MPGDs in Compton imaging with liquid-xenon

The interaction of radiation with liquid xenon, inducing both scintillation and ionization signals, is of particular interest for Compton-sequences reconstruction. We report on the development and recent results of a liquid-xenon time-projection chamber, dedicated to a novel nuclear imaging technique named "3 gamma imaging". In a first prototype, the scintillation is detected by a vacuum photomultiplier tube and the charges are collected with a MICROMEGAS structure; both are fully immersed in liquid xenon. In view of the final large-area detector, and with the aim of minimizing dead-zones, we are investigating a gaseous photomultiplier for recording the UV scintillation photons. The prototype concept is presented as well as preliminary results in liquid xenon. We also present soft x-rays test results of a gaseous photomultiplier prototype made of a double Thick Gaseous Electron Multiplier (THGEM) at normal temperature and pressure conditions.Comment: presented at MPGD09, CRETE, June 2009; to be published in JINST Proceedings, PDF, 10 pages, 11 figure

On the operation of a Micropattern Gaseous UV-Photomultiplier in Liquid-Xenon

Operation results are presented of a UV-sensitive gaseous photomultiplier (GPM) coupled through a MgF2 window to a liquid-xenon scintillator. It consisted of a reflective CsI photocathode deposited on top of a THick Gaseous Electron Multiplier (THGEM); further multiplication stages were either a second THGEM or a Parallel Ionization Multiplier (PIM) followed by a MICROMEsh GAseous Structure (MICROMEGAS). The GPM operated in gas-flow mode with non-condensable gas mixtures. Gains of 10^4 were measured with a CsI-coated double-THGEM detector in Ne/CH4 (95:5), Ne/CF4 (95:5) and Ne/CH4/CF4 (90:5:5), with soft X-rays at 173 K. Scintillation signals induced by alpha particles in liquid xenon were measured here for the first time with a double-THGEM GPM in He/CH4 (92.5:7.5) and a triple-structure THGEM/PIM/MICROMEGAS GPM in Ne/CH4 (90:10) with a fast-current preamplifier.Comment: 12 pages, 9 figures, submitted to JINS

Structural-Properties Of Amorphous Hydrogenated Carbon .3. NMR Investigations

Our NMR studies give experimental evidence of bonding heterogeneity in samples of a-C:H on the nanometer scale. Two classes of protons were identified with distinctly different spin-lattice-relaxation behavior. The difference in the spin-lattice relaxation provides a means of spectral editing of cross-polarization magic-angle spinning, combined rotation and multiple-pulse spectroscopy, dipolar dephasing spectra, and multiple quantum NMR experiments. This combination of the various NMR techniques allows for a detailed structural investigation of a-C:H, e.g., the sp2:sp3 ratio, the relative amount of hydrogenated and nonhydrogenated carbons, etc. A model incorporating the heterogeneity is established and discussed. The NMR results are compared with neutron spectroscopy and diffraction data

A nuclear magnetic resonance study of Al-Mn quasicrystals and related materials

Nuclear magnetic resonance (NMR) results are presented for several aluminum alloy samples prepared using the melt-spinning technique including orthorhombic Al6Mn, Al-Mn quasicrystals both with and without doping with Si and Ru, and a T-phase alloy of A1 and Pt. With the exception of the orthorhombic material, all of the NMR spectra show a broad distribution of sites. No features unique to the quasicrystal phase are observed. For the orthorhombic material the quadrupole field parameters are found to be| vQ | = 1.0 ± 0.1 MHz and 77 = 0.4 + 0.1. © 1987, Materials Research Society. All rights reserved