Multiple-ionization collision dynamics.

Abstract

The 1.4-MeV/u ${\mathrm{U}}^{32+}$+Ne collision system is studied in detail in order to elucidate the dynamics of multiple ionization in energetic, heavy-ion--atom collisions. Differential cross sections versus recoil-ion charge state, calculated by the n-body classical-trajectory Monte Carlo method, are presented for the \ensuremath{\theta} and cphi angle dependences of the projectile, recoil ion, and ejected electrons. The calculations show a high degree of ejected-electron asymmetry towards the projectile side of the target nucleus which strongly effects the transverse-momentum balance between the heavy particles. Experimental and calculated cross sections differential in the recoil-ion charge state and transverse momentum are found to differ by orders of magnitude from those for the projectile, providing evidence for the importance of explicitly considering the ejected electrons' momenta in the determination of the heavy-particle (both the projectile and the recoil-ion) angular differential cross sections. Polarization of the target electrons and screening of the recoil ion by the ejected electrons lead to \ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}6}$-rad negative-angle deflections of the projectile for recoil-ion charge states up to 4+. The angular scattering of the recoil ion departs significantly from that predicted for a two-body collision, and is found to be nearly isotropic for low recoil-ion charge states and peaked to angles \ensuremath{\theta}>90\ifmmode^\circ\else\textdegree\fi{} for high recoil-ion charge states. A stopping-power calculation for this system is in good agreement with the experimental value. Stopping powers differential in impact parameter and for energy deposition to \ensuremath{\delta} electrons and multiple ionization are given to further describe the projectile energy loss.