Interpretation of the Si K{alpha} x-ray spectra accompanying the stopping of swift Ca ions in low-density SiO{sub 2} aerogel

• Published in: Physical review. A, Atomic, molecular, and optical physics Atomic, molecular, and optical physics, 2010-07, Vol.82 (1)
• Main Authors: Rzadkiewicz, J., Institute of Plasma Physics and Laser Microfusion, Hery 23, PL-01-497 Warsaw, Gojska, A., Rosmej, O., Polasik, M., Slabkowska, K.
• Format: Article
• Language: English
• Subjects: APPROXIMATIONS; ATOM COLLISIONS; ATOMIC AND MOLECULAR PHYSICS; ATOMS; CALCIUM IONS; CALCULATION METHODS; CHALCOGENIDES; CHARGED PARTICLES; COLLISIONS; DENSITY; DIFFERENTIAL EQUATIONS; DIMENSIONS; DIRAC EQUATION; ELECTRON TRANSFER; ELECTRONIC STRUCTURE; ELECTRONS; ELEMENTARY PARTICLES; ELEMENTS; ENERGY RANGE; EQUATIONS; FERMIONS; FIELD EQUATIONS; HARTREE-FOCK METHOD; ION COLLISIONS; ION-ATOM COLLISIONS; IONIZATION; IONS; L SHELL; LENGTH; LEPTONS; MEV RANGE; MINERALS; MULTICHARGED IONS; NONMETALS; OXIDE MINERALS; OXIDES; OXYGEN; OXYGEN COMPOUNDS; PARTIAL DIFFERENTIAL EQUATIONS; PHYSICAL PROPERTIES; QUARTZ; SILICON COMPOUNDS; SILICON OXIDES; SPECTRA; VALENCE; WAVE EQUATIONS; X-RAY SPECTRA
• ISSN: 1050-2947; 1094-1622
• DOI: 10.1103/PHYSREVA.82.012703

This article presents a detailed analysis of the K{alpha} x-ray spectra of Si induced by 11.4 MeV/u Ca projectiles penetrating a low-density SiO{sub 2} aerogel target measured with high spectral and spatial resolution at the UNILAC accelerator at GSI-Darmstadt. The low-density material used in the experiment was crucial for the space-resolved studies of the Si x-ray radiation (for different energies of stopping Ca ions). The stopping length of the 11 MeV/u Ca ions reaches up to 10 mm in the low-density SiO{sub 2} aerogel, whereas in regular quartz solid targets it is about 100 times shorter. The analysis of the x-ray spectra emitted by the stopping medium has shown a high level of the L-shell ionization, especially in the later considered phase (E{sub p{approx}}5 MeV/u) of the stopping process. It has been further demonstrated that the population of the highly ionized states produced in the ion-atom collisions can be substantially reduced in the time between the collision and the x-ray emission due to the very intense rearrangement processes occurring in Si situated in the chemical environment of oxygen atoms. Moreover, comparison of the experimental values of the K{alpha} L-shell satellite energy shifts with the results of the multiconfiguration Dirac-Fock calculations allows us to find that Si valence electron configuration is enriched due to electron transfer from valence-electron-rich oxygen atoms into highly ionized silicon atoms. Our results indicate that the Coulomb explosion in a highly ionized track core is prevented by rapid neutralization in the femtosecond time scale.