Nuclear Charge Radii of 9,11Li: The Influence of Halo Neutrons

The nuclear charge radius of {sup 11}Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a {sup 7}Li-{sup 11}Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free 2s {sup 2}S{sub 1/2}{yields}3s {sup 2}S{sub 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 {sup 6}Li to {sup 9}Li, and then increases from 2.217(35) to 2.467(37) fm for {sup 11}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.