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In this paper we present the performance of a new SiPM that is sensitive to blue light and features narrow metal-filled trenches placed in the area around the single-photon avalanche diodes (SPADs) that allow an almost complete suppression the internal optical crosstalk. In particular, we show the benefits of this technological upgrade in terms of electro-optical SiPM performance when compared to the previous technology which had only a partial optical screening between the SPADs. The most relevant effect is the much higher bias voltage that can be applied to the new device before the noise diverges. This allows to optimize and improve both the photon-detection efficiency and the single-photon time resolution. We also coupled the SiPMs to LYSO scintillators to verify the performance for possible application in Positron-Emission Tomography. Thanks to the better electro-optical features we were able to measure an improved coincidence time resolution. Furthermore, the optimal voltage operation region is substantially larger, making this SiPM more suitable for real system application where thousands of channels have to provide stable and reproducible performance.

We present a spectroscopic system constituted by a Silicon Drift Detector (SDD) coupled to a CMOS charge sensitive preamplifier, named SIRIO, specifically designed to reach ultimate low noise levels. The SDD, with an active area of $\hbox{13~mm}^2$ , has been manufactured by optimizing the production processes in order to reduce the anode current, successfully reaching current densities between $\hbox{17~pA/cm}^2$ and $\hbox{25~pA/cm}^2$ at $ + \hbox{20}~^\circ {\rm C}$ for drift fields ranging from 100 V/cm to 500 V/cm. The preamplifier shows minimum intrinsic noise levels of 1.27 and 1.0 electrons r.m.s. at $+\hbox{20}~^{\circ}{\rm C}$ and $-\hbox{30}~^{\circ}{\rm C}$ , respectively. At room temperature ( $ + 20^\circ {\rm C}$ ) the $^{55}{\rm Fe}$ 5.9 keV and the pulser lines have 136 eV and 64 eV FWHM, respectively, corresponding to an equivalent noise charge of 7.4 electrons r.m.s.; the noise threshold is at 165 eV. The energy resolution, as measured on the pulser line, ranges from 82 eV FWHM (9.4 electrons r.m.s.) at $ + \hbox{30}~^\circ {\rm C}$ down to 29 eV FWHM (3.3 electrons r.m.s.) at $ - \hbox{30}~^\circ {\rm C}$ .

We present photon detection efficiency (PDE) measurements of three different silicon photomultipliers (SiPM) and report the temperature coefficient of this parameter using a direct measurement method. This study provides first results in such a wide temperature and wavelength range, from -30°C to 70°C and from 365 nm to 900 nm respectively. To carry out this study we developed a setup providing stable illumination of the device under test in temperature. The PDE is evaluated using a photon-counting method and the wavelength-dependent PDE temperature coefficients of all devices are determined. The different designs are compared and the individual contributors to the temperature dependence of the PDE are discussed. The PDE is shown to be linearly dependent on temperature for all designs and the temperature coefficient depends on wavelength and bias voltage. At shorter wavelengths, the temperature dependency approaches values close to zero for one design whereas all devices show increasing temperature coefficients for increasing wavelengths. This study shows that despite the more complex designs of SiPMs, compared to silicon photodiodes, similar factors contribute to the temperature dependence of the PDE.

High-performance optical power converters (OPCs) enable isolated electrical power and power beaming applications at new wavelengths and higher output powers. Broadcom’s vertical epitaxial heterostructure architecture (VEHSA) multi-junction OPCs permit optical-to-electrical conversion at high efficiency and at manageable external loads. This study provides details of how the power outputs have been extended from 20 W. The work also provides details of how the spectral range options have been extended from 800–830 nm to other key laser diode wavelengths such as 960–990 nm and 1500–1600 nm.

In this paper, we give an overview of the main properties and technological implementation of densely packed Single-photon Avalanche Diode arrays, which are commonly known as Silicon Photomultipliers, or SiPMs. These detectors feature high internal gain, single-photon sensitivity, a high Photon Detection Efficiency, proportional response to weak and fast light flashes, excellent timing resolution, low bias voltage, ruggedness and insensitivity to magnetic field. They compare favorably to the traditional Photomultiplier Tube in several applications. In this overview paper, we go through the SPAD/SiPM theory of operation, the modern SiPM implementations and the typical technological options to build the sensor. This is done in conjunction with the description of the main SiPM parameters, such as the Photon Detection Efficiency, the electrical properties, the primary and correlated noise sources and the Single Photon Time Resolution.

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.

Silicon photomultipliers (SiPMs) have recently obtained a growing attention as an alternative to traditional photomultiplier tubes for detecting low photon fluxes. SiPMs are currently used in many medical and physics applications, but they are also emerging as a valuable option in single-photon or few-photon applications, like light detection and ranging, optical spectroscopy, and bio-medical instrumentation. During last years at Fondazione Bruno Kessler (Trento, Italy) we developed two different SiPM technologies, with peak sensitivity in the green wavelength region and in the blue one. Recently, we also started to develop a new technology with increased sensitivity in the red and near infra-red (NIR) wavelength region. This development poses several technological and design challenges since the single-photon avalanche diode (SPAD) internal structure has to be modified in order to collect carriers generated by photons absorbed at a depth of several microns. In this paper we will describe the first NIR-SiPMs and NIR-SPADs produced in FBK and we will present and discuss their experimental characterization. These devices show promising performance: SiPMs with 35 μ m cell reach a PDE of about 18% at 850 nm and of more than 10% at 900 nm. These values are mainly limited by the SPAD border effect, which will be discussed in the paper by means of TCAD simulations. The full potentiality of these devices, in terms of PDE, will also be demonstrated by PDE measurements on a single SPAD with shielded active-area border.

The ENUBET ERC project (2016–2021) is studying a narrow band neutrino beam where lepton production can be monitored at single particle level. For this purpose, the decay tunnel is instrumented with longitudinally segmented calorimeters. Three different specialized calorimeters have been designed and tested, two of which based on the shashlik calorimetric concept with a compact readout while the third is a less compact version with a lateral readout. All of the prototypes are composed of thick steel absorbers coupled to plastic scintillators. Regarding the shashlik modules, a matrix of 3 × 3 fibers runs transversely with a density of one fiber/cm2. The fibers are coupled individually to silicon photomultipliers mounted on a custom PCB allowing to reduce the dead zones between adjacent modules to an extremely small level compared to the “fiber bundling” configurations. This setup allows a very effective longitudinal segmentation and hence e / π separation. The second shashlik module is based on polysiloxane scintillators which come in liquid form, are poured around the fiber arrays and finally made solid with a thermal treatment. Finally, the lateral readout module, light is collected from both sides of each scintillator tile and the 10 fibers from the same UCM are bundled to a single SiPM. Here are discussed the results of test beams performed in 2016–2018 at the CERN-PS East Area and the characterization of SiPMs of different cell size ( 12 μ m and 15 μ m ) before and after being exposed to neutron fluxes up to 1012/cm2 at the INFN-LNL CN accelerator facility.

We present the first application of polysiloxane-based scintillators as active medium in a shashlik sampling calorimeter. These results were obtained from a testbeam campaign of a $\sim$6$\times$6$\times$45 cm$^3$ (13 $X_0$ depth) prototype. A Wavelength Shifting fiber array of 36 elements runs perpendicularly to the stack of iron (15 mm) and polysiloxane scintillator (15 mm) tiles with a density of about one over cm$^2$. Unlike shashlik calorimeters based on plastic organic scintillators, here fibers are optically matched with the scintillator without any intermediate air gap. The prototype features a compact light readout based on Silicon Photo-Multipliers embedded in the bulk of the detector. The detector was tested with electrons, pions and muons with energies ranging from 1 to 7 GeV at the CERN-PS. This solution offers a highly radiation hard detector to instrument the decay region of a neutrino beam, providing an event-by-event measurement of high-angle decay products associated with neutrino production (ENUBET, Enhanced NeUtrino BEams from kaon Tagging, ERC project). The results in terms of light yield, uniformity and energy resolution, are compared to a similar calorimeter built with ordinary plastic scintillators., Comment: 28 pages, 16 figures. To appear in NIM-A

We present a new compact photonic quantum random number generator based on an emitter (source of entropy) and a single-photon detector integrated in the same silicon chip. Not only they are integrated one close to the other, but also they are fabricated with the same fabrication process. The emitter is a small silicon photomultiplier, composed of passively-quenched single photon avalanche diodes (SPADs), having the same layout of the single SPAD used as the detector. The emitter is a reverse-biased silicon p-n junction, generating photons mainly due to impact ionization during the avalanche breakdown process. The detector is shielded from ambient light by a top metal layer: only photons from the emitter are detected, making this integrated approach more robust. The random bits are extracted with a robust methodology based on the measurement of photon arrival times, using discrete time bins, in a time frame cyclically repeated in time. No postprocessing is required for the raw data to pass the statistical tests.

Within the vast panorama of multimodal systems for clinical diagnosis, PET/MRI has been receiving significant attention. In parallel, new technological solutions have been paving the way to simultaneous SPECT/MRI systems, whose development has been so far delayed due to the challenging compatibility between MRI, gamma-ray detectors, and collimators. This paper presents an silicon photomultiplier (SiPM)-based Anger camera designed for preclinical and clinical SPECT static inserts for standard MR scanners. The gamma-ray detector is based on a continuous CsI(Tl) scintillator readout by arrays of SiPMs and custom ASICs. The design has been adapted to fit with the limited space conditions (23 mm thickness), but also considering mutual compatibility issues. Despite these constraints and thanks to the adoption of an iterative statistical event estimation method simply requiring a flood image, the detector maintains state-of-the-art performance in terms of intrinsic spatial resolution (1.0 mm FWHM within the usable field of view) and an energy resolution below 14% FWHM at 140 keV. The experimental studies here performed show that the camera, designed to operate at 0 °C to reduce the dark current of SiPMs, can operate up to 10 °C without significant worsening of imaging performance.

Silicon photomultipliers (SiPM) are photodetectors that have obtained a growing attention in the last years. They have single photon sensitivity, but also a high dynamic range: the output current signal is proportional to the number of detected photons and it is possible to distinguish up to tens of photon per each light pulse. In Fondazione Bruno Kessler (Trento, Italy) we developed the so called high-density SiPMs, with narrow trenches to isolate the cells (i.e. single-photon avalanche diodes) and with high fill factor. These detectors feature high photon detection efficiency and high dynamic range. Moreover, the reduction of the cell size reduces the correlated noise (i.e. lower crosstalk between cells and lower afterpulsing probability) and it makes the single-cell response faster, increasing the maximum counting rate. These characteristics can be very important in applications like light detection and ranging, spectroscopy, and physics experiments. In this paper, we present the structure of high-density SiPMs and their performance. In particular, the photon detection efficiency, the photon number resolving capabilities, the linearity versus photon flux, and the single-photon time resolution, investigating how these parameters change with the cell pitch.

This work presents a new PET detector concept for compact preclinical hybrid MR-PET. The detector concept is based on Linearly-Graded SiPM produced with current FBK RGB-HD technology. One 7.75 mm x 7.75 mm large sensor chip is coupled with optical grease to a black coated 8 mm x 8 mm large and 3 mm thick monolithic LYSO crystal. The readout is obtained from four readout channels with the linear encoding based on integrated resistors and the Center of Gravity approach. To characterize the new detector concept, the spatial and energy resolutions were measured. Therefore, the measurement setup was prepared to radiate a collimated beam to 25 different points perpendicular to the monolithic scintillator crystal. Starting in the center point of the crystal at 0 mm / 0 mm and sampling a grid with a pitch of 1.75 mm, all significant points of the detector were covered by the collimator beam. The measured intrinsic spatial resolution (FWHM) was 0.74 +/- 0.01 mm in x- and 0.69 +/- 0.01 mm in the y-direction at the center of the detector. At the same point, the measured energy resolution (FWHM) was 13.01 +/- 0.05 %. The mean intrinsic spatial resolution (FWHM) over the whole detector was 0.80 +/- 0.28 mm in x- and 0.72 +/- 0.19 mm in y-direction. The energy resolution (FWHM) of the detector was between 13 and 17.3 % with an average energy resolution of 15.7 +/- 1.0 %. Due to the reduced thickness, the sensitivity of this gamma detector is low but still higher than pixelated designs with the same thickness due to the monolithic crystals. Combining compact design, high spatial resolution, and high sensitivity, the detector concept is particularly suitable for applications where the scanner bore size is limited and high resolution is required — as is the case in small animal hybrid MR-PET.

Silicon photomultipliers (SiPMs) are arrays of many single-photon avalanche diodes (SPADs), all connected in parallel. Each SPAD is sensitive to a single photon. The SiPM output is proportional to the number of detected photons. These sensors are becoming more and more popular in different applications and they have been significantly improved over last years, decreasing the noise, increasing the cell fill-factor, and thus achieving very high photon-detection efficiency. In FBK (Trento, Italy), we developed several different SiPM technologies and recently, pushing the fabrication process limits, we produced the new ultra-high-density (UHD) technology. This technology features deep trenches between cells, for electrical and optical isolation, and is characterized by a very small cell pitch, from 12.5 down to 5 μ m. Such very small cell dimensions pose several issues both in terms of design and fabrication of the SPADs. TCAD simulations have been used to redesign the cell structure, minimizing their border region. As an example, the SiPM with 5 μ m cell pitch has about 40 000 SPADs per squared millimeter, thus a very high dynamic range. These very-small-cells SiPM have a lower correlated noise (including lower afterpulsing probability), faster recharge time, and very good detection efficiency (despite the small SPAD dimension).

In spite of the constant technological improvements in the field of detector development, X-ray fluorescence (XRF) in the soft X-ray regime remains a challenge. The low intrinsic fluorescence yield for energies below 2 keV indeed renders the applicability of low-energy XRF still difficult. Here, we report on a new multi-element multi-tile detection system currently under development, designed to be integrated into a soft X-ray microscopy end station. The system will be installed at the TwinMic beamline of Elettra synchrotron (Trieste, Italy) in order to increase the detected count rate by up to an order of magnitude. The new architecture is very versatile and can be adapted to any XRF experimental setup. Even though the first results of the previous version of such a multi-element system were encouraging, several issues still needed to be addressed. The system described here represents a further step in the detector evolution. It is based on four trapezoidal-shaped monolithic silicon drift detector tiles (matrices) with six hexagonal elements each equipped with a custom ultra-low noise application-specific integrated circuit readout. The whole signal processing chain has been improved leading to an overall increase in performances, namely, in terms of energy resolution and acquisition rates. The design and development of this new detection system will be described, and recent results obtained at the TwinMic beamline at Elettra will be presented. Future perspectives and improvements will also be discussed. Copyright © 2017 John Wiley & Sons, Ltd.

A prototype of a Focused Internal Reflection Cherenkov, equipped with 16 arrays of NUV-SiPM, was tested at CERN SPS in March 2015 with beams of relativistic ions at 13, 19 and 30 GeV/n obtained from fragmentation of an Ar primary beam. The detector, designed to identify cosmic nuclei, features a Fused Silica radiator bar optically connected to a cylindrical mirror of the same material and an imaging focal plane of dimensions ∼4 cm×3 cm covered with a total of 1024 SiPM photosensors. Thanks to the outstanding performance of the SiPM arrays, the detector could be operated in photon counting mode as a fully digital device. The Cherenkov pattern was recorded together with the total number of detected photoelectrons increasing as Z 2 as a function of the atomic number Z of the beam particle. In this paper, we report on the characterization and test of the SiPM arrays and the performance of the Cherenkov prototype for the charge identification of the beam particles.

The scintillator bismuth germanate (BGO) has attractive properties for positron emission tomography (PET) systems such as high stopping power, high photo-fraction, and relatively low cost. However, its moderate scintillation light yield and slow rise and decay time compared to lutetium (yttrium) oxyorthosilicate (L(Y)SO) results in a degradation of coincidence timing resolution when scintillation photons are used for timing. Recently, it has been reported that the coincidence timing resolution of BGO can be improved by detecting Cerenkov photons, while scintillation photons still provide energy information. However, the measured coincidence timing spectrum showed much longer tails compared to the single Gaussian distribution. Because of this, TOF PET detectors based on BGO will perform worse than the full width at half maximum (FWHM) of the distribution, which is the most common metric for timing resolution, would suggest. From simulation studies, during the first few picoseconds, BGO generates ~16 Cerenkov photons per photoelectric interaction, following a 511 keV gamma ray interaction, while the probability of producing a scintillation photon during the first few picoseconds is very small. Therefore, when we configure a BGO crystal with dual-ended readout, the first arriving photons among the two opposing SiPMs are most likely Cerenkov photons, and by selecting the appropriate SiPM, an improvement in coincidence timing resolution can be achieved. In this study, both ends of a 3 × 3 × 20 mm3 BGO crystal were coupled to NUV-HD SiPMs. Trigger time differences from the dual-ended readout of BGO were widely distributed due to detecting a mixture of prompt Cerenkov and scintillation photons on both SiPMs. When using trigger times from only a single SiPM, the estimated coincidence timing resolution between two identical BGO detectors was 463 ps FWHM and 1463 ps FWTM. In contrast, when using trigger times from both SiPMs, the estimated coincidence timing resolution was 399 ps FWHM and 936 ps FWTM with no loss of events. Based on a recent report, high-bandwidth amplifiers were implemented and shown to further improve the estimated coincidence timing resolution to 331 ps FWHM and 923 ps FWTM. In summary, the coincidence timing resolution of BGO, most notably the FWTM, was significantly improved using time information from the dual-ended readout.

In this paper we present the enhanced X-ray Timing and Polarimetry mission - eXTP. eXTP is a space science mission designed to study fundamental physics under extreme conditions of density, gravity and magnetism. The mission aims at determining the equation of state of matter at supra-nuclear density, measuring effects of QED, and understanding the dynamics of matter in strong-field gravity. In addition to investigating fundamental physics, eXTP will be a very powerful observatory for astrophysics that will provide observations of unprecedented quality on a variety of galactic and extragalactic objects. In particular, its wide field monitoring capabilities will be highly instrumental to detect the electro-magnetic counterparts of gravitational wave sources. The paper provides a detailed description of: (1) the technological and technical aspects, and the expected performance of the instruments of the scientific payload; (2) the elements and functions of the mission, from the spacecraft to the ground segment., Accepted for publication on Sci. China Phys. Mech. Astron. (2019)

Different applications require different customizations of silicon photomultiplier (SiPM) technology. We present a review on the latest SiPM technologies developed at Fondazione Bruno Kessler (FBK, Trento), characterized by a peak detection efficiency in the near-UV and customized according to the needs of different applications. Original near-UV sensitive, high-density SiPMs (NUV-HD), optimized for Positron Emission Tomography (PET) application, feature peak photon detection efficiency (PDE) of 63% at 420 nm with a 35 um cell size and a dark count rate (DCR) of 100 kHz/mm2. Correlated noise probability is around 25% at a PDE of 50% at 420 nm. It provides a coincidence resolving time (CRT) of 100 ps FWHM (full width at half maximum) in the detection of 511 keV photons, when used for the readout of LYSO(Ce) scintillator (Cerium-doped lutetium-yttrium oxyorthosilicate) and down to 75 ps FWHM with LSO(Ce:Ca) scintillator (Cerium and Calcium-doped lutetium oxyorthosilicate). Starting from this technology, we developed three variants, optimized according to different sets of specifications. NUV-HD–LowCT features a 60% reduction of direct crosstalk probability, for applications such as Cherenkov telescope array (CTA). NUV-HD–Cryo was optimized for cryogenic operation and for large photosensitive areas. The reference application, in this case, is the readout of liquid, noble-gases scintillators, such as liquid Argon. Measurements at 77 K showed a remarkably low value of the DCR of a few mHz/mm2. Finally, vacuum-UV (VUV)-HD features an increased sensitivity to VUV light, aiming at direct detection of photons below 200 nm. PDE in excess of 20% at 175 nm was measured in liquid Xenon. In the paper, we discuss the specifications on the SiPM related to different types of applications, the SiPM design challenges and process optimizations, and the results from the experimental characterization of the different, NUV-sensitive technologies developed at FBK.

Silicon Photomultipliers with cell-pitch ranging from 12 $\mu$m to 20 $\mu$m were tested against neutron irradiation at moderate fluences to study their performance for calorimetric applications. The photosensors were developed by FBK employing the RGB-HD technology. We performed irradiation tests up to $2 \times 10^{11}$ n/cm$^2$ (1 MeV eq.) at the INFN-LNL Irradiation Test facility. The SiPMs were characterized on-site (dark current and photoelectron response) during and after irradiations at different fluences. The irradiated SiPMs were installed in the ENUBET compact calorimetric modules and characterized with muons and electrons at the CERN East Area facility. The tests demonstrate that both the electromagnetic response and the sensitivity to minimum ionizing particles are retained after irradiation. Gain compensation can be achieved increasing the bias voltage well within the operation range of the SiPMs. The sensitivity to single photoelectrons is lost at $\sim 10^{10}$ n/cm$^2$ due to the increase of the dark current., Comment: 14 pages, 13 figures. To appear in JINST

Bismuth germanate (BGO) was a very attractive scintillator in early-generation positron emission tomography (PET) scanners. However, the major disadvantages of BGO are lower light yield and longer rise and decay time compared to currently popular scintillators such as LSO and LYSO. This results in poorer coincidence timing resolution and it has generally been assumed that BGO is not a suitable scintillator for time-of-flight (TOF) PET applications. However, when a 511 keV photon interacts in a scintillator, a number of Cerenkov photons are produced promptly by energetic electrons released by photoelectric or Compton interactions. If these prompt photons can be captured, they could provide a better timing trigger for PET. Since BGO has a high refractive index (increasing the Cerenkov light yield) and excellent optical transparency down to 320 nm (Cerenkov light yield is higher at shorter wavelengths), we hypothesized that the coincidence timing resolution of BGO can be significantly improved by efficient detection of the Cerenkov photons. However, since the number of Cerenkov photons is far less than the number of scintillation photons, and they are more abundant in the UV and blue part of the spectrum, photosensors need to have high UV/blue sensitivity, fast temporal response, and very low noise in order to trigger on the faint Cerenkov signal. In this respect, NUV-HD silicon photomultipliers (SiPMs) (FBK, Trento, Italy) are an excellent fit for our approach. In this study, coincidence events were measured using BGO crystals coupled with NUV-HD SiPMs. The existence and influence of Cerenkov photons on the timing measurements were studied using different configurations to exploit the directionality of the Cerenkov emissions. Coincidence resolving time values (FWHM) of ~270 ps from 2 × 3 × 2 mm3 BGO crystals and ~560 ps from 3 × 3 × 20 mm3 BGO crystals were obtained. To our knowledge, these are the best coincidence resolving time values reported for BGO to date. With these values, BGO can be considered as a relevant scintillator for TOF PET scanners, especially if photodetectors with even better near UV/blue response can be developed to further improve the efficiency of Cerenkov light detection.

We present a very compact γ -detection module primarily designed for PET applications. On a total area of about 30 × 30 mm 2 , 144 SiPM photodetectors coupled to scintillator crystals are read out individually with fast timing ASICs. The core of the module is a LTCC ceramic substrate with internal water channels for efficient and stable liquid cooling. The top side of the LTCC is covered by 12×12 SiPMs in a regular pitch of 2.5 mm. The SiPMs are designed in the RGB-HD technology from FBK with a single cell size of 25 × 25 μ m 2 , very low dark-count rate and stable performance over a wide temperature range from 0 to 20 °C. The readout of the SiPMs is done with 4 specialized PETA5 ASICs flip-chip mounted to the bottom side of the substrate. Each chip has 36 readout channels (available in single or differential ended configuration) with self-triggered hit detection, a very low noise discriminator, signal amplitude integration and digitization, a TDC with 50 ps binwidth, neighbor logic and fast veto mechanisms. The full height of the assembly, including the connector to the main readout board, is less than 1 cm. In a 1:1 coupling configuration with 10 mm high LYSO scintillator arrays for detection of 511 keV gammas, the module has already reached 205 ps CRT time resolution (FWHM in coincidence between channels on two different modules), sufficient for ToF operation in PET. The module design, details on chip operation and latest results with LYSO arrays are described.

In this paper, we present the full characterization of a new high-density (HD) cell silicon photomultiplier (SiPM) technology for ultraviolet (UV) and blue light detection, named near UV HD SiPM. Thanks to an optimized border region around each cell, we were able to develop devices having a very high detection efficiency and, at the same time, a high dynamic range. We produced SiPMs with a square cell pitch of 15, 20, 25, and 30 $\mu \text{m}$ featuring a peak efficiency in the violet region ranging from 40% to 55%, according to the cell size. We tested this technology for time-of-flight positron emission tomography. Using two $4\times 4$ mm2 SiPMs with a $25 \,\, \times \,\, 25~\mu \text{m}^{2}$ cell pitch coupled to $3\times 3\times 5$ mm3 LYSO scintillators, we reached for the first time 100-ps full-width at half-maximum coincidence time resolution. This result was independent of the temperature in a range from 20 °C to −20 °C. At the same time, thanks to the high dynamic range and low correlated noise, we obtained an energy resolution lower than 9% for 511-keV $\gamma $ -rays.

A small-sized photonic quantum random number generator, easy to be implemented in small electronic devices for secure data encryption and other applications, is highly demanding nowadays. Here, we propose a compact configuration with Silicon nanocrystals large area light emitting device (LED) coupled to a Silicon photomultiplier to generate random numbers. The random number generation methodology is based on the photon arrival time and is robust against the non-idealities of the detector and the source of quantum entropy. The raw data show high quality of randomness and pass all the statistical tests in national institute of standards and technology tests (NIST) suite without a post-processing algorithm. The highest bit rate is 0.5 Mbps with the efficiency of 4 bits per detected photon.

Building on the successful experience in operating the DarkSide-50 detector, the DarkSide Collaboration is going to construct DarkSide-20k, a direct WIMP search detector using a two-phase Liquid Argon Time Projection Chamber (LAr TPC) with an active (fiducial) mass of 23 t (20 t). This paper describes a preliminary design for the experiment, in which the DarkSide-20k LAr TPC is deployed within a shield/veto with a spherical Liquid Scintillator Veto (LSV) inside a cylindrical Water Cherenkov Veto (WCV). This preliminary design provides a baseline for the experiment to achieve its physics goals, while further development work will lead to the final optimization of the detector parameters and an eventual technical design. Operation of DarkSide-50 demonstrated a major reduction in the dominant 39Ar background when using argon extracted from an underground source, before applying pulse shape analysis. Data from DarkSide-50, in combination with MC simulation and analytical modeling, shows that a rejection factor for discrimination between electron and nuclear recoils of $>3 \times 10^{9}$ is achievable. This, along with the use of the veto system and utilizing silicon photomultipliers in the LAr TPC, are the keys to unlocking the path to large LAr TPC detector masses, while maintaining an experiment in which less than $< 0.1$ events (other than $\nu$ -induced nuclear recoils) is expected to occur within the WIMP search region during the planned exposure. DarkSide-20k will have ultra-low backgrounds than can be measured in situ, giving sensitivity to WIMP-nucleon cross sections of $1.2 \times 10^{-47}$ cm2 ( $1.1 \times 10^{-46}$ cm2) for WIMPs of 1 TeV/c2 (10 TeV/c2) mass, to be achieved during a 5 yr run producing an exposure of 100 t yr free from any instrumental background.

In this paper, we present a silicon photomultiplier (SiPM)-based photodetector module designed to readout large cerium-doped lanthanum bromide (LaBr3:Ce) scintillators (cylindrical 1” $\times$ 1” and 2” $\times$ 2”) for nuclear physics experiments. The detector prototype has a modular structure and implements a real-time stabilization of the SiPM gain to compensate for the gain drift with temperature. The SiPM module consists of an array of 5 by 6 near-ultraviolet high-density SiPMs (Fondazione Bruno Kessler, Italy), each one having an active area of 6 mm $\times$ 6 mm and 30- $\mu \text{m}$ microcells. The single array is used for the 1” crystal readout, and it is assembled in a $2{\times} 2$ format to read the 2” scintillator. Spectroscopic measurements were performed with both crystals. The 2” crystal was irradiated with different radioactive sources in an energy range between 122 keV and 1.3 MeV, and an energy resolution of 3.19 ± 0.01% full-width at half-maximum (FWHM) has been achieved at 662 keV. The result is very close to the 3.07 ± 0.03% FWHM measured with Super Bialkali photomultiplier tube (PMT) (Hamamatsu R6233-100) at the same energy with the same 2” crystal. In the framework of the comparison between SiPM and PMT for LaBr3:Ce readout, we provide an analysis of the energy resolution contributions based on the measurements performed with the developed gamma-ray detection system.

An iron- plastic-scintillator shashlik calorimeter with a 4.3 $X_0$ longitudinal segmentation was tested in November 2016 at the CERN East Area facility with charged particles up to 5 GeV. The performance of this detector in terms of electron energy resolution, linearity, response to muons and hadron showers are presented in this paper and compared with simulation. Such a fine-grained longitudinal segmentation is achieved using a very compact light readout system developed by the SCENTT and ENUBET Collaborations, which is based on fiber-SiPM coupling boards embedded in the bulk of the detector. We demonstrate that this system fulfills the requirements for neutrino physics applications and discuss performance and additional improvements., 21 pages, 19 figures. To appear in JINST

We introduce a double-sided variant of low gain avalanche detector, suitable for pixel arrays without dead-area in between the different read-out elements. TCAD simulations were used to validate the device concept and predict its performance. Different design options and selected simulation results are presented, along with the proposed fabrication process.

This work describes the development of a gamma detector based on silicon drift detectors (SDDs) to read out large ${\hbox{LaBr}}_3$ : ${\hbox{Ce}}$ scintillators for gamma-ray astronomy applications, within an activity supported by the European Space Agency (ESA). SDDs, characterized by high quantum efficiency and low electronic noise, when coupled with a scintillator are good candidates for gamma-ray spectroscopy applications in a wide energy range, e.g., from 150 keV to 15 MeV. The gamma-ray detector prototype presented here is composed of a 2 ${^\prime}{^\prime}$ $\times$ 2 ${^\prime}{^\prime}$ ${\hbox{LaBr}}_3$ : ${\hbox{Ce}}$ scintillator coupled with four SDD arrays arranged in a $2 \times 2$ format (a total of 36 SDDs). This detection system is operated with custom readout application specific integrated circuits (ASICs) and a data acquisition (DAQ) system. With this prototype gamma-camera, an energy resolution of 3.4% FWHM at 662 keV has been measured. Spectroscopy measurements have been carried out between 300 keV and 1800 keV and the achieved results are consistent with the electronic noise of the SDD technology. In this work, we report on the SDD based detection head’s design, its X-ray characterization, readout electronics, experimental setups and gamma-ray spectroscopy results. Finally, perspectives with the possible use of an improved SDD technology are discussed.

We characterized and analyzed an important feature of silicon photomultipliers: the single-photon time resolution (SPTR). We characterized the SPTR of new RGB (Red–Green–Blue) type Silicon Photomultipliers and SPADs produced at FBK (Trento, Italy), studying its main limiting factors. We compared time resolution of 1×1 mm 2 and 3×3 mm 2 SiPMs and a single SiPM cell (i.e. a SPAD with integrated passive-quenching), employing a mode-locked pulsed laser with 2-ps wide pulses. We estimated the contribution of front-end electronic-noise, of cell-to-cell uniformity, and intrinsic cell time-resolution. At a single-cell level, we compared the results obtained with different layouts. With a circular cell with a top metallization covering part of the edge and enhancing the signal extraction, we reached ~20 ps FWHM of time resolution.

In this paper, we present the characteristics and performances of new silicon photomultipliers (SiPMs), produced at FBK, for the near-ultraviolet (NUV) light detection, with reduced afterpulsing and delayed optical crosstalk. To study these components of the correlated noise, we manufactured SiPMs on silicon wafers featuring different substrate minority-carrier lifetime. This parameter proved to be crucial in determining the amount of delayed optical crosstalk and afterpulsing caused by photo-generated carriers diffusing from the substrate to the cell active region. With a very low substrate lifetime, we were able to minimize this correlated noise component to few percent at room temperature. Besides reducing the excess noise factor, the lower delayed correlated noise allows biasing the SiPM at higher voltages, reaching higher values of photon detection efficiency.

International audience; Shashlik calorimeters are sampling calorimeters using wavelength shifting fibers running perpendicularly to the scintillating/absorber plates for the light readout. These devices are cost-effective, easy to assemble, and characterized by a good flexibility in terms of energy resolution. On the contrary, the perpendicular optical fiber readout and the resulting fiber bundling to the photosensor pose a strong limitation to the longitudinal segmentation. Recently, the fast development of solid state photosensors allowed for the integration of the readout system directly in the bulk of the calorimeter, opening new possibilities in terms of longitudinal segmentation (SCENTT INFN R &D). In an ultra-compact module every single fiber segment is directly connected to a SiPM; the SiPMs are arranged in arrays on custom PCBs and readout by a fast electronics based on waveform digitizers. This detector technology is the baseline option for ENUBET: a 5 year project (2016-2021) funded by the European Research Council aiming to demonstrate the possibility of a complete instrumentation of the decay tunnel of conventional neutrino beam. This technique allows for a ten-fold reduction on the neutrino flux normalization error. In the talk we will present the results and a detailed performance assessment of the novel ultra-compact design obtained with a prototype of longitudinally segmented shashlik calorimeter, readout with SiPMs embedded in the calorimeter bulk. Tests performed at the CERN PST9 beamline in the 1-5 GeV energy range in November 2016 provided results in terms of linearity, energy resolution and e/π discrimination at various beam angles reproducing the grazing incident conditions typical of neutrino beam decay tunnels. We will also present results from a neutron irradiation campaign of our Silicon Photomultipliers at the INFN-LNL CN accelerator allowing to test neutron fluences of O(1012/cm2) using 5 MeV protons on a Be target.

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.

We present a SiPM-based gamma-ray detection module, which allows to read large LaBr 3 :Ce cylindrical crystals (diameter > 1”), typically adopted in nuclear physics experiments, with spectroscopic performances similar to those achievable with PMTs. High-Density SiPM technology for Near UltraViolet and blue light detection (NUV-HD, Fondazione Bruno Kessler, Italy) were used. These SiPMs show high Photo Detection Efficiency (PDE = 45% at 380 nm) and low Dark Count Rate (DCR 3 :Ce irradiated with 57C, 133Ba, 137Cs and 60Co calibration sources. An energy resolution of 3.19 ± 0.01% was achieved at 662 keV with 2” LaBr 3 :Ce. The same crystal was tested with a Super Bialkali PMT (Hamamatsu R6233-100) showing a similar energy resolution of 3.07 ± 0.03% at 662 keV. Therefore, these results support the equivalence between SiPM and PMT for high-resolution spectroscopy.

Silicon PhotonMultipliers (SiPM) have recently been proposed for Time-of-Flight ranging applications thanks to their high gain and excellent performances in terms of timing resolution. This work reports on the preliminary evaluation of a SiPM-based receiver for a Time-of-Flight (ToF) range meter at different ambient light intensities. A low-power 10-MHz picosecond pulsed laser was used as a light source and a Time-Correlated Single Photon Counting (TCSPC) module was employed to measure the time delay distribution between the emitted and reflected laser signal. Three different SiPMs with the same active area of 1×1 mm2 but different cell-size (40×40 pm2, 20×20 pm2 and 15×15 pm2) have been considered for the receiver. The system dynamic range, distance measurement precision and accuracy have been analysed at different ambient light intensities. Devices with smaller cell size exhibit greater ambient light rejection, with a better single-shot precision, a time walk lower than 25ps and a factor 3 improvement in the maximum tolerated ambient light intensity.

This work is mainly focused on characterization and analysis of cross-talk of a detection module for X-ray spectroscopy which is developed for the SIDDHARTA experiment. The SIDDHARTA experiment is designed to investigate strong nuclear interactions using exotic atoms in the field of nuclear physics. Silicon Drift Detectors (SDDs) used in this experiment are arranged in arrays of 2 $\times$4 elements with total area of 612 $mm^{2}$. At the final stage of SIDDHARTA experiment, 48 SDD arrays are needed to be utilized in a gantry structure to perform X-ray spectroscopy of exotic nuclei, like kaonic deuterium. Each single SDD unit in 2 $\times$4 formation of arrays is coupled to a charge sensitive preamplifier, namely CUBE, which is followed by shaping amplifier, and consequent analog and digital electronics that are all integrated on a custom developed multichannel chip called SFERA. This work aims to study the effect of charge sharing on SDD channels upon absorption of Xrays and background particles on SDD to investigate the performances of such devices when expected to be irradiated with X-rays signals and with a large background due to MIPs of the accelerator.

Silicon photomultipliers (SiPMs) are arrays of many single-photon avalanche diodes (SPADs), all connected in parallel. Each SPAD is sensitive to single photons and the SiPM gives an output proportional to the number of detected photons. These sensors are becoming more and more popular in different applications, from high-energy physics to spectroscopy, and they have been significantly improved over last years, decreasing the noise, increasing the cell fill-factor (FF) and thus achieving very high photon-detection efficiency (PDE). In FBK (Trento, Italy), we developed new SiPM technologies with high-density (HD) and, more recently, ultra-high-density (UHD) of cells (i.e. density of SPADs). These technologies employ deep-trenches between cells, for electrical and optical isolation. As an extreme case the smallest-cell, SiPM, i.e. with 5μm cell pitch, has about 40000 SPADs per squared millimeter. Such small SPAD dimensions gives a significantly high dynamic range to the SiPM. These small-cells SiPM have a lower correlated noise (including lower afterpulsing probability) and a faster recharge time (in the order of few nanoseconds), and they also preserve a very good detection efficiency (despite the small SPAD dimension).

This work reports on the development of the ARDESIA spectrometer. ARDESIA is a SDD-based, multichannel X-ray spectrometer, optimized for synchrotron applications that require a high-rate (Mcps), high-resolution (below 150 eV FWHM at shaping time faster than 200 ns) soft Xray detection. The main applications for which ARDESIA is designed are X-ray fluorescence (XRF) and X-ray absorption fine structure (XAFS) techniques. A compact, low-noise detection module has been developed for the instrument. The detector signals are amplified by a monolithic four-channel CUBE preamplifier and processed by a digital pulse processor to achieve short pulse processing times, to highlight the good performances of the module at high count rates (about 1 Mcps per channel). In this work, the characterization of the second release of the ARDESIA detection module is reported. This second release has fixed few issues presented by the first one and it is now a stable solution for high performances X-ray spectroscopy. After that, the complete 4-channel instrument is presented. The instrument has been realized so that the detection module can properly fit inside a synchrotron scattering chamber with a finger-like structure. The mechanical structure grants cooling, with a double Peltier TEC strategy, vacuum, insulation from the harsh surrounding environment and potential for placing side-by-side several spectrometers.

We demonstrate g(2)function measurement using novelty all solid-state SiPM detectors. The function g(2)is obtain with measurement time of only 500μs at pW light power levels.

A clinical SPECT insert for a commercial MRI scanner has been developed within the INSERT project, allowing simultaneous SPECT/MRI studies of the human brain. Here we present preliminary experimental results. The reconstructed resolution was 6-11 mm and the sensitivity 280-440 s-1/MBq. The INSERT is the first clinical SPECT prototype for simultaneous SPECT/MRI.

In this paper, we present a novel analog silicon photomultiplier (SiPM) structure, characterized by the passive-quenching active-recharge operation of the microcells (PQAR). The structure is obtained by including a MOSFET transistor close to each microcell. The transistor is built without any changes to the standard SiPM micro-fabrication process, and it does not significantly reduce the fill factor of the device. We operated this detector in a periodic pulsed reset mode. The advantages of this approach include a reduction in the effective dark count rate, strong suppression of afterpulsing, very short pulse duration, and lower fabrication cost. In this paper, we provide a description and the results of the preliminary characterization of the first 1 × 1-mm 2 prototype of the structure, with 50 × 50-μm 2 cells, fabricated at Fondazione Bruno Kessler (FBK). The measured duration of the single-cell response is only 3.4 ns FWHM. Employing a pulsed light source, we were able to measure a very sharp pulse-charge spectrum with a good photon counting capability of up to 40 detected photons and more because of the absence of after pulses.

The high light output and fast decay time of LaBr 3 :Ce scintillation detectors leads to excellent timing performance. To realize the potential of timing resolution with LaBr 3 :Ce we have investigated the performance with SiPMs which enable 1-to-1 coupling to individual crystals, and which have been optimized for the near-UV scintillation light emission of LaBr 3 :Ce. Coincidence timing resolution of 100 ps was measured for a 4×4×5 mm3 LaBr 3 :30%Ce crystal coupled to a 4×4 mm2 NUV-SiPM with very little dependence on temperature in the range of −20° to 20°C. Optimal performance was achieved at an over-voltage of 4.5 V, at which high gain and PDE are achieved. Though saturation was evident at 511 keV, an energy resolution of 8% FWHM was measured after correcting for nonlinearity. We also measured 110 ps for a 4×4×5mm3 LaBr 3 :5%Ce crystal and 245 ps for a 4×4×30 mm3 LaBr 3 :5%Ce crystal. The poorer measurement for the 30-mm long crystal is due mainly to variations in the timing offset as a function of DOI. The excellent temperature stability, fast risetime, high gain and low noise of the NUV-SiPM make it a practical and highly appealing photodetector for the readout of a LaBr 3 :Ce TOF PET detector.

In this paper, we report on the characterization of the single-photon time resolution (SPTR) of the RGB (Red-Green-Blue) type silicon photomultipliers (SiPM) produced at FBK. We measured and compared single-photon timing jitter of 1 ×1 mm 2 and 3 ×3 mm 2 SiPMs, and also of square SPADs with integrated passive quenching, identical to the cells composing the SiPMs. We reached a single-photon time resolution of about 180 ps full-width at half-maximum for 3 ×3 mm 2 SiPM, 80 ps for 1 ×1 mm 2 SiPM and less than 50 ps for single cells. From measurements with pinholes placed in front of 1 ×1 mm 2 detector we see a very good cell-to-cell uniformity: it is not a limiting factor for time resolution. We also characterized the timing jitter of SiPMs as a function of the number of photons per laser pulse (N) finding that it does not decrease exactly with the square root of N because of the optical crosstalk between cells.

For a given photon detection efficiency (PDE), the primary, Poisson distributed, dark count rate of the detector (DCR0) is one of the most limiting factors affecting the timing resolution of a silicon photomultiplier (SiPM) in the scintillation light readout. If the effects of DCR0 are removed through a suitable baseline compensation algorithm or by cooling, it is possible to clearly observe another phenomenon that limits the PDE, and thus the timing resolution of the detector. It is caused by the optical crosstalk of the SiPM, which is significantly increased by the presence of the scintillator. In this paper, we describe this phenomenon, which is also easily observed from the reverse I-V curve of the device, and we relate it to the measured coincidence resolving time in 511 keV γ-ray measurements. We discuss its consequences on the SiPM design and, in particular, we observe that there is an optimal cell size, dependent on both SiPM and crystal parameters, that maximizes the PDE in presence of optical crosstalk. Finally, we report on a crosstalk simulator developed to study the phenomenon and we compare the simulation results obtained for different SiPM technologies, featuring different approaches to the reduction of the crosstalk.

This paper describes a setup dedicated to the test of silicon photomultipliers interfaced to a scintillating bar detector. The main item of the setup is a scintillator bar tracker made of extruded bars, readout with wavelength shifter fibers: multiple configurations in terms of number of fibers and readout bar sides are available to test different readout approaches. This setup has been used to test the prototype SiPMs produced by FBK-irst which are characterized by a larger fill factor and photodetection efficiency with respect to standard devices. The SiPMs have been characterized in terms of efficiency, signal to noise ratio and mean photoelectron number using cosmic rays.