PERFORMANCE OF A LIQUID XENON TIME PROJECTION CHAMBER FOR LOW-ENERGY GAMMA-RAYS DETECTION

We detected the ionization charge and the scintillation light produced in liquid xenon by the interactions of gamma-rays emitted by radioactive sources. We could distinguish the multiple interactions of the photons and, by using the prompt scintillation signal, determine the distance of the tracks from the anode. Applying an electric field of 0.4 kV/cm, we obtained an intrinsic energy resolution of (8.4 +/- 0.9)% at 1 MeV and found that the free-ion yield is 4.24 +/- 0.43 independent on the photon energy within few percent in the explored range between 500 keV and 2 MeV. The experimental spectra are the sum of the total energy peaks and the Compton continuum. By selecting the gamma-rays with multiple interactions we could strongly reduce the Compton background and enhance the total energy peaks. All the spectra were consistent with a Monte Carlo simulation of the apparatus. With a sensitive volume of about 200 cm(3) we measured a peak-to-total ratio ranging from almost 100% (500-600 keV gamma-rays) to more than 60% for 2 MeV photons.