Triple-GEM detectors with pad readout have been employed to equip the innermost region (R1) of the first station (M1) within the Muon system of the LHCb experiment. The GEM detectors have been ...operated with an Ar/CO2/CF4 = 45/15/40 gas mixture at a gas gain of about 4000 with an average particle flux of about 250 kHz/cm2. Throughout RUN1 and RUN2, spanning approximately 440 days of colliding beams, the GEM detectors accumulated a charge of up to 0.5 C/cm2. This paper presents a comparative analysis between a global irradiation test of GEM detectors at the Calliope facility (ENEA-Casaccia, 1.25 MeV γ ray flux from a 60Co source) and the GEMs operated at LHCb, focusing on the impacts of a CF4-based gas mixture. In both instances, the detectors were opened and the GEM foils were examined by the EN-MME-MM CERN group with a Field Emission Gun Scanning Electron Microscope (FEG-SEM) for a magnified image analysis and an X-Max Energy Dispersive X-ray Spectroscopy (EDS) for the chemical one.
The combination of neutron time-of-flight spectroscopy and longitudinal polarization analysis opens up the possibility of simultaneously separating cross-section components over vast regions in ...(Q,ΔE) space. In this paper, we describe initial results of a project to install longitudinal polarization analysis on the LET cold neutron spectrometer at the ISIS Neutron and Muon Facility; namely, the design and commissioning of the polarizing primary spectrometer. The polarized neutron beam is generated by a supermirror-based transmission device, for which ray tracing simulations indicate a high neutron polarization P∼96% and transmission T∼40%. Despite the short distance between this device and the precession coil flipper, and the consequent large stray magnetic fields on the latter, careful optimization of the field environment yields predictions of excellent flipping performance ∼99%. Both simulation results are confirmed via measurements using a polarizing Cu2MnAl Heusler crystal as an analyzer.
We report on the design and construction of a neutron polarization analyzer based on a 3He spin filter for the LET spectrometer at the ISIS facility. Its commissioning completes the uniaxial ...polarized mode of the instrument. Besides the 3He spin filter cell, the analyzer consists of a set of electromagnetic coils to provide a uniform magnetic field, and a collimator to eliminate background from the sample environment and analyzer infrastructure. The 3He cell is separated from the LET main tank vacuum by means of a gas tank, which permits rapid cell changeovers and guarantees safe operation. In addition to the analyzer hardware, software has been written to reduce and correct polarized data. The successful operation of the polarized mode was realized for the separation of coherent and incoherent dynamics in an organic solar cell polymer blend.
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