First Measurement of Pure Electron Shakeoff in the $\beta$ Decay of Trapped ${}^6\mathrm{He}^{+}$ Ions

The electron shakeoff probability of ${}^6\mathrm{Li}^{2+}$ ions resulting from the ${\beta }^{-}$ decay of ${}^6\mathrm{He}^{+}$ ions has been measured with high precision using a specially designed recoil ion spectrometer. This is the first measurement of a pure electron shakeoff following nuclear $\beta$ decay, not affected by multielectron processes such as Auger cascades. In this ideal textbook case for the application of the sudden approximation, the experimental ionization probability was found to be $P_{\mathrm{so}}^{\exp }=0.02339(36)$ in perfect agreement with simple quantum mechanical calculations.

Figure 1

Top view of the experimental setup. The inset shows the structure of the six stainless steel rings of the Paul trap. See text for details.

Figure 2

Coincidence events as a function of time within the trapping cycle. The regions 1 and 2 correspond respectively to the selection of “in-trap” and “out-trap” events.

Figure 3

TOF spectrum of recoil ions. The four regions used in the data analysis are delimited by vertical lines. The horizontal gray line indicates the average level of accidental events.

Figure 4

Upper panel: fit of the experimental spectrum with the MC simulations. The range selected for the fit is indicated by the vertical lines. Lower panel: normalized residuals of the fit.