Measurement of Moments and Radii of Light Nuclei by Collinear Fast-Beam Laser Spectroscopy and $\beta$-NMR Spectroscopy

Nuclear Moments and radii of light unstable isotopes are investigated by applying different high-sensitivity and high-resolution techniques based on collinear fast-beam laser spectroscopy. A study of nuclear structure in the sd shell is performed on neon isotopes in the extended chain of $^{17-28}$Ne, in particular on the proton-halo candidate $^{17}$Ne. Measurements of hyperfine structure and isotope shift have become possible by introducing an ultra-sensitive non-optical detection method which is based on optical pumping, state-selective collisional ionization and $\beta$-activity counting. The small effect of nuclear radii on the optical isotope shifts of light elements requires very accurate measurements. The errors are dominated by uncertainties of the Doppler shifts which are conventionally determined from precisely measured acceleration voltages. These uncertainties are removed by measuring the beam energy with simultaneous excitation of two optical lines in parallel / antiparallel beam configuration. One obtains the energy of a 60 keV neon beam to less than 1 eV. This calibration accuracy is sufficient to clearly resolve nuclear structure effects in the radii. Similar measurements on the neutron-rich argon isotopes will complement earlier results and yield a conclusive picture of nuclear radii in the calcium region. Laser excitation in collinear geometry can also be used to produce nuclear-spin polarized beams. Implantation into suitable crystal lattices and detection of an angular asymmetry in the $\beta$-decay gives access to NMR spectroscopy on short-lived isotopes. This technique will be used for a precision measurement of the quadrupole moment of the famous halo nucleus $^{11}$Li. By comparing the quadrupole moments of $^9$Li and $^{11}$Li it will be possible to extract the polarizarion effect of the two halo neutrons on the core.