J. M. F. dos Santos

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An experiment measuring the 2S Lamb shift in muonic hydrogen (/spl mu//sup -/p) is being performed at the Paul Scherrer Institute (PSI), Switzerland. It requires small detectors for 1.9 keV X-rays (2P-1S transition) with an energy resolution around 25%, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic(More)
The performance of a large area avalanche photodiode (LAAPD) has been investigated for X-ray and visible-light detection as a function of temperature. Energy resolution improves significantly with decreasing temperature down to 0/spl deg/C and, below that value, at a much slower rate, achieving 9.6% for 5.9 keV X-rays at 0/spl deg/C and for a gain of 60.(More)
A Xe-based single photon counting X-ray imaging system, based on a micro-hole & strip plate (MHSP), using a resistive charge division method was implemented. The MHSP is a hybrid microstructure that combines in a single element the features of the gas electron multiplier (GEM) and the micro-strip gas chamber (MSGC), presenting two charge multiplication(More)
The performance of a xenon high-pressure gas proportional scintillation counter (GPSC) instrumented with a large area avalanche photodiode (LAAPD) has been investigated for hard x-ray spectrometry. The LAAPD was placed in direct contact with the filling gas. Filling-pressures in the 2- to 6-atm range have been studied. The results obtained are similar to(More)
We present results from our recent investigations on detectors comprising cascaded gas electron multipliers (GEMs) and cascaded GEMs with microhole and strip plate (MHSP) multiplier as a final amplification stage. We discuss the factors governing the operation of these fast radiation-imaging detectors, which have single-electron sensitivity. The issue of(More)
The operation of two photosensors operating face-to-face, having a high pressure xenon medium in between is investigated. Each photosensor consists on a CsI- MicroHole and Strip Plate (MHSP) operating within the pure xenon medium. A cluster of 7 stainless steel grids, with a 1:3mm gap between them, is placed between the photosensors. Applying a high voltage(More)
We report the first laser spectroscopy of muonic deuterium. At the Paul Scherrer Institute, we have measured the frequency of the 2S-2P Lamb shift in muonic deuterium. As in the case of the muonic hydrogen, the observed lines are shifted from the theoretical predictions. Thanks to improved new QED and nuclear structure calculations, an accurate(More)
The curved grid technique has been shown to improve the performance of large-area gas proportional scintillation counters (GPSC) without the need for complex, bulky focusing systems or large-area photomultiplier tubes (PMTs). The technique provides a simple method to compensate for the variation in solid angle viewed by the PMT as a function of the radial(More)
The performance for X-ray spectrometry of neon-xenon gas proportional scintillation counters using a CsI-coated microstrip plate in direct contact with the scintillation gas as a VUV photosensor is investigated for different neon-xenon mixtures. At best operation conditions, the detector gain can reach values about 50% higher than those achieved with pure(More)
A new hybrid gamma detector system combining an assisted scintillation in a high pressure xenon gas medium and two UV photosensors based on microstructures operating face to face, having the xenon medium sandwiched in between, is under investigation for imaging purposes. Recent developments on gas avalanche detectors based on microstructures operating at(More)