Electric dipole excitations near the neutron separation energies in $^{96}$Mo

TL;DR

This study investigates electric dipole excitations near the neutron separation energy in $^{96}$Mo using advanced nuclear models, revealing the isospin nature of pygmy dipole resonances and their implications for nuclear structure and astrophysics.

Contribution

It provides a detailed analysis of the isospin characteristics of PDR states in $^{96}$Mo using HFB and QRPA methods, highlighting their mixed nature and significance.

Findings

Enhanced low-energy dipole strength shows isovector character.

PDR exhibits a mixture of isoscalar and isovector features.

Distinct transition density patterns differentiate PDR from IVGDR.

Abstract

Electric dipole strength near the neutron separation energy significantly impacts nuclear structure properties and astrophysical scenarios. These excitations are complex in nature and may involve the so-called pygmy dipole resonance (PDR). Transition densities play a crucial role in understanding the nature of nuclear excited states, including collective excitations, as well as in constructing transition potentials in DWBA or coupled-channels equations. In this work, we focus on electric dipole excitations in spherical molybdenum isotopes, particularly $^{96}$Mo, employing fully consistent Hartree-Fock-Bogoliubov (HFB) and Quasiparticle Random Phase Approximation (QRPA) methods. We analyze the dipole strength near the neutron separation energy, which represents the threshold for neutron capture processes, and examine the isospin characteristics of PDR states through transition density calculations. Examination of proton and neutron transition densities reveals distinctive features of each dipole state, indicating their isoscalar and isovector nature. We observe that the primary component in the enhanced low-energy region exhibits isovector character. The PDR displays a mixture of isoscalar and isovector nature, distinguishing it from the isovector giant dipole resonance (IVGDR). These findings lay the groundwork for future investigations into the role of transition densities in reaction models and for their application to inelastic scattering calculations.