Laser Spectroscopic Determination of the Nuclear Charge Radius of $^6$He and $^8$He

Laser spectroscopic measurements of atomic isotope shifts provide unique access to the nuclear charge distribution of short-lived isotopes. The isotopes of interest for this study are $^6$He (t$_{1/2}$ = 807 ms) and $^8$He (t$_{1/2}$ = 119 ms), which exhibit a loosely bound neutron halo around an $\alpha$-like core. Charge radii measurements of both isotopes provide corroboration for their halo structure and test nuclear structure theories of light nuclei. We have performed high-resolution laser spectroscopy on individual $^6$He atoms captured in a magneto-optical trap. This technique enabled us to accurately measure the atomic isotope shift between $^6$He and $^4$He in the $2^3S_1 \rightarrow 3^3P_2$ transition. Based on this result and precision atomic theory calculation of this two electron system, the root-mean-square charge radius of the $^6$He nucleus could be determined to be 2.054(14)fm [1]. Currently, we are working to expand this technique to also measure $^8$He and we will report on first results from a $^8$He production experiment at the ATLAS facility at Argonne. [1] L.-B. Wang {\it et al.}, PRL 93, 142501 (2004).\\ {\it This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. W-31-109-ENG-38.}