3,899 research outputs found

    EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

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    The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposedPublisher PDFPeer reviewe

    An ultra-light cylindrical GEM detector as inner tracker at KLOE-2

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    Abstract We are developing a low-mass, fully cylindrical and dead-zone-free GEM detector as inner tracker for the KLOE experiment upgrade at the DA Φ NE Φ factory. The inner tracker will be composed of five concentric layers of cylindrical triple-GEM detectors (C-GEM), completely realized with very thin polyimide foils. The final result is a very light detector: only 0.2% of X 0 per layer inside the active area. We successfully built and tested with an X-ray gun a small-size prototype operated in current mode with an Ar/CO 2 = 70 / 30 gas mixture. The very positive results obtained with the prototype open the way for a completely new and competitive category of ultra-light fully sensitive vertex detectors for high-energy physics experiments

    A glass spark counter for high rate environments

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    The performance of a glass spark counter prototype, built with glass electrodes of about 1010 Ω cm volume resistivity, is described. The measure

    High-resolution tracking in a GEM-Emulsion detector

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    SHiP (Search for Hidden Particles) is a beam dump experiment proposed at the CERN SPS aiming at the observation of long lived particles very weakly coupled with ordinary matter mostly produced in the decay of charmed hadrons. The beam dump facility of SHiP is also a copious factory of neutrinos of all three kinds and therefore a dedicated neutrino detector is foreseen in the SHiP apparatus. The neutrino detector exploits the Emulsion Cloud Chamber technique with a modular structure, alternating walls of target units and planes of electronic detectors providing the time stamp to the event. GEM detectors are one of the possible choices for this task. This paper reports the results of the first exposure to a muon beam at CERN of a new hybrid chamber, obtained by coupling a GEM chamber and an emulsion detector. Thanks to the micrometric accuracy of the emulsion detector, the position resolution of the GEM chamber as a function of the particle inclination was evaluated in two configurations, with and without the magnetic fiel

    u-RANIA: a neutron detector based on \mu -RWELL technology

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    In the framework of the ATTRACT-uRANIA project, funded by the European Community, we are developing an innovative neutron imaging detector based on micro-Resistive WELL (μ\mu -RWELL) technology. The μ\mu -RWELL, based on the resistive detector concept, ensuring an efficient spark quenching mechanism, is a highly reliable device. It is composed by two main elements: a readout-PCB and a cathode. The amplification stage for this device is embedded in the readout board through a resistive layer realized by means of an industrial process with DLC (Diamond-Like Carbon). A thin layer of B4_4C on the copper surface of the cathode allows the thermal neutrons detection through the release of 7^7Li and α\alpha particles in the active volume. This technology has been developed to be an efficient and convenient alternative to the 3^3He shortage. The goal of the project is to prove the feasibility of such a novel neutron detector by developing and testing small planar prototypes with readout boards suitably segmented with strip or pad read out, equipped with existing electronics or readout in current mode. Preliminary results from the test with different prototypes, showing a good agreement with the simulation, will be presented together with construction details of the prototypes and the future steps of the project.Comment: Prepared for the INSTR20 Conference Proceeding for JINS

    Status of the Cylindical-GEM project for the KLOE-2 Inner Tracker

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    The status of the R&D on the Cylindrical-GEM (CGEM) detector foreseen as Inner Tracker for KLOE-2, the upgrade of the KLOE experiment at the DAFNE phi-factory, will be presented. The R&D includes several activities: i) the construction and complete characterization of the full-size CGEM prototype, equipped with 650 microns pitch 1-D longitudinal strips; ii) the study of the 2-D readout with XV patterned strips and operation in magnetic field (up to 1.5T), performed with small planar prototypes in a dedicated test at the H4-SPS beam facility; iii) the characterization of the single-mask GEM technology for the realization of large-area GEM foils.Comment: 4 pages, 10 figures, Presented at Vienna Conference on Instrumentation (Feb 15-20, 2010, Vienna, Austria). Submitted to the Proceeding

    Synthesis of Atropisomeric Hydrazides by One-Pot Sequential Enantio- and Diastereoselective Catalysis

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    The first catalytic enantioselective and diastereoselective synthesis of atropisomeric hydrazides was achieved using a sequential catalysis protocol. This strategy is based on a one-pot sequence of two organocatalytic cycles featuring the enamine amination of branched aldehydes followed by nitrogen alkylation under phase-transfer conditions. The resulting axially chiral hydrazides were obtained directly from commercially available reagents in high yields and with good stereocontrol. The permutation of organocatalysts allowed easy access to all stereoisomers, enabling a stereodivergent approach to enantioenriched atropisomeric hydrazides

    The micro-RWELL layouts for high particle rate

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    The μ\mu-RWELL is a single-amplification stage resistive Micro-Pattern Gaseous Detector (MPGD). The detector amplification element is realized with a single copper-clad polyimide foil micro-patterned with a blind hole (well) matrix and embedded in the readout PCB through a thin Diamond-Like-Carbon (DLC) sputtered resistive film. The introduction of the resistive layer, suppressing the transition from streamer to spark, allows to achieve large gains (≥\geq104^4) with a single amplification stage, while partially reducing the capability to stand high particle fluxes. The simplest resistive layout, designed for low-rate applications, is based on a single-resistive layer with edge grounding. At high particle fluxes this layout suffers of a non-uniform response. In order to get rid of such a limitation different current evacuation geometries have been designed. In this work we report the study of the performance of several high rate resistive layouts tested at the CERN H8-SpS and PSI π\piM1 beam test facilities. These layouts fulfill the requirements for the detectors at the HL-LHC and for the experiments at the next generation colliders FCC-ee/hh and CepC

    A triple GEM gamma camera for medical application

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    Abstract A Gamma Camera for medical applications 10 × 10 cm 2 has been built using a triple GEM chamber prototype. The photon converters placed in front of the three GEM foils, has been realized with different technologies. The chamber, High Voltage supplied with a new active divider made in Frascati, is readout through 64 pads, 1 mm 2 wide, organized in a row of 8 cm long, with LHCb ASDQ chip. This Gamma Camera can be used both for X-ray movie and PET-SPECT imaging; this chamber prototype is placed in a scanner system, creating images of 8 × 8 cm 2 . Several measurements have been performed using phantom and radioactive sources of Tc 99 m ( 140 keV ) and Na 22 ( 511 keV ) . Results on spatial resolution and image reconstruction are presented
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