Nuclear Charge Radii of ^7,9,10Be and the One-Neutron Halo Nucleus ¹¹Be

Nuclear charge radii of ^7,9,10,11Be have been determined by high-precision laser spectroscopy. On-line measurements were performed with collinear laser spectroscopy in the 2s_1/2→2p_1/2 transition on a beam of 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 ⁷Be to ¹⁰Be and then increases for the halo nucleus ¹¹Be. When comparing our results with predictions of ab initio nuclear-structure calculations we find good agreement. Additionally, the nuclear magnetic moment of ⁷Be was determined to be -1.3995(5)μ_N and that of ¹¹Be was confirmed with an accuracy similar to previous β-NMR measurements.