Abstract
Gryzinski's double binary encounter model (1965) using the correct expression for sigma Delta E due to Vriens and the appropriate velocity distribution functions for the bound electrons has been used to calculate the proton impact double-ionisation cross sections of noble-gas atoms (Ne, Ar and Kr). The calculated cross sections are found to be in qualitative agreement with the experimental observations. The effect of the use of Hartree-Fock and hydrogenic velocity distributions for the target electron has also been discussed.