Optical potential approach for positron scattering by metastable 2 ³ S state of helium

Abstract

The momentum space coupled channels optical (CCO) method for positron scattering has been extended to study the scattering of positrons by metastable helium for impact energies in the range from the positronium threshold up to high energies. Both the positronium formation and ionization continuum channels are included in the calculations via a complex equivalent local potential. The positronium formation, ionization, elastic and 2 3 S-2 3 P excitation, and total scattering cross sections are all presented and compared with the available information.

Plasma-screening effects on positronium formation

“…Positronium (Ps) formation, which is a special rearrangement process in positron-atom collision, has been found to significantly affect the scattering process for low projectile energies in a vacuum. [21][22][23][24][25][26][27][28][29][30] As the screening effect increases in Debye plasmas, the Ps-formation threshold decreases, which results in a more important Ps process at low scattering energies. Moreover, the rate of Ps plays a decisive role in the rate of annihilation and measurement of the spectrum and distribution of the annihilation radiation can provide us with fruitful information to develop our understanding regarding the physical properties of the plasma medium.…”