The magnetic moment of 11 Be (T 1͞2 13.8 s) was measured by detecting nuclear magnetic resonance signals in a beryllium crystal lattice. The experimental technique applied to a 11 Be 1 ion beam from a laser ion source includes in-beam optical polarization, implantation into a metallic single crystal, and observation of rf resonances in the asymmetric angular distribution of the b decay (b-NMR). The nuclear magnetic moment m͑ 11 Be͒ 21.6816͑8͒ m N provides a stringent test for theoretical models describing the structure of the 1͞2 1 neutron halo state.

High-precision mass and charge radius measurements on ;{17-22}Ne, including the proton-halo candidate 17Ne, have been performed with Penning trap mass spectrometry and collinear laser spectroscopy. The 17Ne mass uncertainty is improved by factor 50, and the charge radii of ;{17-19}Ne are determined for the first time. The fermionic molecular dynamics model explains the pronounced changes in the ground-state structure. It attributes the large charge radius of 17Ne to an extended proton configuration with an s;{2} component of about 40%. In 18Ne the smaller radius is due to a significantly smaller s;{2} component. The radii increase again for ;{19-22}Ne due to cluster admixtures.

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The nuclear electric quadrupole moments of the isotopes 26 Na, 27 Na, 28 Na and 29 Na were measured by -NMR spectroscopy in single crystals of LiNbO 3 and NaNO 3 . High degrees of nuclear polarization were produced by optical pumping of the sodium atoms in a fast beam with a collinear laser beam. The polarized nuclei were implanted into the crystals and NMR signals were observed in the -decay asymmetries. Preparatory measurements also yielded improved values for the magnetic moments of 27,31 Na and con rmed the spin I = 3=2 for 31 Na. The results are discussed in comparison with large-basis shell-model calculations.

Nuclear moments of odd-A neon isotopes in the range 17 A 25 have been determined from optical hyperfine structures measured by collinear fast-beam laser spectroscopy. The magnetic dipole moments of 17 Ne, 23 Ne, and 25 Ne, as well as the electric quadrupole moment of 23 Ne, are either reported for the first time or improved considerably. The measurements also decide for a 1/2 + ground state of 25 Ne. The behavior of the magnetic moments of the proton drip-line nucleus 17 Ne and its mirror partner 17 N suggests isospin symmetry. Thus, no clear indication of an anomalous nuclear structure is found for 17 Ne. The magnetic moments of the investigated nuclei are discussed in a shell-model approach.

We report on the measurement of optical isotope shifts for 32 40 Ar and for 46 Ar from which the changes in mean square nuclear charge radii across the N = 20 neutron shell closure are deduced. The investigations were carried out by collinear laser spectroscopy in fast beams of neutral argon atoms. The ultra-sensitive detection combines optical pumping, stateselective collisional ionization and counting of -radioactivity. By reaching far into the sd-shell, the results add new information to the systematics of radii in the calcium region (Z 20). Contrary to all major neutron shell closures with N 28, the N = 20 shell closure causes no signicant slope change in the development of the radii. Information from the hyperne structure of the odd-A isotopes includes the magnetic moments of 33 Ar (I = 1 = 2) and 39 Ar (I = 7 = 2), and the quadrupole moments of 35 Ar, 37 Ar (I = 3 = 2) and 39 Ar. The electromagnetic moments are compared to shell-model predictions for the sd-and fp-shell. Even far from stability a v ery good agreement between experiment and theory is found for these quantities. The mean square charge radii are discussed in the framework of spherical SGII Skyrme-type Hartree-Fock calculations.Keywords: NUCLEAR STRUCTURE 32 40;46 Ar; measured isotope shifts, hfs; deduced hyperne constants, spins I, magnetic dipole moments , electric quadrupole moments Q s , mean square charge radii hr 2 i; Collinear fast-beam laser spectroscopy, collisional ionization and -detection; shell model (sd-, fp-shell).

We report on the changes in mean square charge radii of unstable neon nuclei relative to the stable 20 Ne, based on the measurement of optical isotope shifts. The studies were carried out using collinear laser spectroscopy on a fast beam of neutral neon atoms. High sensitivity on short-lived isotopes was achieved thanks to nonoptical detection based on optical pumping and state-selective collisional ionization, which was complemented by an accurate determination of the beam kinetic energy. The new results provide information on the structural changes in the sequence of neon isotopes all across the neutron sd shell, ranging from the proton drip line nucleus and halo candidate 17 Ne up to the neutron-rich 28 Ne in the vicinity of the "island of inversion." Within this range the charge radius is smallest for 24 Ne with N = 14 corresponding to the closure of the neutron d 5/2 shell, while it increases toward both neutron shell closures, N = 8 and N = 20. The general trend of the charge radii correlates well with the deformation effects which are known to be large for several neon isotopes. In the neutron-deficient isotopes, structural changes arise from the onset of proton-halo formation for 17 Ne, shell closure in 18 Ne, and clustering effects in 20,21 Ne. On the neutron-rich side the transition to the island of inversion plays an important role, with the radii in the upper part of the sd shell confirming the weakening of the N = 20 magic number. The results add new information to the radii systematics of light nuclei where data are scarce because of the small contribution of nuclear-size effects to the isotope shifts which are dominated by the finite-mass effect.

We present total single- and double-ionization cross sections for the collision systems pbar + He and pbar + Li+ in the 1–1000 keV impact energy range with emphasis on microscopic response effects during the collision. The calculations rely on the basis generator method. In both collision systems, the response of the effective electronic interaction to the time-dependent density reduces the ionization cross section at low impact energies significantly. It is shown, in comparison with other theories, that this reduction is a consequence of time-dependent screening rather than due to dynamical correlation effects