Barkas Binary

In order to access this option you should select the EXPERT OPTIONS sheet (close to the upper left corner of the main program window).

At lower projectile velocities the original UCA prediction becomes uncertain, since some of the higher-order effects such as polarization and binding effects are not incorporated into the UCA model. This uncertainty affects the close collisions as well as the long-ranged dipolar interactions. Since close encounters are reasonably well described by classical two-body collisions (if the electron orbital velocity is below the projectile velocity), we make use of the Binary model by Sigmund and Schinner [see e.g. P. Sigmund, A. Schinner; NIM-B 195, 64 (2002)]. Hence, the close collision fraction of the stopping cross section

2 Z^2 /b^2 h(2 v b) /v^2

is replaced by

2 Z^2 /b^2 h(2 v b) /v^2  2 T[V]/(T[V]+T[-V]),

where T denotes the energy loss in a classical two-body collision using the interaction potential between the projectile and target electron V(r) (here, according to the Binary model,  the Coulomb part of V_p(r)  is EXTRA screened using the adiabatic radius). No explicit solution has been used for the polarization due to long-ranged dipolar interactions. However, since the Colomb part of V_p(r) is screened by v/w (the adiabiatic radius), part of the polarization in distant collisions may be emulated through the product Ansatz from the UCA method. It has to be noted that while this procedure may be sufficient for calculations of stopping cross-sections, it can provide an unrealistic impact-parameter-dependent energy loss.

This option affects stopping due to target ionization as well as due to projectile-electron loss and makes only sense for UCA calculations. This option is then automatically unchecked for PCA calculations.