Laboratory and balloon flight performance of the liquid xenon gamma ray imaging telescope (LXeGRIT)

This thesis presents the laboratory calibration and in-flight performance of the liquid xenon gamma-ray imaging telescope (LXeGRIT). LXeGRIT is the prototype of a novel concept of Compton telescope, based on a liquid xenon time projection chamber (LXeTPC), developed through several years by Prof. Aprile and collaborators at Columbia. When I joined the collaboration in Spring 1999, LXeGRIT was getting ready for a balloon borne experiment with the goal of performing the key measurement of the background at balloon altitude. After the 1999 balloon flight, a good deal of work was devoted to a thorough calibration of LXeGRIT, both through several tests in the laboratory and through improving the analysis software and developing Monte Carlo simulations. After substantial advancements in our understanding of the detector performance, LXeGRIT was improved and calibrated before a long duration balloon campaign in the Fall of 2000. Data gathered in this flight have allowed a detailed study of the background at balloon altitude and of the sensitivity to celestial gamma-ray sources, the focus of the second part of my thesis. As this dissertation is intended to show, "the LXeGRIT phase"---defined as the prototype work, the experimental demonstration of the LXeTPC concept as a Compton telescope, the measurement of the background and of the detection sensitivity---has been now successfully completed. We are now ready for future implementations of the LXeTPC technology for astrophysics observations. The detailed calibration of LXeGRIT, both as an imaging calorimeter and as a Compton telescope is described in Chapters 2, 3 and 4. In Chapter 5 more details are given of LXeGRIT as a balloon borne instrument and its flight performance in year 2000. The measurement of the background at balloon altitude, based on the data collected in year 2000, is presented in Chapter 6 and the sensitivity of the instrument is derived in Chapter 7. An overview of future developments for the LXeTPC technology in the field of gamma-ray astronomy is given in Chapter 8. The main results from the 1999 balloon flight are summarized in Appendix A.