W. Dominik

New observations with the gas electron multiplier (GEM)

Abstract We describe recent measurements realized with the Gas Electron Multiplier (GEM) mesh added as pre-amplification element to a multiwire and a micro-strip chamber. Large, stable combined gains are obtained, with good uniformity and energy resolution, in a wide range of filling gases including non-flammable mixtures; coupled to a micro-strip plate, the pre-amplification element allows the detector to maintain the high-rate capability and resolution at considerably lower operating voltages, completely eliminating discharge problems. Charge gains are large enough to allow detection of signals in the ionization mode on the last element, permitting the use of a simple printed circuit as read-out electrode; two-dimensional read out can then be easily implemented. The absence of charge multiplication in the last stage avoids charge build-up on the substrate and prevents ageing phenomena. A new generation of simple, reliable and cheap fast position-sensitive detectors seems at hand.

The gas electron multiplier (GEM)

We describe operating principles and results obtained with a new detector element: the Gas Electron Multiplier (GEM). Consisting of a thin composite sheet with two metal layers separated by a thin insulator, and pierced by a regular matrix of open channels, the GEM electrode, inserted on the path of electrons in a gas detector, allows the transfer of charge with an amplification factor approaching ten. Uniform response and high rate capability are demonstrated. Coupled to another device, multiwire or micro-strip chamber, the GEM electrode permits higher gains or less critical operation; separation of the sensitive (conversion) volume and the detection volume have other advantages: a built-in delay (useful for triggering purposes), and the possibility of applying high fields on the photo-cathode of ring imaging detectors to improve efficiency. Multiple GEM grids in the same gas volume allow large amplification factors to be achieved in a succession of steps, leading to the realization of an effective gas-filled photomultiplier.

Studies of light emission by continuously sensitive avalanche chambers

Abstract The optimal conditions for the optical recording of images of electron avalanches between parallel meshes have been studied. The emission spectra of gas mixtures have been investigated, where triethylamine (TEA), tetrakis(dimethylamine)ethylene (TMAE), and nitrogen, are used as the photon-emitting agents. For a given charge gain, the photon intensity decreases with electric field. This favours amplification between parallel meshes instead of wires. The use of intensified CCD cameras permits the recording of the local energy loss along the tracks.

The Gas Photodiode as a Possible Large-Area Photon Detector

Testing extensively a dozen custom-manufactured gas photodiodes, we have observed stable and reproducible characteristics of the argon-filled devices at pressures around 1 Torr, with gains up to 30-40. Methane-filled diodes operate at even higher gains (60-70) at around the same pressure, and have a faster response; they show, however, long-term degradation at relatively low light fluxes. At higher pressures, while the argonfilled device is largely degraded, high quantum efficiency and a good collection plateau is observed in methane. When operated in the collection mode, the CH4 high-pressure device does not show any sign of degradation.

Investigation of light emission from a parallel-plate avalanche chamber filled with noble gases and with TEA, TMAE, and H2O vapours at atmospheric pressure

Abstract The light emission from avalanches in parallel-plate chambers, filled with noble gases and with TEA, TMAE, and H 2 O vapours at a total pressure p = 1 atm under the condition of low gas gain, has been investigated. Three important results have been obtained. 1. (1)|At partial pressures of more than a few Torr, and for a given charge gain, the light output from TEA, TMAE, and H 2 O in the spectral region 200–700 nm is much higher than from all other common quenching gases. 2. (2)|For these vapours, the ratio of light to charge is independent of their concentration when their partial pressure is more than a few Torr. 3. (3)|The best energy resolution achieved with the light-emitting chamber is ∼18% for 5.9 keV. Qualitative models explaining these results are given.

Some applications of the imaging proportional chamber

Photons emitted by avalanches in gases can be detected with an image intensifier coupled to a solid-state camera. Some vapors enhance the emission at wavelengths close to the visible. Progress made in using this technique to image charged particles and Cherenkov photons is described. Results are presented for various gas mixtures containing TEA and TMAE. >

A highly efficient low-pressure UV-rich detector with optical avalanche recording

Abstract UV photons from a Cherenkov radiator are multiplied in a multistep avalanche chamber operating in a gated mode at low gas pressure (40 Torr). The gas mixture is C 2 H 6 -argon ( 80 20 ) and TMAE at 34°C. Visible light emitted from single photoelectron avalanches is detected by a CCD camera coupled to an image intensifier system. The detector was tested with 5 GeV c electrons, using a CH 4 radiator gas at 1 atm. Cherenkov rings essentially free of particle background and of secondary photon feedback were obtained in this mode of operation with a mean number n ≅ 11.5 ( N 0 ≅ 76 cm −1 ). We present this new method and discuss its performance.

Gaseous detectors with parallel electrodes and anode mesh planes

Abstract The amplification of electron avalanches in a uniform electric field between parallel electrodes can be used in single or multistep structures for a great variety of applications in fields such as charged-particle tracking, X-ray imaging, ultraviolet photon detection for ring imaging of Cherenkov light, beta autoradiography, and gamma-ray astrophysics. In this article some observed properties of parallel-electrode structures are analysed and compared with those of wire chambers. Parallel electrodes have advantages over wire chambers in their better energy resolution, better timing resolution, and the fact that they are easier to construct and are more durable. It is now possible to construct proportional gaseous detectors without the need to string wires, with readout options using either electronic charge signals or optical light imaging. For either of these methods the position and energy of the avalanches can easily be determined.

Construction, test and operation in a high intensity beam of a small system of micro-strip gas chambers

Abstract We describe the construction, test and installation procedures, and the experience gained with the operation of a small but complete system of high-rate Micro-Strip Gas Chambers, made on thin borosilicate glass with a diamond-like coating with chromium or gold strips. A set of detectors, fully equipped with read-out electronics and each with an active area of 100 × 100 mm 2 , was exposed during six months to a high-intensity muon beam at CERN with a peak intensity of ∼ 10 4 mm −2 s −1 . Continuous monitoring of the performance of the chambers during the beam runs allowed the evaluation of detection efficiency and the monitoring of accidental rates, as well as the study of ambient induced variations and aging in realistic beam conditions. No significant difference has been found in the operation of under-and over-coated plates. Efficiencies could reach ∼ 98% in best operating conditions, although local lower values were often observed due to missing channels (open strips, broken bonds and dead electronic channels). The long-term operation of the chambers has been more difficult than expected, with the appearance of break-downs and loss of efficiency in some detectors, possibly induced by the presence of small gas leaks, to water permeation or to residual reactivity of the quencher gas (dimethylether).

Mapping of [3H]vasopressin binding sites in the brain of jerboa (Jaculus orientalis) by an high resolution β-radio imager

The distribution of vasopressin receptors in the brain of the jerboa (Jaculus orientalis) was studied using tritiated arginin vasopressin ([3H]vasopressin). beta-Particles emitted from tritiated ligand bound to brain sections were detected by a newly developed beta-radio imager to generate a light spot which was read by a charge coupled device camera. The number and coordinate of the center of gravity of the light spot were recorded. After summation in pixels of the counts collected during 2-20 h, an image was produced representing the distribution of [3H]vasopressin bound to brain sections. Specific vasopressin binding was detected in various brain regions such as the cerebral cortex, islands of Calleja, pallidum, amygdala and the hippocampus as well as in the pituitary gland. The intensity of the binding was quantified directly from the images obtained and expressed in decays/min/surface unit. The linearity of this method of detection allowed a relevant measurement of non-specific binding, therefore its subtraction from images representing the total binding. Three-dimensional reconstructions of labeled structures were also performed. The presence of numerous vasopressin receptors in the jerboa hippocampus suggests a major role for this neuropeptide in this part of the brain.