Use Of Silicon Photomultipliers Research Articles

First demonstration of a Compton gamma imager based on silicon photomultipliers

We are developing a rugged and person-transportable Compton gamma imager for use in security investigations of radioactive materials, and for radiological incident remediation. The imager is composed of layers of scintillator with light collection for the forward layers provided by silicon photomultipliers and for the rear layer by photomultiplier tubes. As a first step, we have developed a 1/5th-scale demonstration unit of the final imager. We present the imaging performance of this demonstration unit for 137Cs at angles of up to 30° off-axis. Results are also presented for 113Sn and 22Na. This represents the first demonstration of the use of silicon photomultipliers as an embedded component for light collection in a Compton gamma imager.

Innovative PET detector concept based on SiPMs and continuous crystals

The use of Silicon Photomultipliers (SiPM) has been proposed for Positron Emission Tomography (PET) readout because they are hardly affected by magnetic fields and their time response enables Time of Flight measurements. This work proposes an array of SiPM to be coupled to a monolithic LYSO crystal by means of a series of optical devices. The emitted light distribution by the scintillation crystal will be accurately determined using an Application Specific Integrated Circuit. The described sensor block aims to determine the planar coordinates and depth of interaction of the gamma ray with sub-millimetrical precision. In this work we present the initial studies regarding edge effects due to thick monolithic crystals and how to overcome these limitations by means of optical devices namely faceplates and light concentrators. We will also discuss on the alignment of such optical devices with the SiPMs.

Development and characterization of a modular acquisition system for a 4D PET block detector

Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard photomultiplier tubes . The use of Silicon Photomultiplier (SiPM) matrices is proposed for the construction of a 4D PET module based on LSO continuous crystals, which is envisaged to replace the standard PET block detector. The expected spatial resolution of the module for the photon hit position is below 1 mm, and it will perform at the same time, the Depth Of Interaction (DOI) calculation and the Time Of Flight (TOF) measurement. The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Digital Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector performances. We have developed a flexible and modular DAQ system for the read-out of two modules in time coincidence for Positron Emission Tomography (PET) applications. The DAQ system is based on a previously developed custom front-end ASIC chip (BASIC) which allows to read-out SiPM matrices preserving their spectroscopy and timing capabilities. Here we describe the acquisition system architecture and its characterization measurements.

Silicon Photomultipliers (SiPM) as novel photodetectors for PET

Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard photomultiplier tubes. The use of Silicon Photomultipliers (SiPMs) is proposed for the construction of a 4D-PET module of 4.8×4.8 cm 2 aimed to replace the standard PMT based PET block detector. The module will be based on a LYSO continuous crystal read on two faces by Silicon Photomultipliers. A high granularity detection surface made by SiPM matrices of 1.5 mm pitch will be used for the x– y photon hit position determination with submillimetric accuracy, while a low granularity surface constituted by 16 mm 2 SiPM pixels will provide the fast timing information ( t) that will be used to implement the Time of Flight technique (TOF). The spatial information collected by the two detector layers will be combined in order to measure the Depth of Interaction (DOI) of each event ( z). The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Data Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector capabilities and to manage many channels. The paper describes the progress made on the development of the proof of principle module under construction at the University of Pisa.

Performance study of silicon photomultipliers as photon detectors for PET

The use of Silicon Photo-Multipliers (SiPMs) as photon detectors in Positron Emission Tomography (PET) modules offers significant advantages over conventional light sensors, including application in a magnetic field, better resolution and easier operation. Different types of SiPMs have been tested: Photonique, 2.1×2.1 mm 2, Hamamatsu 3×3 mm 2 and STMicroelectronics 3.5×3.5 mm 2. Dark noise, surface sensitivity, photon detection efficiency and linearity at low light intensities have been measured. A LYSO crystal was coupled to a SiPM to test the performance as a photon detector for PET. We will present the results of the measurements for different samples and types.

Measurements of Cherenkov Photons with Silicon Photomultipliers

A novel photon detector, the Silicon Photomultiplier (SiPM), has been tested in proximity focusing Ring Imaging Cherenkov (RICH) counters that were exposed to cosmic-ray particles in Ljubljana, and a 2 GeV electron beam at the KEK research facility. This type of RICH detector is a candidate for the particle identification detector upgrade of the BELLE detector at the KEK B-factory, for which the use of SiPMs, microchannel plate photomultiplier tubes or hybrid avalanche photodetectors, rather than traditional Photomultiplier Tubes (PMTs) is essential due to the presence of high magnetic fields. In both experiments, SiPMs are found to compare favourably with PMTs, with higher photon detection rates per unit area. Through the use of hemispherical and truncated pyramid light guides to concentrate photons onto the active surface area, the light yield increases significantly. An estimate of the contribution to dark noise from false coincidences between SiPMs in an array is also presented.

Anti-coincidence rejection of SiPM dark pulses for improved detection of low energy radiation

Neutron and gamma detectors of the CSIRO air cargo scanner are based on scintillators readout by photodiodes (PD). The scanner imaging resolution is limited by the scintillator size. It, in turns, is limited by the number of interactions that can be detected by the PD. Silicon photomultipliers (SiPM) could be used in place of PDs to improve the neutron and gamma detector efficiency. It would ultimately improve the scanner performance in terms of speed, cargo size and image quality. Efficient use of SiPM requires gain stabilisation and dark counts suppression. This work presents a technique to strip the dark counts and the electronic noise off the genuine source-induced spectrum. The method requires the use of a pair of SiPM coupled to the same scintillator. By rejecting the events not detected by both the SiPMs, the background counts were reduced by more than 99%.

Possibilities of using silicon photomultipliers in the scintillation technique

The use of silicon photomultipliers for reading optical information from scintillators was investigated. Measurements were taken with scintillating fibers, tiles, and high-Z scintillators. In experiments with silicon photomultipliers, it was shown that relativistic particles were detected in scintillating fibers with an efficiency of 97–98% and that there were about nine photoelectrons. When information was read out of scintillator tiles via wavelength shifting fibers, the number of photoelectrons was ∼15. The energy resolution of detectors based on LSO crystals was ∼25% for γ rays with energies of 500–600 keV.

Future use of silicon photomultipliers for K aos at MAMI and P¯ANDA at FAIR

A characterization of scintillating fibres with silicon photomultiplier read-out was performed in view of their possible application in fibre tracking detector systems. Such a concept is being considered for the K aos spectrometer at the Mainz Microtron MAMI and as a time-of-flight start detector for the hypernuclear physics programme at the P¯ANDA experiment of the FAIR project. Results on particle detection efficiency and time resolution are discussed. In summary, the silicon devices are very suitable for the detection of the low light yield from scintillating fibres insofar a trigger scheme is found to cope with the noise rate characteristics.