Radiative lifetime of the ${}^1{S}_0$ metastable state in doubly charged Kr ions

The radiative lifetime of the $4s^{2}4p^4{}^1{S}_0$ metastable state in $\mathrm{K}{\mathrm{r}}^{2+}$ ions has been experimentally determined using an electrostatic ion trap of the ion-beam storage type. The radiative lifetime was obtained by measuring the number of 350-nm photons emitted during the ${}^1{S}_0{\to }^3{P}_1$ magnetic dipole transition of $\mathrm{K}{\mathrm{r}}^{2+}$ as a function of the storage time. The storage lifetime of the $\mathrm{K}{\mathrm{r}}^{2+}$ beam in the trap, which is a correction term in the determination of the radiative lifetime, was measured by detecting Kr neutrals produced by electron capture collisions with residual gases in the trap. We have obtained a lifetime value of $17.4\pm 0.4\mathrm{ms}$, which is larger than the previous experimental results, but consistent with theoretical predictions.

Figure 1

Energy-level diagram of the $4s^{2}4p^4$ ground-state configuration of $\mathrm{K}{\mathrm{r}}^{2+}$ ions. The radiation wavelengths and the branching ratios in the figure refer to the energy levels in [12] and the transition probabilities in [4].

Figure 2

(a) Schematic view of the ion trap and its power supply. (b) Apparatus configuration of this experiment with the optical system for the photon measurement.

Figure 3

Counts of photons for the $4s^{2}4p^4{}^1{S}_0\to 4s^{2}4p^4{}^3{P}_1$ transition of $\mathrm{K}{\mathrm{r}}^{2+}$ ions (350 nm) as a function of storage time. The plotted data are the counts combined into time bins of 1 ms.

Figure 4

Neutral Kr counts as a function of the storage time. The background counts were subtracted. The solid curve depicts a fit to the data using Eq. (4).

Figure 5

The same as in Fig. 3, but with the background counts subtracted and the error bars plotted at each data point. A fit to the data using Eq. (3) is shown by the solid curve.