Commissioning of a dual-phase xenon TPC at Nikhef

A dual-phase xenon time-projection chamber was built at Nikhef in Amsterdam as a direct dark matter detection R&D facility. In this paper, the setup is presented and the first results from a calibration with a 22Na gamma-ray source are presented. The results show an average light yield of (5.6±0.3) photoelectrons/keV (calculated to 122 keV and zero field) and an electron lifetime of (429±26) μs. The best energy resolution σE/E is (5.8±0.2)% at an energy of 511 keV. This was achieved using a combination of the scintillation and the ionization signals. A photomultiplier tube gain calibration technique, based on the electroluminescence signals occurring from isolated electrons, is presented and its advantages and limitations are discussed.