Thick Gas Electron Multiplier Research Articles

THE DETERMINATION OF NEUTRON FLUENCE TO ABSORBED DOSE CONVERSION COEFFICIENTS AND RELATIVE BIOLOGICAL EFFECT BASED ON MICRODOSIMETRY MEASUREMENTS.

A tissue-equivalent proportional counter (TEPC) is a reference detector to measure microdosimetric quantities. A conventional spherical TEPC and a novel TEPC based on a ceramic thick gas electron multiplier (THGEM) foil were developed to carry out microdosimetric measurements of lineal energy spectra in monoenergetic and 252Cf/241Am-Be neutron radiation fields, and the absorbed dose values had been derived. In order to go further in radiobiology and therapy, the fluence to absorbed dose conversion coefficients in neutron fields were also determined. According to the dose distribution in lineal energy, the neutron relative biological effect (RBE) values were also calculated using an empirical procedure applying biological weighting functions.

Studies of the delayed discharge propagation in the Gas Electron Multiplier (GEM)

This paper presents an investigation of the delayed discharge propagation (DP) to the readout electrode. After a primary discharge develops inside a GEM foil hole the DP can occur with a time delay in the range of 1–100μs. A single hole THGEM (THick GEM) foil that enables a controlled discharge position and the induction of primary discharge with an over-voltage in the THGEM foil has been used in the initial DP measurements. In order to justify the use of a custom-made THGEM foil, additional measurements were made with a standard GEM foil. Correlated optical (with an ordinary SLR (Single-Lens Reflex) and a high-speed camera) and electrical measurements of the delayed DP were made for a Ne–CO2-N2 (90-10-5) mixture and with different powering configurations. Measurements show that the delayed DP happens without a drift field, with an inverted induction field, inverted THGEM voltages or an inverted drift field. After the primary discharge, there is a charge transfer in the induction region at an induction field value below that of the onset field for DP. In the time between the primary discharge and the delayed DP, three different current regimes are observed, which suggests multiple charge transfer mechanisms in the induction region. High-speed camera recordings provide valuable insight into the time evolution of the primary discharge and the delayed DP, especially when correlated with electrical measurements.

Performance study of a novel sampling TPC prototype detector based on THGEM

Time projection chamber (TPC) with micropattern gaseous detectors (MPGDs) as readout has been one of the research hotspots in recent years. MPGD-based TPC has been applying to many experiments due to its high spatial and energy resolutions in 3D track measurement. A novel sampling TPC detector based on thick gaseous electron multiplier (THGEM) was developed to measure the low-energy electron tracks online from 0.1 to 50 MeV with a 100 $$\upmu \hbox {m}$$ spatial resolution in a vacuum tank. The tracks will be extrapolated to determine the hit positions on a target about 200 mm behind the TPC. A new type of self-developed THGEM detector was chosen as the TPC readout unit. The field cage has two $$50 \times 50\,\hbox {mm}^2$$ windows welded by Gold-plated tungsten wires for low-energy electrons passing through. The front-end electronics was designed with a self-developed application specific integrated circuit chip, i.e., CASA-GEM. Seven columns of readout pads were used to equidistantly sample the electron tracks in a length of 75 mm. Each column has 72 pads of $$0.56 \times 0.56 \,\hbox {mm}^2$$ and two additional strips along each column for drift time measurement. Both Geant4 and Garfield++ were chosen to simulate and optimize the detector, such as the penetration efficiency, electric field in field cage and operating gas pressure. The design and the preliminary performances of the TPC detector were verified by beam test and $$\beta $$ source test. A drift velocity of $$3.415 \pm 0.103\,\hbox {cm}/\upmu \hbox {s}$$ was measured at 125 V/cm in $$\hbox {Ar} + \hbox {iC}_4\hbox {H}_{10} ~(97:3)$$ for $$\pi ^-$$ . The electron detection efficiency is about 88% for $$\beta $$ source. And the gain of the double THGEM reached more than $$1.0 \times 10^4$$ .

One-dimensional parallax-free position-sensitive detector for diffraction measurements based on a home-made thin THGEM.

A large parallax-free gas diffraction meter based on a thinner-THGEM (thick gaseous electron multiplier) has been developed at the Beijing Synchrotron Radiation Facility (BSRF). A thinner-THGEM of thickness 200 µm is adopted, which can be shaped into a curve to eliminate parallax-error effects. The detector is designed to have a 48° open angle positioned 20 cm from the powder samples. A front-end electronics board with 128 channels direct-current mode was adapted for the 8 keV BSRF beamline with 0.2 ns/100 ns stable duty cycle. Two powder samples, TiO2 and SnO2, were tested separately. The measured spectra with an angular resolution of 0.148 ± 0.081° are consistent with the data from the powder diffraction file. Combining the gas gain of the thinner-THGEM with the electronic circuit dynamic range, a very broad dynamic range of about 107 could be obtained.

First imaging results of a bubble-assisted Liquid Hole Multiplier with SiPM readout in liquid xenon

First imaging results in liquid xenon of a Liquid Hole Multiplier (LHM) coupled to a quad-Silicon Photomultiplier (SiPM) array are presented. Ionization electrons deposited in the noble liquid by 5.5 MeV alpha particles, are collected into the holes of a Thick Gas Electron Multiplier (THGEM) electrode having a xenon gas bubble trapped underneath. They drift through the liquid-gas interface, inducing electroluminescence within the bubble. The resulting photons are detected with a Hamamatsu VUV4 quad-SiPM array—providing the deposited energy with a charge-only RMS resolution of 6.6%. The image reconstruction resolution was estimated to be ∼200 μm (RMS).

Study of MicroPattern Gaseous detectors with novel nanodiamond based photocathodes for single photon detection in EIC RICH

Identification of high momentum hadrons at the future EIC is crucial, gaseous RICH detectors are therefore viable option. Compact collider setups impose to construct RICHes with small radiator length, hence significantly limiting the number of detected photons. More photons can be detected in the far UV region, using a windowless RICH approach. QE of CsI degrades under strong irradiation and air contamination. Nanodiamond based photocathodes (PCs) are being developed as an alternative to CsI. Recent development of layers of hydrogenated nanodiamond powders as an alternative photosensitive material and their performance, when coupled to the THick Gaseous Electron Multipliers (THGEM)-based detectors, are the objects of an ongoing R\&D. We report about the initial phase of our studies.

Design and preliminary test of a multi-element tissue-equivalent proportional counter based on the gas electron multiplier

In order to monitor the intense neutron and gamma radiation, multi-element tissue equivalent proportional counters (TEPC) based on the standard gas electron multiplier (GEM) and ceramic thick GEM (THGEM) foils were designed and respectively tested by implanted 55Fe and 241Am sources which would also be used as calibration sources. The performance testing of GEM-TEPC/THGEM-TEPC detectors at various parameters showed that the detectors could work well. The THGEM-TEPC was also used to measure the linear energy spectra in 241Am–Be and intense (108 ncm−2s−1) neutron radiation fields. The results displayed that THGEM-TEPC was available to do microdosimetric research or be a dosimeter in intense neutron/gamma field.

Signal formation in THGEM-like detectors

Numerical simulations were used to study signal formation in a Thick Gaseous Electron Multiplier (THGEM) and in THGEM-based Thick-WELL (THWELL) and Resistive-Plate WELL (RPWELL) detectors. The signal shapes were simulated in mixtures of Argon and Neon with 5% Methane under irradiation with soft x-rays and muons. Anode-induced raw signals were convoluted with the response functions of charge-sensitive and current-sensitive pre-amplifiers. The simulation toolkit was validated by the good agreement reached between the simulated and measured response, with different pre-amplifiers. It indicates that our simulations framework provides valid insight into the inherent complex dynamical processes of the various detectors.

Multiplexing readout method based on switch arrays for position sensitive thermal neutron detectors

To address complexities arising from the increased number of readout channels in large scale neutron detection or imaging systems, a multiplexing readout method is introduced. The proposed method can greatly reduce the scale and cost of the readout electronics. To evaluate the readout method, a prototype involving a front-end circuit and a signal multiplexed circuit for detectors such as multiwire proportional chamber (MWPC), gaseous electron multipliers (GEM) and micro-channel plates (MCP) is evaluated in the laboratory. The multiplexing circuit consists of a switch array and a high speed analog to digital converter (ADC). By controlling the switch timing, multi-channel signals can be readout through only one ADC channel, thereby reducing the number of channels required for readout. Furthermore, the readout speed can be adjusted by changing the switching frequency. The results show that the multiplexing readout method is feasible, and the position resolution for thermal neutron detectors is good. The evaluation board is used to simulate the MWPC detector with 2 mm spacing and a position resolution of 35 μm is obtained with event rate up to 2 MHz. Besides, joint test with a thick gaseous electron multipliers (TGEM) detector with 0.8 mm spacing yields a position resolution of about 400 μm.

Investigation of alpha particle tracks in GEM-type structures based on SQS mode

In this study, the performance of two GEM-type structures for the detection of alpha particle tracks in gaseous detectors based on SQS mode is presented. The operation of these structures was investigated in the presence of air, pure argon and P10 gas. By increasing the applied voltage to GEM-type plates beyond a certain value, each GEM-type’s through-hole individually entered to the SQS mode, when detector operated in the P10 gas. This mode was followed by the appearance of visible streamers in the space of holes exposed to alpha radiation. Two types of Thick Gas Electron Multipliers (TGEM) and Electron Multiplier Assemblies (EMA) with different geometries, as well as a cascade configuration of EMAs, were designed and constructed. Depending on the hole diameters in these structures, the location of the input beams can be determined optically with a specific resolution.

Spatial resolution properties of krypton-based mixtures using a 100 μm thick Gas Electron Multiplier

A gaseous imaging detector based on a cascade of two non-standard gas electron multipliers 100 μm thick GEM) was operated in five different krypton-based mixtures and the achievable position resolution was determined. The micropattern gaseous detector (MPGD) has an active area of 10 × 10cm2. The GEM foils are twice as thick as a standard GEM, being more robust to electric discharges and less prone to sparking-caused damage. Krypton, being the noble gas with the lowest value of intrinsic position resolution in the range 14– 34 keV, is a good candidate for imaging applications based on gaseous detectors. Our measurements have confirmed that krypton-CO2 mixtures showed an improvement in position resolution above 18 keV and up to 30 keV relatively to Ar-CO2 mixtures. The MTF value at 10% in the energy range 22–24 keV was evaluated, being 0.5876(342)lp/cm for Ar-CO2 (70:30) and a maximum of 3.2702(15)lp/cm for the Kr-CO2 (90:10) mixture.

Spatial resolution optimization in a THGEM-based UV photon detector

THick Gas Electron Multiplier (THGEM) is considered in many UV photon detector applications. It has the capability of detecting single photon and imaging with high sensitivity. Operating parameters such as choice of gas mixture, pressure, drift field, drift gap, multiplication voltage, induction field and induction gap play an important role in deciding the spatial resolution of the detector. Detailed simulation study enables to optimize the above-mentioned parameters for a given THGEM-based imaging detector and hence to achieve improved performance for the same. Simulation, using ANSYS and Garfield++, starts with the release of primary electrons at random coordinates on the photocathode plane. They are tracked as they pass through the drift gap and THGEM hole till the electron cloud reaches anode plane. Distribution of electron cloud on the anode plane along X and Y axis is plotted in histogram and fitted with Gaussian function to determine spatial resolution. Ar/CO2 (70:30) mixture, which shows higher ETE and lower transverse diffusion, is chosen for this simulation study. Transverse diffusion has a major impact on both ETE and the spatial resolution. Lower transverse diffusion coefficient is always desired for having better resolution as well as for ETE. It is found from the simulation study that higher gas pressure, lower drift field and induction field, smaller drift and induction gap can provide optimum detection efficiency with the best spatial resolution. The simulation method proposed here can also be extended to X-ray imaging detectors.

First performance evaluation of a Multi-layer Thick Gaseous Electron Multiplier with in-built electrode meshes—MM-THGEM

We describe a new micro-pattern gas detector structure comprising a multi-layer hole-type multiplier (M-THGEM) combined with two in-built electrode meshes: the Multi-Mesh THGEM-type multiplier (MM-THGEM). Suitable potential differences applied between the various electrodes provide an efficient collection of ionization electrons within the MM-THGEM holes and a large charge avalanche multiplication between the meshes. Different from conventional hole-type multipliers (e.g. Gas Electron Multipliers - GEMs, Thick Gas Electron Multipliers—THGEMs, etc.), which are characterized by a variable (dipole-like) field strength inside the avalanche gap, electrons in MM-THGEMs are largely multiplied by a strong uniform field established between the two meshes, like in the parallel-plate avalanche geometry. The presence of the two meshes within the holes allows for the trapping of a large fraction of the positive ions that stream back to the drift region. A gas gain above 105 has been achieved for single photo-electron detection with a single MM-THGEM in Ar/(10%)CH4 and He/(10%)CO2, at standard conditions for temperature and pressure. When the MM-THGEM is coupled to a conventional THGEM and used as first cascade element, the maximum achievable gains reach values above 106 in He/(10%)CO2, while the IBF approaches of 1.5% in the case of optimum detector-bias configuration. This IBF value is several times lower compared to the one obtained by a double GEM/THGEM detector (5–10%), and equivalent to the performance attained by a Micromegas detector.

Studies of an X-ray imaging detector based on THGEM and CCD camera

The photons generated by the electron avalanche in gaseous detectors are known as the secondary scintillation light, of which the spectrum range is from ultraviolet to visible. So it is possible to collect directly the avalanche-induced photons in visible range by light sensors, such as charged-couple device (CCD). The optical readout is a new method for 2-D imaging of high spatial resolution based on the micro-pattern gaseous detectors (MPGDs). The traditional charge readout method for the MPGDs is complicated, expensive, and strongly depends on the technology of application-specific integrated circuit. In some cases, for example, low-frame-rate 2-D imaging, the optical readout has more advantages, such as simple, cheap and easy to use. Therefore, a gaseous detector was developed based on the thick gaseous electron multiplier (THGEM) and the ordinary scientific CCD camera as readout to realize the X-ray imaging instead of charge readout. The THGEMs with $$60\times 60\,\hbox {mm}^2$$ sensitive area were developed to reach high gain, and the $$\hbox {Ar} + \hbox {CF}_4$$ gas mixture was chosen for strong light emission. And so a general scientific CCD can be used for readout and replacing the intensified CCD, which is more expensive than general CCD. Some clear X-ray images were obtained by this optical readout THGEM detector, and the spatial resolution achieved is $$275\,\upmu \hbox {m}$$ . It is indicated that this kind of detectors have promising imaging capability and great potential for practical application.

A new neutron detector based on ceramic THGEM and boron-coated meshes

Boron-coated micro-pattern gaseous detectors, such as gaseous electron multiplier (GEM), are widely studied as the neutron detectors. The existing solution to improve the neutron detection efficiency (NDE) is to coat the boron on the surfaces of the cascade GEM films. So the GEM films themselves will be affected by the complicated coating process and the boron layers, and the $$^{10}$$ B material will be wasted once the GEM films are damaged. Since the neutron conversion and the electron multiplication regions are not separated, the final gains of different layer ionized electrons are very difficult to control and keep consistent. A new neutron detector based on the ceramic thick GEM (THGEM) was proposed. The boron-coated cathode and multilayer meshes were used as the neutron conversion region and separated from the electron multiplication region consisting of only one THGEM film. The sawtooth surface treatment and the double-sided readout method were applied to improve neutron conversion efficiency (NCE). The neutron conversion and the electron collection efficiencies were simulated and studied based on the new structure. The prototype detector was test by using a $$^{252}$$ Cf neutron source. The simulation results show that the cascade boron-coated meshes have good neutron conversion and electron collection efficiencies, and the double-sided readout and sawtooth structure can greatly increase the NCE. The neutron test results show that the detection efficiency of the double-sided readout is 1.6 times higher than that of the common single-sided readout. These indicate that the new detector has high neutron conversion and detection efficiencies and is promising for practical applications.

A New Approach for Alpha Radiography by Triple THGEM using Monte Carlo Simulation and Measurement

In this research, alpha imaging in Self Quenching Streamer (SQS) mode is investigated using a triple Thick Gas Electron Multiplier (THGEM) detector by Monte Carlo method and experimental data. First, a semi-empirical equation is derived to represent the relation between the SQS voltage and the alpha energy in every hole of the triple THGEM. The accuracy of this equation is tested and confirmed by a high degree of consistency. Secondly, the images of objects that are irradiated by Am-241 alpha source (5.49 MeV) are recorded by a CMOS camera using triple THGEM detector in the SQS mode. The resolution of images in this paper is a function of the exposure time. For an alpha source with 150 kBq activity, an optimal time interval for exposure is about 30 sec. For exposure time less or more than 30 sec, the images are incomplete and ambiguous, respectively. The overall objective of this work is to facilitate the alpha radiography in nuclear imaging through a triple THGEM without any amplifier or complicated electrical equipment.

Measurements of charging-up processes in THGEM-based particle detectors

The time-dependent gain variation of detectors incorporating Thick Gas Electron Multipliers (THGEM) electrodes was studied in the context of charging-up processes of the electrode's insulating surfaces. An experimental study was performed to examine model-simulation results of the aforementioned phenomena, under various experimental conditions. The results indicate that in a stable detector's environment, the gain stabilization process is mainly affected by the charging-up of the detector's insulating surfaces caused by the avalanche charges. The charging-up is a transient effect, occurring during the detector's initial operation period; it does not affect its long-term operation. The experimental results are consistent with the outcome of model-simulations.

Development of an advanced two-dimensional microdosimetric detector based on THick Gas Electron Multipliers.

The THick Gas Electron Multiplier (THGEM)-based tissue-equivalent proportional counter (TEPC) has been proven to be useful for microdosimetry due to its flexibility in varying the gaseous sensitive volume and achieving high multiplication gain. Aiming at measuring the spatial distribution of radiation dose for mixed neutron-gamma fields, an advanced two-dimensional (2D) THGEM-TEPC was designed and constructed at McMaster University which will enable us to overcome the operational limitation of the classical TEPCs, particularly for high-dose rate fields. Compared to the traditional TEPCs, anode wire electrodes were replaced by a THGEM layer, which not only enhances the gas multiplication gain but also offers a flexible and convenient fabrication for building 2D detectors. The 2D THGEM TEPC consists of an array of 3 × 3 sensitive volumes, equivalent to nine individual TEPCs, each of which has a dimension of 5 mm diameter and length. Taking the overall cost, size and flexibility into account, to process nine detector signals simultaneously, a multi-input digital pulse processing system was developed by using modern microcontrollers, each of which is coupled with a 12-bit sampling ADC. Using the McMaster Tandetron 7 Li(p,n) accelerator neutron source, both fundamental detector performance, as well as neutron dosimetric response of the 2D THGEM-TEPC, has been extensively investigated and compared to the data acquired by a standard spherical TEPC. It was shown that the microdosimetric response and the measured absorbed dose rate of the 2D THGEM detector developed in this study are comparable to the standard 1/2" TEPC which is commercially available. This study proved that the 2D TEPC based on the THGEM technology can be effectively used in microdosimetry studies and is a promising detector for measuring the absorbed dose rate distribution over an area in mixed radiation fields. This unique small gas cavity detector opens new possibilities in applications for high-intensity mixed radiation fields as well as in nanodosimetry.

An Extensible Induced Position Encoding Readout Method for Micropattern Gas Detectors

The large number of electronics channels has become an issue to the further applications of micropattern gas detectors (MPGDs) and poses a big challenge for the integration, power consumption, cooling, and cost. Induced position encoding readout technique provides an attractive way to significantly reduce the number of readout channels. In this paper, we present an extensible induced position encoding readout method for MPGDs. The method is demonstrated by the Eulerian path of the graph theory. A standard encoding rule is provided, and a general formula of encoding and decoding for n channels is derived. Under the premise of such method, a 1-D induced position encoding readout prototyping board is designed on a $5\times 5$ cm2 thick gas electron multiplier, where 47 anode strips are readout by 15 encoded multiplexing channels. Verification tests are carried out on an 8-keV Cu X-ray source with 100- $\mu \text{m}$ slit. The test results show a robust feasibility of the method and have a good spatial resolution and linearity in its position response. This method can dramatically reduce the number of readout channels, has potential to build large-area detectors, and can be easily adapted to other detectors like MPGDs.

Simulation of gain stability of THGEM gas-avalanche particle detectors

Charging-up processes affecting gain stability in Thick Gas Electron Multipliers (THGEM) were studied with a dedicated simulation toolkit. Integrated with Garfield++, it provides an effective platform for systematic phenomenological studies of charging-up processes in MPGD detectors. We describe the simulation tool and the fine-tuning of the step-size required for the algorithm convergence, in relation to physical parameters. Simulation results of gain stability over time in THGEM detectors are presented, exploring the role of electrode-thickness and applied voltage on its evolution. The results show that the total amount of irradiated charge through electrode's hole needed for reaching gain stabilization is in the range of tens to hundreds of pC, depending on the detector geometry and operational voltage. These results are in agreement with experimental observations presented previously.