Cascade emission in electron beam ion trap plasma of W25+^{25+} ion

Spectra of the W$^{25+}$ ion are studied using the collisional-radiative model (CRM) with an ensuing cascade emission. It is determined that the cascade emission boosts intensities only of a few lines in the $10 - 3$ nm range. The cascade emission is responsible for the disappearance of structure of lines at about 6 nm in the electron beam ion trap plasma. Emission band at 4.5 to 5.3 nm is also affected by the cascade emission. The strongest lines in the CRM spectrum correspond to $4d^{9} 4f^{4} \rightarrow 4f^{3}$ transitions, while $4f^{2} 5d \rightarrow 4f^{3}$ transitions arise after the cascade emission is taken into account.Comment: 16 pages including 4 figures and 3 table

The prospective search for highly ionized technetium in hot (pre-) white dwarfs

The discovery of technetium (Tc) in the atmospheres of red giants by Merrill (1952, ApJ, 116, 21) constituted convincing proof that s-process nucleosynthesis is indeed occurring in evolved stars. In principle, Tc should still be present in the atmospheres of hot post-AGB stars and (pre-) white dwarfs although, due to radioactive decay, it should be present in decreasing quantities along post-AGB evolution. The recent discovery of a large number of trans-iron group elements in hot white dwarfs with atomic numbers in the range A = 30–56 (Zn to Ba) raises the prospect that Tc (A = 43) may also be detected. However, this is currently not feasible because no atomic data exist for ionization stages beyond Tc i

Electron-impact ionization of W5+

Electron-impact single-ionization cross sections for the W5+ ion have been studied experimentally and theoretically. Measurements of a detailed ionization spectrum and of absolute cross sections were performed employing the crossed-beams method in the energy range from the ionization onset up to 1000 eV. The experimental data show a prominent contribution of W5+ ions in metastable states. The theoretical analysis includes level-to-level calculations from the 4f145s25p65d ground configuration and long-lived levels of the 6s, 5p55d2, 4f135d2, and 4f135d6s configurations. Direct-ionization and excitation-autoionization contributions to the total single-ionization cross sections were calculated employing a distorted-wave approximation. Radiative damping was taken into account. It is shown that correlation effects play an important role and lead to substantial reduction of cross sections. Theory and experiment are in quite good agreement when, within a statistical model, a (85±9)% fraction of parent ions in the ground configuration is assumed. The strongest contributions of metastable parent ions arise from the 5p55d2 and 4f135d2 configurations.The experimental part of this study was supported by the Deutsche Forschungsgemeinschaft under Project No. Mu 1068/20. M.F.G. acknowledges the Deutsche Forschungsgemeinschaft for supporting his research stays at the Gießen Institut für Atom-und Molekülphysik through Grants No. Mu-1068/19 and No. Mu-1068/21. A.B. is supported by the German Federal Ministry of Education and Research (BMBF) through Grant No. 05P19RGFA1. Part of the computations were performed using resources of the High Performance Computing Center “HPC Sauletekis” in Vilnius University Faculty of Physics. We thank K. Spruck, A. Becker, J. Hellhund, and J. Rausch for their help in the present experimental program.Scopu