  In order to assess the performance of liquid xenon detectors for use in
positron emission tomography we studied the scintillation light and ionization
charge produced by 511 keV photons in a small prototype detector. Scintillation
light was detected with large area avalanche photodiodes while ionization
electrons were collected on an anode instrumented with low noise electronics
after drifting up to 3 cm. Operational conditions were studied as a function of
the electric field. Energy resolutions of <10 % (FWHM) were achieved by
combining the scintillation light and ionization charge signals. The
relationship between scintillation light and ionization signals was
investigated. An analysis of the sources of fluctuations was performed in order
to optimize future detector designs.
