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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.

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.

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.

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.

Liquid scintillators loaded with boron-10 or lithium-6 are capable to detect gamma rays, fast neutrons and also thermal neutrons. One of the popular methods applied in order to distinguish events originating from different particles is the pulse shape discrimination (PSD). The previously presented study of boron-10 loaded liquid scintillators using the PSD method showed different discrimination performance in scintillators such as BC523A, BC523A2, EJ339A2 and EJ309B5. It triggered a further study of the light pulse shapes in these scintillators originating from events related to gamma rays, fast and thermal neutrons. The light pulse shapes, measured using the single photon method, were recorded together with the 2-dimensional n/gamma discrimination data. Next, the recorded light pulses were gated using energy and the PSD information to extract pulses characteristic of the only one kind of particles. Finally, the analysis of the light pulse shapes with multi-exponential fits and calculation of decay time constants and intensities of components were performed. The results were compared with the data obtained for liquid scintillators not sensitive to thermal neutrons BC501A, EJ301 and EJ309.