Ionization of liquid xenon by 241Am and 210Po alpha particles

The ionization yield of 241Am 5.49 MeV and 210Po 5.31 MeV alpha particles in liquid xenon has been measured as a function of electric field strength in the range 0.05 kV/cm to 20 kV/cm. Consistent results are obtained with the two sources. The maximum charge collected at 10 kV/cm is less than 10% of the total and the noise subtracted energy resolution is 2.5% FWHM at 5.49 MeV, dominated by statistical fluctuations in the number of electron—ion pairs escaping recombination. A comparison with our alpha particle data in liquid argon shows a much worse energy resolution and a different slope of the ionization curve at a given field. The different response of the two liquids is explained in terms of track ionization density and recombination dependence on track emission angle.