Coulomb excitation of 124,126,128Sn(Z = 50)

High-precision measurements of matrix elements from the Coulomb excitationof 124,126,128Sn(Z = 50) impinging on a 12C target are presented. The matrix elements and related B(E2) values decrease monotonically as the N = 82 shell closure is approached from N = 74 to 78, despite a near constancy in the first 2+ level energy, E(2_1+). Furthermore, results are presented for the Coulomb excitationof 124,126,128Sn using an enriched 50Ti target, which, combined with the results from the 12C target, provide a measure of the matrix elements and related static quadrupolemoments, Q(2_1+) (expected to be ~0 for a spherical shape). These new results indicate that the Sn isotopes have a deformation consistent with zero. The present study marks the first report on measured 2_1+ static quadrupolemoments for the unstable Sn isotopes.