A high pressure ionization chamber to observe ββ-decay in 136Xe

Abstract The energy resolution of liquid ionization detectors is limited by the initial recombination of ions and electrons formed by δ-electrons along the ionization track. We have constructed a high pressure ionization chamber in which the recombination problem has been overcome by reducing the density of the medium. Energy resolution is 2% at 1 MeV in argon at 108 atm and a drift field of 0.7 kV/cm and 5% in xenon at 30 atm. We measure the pressure-dependent effects of electronegative impurities. We will use this detector to do a ββ-decay experiment in 136 Xe.