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Register a new userCharacterization of Silicon-Photomultipliers for a Cosmic Muon Veto detector
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A Cosmic Muon Veto (CMV) detector using extruded scintillators is being designed around the mini-Iron Calorimeter detector at the transit campus of the India-based Neutrino Observatory at Madurai for measuring its efficiency at shallow depth underground experiments. The scintillation signal is transmitted through a Wavelength Shifting (WLS) fibre and readout by Hamamatsu Silicon-Photomultipliers (SiPMs). A Light Emitting Diode (LED) system is included on the front-end readout for in-situ calibration of the gain of each SiPM. A characterization system was developed for the measurement of gain and choice of the overvoltage (Vov) of SiPMs using LED as well as a cosmic muon telescope. The Vov is obtained by studying the noise rate, the gain of the SiPM, and the muon detection efficiency. In case of any malfunction of the LED system during the operation, the SiPM can also be calibrated with the noise data as well as using radioactive sources. This paper describes the basic characteristics of the SiPM and the comparison of the calibration results using all three methods, as well as the Vov of the SiPMs and muon selection criteria for the veto detector.
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Silicon Photomultipliers (SiPMs) are attractive candidates for light detectors for next generation liquid xenon double-beta decay experiments, like nEXO. In this paper we discuss the requirements that the SiPMs must satisfy in order to be suitable for nEXO and similar experiments, describe the two test setups operated by the nEXO collaboration, and present the results of characterization of SiPMs from several vendors. In particular, we find that the photon detection efficiency at the peak of xenon scintillation light emission (175-178 nm) approaches the nEXO requirements for tested FBK and Hamamatsu devices. Additionally, the nEXO collaboration performed radioassay of several grams of bare FBK devices using neutron activation analysis, indicating levels of 40K, 232Th, and 238U of the order of <0.15, (6.9e10-4 - 1.3e10-2), and <0.11 mBq/kg, respectively.
The motivation for a cosmic muon veto (CMV) detector is to explore the possibility of locating the proposed large Iron Calorimeter (ICAL) detector at the India based Neutrino Observatory (INO) at a shallow depth. An initial effort in that direction, through the assembly and testing of a $sim$ 1 m $times$ 1 m $times$ 0.3 m plastic scintillator based detector, is described. The plan for making a CMV detector for a smaller prototype mini-ICAL is also outlined.
This paper describes the characterization of crystal matrices and silicon photomultiplier arrays for a novel Positron Emission Tomography (PET) detector, namely the external plate of the EndoTOFPET-US system. The EndoTOFPET-US collaboration aims to integrate Time-Of-Flight PET with ultrasound endoscopy in a novel multimodal device, capable to support the development of new biomarkers for prostate and pancreatic tumors. The detector consists in two parts: a PET head mounted on an ultrasound probe and an external PET plate. The challenging goal of 1 mm spatial resolution for the PET image requires a detector with small crystal size, and therefore high channel density: 4096 LYSO crystals individually readout by Silicon Photomultipliers (SiPM) make up the external plate. The quality and properties of these components must be assessed before the assembly. The dark count rate, gain, breakdown voltage and correlated noise of the SiPMs are measured, while the LYSO crystals are evaluated in terms of light yield and energy resolution. In order to effectively reduce the noise in the PET image, high time resolution for the gamma detection is mandatory. The Coincidence Time Resolution (CTR) of all the SiPMs assembled with crystals is measured, and results show a value close to the demanding goal of 200 ps FWHM. The light output is evaluated for every channel for a preliminary detector calibration, showing an average of about 1800 pixels fired on the SiPM for a 511 keV interaction. Finally, the average energy resolution at 511 keV is about 13 %, enough for effective Compton rejection.
AMIGA (Auger Muons and Infill for the Ground Array) is an upgrade of the Pierre Auger Observatory designed to extend its energy range of detection and to directly measure the muon content of the cosmic ray primary particle showers. The array will be formed by an infill of surface water-Cherenkov detectors associated with buried scintillation counters employed for muon counting. Each counter is composed of three scintillation modules, with a 10 m$^2$ detection area per module. In this paper, a new generation of detectors, replacing the current multi-pixel photomultiplier tube (PMT) with silicon photo sensors (aka. SiPMs), is proposed. The selection of the new device and its front-end electronics is explained. A method to calibrate the counting system that ensures the performance of the detector is detailed. This method has the advantage of being able to be carried out in a remote place such as the one where the detectors are deployed. High efficiency results, i.e. 98 % efficiency for the highest tested overvoltage, combined with a low probability of accidental counting ($sim$2 %), show a promising performance for this new system.
The design, optimisation and construction of an anti-coincidence veto detector to complement the ZEPLIN-III direct dark matter search instrument is described. One tonne of plastic scintillator is arranged into 52 bars individually read out by photomultipliers and coupled to a gadolinium-loaded passive polypropylene shield. Particular attention has been paid to radiological content. The overall aim has been to achieve a veto detector of low threshold and high efficiency without the creation of additional background in ZEPLIN-III, all at a reasonable cost. Extensive experimental measurements of the components have been made, including radioactivity levels and performance characteristics. These have been used to inform a complete end-to-end Monte Carlo simulation that has then been used to calculate the expected performance of the new instrument, both operating alone and as an anti-coincidence detector for ZEPLIN-III. The veto device will be capable of rejecting over 65% of coincident nuclear recoil events from neutron background in the energy range of interest in ZEPLIN-III. This will reduce the background in ZEPLIN-III from ~0.4 to ~0.14 events per year in the WIMP acceptance region, a significant factor in the event of a non-zero observation. Furthermore, in addition to providing valuable diagnostic capabilities, the veto is capable of tagging over 15% for gamma-ray rejection, all whilst contributing no significant additional background. In conjunction with the replacement of the internal ZEPLIN-III photomultiplier array, the new veto is expected to improve significantly the sensitivity of the ZEPLIN-III instrument to dark matter, allowing spin independent WIMP-nucleon cross sections below 1E-8 pb to be probed.
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