Nuclear charge radius of He8

Abstract

The root-mean-square (rms) nuclear charge radius of He8, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of He6 was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from He6 to He8 is an indication of the change in the correlations of the excess neutrons and is consistent with the He8 neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.