Restoration of the N=82 shell gap from direct mass measurements of 132,134Sn

A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of Sn-134 from the currently accepted value. The corrected mass assignment of this neutron-rich nuclide restores the neutron-shell gap at N=82, previously considered to be a case of shell quenching. In fact, the new shell gap value for the short-lived Sn-132 is larger than that of the doubly magic Ca-48 which is stable. The N=82 shell gap has considerable impact on fission recycling during the r process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides.