Parallel Plate Avalanche Chamber Research Articles

An ultra fast, radiation-resistant fast neutron detector

This paper describes a study on 14-MeV neutron detection based on the combination of a parallel plate avalanche chamber with a sheet of polypropylene as fast neutron-to-charged-particle converter. By employing a carefully shielded chamber, neutron-induced charged particles background from the chamber body was successfully reduced to <6 x 10(-5) count per incident neutron. Fast signals, with approximately 7 ns pulse width were observed. The obtained detection efficiency is 0.15%.

Precise measurement of first Townsend coefficient, using parallel plate avalanche chamber

By employing iso-C4H10 gas, we have studied the effective parameters in the first Townsend coefficient measurement using parallel plate avalanche chamber (PPAC). Obtained results are free from space charge and gap deformation effects, which have seriously affected previous PPAC-based measurements. The required conditions for a reliable Townsend coefficient measurement are presented as well.

An X-ray scanner prototype based on a novel hybrid gaseous detector

We have developed a prototype of a new type of hybrid X-ray detector. It contains a thin wall (few μm) edge- illuminated lead glass capillary plate (acting as a converter of X-rays photons to primary electrons) combined with a microgap parallel-plate avalanche chamber operating in various gas mixtures at 1 atm. The operation of these converters was studied in a wide range of X-ray energies (from 6 to 60 keV) at incident angles varying from 0° to 90°. The detection efficiency, depending on the geometry, photon's energy, incident angle and the mode of operation, was between a few and ∼40%. The position resolution achieved was ∼50 μm in digital form and was practically independent of the photon's energy or gas mixture. The developed detector may open new possibilities for medical imaging, for example in mammography, portal imaging, radiography (including security devices), crystallography and many other applications.

A high position resolution X-ray detector: an "Edge on" illuminated capillary plate combined with a gas amplification structure

We have developed and successfully tested a prototype of a new type of high position resolution hybrid X-ray detector. It contains a thin wall lead glass capillary plate converter of X-rays combined with a microgap parallel-plate avalanche chamber filled with gas at 1 atm. The operation of these converters was studied in a wide range of X-ray energies (from 6 to 60 keV) at incident angles varying from 0-90 degree. The detection efficiency, depending on the geometry, photon energy, incident angle and the mode of operation, was between 5-30 percent in a single step mode and up to 50 percent in a multi-layered combination. Depending on the capillary geometry, the position resolution achieved was between 0.050-0.250 mm in digital form and was practically independent of the photon energy or gas mixture. The usual lead glass capillary plates operated without noticeable charging up effects at counting rates of 50 Hz/mm2, and hydrogen treated capillaries up to 10E5 Hz/mm2. The developed detector may open new possibilities for medical imaging, for example in mammography, portal imaging, radiography (including security devices), crystallography and many other applications.

Recent technologic developments on high-resolution beta imaging systems for quantitative autoradiography and double labeling applications

Two novel beta imaging systems, particularly interesting in the field of radiopharmacology and molecular biology research, were developed these last years. (1) a beta imager was derived from research conducted by Pr Charpak at CERN. This parallel plate avalanche chamber is a direct detection system of β radioactivity, which is particularly adapted for qualitative and quantitative autoradiography. With this detector, autoradiographic techniques can be performed with emitters such as 99mTc because this radionuclide emits many low-energy electrons and the detector has a very low sensitivity to low-range γ-rays. Its sensitivity (smallest activity detected: 0.007cpm/mm2 for 3H and 0.01 for 14C), linearity (over a dynamic range of 104) and spatial resolution (50μm for 3H or 99mTc to 150μm for 32P or 18F (β+)) gives a real interest to this system as a new imaging device. Its principle of detection is based on the analysis of light emitted during the interaction with an intensified CCD camera. This property may suggest new potential applications, particularly in the field of β-rays selection according to their energy. This detector provides a new fast way to detect all β-emitting isotopes in biological samples up to 20cm×25cm (electrophoresis gels, hybridization membranes, tissue sections on glass slides, TLC plates and any other planar two-dimension samples). It is ideal for tritium detection, 500 times faster than classical film, thus maximizing the research productivity. (2) A micro imager is based on contact imaging through a solid scintillator sheet. Light emitted is amplified through an image intensifier tube and is analyzed with a CCD camera. The full field of view is smaller than the first one (24mm×32mm) but a better spatial resolution is obtained (typically 15μm for 3H, 20μm for 14C and 35S). The specifications of this detector are: efficiency 50–100% depending on isotope, linear response over a dynamic range of 104, smallest activity detected: 0.4cpm/mm2 for 3H and 0.04cpm/mm2 for 14C. Using these detectors, quantification is much easier and more precise than that of the radiological film because of direct counting of radioactivity. However, this quantification imposes a few limitations among which are the necessity of fabrication and simultaneous measurement of standards. With new developments of these devices it is possible to detect in the same sample two different isotopes: 3H and 14C for example, which is very attractive to many researchers today.

Novel, photon counting X-ray detectors

A novel sealed gaseous parallel plate avalanche chamber detector is described which is significantly less prone to discharges and can consequently achieve high gas gains at high counting rates. The detector has demonstrated stable gains greater than 104 at counting rates in excess of 107 counts/mm2 s.

Medium-term stability of a Parallel Plate Avalanche Chamber with a bakelite electrode operated in high-radiation flux

A gas detector made of three parallel electrodes (bakelite electrode and two metallic mesh electrodes) and working in proportional mode allows monitoring of the gas gain under various intensities of X-rays over long period of time. The detector performance, when irradiated with an intense radiation flux, and possible effects of variation of the bakelite electrode conductivity on a medium-term stability of operation are reported. The results shown in this paper were obtained for detector filled with argon/isobutane gas mixture.

Bakelite chambers for time-of-flight measurements

We report on the search of composite organic materials with the volume resistivity ranging from 10 8 to 10 11 Ω cm. Materials having resistivity in this range may be used for electrodes of thin gap Parallel Plate Avalanche Chambers. Gas detectors of such structure and operated at increased gas pressure allow, potentially, a sub-nanosecond time resolution. Using bakelite-like material with electrical properties well tuned during manufacturing opens the possibility to overcome limitations related to the semi-conductive glass employed usually for ultrafast gas detectors of parallel plate structure for time-of-flight technique.

High DQE performance X-and gamma-ray fast imagers:: Emergent concepts

Challenges for the design of quantum sensitive 2D imaging detectors for high-energy photons are reviewed. Conception rules and universal data plot are presented. They allow the optimization of pixel dimensions versus incident fluence and the contrast of the radiant image for several interesting materials such as photoconductors, scintillators and metallic X-converters. Firstly, a 2D very sensitive CdZnTe imaging matrix and its performance are presented. Secondly, the performance of a large size gaseous detector (Parallel Plate Avalanche Chamber), coupled with a structured high stopping power metallic X-ray converter are reviewed. Finally, we make comparison to performances obtained with more classical technologies made of segmented heavy scintillators.

Rate and gain limitations of MSGCs and MGCs combined with GEM and other preamplification structures

We have studied the rate and gain limits of diamond-coated Microstrip Gas Counters (MSGCs) and Micro-Gap Counters (MGCs) when combined with various preamplification structures: Gas Electron Multiplier (GEM), Parallel-Plate Avalanche Chamber (PPAC) or a MICROMEGAS-type structure. Measurements were done both with X-rays and alpha particles with various detector geometries and in different gas mixtures at pressures from 0.05 to 10atm.The results obtained varied significantly with detector design, gas mixture and pressure, but some general features can be identified. We found that in all cases, bare MSGCs, MGCs, PPACs and MICROMEGAS, the maximum achievable gain drops with rate. The addition of preamplification structures significantly increases the gain of MSGCs and MGCs, but this gain is still rate dependent.There would seem to be a general rate-dependant effect governing the usable gain of all these detectors. We speculate on possible mechanisms for this effect, and identify a safe, spark-free, operation zone for each system (detector + preamplification structure) in the rate-gain coordinate plane.

Breakdown features of various microstrip-type gas counter designs and their improvements

Breakdown mechanisms and spurious pulses, the precursors to some breakdowns, were studied experimentally for both uncoated and coated microstrip gas counters (MSGCs) of different geometries, as well as for microgap counters (MGCs) and for the Compteur A Trou (CAT). It was found that in all cases the breakdowns occurred through surface streamers, although the exact mechanism of streamer formation depended on the particular detector design. Based on these studies, new designs of microstrip detectors, in which the role of the substrate was minimized, were elaborated and tested. In some of these detectors, especially with large pitches (>2 mm), gains up to 2-3/spl times/10/sup 5/ were achieved together with good rate characteristics. The ultimate gain limit in all geometries was still set by spark-inducing streamers which appeared at some critical charge density in the avalanche. To avoid this, and particularly to enhance the performance of small-pitch MSGCs, preamplification structures can be used. Utilizing a parallel plate avalanche chamber as a front end to an MSGC resulted in an overall gain of /spl sim/10/sup 6/, limited in this case only by charge saturation.

Photon emission from 511 keV gamma rays incident on BaF 2 and LaF 3:Nd 3+ crystals using a cesium iodide photocathode detector

We have studied the possibility of using BaF 2 and LaF 3 doped with Nd 3+, concentrations ranging from 0.1 to 15 mol% as efficient converters of 511 keV gamma rays. We have measured the number of photoelectrons/MeV for both crystals using a parallel-plate avalanche chamber operating with a CsI photocathode. The photocathode is sensitive to wavelengths in the range 160–220 nm. The fast component of the BaF 2 emission spectrum has peaks at roughly 175, 195 and 200 nm, and the LaF 3:Nd 3+ emission spectrum peaks at 173 nm. We measure 3.71 ± 0.04 ± 1.11 photoelectrons/MeV for the BaF 2 and 4.81 ± 0.04 ± 1.44 photoelectrons/MeV for the LaF 3:Nd 3−. The results for BaF 2 and LaF 3:Nd 3+ are consistent with measured scintillation properties of these crystals and CsI photocathode quantum efficiencies.

A model of breakdown in parallel-plate detectors

Parallel-plate avalanche chambers (PPACs) have many desirable properties, such as a fast, large area particle detector. However, the maximum gain is limited by a form of violent breakdown that limits the usefulness of this detector, despite its other evident qualities. The exact nature of this phenomenon is not yet sufficiently clear to sustain possible improvements. A previous experimental study is complemented in the present work by a quantitative model of the breakdown phenomenon in PPACs, based on the streamer theory. The model reproduces well the peculiar behavior of the external current observed in PPAC's and resistive-plate chambers. Other breakdown properties measured in PPAC's are also well reproduced.

Use of primary electron counting for detection of ultrasoft x-rays with a low-pressure multistep gaseous detector

The use of primary electron counting techniques as an alternative to the more usual parallel plate avalanche chamber that has been employed in soft x-ray scattering experiments is being investigated at the National Synchrotron Light Source. The theoretical aspects of primary electron counting and motivation behind building a primary electron counting detector are described, as well as characteristics and future improvements of the device constructed at the NSLS. The detector consists of a low electric field drift region and a low pressure multistep avalanche region which can be operated with two or three stages of electron multiplication. The device has worked well in extensive tests as a simple parallel plate avalanche chamber, providing energy resolutions of 58% and 43% at 277 and 500 eV, respectively. Operated as a primary electron counter, preliminary results show an energy resolution of 38% at 500 eV.

A measurement of the first Townsend coefficient as a function of the electric field for a TMAE-He mixture

TMAE (tetrakis-dimethylamino-ethylene) has been widely used in photo-ionization detectors in the last decade. As a gas photocathode, it has one of the lowest ionization potentials of the organic compounds studied to date, a high quantum efficiency, and adequate vapor pressures at just above room temperatures. In order to understand the gas amplification mechanism of an avalanche chamber filled with a TMAE-based gas mixture operated at a low gas pressure, we have measured the first Townsend coefficient for a TMAE-He mixture with a parallel plate avalanche chamber. Based on this result, the gas amplification process in wire chambers operated at low gas pressure is discussed. >

Results of a first beam test of hadron blind trackers

We describe the experimental results of a new type of electron tracker, called Hadron Blind Detector or HBD. An HBD prototype was tested with gas mixtures of CF 4 with He or Ne and a parallel plate avalanche chamber having a CsI photocathode of eight pads. Beam tests confirm the large Cherenkov light bandwidth in the EUV region that can be obtained with such gas mixtures. It results in a large quality factor of about 500 cm −1 which allows HBD operation with a much shorter radiator thickness than conventional Cherenkov counters. Full electron efficiency was obtained, while pions were rejected up to momenta of 9 GeV/ c. HBD is unique in measuring electron trajectories near the vertex, vetoing Dalitz pairs, and providing trigger on electrons among heavy hadron background. We discuss the use of such detectors for lepton identification and detection in high energy physics experiments and especially in heavy ion colliders.

Properties of reflective and semitransparent CsI photocathodes

Various aspects related to the quantum efficiency of the reflective and semitransparent CsI photocathodes have been investigated experimentally. The investigation explored the dependence of the quantum efficiency on the following: the thickness of the photocathode film, the gas used in the parallel-plate avalanche chamber, exposure to water vapor, and the density of the CsI film. With reflective CsI photocathodes quantum efficiencies of more than 25% at 180 nm have achieved in three different gases: CH 4, C 2H 6, and C 4H 10. Our study reveals that high quantum efficiency is also achievable for the semitransparent CsI photocathodes. For a 95-Å semitransparent photocathode the quantum efficiency at 185 nm can be as high as 20%. A simple model to explain the dependence of quantum efficiency on the thickness of CsI photocathodes is suggested, which may be a useful guide for further improvement of the performance of CsI photocathodes. Also reported are UV-transmittance measurements for various materials used in our studies, such as methane, ethane, isobutane, CF 4, CO 2, helium, neon, air, TMAE vapor, thin CsI films, and quartz windows, all in the wavelength range 115 nm to 230 nm.

Results of a high energy gamma telescope

We report on experimental results obtained using a new type of detector for high energy gamma astrophysics. The apparatus can detect gamma-rays in the GeV range, with an angular resolution of a few mrad and an acceptance of 50°. The telescope is based on the imaging of the Cherenkov light produced in a dense medium (liquid or solid) backed by a parabolic or spherical reflecting surface. The high energy electrons, produced at the start of the electromagnetic shower, generate a ring-shaped photon image which may produce tens or hundreds of photoelectrons on an appropriate photon imaging detector placed at the focal plane of the system on the entrance surface of the converter. A prototype consisting of a liquid radiator (C 6F 14), a multistep parallel-plate avalanche chamber and an optical readout system has been tested in a 1–10 GeV c charged particle beam. The analysed data indicate that the initial direction of particles can be reconstructed with an angular resolution of approximatelly 3.5 mrad. Furthermore, the capability of such a detector to separate e π in the GeV range seems promising. Possible use of the apparatus in a space-borne experiment for distinct gamma-ray sources is also discussed.

Helium gas mixtures for ring imaging Cherenkov detectors with CsI photocathodes

Use of He gas mixtures at atmospheric pressure (instead of low-pressure hydrocarbon gases) will ease the construction and operation of large-scale parallel-plate RICH detectors with CsI photocathodes. Due to the low density of He gas the number of primary electrons created by minimum-ionizing particles is very small even at atmospheric pressure. Therefore the Cherenkov detector will be nearly blind to ionizing tracks. However, He alone is not a good counting gas; a suitable quenching component must be added for stable operation of the chamber at high gas gain. Five different quenching gases, CH4, C2H6, isobutane, CF4 and CO2 have been tested at a mixing ratio of 5%. The first three gas mixtures show very promising performance. The parallel-plate avalanche chamber (PPAC) can be operated up to gains ≈ 5×105 without secondary avalanches. When the He gas mixture includes 5% of the quenching gas (38 Torr) the efficiency for minimum-ionizing particles is calculated to be < 20% using a Monte Carlo simulation based on measured gas-gain spectra. Experimental investigation shows that the ratio of the quantum efficiency of a CsI photocathode in an atmospheric-pressure He/i-C4H10 (95/5) gas mixture to that in low-pressure i-C4H10 gas is ≈ 75% for PPAC operation. The effect of mechanical tolerance on uniformity of gas gain at various pressures is also discussed in detail, and He/i-C4H10 (95/5) has the least variation of gain with gap thickness of the mixtures tested.

FASA - A 4π detector setup for the investigation of target multifragmentation in nucleus-nucleus collisions

The FASA setup, installed at the JINR synchrophasotron providing light ion beams with energies up to 3.65 GeV/nucleon, is a fragment multiplicity detector, consisting of 55 scintillation counters made of thin CsI(TI) films, five time-of-flight telescopes and a large-area position-sensitive parallel-plate avalanche chamber. The basic aim of the device is to determine with high precision the energy, mass, and velocity of the fragments detected in the time-of-flight telescopes (TOF) while for the other fragments global multiplicity information is obtained. Therefore, the TOF telescopes serve as a trigger. In addition, angular correlations and distributions and relative velocity correlations for coincident fragments can be measured with the FASA setup.