Using channeling properties for studying the impact-parameter dependence of electron capture by 20-MeV/u uranium ions in a silicon crystal

E. TESTA; P. ABUFAGER; A.BRAUNING-DEMAIN; H. BRAUNING; M. CHEVALLIER; C. COHEN; D. DAUVERGNE; A. GUMBERIDZE; R. KIRSCH; C. KOZHUHAROV; D. LIESEN; P.H. MOKLER; J.C. POIZAT; C. RAY; R.D. RIVAROLA; J.P. ROZET; TH. STOHLKER; S. TOLEIKIS; M. TOULEMONDE; D. VERNHET; P. VERMA

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

The American Physical Society

Año: 2007 p. 62901 - 62911

1050-2947

The impact-parameter dependence of electron capture by 20-MeV/u U91+ ions has been studied by means of channeling in a 11- μm-thick silicon crystal. Such ions are far from their equilibrium charge state in matter, and channeling offers a unique opportunity to study electron capture in conditions going from the extreme case of a single capture event for the best channeled ions to the case of multiple charge exchange events leading to charge state equilibrium for unchanneled ions . For each incident ion, the charge states at emergence, energy loss, electron emission-, and x-ray yields are measured. The correlations between these quantities are studied. The data are reproduced by simulations based on the ion flux distribution. We show that the mechanical electron capture dominates at impact parameters smaller than 0.5 Ẵ, whereas radiative electron capture is the only process occurring beyond. Specific features associated with highly charged heavy ions at intermediate velocities are discussed, in particular the ionization following capture into highly excited states and the local electron density enhancement due to the electron gas polarization. The measured impact-parameter dependence of capture probabilities is compared to continuum-distorted-wave eikonal-initial-state calculations, extrapolated to n>5 final states.