Understanding the mechanisms of L-shell x-ray emission from Os atoms bombarded by 4–6 MeV/u fluorine ion

Abstract

The L-subshell ionization mechanism is studied in an ultra-thin Os target bombarded by 4-6 MeV/u fluorine ions. Multiple ionization effects are considered through the change of fluorescence and Coster-Kronig yields while determining L-subshell ionization cross sections from L X-ray production cross sections. The present experimental values are compared with various theoretical approximations: (i) the relativistic semi-classical approximation (RSCA), (ii) the shellwise local plasma approximation (SLPA), and (iii) the ECUSAR theory. We also take into account the vacancy sharing among the subshells by the coupled-states model (CSM) and the electron capture (EC) by a standard formalism. We find that the ECUSAR-CSM-EC describes the measured excitation function curves the best. However, the theoretical calculations are still about a factor of two smaller than the measured values even though the recent fluorescence and Coster-Kronig yields are considered. Hence, a re-evaluation of these parameters is a challenge for the theoretical works. Whatsoever, this work leads to demonstrate that in the present energy range the heavy-ion induced inner-shell ionization of the heavy atoms can be understood by combining the direct Coulomb ionization, the electron capture, and the vacancy sharing among subshells, together with optimizing the atomic parameters. Optimization of the atomic parameters shows that our experimental results agree with theoretical vacancy production theories if the L1 fluorescence yield is nearly doubled. Such a optimization is validated by the proton induced L-shell ionization data of uranium atoms.

Theoretical studies on multiple ionization and electron capture processes in heavy ion induced M-shell ionization

“…3. Note that for DCI, we used ECPSSR theory as it gives the best representation for the K-and L-shell ionisation as shown in our recent studies [16,34]. Furthermore, when united atom is considered within the ECPSSR theory, it is called ECUSAR theory.…”

“…It suggests that the atomic parameters used for bismuth [39] and electron capture cross section calculations are responsible. The atomic parameters need to be optimised as done for osmium in our recent work Chatterjee et al [16]. However, it can be revealed with the proton induced M-shell ionization measurements.…”

“…It is well-known that for asymmetric collisions, Z 1 /Z 2 < 1, the direct coulomb ionization (DCI) is dominant, whereas for symmetric collisions, Z 1 /Z 2 ≈ 1, the multiple ionization (MI) and electron capture (EC) processes become increasingly important. Chatterjee et al showcased few such cases for the K-shell ionization [15] and the L-shell ionization [16], and resolved the existing discrepancies between between experiment and theory. They demonstrated that besides the MI process, K-K and K-L electron capture must be taken into account in the theory to sort out such differences.…”

“…Contrary to the agreement found in K-shell case, the contribution from the MI and EC does not account for all the discrepancies found between the measurements and the theoretical descriptions. It was found that the presently available atomic parameters for L-shell [16] (the fluorescence and Coster-Kronig yields) are unable to achieve agreement between the experiment and the theory. So, they have optimised these values iteratively until a good agreement was achieved.…”

“…They report a theoretical methodology to predicting the charge state distributions inside (CSD-I) the target. The same approach has also been applied to study the L-subshell vacancy production by considering the DCI, the MI, and the EC by performing a detailed comparison between experiment and theory [16]. Contrary to the agreement found in K-shell case, the contribution from the MI and EC does not account for all the discrepancies found between the measurements and the theoretical descriptions.…”