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

TL;DR

This study measures the lifetimes and transition rates of $^{76}$Sr and $^{78}$Sr, revealing mutually enhanced collectivity and shape coexistence at $N=Z=38$, indicating highly deformed nuclei.

Contribution

It provides the first experimental evidence of mutually enhanced collectivity at $N=Z=38$ in $^{76}$Sr, highlighting shape coexistence and extreme deformation.

Findings

Large deformation parameters for $^{76}$Sr and $^{78}$Sr.

Evidence of shape coexistence in $^{76}$Sr.

Mutually enhanced collectivity at $N=Z=38$.

Abstract

The lifetimes of the first 2$^{+}$ states in the neutron-deficient $^{76,78}$Sr isotopes were measured using a unique combination of the $\gamma$-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 $\beta_2$ = 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.