Static Moments of Neutron-Rich Ground States and Isomers Produced by Projectile Fragmentation

New achievements in nuclear moment measurements on nuclei produced and spin-oriented in intermediate energy (50–80 MeV/u) projectile fragmentation reactions are presented. By combining different types of spin-orientation with different experimental techniques, we show that the magnetic dipole moments and electric quadrupole moments of exotic neutron rich nuclei in their ground state as well as in their excited isomeric states can be measured. A selection of recent experiments performed at the LISE spectrometer at GANIL (Caen, France) is described. This revised version was published online in September 2006 with corrections to the Cover Date.     

The “island of inversion" from a nuclear moments perspective and the g factor of 35Si

This paper reviews recent results from electromagnetic moment measurements on isotopes in the island of inversion around N=20. The obtained moments on neutron rich Na, Mg, Al and Si isotopes allow to draw conclusions on the amount of intruder components in their ground state wave function, demonstrating a gradual transition from the normal sd-shell region into the island of inversion, starting at N=18 for Na, N=19 for Mg and N=20 for Al isotopes. A measurement of the ground state g factor of ³⁵Si (N=21), using a polarized fragment beam at GANIL, is discussed in more detail. The magnetic moment μ(³⁵Si, I^π= 7/2^-) = (-)1.638(4) μ_N is consistent with a normal ground state structure, dominated by a νf_7/2 neutron.     

Magnetic moment of the fragmentation-aligned 61Fe (9/2(+)) isomer

We report on the g factor measurement of an isomer in the neutron-rich (61)(26)Fe (E(*)=861 keV and T(1/2)=239(5) ns). The isomer was produced and spin aligned via a projectile-fragmentation reaction at intermediate energy, the time dependent perturbed angular distribution method being used for the measurement of the g factor. For the first time, due to significant improvements of the experimental technique, an appreciable residual alignment of the nuclear spin ensemble has been observed, allowing a precise determination of its g factor, including the sign: g=-0.229(2). In this way we open the possibility to study moments of very neutron-rich short-lived isomers, not accessible via other production and spin-orientation methods.     

Measurement of the g factors of isomers near the proposed N ≈ 40 subshell closure

We report results from a pioneering experiment to measure the g factors of isomeric states of neutron-rich nuclei around ⁶⁸Ni, far from the valley of β stability.For the first time, the time-dependent perturbed angular distribution method was applied in combination with the heavy-ion-γ correlation technique to study g factors of spin-aligned isomers produced in a projectile fragmentation reaction and mass-separated. Some technical aspects are discussed and illustrated with preliminary results.     

Nuclear charge radii of (21-32)Mg

Charge radii of all magnesium isotopes in the sd shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on (24)Mg and (32)Mg. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards N=8 and collectivity near N=20 is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.