No Arabic abstract
The performance of a silicon photomultiplier has been assessed at low temperature in order to evaluate its suitability as a scintillation readout device in liquid argon particle physics detectors. The gain, measured as 2.1E6 for a constant over-voltage of 4V was measured between 25degC and -196degC and found to be invariant with temperature, the corresponding single photoelectron dark count rate reducing from 1MHz to 40Hz respectively. Following multiple thermal cycles no deterioration in the device performance was observed. The photon detection efficiency (PDE) was assessed as a function of photon wavelength and temperature. For an over-voltage of 4V, the PDE, found again to be invariant with temperature, was measured as 25% for 460nm photons and 11% for 680nm photons. Device saturation due to high photon flux rate, observed both at room temperature and -196degC, was again found to be independent of temperature. Although the output signal remained proportional to the input signal so long as the saturation limit was not exceeded, the photoelectron pulse resolution and decay time increased slightly at -196degC.
This work illustrates and compares some methods to measure the most relevant parameters of silicon photo-multipliers (sipm{}s), such as photon detection efficiency as a function of over-voltage and wavelength, dark count rate, optical cross-talk, afterpulse probability. For the measurement of the breakdown voltage, $V_{BD}$, several methods using the current-voltage $IV$ curve are compared, such as the IV Model, the relative logarithmic derivative, the inverse logarithmic derivative, the second logarithmic derivative, and the third derivative models. We also show how some of these characteristics can be quite well described by few parameters and allow, for example, to build a function of the wavelength and over-voltage describing the photodetection efficiency. This is fundamental to determine the working point of SiPMs in applications where external factors can affect it. These methods are applied to the large area monolithic hexagonal SiPM S10943-2832(X), developed in collaboration with Hamamatsu and adopted for a camera for a gamma-ray telescope, called the SST-1M. We describe the measurements of the performance at room temperature of this device. The methods used here can be applied to any other device and the physics background discussed here are quite general and valid for a large phase-space of the parameters.
To increase the light yield of a liquid Ar (LAr) detector, we optimized the evaporation technique of tetraphenyl butadiene (TPB) on the detector surface and tested the operability of a silicon photomultiplier (SiPM), namely, the multi-pixel photon counter with through-silicon-via (TSV-MPPC, Hamamatsu Photonics K.K.) at LAr temperature. TPB converts the LAr scintillations (vacuum ultraviolet light) to visible light, which can be detected by high-sensitivity photosensors. Because the light yield depends on the deposition mass of TPB on the inner surface of the detector, we constructed a well-controlled TPB evaporator to ensure reproducibility and measured the TPB deposition mass using a quartz crystal microbalance sensor. After optimizing the deposition mass of TPB (30 $mu g/cm^2$ on the photosensor window and 40 $mu g/cm^2$ on the detector wall), the light yield was 12.8 $pm$ 0.3 p.e./keVee using PMTs with a quantum efficiency of approximately 30% for TPB-converted light. We also tested the low-temperature tolerance of TSV-MPPC, which has a high photon-detection efficiency, in the LAr environment. The TSV-MPPC detected the LAr scintillations converted by TPB with a photon-detection efficiency exceeding 50%.
ArDM-1t is the prototype for a next generation WIMP detector measuring both the scintillation light and the ionization charge from nuclear recoils in a 1-ton liquid argon target. The goal is to reach a minimum recoil energy of 30,keVr to detect recoiling nuclei. In this paper we describe the experimental concept and present results on the light detection system, tested for the first time in ArDM on the surface at CERN. With a preliminary and incomplete set of PMTs, the light yield at zero electric field is found to be between 0.3-0.5 phe/keVee depending on the position within the detector volume, confirming our expectations based on smaller detector setups.
Presented here are first tests of a Gaseous Photomultiplier based on a cascade of Thick GEM structures intended for gamma-ray position reconstruction in liquid Argon. The detector has a MgF$_2$ window, transparent to VUV light, and a CsI photocathode deposited on the first THGEM. A gain of $8cdot10^{5}$ per photoelectron and $sim100%$ photoelectron collection efficiency are measured at stable operation settings. The excellent position resolution capabilities of the detector (better than 100 $mu$m) at 100 kHz readout rate, is demonstrated at room temperature. Structural integrity tests of the detector and seals are successfully performed at cryogenic temperatures by immersing the detector in liquid Nitrogen, laying a good foundation for future operation tests in noble liquids.
A mini-PET style detector system is being developed for a plant imaging application with a compact array of silicon photomultipliers (SiPM) replacing position sensitive photomultipliers (PSPMT). In addition to compactness, the use of SiPMs will allow imaging setups involving high strength MRI-type magnetic fields. The latter will allow for better position resolution of the initial positron annihilations in the plant tissue. In the present work, prototype arrays are tested for the uniformity of their response as it is known that PSPMTs require significant gain compensation on the individual channels to achieve an improved uniformity in response. The initial tests indicate a high likelihood that the SiPM arrays can be used without any gain compensation.