5,904 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
Detection of liquid xenon scintillation light with a Silicon Photomultiplier
We have studied the feasibility of a silicon photomultiplier (SiPM) to detect
liquid xenon (LXe) scintillation light. The SiPM was operated inside a small
volume of pure LXe, at -95 degree Celsius, irradiated with an internal Am-241
alpha source. The gain of the SiPM at this temperature was estimated to be 1.8
x 10^6 with bias voltage at 52 V. Based on the geometry of the setup, the
quantum efficiency of the SiPM was estimated to be 22% at the Xe wavelength of
178 nm. The low excess noise factor, high single photoelectron detection
efficiency, and low bias voltage of SiPMs make them attractive alternative UV
photon detection devices to photomultiplier tubes (PMTs) for liquid xenon
detectors, especially for experiments requiring a very low energy detection
threshold, such as neutralino dark matter searches
Performance of a Large Area Avalanche Photodiode in a Liquid Xenon Ionization and Scintillation Chamber
Scintillation light produced in liquid xenon (LXe) by alpha particles,
electrons and gamma-rays was detected with a large area avalanche photodiode
(LAAPD) immersed in the liquid. The alpha scintillation yield was measured as a
function of applied electric field. We estimate the quantum efficiency of the
LAAPD to be 45%. The best energy resolution from the light measurement at zero
electric field is 7.5%(sigma) for 976 keV internal conversion electrons from
Bi-207 and 2.6%(sigma) for 5.5 MeV alpha particles from Am-241. The detector
used for these measurements was also operated as a gridded ionization chamber
to measure the charge yield. We confirm that using a LAAPD in LXe does not
introduce impurities which inhibit the drifting of free electrons.Comment: 13 pages, 8 figure
Gamma Ray Spectroscopy with Scintillation Light in Liquid Xenon
Scintillation light from gamma ray irradiation in liquid xenon is detected by
two Hamamatsu R9288 photomultiplier tubes (PMTs) immersed in the liquid. UV
light reflector material, PTFE, is used to optimize the light collection
efficiency. The detector gives a high light yield of 6 photoelectron per keV
(pe/keV), which allows efficient detection of the 122 keV gamma-ray line from
Co-57, with a measured energy resolution of (8.8+/-0.6)% (sigma). The best
achievable energy resolution, by removing the instrumental fluctuations, from
liquid xenon scintillation light is estimated to be around 6-8% (sigma) for
gamma-ray with energy between 662 keV and 122 keV
Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy
The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results were obtained on the following topics: (1) long distance drift of free electrons in LXe (purity); (2) scintillation light yield for electrons and alphas in LXe (triggering); and (3) ionization yield for electrons and gamma rays in LXe (energy resolution). The major results from the investigations are summarized
A Simple Holographic Model of a Charged Lattice
We use holography to compute the conductivity in an inhomogeneous charged
scalar background. We work in the probe limit of the four-dimensional
Einstein-Maxwell theory coupled to a charged scalar. The background has zero
charge density and is constructed by turning on a scalar source deformation
with a striped profile. We solve for fluctuations by making use of a Fourier
series expansion. This approach turns out to be useful for understanding which
couplings become important in our inhomogeneous background. At zero
temperature, the conductivity is computed analytically in a small amplitude
expansion. At finite temperature, it is computed numerically by truncating the
Fourier series to a relevant set of modes. In the real part of the conductivity
along the direction of the stripe, we find a Drude-like peak and a delta
function with a negative weight. These features are understood from the point
of view of spectral weight transfer.Comment: 25 pages, 5 figures. v2: minor revision
XMASS
The XMASS detector is a large single phase liquid Xenon scintillator.After
its feasibility had been studied using a 100 kg size prototype detector, an 800
kg size detector is being built for dark matter search with the sensitivity of
region in spin-independent cross section. The results of
R\&D study for 800 kg detector, especially ultra low background technologies,
and the prospects of the experiment are described.Comment: 6 pages, 7 figures, for the proceedings of the 1st International
Workshop towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010,
will be published in Journal of Physics, Conference Series (Editors: T.
Hasegawa and A. Rubbia)
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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