Observation of mutually enhanced collectivity in self-conjugate ${}_{38}^{76}$Sr${}_{38}$

Abstract

The lifetimes of the first 2${}^{+}$ states in the neutron-deficient ${}^{76,78}$Sr isotopes were measured using a unique combination of the ${\hat{I}}^3$-ray line-shape method and two-step nucleon exchange reactions at intermediate energies. The transition rates for the 2${}^{+}$ states were determined to be $B$(E2;2${}^{+}$$\to 0^{+}$) = 2220(270) e${}^2$fm${}^4$ for ${}^{76}$Sr and 1800(250) e${}^2$fm${}^4$ for ${}^{78}$Sr, corresponding to large deformation of ${\hat{I}}_2^2$ = 0.45(3) for ${}^{76}$Sr and 0.40(3) for ${}^{78}$Sr. The present data provide experimental evidence for mutually enhanced collectivity that occurs at $N$ = $Z$ = 38. The systematic behavior of the excitation energies and $B$(E2) values indicates a signature of shape coexistence in ${}^{76}$Sr, characterizing ${}^{76}$Sr as one of most deformed nuclei with an unusually reduced $E$(4${}^{+}$)/$E$(2${}^{+}$) ratio.

Accepted for publication in Physical Review C Rapid Communication