Gas Multiplication Factor Research Articles

Calibrating an optical scanner for quality assurance of large area radiation detectors

A gas electron multiplier (GEM) is a particle detector used in high-energy physics. Its main component is a thin copper-polymer-copper sandwich that carries Ø =70 ± 5 µm holes. Quality assurance (QA) is needed to guarantee both long operating life and reading fidelity of the GEM. Absence of layer defects and conformity of the holes to specifications is important. Both hole size and shape influence the detector’s gas multiplication factor and hence affect the collected data. For the scanner the required lateral measurement tolerance is ± 5 µm. We calibrated a high aspect ratio optical scanning system (OSS) to allow ensuring the quality of large GEM foils. For the calibration we microfabricated transfer standards, which were imaged with the OSS and which were compared to corresponding scanning electron microscopy (SEM) images. The calibration fulfilled the ISO/IEC 17025 and UKAS M3003 requirements: the calibration factor was 1.01 ± 0.01, determined at 95% confidence level across a 950 × 950 mm2 area. The proposed large-scale scanning technique can potentially be valuable in other microfabricated products too.

Multiplication factors in ethylene-filled proportional counters

Gas multiplication factors were measured in a proportional counter filled with high-purity ethylene in the pressure range 10-40 Torr. The multiplication factors were measured as a function of the reduced electric field S(a). The results show that, within the range of the high values of reduced electric field applied in this work (2648 < or = S(a) < or = 6455 V cm(-1) Torr(-1)), the reduced first Townsend coefficient alpha/P for ethylene may still be considered a function of S(a) alone. Good agreement was found with a model proposed by Akande.

Experimental Study of Xe-Ne Proportional Counters for X-Ray Detection

The use of appropriate mixtures of noble gases in proportional counters can take advantage of the Penning effect, a process of energy transfer between the two species which produces extra electrons. The Penning effect can occur in Xe-Ne mixtures and recent Monte Carlo simulation measurements have shown that a small percentage of Xe (below ~1%Xe) brings to a minimum the fluctuations in the formation of the primary electron cloud and decreases the w-value to a magnitude near that for pure Xe. In addition, the excitation and ionization thresholds and the fluctuations in charge multiplication become lower and the ionization efficiency becomes higher than in pure Xe, indicating that improved energy resolution can be achieved at low applied voltages for a Xe-Ne filled proportional counter. In this work, we present an experimental study of the performance of a cylindrical proportional counter filled with several Xe-Ne mixtures at atmospheric pressure, for 5.9 keV x-rays. Results are presented for the energy resolution and gas multiplication factor and a discussion of the experimental results is made

Gas multiplication process in mixtures based on Ar, [formula omitted], [formula omitted

Systematic measurements of the gas multiplication factor over the range 1.0 – 5 * 10 5 have been made for Ar / CF 4 , Ar / CO 2 / CF 4 and CO 2 / CF 4 mixtures as a function of the applied voltage between cathode and anode at atmospheric pressure for wide range component concentrations.

Advances in Thick GEM-like gaseous electron multipliers—Part I: atmospheric pressure operation

Thick GEM-like (THGEM) gaseous electron multipliers are made of standard printed-circuit board perforated with sub-millimeter diameter holes, etched at their rims. Effective gas multiplication factors of 10 5 and 10 7 and fast pulses in the few nanosecond rise-time scale were reached in single- and cascaded double-THGEM elements, in atmospheric-pressure standard gas mixtures with single photoelectrons. High single-electron detection efficiency is obtained in photon detectors combining THGEMs and semitransparent UV-sensitive CsI photocathodes or reflective ones deposited on the top THGEM face; the latter benefits of a reduced sensitivity to ionizing background radiation. Stable operation was recorded with photoelectron fluxes exceeding MHz/mm 2. The properties and some potential applications of these simple and robust multipliers are discussed.

GOSSIP: A vertex detector combining a thin gas layer as signal generator with a CMOS readout pixel array

A small TPC has been read out by means of a Medipix2 chip as direct anode. A Micromegas foil was placed 50 μ m above the chip, and electron multiplication occurred in the gap. With a He/isobutane 80/20 mixture, gas multiplication factors up to tens of thousands were achieved, resulting in an efficiency for detecting single electrons of better than 90%. With this new readout technology for gas-filled detectors we recorded many image frames containing 2D images with tracks from cosmic muons. Along these tracks, electron clusters were observed, as well as δ -rays. With a gas layer thickness of only 1 mm, the device could be applied as vertex detector, outperforming all Si-based detectors.

An integrated readout system for drift chambers: the application of monolithic CMOS pixel sensors as segmented direct anode

A small TPC has been read out by means of a MediPix2 readout chip as direct anode. A Micromegas foil was placed 50 μm above the chip, and electron multiplication occurred in the gap. With a He/Isobutane 80/20 mixture, gas multiplication factors up to tens of thousands were achieved, resulting in an efficiency for detecting single electrons of better than 90%. We recorded many frames containing 2D images with tracks from cosmic muons. Along these tracks, electron clusters were observed, as well as δ-rays.

Simulation study of electron drift and gas multiplication in Micro Pixel Chamber

The physical processes of charge collection and gas multiplication of a Micro Pixel Chamber ( μ -PIC) were studied in detail using a three-dimensional (3D) simulation. The collection efficiencies of primary electrons and gas multiplication factors were calculated for several electrode structures. Based on those studies, we analyzed the optimization of the electrode structure of the μ -PIC, in order to obtain a high gas gain of more than 10 4 and a simultaneous suppression of discharges. Consequently, we found that these characteristics strongly depend on the substrate thickness and the anode diameter of the μ -PIC. In addition, a gas gain of 10 5 would be expected for a μ -PIC having a thick substrate of > 150 μ m .

Detection of single electrons by means of a Micromegas-covered MediPix2 pixel CMOS readout circuit

A small drift chamber was read out by means of a MediPix2 readout chip as a direct anode. A Micromegas foil was placed 50 μ m above the chip, and electron multiplication occurred in the gap. With a He/isobutane 80/20 mixture, gas multiplication factors up to tens of thousands were achieved, resulting in an efficiency for detecting single electrons of better than 90%. We recorded many frames containing 2D images with tracks from cosmic muons. Along these tracks, electron clusters were observed, as well as δ -rays.

Plasma Charging Damage Reduction in IC Processing by A Self-balancing Interconnect

A small TPC has been read out by means of a Medipix2 chip as direct anode. A Micromegas foil was placed Click to view the MathML source above the chip, and electron multiplication occurred in the gap. With a He/isobutane 80/20 mixture, gas multiplication factors up to tens of thousands were achieved, resulting in an efficiency for detecting single electrons of better than 90%. With this new readout technology for gas-filled detectors we recorded many image frames containing 2D images with tracks from cosmic muons. Along these tracks, electron clusters were observed, as well as ?-rays. With a gas layer thickness of only 1 mm, the device could be applied as vertex detector, outperforming all Si-based detectors.

Response of multiwire proportional counter for energy loss measurement

A multiwire proportional counter has been developed in order to experimentally simulate the energy deposited by high-energy heavy ions, such as C, Ne, and Ar of several hundred MeV/nucleon, in length as small as 5 μm in soft tissue of a human body. Four sensors with wire spacings of 2, 3, 4, and 5 mm have been prepared for comparison. To estimate the performance of these sensors, the collimated alpha particle beam from 241Am is used as a substitute for heavy ion beams in this work. The relative gas multiplication factor and the response to the position of the incident particles are measured for these four sensors with a tissue equivalent gas, and for the 5 mm spacing sensor with various gases. The signal-to-noise ratio is also estimated. For the 5 mm spacing sensor, P-10 gas shows the best performance among the gases examined in this work. The uniformity of the response is not so good for a tissue equivalent gas that is often used to simulate measurements in a human body. The response of the sensor, which depends strongly on the gas used, can be understood qualitatively by the electronegativity of the gas. The energy loss in soft tissue is obtained by multiplying the value measured in P-10 gas by the ratio of the energy loss in a tissue equivalent gas to that in P-10 gas.

Monte Carlo simulation of gamma-ray response functions for a proportional counter used for neutron measurement

It is often required in neutron calibration fields to determine the dose of gamma-rays produced in a neutron source and in the surroundings, because some neutron detectors are sensitive both to neutrons and gamma-rays. As a first step estimating neutron and gamma-ray energy spectra and fluences simultaneously in a neutron field, the gamma-ray response function for a 3 He proportional counter was calculated using EGS4/PRESTA code. In the simulation, the gas multiplication factor, which depends on the detection position in the gas region along an anode wire, was taken into account to obtain the precise response function. For comparison, we measured response functions using different reference gamma-ray sources such as 241 Am , 137 Cs , and 60 Co , which were located vertically 55 mm away from the center of the anode wire. Calculated response functions agreed well with experimental ones. Monte Carlo code EGS4 is thus useful for the simulation of gamma response functions for neutron counters.

Energy resolution of xenon proportional counters: Monte Carlo simulation and experimental results

The gas multiplication factor M and energy resolution R of xenon gas cylindrical proportional counters are investigated experimentally and calculated theoretically using a Monte Carlo technique to simulate the growth of single-electron-initiated avalanches. A good agreement is found between calculated and experimental data. The experimental and the calculated results are presented as a function of the reduced voltage K and the reduced anode radius Na, where N is the number density and a the anode radius. The Monte Carlo results for the intrinsic energy resolution R/sub int/ are discussed in terms of the parameter f which characterizes the statistical fluctuations of the avalanche gains. The present calculations have revealed that there is an intrinsic dependence of f on the critical value S/sub c/ of the reduced electric field at the onset of multiplication. This has enabled the parameterization of f and of the intrinsic energy resolution R/sub int/ in terms of the reduced voltage K only and has explained why, for a given range of operating values for M, energy resolution in a cylindrical proportional counter is improved for thinner anode wires and lower pressures.

Multidrift module simulation

The main results of simulating multidrift module (MDM) characteristics are presented. Using the GARFIELD program, the electric field equipotential lines for a seven-cell structure were simulated. We attempted to calculate the gas multiplication factor for the MDM cell filled with DME assuming various types of Townsend coefficient dependences on the field intensity E. The best agreement with the experimental data was obtained assuming that αp is proportional to (Ep)2. The x(t)-relation for the MDM cell was calculated with the help of the GARFIELD procedure for electron arrival time distribution calculations for a track. Good agreement with the experimental curve was obtained under the condition that for E > 20 kV/cm the electron drift velocity in DME is proportional to (Ep)12. On the basis of the electron arrival time distributions the coordinate accuracy was calculated for a single MDM cell. The results obtained completely agree with the experimental data.

Space charge effect in SQS transition in a gas counter

Systematic investigation of the gas multiplication characteristics in the transition region from the proportional to SQS mode in a cylindrical proportional counter has been performed. The property of saturation of the gas multiplication factor can be reproduced using the effective electric field which is corrected for the space charge related to the positive ion density in the avalanche. Photon-mediated gas multiplication can explain the large jump phenomenon of the SQS transition. It is shown that the effective electric field in the avalanche becomes almost zero near the anode surface (Meek's streamer condition) at the 50% transition voltage and the region of its maximum moves slightly away from the anode surface.

Determination of the Townsend Primary Ionization Coefficient Using a Parallel Plate Avalanche Counter

Gas multiplication factors were obtained from the observed fast pulse of a parallel plate avalanche counter and the Townsend primary ionization coefficients for methane and isobutane were determined from the data over the ranges E/P=150–228 V/cm·Torr and 183–411 V/cm·Torr, respectively. The results for methane agreed well with the values obtained by Heylen.

比例計数管による低濃度トリチウムガスのオンライン測定システム

An on-line measurement system was designed and constructed for low level tritium gas. The system consists of a proportional counter, amplifiers, a discriminator and a scaler interfaced to a micro-computer. Characteristics of the proportional counter were examined for pure He and Ar counting gases using 5.9 keV 55Fe X-rays; it worked with pure rare gases in the proportional mode up to the gas multiplication factor of about 100. The developed system was used to measure the release rate of tritium out of Al-Mg-Li alloys irradiated by thermal or 14 MeV neutrons. Applicability of the system with a proportional counter has been confirmed for measurements of low level tritium gas carried by pure He or Ar gas. The system has the maximum sensitivity of 0.1 pCi/cm3 for a 50 cm3 sensitive volume.

Growth of the avalanche around the anode wire in a gas counter

The shape of the avalanche around the anode wire in a gas counter was investigated as a function of the gas multiplication factor M . A heart-shaped avalanche was found for M between 10 3 and 10 4 , and there exists a proportionality law of discharge.

Exo-electron emission from platinum wires cooling in hydrocarbons and other gases as observed in a modified proportional counter

A proportional counter has been modified to contain a platinum filament which could be electrically heated. The counter was characterised by field-plotting, voltage changes, gas flow etc. and its gas multiplication factor determined: it operated successfully over a temperature range between ≈ 800 and 298 K with a wide variety of gaseous fillings.

Optimization of the energy resolution of methane filled cylindrical proportional counters

The energy resolution of proportional counters depends on the axial and the statistical fluctuations of the gas multiplication factor. It is shown how these fluctuations can be minimized by an appropriate choice of the counter dimensions.