Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions

Abstract

The K shell excitation of H-like uranium (U(91+)) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.

Atomic-number dependence of the magnetic-sublevel population in the autoionization state formed in dielectronic recombination

“…For instance, the resonance strengths of DR into highly charged heavy ions are greatly enhanced by the Breit interaction, as shown in our previous work [26] and also by Bernhardt et al [27]. The Breit interaction also plays an important role in the quantum interference between resonant DR and nonresonant radiative recombination (RR) processes [28,29] as well as electron-impact excitation [30,31] and ionization [32,33].…”

Calculation of the relativistic rise in electron-impact-excitation cross sections for highly charged ions

“…For example, this was necessary in the polarization of x rays emitted during electron-impact excitation of highly charged ions [1,2], dielectronic and radiative recombination effects [3][4][5], electron-impact-ionization experiments [6][7][8], and electron-and proton-impact excitation experiments [9]. For electron-impact excitation of highly charged hydrogenlike ions, Walker [10], Fontes et al [11], and Moores and Pindzola [12] have demonstrated that the Møller interaction or GBI can increase electron-impact-excitation cross sections by up to 50% in comparison to calculations that employ only the Coulomb interaction.…”

Linear polarization of x-ray transitions due to dielectronic recombination in highly charged ions

“…A pplication o f the C om pton polarim etry technique provides a significant advantage over the Bragg polarim etry technique, previously used at EBITs [17,48,[72][73][74], by m easuring, in addition to the degree o f polarization, the angle o f polariza tion [42,61 ] and by being effective in a broader range o f ener gies [41,75], O ur im plem entation o f the C om pton polarim etry is also significantly more accurate [26,41,42,60,61,76] than a sim ilar techniques used in nuclear physics [77][78][79][80], The high polarim etry accuracy allows deep probes o f the electronim pact ionization and excitation [48,[72][73][74]81,82], resonant excitation [83], and radiative recom bination [26,51,84] by revealing the alignm ent [51,84,85] …”