Z=50 shell gap near ${}^{100}$Sn from intermediate-energy Coulomb excitations in even-mass ${}^{106--112}$Sn isotopes

Abstract

Rare isotope beams of neutron-deficient ${}^{106,108,110}$Sn nuclei from the fragmentation of ${}^{124}$Xe were employed in an intermediate-energy Coulomb excitation experiment yielding $B(E2,0_1^{+}\to 2_1^{+})$ transition strengths. The results indicate that these $B(E2,0_1^{+}\to 2_1^{+})$ values are much larger than predicted by current state-of-the-art shell model calculations. This discrepancy can be explained if protons from within the Z = 50 shell are contributing to the structure of low-energy excited states in this region. Such contributions imply a breaking of the doubly-magic ${}^{100}$Sn core in the light Sn isotopes.

4 pages, 4 figures