Excitation energy and strength of the pygmy dipole resonance in stable tin isotopes

TL;DR

This study investigates the excitation energies and strength of the pygmy dipole resonance in stable tin isotopes using photon scattering experiments, providing experimental data that tests nuclear models and enhances understanding of nuclear structure.

Contribution

It provides new experimental measurements of PDR properties in stable tin isotopes and compares these with theoretical models, highlighting discrepancies with relativistic predictions.

Findings

PDR centroid energies are consistent with nonrelativistic models.

Summed PDR strengths are established for multiple isotopes.

Discrepancies observed with relativistic model predictions.

Abstract

The $^{112,120}$Sn$(\gamma,\gamma')$ reactions have been studied at the S-DALINAC. Electric dipole (E1) strength distributions have been determined including contributions from unresolved strength extracted by a fluctuation analysis. Together with available data on $^{116,124}$Sn, an experimental systematics of the pygmy dipole resonance (PDR) in stable even-mass tin isotopes is established. The PDR centroid excitation energies and summed strengths are in reasonable agreement with quasiparticle-phonon model calculations based on a nonrelativistic description of the mean field but disagree with relativistic quasiparticle random-phase approximation predictions.