Oscillations of the charge exchange cross sections and the average equilibrium charge of helium ions

Charge distributions and energy losses of ions in solids

“…The energy losses reach the maximum in the energy range E % 0.4 MeV/amu and then decrease with increasing E. For fast collisions (E > 10 MeV/amu), the calculated results (15) and the theoretical values obtained using CASP (Convolution Approximation for Swift Particles) [6] and PASS [7] codes coincide with each other and with the empirical results obtained using the SRIM code [5]. At the maximum of energy losses the theoretical estimates [6,7] turn out to be less than the empirical SRIM data, because the inelastic energy losses during the ion charge exchange are ignored there.…”

“…The values of the (ÀdE/dx) el (15) exceed the SRIM data by 15-20% at the maximum, but this discrepancy is comparable with the difference between the experimental results. For E < 0.1 MeV/ amu, the values of (ÀdE/dx) el (15) and the results of the calculation using CASP decrease and become less than the experimental data. This is explained by the fact that sum (15) does not take into account inelastic channels with small energy losses (formation of excited ion states, two-step processes, and so on).…”

“…When determining the interpolation coefficients A q,q±1 (Z,Z t ), the dependence of the charge exchange cross sections on Z t can be nonmonotonous because of the shell structure of atoms [15]. Therefore, to calculate A q,q±1 (Z,Z t ), we take this effect into account, using the Oppenheimer-Brinkman-Kramers approximation including the Coulomb interaction in the final state [16].…”

“…6 shows the results of the energy loss calculations for nitrogen ions in celluloid under the assumption of different interaction processes. The atom ionization (ÀdE/dx) i contributes mainly to sum (15) in the energy range E > 0.5 MeV/amu, where the contribution of the charge exchange (ÀdE/dx) q±1 and excitation (ÀdE/ dx) nl can be regarded as a correction. The energy losses (ÀdE/ dx) q±1 (16) decrease with increasing collision energy E more rapidly than (ÀdE/dx) i (17), because as E increases, the ion charge q increases and the electron loss cross sections decrease.…”