Isoscalar Giant Resonances in Highly-Deformed $^{172}$Yb

TL;DR

This study investigates isoscalar giant resonances in highly-deformed $^{172}$Yb using inelastic alpha scattering, revealing resonance splitting, bimodal structures, and deformation effects, with results supported by theoretical calculations.

Contribution

First detailed measurement of isoscalar giant resonances in a highly-deformed nucleus using alpha scattering and multipole analysis, highlighting resonance coupling and deformation effects.

Findings

ISGMR exhibits splitting due to coupling with ISGQR.

Bimodal structure observed in ISGDR strength distribution.

Enhanced ISGQR strength near 25 MeV linked to overtone mode.

Abstract

To study the isoscalar giant resonances in a deformed case, background-free $\alpha$-particle inelastic scattering measurements using a 386 MeV $\alpha$ beam were performed on the highly-deformed $^{172}$Yb nucleus using the Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP) at very forward angles, including $0^\circ$. The strength distributions for the isoscalar giant resonances up to $L \leq 3$ were obtained using multipole decomposition analysis. The isoscalar giant monopole resonance (ISGMR) strength exhibits a splitting into two components, interpreted as the coupling of the ISGMR with the $K=0$ component of the isoscalar giant quadrupole resonance (ISGQR). A \textit{bimodal} structure is observed in the strength distribution of the isoscalar giant dipole resonance. The ISGQR strength shows an enhancement near 25 MeV, attributed to the excitation of an overtone mode, while the broadening of the main-tone peak is associated with nuclear deformation. The experimental results are well reproduced by theoretical strength distributions calculated using the quasiparticle finite amplitude method for $L \leq 3$.