Multiple shape coexistence near Sn118: First 03+ lifetime measurement

Abstract

The intruder bands in Sn isotopes, built on the 2p-2h excitation across the $Z=50$ proton shell gap, are well-known examples of shape coexistence near the neutron mid-shell region. Spectroscopic signatures for shape coexistence include enhanced $E0$ transitions between the $0^{+}$ band heads. However, the underlying shape coexistence and mixing has been unclear because lifetime information for the excited $0^{+}$ states was incomplete in ${}^{118}$Sn. We thus present here the first measurement of the $0_3^{+}$ lifetime in ${}^{118}$Sn using the fast-timing technique following thermal-neutron capture. The observed enhancement in $\ddot{I}{}^2(E0;0_3^{+}\to 0_2^{+})$ of 150(30) milliunits provides compelling indications for multiple shape coexistence in ${}^{118}$Sn. Additionally, three distinct shapes in ${}^{116,118,120}$Sn naturally emerged in theoretical calculations based on the quantum-number-projected generator coordinate method employing a relativistic energy density functional.

7 pages, 2 figures, Supplemental material: https://journals.aps.org/prc/supplemental/10.1103/npjn-xpfj/Supp.pdf