Results on 8,9Li

The isotopes ⁸Li and ⁹Li  have lifetimes of 840 ms and 178 ms respectively. They were produced at the GSI on-line mass separator by impinging ¹²C ions at 11.4 MeV/u onto a graphite (⁸Li) or a tungsten (⁹Li) target. The experimental run was performed in December 2003. Typical recorded Spectra for both isotopes are shown in figure (a) and (b). The resonance frequencies are obtained from a fit of Voigt profiles to the hyperfine components. The laser-light induced AC Stark effect must be taken into account when extracting the isotope shift. Therefore, measurements were performed for ^6,7,8Li at different levels of laser power as shown in (c). We observed the same behavior for all three isotopes within the experimental uncertainty. For ⁹Li, measurements of the short-lived isotope were referenced to the stable reference isotope ⁷Li, measured with the same laser power. Figure (d) shows the extracted charge radii (red symbols). They are compared with predictions from various nuclear theories, electron scattering results (^6,7Li only) and charge radii extracted from nuclear reactions (Tan88, model-dependent). More details can be found in our publications (Ewald et al., PRL 93, 113002 and Ewald et al., PRL 94, 039901).

In September 2004 we have remeasured the isotope shift of ^8,9Li at the ISAC  mass separator at TRIUMF, where the yields for these isotopes are approximately 1000 times higher than at the online mass separator at GSI. We found good agreement with the results presented here and could improve the accuracy considerably. Publication of the results is in preparation.