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Micro-hole and strip plate-based photosensor
Freitas, E. D. C.; Veloso, J. F. C. A.; Breskin, A.; Chechik, R.; Amaro, F. D.; Ferreira, L. F. Requicha; Maia, J. M.; Santos, J. M. F. dosThe performance of a new VUV photosensor, based on an micro-hole and strip plate (MHSP) electron multiplier with a CsI photocathode deposited on its top electrode, is described. This photosensor presents gains above 104 when operating in an Ar-5%Xe gas mixture at 1 atm. Although the gain of a single MHSP is not sufficient for efficient detection of single photons, this simple UV photosensor may be useful for th...
Operation of a single-GEM in noble gases at high pressures
Amaro, F. D.; Conceição, A. S.; Veloso, J. F. C. A.; Coelho, L. C. C.; Fernandes, L. M. P.; Ferreira, L. F. Requicha; Lopes, J. A. M.We report the performance of a single-Gas Electron Multiplier (GEM) operating in pure Ar, Xe, and in Ar-50lmbar Xe mixtures, in the range of 1-7lbar. The maximum gain and voltage that can be applied to the GEM are investigated as a function of filling pressure and compared to the results obtained with triple-GEM and MHSP (Micro Hole and Strip Plate) multipliers. The maximum gain achieved at 1lbar Xe is about 10...
High-pressure operation of a xenon-GPSC/MSGC hybrid detector for hard X-ray spe...
Coelho, L. C. C.; Veloso, J. F. C. A.; Covita, D. S.; Ferreira, L. F. Requicha; Santos, J. M. F. dosThe performance of a high-pressure xenon gas proportional scintillation counter/microstrip gas chamber (GPSC/MSGC) hybrid detector has been investigated for filling pressures from 1 up to 10 bar, for 22-, 30- and 60-keV photons. GPSC/MSGC hybrid detectors are based on a xenon-GPSC instrumented with a CsI-coated microstrip plate photosensor placed directly within the xenon envelope, as a substitute for the photo...
MHSP operation in pure xenon
Luz, H. Natal da; Veloso, J. F. C. A.; Amaro, F. D.; Ferreira, L. F. Requicha; Santos, J. M. F. dos; Breskin, A; Chechik, R.We present latest results of a micro-hole and strip plate (MHSP) electron multiplier operating in pure xenon at atmospheric pressure. We report on avalanche gain of ~2×104, stable within ~3% after an accumulated charge of 4 [mu]C/mm2, when irradiated with 0.5 kHz/mm2 5.9 keV photons. No photon-induced secondary effects or discharges have been observed at this gain. An energy resolution of 14% was obtained with ...
Energy non-linearity effects in the response of ionic crystal scintillators to ...
Ferreira, L. F. Requicha; Ferreira, H. M. N. B. L.; Veloso, J. F. C. A.; Santos, J. M. F. dosThe response of a YAP, NaI(Tl) and BaF2 scintillators to X-rays with energies around the Y, I, and Ba K-absorption edges, respectively, was investigated. For all the scintillators, the amplitude response follows different linear trends for X-ray energies below and above the respective K-edges, presenting a discontinuity at these energies. An abrupt decrease of about 3%, 5% and 2% were observed in the detector a...
The X-ray performance of a driftless gas proportional scintillation counter usi...
Covita, D. S.; Simões, P. C. P. S.; Fernandes, L. M. P.; Freitas, E. D. C.; Ferreira, L. F. Requicha; Veloso, J. F. C. A.; Santos, J. M. F. dosPerformance characteristics are evaluated for a xenon driftless gas proportional scintillation counter (GPSC), for which detector pulses are formatted using very short shaping-time constants (~50 ns), and directly analyzed by the MCA without previous pulse time duration analysis and amplitude correction. The present detector and method allow the achievement of detector energy linearity and energy resolution sim...
Development of portable gas proportional scintillation counters for x-ray spect...
Santos, J. M. F. dos; Lopes, J. A. M.; Veloso, J. F. C. A.; Simões, P. C. P. S.; Dias, T. H. V. T.; Santos, F. P.; Rachinhas, P. J. B. M.A review on gas proportional scintillation counters (GPSCs) is presented. Recent achievements towards the portability of simple, inexpensive and compact GPSCs are discussed. Compensation of solid angle effects with the curved grid technique can be used to produce non-focused GPSCs with medium-sized radiation windows, at least up to 80% of the photosensor active diameter, without degradation of detector performa...
Cascade-Encoder Technique for High Speed Analog-to-Digital Conversion
Ferreira, L. F. Requicha; Conde, C. A. N.A simple circuit based on a fast operational amplifier, a comparator and a few additional components is used as the basic building block for a high speed analog-to-digital converter of the cascade-encoder type. The properties of this circuit and the performance of an implementation using standard components are discussed. Its potential for LSI is considered
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