" 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
accelerated particle interactions and sources, and high energy processes around
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
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."