Nuclear Charge Radii of ${}^{9,11}\mathrm{Li}$: The Influence of Halo Neutrons

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

Figure 1

Resonances in the $2s\to 3s$ transition of ${}^{11}\mathrm{Li}$ as a function of the beat frequency between the Ti:sapphire laser and the reference diode laser. Error bars are simple counting statistics on the number of observed ion counts.

Figure 2

Experimental charge radii of lithium isotopes (red, ●) compared with theoretical predictions: △: GFMC calculations [4, 22], ▽: SVMC model [27, 28] (▼: assuming a frozen ${}^9\mathrm{Li}$ core), ⊕: FMD [26], ○: DCM [19], □ and ◇: ab initio NCSM [23, 24].