Nuclear charge radii of ${}^{7,9,10,11}\mathrm{Be}$ have been determined by high-precision laser spectroscopy. On-line measurements were performed with collinear laser spectroscopy in the $2s_{1/2}\to 2p_{1/2}$ transition on a beam of ${\mathrm{Be}}^{+}$ ions. Collinear and anticollinear laser beams were used simultaneously, and the absolute frequency determination using a frequency comb yielded an accuracy in the isotope-shift measurements of about 1 MHz. Combining this with accurate calculations of the mass-dependent isotope shifts yields nuclear charge radii. The charge radius decreases from ${}^7\mathrm{Be}$ to ${}^{10}\mathrm{Be}$ and then increases for the halo nucleus ${}^{11}\mathrm{Be}$. When comparing our results with predictions of ab initio nuclear-structure calculations we find good agreement. Additionally, the nuclear magnetic moment of ${}^7\mathrm{Be}$ was determined to be $-1.3995(5){\mu }_N$ and that of ${}^{11}\mathrm{Be}$ was confirmed with an accuracy similar to previous $\beta$-NMR measurements.

The nuclear charge radius of ${}^{11}\mathrm{Li}$ has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a ${}^7\mathrm{Li}–{}^{11}\mathrm{Li}$ isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free $2s{}^{2}S_{1/2}\to 3s{}^{2}S_{1/2}$ transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from ${}^6\mathrm{Li}$ to ${}^9\mathrm{Li}$, and then increases from 2.217(35) to 2.467(37) fm for ${}^{11}\mathrm{Li}$. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

Atomic physics techniques for the determination of ground-state properties of radioactive isotopes are very sensitive and provide accurate masses, binding energies, Q-values, charge radii, spins and electromagnetic moments. Many fields in nuclear physics benefit from these highly accurate numbers. They give insight into details of the nuclear structure for a better understanding of the underlying effective interactions, provide important input for studies of fundamental symmetries in physics, and help to understand the nucleosynthesis processes that are responsible for the observed chemical abundances in the Universe. Penning-trap and storage-ring mass spectrometry as well as laser spectroscopy of radioactive nuclei have now been used for a long time but significant progress has been achieved in these fields within the last decade. The basic principles of laser spectroscopic investigations, Penning-trap and storage-ring mass measurements of short-lived nuclei are summarized and selected physics results are discussed.

One of the most important global properties of the atomic nucleus is its size. Experimentally determined nuclear charge radii carry unique information on the nuclear force and complex dynamics of protons and neutrons moving inside the nucleus. The intricate behaviour of charge radii along the chain of Ca isotopes, including the unexpectedly large charge radius of neutron-rich ⁵²Ca, poses a daunting challenge for nuclear theory¹. Here we present the measurements of the charge radii of proton-rich isotopes ^36,37,38Ca, whose properties are impacted by the interplay between nuclear superfluidity and weak binding. Calculations carried out within nuclear density functional theory show that the combination of a novel interaction² and a state-of-the-art theoretical method can successfully explain the behaviour of charge radii from the lightest to the heaviest Ca isotopes. Through this model, we show how the new data on ^36,37,38Ca elucidate the nature of nucleonic pairing in weakly bound proton-rich isotopes.

Collinear laser spectroscopy was performed on Ga ($Z=31$) isotopes at ISOLDE, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend measurements towards very neutron-rich isotopes ($N=36–50$). A ground state (g.s.) spin $I=1/2$ is measured for ${}^{73}\mathrm{Ga}$, being near degenerate with a $3/2^{-}$ isomer ($75\mathrm{eV}\lesssim E_{\mathrm{ex}}\lesssim 1\mathrm{keV}$). The ${}^{79}\mathrm{Ga}$ g.s., with $I=3/2$, is dominated by protons in the $\pi f_{5/2}$ orbital and in ${}^{81}\mathrm{Ga}$ the $5/2^{-}$ level becomes the g.s. The data are compared to shell-model calculations in the $f_{5/2}p{g}_{9/2}$ model space, calling for further theoretical developments and new experiments.