Diagnostics of a positronium beam

Abstract
A time-of-flight technique has been used to characterize the components of a positronium (Ps) beam generated by charge-exchange reactions of positrons in helium and argon gases. Ground and excited states of positronium have been resolved and the ratios of the signal rates of Ps to both scattered and incident positrons have been quantified in the Ps energy range 7-41 eV. By observing the pressure dependence of these ratios estimates of the Ps total scattering cross sections have been extracted for both gases at energies in the same range.