MHSP in reversed-biased operation mode for ion blocking in gas-avalanche multipliers

We present recent results on the operation of gas-avalanche detectors comprising a cascade of gas electron multipliers (GEMs) and Micro-Hole and Strip Plates (MHSPs) multiplier operated in reversed-bias (R-MHSP) mode. The operation mechanism of the R-MHSP is explained and its potential contribution to ion-backflow (IBF) reduction is demonstrated. IBF values of 4E-3 were obtained in cascaded R-MHSP and GEM multipliers at gains of about 1E+4, though at the expense of reduced effective gain in the first R- MHSP multiplier in the cascade.Comment: 23 pages, 8 figure

Ion-induced effects in GEM & GEM/MHSP gaseous photomultipliers for the UV and the visible spectral range

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 detector's stability and the photocathode's liftime. We report on the significant progress in ion-blocking and provide first results on bialkali-photocathode aging under gas multiplication.Comment: 6 pages, 8 figure

Avalanche-ion back-flow reduction in gaseous electron multipliers based on GEM/MHSP

We report on avalanche-ion back-flow measurements in the novel Micro-Hole and Strip-Plate (MHSP) multiplier and in gaseous photomultipliers comprising Gas Electron Multipliers (GEMs) followed by an MHSP. In a 3-GEMs/MHSP photomultiplier with reflective photocathode, avalanche-ion back-flow fraction of ~7% and ~2% were recorded for respective effective gains of 107 and 106, in Ar/CH4 (95/5) at 760 Torr. This is about one order of magnitude reduction in ion back-flow compared to the best values measured in 4-GEMs photomultiplier at the same gain. We describe the mode of operation of the MHSP and explain its ion back-flow reduction features.http://www.sciencedirect.com/science/article/B6TJM-4BMBDH7-C/1/cdedfd1e72d3adbcfc9431895ab3e61

Single crystal hall effect and stoichiometry in ‘Bi2Sr2CuO6’

Crystals of the material with the nominal composition Bi2Sr2CuO6 exist as an oxygen deficient solid solution in which strontium atoms are replaced by bismuth. Results are presented from a series of measurements of the Hall coefficient as a function of temperature on crystals from across the range of stoichiometry. In superconducting crystals the Hall coefficient has a maximum at 70K which is shown to be a property of the normal state