Precision measurement of 11Li moments: influence of halo neutrons on the 9Li core.

The electric quadrupole moment and the magnetic moment of the 11Li halo nucleus have been measured with more than an order of magnitude higher precision than before, |Q| = 33.3(5) mb and mu = +3.6712(3)muN, revealing a 8.8(1.5)% increase of the quadrupole moment relative to that of 9Li. This result is compared to various models that aim at describing the halo properties. In the shell model an increased quadrupole moment points to a significant occupation of the 1d orbits, whereas in a simple halo picture this can be explained by relating the quadrupole moments of the proton distribution to the charge radii. Advanced models so far fail to reproduce simultaneously the trends observed in the radii and quadrupole moments of the lithium isotopes.

Quadrupole moment of the 11(-) intruder isomer in 196Pb and its implications for the 16(-) shears band head.

The quadrupole moment of the 11(-) isomer in 196Pb has been measured by the level mixing spectroscopy method. This state has a pi(3s(-2)(1/2)1h(9/2)1i(13/2))11(-) configuration which is involved in most of the shears band heads in the Pb region. The first directly measured value of Q(s)(11(-)) = (-)3.41(66) b, coupled to the previously known quadrupole moment of the nu(1i(-2)(13/2))12(+) isomer allows us to estimate the quadrupole moment of the 16(-) shears band head as Q(s)(16(-)) = -0.32(10) b. The experimental values are compared to tilted axis cranking calculations, giving insight into the validity of the additivity approach to couple quadrupole moments and on the amount of deformation in the shears bands.

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.