Gas pressure and reduced electric field effects in gas scintillation proportional counters

The technique of high speed pulse digitization is applied to a driftless gas scintillation proportional counter in order to study electron drift velocities, longitudinal diffusion of the electron cloud and the light emitting process. Drift velocities and longitudinal diffusion coefficients for pure xenon have been determined over the range 2.0-4.5 kV/cm bar. A study of the pulse fall time as a function of pressure for fixed reduced fields strongly suggests that a three-body process dominates the light production (i.e. has the lowest probability), which can be associated with the creation of the Xe dimer (vibrationally unrelaxed). A rate coefficient of 3.3x10-32 cm6/s is measured for the process. (orig.)