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

We have measured total (QT) and positronium formation (QPs) cross sections for 1 endash 302-eV positrons (e+close-quote s) and QT close-quote s for electrons (e-close-quote s) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure QT close-quote 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. QPs close-quote s are measured using the same scattering cell by detecting coincidences of 511-keV annihilation γ 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 e+-H QT close-quote s and QPs close-quote s agree very well with theoretical calculations. Comparisons of the present e+ and e--H QT close-quote s show a merging to within 20% for energies above 12 eV. copyright 1997 The American Physical Society