Gas Scintillators for Imaging of Low Energy Isotopes

We have constructed a large area (25 cm diameter), pressurized (4 atmosphere) xenon-helium gas scintillator for imaging shortlived isotopes in the 60 - 80 keV range. The scintillator is viewed by an array of quartz windowed PMT´s arranged in a simple Anger type readout. The energy and time resolution have been measured for various mixtures of xenon-helium. For Xe-133 (81 keV), an energy resolution of 6% FWHM has been obtained. The light output of the detector is a Gaussian shaped pulse with a width of 2 ¿s at the base. Spatial resolution has been measured at 3 - 4 mm FWHM. The physical limitations of the detector as well as design changes which will improve energy and spatial resolution are discussed. These improvements should permit the development of imaging detectors with simultaneous high rate and high energy resolution for applications such as first-pass studies with shortlived isotopes or imaging of low energy isotopes where contrast is reduced by scatter.