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Register a new userEfficient ion blocking in gaseous detectors and its application to gas-avalanche photomultipliers sensitive in the visible-light range
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A novel concept for ion blocking in gas-avalanche detectors was developed, comprising cascaded micro-hole electron multipliers with patterned electrodes for ion defocusing. This leads to ion blocking at the 10^{-4} level, in DC mode, in operation conditions adequate for TPCs and for gaseous photomultipliers. The concept was validated in a cascaded visible-sensitive gas avalanche photomultiplier operating at atmospheric pressure of Ar/CH_{4} (95/5) with a bi-alkali photocathode. While in previous works high gain, in excess of 10^{5}, was reached only in a pulse-gated cascaded-GEM gaseous photomultiplier, the present device yielded, for the first time, similar gain in DC mode. We describe shortly the physical processes involved in the charge transport within gaseous photomultipliers and the ion blocking method. We present results of ion backflow fraction and of electron multiplication in cascaded patterned-electrode gaseous photomultiplier with K-Cs-Sb, Na-K-Sb and Cs-Sb visible-sensitive photocathodes, operated in DC mode.
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We report on the progress in the study of cascaded GEM and GEM/MHSP gas avalanche photomultipliers operating at atmospheric pressure, with CsI and bialkali photocathodes. They have single-photon sensitivity, ns time resolution and good localization properties. We summarize operational aspects and results, with the highlight of a high-gain stable gated operation of a visible-light device. Of particular importance are the results of a recent ion-backflow reduction study in different cascaded multipliers, affecting the detectors stability and the photocathodes liftime. We report on the significant progress in ion-blocking and provide first results on bialkali-photocathode aging under gas multiplication.
We review latest progress in gaseous photomultipliers (GPM) combining solid photocathodes and various types of novel electron multipliers. Cascaded gaseous electron multipliers (GEM) coated with CsI photocathodes can efficiently replace UVsensitive wire chambers for single-photon recording in Cherenkov and other detectors. Other hole-multipliers with patterned electrodes (Micro-Hole and Strip Plates) and improved ion-blocking properties are discussed; these permit reducing considerably photon- and ion-induced secondary effects. Photon detectors with other electron-multiplier techniques are briefly described, among them GPMs based on Micromegas, capillary-plates, Thick-GEMs and resistive Thick GEMs. The two latter techniques, robust and economically produced, are particularly suited for large-area GPM applications, e.g. in RICH. Cascaded hole-multipliers with very high ion-blocking performance permitted the development and the first demonstration of DC-operated visible-sensitive gaseous photomultipliers with bialkali photocathodes and single-photon sensitivity. Recent progress is described in GPMs operated at cryogenic temperatures for rare-event noble-liquid detectors and medical imaging.
The properties of UV-photon imaging detectors consisting of CsI-coated THGEM electron multipliers are summarized. New results related to detection of Cherenkov light (RICH) and scintillation photons in noble liquid are presented.
Position sensitive detectors based on gaseous scintillation proportional counters with Anger-type readout are being used in several research areas such as neutron detection, search for dark matter and neutrinoless double beta decay. Design and optimization of such detectors are complex and time consuming tasks. Simulations, while being a powerful tool, strongly depend on the light transport models and demand accurate knowledge of many parameters, which are often not available. Here we describe an alternative approach based on the experimental evaluation of a detector using an isotropic point-like light source with precisely controllable light emission properties, installed on a 3D positioning system. The results obtained with the developed setup at validation conditions, when the scattered light is strongly suppressed, show good agreement with simulations.
Future tonne-scale liquefied noble gas detectors depend on efficient light detection in the VUV range. In the past years Silicon Photomultipliers (SiPMs) have emerged as a valid alternative to standard photomultiplier tubes or large area avalanche photodiodes. The next generation double beta decay experiment, nEXO, with a 5 tonne liquid xenon time projection chamber, will use SiPMs for detecting the $178,text{nm}$ xenon scintillation light, in order to achieve an energy resolution of $sigma / Q_{betabeta} = 1, %$. This paper presents recent measurements of the VUV-HD generation SiPMs from Fondazione Bruno Kessler in two complementary setups. It includes measurements of the photon detection efficiency with gaseous xenon scintillation light in a vacuum setup and dark measurements in a dry nitrogen gas setup. We report improved photon detection efficiency at $175,text{nm}$ compared to previous generation devices, that would meet the criteria of nEXO. Furthermore, we present the projected nEXO detector light collection and energy resolution that could be achieved by using these SiPMs.
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