Strong suppression of positron-induced double ionization of helium at low-to-intermediate velocities

Abstract

Based on our previous work of the classical over-barrier ionization model, the single- and double-ionization cross sections of positron-helium impact are calculated. The calculation results are consistent with the experimental data. The screened Coulomb potential is used to obtain the trajectory of the positron in single-ionization process. The positron is seemed to be scattered by the rest $\mathrm{H}{\mathrm{e}}^{+}$ core in double ionization. The strong Coulomb defection effect makes the double ionization to be significantly suppressed at low velocities.