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An approximate formula has been derived for gain fluctuations in cascaded gaseous detectors such as Gas Electron Multipliers (GEMs), based on the assumption that the charge collection, avalanche formation, and extraction steps are independent cascaded processes. In order to test the approximation experimentally, a setup involving a standard GEM lay...
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We analyze charge fluctuations in a parasitic state strongly coupled to a superconducting Josephson-junction-based charge detector. The charge dynamics of the state resembles that of electron transport in a quantum dot with two charge states, and hence we refer to it as a two-level fluctuator. By constructing the distribution of waiting times from...
Citations
... When aiming at the best possible energy resolution, approaching the physical limits due to fluctuations of the generated charge, one has to pay attention to other effects, namely, variation in the gas amplification factor across the detector and dependence of the gas amplification factor on the radiation intensity. In the literature, one can find very different numbers on the energy resolution of GEM detectors from 18% to 27% FWHM for X-ray energy of 5.9 keV [37][38][39][40]. The energy at the level of 18% FWHM is usually measured using a focused X-ray beam so that the gas amplification factor is constant over a small examined area of the detector. ...
The goal of the work was to investigate the possible application of factor analysis methods for processing X-ray Fluorescence (XRF) data acquired with a full-field XRF spectrometer employing a position-sensitive and energy-dispersive Gas Electron Multiplier (GEM) detector, which provides only limited energy resolution at a level of 18% Full Width at Half Maximum (FWHM) at 5.9 keV. In this article, we present the design and performance of the full-field imaging spectrometer and the results of case studies performed using the developed instrument. The XRF imaging data collected for two historical paintings are presented along with the procedures applied to data calibration and analysis. The maps of elemental distributions were built using three different analysis methods: Region of Interest (ROI), Non-Negative Matrix Factorisation (NMF), and Principal Component Analysis (PCA). The results obtained for these paintings show that the factor analysis methods NMF and PCA provide significant enhancement of selectivity of the elemental analysis in case of limited energy resolution of the spectrometer.
... For the reconstruction of the relative gain we used the same methods as for setup 1. In addition, we tested various field configurations, and confirmed two earlier findings [25]. One is that the relative gas gain variations of the GEM did not substantially change when changing the drift field between 0.2 and 1.2 kV (full collection). ...
It is well known and has been shown that the gain performance of Gaseous Electron Multipliers (GEM) depends on the size of the holes. With an optical scanner it is possible to measure the dimensions of the holes, and to predict the performance of GEMs. However, the gain prediction of GEMs that are manufactured with a double mask etching technique is not straightforward. With the hole size information alone, it is not possible to make precise prediction of the gain. We show that the alignment of the photo-masks between the two sides of the GEM foils plays a crucial role. A misalignment of a few microns can lower the gain substantially. The study is performed by using the Helsinki high definition optical scanner for quality control of GEM foils, and this will show its true potential.
Muography is an innovative imaging technique used for inspecting and monitoring density-length variations of large-sized natural or human-made objects based on the measurement of the absorption rate of cosmic-ray muons. The first large-sized, high-resolution muography observatory based on Multi-Wire Proportional Chamber (MWPC) technology is being developed to monitor the mass density variations in the vicinity of Minami-dake crater of Sakurajima volcano. We found that the track rates provided by five ongoing tracking systems with a total surface area of 4 m2 are stable within ±3% from the backward direction, which demonstrates that the MWPC-based Muographic Observation System (MMOS) is applicable for the detection of average density variations above 2%, which is well below the practical limit of 5%. We quantified the time resolution of the designed muography observatory by modeling the muon flux across the volcano; the average density-length variation of 5 (10)% is expected to be detected within 5–20 (2–8) days at a 1σ (68%) confidence level (CL) with an MMOS orientation of 10.86° above the horizon. An automated analysis framework was developed as a data base for raw data reconstruction, analysis, and preparation, and which is accessible via web-server. We observed a more than 2σ CL decrease in average density across the West side of Crater A during the ongoing data collection period. The observed density decrease suggests that the amount of material has decreased inside Crater A due to the consecutive eruptions of Minami-dake during the data collection period from November 30, 2018 to January 11, 2019.
In this paper measurement results and experimental methodology is presented on the determination of multiplication distributions of avalanches in GEM foils initiated by a single electron. The measurement relies on the amplification of photoelectrons by the GEM under study, which is subsequently amplified in an MWPC. The intrinsic detector resolution, namely the sigma over mean ratio of this distribution is also elaborated. Small gain dependence of the avalanche size is observed in the range of net effective gain of 15 to 100. The distribution has an exponentially decaying tail at large amplitudes, whereas the applied working gas is seen to have a well visible effect on the shape of the multiplication distribution at low amplitudes; or equivalently, the working gas has an influence on the intrinsic detector resolution of GEMs via suppression of the low amplitude responses. A sigma over mean ratio down to 0.75 was reached using neon based mixture, whereas other gases provided an intrinsic detector resolution closer to 1, meaning a multiplication distribution closer to the idealized exponential case.
