Comparison of Impact-Ionisation and Charge-Transfer Cross Sections for Positron and Proton Scattering on Helium
Cross sections for impact ionisation of helium by positrons and protons as well as charge transfer cross sections for positron-helium and proton-helium scattering are usually compared at equal velocities of the incident projectiles (vi) because the size of the cross sections depends on the duration of the interaction between projectile and target particle. The left parts of Figs. 1 and 2 show our measured values1 of cross sections for impact ionisation and charge transfer and literature values2-9 for the corresponding proton scattering processes. The charge transfer cross sections for positron and proton scattering on Helium intersect at vi = 4 x 106 m/s; at high velocities σPs is significantly greater than σH.
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