Performance of a liquid xenon time projection chamber for low-energy γ-rays detection

We detected the ionization charge and the scintillation light produced in liquid xenon by the interactions of γ-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. perimental spectra are the sum of the total energy peaks and the Compton continuum. By selecting the γ-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 cm3 we measured a peak-to-total ratio ranging from almost 100% (500–600 keV γ-rays) to more than 60% for 2 MeV photons.