Development of a liquid xenon time projection chamber for gamma-ray astronomy

Abstract

Work is in progress at the Columbia Astrophysics Laboratory on the development of a liquid xenon imaging chamber for gamma‐ray astronomy. Such an instrument will combine high detection efficiency, good energy and position resolution with a large effective area. These properties, together with the excellent background rejection capability provided by 3‐dimensional imaging, will allow orders of magnitude better sensitivity than currently used instruments, for the detection of weak gamma‐ray sources in space.We have started with studies of the maximum energy resolution achievable with noble liquid ionization chambers. A value of 26 keV FWHM for 1 MeV electrons has been measured in liquid argon, dominated mostly by recombination straggling on highly ionizing delta electrons produced in large number along the primary ionizing track.We are presently working on liquid xenon to establish the most efficient gas purification scheme and the best spectroscopic performance. The initial result of about 38 keV FWHM for the energy resolution of the dominant 570 keV gamma rays from 207Bi, measured with a gridded ionization chamber, is very encouraging.Our final goal is the construction of a large area (∼1000 cm2) liquid xenon imaging chamber with 20 keV FWHM energy resolution at 1 MeV and a few millimeters spatial resolution, which will be capable of exploring a wide range of astrophysics phenomena expected to produce gamma‐rays in the energy range of 0.1 to 10 MeV. As a first application of this instrument we are planning on a spring 1990 balloon flight out of Australia to observe the 122 keV gamma‐ray line of 57Co produced by the supernova 1987A with a 3σ sensitivity of 2×10−5 ph cm−2 sec−1.