Evidence for reduced collectivity around the neutron mid-shell in the stable even-mass Sn isotopes from new lifetime measurements

Precise measurements of the lifetimes of the first excited 2(+) states in the stable even-A Sn isotopes Sn112-124 have been performed using the Doppler shift attenuation technique. For the isotopes Sn-112, Sn-114 and Sn-116 the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously reported values and indicate a shallow minimum at N = 66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the S-1/2 neutron orbital in generating collectivity when near the Fermi level. (C) 2010 Elsevier B.V. All rights reserved.