New shell closure for neutron-rich Sn isotopes

The variation of E(2(1)(+)) of Sn134-140 calculated with empirical SMPN interaction has striking similarity with that of experimental E(2(1)(+)) of even-even O18-22 and Ca42-48, showing clearly that N = 84-88 spectra exhibit the effect of gradually filling up the nu(2f(7/2)) orbital, which finally culminates in a new shell closure at N = 90. Realistic two-body interaction CWG does not show this feature. Spin-tensor decomposition of SMPN and CWG interactions and variations of their components with valence neutron number reveals that the origin of the shell closure at Sn-140 lies in the three-body effects. Calculations with CWG3M, which is obtained by including a simple three-body monopole term in the CWG interaction, predict decreasing E(2(1)(+)) for Sn-136,Sn-138 and a shell closure at Sn-140.