A liquid xenon time projection chamber for γ-ray imaging in astrophysics: present status and future directions

A liquid xenon time projection chamber (LXeTPC) has been developed to image cosmic γ-rays in the energy band 0.2–20 MeV. Its performance as Gamma Ray Imaging Telescope (LXeGRIT instrument) has been tested during a high altitude balloon flight (Spring ’99, New Mexico). The detector, with 400 cm2 area and 7 cm drift gap, is filled with 7 l high purity LXe. Both ionization and scintillation light signals are detected to measure the energy deposits and the three spatial coordinates of individual γ-ray interactions within the sensitive volume. During the pre-flight calibration experiments the LXeGRIT instrument was extensively tested with γ-ray sources in the laboratory: a 10% FWHM energy resolution at 1 MeV was determined, scaling with 1/ E . The detector shows a linear response in the energy range 511 keV–4.4 MeV.