Strong continuum-continuum couplings in the direct ionization of Ar and He atoms by 6-MeV/uU38+andTh38+projectiles

Doubly differential cross sections have been measured as a function of the electron energy and observation angle for electron emission following collisions of 6-MeV/u ${\mathrm{U}}^{38+}$ and ${\mathrm{Th}}^{38+}$ on He and Ar. The electron-emission data show an enhancement at forward angles and a decrease at backward angles with respect to scaled-cross-section results based on the Born approximation. Comparison with classical-trajectory Monte Carlo calculations suggests that the deviation from the Born approximation can be explained by continuum-continuum couplings. By comparing with previously published data, we found that the forward enhancement as well as the backward decrease follow a q/$v_p$ (q,$v_p$ are the projectile charge and velocity) scaling.