Origin of Low-Lying Enhanced E1 Strength in Rare-Earth Nuclei

TL;DR

This paper investigates the origin of low-lying enhanced E1 strength in rare-earth nuclei, suggesting it is linked to isospin symmetry breaking and alpha clustering, supported by experimental data and theoretical modeling.

Contribution

It introduces a novel interpretation of low-lying E1 strength as arising from alpha clustering, supported by spdf interacting boson model calculations.

Findings

Enhanced E1 strength correlates with alpha cluster formation.

Experimental data shows local isospin symmetry breaking.

Theoretical models reproduce observed E1 strength distributions.

Abstract

The experimental $E1$ strength distribution below 4 MeV in rare-earth nuclei suggests a local breaking of isospin symmetry. In addition to the octupole states, additional $1^-$ states with enhanced E1 strength have been observed in rare-earth nuclei by means of ($\gamma,\gamma'$) experiments. By reproducing the experimental results, the spdf interacting boson model calculations provide further evidence for the formation of an $\alpha$ cluster in medium-mass nuclei and might provide a new understanding of the origin of low-lying E1 strength.