653 research outputs found
A Study of the LXeGRIT Detection Efficiency for MeV Gamma-Rays during the 2000 Balloon Flight Campaign
LXeGRIT - Liquid Xenon Gamma-Ray Imaging Telescope - is the first prototype
of a Compton telescope for \MeV \g-ray astrophysics based on a LXe time
projection chamber. One of the most relevant figures of merit for a Compton
telescope is the detection efficiency for \g-rays, which depends on diverse
contributions such as detector geometry and passive materials, trigger
efficiency, dead time, etc. A detailed study of the efficiency of the LXeGRIT
instrument, based both on laboratory measurements and Monte Carlo simulations,
is presented in this paper.Comment: 20 pages, 15 figures; submitted to NIM
Effect of CH addition on excess electron mobility in liquid Kr
The excess electrons mobility has been measured recently in liquid
mixtures of Kr and CH as a function of the electric field up to and of the CH concentration up to at
temperatures fairly close to the normal boiling point of Kr
(folegani). We present here new data which extend the
previous set in the region of low electric field. The experimental results are
interpreted in terms of a kinetic model previously proposed to explain the
concentration dependent behavior of in liquid Ar--Kr and Ar--Xe mixtures.
The main result is that CH is more effective in enhancing
energy--transfer rather than momentum--transfer in comparison with mixtures of
liquified noble gases. The field dependence of is quite complicate. In
particular, at intermediate values of the field, there appears to be a
crossover between two different electric--field dependent behaviors of
The electric field strength at crossover is well correlated with the
concentration of CH This fact suggests that different excitations of the
molecular solute might be involved in the momentum-- and energy--transfer
processes for different values of the mean electron energy.Comment: 17, pages,7 figures, RevTeX4, submitted to J.Chem.Phy
Performance evaluation of novel square-bordered position-sensitive silicon detectors with four-corner readout
We report on a recently developed novel type of large area (62 mm x 62 mm)
position sensitive silicon detector with four-corner readout. It consists of a
square-shaped ion-implanted resistive anode framed by additional
low-resistivity strips with resistances smaller than the anode surface
resistance by a factor of 2. The detector position linearity, position
resolution, and energy resolution were measured with alpha-particles and heavy
ions. In-beam experimental results reveal a position resolution below 1 mm
(FWHM) and a very good non-linearity of less than 1% (rms). The energy
resolution determined from 228Th alpha source measurements is around 2% (FWHM).Comment: 13 pages, 10 figures, submitted to Nucl. Instr. and Meth.
Performance and Fundamental Processes at Low Energy in a Two-Phase Liquid Xenon Dark Matter Detector
We extend the study of the performance of a prototype two-phase liquid xenon
WIMP dark matter detector to recoil energies below 20 keV. We demonstrate a new
method for obtaining the best estimate of the energies of events using a
calibrated sum of charge and light signals and introduce the corresponding
discrimination parameter, giving its mean value at 4 kV/cm for electron and
nuclear recoils up to 300 and 100 keV, respectively. We show that fluctuations
in recombination limit discrimination for most energies, and reveal an
improvement in discrimination below 20 keV due to a surprising increase in
ionization yield for low energy electron recoils. This improvement is crucial
for a high-sensitivity dark matter search.Comment: 4 pages, 6 figures, submitted to DM06 conference proceedings in Nucl
Phys
Detection of Noble Gas Scintillation Light with Large Area Avalanche Photodiodes (LAAPDs)
Large Area Avalanche Photodiodes (LAAPDs) were used for a series of
systematic measurements of the scintillation light in Ar, Kr, and Xe gas.
Absolute quantum efficiencies are derived. Values for Xe and Kr are consistent
with those given by the manufacturer. For the first time we show that argon
scintillation (128 nm) can be detected at a quantum efficiency above 40%.
Low-pressure argon gas is shown to emit significant amounts of non-UV
radiation. The average energy expenditure for the creation of non-UV photons in
argon gas at this pressure is measured to be below 378 eV.Comment: 16 pages, 7 figure
Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration
We report the preparation of neutron-activated xenon for the calibration of
liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable
states, produced by fast neutron activation, were detected and their activities
measured in a LXe scintillation detector. Following a five-day activation of
natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two
gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable
states, were measured at about 95 and 130 Bq/kg, respectively. We also observed
three additional lines at 35 keV, 100 keV and 275 keV, which decay away within
a few days. No long-lifetime activity was observed after the neutron
activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the
previous versio
High-Temperature Superconducting Level Meter for Liquid Argon Detectors
Capacitive devices are customarily used as probes to measure the level of
noble liquids in detectors operated for neutrino studies and dark matter
searches. In this work we describe the use of a high-temperature
superconducting material as an alternative to control the level of a cryogenic
noble liquid. Lab measurements indicate that the superconductor shows a linear
behaviour, a high degree of stability and offers a very accurate determination
of the liquid volume. This device is therefore a competitive instrument and
shows several advantages over conventional level meters.Comment: 13 pages, 11 figures. Accepted for publication in JINS
Spectroscopy and Imaging Performance of the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)
LXeGRIT is a balloon-borne Compton telescope based on a liquid xenon time
projection chamber (LXeTPC) for imaging cosmic \g-rays in the energy band of
0.2-20 MeV. The detector, with 400 cm area and 7 cm drift gap, is filled
with high purity LXe. Both ionization and scintillation light signals are
detected to measure the energy deposits and the three spatial coordinates of
individual \g -ray interactions within the sensitive volume. The TPC has been
characterized with repeated measurements of its spectral and Compton imaging
response to \g -rays from radioactive sources such as \na, \cs, \yt and Am-Be.
The detector shows a linear response to \g -rays in the energy range 511 keV
-4.4 MeV, with an energy resolution (FWHM) of \Delta E/E=8.8% \: \sqrt{1\MeV
/E}. Compton imaging of \yt \g -ray events with two detected interactions is
consistent with an angular resolution of 3 degrees (RMS) at 1.8 MeV.Comment: To appear in: Hard X-Ray, Gamma-Ray and Neutron Detector Physics XI,
2000; Proc. SPIE, vol. 4140; K.A. Flanagan & O.H. Siegmund, ed
Compton Imaging of MeV Gamma-Rays with the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)
The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is the first
realization of a liquid xenon time projection chamber for Compton imaging of
MeV gamma-ray sources in astrophysics. By measuring the energy deposit and the
three spatial coordinates of individual gamma-ray scattering points, the
location of the source in the sky is inferred with Compton kinematics
reconstruction. The angular resolution is determined by the detector's energy
and spatial resolutions, as well as by the separation in space between the
first and second scattering. The imaging response of LXeGRIT was established
with gamma-rays from radioactive sources, during calibration and integration at
the Columbia Astrophysics Laboratory, prior to the 2000 balloon flight mission.
In this paper we describe in detail the various steps involved in imaging
sources with LXeGRIT and present experimental results on angular resolution and
other parameters which characterize its performance as a Compton telescope.Comment: 22 pages, 20 figures, submitted to NIM
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