1,968 research outputs found
Comparison between high-energy proton and charged pion induced damage in Lead Tungstate calorimeter crystals
A Lead Tungstate crystal produced for the electromagnetic calorimeter of the
CMS experiment at the LHC was cut into three equal-length sections. The central
one was irradiated with 290 MeV/c positive pions up to a fluence of (5.67 +-
0.46)x10^13 /cm^2, while the other two were exposed to a 24 GeV/c proton
fluence of (1.17 +- 0.11) x 10^13/ cm^2. The damage recovery in these crystals,
stored in the dark at room temperature, has been followed over two years. The
comparison of the radiation-induced changes in light transmission for these
crystals shows that damage is proportional to the star densities produced by
the irradiation.Comment: 7 pages, 4 figure
Detection of Cherenkov light from air showers with Geiger-APDs
We have detected Cherenkov light from air showers with Geiger-mode APDs
(G-APDs). G-APDs are novel semiconductor photon-detectors, which offer several
advantages compared to conventional photomultiplier tubes in the field of
ground-based gamma-ray astronomy. In a field test with the MAGIC telescope we
have tested the efficiency of a G-APD / light catcher setup to detect Cherenkov
light from air showers. We estimate a detection efficiency, which is 60% higher
than the efficiency of a MAGIC camera pixel. Ambient temperature dark count
rates of the tested G-APDs are below the rates of the night sky light
background. According to these recent tests G-APDs promise a major progress in
ground-based gamma-ray astronomy.Comment: 4 pages, 5 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
Infrared scintillation yield in gaseous and liquid argon
The study of primary and secondary scintillations in noble gases and liquids
is of paramount importance to rare-event experiments using noble gas media. In
the present work, the scintillation yield in gaseous and liquid Ar has for the
first time been measured in the near infrared (NIR) and visible region, both
for primary and secondary (proportional) scintillations, using Geiger-mode
avalanche photodiodes (G-APDs) and pulsed X-ray irradiation. The primary
scintillation yield of the fast component was measured to be 17000 photon/MeV
in gaseous Ar in the NIR, in the range of 690-1000 nm, and 510 photon/MeV in
liquid Ar, in the range of 400-1000 nm. Proportional NIR scintillations
(electroluminescence) in gaseous Ar have been also observed; their
amplification parameter at 163 K was measured to be 13 photons per drifting
electron per kV. Possible applications of NIR scintillations in high energy
physics experiments are discussed.Comment: 6 pages, 5 figures. Submitted to Europhysics Letter. Revised Figs. 3
and
Non-adiabatic effects in the phonon dispersion of Mg 1--x Al x B 2
Superconducting MgB shows an E zone center phonon, as measured
by Raman spectroscopy, that is very broad in energy and temperature dependent.
The Raman shift and lifetime show large differences with the values elsewhere
in the Brillouin Zone measured by Inelastic X-ray Scattering (IXS), where its
dispersion can be accounted for by standard harmonic phonon theory, adding only
a moderate electron-phonon coupling. Here we show that the effects rapidly
disappear when electron-phonon coupling is switched off by Al substitution on
the Mg sites. Moreover, using IXS with very high wave-vector resolution in
MgB, we can follow the dispersion connecting the Raman and the IXS signal,
in agreement with a theory using only electron-phonon coupling but without
strong anharmonic terms. The observation is important in order to understand
the effects of electron-phonon coupling on zone center phonons modes in
MgB, but also in all metals characterized by a small Fermi velocity in a
particular direction, typical for layered compounds
Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer
We have measured scintillation properties of pure CsI crystals used in the
shower calorimeter built for a precise determination of the pi+ -> pi0 e+ nu
decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals
painted with a special wavelength-shifting solution were examined in a
custom-build detection apparatus (RASTA=radioactive source tomography
apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light
emitting diode as complementary probes of the scintillator light response. We
have extracted the total light output, axial light collection nonuniformities
and timing responses of the individual CsI crystals. These results predict
improved performance of the 3 pi sr PIBETA calorimeter due to the painted
lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment
did not affect appreciably the total light output and timing resolution of our
crystal sample. The predicted energy resolution for positrons and photons in
the energy range of 10-100 MeV was nevertheless improved due to the more
favorable axial light collection probability variation. We have compared
simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a
Monte Carlo calculation of an ideal detector light response.Comment: Elsevier LaTeX, 35 pages in e-print format, 15 Postscript Figures and
4 Tables, also available at
http://pibeta.phys.virginia.edu/~pibeta/subprojects/csipro/tomo/rasta.p
A novel camera type for very high energy gamma-ray astronomy based on Geiger-mode avalanche photodiodes
Geiger-mode avalanche photodiodes (G-APD) are promising new sensors for light
detection in atmospheric Cherenkov telescopes. In this paper, the design and
commissioning of a 36-pixel G-APD prototype camera is presented. The data
acquisition is based on the Domino Ring Sampling (DRS2) chip. A sub-nanosecond
time resolution has been achieved. Cosmic-ray induced air showers have been
recorded using an imaging mirror setup, in a self-triggered mode. This is the
first time that such measurements have been carried out with a complete G-APD
camera.Comment: 9 pages with 11 figure
Scintillation counter with MRS APD light readout
START, a high-efficiency and low-noise scintillation detector for ionizing
particles, was developed for the purpose of creating a high-granular system for
triggering cosmic muons. Scintillation light in START is detected by MRS APDs
(Avalanche Photo-Diodes with Metal-Resistance-Semiconductor structure),
operated in the Geiger mode, which have 1 mm^2 sensitive areas. START is
assembled from a 15 x 15 x 1 cm^3 scintillating plastic plate, two MRS APDs and
two pieces of wavelength-shifting optical fiber stacked in circular coils
inside the plastic. The front-end electronic card is mounted directly on the
detector. Tests with START have confirmed its operational consistency, over 99%
efficiency of MIP registration and good homogeneity. START demonstrates a low
intrinsic noise of about 10^{-2} Hz. If these detectors are to be
mass-produced, the cost of a mosaic array of STARTs is estimated at a moderate
level of 2-3 kUSD/m^2.Comment: 6 pages, 5 figure
On the low-temperature performances of THGEM and THGEM/G-APD multipliers in gaseous and two-phase Xe
The performances of THGEM multipliers in two-phase Xe avalanche mode are
presented for the first time. Additional results on THGEM operation in gaseous
Xe at cryogenic temperatures are provided. Stable operation of a double-THGEM
multiplier was demonstrated in two-phase Xe with gains reaching 600. These are
compared to existing data, summarized here for two-phase Ar, Kr and Xe
avalanche detectors incorporating GEM and THGEM multipliers. The optical
readout of THGEMs with Geiger-mode Avalanche Photodiodes (G-APDs) has been
investigated in gaseous Xe at cryogenic temperature; avalanche scintillations
were recorded in the Near Infrared (NIR) at wavelengths of up to 950 nm. At
avalanche charge gain of 350, the double-THGEM/G-APD multiplier yielded 0.07
photoelectrons per initial ionization electron, corresponding to an avalanche
scintillation yield of 0.7 NIR photons per avalanche electron over 4pi. The
results are compared with those of two-phase Ar avalanche detectors. The
advantages, limitations and possible applications are discussed.Comment: 22 pages, 14 figures. Revised Figs. 10,11 and Table 1. To be
published in JINS
Lattice dynamics and electron-phonon coupling in transition metal diborides
The phonon density-of-states of transition metal diborides TMB2 with TM = Ti,
V, Ta, Nb and Y has been measured using the technique of inelastic neutron
scattering. The experimental data are compared with ab initio density
functional calculations whereby an excellent agreement is registered. The
calculations thus can be used to obtain electron-phonon spectral functions
within the isotropic limit. A comparison to similar data for MgB2 and AlB2
which were subject of prior publications as well as parameters important for
the superconducting properties are part of the discussion.Comment: 4 pages, 3 figure
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