J. D. Garcia

Classical-quantal coupling in the capture of muons by hydrogen atoms

The authors describe a self-consistent semiclassical approach to the problem of muon capture by hydrogen atoms. The dynamics of the heavier muon and proton are treated classically, and the electron quantally, with the potentials for both being self-consistently determined. Their numerical results are compared to classical-trajectory Monte Carlo (CTMC) and adiabatic ionisation (AI) results. Their capture cross sections are larger at low energy but fall more rapidly to zero. Their results provide the corrections to the dynamics beyond the adiabatic picture, which were missing in other approaches; interesting questions concerning the quantal nature of the events are discussed.

Direct observation of multiple L-shell vacancy effects in energetic heavy ion collisions☆

Abstract Observations have been made of soft L X-ray spectra resulting from collisions of 8–20 MeV oxygen ions and Ni, Cu and Zn atoms. These observations provide confirmation of the multiple L-shell vacancies proposed to explain recent experimental determinations of K-shell X-ray energy shifts in such collisions. The energy dependence of the single vacancy shifts indicate that the probability of outer shell ionization is a decreasing function of ion energy in this energy range.

Development of B-spline techniques for dynamic ion-metal interaction theories

Abstract A three-dimensional time-dependent mean-field (TDMF) treatment for this problem is made computationally feasible by careful use of symmetries, incorporation of B-spline techniques and operator splitting concepts in the development of the method. The TDMF theory used is an adaptation of time-dependent Hartree-Fock theory used in atomic and nuclear physics for dealing with similar short-duration, strong, nonlinear collision interactions. Results of preliminary numerical studies are described.

Ion‐metal and ion‐atom collisions instant replays and mean‐field theories

In this paper, we describe the results of our general long‐term programmatic goal of investigating the strengths and weaknesses of time‐dependent mean‐field theories for collisions. We have made some progress in: (a) obtaining a better formulation of the theory, which has the exact full Schrodinger equation as one limit and permits appropriate classical treatment of heavy particles correctly coupled to the quantally treated electrons; (b) restructuring our numerical treatment to make it fully three‐dimensional, improve accuracy and decrease cycle time, so that larger problems more in keeping with the mean‐field concept can be treated; and (c) incorporating the electrons in the conduction band of a metal into our quantal treatment, making possible the description of collisions of atoms and ions with solids. Numerical results for protons tranversing a thin metallic foil, among other examples, are presented and discussed.

Solution of quantum evolution equations by finite-difference

Abstract We report some recent improvements on the rotation-frame cylindrical-coordinate finite-difference scheme for solving quantum evolution equations in atomic collisions. A Hermitian discretization of the Coriolis term in the rotating Hamiltonian is discussed. Illustrative results from calculations of muon capture by helium atoms are also presented. In other collision calculations involving helium, parametrized Hartree-Slater wavefunctions of helium excited states are used as final projection states. The values of the parameters for states up to 1s4f are tabulated here in the hope that they might be useful in other contexts.

Production of multiple inner-shell vacancies in sulphur projectiles moving in a solid target

Abstract L X-ray spectra from sulphur projectiles moving in a graphite target are reported and compared with similar spectra produced in collisions with a gas target. The projectile spectra in solid targets are found to be influenced predominately by multiple collision effects which take place after the production and before the decay of the inner-sheel vacancy.

Capture of a classical muon by a quantal hydrogen atom

Using a self‐consistent method that treats the muon classically and the electron quantum mechanically, we have calculated the capture cross sections of μ‐ by atomic hydrogen at low incident energies.