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The operation of Thick Gaseous Electron Multipliers (THGEM) in Ne and Ne/CH4 mixtures, features high multiplication factors at relatively low operation potentials, in both single- and double-THGEM configurations. We present some systematic data measured with UV-photons and soft x-rays, in various Ne mixtures. It includes gain dependence on hole diameter and gas purity, photoelectron extraction efficiency from CsI photocathodes into the gas, long-term gain stability and pulse rise-time. Position resolution of a 100x100 mm^2 X-rays imaging detector is presented. Possible applications are discussed.
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The article deals with the detection efficiency of UV-photon detectors consisting of Thick Gas Electron Multipliers (THGEM) coated with CsI photocathode, operated in atmospheric Ne/CH4 and Ne/CF4 mixtures. We report on the photoelectron extraction efficiency from the photocathode into these gas mixtures, and on the photoelectron collection efficiency into the THGEM holes. Full collection efficiency was reached in all gases investigated, in some cases at relatively low multiplication. High total detector gains for UV photons, in excess of 10^5, were reached at relatively low operation voltages with a single THGEM element. We discuss the photon detection efficiency in the context of possible application to RICH.
A detector has been constructed for measuring ion mobilities of gas mixtures at atmospheric pressure and room temperature. The detector consists of a standard triple GEM amplification region and a drift region where ions drift. A method has been developed to measure the ions arrival time at a cathode wire-grid by differentiating the recorded signals on this electrode. Simulations prove that this method is accurate and robust. The ion mobility in different gas mixtures is measured while applying different drift field values ranging from 200 V cm$^{-1}$ to 1100 V cm$^{-1}$. From an extrapolation of a Blancs law fit to measurements in Ar-CO$_2$ mixtures we find the reduced mobility of the drifting (cluster) ion species in pure argon to be $1.94pm0.01$ cm$^{2}$ V$^{-1}$ s$^{-1}$ and in pure carbon-dioxide to be $1.10pm0.01$ cm$^{2}$ V$^{-1}$ s$^{-1}$. Applying the same procedure to our measurements in Ne-CO$_2$ yields $4.06pm0.07$ cm$^{2}$ V$^{-1}$ s$^{-1}$ and $1.09pm0.01$ cm$^{2}$ V$^{- 1}$ s$^{-1}$ for the reduced mobilities in pure neon and carbon-dioxide, respectively. Admixtures of N$_2$ to Ne-CO$_2$ reduce somewhat the mobility. For the baseline gas mixture of the future ALICE Time Projection Chamber, Ne- CO$_2$-N$_{2}$ (90-10-5), the measured reduced mobility of the drifting ions is $2.92pm0.04$ cm$^{2}$ V$^{-1}$ s$^{-1}$. Ion mobilities are examined for different water content ranging from 70 ppm to about 2000 ppm in the gas using Ar-CO$_2$ (90-10) and Ne-CO$_2$ (90-10). A slight decrease of ion mobility is observed for the addition of several hundred ppm of water.
We present the results of our recent studies of a Thick Gaseous Electron Multiplier (THGEM)-based detector, operated in Ar, Xe and Ar:Xe (95:5) at various gas pressures. Avalanche-multiplication properties and energy resolution were investigated with soft x-rays for different detector configurations and parameters. Gains above 10E4 were reached in a double-THGEM detector, at atmospheric pressure, in all gases, in almost all the tested conditions; in Ar:Xe (95:5) similar gains were reached at pressures up to 2 bar. The energy resolution dependence on the gas, pressure, hole geometry and electric fields was studied in detail, yielding in some configurations values below 20% FWHM with 5.9 keV x-rays.
The PADME experiment at the DA$Phi$NE Beam-Test Facility (BTF) aims at searching for invisible decays of the dark photon by measuring the final state missing mass in the process $e^+e^- to gamma+ A$, with $A$ undetected. The measurement requires the determination of the 4-momentum of the recoil photon, performed using a homogeneous, highly segmented BGO crystals calorimeter. We report the results of the test of a 5$times$5 crystals prototype performed with an electron beam at the BTF in July 2016.
Sorption and the subsequent desorption of 4He, H2,Ne, N2, CH4 and Kr gas impurities by graphene oxide (GO), glucose-reduced GO (RGO-Gl) and hydrazine-reduced GO (RGO-Hz) powders have been investigated in the temperature interval 2-290 K. It has been found that the sorptive capacity of the reduced sample RGO-Hz is three to six times higher than that of GO. The reduction of GO with glucose has only a slight effect on its sorptive properties. The temperature dependences of the diffusion coefficients of the GO, RGO-Gl and RGO-Hz samples have been obtained using the measured characteristic times of sorption. It is assumed that the temperature dependences of the diffusion coefficients are determined by the competition of the thermally activated and tunneling mechanisms, the tunneling contribution being dominant at low temperatures.
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