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A curved-grid gas proportional scintillation counter instrumented with a 25-mm ...
Monteiro, C. M. B.; Morgado, R. E.; Santos, J. M. F. dos; Conde, C. A. N.The curved-grid technique provides a simple method to compensate for the variation in solid angle viewed by the PMT in large-area gas proportional scintillation counters (GPSC), improving their performance. The scintillation region is delimited by a planar grid and a curved one, whose shape is calculated to produce a radially increasing scintillation yield, compensating for the decrease in the solid angle. In t...
A new method for pulse analysis of driftless-gas proportional scintillation cou...
Simões, P. C. P. S.; Covita, D. S.; Veloso, J. F. C. A.; Santos, J. M. F. dos; Morgado, R. E.A new method for pulse analysis of driftless-gas proportional scintillation counters (GPSCs) is presented. With this method the requirement for additional analog or digital signal time-analysis and pulse-amplitude correction currently used is eliminated. In contrast to conventional- and driftless-GPSCs that have always relied on long shaping-time constants (several [mu]s), the use of very short linear amplifier...
VUV detection in large-area avalanche photodiodes as a function of temperature
Lopes, J. A. M.; Fernandes, L. M. P.; Santos, J. M. F. dos; Morgado, R. E.; Conde, C. A. N.The response of a Peltier-cooled large-area avalanche photodiode to VUV-light is investigated as a function of the operation temperature. The reduction of the temperature down to 5°C will improve both photodiode light-level detection limit and statistical fluctuations; further temperature reduction will not result in improved performance. Optimum operation characteristics are already achieved for gains around 1...
A metastable xenon isotope detector for treaty verification
Lopes, J. A. M.; Morgado, R. E.; Conde, C. A. N.A system to selectively detect and quantify the xenon metastable isotopes 131mXe, 133mXe, 133Xe, and 135Xe has been designed, fabricated, and tested. The system combines high-resolution electron and gamma-ray spectrometry with coincidence/anti-coincidence timing for signal selectivity and background rejection. By utilizing X-ray-fluorescence gating, backgrounds from other sources are expected to be reduced to t...
Non-linear behaviour of large-area avalanche photodiodes
Fernandes, L. M. P.; Lopes, J. A. M.; Monteiro, C. M. B.; Santos, J. M. F. dos; Morgado, R. E.The characterisation of photodiodes used as photosensors requires a determination of the number of electron-hole pairs produced by scintillation light. One method involves comparing signals produced by X-ray absorptions occurring directly in the avalanche photodiode with the light signals. When the light is derived from light-emitting diodes in the 400-600 nm range, significant non-linear behaviour is reported....
Digital rise-time discrimination of large-area avalanche photodiode signals in ...
Fernandes, L. M. P.; Simões, P. C. P. S.; Santos, J. M. F. dos; Morgado, R. E.Large-area 1.9-keV X-ray detectors operating in magnetic fields up to 5 T are required for the μp-Lamb shift experiment. Xenon gas proportional scintillation counters provide high detection efficiency together with good energy and timing resolutions. Three prototypes with alternative vacuum ultraviolet photosensors of the xenon scintillation light are explored and discussed: a CsI-coated microstrip plate either...
Energy linearity of high-purity germanium detectors in the region of the Ge K-a...
Santos, J. M. F. dos; Monteiro, C. M. B.; Morgado, R. E.; Conde, C. A. N.Non-linearities in the energy response of gas detectors in the regions of the absorption edges of the detection medium are well documented. Monte Carlo calculations show that the non-linearity results from differences in efficiencies for converting absorbed radiation into ionisation for different atomic sub-shells. Energy non-linearity in germanium-based solid-state detectors in the region of the germanium 11.1...
Simulation and experimental results for the detection of conversion electrons w...
Rachinhas, P. J. B. M.; Simões, P. C. P. S.; Lopes, J. A. M.; Dias, T. H. V. T.; Morgado, R. E.; Santos, J. M. F. dos; Stauffer, A. D.; Conde, C. A. N.The application of gas proportional scintillation counters (GPSC) to the detection and identification of conversion electrons in the medium energy range is investigated. Experimental and Monte Carlo results are presented for the response of a xenon GPSC, filled at atmospheric pressure, to the decay of a 109Cd source. This source emits 88.0 keV [gamma]-rays, eL=84.6 keV and eK=62.5 keV conversion electrons, as w...
A new integrated photosensor for gas proportional scintillation counters based ...
Lopes, J. A. M.; Santos, J. M. F. dos; Conde, C. A. N.; Morgado, R. E.The performance of a novel integrated photosensor for use in a xenon gas proportional scintillation detector is described. Earlier integrated photo-sensor designs were limited in charge gains due to the onset of electrical breakdown, which was ascribed to optical positive feedback from scintillation photons produced in the charge amplification stage. The present design uses a gas electron multiplier (GEM) compo...
The effect of grid misalignment on the uniformity of response of gas proportion...
Bento, A. C. S. S. M.; Santos, J. M. F. dos; Morgado, R. E.In the present work we revisit the simplifying assumptions of an earlier theoretical treatment on the effects of grid misalignment on the performance of a planar gas proportional scintillation counter (GPSC). We present new experimental and computational results to establish the dependence of the effects of misalignment in terms of the reduced electric field in the scintillation region, the finite size of the e...
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