Pairing-quadrupole interplay in the neutron-deficient tin nuclei: first lifetime measurements of low-lying states in ${}^{106,108}$Sn

Abstract

The lifetimes of the low-lying excited states $2^{+}$ and $4^{+}$ have been directly measured in the neutron-deficient ${}^{106,108}$Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted ${\hat{I}}^3$ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the $B(E2;2_1^{+}\to 0_{g.s.}^{+})$ values and it describes well the experimental pattern for ${}^{104-114}$Sn; the $B(E2;4_1^{+}\to 2_1^{+})$ values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in ${}^{108}$Sn. This result provides insight in the hitherto unexplained $B(E2;4_1^{+}\to 2_1^{+})/B(E2;2_1^{+}\to 0_{g.s.}^{+})<1$ anomaly.

V1: 6 pages, 3 figures, 1 table, theoretical interpretation described in detail in the arXiv paper of A.P.Zuker (cross-reference) V2: added reference to A.P. Zuker paper (arXiv:1905.11479)