Radiation Effect On Gas Electron Multiplier Detector Performance

The Gas Electron Multiplier (GEM) was first introduced by Fabio Sauli in 1997, which is a thin layer of an insulating polymer, coated on both sides with copper and chemically perforated with a high density of microscopic holes. The GEM detectors, which are built using GEM foils, have been utilized for various applications due to their excellent spatial resolution, high rate capabilities and flexibility in design. Large area of triple GEM detectors are planned in experiments as it is the case in the upgrade of the CMS forward muon system. During the assembly of these detectors, the GEM foils are manually stretched to maintain the required gap configuration throughout the detector area. This stretching procedure can introduce local variation in the size or the shape of the perforated holes in GEM foil which can further vary the operational characteristics of the foil as well as the detector. Therefore, the distribution and size of the holes over a GEM foil should be uniform to achieve homogeneous functionality of the detector over the active surface. We can prevent the deformation of the perforated holes by optimizing the stretching force which is used during the assembly.

During the past decade, Gas Electron Multiplier (GEM) detectors have been greatly developed and utilized in numbers of applications including advanced nuclear and particle researches, medical imaging, astrophysics, and neutron detection for national security. Our GEM research group at the Department of Applied Radiation and Isotopes, Faculty of Science, Kasetsart University, Thailand, realized in its excellent properties/potentials and started extensive researches on GEM detectors. To build a strong foundation on our research group, two 10 cm × 10 cm triple GEM detectors were characterized on their important properties including absolute gains and detection uniformity. Moreover, to widen applications of the GEM detector, our group had modified the GEM detector by introducing either solid or gaseous neutron converters to the detector so that the detector could effectively detect neutrons. These modifications included coating a thin film of 10B and natB to the GEM drift cathode for thermal neutron detection and flowing a gas mixture of He/CO2 (80:20 and 70:30) and C4H10/He/CO2 (7:70:23) for fast neutron detection. Results showed that the modified GEM-based neutron detector could detect both types of neutrons with different relative efficiencies and gains depending on thicknesses and types of neutron converters. This article discusses basic knowledge of the GEM detector, construction and testing procedures, results, and discussion.

Gem detectors for X-ray astronomy

Production and validation of industrially produced large-sized GEM foils for the Phase-2 upgrade of the CMS muon spectrometer

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BM@N (Baryonic Matter at the Nuclotron) is a fixed target experiment aimed to study nuclear matter in the relativistic heavy-ion collisions at the Nuclotron accelerator in JINR. The BM@N tracking system is based on Gas Electron Multipliers (GEM) detectors mounted inside the BM@N analyzing magnet. The Cathode Strip Chamber (CSC) is installed outside the magnet. The CSC is used for improvement of particles momentum identification. The structure of the GEM detectors and the CSC prototype and the results of study of their characteristics are presented. The GEM detectors and CSC are integrated into the BM@N experimental setup and data acquisition system. The results of first tests of the GEM tracking system and CSC in last runs are shortly reviewed.

A Gas Electron Multiplier (GEM) detector is one of the most promising particle detectors nowadays due to its excellences in high rates of detection capability, good spatial resolution, and flexibility in designs. In addition to typical applications of ionizing particle detection, the GEM detector could also be modified to detect thermal neutrons by coating suitable solid neutron converters to its GEM drift cathode. Although, wide selections of materials are available to be used as neutron converters, most suitable ones must have high neutron-absorption-cross-section properties as more chances of nuclear interactions between thermal neutrons and their nuclei are desirable. Another factor that plays important roles to detection efficiencies in addition to types of materials is thicknesses of coating layers. Although thicker layers mean higher numbers of nuclei available for interactions with neutrons, ionizing particles produced after the interactions have less chances of successfully penetrate thick layers to ionize gas molecules for detection. Consequently, an optimum thickness for each material is crucial for GEM-based thermal neutron detector and must be carefully determined. This article aims to illustrate in-depth calculations to find these optimum thicknesses and their corresponding relative efficiencies for different solid neutron converters including 6Li, natLi, 10B, natB, 113Cd, natCd, 149Sm, and natSm, using a simulation and actual data of GEM’s properties. Basic information of GEM detector and neutron detection, simulations, efficiency calculations, results, and discussion will be thoroughly reported in this article.

Accurate, high-spatial resolution dosimetry in proton therapy is a time consuming task, and may be challenging in the case of small fields, due to the lack of adequate instrumentation. The purpose of this work is to develop a novel dose imaging detector with high spatial resolution and tissue equivalent response to dose in the Bragg peak, suitable for beam commissioning and quality assurance measurements.A scintillation gas electron multiplier (GEM) detector based on a double GEM amplification structure with optical readout was filled with a He/CF4 gas mixture and evaluated in pristine and modulated proton beams of several penetration ranges. The detector’s performance was characterized in terms of linearity in dose rate, spatial resolution, short- and long-term stability and tissue-equivalence of response at different energies. Depth-dose profiles measured with the GEM detector in the 115–205 MeV energy range were compared with the profiles measured under similar conditions using the PinPoint 3D small-volume ion chamber.The GEM detector filled with a He-based mixture has a nearly tissue equivalent response in the proton beam and may become an attractive and efficient tool for high-resolution 2D and 3D dose imaging in proton dosimetry, and especially in small-field applications.

The Gas Electron Multiplier (GEM) detector has evolved into a vital instrument for radiation imaging due to its high particle detection efficiency, excellent timing and spatial resolution. Their low-cost construction allows for the production of large-area imaging detectors, making it appropriate for a wide range of applications such as cargo scanning, geophysical studies, and soil imaging. In this article, we explore the application of GEM detectors in soil and clay studies, where their ability to detect minute density variations provides useful information regarding soil composition and moisture levels. These tracts are crucial for improving methods of cultivation and crop health. The findings demonstrate the GEM detector's potential as an alternative instrument for non-invasive and quantitative measurements in a wide range of scientific and industrial applications include agriculture practices.

Visual investigation of possible degradation in GEM foil under test

Gas Electron Multiplier (GEM) detectors have been successfully operated in the LHCb experiment and they will be installed in the CMS and ALICE experiments during LHC Long Shutdown 2. As for others LHC gaseous detector systems, gas mixture is individually provided by dedicated Gas Systems. Several studies have been performed in laboratory to characterize GEM performance from the point of view of their use in LHC Gas Systems, where many variables can influence detectors operation. A Triple-GEM prototype was tested with the aim of probing the possible effects of specific changes that could occur in the Gas System, such as variations in gas mixture composition, input gas flow and presence of impurities. A complete overview of the obtained results will be presented. The test confirms the importance of having a stable gas mixture composition, as it influences GEMs working point, with significant variations in the amplification gain. It was also seen how the input gas flow can affect GEMs performance, since it conditions the accumulation of humidity and air. Moreover, it was found that the presence of pollutants such as O2, N2 and H2O, commonly present during operation in the experiments, influences GEMs performance in terms of signal efficiency and amplification gain. While detector gain is weakly affected by the presence of N2, the presence of even small concentrations of O2 causes a significant performance decrease in terms of amplification gain.

With the planned upgrade of the ALICE Time Projection Chamber (TPC) the current readout technology will be replaced by a Gas Electron Multiplier (GEM)—based readout technology in order to allow for a continuous operation at high interaction rates up to 50 kHz. A stack of four GEM stages with non-standard field configuration was chosen to achieve a suppression of the ion backflow below 1%, while maintaining a good energy resolution below σ / E= \\unit[12]% for 55 Fe. A discharge probability of 10−10 for α-particles was confirmed for this low ion backflow field configuration. This is comparable to standard triple GEM detectors in low discharge settings. To upgrade all the Inner and Outer Readout Chambers of ALICE, 576 GEM foils will be needed. Only GEM foils that fullfill the highest quality criteria can be used. Therefore a quality assurance scheme has been developed that includes a large set of quality assurance measurements.

The LHC will undergo a major upgrade, named the High-Luminosity LHC (HL-LHC), that will deliver instantaneous luminosity as high as 7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . To cope with the higher event rates and with the increased radiation doses, the Compact Muon Solenoid (CMS) experiment will undergo several upgrades including the installation of additional muon detectors based on the Gas Electron Multiplier (GEM) technology.GEM foils, the core of GEM-based detectors, are currently produced with either double-mask or single-mask etching. Single-mask etching is a promising method, but results in an asymmetry in the shape of the holes. The effect of the hole asymmetry on the detector performance was studied with a twofold approach. Experimental data were collected using GEM foils with different hole geometries and detailed simulations were performed matching the experimental conditions. We present an overview of GEM detectors in CMS and describe a study to assess the impact of the GEM hole asymmetry on the detector performance.

Recent progress in GEM manufacturing and operation

An optical Quality Assurance (QA) system has been developed at the Detector Laboratory of the Helsinki Institute of Physics. The diameters of the holes in a Gas Electron Multiplier (GEM)-foil, both in the copper and in the polyimide, can be measured with the system. The system is utilized for the QA of the GEM foils of the TPC Read-Out Chambers (ROC) being assembled for the upgrade of the TPC readout chambers of the ALICE experiment at CERN. The correlation between the GEM hole size variation and the corresponding gain variation has been studied with several different gas compositions and operating voltages. A clear correlation has been shown to exist between the size of the GEM holes and the gain of the foil. Furthermore the relative gain of the foil can be estimated within 10 % based solely on the GEM hole size variation. The current correlation results are shown, as well as the progress towards a quantitative prediction of the gain of individual GEM foils. The possibility of predicting the gain of a full GEM stack is discussed. This study has been made in collaboration between Helsinki Institute of Physics and Wigner Research Centre in Budapest as part of the QA effort of the ALICE TPC upgrade project.