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 (gamma) -rays in the energy band of 0.2 - 20 MeV. The detector, with 400 cm2 area and 7 cm drift gap, is filled with high purity LXe. Both ionization and scintillation light signal are detected to measure the energy deposits and the three spatial coordinates of individual (gamma) -ray interactions within the sensitive volume. The TPC has been characterized with repeated measurements of its spectral and Compton imaging response to (gamma) -rays from radioactive sources such as 22Na, 137Cs, 88Y 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 equals 8.8% (root)1MeV/E. Compton imaging of 88Y (gamma) -ray events with two detected interactions is consistent with an angular resolution of approximately 3 degrees (RMS) at 1.8 MeV.