Magnetic moments of 21+ states in 124^,126^,128Sn

The g factors of the first-excited states of stable 124Sn and radioactive 126^,128Sn were measured by the recoil-in-vacuum method with comparatively high precision. The experiments were performed at the Holifield Radioactive Ion Beam Facility by Coulomb exciting ∼3 MeV/u beams in inverse kinematics on carbon and titanium targets. The results for 124Sn and 126Sn are in excellent agreement with recent shell-model calculations. For 128Sn the experiment suggests an increase in the magnitude of g(21+), as predicted by some models. The present results provide a sensitive probe of the valence orbitals that contribute to the 21+ wave functions as the double-shell closure at 132Sn is approached.