[en] The authors describe recent developments of the Gas Electron Multiplier (GEM), a thin composite mesh acting as proportional avalanche amplifier in gas counters. In beam tests the authors have verified the excellent efficiency, time resolution and localization accuracy for a GEM with micro-strip read-out. Efficiency, localization accuracy and operation in strong magnetic fields has been verified; operation at rates above 10⁶ Hz/mm² and lifetimes corresponding to at least 10 mC/cm of collected charge have been demonstrated. Refinements in the manufacturing technology have permitted the realization of large size detectors (27 by 25 cm²), to be used in conjunction with micro-stripe gas chambers. With an improved design, stable gains above two thousand have been reached (GEM2000); larger gains can be obtained increasing the thickness of the foils, cascading two GEMs at some distance or in electrical contact. Further developments of the technology and prospective applications are discussed

No abstract available

[en] We describe the development and operation of the gas electron multiplier (GEM), a thin insulating foil metal-clad on both sides and perforated by a regular pattern of small holes. The mesh can be incorporated into the gas volume of an active detector to provide a first amplification channel for electrons, or used as stand alone. We report on the basic properties of GEMs manufactured with different geometries and operated in several gas mixtures as well as on their long-term stability after accumulation of charge equivalent to several years of operation in high-luminosity experiments. Optimized GEMs reach gains close to 10000 at safe operating voltages, permitting the detection of ionizing tracks, without other amplifying elements, on a simple printed circuit board (PCB), opening new possibilities for detector design. (author)

[en] AMIC architecture has been introduced in previous works in order to provide a generic and expandable solution for implementing large number of outputs SiPM array/PMT detectors. The underlying idea in AMIC architecture is to calculate the moments of the detected light distribution in an analog fashion. These moments provide information about energy, x/y position, etc. of the light distribution of the detected event. Moreover this means that a small set of signals contains most of the information of the event, thus reducing the number of channels to be acquired. This paper introduces a new front-end device AMIC2GR which implements the AMIC architecture improving the features of the former integrated devices. Higher bandwidth and filtering coefficient precision along with a lower noise allow to apply some detector enhancements. Inhomogeneity among detector elements throughout the array can be reduced. Depth of interaction measurements can be obtained from the light distribution analysis. Also a common trigger signal can be obtained for the whole detector array. Finally AMIC2GR preamplifier stage close to SiPM output signals optimizes signal to noise ratio, which allows to reduce SiPM gain by using lower operating voltages thus reducing dark noise.

[en] A method to improve light collection efficiency of γ-ray imaging detectors by using retroreflector arrays has been tested, simulations of the behaviour of the scintillation light illuminating the retroreflector surface have been made. Measurements including retroreflector arrays in the setup have also been taken. For the measurements, positron emission tomography (PET) detectors with continuous scintillation crystals have been used. Each detector module consists of a continuous LSO-scintillator of dimensions 49x49x10 mm³ and a H8500 position-sensitive photo-multiplier (PSPMT) from Hamamatsu. By using a continuous scintillation crystal, the scintillation light distribution has not been destroyed and the energy, the centroids along the x- and y-direction and the depth of interaction (DOI) can be estimated. Simulations have also been run taking into account the use of continuous scintillation crystals. Due to the geometry of the continuous scintillation crystals in comparison with pixelated crystals, a good light collection efficiency is necessary to correctly reconstruct the impact point of the γ-ray. The aim of this study is to investigate whether micro-machine retro-reflectors improve light yield without misestimation of the impact point. The results shows an improvement on the energy and centroid resolutions without worsening the depth of interaction resolution. Therefore it can be concluded that using retroreflector arrays at the entrance side of the scintillation crystal improves light collection efficiency without worsening the impact point estimation

[en] In this work the implementation of a Time-to-Digital Converter (TDC) using a Nutt delay line FPGA-based and applied on a Positron Emission Tomography (PET) device is going to be presented in order to check the system's suitability for Time of Flight (TOF) measurements. In recent years, FPGAs have shown great advantages for precise time measurements in PET. The architecture employed for these measurements is described in detail. The system developed was tested on a dedicated breast PET prototype, composed of LYSO crystals and Positive Sensitive Photomultipliers (PSPMTs). Two distinct experiments were carried out for this purpose. In the first test, system linearity was evaluated in order to calibrate the time measurements, providing a linearity error of less than 2% and an average time resolution of 1.4 ns FWHM. The second set of measurements tested system resolution, resulting in a FWHM as good as 1.35 ns. The results suggest that the coincidence window for the current PET can be reduced in order to minimize the random events and thus, achieve better image quality

[en] The radiation sensitive part of the wide-field, small gamma camera Sentinella™ 108 consists of a monolithic, 102 × 102 mm² wide CsI(Na) crystal coupled to four position-sensitive photomultipliers. These are read out via a resistor mesh reducing the 256 PMT channels to four digitized values which allow for an image reconstruction, based on polynomials, with high spatial resolution. The sensor areas between neighboring PMTs suffer from reduced detection efficiency for scintillation light. The corresponding lack of signal amplitude translates to a poor uniformity and additional image compression in the border regions of the images after the first step of reconstruction. These effects cannot be completely eliminated by a global calibration procedure alone. We have developed and evaluated two classes of algorithms to compensate for this reduction of signal amplitude. Corrections are applied for each detected event separately, maintaining the real-time capability of the gamma camera. Algorithm 1 is based on a four-parameter, geometric calculation of the four output signals. This model aims to attack the underlying lack of detection efficiency without further assumptions on the true event distribution, preserving the global polynomial image decompression. Algorithm 2, to the contrary, starts from measured reference distributions of point sources which are used to model local deformations and energy loss without further information on the underlying detector geometry. Here too, a good image quality has been obtained after application of the deduced corrections. These algorithms are applied in the first step of event reconstruction. Within an energy interval of ±0.2E_p around the photopeak position of ^99mTc, E_p = 140.5 keV, and comparing several cameras, global uniformities around 5–8% have been obtained with both models. Measured energy resolutions are about 9–14%

[en] The splitting of the field of view (FOV) in polar voxels is proposed in this work in order to obtain an efficient description of a cone-beam computed tomography (CT) scanner. The proposed symmetric-polar pixelation makes it possible to deal with the 3D iterative reconstruction considering a number of projections and voxel sizes typical in CT preclinical imaging. The performance comparison, between the filtered backprojection (FBP) and 3D maximum likelihood expectation maximization (MLEM) reconstruction algorithm for CT, is presented. It is feasible to achieve the hardware spatial resolution limit with the considered pixelation. The image quality achieved with MLEM and FBP have been analyzed. The results obtained with both algorithms in clinical images have been compared too. Although the polar-symmetric pixelation is presented in the context of CT imaging, it can be applied to any other tomographic technique as long as the scan comprises the measurement of an object under several projection angles.

[en] We have developed two prototypes of portable gamma cameras for medical applications based on a previous prototype designed and tested by our group. These cameras use a CsI(Na) continuous scintillation crystal coupled to the new flat-panel-type multianode position-sensitive photomultiplier tube, H8500 from Hamamatsu Photonics. One of the prototypes, mainly intended for intrasurgical use, has a field of view of 44x44 mm², and weighs 1.2 kg. Its intrinsic resolution is better than 1.5 mm and its energy resolution is about 13% at 140 keV. The second prototype, mainly intended for osteological, renal, mammary, and endocrine (thyroid, parathyroid, and suprarenal) scintigraphies, weighs a total of 2 kg. Its average spatial resolution is 2 mm; it has a field of view of 95x95 mm², with an energy resolution of about 15% at 140 keV. The main advantages of these gamma camera prototypes with respect to those previously reported in the literature are high portability and low weight, with no significant loss of sensitivity and spatial resolution. All the electronic components are packed inside the mini gamma cameras, and no external electronic devices are required. The cameras are only connected through the universal serial bus port to a portable PC. In this paper, we present the design of the cameras and describe the procedures that have led us to choose their configuration together with the most important performance features of the cameras. For one of the prototypes, clinical tests on melanoma patients are presented and images are compared with those obtained with a conventional camera

[en] Large-scale fabrication of targets for laser-driven acceleration of ion beams is a prerequisite to establish suitable applications, and to keep up with the challenge of increasing repetition rate of currently available high-power lasers. Here we present manufacturing and test results of large arrays of solid targets for TNSA laser-driven ion acceleration. By applying micro-electro-mechanical-system (MEMS) based methods allowing for parallel processing of thousands of targets on a single Si wafer, sub-micrometric, thin-layer metallic membranes were fabricated by combining photolithography, physical and chemical vapor deposition, selective etching, and Si micromachining. These structures were characterized by using optical and atomic force microscopy. Their performance for the production of laser-driven proton beams was tested on a purpose-made table-top Ti:Sapphire laser system running at 3 TW peak power with a contrast over ASE of 10⁸. We have performed several test series achieving maximum proton energy values around 2 MeV. (paper)