Detection of γ-rays with a 3.5 l liquid xenon ionization chamber triggered by the primary scintillation light

A gridded ionization chamber with a drift length of 4.5 cm and a total volume of 3.5 l, was operated with high-purity liquid xenon and extensively tested with γ-rays from 137Cs, 22Na and 60Co radioactive sources. An electron lifetime in excess of 1 ms was inferred from two independent measurements. The electric field dependence of the collected charge and energy resolution was studied in the range 0.1–4 kV/cm, for different γ-ray energies. With an electric field of 4 kV/cm, the spectral performance of the detector is consistent with an energy resolution of 5.9% at 1 MeV, scaling with energy as E−0.5. The chamber was also used to detect the primary scintillation light produced by γ-ray interactions in liquid xenon. The light signal was successfully used to trigger the acquisition of the charge signal with a FADC readout. A trigger efficiency of ∼85% was measured at 662 keV.