Probing the Structure of Exotic Nuclei by Dedicated Laser-Spectroscopy Methods: Recent Highlights and Perspectives
D. T. Yordanov (CERN-COLLAPS collaboration) - 11h - GANIL seminar room
The most recent highlights from collinear laser-spectroscopy at ISOLDE-CERN will be presented, including the magnesium charge radii in the sd shell, the charge-radius of the one-neutron halo 11Be and the properties of exotic copper and gallium isotopes. Specialized techniques have been used in each of these cases, respectively b-asymmetry detection after optical pumping, absolute frequency determinations with a frequency comb and cooling and bunching in a RF Paul trap. The idea of b-delayed g spectroscopy on laser polarized beams will be presented as well.
The island of inversion is commonly regarded as an island of deformation. Yet, the transition to a deformed configuration in the isotopes of magnesium is not well understood. This problem cannot be addressed by quadrupole-moment measurements due to nuclear spins 0 or 1/2 of most key isotopes. Experimental evidence from reaction studies and the ground-state properties of 31,33Mg are consistent with considerable prolate deformation. However, in order to obtain a continuous picture of the evolution of the nuclear shape along the magnesium chain one has to measure a quantity accessible for all isotopes (odd and even) with the same experimental technique. Accordingly, a measurement of the rms charge radii of 21-32Mg will be presented with emphasis on the new methodology for isotope-shift measurements based on combining fluorescence with b detection.
The potential of a novel b-delayed g spectroscopy, utilizing the strong nuclear orientation produced by optical pumping will be presented. This method will extend the reach of collinear laser spectroscopy to new physics by introducing the capability of measuring spins and parities of ground and excited nuclear states. The technique would be a powerful expansion of both: (i) the classical b-NMR laser spectroscopy, which can directly determine only the spins of ground states and long-lived isomers, and (ii) the classical b-delayed g spectroscopy, whose spin and parity assignments are relative and insufficiently constrained by the selection rules. An elaborate discussion of the methodology will be presented and considered in the context of future ISOL facilities.
The charge radii of 7-11Be have been determined by a high-precision collinear-anticollinear spectroscopy combined with absolute frequency determination by a frequency comb. The achieved accuracy of the isotope shifts in the transition 2s1/2®2p1/2 of Be+ is better than 1 MHz. Accurate atomic-physics calculations are used to eliminate the mass-dependent isotope shift and extract the nuclear volume effect. The charge radii decrease from 7Be to 10Be and increase again for the halo nucleus 11Be. From a simple frozen-core two-body model a root mean square distance of about 7 fm between the halo neutron and the center of mass in 11Be is obtained.
The first results from online laser spectroscopy with the ISOLDE radio-frequency cooler and buncher (ISCOOL) will be presented, namely the hyperfine-structure and isotope-shift measurements of neutron-rich gallium and copper isotopes. The case of copper will be discussed in terms of the π 1f5/2 monopole migration. Gallium will be presented as a show case of discovering isomeric states by laser spectroscopy.
