Novel data and a new parametrization of the electric dipole strength in nuclei with 88 < A < 116

TL;DR

This paper introduces a novel experimental method to determine the photon strength function in nuclei with 88<A<116, providing a new parameterization that improves nuclear reaction models relevant for astrophysics.

Contribution

It develops an unexplored experimental approach to measure the photon strength function and proposes a new parameterization applicable across a range of nuclei with minimal parameters.

Findings

Good agreement between measured and literature photon strengths.

New parameterization differs from existing models significantly.

Provides a comprehensive basis for nuclear reaction calculations.

Abstract

A hitherto unexplored method for the experimental determination of the photon strength function up to the neutron separation energy was developed at the Radiation Source ELBE in Dresden. It was applied to various heavy nuclei, preferentially to nuclides with increasing distance to the N=50 neutron shell, and it covers the high level density excitation energy range above 4 MeV. The observed quasi-continuous spectra of scattered photons can be -- after a proper correction for multi-step processes -- directly combined to nuclear photo effect data from literature. A remarkably good match of the photon strengths as measured below and above the neutron emission threshold is observed. The wide energy coverage of the combined data forms an excellent basis to derive a parameterization for the dipole strength function fully covering the range across the nucleon separation energies. In addition to the parameters defining the deformation of the nuclear ground states only one additional constant is needed to describe the dipole strength in the nuclei with 88<A<116. The new parameterization differs significantly from the prescriptions generally used in network calculations, e.g. those of interest for the cosmic nucleo-synthesis.