Gas Electron Multiplier Foils Research Articles

X-ray imaging with GEMs using 100 μm thick foils

A simple X-ray imaging system using off-the-shelf electronics and simple reconstruction algorithms aiming a spatial resolution of 1.7 mm ( ∼ 3 % of the detector length) is described in this work. For this, two 100 cm2 Gas Electron Multiplier (GEM) foils with a thickness of 100 μm (2-fold thicker than the standard ones) were immersed in a mixture of argon and carbon dioxide (70:30). The charge readout with 2D position determination was done with resistive charge division.Due to their higher thickness with respect to the standard GEMs, the 100 μm thick GEM foils were found to be less prone to damage caused by the electrical discharges.X-ray images are shown and some descriptions of the physical processes involved are presented. We describe the advantages of this method that allows counting each X-ray photon or particle entering the detector, its interaction position, as well as measuring of its energy. The results of our present work show a position resolution below 2 mm, being limited by the gas mixture used, and not the detecting system, with a very good cost effectiveness. Future work is being carried out to optimize the present system for a medical application as a proton beam monitor.

GEM based R&D for muon chambers of CBM experiment at FAIR

A Gas Electron Multiplier (GEM) based detector system has been envisaged for use in a muon tracker in the CBM experiment at FAIR. The choice of the detector technology is mainly guided by the stringent requirements of rate capability and radiation tolerance in the harsh CBM environment, where the particle rates reach upto about 1 MHz/cm2. Several 10 cm × 10 cm triple GEM prototypes have been built at VECC and tested with radioactive sources and with proton and pion/muon beams. Owing to high rate requirements, all the detectors in CBM will have to be operated in a self triggered mode of readout. The readout electronics also have to be appropriately tuned to cater to high rates. A detailed investigation of the self triggered readout electronics including its appropriate setting parameters have been carried out. Prototype tests based on self triggered mode of readout showed a charged particle detection efficiency of more than 90%. The Muon detector modules would employ large area GEM foils. First attempts to stretch and frame large area GEMs, foils of 31 cm × 31 cm have been carried out locally using thermal techniques. A relative gain variation of less than 10% has been observed.

Development of GEM-based Read-Out Chambers for the upgrade of the ALICE TPC

ALICE at the LHC at CERN is planning a major upgrade of the central barrel detectors, including the TPC, to cope with an increase of the LHC luminosity after 2018. A prototype of an ALICE TPC Inner Read-Out Chamber (IROC) was equipped with three large-size Gas Electron Multiplier (GEM) foils as amplification stage to demonstrate the feasibility of replacing the current readout by Multi-Wire Proportional Chambers (MWPC) with such technology. The GEM IROC was installed within a test field cage with a drift length of 115 mm and commissioned with radioactive sources. The dE/dx resolution of the prototype was evaluated in a test beam campaign at the CERN PS and is comparable to the resolution of the MWPC IROC. Stability under LHC conditions was tested during the ALICE p-Pb beam time, when the prototype was mounted underneath LHC beam pipe, close to the interaction point.

Development of thin gaseous ionization detectors for measurements of high-energy hadron beams

Thin gaseous ionization detectors have been developed based on a current-integration mode for measurements of high-energy hadron beams. In the present detector R&D, two different types of prototype detectors with an active area of 16 × 16 cm2, each equipped with 256-signal processing channels, were manufactured and tested with 43-MeV protons provided by the MC50 proton cyclotron at the Korea Institute of Radiological and Medical Science (KIRAMS). The first one was equipped with a single gas electron multiplier (GEM), and the second one was a thin-plane ionization detector without the GEM foil loaded. The linearities of the detector responses for both detectors were examined for various proton-beam intensities. The quantitative accuracies for the channel-response data and for the total detector responses measured for 43-MeV protons were 0.4% and 0.34%, respectively. We conclude from the beam test that operating both types of detectors in the current-integration mode will allow quality measurements of dynamic-mode hadron beams to be performed with accuracies of better than 1%.

Property of LCP-GEM in pure dimethyl ether at low pressure

We present a systematic investigation of the gain properties of a gas electron multiplier (GEM) foil in pure dimethyl ether (DME) at low pressures. The GEM is made from copper-clad liquid crystal polymer insulator (LCP-GEM) designed for space use, and is applied to a time projection chamber filled with low-pressure DME gas to observe the linear polarization of cosmic X-rays. We have measured gains of a 100 μm-thick LCP-GEM as a function of the voltage between GEM electrodes at various gas pressures ranging from 10 to 190 Torr with 6.4 keV X-rays. The highest gain at 190 Torr is about 2 × 104, while that at 20 Torr is about 500. We find that the pressure and electric-field dependence of the GEM gain is described by the first Townsend coefficient. The energy scale from 4.5 to 8.0 keV is linear with non-linearity of less than 1.4% above 30 Torr.

A novel self-supporting GEM-based amplification structure for a Time Projection Chamber at the ILC

Modern Time Projection Chambers are increasingly based on micro-pattern gas detector readout systems.In this paper a self-supporting method used to mount Gas Electron Multiplier foils is presented. It is based on light weight ceramic grids, and promises to cover large readout areas with minimum dead zones and material, while ensuring a flat and mechanically stable mounting. The structure has been tested in a Time Projection Chamber prototype, using cosmic muon tracks.The impact of the mounting structure on the charge measurement, the track reconstruction and the single point resolution is quantified.

A time projection chamber for high-rate experiments: Towards an upgrade of the ALICE TPC

A Time Projection Chamber (TPC) is a powerful detector for three-dimensional tracking and particle identification for ultra-high multiplicity events. It is the central tracking device of many experiments, e.g. of the ALICE experiment at CERN. The necessity of a switching electrostatic gate, which prevents ions produced in the amplification region of the MWPCs from entering the drift volume, however, restricts its application to trigger rates of the order of 1kHz.Charge amplification by Gas Electron Multiplier (GEM) foils instead of proportional wires offers an intrinsic suppression of the ion backflow, although not to the same level as a gating grid. Detailed Monte Carlo simulations have shown that the distortions due to residual space charge from back-drifting ions can be limited to a few cm, and thus can be corrected using standard calibration techniques. A prototype GEM-TPC has been built with the largest active volume to date for a detector of this type. It has been commissioned with cosmic rays and with particle beams at the FOPI experiment at GSI, and was employed for a physics measurement with pion beams.For the future operation of the ALICE TPC at the CERN LHC beyond 2019, where Pb–Pb collision rates of 50kHz are expected, it is planned to replace the existing MWPCs by GEM detectors, operated in a continuous, triggerless readout mode, thus allowing an increase in event rate by a factor of 100. As a first step of the R&D program, a prototype of an Inner Readout Chamber was equipped with large-size GEM foils and exposed to beams of protons, pions and electrons from the CERN PS.In this paper, new results are shown concerning ion backflow, spatial and momentum resolution of the FOPI GEM-TPC, detector calibration, and dE/dx resolution with both detector prototypes. The perspectives of a GEM-TPC for ALICE with continuous readout will be discussed.

Simulation of space-charge effects in an ungated GEM-based TPC

A fundamental limit to the application of Time Projection Chambers (TPCs) in high-rate experiments is the accumulation of slowly drifting ions in the active gas volume, which compromises the homogeneity of the drift field and hence the detector resolution. Conventionally, this problem is overcome by the use of ion-gating structures. This method, however, introduces large dead times and restricts trigger rates to a few hundred per second. The ion gate can be eliminated from the setup by the use of Gas Electron Multiplier (GEM) foils for gas amplification, which intrinsically suppress the backflow of ions. This makes the continuous operation of a TPC at high rates feasible.In this work, Monte Carlo simulations of the buildup of ion space charge in a GEM-based TPC and the correction of the resulting drift distortions are discussed, based on realistic numbers for the ion backflow in a triple-GEM amplification stack. A TPC in the future p¯anda experiment at FAIR serves as an example for the experimental environment. The simulations show that space charge densities up to 65fCcm−3 are reached, leading to electron drift distortions of up to 10mm. The application of a laser calibration system to correct these distortions is investigated. Based on full simulations of the detector physics and response, we show that it is possible to correct for the drift distortions and to maintain the good momentum resolution of the GEM-TPC.

Study on the performance of a high-gain gas electron multiplier-MicroMegas chamber

With the continuous development of the micro-structure of gas detectors, many different new detection requirements have been proposed. For more stable working time, lower discharge rate with long term and high effective gain, a new structure detector has been designed. Combined with the detection's advantages of MicroMegas and gas electron multiplier (GEM), it is composed of a MicroMagas chamber with one GEM foil as preamplifier. In this paper, the structure of the detector and detection principle are presented in detail. Using a 55Fe X-ray radioactive source in the operation mixtures gas of argon and isobutene (Ar/Iso =95/5), the performances of the detector gain, discharge rate, energy resolution and stable working time are investigated. Compared with standard MicroMegas detectors with no GEM foil, our detector show that a stable working time could reach more than 30 h of continuous work, the gain of the detector could exceed 106 and the discharge rate could be reduced by nearly 100 times at the same gain.

Two-dimensional Neutron Detector with GEM and its Applications

To improve material structure analysis using thermal (cold) neutrons at several pulsed neutron sources, we have developed a new gas detector for neutrons that employs a gas electron multiplier (GEM) as the detector. For neutron detection, both surfaces of a single GEM foil are coated with boron, and to increase efficiency, several GEM foils are stacked in a chamber. A prototype chamber was constructed with 10 cm × 10 cm GEM foils, and several beam tests were performed at a research reactor in Japan and at pulsed neutron sources (Hokkaido University and the Japan Proton Accelerator Research Complex). We achieved a detection efficiency of 30% for 0.22-nm thermal neutrons and a position resolution of ∼0.5 mm. In addition, we demonstrate two applications.

Application of Large Scale GEM for Digital Hadron Calorimetry

Abstract The detectors proposed for future e+e- colliders (ILC and CLIC) demand a high level of precision in the measurement of jet energies. Various technologies have been proposed for the active layers of the digital hadron calorimetry to be used in conjunction with the Particle Flow Algorithm (PFA) approach. The High Energy Physics group of the University of Texas at Arlington has been developing Gas Electron Multiplier (GEM) detectors for use as the calorimeter active gap detector. To understand this application of GEMs, two kinds of prototype GEM detectors have been tested. One has 30x30 cm 2 active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap. The other one has two 2x2 cm 2 GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. We will summarize the results of tests of these prototypes, using cosmic rays and sources, in terms of their applicability to a digital hadron calorimeter system. We will discuss plans for the construction of 1m 2 layers of GEM digital hadron calorimetry to be used as part of a 1m 3 stack to be used in a major test beam study of hadronic showers.

Development of Large Area GEM Chambers

The High Energy Physics group of the University of Texas at Arlington Physics Department has been developing Gas Electron Multiplier (GEM) detectors for use as the sensitive gap detector in digital hadron calorimeters (DHCAL) for the future International Linear Collider. In this study, two kinds of prototype GEM detectors have been tested. One has 30x30 cm 2 active area double GEM structure with a 3 mm drift gap, a 1 mm transfer gap and a 1 mm induction gap. The other one has two 2x2 cm 2 GEM foils in the amplifier stage with a 5 mm drift gap, a 2 mm transfer gap and a 1 mm induction gap. We present characteristics of these detectors obtained using high-energy charged particles, cosmic ray muons and 106 Ru and 55 Fe radioactive sources. From the 55 Fe tests, we observed two well-separated X-ray emission peaks and measured the chamber gain to be over 6500 with a high voltage of 395 V across each GEM electrode. Both the spectra from cosmic rays and the 106 Ru fit well to Landau distributions as expected from minimum ionizing particles. We also present the chamber performance after high dosage exposure to radiation as well as the pressure dependence of the gain and correction factors. Finally, we discuss the quality test results of the first set of large scale GEM foils and discuss progress and future plans for constructing large scale (100cmx100 cm) GEM detectors.

Development of a Two-Dimensional Gaseous Detector for Energy-Selective Neutron Radiography

Abstract Energy-selective neutron radiography is a new method for studying the fine structure of heavy materials by using pulsed neutron sources. To perform such radiography, precise measurements of temporal information and twodimensional position are essential. Therefore, we developed a gaseous neutron detector using the gas electron multiplier (GEM). In addition, to detect neutrons, a single surface of an aluminium cathode plate and both surfaces of two GEM foils were coated with boron-10. Two normal GEM foils were stacked in a chamber for gas amplification. An anode plate with two-dimensional strips (0.8-mm pitch) was mounted in order to precisely reconstruct neutron incident positions. To allow high-speed data transfer, a compact readout system with new application-specific integrated circuit (ASIC) chips and a field programmable gate array (FPGA) was developed. Finally, several beam tests were conducted with pulsed neutron sources and two interesting applications were demonstrated.

A Large GEM-TPC Prototype Detector for anda

The PANDA spectrometer will be a state of the art universal detector for strong interaction studies at the High-Energy Storage Ring (HESR) in the future international Facility for Anti-proton and Ion Research (FAIR) at GSI, Darmstadt. The detector is designed to take advantage of the extraordinary physics potential which will be available utilizing high intensity, phase space cooled anti-proton beams. This facility will provide a cooled anti-proton beam −2 with momenta of 1.5-15 GeV/c, a maximal luminosity of 2×10 32 cms −1 that translates into 2×10 7 pp annihilations per second. A GEM based Time Projection Chamber (TPC) was one of the central tracker candidates for the PANDA experiment. To check the feasibility of such a detector system, a large prototype GEM-TPC was built and tested inside the FOPI Spectrometer at GSI. A set of three Gas Electron Multiplier (GEM) foils were used as amplification stage instead of Multi Wire Proportional Chambers. In this report, the design, construction, characterization of the prototype-detector system will be discussed in detail along with the results of recent beam tests.

A new gamma camera with a Gas Electron Multiplier

We have developed a prototype gaseous gamma camera with a Gas Electron Multiplier (GEM) for biomolecular analysis and medical applications. The system consists of three devices: a detector, an Ethernet hub, and a PC. The detector consists of a GEM-chamber and integrated readout electronics. The GEM-chamber consists of three parts: the gamma-ray conversion and amplification layers consisting of GEM foils, and a readout component. To increase gamma-ray-detection efficiency, we constructed a new type of GEM foil. The gamma-ray conversion layers are plated with gold 3 μm thick on both surfaces. In order to test the performance of the prototype camera, several measurements were performed with a phantom filled with 99mTc (141 keV) as the radioactive source, and two-dimensional (2D) images were obtained using a pinhole collimator. The camera showed good capability to resolve objects of a few mm2. We believe that this system will offer new knowledge in biomolecular analysis and medical applications.

Neutron beam monitor based on a boron-coated GEM

A new thermal neutron beam monitor with a Gas Electron Multiplier (GEM) is developed to meet the needs of the next generation of neutron facilities. A prototype chamber has been constructed with two 100 mm×100 mm GEM foils. Enriched boron-10 is coated on one surface of the aluminum cathode plate as the neutron convertor. 96 channel pads with an area of 8 mm×8 mm each are used for fast signal readout. In order to study the basic characteristics of a boron-coated GEM, several irradiation tests were carried out with α source 239Pu and neutron source 241Am(Be). The signal induced by the neutron source has a high signal-to-noise ratio. A clear image obtained from α source 239Pu is presented, which shows that the neutron beam monitor based on a boron-coated GEM has a good two-dimensional imaging ability.

A new gamma-ray detector with gold-plated gas electron multiplier

For biomolecular analysis and nuclear medicine, we are developing a novel gamma camera based on a gaseous detector that uses gas electron multipliers (GEMs). To increase the gamma-ray-detection efficiency, we have constructed a novel GEM foil. The gamma-ray-conversion layers of the GEM foils are plated with 3μm of gold on both surfaces. To evaluate the detection efficiency of the gamma-ray energy that corresponds to 99mTc, which is the target isotope for our gamma camera, the measurements were performed using 241Am and 57Co as gamma-ray sources. Our measured detection efficiency was 0.81% (241Am) and 0.75% (57Co) for the sources, which agreed well with a Monte Carlo simulation based on Geant4. In addition, we were able to increase the efficiency using multiple gold-plated GEM foils.

Characterization of a 2D soft x-ray tomography camera with discrimination in energy bands

A gas detector with a 2D pixel readout is proposed for a future soft x-ray (SXR) tomography with discrimination in energy bands separately per pixel. The detector has three gas electron multiplier foils for the electron amplification and it offers the advantage, compared with the single stage, to be less sensitive to neutrons and gammas. The energy resolution and the detection efficiency of the detector have been accurately studied in the laboratory with continuous SXR spectra produced by an electronic tube and line emissions produced by fluorescence (K, Fe, and Mo) in the range of 3-17 keV. The front-end electronics, working in photon counting mode with a selectable threshold for pulse discrimination, is optimized for high rates. The distribution of the pulse amplitude has been indirectly derived by means of scans of the threshold. Scans in detector gain have also been performed to assess the capability of selecting different energy ranges.

CASCADE, neutron detectors for highest count rates in combination with ASIC/FPGA based readout electronics

The CASCADE detector system described herein is designed for high intensity neutron applications with high demands on the dynamical range, contrast as well as background. The detector front-end is a hybrid, solid converter gas detector using several gas electron multiplier (GEM) foils as charge transparent substrates to carry solid 10B layers. These coated GEMs are then stacked (“cascaded”) one behind the other to cumulate the detection efficiency of every layer without loosing position information. The use of GEM foils allows high count rates up to 10 7 n/cm 2 s. The well-defined neutron absorption locus inside the thin boron layer provides sub-microsecond absolute time resolution, which opens the door towards new TOF applications. Because 96% isotopically enriched boron is available in large quantities in contrast to 3He, 10B-converter based neutron detector technology is one of the very few technological alternatives to 3He in view of the imminent crisis in world-wide supply of 3He. Using GEM foils, the neutron detection bottleneck shifts to data read-out electronics and its bandwidth. The CASCADE detector uses an ASIC electronic front-end paired with an adaptable integrated FPGA data processing unit to provide high rate capacity and realtime event reconstruction.

Development of the GEM-MSTPC for measurements of low-energy nuclear reactions

We have developed an active target type gas detector, multi-sampling tracking proportional chamber (MSTPC) for studies of low-energy nuclear reactions such as (α,n) and (α,p). For higher rate capability, a gas electron multiplier (GEM) foil was adopted, instead of a multi-wire proportional counter, as a component of the MSTPC. We studied the basic properties of gas gain in a 400μm thick GEM (THGEM), which was compared to those of standard CERN GEMs. The THGEM was examined for gain instability and positive-ion feedback, especially with low-pressure He-base mixed gas. The THGEM was found to be applicable as a proportional counter using our gas target and He as the operating gas.