Laser Trapping and Probing of Exotic Helium Isotopes

We have succeeded in laser trapping and cooling of the exotic helium isotopes, both $^{6}$He (t$_{1/2}$ = 0.8 sec) and $^{8}$He (t$_{1/2}$ = 0.1 sec), and have performed precision laser spectroscopy on individual trapped atoms. Based on the atomic isotope shifts measured along the isotope chain $^{3}$He - $^{4}$He - $^{6}$He - $^{8}$He, and on the precise theory of the atomic structure of helium, the nuclear charge radii of $^{6}$He and $^{8}$He are determined for the first time in a method independent of nuclear models. The results are compared with the values predicted by a number of nuclear structure calculations and test their ability to characterize these neutron rich, loosely bound halo nuclei. The $^{6}$He measurement was performed at ATLAS of Argonne, and the $^{8}$He measurement at GANIL, France. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.