94 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
Compton scattering sequence reconstruction algorithm for the liquid xenon gamma-ray imaging telescope (LXeGRIT)
The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon born
experiment sensitive to \g -rays in the energy band of 0.2-20 MeV. The main
detector is a time projection chamber filled with high purity liquid xenon
(LXeTPC), in which the three-dimensional location and energy deposit of
individual \g -ray interactions are accurately measured in one homogeneous
volume. To determine the \g -ray initial direction (Compton imaging), as well
as to reject background, the correct sequence of interactions has to be
determined. Here we report the development and optimization of an algorithm to
reconstruct the Compton scattering sequence and show its performance on Monte
Carlo events and LXeGRIT data.Comment: To appear in: Hard X-Ray, Gamma-Ray, and Neutron Detector Physics II,
2000; Proc. SPIE, vol. 4141; R.B. James & R.C. Schirato, ed
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
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
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
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