1 5 Se p 20 08 Hyperfine induced 1 s 2 s 1 S 0 → 1 s 2 1 S 0 M 1 transition of He - like ions

Hyperfine induced 1s2s S0 → 1s 2 S0 M1 transition probabilities of He-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. Present results for Eu and Gd are in good agreement with previous calculations [Phys. Rev. A 63, 054105 (2001)]. Electronic data are given in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine induced decay rates to be estimated for any isotope. The results should be helpful for future experimental investigations on QED and parity non-conservation effects. PACS: 31.30.Gs, 31.15.V-, 31.15.ag The hyperfine structure of atomic levels is caused by the interaction between the electrons and the non-central electromagnetic multipoles of the nucleus. The interaction, although weak, not only shifts and splits the individual J levels, but also mixes wavefunctions with different J quantum numbers [1]. The mixing may open new decay channels and induce radiative transitions such as J = 0 → J ′ = 0. The study of hyperfine induced transitions (HIT) is attractive in view of getting a more subtle understanding of electron correlation and relativistic effects [2, 3, 4], testing the standard model [5], obtaining nuclear properties [6, 7, 8], developing ultra-precise atomic clocks [9, 10, 11, 12], analyzing stellar spectra [13], and determining isotopic abundance ratios and electron densities of plasma [14, 15]. He-like systems are interesting due to their relative simplicity, and important effects such as electron correlation [16], quantum electrodynamics (QED) [17, 18, 19] and parity non-conservation (PNC) phenomena [20, 21, 22, 23] can be investigated in detail. Gorshkov and Labzovskǐi [20] and Labzowsky et al. [23] have proposed that the mixed hyperfineand weak-quenching can be used to test parity-violation effects. The one photon transition 1s2s S0 → 1s 2 S0 of He-like ions is considered a good candidate for these tests and experiments will be carried out at GSI [24]. Therefore, accurate hyperfine induced 1s2s S0 → 1s 2 S0 M1 transition probabilities of He-like ions are important. Relevant data are however still insufficient and in response to this we have performed systematic calculations along the He-like iso-electronic sequence using GRASP2K [25] based on the multi-configuration Dirac-Hartree-Fock method and the HFST [26] package. From computed hyperfine induced transitions for 14 ions and corresponding electronic quantities we have derived a scaling formula in Z that allows the induced transition rate to be computed for any isotope. When the hyperfine interaction is included the wavefunctions of the combined electronic and nuclear system can be represented as