Measurements of total and positronium formation cross sections for positrons and electrons scattered by hydrogen atoms and molecules

Abstract

We have measured total (${\mathrm{Q}}_{\mathrm{T}}$ ) and positronium formation (${\mathrm{Q}}_{\mathrm{Ps}}$ ) cross sections for 1--302-eV positrons (${\mathrm{e}}^{+}$ 's) and ${\mathrm{Q}}_{\mathrm{T}}$ 's for electrons (${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ 's) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure ${\mathrm{Q}}_{\mathrm{T}}$ 's where the projectile beam passes through a low-temperature scattering cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. ${\mathrm{Q}}_{\mathrm{Ps}}$ 's are measured using the same scattering cell by detecting coincidences of 511-keV annihilation \ensuremath{\gamma} rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the scattering cell in which the Ps is formed. The present ${\mathrm{e}}^{+}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's and ${\mathrm{Q}}_{\mathrm{Ps}}$ 's agree very well with theoretical calculations. Comparisons of the present ${\mathrm{e}}^{+}$ and ${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's show a merging to within 20% for energies above 12 eV.