Nuclear Charge Radii of 8,9Li Determined by Laser Spectroscopy

The 2S -> 3S transition of 6,7,8,9Li was studied by high-resolution laser spectroscopy using two photon Doppler-free excitation and resonance-ionization detection. The hyperfine structure splitting and the isotope shift were determined with precision at the 100 kHz level. Combined with recent theoretical work, the changes in nuclear charge radii of 8,9Li were determined. These are now the lightest short-lived isotopes for which the charge radii have been measured. It is found that the charge radii monotonically decrease with increasing neutron number from 6Li to 9Li.