Storage-Ring Measurement of the Hyperfine Induced ${}^{47}\mathrm{Ti}^{18+}(2s2p{}^{3}P_0\to 2s^2{}^{1}S_0)$ Transition Rate

The hyperfine induced $2s2p{}^{3}P_0\to 2s^2{}^{1}S_0$ transition rate $A_{\mathrm{HFI}}$ in berylliumlike ${}^{47}\mathrm{Ti}^{18+}$ is measured. Resonant electron-ion recombination in a heavy-ion storage ring is employed to monitor the time dependent population of the ${}^{3}P_0$ state. The experimental value $A_{\mathrm{HFI}}=0.56(3){\mathrm{s}}^{-1}$ is almost 60% larger than theoretically predicted.

Figure 1

Simplified level diagram for berylliumlike ${\mathrm{Ti}}^{18+}$. The level energies were taken from the NIST Atomic Spectra Data Base [25], and the lifetimes (in s) labeling the excited levels were calculated from theoretical one-photon transition rates [27] that do not account for hyperfine effects. Numbers in square brackets denote powers of 10. In case of nonzero nuclear spin the hyperfine induced (HFI) ${}^{3}P_0\to {}^{1}S_0$ transition rate $A_{\mathrm{HFI}}$ acquires a finite value. The ${}^{1}P_1\to {}^{1}S_0$ electric dipole (E1), ${}^{3}P_2\to {}^{1}S_0$ magnetic quadrupole (M2), and ${}^{3}P_1\to {}^{1}S_0$ intercombination (IC) transitions are also shown.

Figure 2

Measured rate coefficients for the electron-ion recombination of ${}^{48}\mathrm{Ti}^{18+}$ (a) and ${}^{47}\mathrm{Ti}^{18+}$ (b) in the energy range of interest. The resonances that are formed by resonant dielectronic capture of the initially free electron are assigned to doubly excited ${\mathrm{Ti}}^{17+}$ states as indicated with the aid of theoretical calculations using the autostructure code [19]. A comprehensive plot of the ${}^{48}\mathrm{Ti}^{18+}$ recombination spectrum extending over the entire experimental energy range of 0–80 eV can be found in Ref. 28.

Figure 3

Measured ${}^{48}\mathrm{Ti}^{17+}$ and ${}^{47}\mathrm{Ti}^{17+}$ recombination count rates as a function of storage time. Both panels show the same curves on different time scales. Clearly, the $A=47$ curve has a fast decaying component that is absent in the $A=48$ curve. The solid lines are the results of the fits of Eq. (1) to the experimental data points (symbols). In the right panel the fitted $c_g^{(A)}\exp (-{\lambda }_g^{(A)}t)$ components are shown as dashed lines. The fit results are summarized in Table .