Breakdown Limit Studies in High Rate Gaseous Detectors

We report results from a systematic study of breakdown limits for novel high rate gaseous detectors: MICROMEGAS, CAT and GEM, together with more conventional devices such as thin-gap parallel-mesh chambers and high-rate wire chambers. It was found that for all these detectors, the maximum achievable gain, before breakdown appears, drops dramatically with incident flux, and is sometimes inversely proportional to it. Further, in the presence of alpha particles, typical of the backgrounds in high-energy experiments, additional gain drops of 1-2 orders of magnitude were observed for many detectors. It was found that breakdowns at high rates occur through what we have termed an "accumulative" mechanism, which does not seem to have been previously reported in the literature. Results of these studies may help in choosing the optimum detector for given experimental conditions

High Resolution RPC's for Large TOF Systems

Here we report on a particular type of RPC that presents up to 99% efficiency for minimum ionizing particles and a very sharp time resolution, below 50 ps sigma in the most optimized conditions. Our 9 cm2 cells, made with glass and metal electrodes that form accurately spaced gaps of a few hundred micrometers, are operated at atmospheric pressure in non-flammable gases and can be economically produced in large quantities, opening perspectives for the construction of large area time of flight systems.Comment: 10 pages, 8 figure

Measurements of Scintillation Efficiency and Pulse-Shape for Low Energy Recoils in Liquid Xenon

Results of observations of low energy nuclear and electron recoil events in liquid xenon scintillator detectors are given. The relative scintillation efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40 keV - 70 keV. Under the assumption of a single dominant decay component to the scintillation pulse-shape the log-normal mean parameter T0 of the maximum likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~ 15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by single exponential functions although some evidence is found for a double exponential form for the nuclear recoil pulse-shape.Comment: 11 pages, including 5 encapsulated postscript figure

The HERA-B Ring Imaging Cherenkov Counter

The HERA-B RICH uses a radiation path length of 2.8 m in C_4F_10 gas and a large 24 square meters spherical mirror for imaging Cherenkov rings. The photon detector consists of 2240 Hamamatsu multi-anode photomultipliers with about 27000 channels. A 2:1 reducing two-lens telescope in front of each PMT increases the sensitive area at the expense of increased pixel size, resulting in a contribution to the resolution which roughly matches that of dispersion. The counter was completed in January of 1999, and its performance has been steady and reliable over the years it has been in operation. The design performance of the RICH was fully reached: the average number of detected photons in the RICH for a beta=1 particle was found to be 33 with a single hit resolution of 0.7 mrad and 1 mrad in the fine and coarse granularity regions, respectively.Comment: 29 pages, 23 figure

Liquid Cryogen Absorber for MICE

The Muon Ionization Cooling Experiment (MICE) will test ionization cooling of muons. In order to have effective ionization cooling, one must use an absorber that is made from a low-z material. The most effective low z materials for ionization cooling are hydrogen, helium, lithium hydride, lithium and beryllium, in that order. In order to measure the effect of material on cooling, several absorber materials must be used. This report describes a liquid-hydrogen absorber that is within a pair of superconducting focusing solenoids. The absorber must also be suitable for use with liquid helium. The following absorber components are discussed in this report; the absorber body, its heat exchanger, the hydrogen system, and the hydrogen safety. Absorber cooling and the thin windows are not discussed here

A pair production telescope for medium-energy gamma-ray polarimetry

We describe the science motivation and development of a pair production telescope for medium-energy (∼5–200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (∼0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3 × 10−6 MeV cm−2 s−1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 106 s.submittedVersionFil: Hunter, Stanley D. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Bloser, Peter F. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Depaola, Gerardo Osvaldo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Dion, Michael P. Department of Energy. Office of Science. Pacific Northwest National Laboratory; Estados Unidos de América.Fil: DeNolfo, Georgia A. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Hanu, Andrei. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Iparraguirre, Lorenzo Marcos. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Legere, Jason. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Longo, Francesco. Università Degli Studi de Trieste. Dipartimento di fisica; Italia.Fil: McConnell, Mark L. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Nowicki, Suzanne F. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Nowicki, Suzanne F. University of Maryland, Baltimore County. Department of Physics; Estados Unidos de América.Fil: Ryan, James M. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Son, Seunghee. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Son, Seunghee. University of Maryland, Baltimore County. Department of Physics; Estados Unidos de América.Fil: Stecker, Floyd W. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Física de Partículas y Campo

Breakdown limit studies in high-rate gaseous detectors

We report results from a systematic study of breakdown limits for novel high-rate gaseous detectors: MICROMEGAS, CAT and GEM, together with more conventional devices such as thin-gap parallel-mesh chambers and high-rate wire chambers. It was found that for all these detectors, the maximum achievable gain, before breakdown appears, drops dramatically with incident flux, and is sometimes inversely proportional to it. Further, in the presence of alpha particles, typical of the breakgrounds in high-energy experiments, additional gain drops of 1-2 orders of magnitude were observed for many detectors. It was found that breakdowns at high rates occur through what we have termed an "accumulative" mechanism, which does not seem to have been previously reported in the literature. Results of these studies may help in choosing the optimum detector for given experimental conditions.http://www.sciencedirect.com/science/article/B6TJM-3VR1CVW-25/1/9bfb8c65132c9b4b8673fa6d100f916