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We use the Gross-Pitaevskii equation to determine the spatial structure of the condensate density of interacting bosons whose energy dispersion ϵ has two degenerate minima at finite wave-vectors ± q. We show that in general the Fourier transform of the condensate density has finite amplitudes for all integer multiples of q. If the interaction is such that many Fourier components contribute, the Bose condensate is localized at the sites of a one-dimensional lattice with spacing 2 π/| q|; in this case Bose-Einstein condensation resembles the transition from a liquid to a crystalline solid. We use our results to investigate the spatial structure of the Bose condensate formed by magnons in thin films of ferromagnets with dipole-dipole interactions. [ABSTRACT FROM AUTHOR]

Motivated by recent experiments on thin films of the ferromagnetic insulator yttrium-iron garnet (YIG), we have developed an efficient microscopic approach to calculate the spin-wave spectra of these systems. We model the experimentally relevant magnon band of YIG using an effective quantum Heisenberg model on a cubic lattice with ferromagnetic nearest neighbour exchange and long-range dipole-dipole interactions. After a bosonization of the spin degrees of freedom via a Holstein-Primakoff transformation and a truncation at quadratic order in the bosons, we obtain the spin-wave spectra for experimentally relevant parameters without further approximation by numerical diagonalization, using efficient Ewald summation techniques to carry out the dipolar sums. We compare our numerical results with two different analytic approximations and with predictions based on the phenomenological Landau-Lifshitz equation. [ABSTRACT FROM AUTHOR]

Abstract: A controlled-voltage Gas Electron Multiplier (GEM) can be used to block the re-injection of positive ions in large volume Time Projection Chambers (TPC). With proper choice of geometry, gas filling and external fields, good electron transmission can be obtained at very low GEM voltages; pulsed ion gating is then much easier than with conventional wire grids, requiring hundreds of volts. Gating schemes suited for the TPC detector planned for the International Linear Collider detector are described. The possibility of GEM-based DC-operated ion filters, exploiting the difference in diffusion properties of ions and electrons, is also discussed. [Copyright &y& Elsevier]

Abstract: We report the observation of radiation-induced primary and field-enhanced gas scintillation in xenon with a Gas Electron Multiplier (GEM) detector, having an internal CsI photocathode. The measurement of the time lag between prompt and delayed pulses can be exploited to reduce the parallax error in X-ray detectors having thick conversion volumes. [Copyright &y& Elsevier]

We describe systematic measurements carried out with single and double GEM detectors with printed circuit readout. The maximum safe operating gain has been measured at increasing radiation flux and under exposure to heavily ionizing tracks. Detection efficiency, localization accuracy and cluster size have been measured in a minimum ionizing particle beam. With a suitably configured readout electrode, fast, two-dimensional localization of radiation is demonstrated [ABSTRACT FROM PUBLISHER]

Abstract: We present preliminary results obtained with a method permitting the determination of the conversion depth (DOI) in a position-sensitive, multi-layer γ-ray or neutron detector making use of a stack of Gas Electron Multipliers and converter foils. [Copyright &y& Elsevier]

Crystallography or X-ray fluorescence experiments which require good signal to noise ratios and high position resolution can take advantage of the outstanding signal amplification capabilities of MicroPattern Gaseous Detectors (MPGDs) such as Gaseous Electron Multipliers (GEMs) coupled with the position resolution achieved by optical readout realized with CCD or CMOS cameras. Increasing the detection probability of incident radiation with thicker drift volumes in these detectors leads to a spatial resolution-limiting parallax error when employing parallel electric field lines in the drift region. We describe a new GEM-based detector concept, consisting of a cathode, GEM electrodes and field shaping rings suitably segmented and powered to create a radial electric field, thus minimizing the parallax error. A CCD camera is used to record scintillation light originating from charge multiplication in the high field of the GEM holes in an Ar/CF 4 (80/20%) gas mixture. Assembled as pinhole camera, the device permits to obtain high detection efficiencies for soft X-rays, exempt from the parallax error intrinsic in the use of standard gaseous detectors with thick conversion layers. The use of several GEMs in cascade allows for high charge multiplication factors. Switching from straight to radially focused drift field lines, a significant reduction of the parallax error as well as an increased signal-to-noise ratio were achieved, effectively paving the way for applications such as X-ray crystallography realized with optically read out GEMs. [ABSTRACT FROM AUTHOR]

We describe the development of a position-sensitive Gas Electron Multiplier detector prototype, providing for each ionizing event three coordinates: the cartesian X and Y, and U at 45 °. Simultaneous recording of the three projections permits ambiguity-free reconstruction of multiple tracks, and aims at operation in very high intensity radiation fields. [ABSTRACT FROM AUTHOR]

We describe the development, construction and preliminary results obtained with medium-size Multi-Gap Resistive Plate Chambers prototypes designed to detect and localize 511 keV photons for Positron Emission Tomography imaging applications. The devices are intended for in-beam monitoring of the treatment plans throughout deep tumor therapy with hadron beams; emphasis is put on achieving coincidence time resolutions of few hundred ps, in order to exploit optimized reconstruction algorithm and reduce the heavy non-correlated background contributions distinctive of this operation. Using technologies developed for high energy physics experiments, the detectors can be built for covering large areas, thus leading the way to the conception of full-body PET systems at low cost. [ABSTRACT FROM AUTHOR]

Abstract: We describe the development of a Proton Range Radiography system with an imaging area of 30×30cm2 for two dimensional mapping of the integrated density in a target. Proton transmission radiographic images are produced by measuring, with a pair of position-sensitive detectors (GEM chambers), the direction of the protons transmitted through the patient and, with a stack of scintillators, the residual range of the protons leaving the patient. To match the data rate requirements of an in-beam diagnostic, a novel data acquisition system for the tracking detectors has been designed to operate at 1MHz data flow. Laboratory tests exposing the GEM detector with high flux X-rays confirm the fast response of the new data acquisition system. Images of several phantoms have been recorded to demonstrate the GEM position accuracy. [Copyright &y& Elsevier]

Abstract: We describe the design and implementation of a fast data acquisition (DAQ) system for Gas Electron Multiplier (GEM) trackers applied to imaging and dosimetry in hadrontherapy. Within the AQUA project of the TERA foundation a prototype of Proton Range Radiography of 30×30cm2 active area has been designed and built to provide in-beam integrated density images of the patient before treatment. It makes use of a pair of GEMs to record position and direction of protons emerging from the target. A fast data acquisition rate close to 1MHz will allow obtaining a good resolution in-beam proton radiography in a few seconds. A dedicated fast front-end circuit for GEM detectors (GEMROC by AGH-Crakow University) is read by the FPGA based DAQ card (GR_DAQ), developed by the AQUA group. The same system is under evaluation (within the ENVISION European project) to realize the in-vivo dosimetry, based on detecting secondary light particles during the treatment of the patient. [Copyright &y& Elsevier]

Abstract: The charging up effect is well-known in detectors containing dielectric materials and it is due to electrons and ions liberated in an avalanche and collected on the dielectric surfaces. In particular in Gas Electron Multiplier (GEM) based detectors, charges can be captured by the Kapton that separates top and bottom electrodes. The collection of a substantial number of charges on the dielectric surfaces induces a modification of the field inside the GEM holes that implies important consequences on some fundamental parameters such as the electron transparency and the effective gain. The correct simulation of this effect opens new ways to the detailed study of the processes that happens in a GEM-based detector and gives the possibility to optimise the GEM geometry in order to avoid it. This paper compares results of the measurements and the simulations, with and without the introduction of the charging-up effect, of the GEM electron transparency in the case of a single GEM detector. The introduction of the charging up effect in the simulation resulted to be crucial in order to get the proper agreement with the measurements. The measurements and simulations of the GEM effective gain will be the subject of a future work. [Copyright &y& Elsevier]

Abstract: We describe a Proton Range Radiography system with an imaging area of 10×10cm2, deploying a pair of Gas Electron Multiplier position-sensitive detectors and a scintillator stack to measure the residual proton range after crossing a target. The detector has been tested in the laboratory and in beam exposures at the Paul Scherrer Institute; images recorded with several phantoms of variable thickness and composition confirm the sub-millimetre accuracy and few percent energy resolution of the instrument. A new device with identical design and larger acceptance, 30×30cm2, is in construction. [ABSTRACT FROM AUTHOR]

Abstract: We report on the activity of CERN and INFN-LNF groups on the development of large area GEM detectors. The two groups work together within the RD51 Collaboration, to aim at the development of Micro-pattern Gas detectors technologies. The vast request for large area foils by the GEM community has driven a change in the manufacturing procedure by the TS-DEM-PMT laboratory, needed to overcome the previous size limitation of . Now a single-mask technology is used allowing foils to be made as large as . The limitation in the short size, due to the definite width of the raw material, can be overcome by splicing more foils together. A GEM detector with the new single-mask foil has been tested with X-rays and the results are shown. Possible future applications for large area GEM are the TOTEM experiment upgrade at CERN, and the KLOE-2 experiment at the Dafne -factory in Frascati. [Copyright &y& Elsevier]

Abstract: COMPASS is a high-luminosity fixed target experiment at CERN''s SPS, which has been taking data with a muon beam since 2001. The tracking of charged particles in the near-beam area is achieved by a set of twenty novel large-area micropattern gas detectors based on the Gas Electron Multiplier (GEM). Owing to a two-dimensional readout of signals, each of these detectors delivers two track projections. Distributed over a distance of throughout the spectrometer, the GEM detectors constitute the backbone of the small-area tracking system of COMPASS. The performance of these detectors in the high intensity muon beam with particle rates up to is investigated. [Copyright &y& Elsevier]

The optical readout of GEMs, presented a few years ago, is currently being considered for several detector projects. Although using suitable gaseous mixtures the GEM avalanches emit a large number of photons in the visible and/or NIR regions, many gaseous mixtures of great interest for detectors scintillate mainly in the UV, and the readout of these detectors is usually inefficient or very expensive. In this work we report on the operation of GEMs coated with a wavelength converter. We show that using a GEM with an optimal geometry the wavelength conversion process can be quite efficient and does not degrade the intrinsic position resolution of the detector, an usual drawback of the utilisation of wavelength shifters. [Copyright &y& Elsevier]

Continuing previous aging measurements with detectors based on the Gas Electron Multiplier (GEM), we investigated a 31×31 cm2 triple-GEM detector, as used in the small area tracking of the COMPASS experiment at CERN. With a detector identical to those installed in the experiment, long-term high-rate exposures to 8.9 keV X-ray radiation were performed to study its aging properties. In standard operation conditions, with Ar/CO2 (70:30) gas filling and operated at an effective gain of 8.5×103, no change in gain and energy resolution is observed after collecting a total charge of 7 mC/mm2, corresponding to seven years of normal operation.This observation confirms previous results demonstrating the relative insensitivity of GEM detectors to aging, even when manufactured with common materials. [Copyright &y& Elsevier]

Examines the gas electron multiplier (GEM) detectors installed in Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS). Description of the COMPASS GEM detectors; Performance of the detectors in particle beams.

The Small Area Tracking system of the COMPASS experiment at CERN includes a set of 20 large area, fast position-sensitive Gas Electron Multiplier detectors, designed to reliably operate in the harsh radiation environment of the experiment. We describe in detail the design, choice of materials, assembly procedures and quality controls used to manufacture the devices. The test procedure in the laboratory, the performance in test beams and in the initial commissioning phase in the experiment are presented and discussed. [Copyright &y& Elsevier]

The gas electron multiplier (GEM) used as single proportional counter or in a cascade of two or more elements, permits to attain high gains and to perform detection and localization of ionizing tracks at very high radiation rates. As in other micro-pattern detectors, however, the occasional occurrence of heavily ionizing trails may trigger a local breakdown, with possible harmful consequences on the device itself and on the readout electronics. This paper describes a systematic investigation of the discharge mechanisms in single and multiple GEM structures, and suggests various strategies to reduce both the energy and the probability of the discharges. [Copyright &y& Elsevier]

Modern micropattern gas counters are able to detect soft X-rays with high spatial resolution. Based on the principle of gas amplification, this detector type has a wide dynamic range and provides energy selection during image reconstruction. One of the most recent developments is the Multi-GEM, an efficient, high-rate capable micropattern gas detector. Owing to the separation of gas amplification and readout stage, this detector allows high flexibility in the geometry of the readout structure.With a two-dimensional projective readout, GEM detectors have shown good capability in providing X-ray absorption radiographies of small mammals. We present a detector with a novel design where the readout board consists of micropads connected to three layers of strips in such a way that two-dimensional spatial reconstruction and an unambiguous resolution of events with multiple hits is possible. [Copyright &y& Elsevier]

Features detectors that have been built based on a gas electron multiplier (GEM) for small-area tracking of particles within common muon and proton apparatus for structure and spectroscopy (COMPASS). Operational characteristics of the detectors in a real COMPASS beam; Results obtained by comparing the discharge behavior of a double and a triple GEM detector; What makes up a GEM detector.

Describes the development of the Gas Electron Multiplier (GEM), a composite mesh which acts as a proportional avalanche amplifier in gas counters. Efficiency, time resolution, and localization accuracy of the GEM; What the GEM mesh consists of; Use of the wet etching technology on the development of the GEM; Results of systematic testing of the GEM.

Electrode sectorization is an important design principle for large area GEM based detectors. It reduces the energy of discharges and permits to disconnect defective or shorted sectors, but induces a local signal distortion and a potential efficiency loss. We implemented and evaluated a new design approach for the insulating gaps between electrode sectors, to minimize or mitigate distortions and dead regions. By preserving the hole pattern of GEMs even in the insulating region between electrode sectors, the response of the detector in these regions was partly recovered resulting in reduced distortions. Single-side sectored GEMs were optically read out to study the influence of different sectorization patterns. Recorded images show a clear improvement with full holes both aligned with the rows and with a random alignment as compared to the traditional blank insulating strip between sectors. A sectored GEM manufactured on a substrate coated with a resistive DLC layer was evaluated and shown to minimize distortions. The investigated sectorization patterns provide a way of recovering signals in the insulating or resistive regions between sectors in GEM-based detectors. [ABSTRACT FROM AUTHOR]

Abstract: Controlled etching of copper electrodes in Gas Electron Multiplier foils allows a reduction of the material budget by more than a factor of two for a triple-GEM detector. Detectors making use of thinned foils provide performances similar to those obtained with standard devices—a gain above 104 for a double-GEM, with energy resolution of 27% fwhm for 5.9keV X-rays. [Copyright &y& Elsevier]

Abstract: We describe the test results of a Proton Range Radiography system, designed to provide in-beam integrated density images of the patients before treatment at hadrontherapy centers. The instrument includes a set of position-sensitive detectors and a scintillator stack read out with solid-state sensors to record the Bragg energy loss profile for each track. [Copyright &y& Elsevier]

Abstract: We report on first results obtained with a triple GEM detector using GEM foils produced by Tech-Etch Inc. in comparison to GEM foils produced at CERN. [Copyright &y& Elsevier]