Isoscalar Giant Monopole, Dipole, and Quadrupole Resonances in $^{90,92}$Zr and $^{92}$Mo

TL;DR

This study investigates the isoscalar giant resonances in $^{90,92}$Zr and $^{92}$Mo using inelastic alpha scattering, revealing that these collective excitations are consistent across nuclei and unaffected by shell structure near mass 90.

Contribution

It provides the first comprehensive comparison of giant resonance strength distributions in these nuclei, challenging previous claims about shell effects.

Findings

Giant resonance strength distributions are nearly identical across the three nuclei.

Collective giant resonances are not significantly influenced by nuclear shell structure near A~90.

The results contradict recent claims suggesting shell effects impact these resonances.

Abstract

The isoscalar giant monopole, dipole, and quadrupole strength distributions have been deduced in $^{90, 92}$Zr, and $^{92}$Mo from "background-free" spectra of inelastic $\alpha$-particle scattering at a beam energy of 385 MeV at extremely forward angles, including 0$^{\circ}$. These strength distributions were extracted by a multipole-decomposition analysis based on the expected angular distributions of the respective multipoles. All these strength distributions for the three nuclei practically coincide with each other, affirming that giant resonances, being collective phenomena, are not influenced by nuclear shell structure near $A\sim$90, contrary to the claim in a recent measurement.