The nuclear magnetic moment of ²⁰⁸Bi and its relevance for a test of bound-state strong-field QED

The hyperfine structure splitting in the 6p2 4S3/2 -> 6p27s 4P1/2 transition at 307 nm in atomic 208Bi was measured with collinear laser spectroscopy at ISOLDE, CERN. The hyperfine A and B factors of both states were determined with an order of magnitude improved accuracy. Based on these measurements, theoretical input for the hyperfine structure anomaly, and results from hyperfine measurements on hydrogen-like and lithium-like 209Bi80+,82+, the nuclear magnetic moment of 208Bi has been determined to μ(208Bi) =+4.570(10) μN . Using this value, the transition energy of the ground-state hyperfine splitting in hydrogen-like and lithium-like 208Bi80+,82+ and their specific difference of −67.491(5)(148) meV are predicted. This provides a means for an experimental confirmation of the cancellation of nuclear structure effects in the specific difference in order to exclude such contributions as the cause of the hyperfine puzzle, the recently reported 7-σ discrepancy between experiment and bound-state strong-field QED calculations of the specific difference in the hyperfine structure splitting of 209Bi80+,82+

Positron creation probabilities in low-energy heavy-ion collisions

The previously developed technique for calculation of ionization probabilities in low-energy heavy-ion collisions [A.I. Bondarev et al., Phys. Scr. T156, 014054 (2013)] is extended to evaluation of positron creation probabilities. The differential probabilities are evaluated by two alternative methods. The first one uses hydrogenic continuum wave functions, while the second one uses discretized continuum wave functions corresponding to a finite basis expansion. These methods are applied to the calculation of the differential positron creation probabilities in the U91 +(1s)-U92+ collision. The results obtained by both methods are found in good agreement

Ab initio electronic factors of the A and B hyperfine structure constants for the 5s(2)5p6s( 1,3)P(1)(0) states in Sn I

Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s(2)5p6s( 1,3)P(1)(0)excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s(2)5p6s( 1)P(1)(0) state, the final value of B/Q = 703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range Sn117-131 from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s(2)5p6s( 1)P(1)(0) state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.Peer reviewe

Lithiation Products of a Silicon Anode Based on Soft X‑ray Emission Spectroscopy: A Theoretical Study

Because of its exceptional lithium storage capacity, silicon is considered as a promising candidate for anode material in lithium-ion batteries (LIBs). In the present work, we demonstrate that methods of soft X-ray emission spectroscopy can be used as a powerful tool for the comprehensive analysis of the electronic and structural properties of lithium silicides Li<i>_x</i>Si forming in LIB’s anode upon Si lithiation. On the basis of density functional theory and molecular dynamics simulations, it is shown that the coordination number of Si atoms in Li<i>_x</i>Si decreases with an increase in Li concentration both for the crystalline and amorphous phases. In amorphous a-Li<i>_x</i>Si alloys, Si tends to cluster, forming Si–Si covalent bonds even at the high lithium concentration. It is demonstrated that the Si-L_2,3 emission bands of the crystalline and amorphous Li<i>_x</i>Si alloys show different spectral dependencies, reflecting the process of disintegration of Si–Si network into Si clusters and chains of the different sizes upon Si lithiation. The Si-L_2,3 emission bands of Li<i>_x</i>Si alloys become narrower and shift toward higher energies with an increase in Li concentration. The shape of the emission band depends on the relative contribution of the X-ray radiation from the Si atoms having different coordination numbers. This feature of the Si-L_2,3 spectra of Li<i>_x</i>Si alloys can be used for the detailed analysis of the Si lithiation process and LIB’s anode structure identification