Abstract
Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the E1 and M1 absorption γ-ray strength function obtained in the framework of the axially-symmetric deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force to the determination of the de-excitation strength function. To do so, shell-model calculations of the de-excitation dipole strength function as well as experimental data are considered to provide insight in the low-energy limit and to complement the QRPA estimate phenomenologically. We compare our final prediction of the E1 and M1 strengths with available experimental data at low energies and show that a relatively good agreement can be obtained. Its impact on the average radiative width as well as radiative neutron capture cross section is discussed.
Highlights
Radiative neutron capture cross sections play a key role in almost all nuclear applications
As far as the HFB+quasiparticle random phase approximation (QRPA) prediction of the M1 spin flip is concerned, it is almost always insignificant with respect to the stronger E1 contribution at the relevant energies of 8-9 MeV, so that its impact on the Maxwellian-averaged neutron capture cross sections (MACS) is reduced to typically 10% in comparison with the MACS obtained with a standard Lorentzian (SLO) M1 strength [3]
HFB+QRPA models are available for applications and have shown their capacity to predict photoabsorption γ-ray strength functions
Summary
Radiative neutron capture cross sections play a key role in almost all nuclear applications. Despite a huge effort to measure such radiative neutron capture cross sections, theoretical predictions are required to fill the gaps, both for nuclei for which measurements are not feasible at the present time, in particular for unstable targets, and for energies that cannot be reached in the laboratory. Axially-symmetric-deformed QRPA calculations based on Hartree-Fock-Bogoliubov (HFB) calculations using the finite-range Gogny interaction have been shown to provide rather satisfactory predictions of the E1 [7] and M1 strengths [8] Such QRPA calculations only describe the photoabsorption and it is well known that the de-excitation strength function may differ from the photoabsorption one, especially for low photon energies [3, 10].
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