39 research outputs found
Investigations of a THGEM-based imaging detector
We present the results of our recent studies on a Thick Gas Electron
Multiplier (THGEM)-based imaging detector prototype. It consists of two 100x100
mm^2 THGEM electrodes in cascade, coupled to a resistive anode. The event
location is recorded with a 2D double-sided readout electrode equipped with
discrete delay-lines and dedicated electronics. The THGEM electrodes, produced
by standard printed-circuit board and mechanical drilling techniques, a 0.4 mm
thick with 0.5 mm diameter holes spaced by 1 mm. Localization resolutions of
about 0.7 mm (FWHM) were measured with soft x-rays, in a detector operated with
atmospheric-pressure Ar/CH4; good linearity and homogeneity were achieved. We
describe the imaging-detector layout, the resistive-anode 2D readout system and
the imaging properties. The THGEM has numerous potential applications that
require large-area imaging detectors, with high-rate capability,
single-electron sensitivity and moderate (sub-mm) localization resolution.Comment: Published in JINST, 22 pages, 18 figure
Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy
Electronic autoionization in molecular ion formation
A phenomenological description of molecular electronic autoionizatlon is given. It is shown how the degree of autoionization competing with neutral fluorescence and dissociation can be estimated from photoionization data alone. A discussion is presented of the effect of electronic autoionization on electronic and vibrational branching ratios in photoionization cross sections, as well as on ion yield curves. All the effects are documented by experimental examples
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Photelectron-photoion coincidence spectroscopy
Achievements of the technique of photoelectron-photoion coincidence measurements since 1967 are reviewed
Triple ionization spectra by coincidence measurements of double Auger decay : The case of OCS
By combining multiple electron coincidence detection with ionization by synchrotron radiation, we have obtained resolved spectra of the OCS3+ ion created through the double Auger effect. The form of the spectra depends critically on the identity of the atom bearing the initial hole. High and intermediate level electron structure calculations lead to an assignment of the resolved spectrum from ionization via the S 2p hole. From the analysis it appears that the double Auger effect from closed shell molecules favors formation of doublet states over quartet states. Molecular field effects in the double Auger effect are similar to those in the single Auger effect in linear molecules
Triple ionisation of methane by double Auger and related pathways
Triple ionisation of methane by decay of the singly charged ion with a 1s vacancy produces a trication spectrum starting near 70 eV binding energy. Vibrational excitation in the initial hole state broadens and shifts the triple ionisation bands. Ionisation through core-valence doubly ionised states gives lower triple ionisation onsets and changes the spectral intensity pattern in accordance with retention of the initial valence holes in course of the double Auger effect. The double Auger effects occur both directly and as cascades, the different pathways producing different electron distributions and final state spectra. (C) 2009 Elsevier B. V. All rights reserved