Investigation into the semimagic nature of the tin isotopes through electromagnetic moments

A complete set of electromagnetic moments, B(E2;01+→21+),Q(21+), and g(21+), have been measured from Coulomb excitation of semimagic Sn112,114,116,118,120,122,124 (Z=50) on natural carbon and titanium targets. The magnitude of the B(E2) values, measured to a precision of ∼4%, disagree with a recent lifetime study [Phys. Lett. B 695, 110 (2011)PYLBAJ0370-269310.1016/j.physletb.2010.11.012] that employed the Doppler-shift attenuation method. The B(E2) values show an overall enhancement compared with recent theoretical calculations and a clear asymmetry about midshell, contrary to naive expectations. A new static electric quadrupole moment, Q(21+), has been measured for Sn114. The static quadrupole moments are generally consistent with zero but reveal an enhancement near midshell; this had not been previously observed. The magnetic dipole moments are consistent with previous measurements and show a near monotonic decrease in value with neutron number. The g-factor measurements in Sn112,114 establish the recoil-in-vacuum method for states with τ∼0.5 ps and hence demonstrate that this method can be used for future g-factor measurements on proton-rich isotopes toward Sn100. Current theory calculations fail to reproduce the electromagnetic moments of the tin isotopes. The role of 2p-2h and 4p-4h intruders, which are lowest in energy at midshell and outside of current model spaces, needs to be investigated in the future.