Figure 1

King plot of the isotope shifts of the $7s{}^2{S}_{1/2}$-$7p{}^2{P}_{1/2}$ transition in ${\mathrm{Ra}}^{+}$ at 468 nm [23] against the $6d{}^2{D}_{3/2}$-$7p{}^2{P}_{1/2}$ transition in ${\mathrm{Ra}}^{+}$ at 1080 nm [6]. The slope of the line is $F_{1080}/F_{468}=-0.244\left(11\right)$, and the line intersects the $y$ axis at $k_{1080}^{\mathrm{sms}}=-2.0\left(11\right)$ THz amu. The errors on the $x$ coordinates are smaller than the symbols. For comparison with theoretical predictions, see Table .Reuse & Permissions

Figure 2

The relevant low-lying levels and transitions in Ra${}^{+}$ and Ra. The wavelengths are taken from Refs. [31, 32].Reuse & Permissions

Figure 3

The values of $\delta \langle r^2\rangle$, relative to ${}^{214}$Ra, for the Ra isotopes, as calculated in different atomic and nuclear approaches. The figure shows our results including (dashed black lines) and excluding deformations (dashed red lines). The results of the ISOLDE collaboration [25] are depicted in the same plot: The solid purple lines with solid circles are their Dirac-Fock results, while the solid gray lines with the solid circles are their preferred semiempirical results; their $10\%$ calibration error towards higher absolute values is indicated by the gray scaling. The dotted orange lines with stars are from Ref. [21]. The blue dash-dotted lines with the open circles are from the liquid-drop model from Ref. [22]. The green dashed lines with diamonds are from the generalized liquid-drop model of Ref. [36].Reuse & Permissions