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Abstract Silicon photomultipliers present saturation effects as they have a limited number of pixels and work in Geiger mode. Their response to light pulses in the nonlinear region is very complex for two reasons: pixel recharging after an avalanche affects the trigger probability and charge multiplication of subsequent avalanches, and non-trivial effects due to crosstalk and afterpulsing. A parametrization of the nonlinear response of silicon photomultipliers was developed where the above effects were readily accounted for. The model was tested on a setup of γ -ray spectrometry using different combinations of scintillation crystals and detectors. The model parameters were interpreted in terms of fundamental characteristics of the setup (e.g., lifetime of the scintillation crystal and pixel recovery time). The proper conversion from signal resolution to energy resolution was provided. [ABSTRACT FROM AUTHOR]

Methods are developed, which use the pulse-height spectra of SiPMs measured in the dark and illuminated by pulsed light, to determine the pulse shape, the dark-count rate, the gain, the average number of photons initiating a Geiger discharge, the probabilities for prompt cross-talk and after-pulses, as well as the electronics noise and the gain fluctuations between and in pixels. The entire pulse-height spectra, including the background regions in-between the peaks corresponding to different number of Geiger discharges, are described by single functions. As a demonstration, the model is used to characterise a KETEK SiPM with 4384 pixels of 15 μ m × 15 μ m area for voltages between 2.5 and 8 V above the breakdown voltage. The results are compared to other methods of characterising SiPMs. Finally, examples are given, how the complete description of the pulse-eight spectra can be used to optimise the operating voltage of SiPMs, and a method for an in-situ calibration and monitoring of SiPMs, suited for large-scale applications, is proposed. [ABSTRACT FROM AUTHOR]

Gaseous detectors of ionizing particles have been playing a central role in the progress of fundamental research in nuclear and later particle physics since the invention in 1908 of the very first device: the Geiger Counter. The introduction in 1968 of the Multi-Wire Proportional Chamber (MWPC) concept by G. Charpack provided for the first time fine space resolution and this remained the only option for fine space resolution until the introduction of the solid state trackers. Nowadays gaseous detectors continue to play a key role in frontier particle and nuclei experiments. They provide the only possibility to equip large volumes at a reasonable cost, with good space resolution and limited material budget: an outstanding example is offered by the muon system of the ATLAS experiment at CERN LHC. Resistive Plate Chambers (RPC) provide time resolution better than 1 ns in extended counters and are therefore used in the trigger systems of the largest experiments at CERN LHC: ALICE, ATLAS, and CMS. In the ALICE RPC-based TOF system, the time resolution is as low as 80–110 ps. [ABSTRACT FROM PUBLISHER]

A prototype array of modular sensors for online monitoring of radioactive waste was developed at INFN-LNS. We implemented a new kind of gamma mini-sensor, based on Silicon PhotoMultipliers and scintillating fibers, that behaves like a cheap scintillating Geiger-Muller counter. It can be placed in shape of a fine grid around each single waste drum in a repository. After simulating the counting response of thin scintillating fibers to gamma radiation, we verified our simulation results with measurements using radioactive sources. Front-end electronics and an FPGA-based counting system were developed to handle the field data, also implementing data transmission, a graphical user interface and a data storage system. A test of four sensors in a real radwaste storage site was performed with promising results. [ABSTRACT FROM AUTHOR]

Abstract: Characteristic properties of a Geiger Mode APD (G-APD) in a THGEM-based cryogenic two-phase Ar avalanche detector were studied in view of potential applications in rare-event experiments. G-APD signal amplitude and noise characteristics at cryogenic temperatures turned out to be superior to those at room temperature. The effective detection of avalanche scintillations from THGEM-multiplier holes in two-phase Ar has been demonstrated using a G-APD without wavelength shifter. At an avalanche gain of 60, the avalanche scintillation yield measured by the G-APD was as high as 0.9 photoelectrons per avalanche electron, extrapolated to 4π acceptance. [ABSTRACT FROM AUTHOR]

Geiger-mode multi-pixel APD is being recognized as the best alternative solid-state photo-sensor to vacuum PMT for various specific applications. Especially, its magnetic field immunity and high gain made it popular in MR/PET detector research. In this paper, we utilized its compactness, high gain and high photon detection efficiency in the design of TOF PET detector. In a typical block detector based on PMT, the full timing capability of both PMT and scintillator could not be achieved due to its light sharing for Anger logic scheme. Since Geiger-mode APD is a solid-state based technology, we can apply one-to-one coupling between a scintillator and the photo-sensor to optimize the signal-to-noise ratio. Also, the high photon detection efficiency of MPPC, Geiger mode APD from Hamamatsu, would help to improve timing resolution. So, we made a block detector based on a 4 \times 4 array of 3\times 3\ mm^2 MPPC coupled to a 4 \times 4 array of 3\times 3\times 25\ mm^3 LYSO crystals to evaluate its performance. We have achieved the average of 9% energy resolution and 314 ps coincidence timing resolution with very good uniformity. This block timing resolution showed no degradation in timing compared to individual single channel timing resolution as expected from one-to-one readout. On top of that, the result proves that the solid-state based photo-sensor can be used for TOF PET detector. During the development and setup of the detector, we recognized that a compact and low power electronics readout scheme is one of the biggest challenges, including its cost, for MPPC or other Geiger-mode APD to be used in products. [ABSTRACT FROM AUTHOR]

Abstract: Pixelated Photon Detectors (PPDs) are arrayed APDs operated in Geiger-mode. Multi-Pixel Photon Counter (MPPC) is a PPD produced by Hamamatsu Photonics K.K. Test of dark noise rate of a 1600 pixel MPPC as a function of over-voltage at room temperature indicates that the over-voltage is limited up to a few volts because of explosive increase of noise rate. The over-voltage dependence of random noise rate is nevertheless mostly linear. We confirmed this is due to multiplication effect of noises because of after-pulsing and crosstalk. Over-voltage dependence of random noise and photon detection efficiency are qualitatively different. Considering the electric field structure of MPPC (p-on-n type) and Geiger-efficiency as a function of the position of initial pair creation, these characteristics are possible to be understood. One suggestion for p-on-n type PPD from these results is narrowing the depletion layer below the multiplication layer to reduce random noise and after-pulsing. Another proposal is to put additional buffer capacitance parallel to the diode to accomplish higher gain with lower over-voltage simultaneously with lower noise rate. [Copyright &y& Elsevier]

Abstract: Geiger APD technology, which has been used for a few years now [ R.H. Haitz, J. Appl. Phys. 35 (5) (1964) 1370], is evolving towards better performances, including integration in multifunctional microsystems; one such achievement today is the so-called SiPM [ P. Buzhan, et al., Nucl. Instr. and Meth. A 567 (2006) 78]. The present work has been conducted by a consortium of researchers from CESR and LAAS/CNRS and the manufacturing of components was achieved in the clean room of LAAS/CNRS. We present here an original N/P technology of photodiode, designed so as to offer a very good homogeneity in the electrical operating characteristics. For this, we have chosen a design and technological process that defines the breakdown voltage from the substrate doping. We present the technological process we developed, in which we took special care to maintain, by low transit temperature processes, at the highest quality level the initial characteristics of the materials. We will also present the performances of the diodes produced, with sizes ranging from 10 to 100μm, as a function of many parameters (gain, dark current, etc). We also produced SiPM, and also 8×8 arrays of SiPM. Typical characteristics for a single diode are a V br between 43 and 44V, and a dark current below 1pA at ambient temperature. But the most important feature seems to be the high homogeneity of these performances all over the wafer surface. This gives us great confidence in the next step of our work, which is the manufacturing of very high-sensitivity imaging devices. [Copyright &y& Elsevier]

Abstract: We have detected Cherenkov light from air showers with Geigermode-APDs (G-APDs). G-APDs are novel semiconductor photon detectors, which offer several advantages compared to conventional photomultiplier tubes in the field of ground-based very high energy (VHE) -ray astronomy. In a field test with the MAGIC telescope we have tested the efficiency of a G-APD/light catcher setup to detect coinciding Cherenkov light from air showers. From our test we estimate a detection efficiency of our G-APD/light catcher setup to be higher than the efficiency of a MAGIC camera pixel. The dark count rates of the tested G-APD at ambient temperature are 10 times lower than the rates of detected photons from the night sky light background (NSB). This relaxes the need for cooling the G-APD to the level where the noise rate is sufficiently low. According to this recent test, G-APDs promise a major progress in ground-based VHE γ-ray astronomy. [Copyright &y& Elsevier]

The Multi-Pixel Photon Counter (MPPC) is a Geiger-mode avalanche photo-diode (APD) developed by Hamamatsu Corp. We propose that it could be a suitable photo-sensor for next-generation time-of-flight PET detectors due to its high photon detection efficiency. We concentrate on the measurement of coincidence timing performance of various MPPCs in conjunction with LYSO crystal scintillators. With 3 mm × 3 mm devices of 50 μm sub-pixels coupled to 3 mm × 3 mm × 10 mm LYSO crystals, we have demonstrated a strong dependence of timing performance on over-voltage and temperature, and analyzed how changes in photon detection efficiency and dark counts would explain the measurements. The best coincidence timing resolution we have achieved between two identical LYSOIMPPC detectors was 240 Ps in FWHM. This was worse than the timing resolution of 220 ps obtained with a Hamamatsu H6533 fast PMT, and contradicted the expected improvement from higher photon detection efficiency. The contradiction could be explained by the slow rise-time of MPPC pulse shape, transit time spread, dark counts and electronic noise from the large capacitance of the MPPC. In particular, the slow rise-time of the MPPC pulse suggests the need for a very low trigger threshold on the timing circuit. Since this makes the detector system more sensitive to noise, this poses additional challenges for ganging multiple devices together into a commercially viable time-of-flight PET block detector. We will discuss this work in detail including other challenge imposed by MPPC characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Solid-state photodetectors working in the Geiger mode—known as Silicon PhotoMultipliers (SiPM) or MultiPixel Photon Counters (MPPC)—are currently being developed with increasingly large active areas. Potential applications for low-light-level detection were investigated with a MPPC, recently made available by Hamamatsu. The device was optically coupled with a scintillator and its performances, in terms of single photoelectron discrimination, were studied in a series of measurements under different operating conditions. An active control of the gain was implemented by a linear feedback on the operating voltage. The results of the tests are discussed. [Copyright &y& Elsevier]

The fabrication of silicon shallow junction photodiodes is a relevant topic for the detection of blue and near ultraviolet weak photon fluxes. In this paper we present a simple model to calculate the Quantum Detection Efficiency (QDE) of a Geiger Mode Avalanche Photodiode (GMAP) as a function of the dead layer thickness above the junction depletion layer. A comparison between calculated and experimental data is also presented. Moreover, by using the same model, an analysis of the QDE at 420 nm wavelength of conventional GMAPs based on shallow N[sup+] - P and P[sup+] - N junctions is given. [ABSTRACT FROM AUTHOR]

A new type of silicon device has been realized that has many properties comparable to, or better than, a conventional PMT (Photomultiplier Tube). This paper presents the first results of using these photodetectors in place of a PMT in the readout of scintillators for possible PET (Positron Emission Tomography) applications. This device, the Silicon Photomultiplier (SiPM), is effectively an avalanche photodiode operated in Geiger mode. In Geiger-mode detectors, a very large current signal is produced regardless of the size of the input, giving just logical rather than proportional information. However, the SiPM is subdivided into a large number (1440) of microcells that act as independent and virtually identical Geiger-mode photodiodes. The outputs of all these individual microcells are connected so that the total output signal is the sum of the signals from all of the microcells that were activated. In this way proportional information can be obtained. As a consequence of their design, these detectors have potentially very fast timing, high gain (105 - 106) at low bias voltage (∼50 V), a high quantum efficiency (35% at 500 nm), excellent single photoelectron resolution and are cheap to manufacture. Here we present results obtained with this new photodetector when used with pulsed LED and scintillator pixels. [ABSTRACT FROM AUTHOR]

Abstract: A prototype demonstrator for the online monitoring of short–medium term radioactive waste repositories is currently under development at INFN-LNS. Such a system is planned to be distributed, fine-grained, robust, reliable, and based on low-cost components. With the main purpose of counting gamma radiation, we implemented a new kind of mini-detector based on silicon photomultipliers and scintillating fibers that behaves like a cheap scintillating Geiger–Muller counter and is suitable to be deployed in the shape of a grid around waste drums. [Copyright &y& Elsevier]

Abstract: A Pixelized Photon Detector (PPD) is a generic name for the semiconductor devices operated in the Geiger-mode, such as Silicon PhotoMultiplier and Multi-Pixel Photon Counter, which has high photon counting capability. While the internal mechanisms of the PPD have been intensively studied in recent years, the existing models do not include the avalanche process. We have simulated the multiplication and quenching of the avalanche process and have succeeded in reproducing the output waveform of the PPD. Furthermore our model predicts the existence of dead-time in the PPD which has never been numerically predicted. For searching the dead-time, we also have developed waveform analysis method using deconvolution which has the potential to distinguish neighboring pulses precisely. In this paper, we discuss our improved model and waveform analysis method. [Copyright &y& Elsevier]