Sensitive Silicon Photomultipliers Research Articles

Large area tiles of position-sensitive silicon photomultipliers

Silicon photomultipliers (SiPMs) are highly sensitive photodetectors emerging as the technology of choice for many applications. In FBK, we developed a position sensitive SiPM technology, called “linearly graded” (LG-SiPM), which is based on an avalanche-current position-weighted partitioning approach. In particular, we recently developed a new version of LG-SiPM with a larger chip area (10 × 10 mm2) and based on NUV-HD technology, having a peak photon detection efficiency at 420 nm. These SiPMs have been characterized in terms of noise, detection efficiency and position resolution.We also developed tiles of 2x2 and 3x3 elements with such SiPMs, reaching very large sensitive areas of about 20 × 20 mm2 and 30 × 30 mm2. In such large area tiles we implemented a “smart channel” configuration, being able to have just 6 output channels and 8 channels respectively, with a position resolution below 0.5 mm. These detectors provide great advantages in all application requiring position resolution but with a small number of readout channels and reduced system complexity.

Study of Silicon Photomultiplier external cross-talk

ptical cross-talk is a critical characteristic of Silicon Photomultipliers (SiPMs) and represents a significant source of the excess noise factor, exerting a substantial influence on detector performance. During the avalanche process of SiPMs, photons generated can give rise to both internal cross-talk within the same SiPM and external cross-talk when photons escape from one SiPM and trigger avalanches in others. In scenarios where SiPMs are arranged in a compact configuration and positioned facing each other, the external cross-talk could even dominate the cross-talk phenomenon. This paper investigates two distinct methods for measuring external cross-talk: the counting method, which involves operating SiPMs face-to-face and measuring their coincident signals, and the reflection method, which employs a highly reflective film attached to the surface of the SiPMs. External cross-talk measurements have been conducted on several types of SiPMs, including Vacuum Ultra-Violet (VUV) sensitive SiPMs that Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics Inc (HPK) produced for nEXO as well as visible-sensitive SiPMs provided by FBK, HPK and SensL Technologies Ltd (SenSL) for JUNO-TAO. The results reveal a significant presence of external cross-talk in all tested SiPMs, with HPK's SiPMs exhibiting a dominant external cross-talk component due to the implementation of optical trenches that effectively suppress internal cross-talk. Furthermore, we found that the number of fired SPADs resulting from internal cross-talk can be described by combining Geometric and Borel models for all tested SiPMs, while the external cross-talk can be predicted using a pure Borel model. These distinct probability distributions lead to different excess noise factors, thereby impacting the detector performance in varying ways.

SiPM joint likelihood reception for mobile LED-optical communication under pointing errors.

Light-emitting diode (LED)-optical communication is a novel spectrum communication with wide field of view (FOV), light weight, and long-distance free-space capabilities. Due to atmospheric turbulence attenuation and pointing errors caused by long-distance communication, this Letter proposes a multi-pixel channel joint maximum likelihood (JML) reception method using a highly sensitive silicon photomultiplier (SiPM). To evaluate the performance of the SiPM under mobile terminal jittering communication, we analyze the effect of optical transmitting power, pointing errors, and signal-to-noise ratio (SNR) gain on optical communication by comparing JML with signal channel using the maximum likelihood (ML) algorithm. Both simulation analysis and experimental results demonstrate that the proposed JML algorithm to process signals received from SiPM multi-pixel channels can effectively mitigate the impact of pointing errors on the bit error rate (BER) of optical communications by two orders of magnitude at large jitter radians and SNR.

Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0nu beta beta ), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0nu beta beta of ^{136}Xe with projected half-life sensitivity of 1.35times 10^{28} yr. To reach this sensitivity, the design goal for nEXO is le 1% energy resolution at the decay Q-value (2458.07pm 0.31 keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163 K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay Q-value for the nEXO design.

NUV and VUV sensitive Silicon Photomultipliers technologies optimized for operation at cryogenic temperatures

The silicon photomultipliers (SiPMs) emerged as a promising solution in many applications, like high-energy physics experiments and recently, they are the detector of choice for the readout of liquid noble gases scintillators (e.g. liquid Xenon and liquid Argon) in large-area physics experiments. Here the SiPMs are operated at cryogenic temperatures. Important studies have been done to optimize SiPM performance for such conditions and we developed the NUV-HD-cryo and the VUV-HD-cryo technologies, with sensitivity optimized for the blue-wavelength and NUV range, or for the VUV range respectively. Important technological improvements have been demonstrated: (i) reduction of electric field, to lower band-to-band tunneling, (ii) doping profiles modifications to reduce afterpulsing at low temperatures and (iii) reduction of quenching resistor variation over temperature.In this work we show and compare the recent characterization results of primary noise, correlated noise and the dependences of the photon detection efficiency (PDE) and photon-number resolution of these SiPMs over temperature, between 300 K and 75 K.Primary dark count rate reduces to few counts per second already at 200 K, and of 7 orders of magnitude going towards liquid nitrogen temperature and the afterpulsing increment is mitigated. The PDE in the blue-wavelength region remain high in the investigated temperature range (>45%), while it changes at longer wavelengths and a good photon number resolution is preserved.

Continuous bed motion in a silicon photomultiplier-based scanner provides equivalent spatial resolution and image quality in whole body PET images at similar acquisition times using the step-and-shoot method.

This study investigated the spatial resolution and image quality of the continuous bed motion (CBM) method in a sensitive silicon photomultiplier (SiPM)-based positron emission tomography (PET)/computed tomography (CT) system compared with the traditional step-and-shoot (SS) method. Methods: Siemens Biograph Vision was used in this study. Data acquisition using the SS method was performed for 3 min per bed. In the CBM method, the bed speed ranged from 0.5 to 3.3 mm/s. The acquisition time equivalent to the SS method was 1.1 mm/s for 2-bed ranges and 0.8 mm/s for seven-bed ranges. The spatial resolution was investigated using 18F point sources and evaluated using the full width at half maximum. Image quality was investigated using a National Electrical Manufacturers Association International Electrotechnical Commission body phantom with six spheres 10-, 13-, 17-, 22-, 28-, and 37-mm inner diameters. The radioactivity concentration ratio of the 18F solution in all spheres and the background was approximately 4:1. The detectability of each sphere was visually evaluated on a five-step score. Image quality was physically evaluated using the noise equivalent count rate (NECphantom), contrast percentage of the 10-mm hot sphere (QH,10mm), background variability percentage (N10mm), and contrast-noise ratio (QH,10mm/N10mm). Results: The spatial resolution was not affected by the difference of acquisition methods and bed speeds. The detectability of the 10-mm sphere with a bed speed of 2.2 mm/s or faster was significantly inferior to that of the SS 2-bed method. In evaluating image quality, no significant difference in the contrast percentage was observed among the acquisition methods and speeds in the CBM method. However, the increasing bed speed in the CBM method increased the N10mm and decreased the NECphantom. When comparing the SS 2-bed method with the CBM method at 0.8 mm/s, no significant differences in all parameters were observed. Conclusion: In a SiPM-based PET/CT scanner, the CBM method provides equivalent spatial resolution and image quality in whole body PET images with same acquisition time using the SS method.

Experimental Demonstration of Over 14 AL Underwater Wireless Optical Communication

Turbidity of water significantly affect the system performance of underwater wireless optical communication (UWOC). In this letter, we proposed and experimentally demonstrated a loss-tolerant UWOC system using a compact high-power 520-nm laser diode (LD) and a highly sensitive silicon photomultiplier (SiPM). The LD is directly modulated by the on-off keying-non-return-to-zero (OOK-NRZ) data. A precise collimation system is designed in the transmitter so that the maximum beam divergence angle is fixed at 0.75 mrad. The performance of the proposed system is investigated over a 24-m underwater channel with different attenuation lengths (ALs) mimicking the different levels of water turbidity in coastal water. Experimental results show that the data rates of 20 Mbps, 40 Mbps, 80 Mbps and 100 Mbps can be achieved under 14.3 AL, 13.2 AL, 13.2 AL and 12.3 AL with bit error rates (BERs) lower than the forward error correction (FEC) limit.

Exploiting Cross-Luminescence in BaF2 for Ultrafast Timing Applications Using Deep-Ultraviolet Sensitive HPK Silicon Photomultipliers

Time resolution of scintillation-based detectors is becoming continuously more important. In medical applications, especially in positron emission tomography (PET), better time of flight (TOF) information of the emitted gammas leads to a higher signal-to-noise ratio in the reconstructed image. Benefits are lower doses applied to and/or shorter scanning times for the patient. In high energy physics (HEP) ultrafast timing becomes increasingly important for reducing pile up effects in future high luminosity colliders and therefore increasing the detector sensitivity in the search for rare events and new physics. This article is an initial study on exploiting the fast cross-luminescence emission in the inorganic BaF2 scintillator with deep ultraviolet-sensitive silicon photomultipliers (SiPMs) from Hamamatsu for precise timing in PET and HEP. Using BaF2 read out by these photodetectors with a photon detection efficiency (PDE) of only about 15% in the desired 200nm emission region, a time resolution of 94±5ps FWHM is achieved when coupling with air. This figure improves to 78$±4ps FWHM when coupling the BaF2 crystal with UV transparent optical grease, Viscasil, to the photodetector. This CTR performance obtained with BaF2 is already better than that measured with LYSO:Ce, a commonly used state-of-the-art inorganic scintillator in PET, when coupled to another Hamamatsu photodetector (S13360) and coupled with Meltmount. Assuming that one could increase the PDE in the ultraviolet to values of 60% obtained today at 420nm, the emission wavelength of LYSO, one could ultimately achieve CTRs below 40ps FWHM. Further improvements in CTR beyond these values could be envisaged if also the single photon time resolution (SPTR) of the ultraviolet sensitive SiPM could be enhanced. Studying the emission of BaF2 more in detail, a very fast decay component of less than 100ps has recently been observed, being of high interest in the domain of ultrafast timing. Hence, in depth investigation of this decay component would give an additional handle to improve time resolution. In view of the prospects in advancing technologies for ultraviolet sensitive SiPMs, with high PDE and SPTR, and further advancements in producing high quality BaF2, one could imagine the development of sub-30ps FWHM TOF-PET systems.

Characterization of the Hamamatsu VUV4 MPPCs for nEXO

In this paper we report on the characterization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Silicon Photo-Multipliers (SiPMs) as part of the development of a solution for the detection of liquid xenon scintillation light for the nEXO experiment. Various SiPM features, such as: dark noise, gain, correlated avalanches, direct crosstalk and Photon Detection Efficiency (PDE) were measured in a dedicated setup at TRIUMF. SiPMs were characterized in the range $163 \text{ } \text{K} \leq \text{T}\leq 233 \text{ } \text{K}$. At an over voltage of $3.1\pm0.2$ V and at $\text{T}=163 \text{ }\text{K}$ we report a number of Correlated Avalanches (CAs) per pulse in the $1 \upmu\text{s}$ interval following the trigger pulse of $0.161\pm0.005$. At the same settings the Dark-Noise (DN) rate is $0.137\pm0.002 \text{ Hz/mm}^{2}$. Both the number of CAs and the DN rate are within nEXO specifications. The PDE of the Hamamatsu VUV4 was measured for two different devices at $\text{T}=233 \text{ }\text{K}$ for a mean wavelength of $189\pm7\text{ nm}$. At $3.6\pm0.2$ V and $3.5\pm0.2$ V of over voltage we report a PDE of $13.4\pm2.6\text{ }\%$ and $11\pm2\%$, corresponding to a saturation PDE of $14.8\pm2.8\text{ }\%$ and $12.2\pm2.3\%$, respectively. Both values are well below the $24\text{ }\%$ saturation PDE advertised by Hamamatsu. More generally, the second device tested at $3.5\pm0.2$ V of over voltage is below the nEXO PDE requirement. The first one instead yields a PDE that is marginally close to meeting the nEXO specifications. This suggests that with modest improvements the Hamamatsu VUV4 MPPCs could be considered as an alternative to the FBK-LF SiPMs for the final design of the nEXO detector.

Timing properties of Ce-doped YAP and LuYAP scintillation crystals

Abstract The timing performance of radiation detectors based on Ce-doped perovskites YAlO3 (YAP) and (Lu 1−x - Y x )AlO3 (LuYAP) coupled with near-UV sensitive silicon photomultipliers (NUV-HD SiPMs) have been compared in coincidence time resolution (CTR) experiments. The single-detector time resolution full width at half maximum (FWHM) of YAP was found to be 169 ps, i.e., by a factor of two better than that observed earlier with photomultiplier readout. Introduction of lutetium into YAP structure deteriorates the time resolution to 286 ps and 309 ps for a Lu/Y atomic ratio of 1:1 and 0.7:0.3, respectively. The study of the dynamics of Ce 3 + excited state population after selective optical excitation with short (200 fs) pulses by using the differential absorption technique in pump and probe configuration evidenced the importance of electron trapping, which is enhanced by antisite Lu Al defects having favorable conditions to occur in LuAP.

Wearable and modular functional near-infrared spectroscopy instrument with multidistance measurements at four wavelengths.

.With the aim of transitioning functional near-infrared spectroscopy (fNIRS) technology from the laboratory environment to everyday applications, the field has seen a recent push toward the development of wearable/miniaturized, multiwavelength, multidistance, and modular instruments. However, it is challenging to unite all these requirements in a precision instrument with low noise, low drift, and fast sampling characteristics. We present the concept and development of a wearable fNIRS instrument that combines all these key features with the goal of reliably and accurately capturing brain hemodynamics. The proposed instrument consists of a modular network of miniaturized optode modules that include a four-wavelength light source and a highly sensitive silicon photomultiplier detector. Simultaneous measurements with short-separation (7.5 mm; containing predominantly extracerebral signals) and long-separation (20 mm or more; containing both extracerebral and cerebral information) channels are used with short-channel regression filtering methods to increase robustness of fNIRS measurements. Performance of the instrument was characterized with phantom measurements and further validated in human in vivo measurements, demonstrating the good raw signal quality (signal-to-noise ratio of 64 dB for short channels; robust measurements up to 50 mm; dynamic optical range larger than 160 dB), the valid estimation of concentration changes (oxy- and deoxyhemoglobin, and cytochrome-c-oxidase) in muscle and brain, and the detection of task-evoked brain activity. The results of our preliminary tests suggest that the presented fNIRS instrument outperforms existing instruments in many aspects and bears high potential for real-time single-trial fNIRS applications as required for wearable brain–computer interfaces.

Characterization of three high efficiency and blue sensitive silicon photomultipliers

We report about the optical and electrical characterization of three high efficiency and blue sensitive Silicon photomultipliers from FBK, Hamamatsu, and SensL. Key features of the tested devices when operated at 90% breakdown probability are peak photon detection efficiencies between 40% and 55%, temperature dependencies of gain and PDE that are less than 1%/°C, dark rates of ∼50kHz/mm2 at room temperature, afterpulsing of about 2%, and direct optical crosstalk between 6% and 20%. The characteristics of all three devices impressively demonstrate how the Silicon-photomultiplier technology has improved over the past ten years. It is further demonstrated how the voltage and temperature characteristics of a number of quantities can be parameterized on the basis of physical models. The models provide a deeper understanding of the device characteristics over a wide bias and temperature range. They also serve as examples how producers could provide the characteristics of their SiPMs to users. A standardized parameterization of SiPMs would enable users to find the optimal SiPM for their application and the operating point of SiPMs without having to perform measurements thus significantly reducing design and development cycles.

Characterization of VUV sensitive SiPMs for nEXO

Silicon Photomultipliers (SiPMs) are currently being investigated for use in nEXO, a liquid xenon double-beta decay experiment. These detectors must be able to detect photons at 175 nm with high photon detection efficiency (PDE) and low noise. Several manufacturers are collaborating with nEXO to develop devices with high sensitivity at 175 nm. Devices produced by FBK and Hamamatsu have been tested in gas/vacuum and in liquid xenon. Their PDE at 175-180 nm was characterized in liquid xenon and in gas/vacuum and their dark and correlated noise rates were measured at 173 K. This paper will describe the setups, the measurements and analysis, as well as show the performances of SiPMs coated with an organic wavelength shifting material.

Position Sensitive Silicon Photomultiplier With Intrinsic Continuous Cap Resistive Layer

A high-gain, position-sensitive photon number discriminating detector based on silicon photomultiplier (PS-SiPM) is proposed and fabricated. The device, compatible with standard CMOS fabrication process, is easy to implement owing to the intrinsic continuous and uniform cap resistive layer featured by an SiPM structure with bulk quenching resistor. Both the 2-D position information and the photon number of incident pulse light can be obtained from a tetralateral type configuration using a simple algebra calculation of its four readout signals. If one of the four anode electrodes on front side or the cathode electrode on rear side is used for signal output, the PS-SiPM can function as a regular SiPM with high resolved photon number discrimination. The device, with an active area of 2.2 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\times 2.2\) </tex-math></inline-formula> mm, demonstrated spatial resolution of 78–97 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> m, gain of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(1.4 \times 10^{5}\) </tex-math></inline-formula> and 46-ps time jitter of transmission delay for multiple photons.

Development of High Precision Timing Counter Based on Plastic Scintillator with SiPM Readout

High-time-resolution counters based on plastic scintillator with silicon photomultiplier (SiPM) readout have been developed for applications to high energy physics experiments for which relatively large-sized counters are required. We have studied counter sizes up to $120\times40\times5$ mm^3 with series connection of multiple SiPMs to increase the sensitive area and thus achieve better time resolution. A readout scheme with analog shaping and digital waveform analysis is optimized to achieve the highest time resolution. The timing performance is measured using electrons from a Sr-90 radioactive source, comparing different scintillators, counter dimensions, and types of near-ultraviolet sensitive SiPMs. As a result, a resolution of $\sigma =42 \pm 2$ ps at 1 MeV energy deposition is obtained for counter size $60\times 30 \times 5$ mm^3 with three SiPMs ($3\times3$ mm^2 each) at each end of the scintillator. The time resolution improves with the number of photons detected by the SiPMs. The SiPMs from Hamamatsu Photonics give the best time resolution because of their high photon detection efficiency in the near-ultraviolet region. Further improvement is possible by increasing the number of SiPMs attached to the scintillator.

A Novel Technique for the Stabilization of SiPM Gain Against Temperature Variations

In several applications of Silicon Photo-Multipliers (SiPM), drifts of the detector gain with the temperature represent a severe drawback which prevents from achieving optimal performance. We propose an original technique to address this issue, based upon the use of a SiPM not exposed to the light as a temperature sensor. The average amplitude of the dark pulses produced by this detector is measured and controlled to a constant reference value by means of a negative feedback loop, which automatically varies the bias voltage of the SiPM. The same bias voltage variations generated by the feedback loop are also applied to the sensitive SiPMs used in the specific application, thus making constant their gain. The effectiveness of the proposed compensation scheme has been experimentally demonstrated by using two SiPMs from FBK-irst (1 mm × 1 mm, 400 micro-cells, breakdown voltage Vbr ≅ 29 V), one as temperature sensor involved in the negative feedback loop and the other as light sensitive device. Both detectors have been enclosed in a thermally isolated box with temperature varied in the interval between 20 °C and 30 °C : the variation of the SiPM gain can be reduced from more than 20%, without compensation, to about 2%.

Imaging with SiPMs in noble-gas detectors

Silicon photomultipliers (SiPMs) are photosensors widely used for imaging in a variety of high energy and nuclear physics experiments. In noble-gas detectors for double-beta decay and dark matter experiments, SiPMs are attractive photosensors for imaging. However they are insensitive to the VUV scintillation emitted by the noble gases (xenon and argon). This difficulty is overcome in the NEXT experiment by coating the SiPMs with tetraphenyl butadiene (TPB) to convert the VUV light into visible light. TPB requires stringent storage and operational conditions to prevent its degradation by environmental agents. The development of UV sensitive SiPMs is thus of utmost interest for experiments using electroluminescence of noble-gas detectors. It is in particular an important issue for a robust and background free ββ0ν experiment with xenon gas aimed by NEXT.The photon detection efficiency (PDE) of UV-enhanced SiPMs provided by Hamamatsu was determined for light in the range 250–500 nm. The PDE of standard SiPMs of the same model (S10362-33-50C), coated and non-coated with TPB, was also determined for comparison. In the UV range 250–350 nm, the PDE of the standard SiPM is shown to decrease strongly, down to about 3%. The UV-enhanced SiPM without window is shown to have the maximum PDE of 44% at 325 nm and 30% at 250 nm. The PDE of the UV-enhanced SiPM with silicon resin window has a similar trend in the UV range, although it is about 30% lower.The TPB-coated SiPM has shown to have about 6 times higher PDE than the non-coated SiPM in the range 250–315 nm. This is however below the performance of the UV-enhanced prototypes in the same wavelength range. Imaging in noble-gas detectors using UV-enhanced SiPMs is discussed.

Simultaneous Noninvasive Clinical Measurement of Lens Autofluorescence and Rayleigh Scattering Using a Fluorescence Biomicroscope

Lens autofluorescence increases with the age of the subject, and the fluorophores responsible are associated with cataract, retinopathy, and other complications of diabetes. We built a scanning confocal lens fluorescence biomicroscope suitable for routine clinical measurement of lens autofluorescence and light scattering and report data from 127 healthy subjects. The fluorescence biomicroscope focuses a beam of light from a blue light-emitting diode on the lens and measures fluorescent green light and blue scattered light using a sensitive silicon photomultiplier. The system includes a target fixation light and a video camera for alignment and automatic pupil tracking. Under software control, a volume of measurement is scanned from behind the posterior lens capsule, through the lens to the aqueous humor, and then back again. Software computes the average ratio of lens autofluorescence to scattered light in the central portion of the lens. Self-reported healthy nondiabetic subjects were examined by an optometrist; if their eyes were healthy and without significant cataract, they were entered into the study. Valid lens autofluorescence data were collected from 127 subjects between 21 and 70 years of age. A linear model for lens autofluorescence intensity with age was highly statistically significant, and the improvement in fit for higher-order polynomial models was not statistically significant. The ratio of lens autofluorescence to light scatter was also calculated; regression analysis showed significant curvature for the relationship of the fluorescence ratio to age, so a nonlinear model was used to estimate the mean ratio of autofluorescence to scatter and its prediction intervals as a function of age. Our observation of a strongly significant linear regression of fluorescence intensity with age of the subjects agrees with the results from previous studies, as does a nonlinear model for the fluorescence ratio. The fluorescence biomicroscope enables the clinician to identify patients with fluorescence ratio significantly higher than expected for their age.

Small prototype gamma camera based on wavelength-shifting fibres

We are studying and developing a small field of view gamma camera based on wavelength-shifting optical fibres coupled to both sides of an inorganic scintillation crystal and using for the light readout highly sensitive photon detectors, namely silicon photomultipliers (SiPMs) and high efficiency multi-anode photomultiplier tubes (MaPMTs). The coupling of the fibres in orthogonal directions allows obtaining 2D position information, while the energy signal is provided by a PMT. A first prototype laboratory system has been developed using a custom-made 50 × 50 × 3 mm3 CsI(Na) crystal with embedded 1 mm diameter fibres and reading out the light from several fibres in each direction, both with individual SiPMs and with a MaPMT. Proof-of-concept studies and results obtained with these systems using 57Co are presented and compared. The application of optical fibres combined with highly sensitive SiPMs or MaPMTs as light sensors in a compact gamma camera has the potential to improve the spatial resolution to the 1-2 mm FWHM level, thus improving the sensitivity of typical scintigraphy techniques and making such camera clinically useful. Results demonstrate the feasibility and imaging capability of the system using both types of photon detectors for imaging. In the case of SiPMs, a temperature cooling system is necessary to improve the SNR and consequently achieve a better imaging performance. The development of larger prototypes with 10 × 10 cm2 and 12 × 12 cm2 is under way, using 1 mm2 SiPMs and 64 anode PMTs, respectively.

SiPM development for the imaging Cherenkov and fluorescence telescopes

A silicon photomultiplier (SiPM) is a novel solid state photodetector which has an outstanding photon counting ability. The device has excellent features such as high quantum efficiency (QE), good charge resolution, fast response (<100ps), very compact size, high gain (up to 2∼3×106), very low power consumption with low bias voltages (30∼70V), immunity to the magnetic field. In the last few years, UV sensitive SiPMs with a p-on-n structure have been developed by a few companies such as Hamamatsu, Photonique, Zecotek Photonics Inc., and institutes such as the MPI-HLL (Max-Planck-Institute for Physics—Max-Planck-Institute Semiconductor Laboratory) as well as the MPI-MEPhI (Max-Planck-Institute for Physics—Moscow Engineering Physical Institute). UV sensitive SiPMs are particularly promising for astroparticle physics applications in imaging atmospheric Cherenkov telescopes (IACTs), such as MAGIC/MAGIC-II [1] and CTA [2], and a fluorescence telescope in the space, JEM-EUSO [3].The current status of the SiPM development by MPI-HLL, MPI-MEPhI, and the study of the application to the telescopes noted above will be reported.