THERMALIZATION OF POSITRONIUM IN GASES

The thermalization of positronium (Ps) formed at a few eV in gases is investigated using time-resolved, Doppler broadening measurements of t he annihilation photons. Magnetic quenching permits energy measurement s about 40 ns after Ps is formed in H-2, N-2, He, Ne, Ar, isobutane, a nd neopentane. The thermalization rate is measured by changing the gas density, and a classical elastic scattering cross section and a Ps fo rmation energy are determined. The impact of Ps thermalization on deca y rate experiments using gases is also discussed.