possible optimization of data acquisition electronics is presented.

The linearity of a silicon photomultiplier (SiPM) response depends on the number of APD cells and its effective recovery time and it is related to the intensity and duration of the detected light pulses. The aim of this study was to determine the effective recovery time on the basis of the measured SiPM response to light pulses of different durations. A closer analysis of the SiPM response to the light pulses shorter than the effective recovery time of APD cells led to a method for the evaluation of the single photoelectron response of the devices where the single photoelectron peak cannot be clearly measured. This is necessary in the evaluation of the number of fired APD cells (or the number of photoelectrons) in measurements with light pulses of various durations. Measurements were done with SiPMs manufactured by two companies: Hamamatsu and SensL.

We have studied the scintillation properties of cerium doped gadolinium aluminum gallium garnet (GAGG:Ce) scintillators with various Al-to-Ga ratio. Having many advantages, like high density (6.63 g/cm3), high light output, fair energy resolution and quite fast decay time, the scintillators are an excellent solution for gamma rays detection. In this paper performance of the GAGG:1%Ce crystals with different Al-to-Ga ratios is presented. The study covered measurements of emission spectra, light output, energy resolution and non-proportionality for each crystal. It was observed that the light output of the recently obtainable crystals varies from 40,000 to 55,000 ph/MeV. Maximum emission wavelength of about 520 nm promotes silicon based photodetectors for use with these scintillators. The best energy resolution of 3.7% at 662 keV, measured with Hamamatsu S8664-1010 APD, was obtained for the sample with the minimum gallium content. This result is close to these obtained with the group of scintillators retaining very good energy resolution, like LaCl3 and CeBr3.

Hamamatsu recently announced the launch of a new type of a photodetector, a micro photomultiplier (microPMT or μPMT). This detector works like a classic photomultiplier but the whole device is made directly in a silicon wafer sandwiched between two glass layers. A microPMT has dimensions of only 13×10×2mm and its photocathode has size of 3×1mm. According to the producers, this newly developed photodetector keeps all the advantages of a classic photomultiplier such as high gain, high sensitivity, low noise, high speed, and low temperature dependence. The aim of the work is to verify usefulness of a microPMT in gamma spectrometry with scintillators and fast timing. In the first part of the study analysis of the energy resolution obtained with 3×3×1mm LSO, BGO and CsI(Tl) scintillators is made. The light pulse shapes of a single photoelectron and scintillation signal of LSO are also showed. The important part of the study are measurements of the number of photoelectrons and estimation of the excess noise factor. In the second part, measurements of the time jitter and timing resolution with LSO crystal for 511keV annihilation quanta are reported. All the results are compared with data obtained with classic PMTs.

Timing resolution is one of the most important parameters of scintillation detectors in many applications One of the major fields in which timing resolution with SiPMs is studied are pixelated detectors for medical imaging and TOF PET. However there are many applications in which timing information from large, monolithic crystals is needed. The aim of this work is to study the timing resolution of large SiPM arrays in readout of various, monolithic scintillators. The presented measurements are made with S12642-1616PB-50(X) Hamamatsu TSV MPPC array having a 50×50 μm cell size and effective active area of 48×48 mm (16×16 channels). During the tests, MPPC is treated as a single/large detector. The different active areas of MPPC are achieved by readout of subareas of the device. In the first part of the study, experiments are made with the smallest 10×10×5 mm LSO scintillator and various number of readout channels in order to understand the influence of the detector area (or capacitance). Next, the timing spectra are recorded for 4 types of scintillators: CeBr 3 (1”, 2”), LaBr 3 (1”, 2”), Nal(Tl) (1”, 2”) and BC408 (2”). The optimization steps and the main aspects affecting the timing resolution of large MPPC arrays are discussed.

A technique is presented to algorithmically evaluate prompt gamma neutron activation spectra, which were produced through excitation of specific material samples. The excitation is done with a neutron generator that provides a switchable, artificial form of neutron radiation. To evaluate the spectra, a extension to prior peak based analysis methods is proposed that dynamically incorporates the detector resolution over the full energy range. Based on this technique a series of measured response spectra are analyzed and the material composition or the samples is identified. Materials of cement and coal mining industry are considered. Limits of the detection limits and confidence thresholds are presented.

Presently, a majority of studies concerning application of silicon photomultipliers (SiPMs) in positron emission tomography detectors are focused on scintillators containing lanthanum (LaBr3) or lutetium (LSO, LYSO, or LFS). However, the modules with the well-known BGO in combination with SiPM light readout are also interesting, owing unique features of SiPMs. In this paper, the two types of detectors, based on BGO and LSO scintillators, are compared in terms of requirements for positron emission tomography scanners. The presented studies are performed with two Hamamatsu Multi Pixel Photon Counter (MPPC) arrays of 2 × 2 channels, with the total area of 6 × 6 mm2 and micro-pixel size of 25 μm (S10985-025C) and 50 μm (S10985-050C). The measurements of a number of photoelectrons, energy resolution at 511 keV and 22Na time resolution are reported for various sizes of the scintillators, including 2.75 × 2.75 × 20 mm3 pixel and single crystals covering the whole MPPC active area. The paper is more focused on optimization of the system with BGO as its performance in combination with SiPM light readout is less known. The aim of this work is to show advantages of a SiPM-based detector, especially in combination with BGO, in respect to the block detectors where classic photomultipliers are used.

Performance of cerium-doped Gd3Al2Ga3O12 (GAGG:Ce) scintillator in gamma-ray spectrometry has been investigated. The measurements of two samples of GAGG:Ce cover the tests of emission spectra (maximum of emission at about 530 nm), light output, non-proportionality, energy resolution, time resolution and decay time of light pulses. We compare the results with commonly known scintillators, such as NaI(Tl), LSO, LuAG etc. The results show that GAGG:Ce has a high light yield of about 33000 ph/MeV as measured with Hamamatsu S3590–18 Si PiN photodiode [1] . The total energy resolution for 662 keV gamma-rays from 137Cs source is equal to about 6%, whereas intrinsic resolution is equal to 5.2%. Additionally, we made basic measurements of photoelectron yield, non-proportionality and total energy resolution of small sample (5×5×5 mm3) of GAGG:Ce crystal coupled to Hamamatsu MPPC array (6×6 mm2). The results show that the performance of GAGG:Ce measured with the MPPC array are similar to those measured with the PMT.

The aim of this work is the characterization of a ∅ 9×9 mm CsI:Tl scintillator at a wide temperature range of −40 °C to +22 °C. A tested crystal with dimensions of ∅ 9×9 mm was coupled to a 16 mm diameter large area Avalanche photodiode (LAAPD). The crystal and the LAAPD were cooled down in a cryostat with a built-in Peltier element. Properties such as the number of electron–hole pairs per 1 MeV, the nonproportionality, the energy resolution and the intrinsic resolution were inspected with eight different peaking times – i.e., 0.6 μs, 1.2 μs, 2.4 μs, 4.8 μs, 7.2 μs, 9 μs, 14.4 μs, 28.8 μs – and discussed in terms of the light pulse shapes measured by a single photon method.

The aim of this work is to provide the characteristics of MPPC arrays with an active area of 6 × 6 mm2 in gamma-ray spectrometry with CsI:Tl, LSO:Ce:Ca, LaBr3:Ce and BGO scintillators. The chosen scintillators have significantly different decay times of the scintillation pulses and different wavelengths of emission peaks. This allowed an investigation into the dependence of MPPC readout features on the MPPC and scintillator characteristics. The study of influence of effective dead time and the number of MPPC pixels on a readout response in relation to the brightness and speed of the scintillator were performed. The measurements covered a selection of MPPC optimum operating voltage, verification of the linearity range for a given decay time of the crystals, verification of the excess noise factor for the optimal voltage and evaluation of the Photon Detection Efficiency (PDE). The results of energy resolution and non-proportionality obtained with the MPPC array readout of CsI:Tl and BGO were compared to those obtained for the same crystals with the XP2020Q PMT readout. The results show that an MPPC can be used as effectively as a PMT for gamma spectrometry measurements in the whole tested energy ranges (up to 1.3 MeV) and for many types of scintillation crystals (BGO, CsI:Tl).

In forthcoming deuterium-tritium (DT) experiments on JET a significant population of alpha-particles will be produced. For operating alpha-particle diagnostics at high DT neutron fluxes, specific improvements have to be made. Proposed new detectors for gamma-ray measurements will be based on CeBr3 and LaBr3:Ce scintillators. They are characterized by a good energy resolution, a relatively high detection efficiency for a few MeV gamma-rays and a fast response time. An overview of scintillator parameters is presented. A description of the properties of photodetectors is given to indicate optimal setups. Results of measurements, using gamma-ray sources with energies up to a few MeV, are discussed with relation to the DT campaign requirements.

Performance of Lutetium Fine Silicate (LFS-3) scintillator in gamma-ray spectrometry has been investigated in comparison with the well known LSO crystal. The tests covered measurements of light output in terms of number of photoelectrons, energy resolution and non-proportionality. Time resolution was measured in coincidence experiments with 511 keV annihilation quanta from a 22Na gamma source. Decay time constants of the light pulse were calculated on the basis of timing spectra obtained using Thomas–Bollinger single photon method. Afterglow was measured about 30 ms after the crystal was irradiated by a strong 13.9 GBq 241Am source. Improvement in the energy resolution for 662 keV γ-rays from 137Cs, shorter decay time constants and better time resolution were observed in case of LFS-3, when compared with LSO. For LFS-3 energy resolution for 662 keV from 137Cs, decay time and time resolution were equal to about 7.66±0.23%, 40.5±1.2 ns and 161±5 ps, respectively, whereas for LSO the same parameters were equal to 8.13±0.23%, 43.9±1.3 ns and 173±5 ps, respectively. The study showed that LFS-3 crystal is an excellent substitute for LSO crystal.

The purpose of this study is to investigate the behavior of the new generation of SensL SiPM arrays, ArrayB and ArrayM, for PET/MR applications. The evaluation of the SiPMs performance underwent with pixelated GaGG and BGO scintillators with 2x2x5 mm3 pixel size and various coupling schemes for 511keV and 662keV energies. To acquire raw images, we used a symmetric resistive voltage division network and the 4x4 SiPMs anodes reduced to 2X and 2Y position signals. A FPGA Spartan 6 LX150T was used for triggering and digital processing of the pulses acquired using free running ADCs. The first step of our work was optimization of the bias voltage of the two SiPM arrays. The optimal bias voltage is a tradeoff between high photon detection efficiency and low excess noise factor. The SiPMs were coupled to homogeneous 16x16x10 mm3 CsITl scintillator and irradiated with 137Cs source. The energy resolution calculated in overvoltages between 26.5V and 30.5V for ArrayB and between 28.3V and 31.3V for ArrayM. The bias voltage with the best energy resolution was used for the evaluation of the SiPMs. The clear visualization of the GaGG and BGO crystal elements is expressed quantitatively by the mean peak-valley ratio of a horizontal profile in the raw images. The best optical coupling for the BGO was 2 mm thick glass. In the case of the GaGG 1 mm thick glass was adequate. The mean energy resolution of the GaGG scintillator is about two times better than the BGO for both type of SiPMs, after applying correction for their non-linear response. The low light output of the BGO scintillator in comparison with the GaGG as well as different emission spectra and the different PDE of the two types of SiPMs explain the differences in the behavior of the tested SiPMs arrays.

In the comparative measurements, done in the same experimental conditions, various samples of NaI:Tl, CsI:Na, BGO, GSO, LSO, LuAG:Pr, LaBr3 and GAGG scintillators were tested. The temperature dependence of the light output, energy resolution and decay time constants of the light pulses were measured over the temperature range of −30 to 50 °C. The XP2020 photomultiplier was used with two different dividers: one optimized for light output and energy resolution measurement and the other one for the decay time constant. In the study of the light output the number of photoelectrons per energy unit (phe/MeV) was measured using Bertolaccini method. The light pulse shape was taken using the anode signal recorded by a digital oscilloscope triggered by a single channel analyzer set on 662 keV energy.

The main aim of this work was characterization of the newest MPPC arrays (with 12×12mm and 24×24mm active area) made using through silicon via (TSV) technology in gamma-ray spectrometry with five different scintillators: CsI:Tl, NaI:Tl, LSO/LYSO, BGO, LaBr3. The results of the study are compared with that obtained previously with the older sample of the 12×12mm MPPC array made as a monolithic device. TSV MPPC array with the size of 24×24mm is one of the first commercially available SiPM with so large active area and with the dead space between channels minimized to only 0.2mm. Moreover in these devices Hamamatsu introduced resistors made with a new type of material. Such a change allowed lowering of crosstalks and afterpulses. These improved TSV MPPC arrays can be commercially used for scintillation light readout of “large” crystals with diameter of 1×1inch or 2×2inch, suitable for gamma spectrometry. Such combination may allow replacement of PMTs in monitoring handheld devices. The presented studies with MPPCs were carried out in the two main experimental conditions: direct illumination of the SiPM using a LED pulser and measurements with scintillators. The first method allowed the measurements of basic parameters of MPPCs such as breakdown voltage and excess noise factor (ENF). The second method allowed the measurements of the full scintillation detector parameters, such as: optimum operating voltage, number of photoelectrons (number of fired APD cells), photon detection efficiency (PDE), linearity and energy resolution.

This publication reports on the methods for measuring the scintillators relative light yield from gamma-rays and protons or heavier ions. The results are presented as a function of velocity of primary ionizing particle in order to investigate quenching of scintillation light in wide range of ionization densities. Measured velocity is also transformed into electron equivalent energy, in order to show that this approach allows for extrapolation of non-proportionality characteristics below low light threshold limits encountered in experiments performed with γ-rays, X-rays and electrons. The experiments were performed with EJ301 liquid scintillator and thallium doped CsI. In the case of EJ301 the response to γ-rays was measured using Compton scattered γ-rays, whereas proton response was registered via fast neutron elastic scattering. In the case of CsI:Tl the response to γ-rays was measured using full energy peak detection, whereas proton and deuteron response was registered by means of the van de Graaff accelerator and the C-30 cyclotron.

The aim of this work is to provide the characteristics of MPPC as a part of neutron detector based on scintillators with n/γ discrimination capabilities. Measurements presented in the work cover: characterization of n/γ discrimination properties by means of Figure of Merit (FOM); comparison of scintillation light pulse shape measured with MPPC and PMT (rise time and fall time) and its influence on the ZC method; estimation of the number of photoelectrons per energy unit (phe/MeV) done by Bartolaccini method.

Recently, a silicon photomultiplier (SiPM) became one of the strongest candidates for application in PET–MR or SPECT–MR dual-modality scanners. However, optimization of the scintillation detectors with SiPM light readout requires different approach than in the case of classic photomultipliers. The finite number of micro-cells in a SiPM creates nonlinear response for high number of incident photons. Moreover, the size and total number of micro-cells defines fill factor, which in turn affects the photon detection efficiency (PDE). Response of SiPMs is also highly sensitive to bias voltage causing changes in PDE and excess noise factor (ENF). Finally, each cell posses an effective dead time needed to fully recharge that cell after the photon detection. In this work the listed above unique features of SiPMs are overviewed. The reported data also contain measurements of energy resolution and 22 Na time resolution.

The aim of this work is to provide the characteristics of Fondazione Bruno Kessler (FBK) high-density SiPMs with an active area of 2.2×2.2 mm2 (15×15 µm2 single cell size) in gamma-ray spectrometry with LSO and CsI:Tl scintillators. The measurements presented in this work covered: measurements of the single photoelectron spectra, characteristics of the breakdown voltage versus temperature, verification of the excess noise factor, selection of the optimum operating voltage for energy resolution, verification of the linearity of the SiPM response for both used scintillators, verification of the number of photoelectrons and gamma-ray spectrometry for a wide range of X and gamma ray energies from 22.1 to 1408 keV. The results of energy resolution obtained with the FBK SiPMs readout and two different scintillators were compared to those obtained for the same scintillator with the XP2020Q PMT.

Time jitter, it means timing distribution of a detector response to single photons is one of the key parameters describing the timing resolution capabilities of any photodetector. In this work, the time jitter measurements of silicon photomultipliers (SiPMs) with active area from 1 to 36 mm2 are presented. These measurements were made using fast picosecond laser PicoQuant LDH P C-405 with wavelength of 405 nm and pulse width below 70 ps. The measurements were done with Hamamatsu Multi-Pixel Photon Counters (MPPCs) with micropixel size of 50 μm (050C). Additional data were also recorded when only a part of an active area of the tested MPPCs was illuminated. The MPPC output was fed into fast amplifier MiniCircuits ERA-4SM+ with 4GHz bandwidth and then further amplified by NIM modules and processed by constant fraction discriminator. In each experiment the noise component was measured and subtracted from the raw timing data. The aim of the study was to understand the influence of the SiPM's capacitance and rise time on the time jitter and also to distinguish differences resulting from the electronics optimization from those due to physical effects connected with an active or illuminated area of a detector.

The aim of this work is to provide the characteristics of MPPC arrays with an active area of 12×12 mm2 in gamma-ray spectrometry with ten scintillators (CsI:TI, BGO, LSO, GAGG, La Br3, NaI:TI, CsI:Na, LaCI3, CaF2:Eu, CdWO4). The measurements presented in this work covered: verification of the breakdown voltage for each channel of MPPC array, selection of the optimum operating voltage for MPPC array, verification of the linearity of MPPC response for all used crystals, verification of number of photoelectrons and gamma-ray spectrometry with crystals. The results of energy resolution and non-proportionality obtained with the MPPC array readout and ten scintillators were compared to those obtained for the same scintillator with the XP2020Q PMT readout.

The aim of this work is to provide the characteristics of MPPC arrays with an active area of 6x6 mm2 in gamma-ray spectrometry with 5x5x5mm3 CsI:TI scintillator at a wide temperature range. The measurements presented in this work covered: characteristics of breakdown voltage, selection of MPPC optimum operating voltage, verification of excess noise factor, measurement of energy resolution and the number of photoelectrons per 1 MeV. All measurements were carried out as a function of temperature and compared with similar results obtained previously with CsI:TI crystal coupled to a Large Area Photodiode (LAAPD).

The linear response of the silicon photomultiplier (SiPM) device depends on the number of APD cells, their effective dead time and is related to a width of the detected light pulses or a decay time of a scintillation crystal. The aim of this work was determination of the effective dead time of APD cells on the basis of the measured linear response of the SiPM for light pulses of different width. A closer analysis of the SiPM response to the light pulses shorter than the effective dead time of pixels, made possible evaluation of a number of fired pixels (or number of photoelectrons) in cases when a single photoelectron peak was not well defined. This analysis also allows determination of the position of the single photoelectron peak, necessary in case of measurements of the number of photoelectrons for light pulses with various widths. Measurements were done with SiPMs manufactured by three companies: Hamamatsu, Zecotek and SensL.

The aim of this work is characterization of MPPC arrays with active area of 6×6 mm in gamma-ray spectrometry with four scintillators CsI(Tl), LSO:Ce(Ca), LaBr 3 and BGO. The chosen scintillators have significantly different decay times of a scintillation pulse and different wavelength of emission peaks. It allowed study of the influence of MPPC effective dead time on a device response and calculation of a Photon Detection Efficiency (PDE) of MPPC. The measurements covered : a selection of the optimum operating voltage, a verification of the linearity range for a given decay time of the crystals, a verification of the excess noise factor for the optimal voltage and calculation of the PDE of MPPC. Measurements of energy resolution and non-proportionality obtained with the MPPC arrays and CsI(Tl) or BGO were compared to the similar measurements performed with XP2020Q PMT.

A development of silicon photomultipliers (SiPM), with a large number of micro-pixels and improved linearity of the pulse height response, allow discussing their possible application to gamma spectrometry with scintillators. Most of the measurements were done with Hamamatsu MPPCs sensors equipped with 3600 and 14400 pixels because of their well pronounced single photoelectron spectra. It allowed precisely measure the photoelectron (phe) numbers/fired pixels and then to discuss in a quantitative manner an obtainable energy resolution. The studied detectors were characterized first by means of a laser light pulser and then by 3×3×3 mm3 LFS and CsI(Tl) crystals coupled to 3×3 mm2 Hamamatsu MPPC. In the study with the light pulser, the linearity of the MPPC response, expressed in the photoelectron number measured in relation to the first photoelectron, versus a light pulse intensity observed with PMT was checked and then the pulse height resolution was measured. Through analysis of the energy resolution the lower limit of the phe number was derived, assuming Poisson statistic. Further on, based on a directly measured phe number, the discussion of an excess noise factor of MPPC was done. In scintillation tests the measurements of the energy resolution and non-proportionality of the light yield were done with LFS and CsI(Tl) and discussed in a quantitative way, based on the measured PHE number, for both types of 3×3 mm2 MPPC detectors.

The Wide-Angle Compton Coincidence (WACC) technique was adapted to measure the electrons produced in cadmium zinc telluride (CZT) detector by Compton scattered gamma rays of 662 keV energy emitted by a 137Cs source. The measurements were carried out with a 4 × 4 pixel anode array build on a 5 mm thick CZT crystal with 1.1 mm pitch. A High Purity Germanium (HPGe) detector operating in coincidence mode measured energy of the scattered photons. The coincidence pulse height data from the CZT and HPGe detectors were recorded in a list mode. The CZT electron spectra were determined by subtracting the energy of the scattered photons from the incident photon energy. The scattering angle was determined by selecting a narrow energy window in the collected HPGe spectra. The CZT electron linearity and resolution were measured in the energy range of 100 keV-300 keV corresponding to the scattering angle range of 31°-66°.

Homeland security applications demand high performance Compton-camera systems, with high detector efficiency, good nuclide identification and able to operate in-field conditions. A low-Z scintillator has been proposed and studied as a promising candidate for use in the scattering plane of a scintillator-based Compton camera: CaF 2 (Eu). All the relevant properties for the application of this scintillator in a mobile Compton camera system have been addressed: the energy resolution and the non-linearity at room temperature and in the temperature range of −20°C to +55°C, the photoelectron yield and the relative light yield in the relevant temperature range. A new method of inferring the relative light output of scintillators as a function of temperature has been proposed.

Silicon photomultipliers (SiPM) are relatively new photodetectors studied presently by many groups in the world. Experiments requiring good time resolution are one of the areas of interest for application of SiPMs. Experiments with high photon statistics and fast picosecond lasers showed that SiPMs time resolution can be extremely good, much below 100 ps. Unfortunately, in case of a full detector with a scintillation crystal like LSO, a high capacitance of this type of devices deteriorates the rise time of the output pulse. In consequence, the timing resolution measured with the slow pulses from SiPM could be worse than results obtained with photomultipliers. In this work a detailed studies of the time resolution with scintillation detectors based on a 3×3 mm2 Multi Pixel Photon Counters (MPPCs) from Hamamatsu and LSO or LFS-3 crystals are presented. Most of the measurements were done using a detector with a pixel size of 50 μm (S10362–33–050C). The results of coincidence experiments with an 22Na gamma source are analyzed in terms of number of photoelectrons, time jitter, excess noise factor and output pulse characteristics. The aim of the work is to present timing capabilities of scintillation detectors based on MPPC in comparison with detectors based on classic timing photomultipliers.

An optimization of the performance of CsI(Na) scintillators coupled to a photomultiplier and irradiated by γ rays is presented. Earlier studies showed that scintillators exhibiting two or more light pulse components in the deexcitation process (e.g. CsI(Tl), Nal(Tl) in reduced temperatures) perform better when longer integration time is set in the amplifier. Such properties like energy resolution and non-proportional response improve while lengthening shaping time in the amplifier. At 12 μs shaping time constant the measured energy resolution for a special grade 1"xl" CsI(Na) sample was as good as 5.8±0.1%. Light pulse shape measurements showed that CsI(Na) scintillators irradiated by γ rays deexcite mostly in the microsecond range and the light pulse consists of three components: -470 ns (fast), -1.8 μβ (slow) and -8 μs (tail) with the relative intensities about 41%, 28% and 31%, respectively. From the point of view of a potential use of CsI(Na) in homeland security applications the crystal was compared to commonly used Nal(Tl) with taking into account such parameters as: energy resolution, non-proportionality, photopeak efficiency and others.