Liquid Xenon Gama-Ray Imaging Telescope

Scientific Motivation

The following is taken from the Columbia Physics Dept. page of the Principal Investigator Professor Elena Aprile.

" My current research program is centered on the development of a next generation imaging Compton telescope for observations of the gamma-ray sky at energies between 300 keV and 10 MeV.

Gamma-rays in this nuclear transition region offer a direct means of studying many of the most energetic phenomena in the universe, including explosive nucleosynthesis, accelerated particle interactions and sources, and high energy processes around compact objects such as neuron stars, black holes, and the nuclei of active galaxies. The great potential of observations at MeV energies, with its richness of both line and continuum emission, has been recognized for decades. However, the realization of this potential has been slow because of the extreme technical challenges presented by the detection and imaging of MeV gamma-rays. The field is still in a discovery phase. Despite the success of the Compton Gamma-Ray Observatory, many of the high energy sources studied remain a mystery: gamma-ray bursts, unidentified sources in the galactic plane, the cosmic diffuse gamma-ray background and two strong gamma-ray lines, the 0.511 MeV annihilation line, and the 1.809 MeV line from radioactive 26Al remain of unknown origin
To resolve these and other outstanding problems in gamma-ray astrophysics, the field needs improved imaging telescopes with at least a factor of 10 better sensitivity than existing ones. My studies of the properties of liquid argon, krypton and xenon and their application in innovative radiation detectors, have led me to the proposal of a Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) as spectrometer and Compton imager for space-borne observations of MeV cosmic sources.
A first prototype of this new telescope concept has been developed by our group at the Astrophysics Laboratory, with NASA support and with collaborators from Waseda University (Japan), the University of New Hampshire, and NASA Marshall Space Flight Center . The balloon-borne LXeGRIT is based on a 10 liter liquid xenon time projection chamber (LXeTPC) with 400 cm2 area and 7~cm drift. The TPC approach provides unique background reduction capabilities due to the precise three-dimensional localization of interactions and, together with the great efficiency of the homogeneous detector, addresses the primary instrumental limitations encountered in this energy band. Following its first engineering demonstration at balloon altitude in the Summer of 1997, the LXeGRIT payload is currently being refurbished in preparation for a longer duration balloon flight in 1999.
With a succession of flights, from both hemispheres, we will address a broad range of scientific objectives, from stellar nucleosynthesis gamma-ray lines to continuum emission from pulsars, binary systems and active galactic nuclei."