Mixed-symmetry octupole and hexadecapole excitations in the N=52 isotones

TL;DR

This study investigates mixed-symmetry octupole and hexadecapole excitations in the N=52 isotone $^{96}$Ru using proton scattering experiments and IBM-2 calculations, revealing strong M1 transitions and confirming mixed-symmetry character.

Contribution

It provides experimental evidence and theoretical analysis of octupole and hexadecapole mixed-symmetry states in $^{96}$Ru, extending understanding of nuclear excitation modes.

Findings

Strong M1 transitions observed between 3^- and 4^+ states.

Evidence for one-phonon mixed-symmetry character in specific states.

IBM-2 calculations agree with experimental data, confirming mixed-symmetry nature.

Abstract

Background: Excitations with mixed proton-neutron symmetry have been previously observed in the $N=52$ isotones. Besides the well established quadrupole mixed-symmetry states (MSS), octupole and hexadecapole MSS have been recently proposed for the nuclei $^{92}$Zr and $^{94}$Mo. Purpose: The heaviest stable $N=52$ isotone $^{96}$Ru was investigated to study the evolution of octupole and hexadecapole MSS with increasing proton number. Methods: Two inelastic proton-scattering experiments on $^{96}$Ru were performed to extract branching ratios, multipole mixing ratios, and level lifetimes. From the combined data, absolute transition strengths were calculated. Results: Strong $M1$ transitions between the lowest-lying $3^-$ and $4^+$ states were observed, providing evidence for a one-phonon mixed-symmetry character of the $3^{(-)}_2$ and $4^+_2$ states. Conclusions: $sdg$-IBM-2 calculations were performed for $^{96}$Ru. The results are in excellent agreement with the experimental data, pointing out a one-phonon hexadecapole mixed-symmetry character of the $4^+_2$ state. The $\big< 3^-_1||M1||3^{(-)}_2\big>$ matrix element is found to scale with the $<2^+_{\mathrm{s}}||M1||2^+_{\mathrm{ms}}>$ matrix element.