Influence of ionised electrons on heavy nuclei angular differential scattering cross sections

Abstract

For the collision systems 1.4 MeV u-1 U32+ and 5.9 MeV u-1 U65+ on Ne, transverse (with respect to the beam axis) momentum distributions of recoiling target atoms have been measured applying a time-of-flight technique. In the case of isotropic electron emission, the transverse momenta of the recoil ion pR perpendicular to and the projectile pp perpendicular to after the collision are identical. This allows the transformation of measured pR perpendicular to distributions into projectile related differential scattering cross sections d sigma /d theta . Using such an analysis, the authors have measured differential cross sections in the scattering angle regime of 1*10-6 rad<or= theta >4*10-5 rad. The shape, as well as the absolute magnitude of the derived experimental d sigma /d theta is in reasonable agreement with Rutherford differential cross sections at large theta using a projectile nuclear charge of Zp=qP and a target nuclear charge of ZT=5. For theta <or approximately=1*10-5 rad, n-body classical trajectory Monte Carlo (nCTMC) calculations predict that the balance between pR perpendicular to and pP perpendicular to is strongly influenced by the momenta of anisotropically emitted ionised electrons. From the comparison between the derived experimental cross sections d sigma /d theta with the theoretical values, as well as from the agreement between experimental and theoretical transverse recoil-ion momentum distributions, they conclude that the momenta of the ejected electrons have a considerable influence on the scattering dynamics of the heavy nuclei. Furthermore, the calculations indicate that the projectile is scattered to negative angles at impact parameters of b>or approximately=3 alpha 0 due to anisotropic electron emission and strong polarisation of the target electron cloud by the Coulomb potential of the projectile. The possibility of rainbow scattering at theta approximately=1*10-6 rad is predicted.