M. Keim

Measurement of nuclear moments and radii by collinear laser spectroscopy and by β-NMR spectroscopy

Experiments using laser spectroscopy and nuclear magnetic resonance techniques have been performed at ISOLDE on the unstable isotopes of several light elements. The results include nuclear ground state spins, magnetic dipole and electric quadrupole moments, and the behaviour of mean square nuclear charge radii within isotopic strings. These give important information about the nuclear structure at shell closures and close to the drip lines.

OPTICAL POLARIZATION OF NEUTRON-RICH SODIUM ISOTOPES AND BETA -NMR MEASUREMENTS OF QUADRUPOLE MOMENTS

The nuclear quadrupole moments of neutron-rich sodium isotopes are being investigated with the help of in-beam polarization by optical pumping in combination withβ-NMR techniques. First measurements have yielded the quadrupole splittings of NMR signals in the lattice of LiNbO3 for the isotopes26Na,27Na and28Na. Interaction constants and ratios of the electric quadrupole moments are derived. In view of future experiments,β-decay asymmetries for the sequence of isotopes up to theN=20 neutron shell closure,26–31Na, have been measured.

Accurate isotope shift measurements on short-lived neon isotopes

We report on fast beam collinear laser spectroscopy measurements that demonstrate the feasibility of accurate isotope shift measurements for short lived Ne isotopes including the proton halo candidate 17Ne. Ultra high sensitivity is achieved by the application of an efficient resonance detection scheme based on collisional ionization and ion counting via the β decay. A direct measurement of the kinetic energy of the atomic Ne beam provides the required high accuracy.

Recent measurements of nuclear moments far from stability

Measurements of nuclear moments far from stability have been performed mainly applying laser spectroscopy and β-NMR spectroscopy. A short overview of the experimental techniques are given. The β-NMR experiments on the quadrupole moments of sodium isotopes and of the magnetic moment of 11Be, both using optically pumped radioactive beams, are discussed in more detail.

β-NMR in II–VI semiconductors

Abstractβ-active probe nuclei are implanted in nominally undoped ZnSe crystals. β-radiation detected nuclear magnetic resonance (β-NMR) studies are described for two different probe nuclei, 8Li and 12B. This way, the implantation behavior of two “opposite”dopants, one acceptor (Li) and one donor (B) can be characterized by the same microscopic technique. Such characterizations are attempted in terms of the structure of intermediate or final lattice sites, defect charge states, or the kinetics of defect reactions and site changes.

β-NMR measurement of the nuclear quadrupole moments of 20,26–31Na

The quadrupole moments of the neutron-rich isotopes {sup 26-31}Na and of the neutron-deficient {sup 20}Na were measured by {beta}-NMR after implantation of the short-lived nuclei into the host crystal lattices of Mg, LiNbO{sub 3} and NaNO{sub 3}. The ion beams from ISOLDE were neutralized and polarized by in-beam optical pumping. Of particular interest are the isotopes close to N=20 for which various experimental observations suggest rather strong deformation.

Measurement of the magnetic moments of 7Be and of the halo nucleus 11Be

Recently the CERN/ISOLDE laser ion source was optimized to provide intense beryllium ion beams. This allowed us to perform optical spectroscopy on 7,9,10Be yielding the unknown magnetic moment of 7Be and the isotope shifts in the lithium-like spectrum of Be+. Furthermore we measured the magnetic moment of the neutron halo nucleus 11Be via β-NMR on optically polarized nuclei.

Implanted light dopants in ZnSe

Spin polarized radioactive 12B, 12N, and 8Li probe nuclei are implanted in nominally undoped ZnSe at stationary concentrations ≤ 1010 cm-3. These light dopants, one donor and two acceptors, are characterized by β-radiation detected nuclear magnetic resonance (β-NMR) measurements. The donor 12B and the acceptor 12N show quite similar and rather simple implantation behaviour, the situation is markedly different for the second acceptor 8Li, however. This contrast indicates that in semi-insulating ZnSe the structure of dilute impurities is controlled by individual, element-specific properties.