Experimental study of the electric dipole strength in the even Mo nuclei and its deformation dependence

TL;DR

This study measures the electric dipole strength in even Mo isotopes using bremsstrahlung methods, revealing deformation effects and testing a new parameterization that impacts astrophysics and nuclear technology.

Contribution

It provides new experimental data on E1 strength in Mo isotopes and introduces a novel parameterization for dipole strength functions considering nuclear deformation.

Findings

Good agreement between photon scattering and photo-activation data.

Deviations from traditional models increase with nuclear deformation.

Supports a new parameterization for dipole strength in nuclei with A>80.

Abstract

Two methods based on bremsstrahlung were applied to the stable even Mo isotopes for the experimental determination of the photon strength function covering the high excitation energy range above 4 MeV with its increasing level density. Photon scattering was used up to the neutron separation energies Sn and data up to the maximum of the isovector giant resonance(GDR) were obtained by photo-activation. After a proper correction for multi-step processes the observed quasi-continuous spectra of scattered photons show a remarkably good match to the photon strengths derived from nuclear photo effect data obtained previously by neutron detection and corrected in absolute scale using the new activation results. The combined data form an excellent basis to derive a shape dependence of the E1 strength in the even Mo isotopes with increasing deviation from the N = 50 neutron shell, i.e. with the impact of quadrupole deformation and triaxiality. The wide energy coverage of the data allows for a stringent assessment of the dipole sum-rule, and a test of a novel parameterization developed previously which is based upon. This parameterization for the electric dipole strength function in nuclei with A>80 deviates significantly from prescriptions generally used previously. In astrophysical network calculations it may help to quantify the role the p-process plays in the cosmic nucleosynthesis. It also has impact on the accurate analysis of neutron capture data of importance for future nuclear energy systems and waste transmutation.