Abstract
Charge state evolution of the projectile ions while traversing through the solid target medium has been explored using the radiative electron capture process. The measured centroid energies of the convoluted radiative electron capture peak structures have been used to determine the mean K-shell binding energies and mean charge state of the projectile ions. It has been observed that the mean charge states of present measurements are lower than the earlier measurements done using the characteristic ${\mathrm{K}}_{\ensuremath{\alpha}}$ x-ray transitions. The difference is due to the capture of target electrons in the inner-shell vacancies, created during the collision process, of projectile ions. Further, the measured mean charge states are compared with the empirical predictions. A significant discrepancy between experimental and theoretical values has been observed, which is attributed to the multielectron capture by projectile ions due to nonradiative electron capture process from the exit surface while exiting from the foil. The significant variation between mean charge state values obtained from different tools provides a clear indication of the dynamic nature of the charge-changing mechanism at different regions (entrance surface, bulk, and exit surface) of the ion-solid interaction. The present results can be used to validate the departure between the theory and experiment on the charge state dependent stopping powers.
Highlights
The study of the charge state evolution of projectile ions traversing solid or gaseous targets has been a subject of great interest for more than 100 years [1,2,3]
The Kα peak structure has been used to obtain the charge state distribution (CSD) produced at the bulk only during the ion-solid collisions, which excludes the atomic processes leading to radiative electron capture (REC), metastable and any high Rydberg states that may occur at the bulk [31]
We focus only on the K-REC peak to obtain the CSD, which accounts for all the atomic processes occurring at the bulk responsible for the creation of K-shell vacancies along with the REC contributions arising from the bulk as well as the surface of the foil
Summary
The study of the charge state evolution of projectile ions traversing solid or gaseous targets has been a subject of great interest for more than 100 years [1,2,3]. The excited states produced by any of the above processes can be further affected by the surface energy loss field (SELF) at the exit surface [15]. These charge-changing processes can be investigated through the distribution of charge state fractions (CSF) called charge state distribution (CSD) for both experiments and theories. Several extensive reviews on CSDs can be found in the literature including that of Allison [16], Betz [17], Wittkower and Betz [18], Shima et al [19,20] These reviews provide a crucial theoretical background in terms of the data collection to date. In some distinct cases, like, calculation of non-equilibrium charge state distribution [26,27], estimation of equilibrium target thickness [28], etc., the empirical
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