Narrowing of the neutron sd-pf shell gap in 29Na

The wave-function composition for the low-lying states in Na-29 was explored by measuring their electromagnetic properties using the Coulomb-excitation technique. A beam of Na-29 ions, postaccelerated to 70 MeV, bombarded a Pd-110 target with a rate of up to 600 particles per second at the recently commissioned ISAC-II facility at TRIUMF. Six segmented HPGe clover detectors of the TIGRESS gamma-ray spectrometer were used to detect deexcitation gamma rays in coincidence with scattered or recoiling charged particles in the segmented silicon detector, BAMBINO. The reduced transition matrix element vertical bar < 5/2(1)(+)vertical bar vertical bar E2 vertical bar vertical bar 3/2(gs)(+)>vertical bar in Na-29 was derived to be 0.237(21) e b from the measured gamma-ray yields for both projectile and target. This first-time measured value is consistent with the most recent Monte Carlo shell-model calculation, indicating a significant admixture of both sd and pf components in the wave function, and also providing evidence for the narrowing of the neutron sd-pf shell gap from similar to 6 MeV for stable nuclei to similar to 3 MeV for Na-29. (C) 2009 Elsevier B.V. All rights reserved.