Coulomb excitation of 124,126,128Sn

High-precision measurements of < 0(1)vertical bar vertical bar M(E2)vertical bar vertical bar 2(1)> matrix elements from the Coulomb excitation of Sn-124,Sn-126,Sn-128 on a C-12 target are presented. The extracted B(E2) values decrease monotonically from the neutron midshell toward the Sn-132 double-shell closure, despite a near constancy in the first 2(+) level energy. Furthermore, Coulomb excitation of Sn-124,Sn-126,Sn-128 on an enriched Ti-50 target, combined with the results from the C-12 target, provide a measure of the static quadrupole moments, Q(2(1)(+)) (expected to be zero for a spherical shape). These new results confirm that the unstable neutron-rich Sn-126,Sn-128 isotopes have deformations consistent with zero. The present study marks the first report on measured 2(1)(+) static quadrupole moments for unstable closed-shell nuclei.