Improved predictions of nuclear reaction rates for astrophysics applications with the TALYS reaction code

Abstract

Abstract. Nuclear reaction rates for astrophysics applications are traditionally determined on the basis of HauserFeshbach reaction codes, like MOST. These codes use simplified schemes to calculate the capture reaction cross section on a given target nucleus, not only in its ground state but also on the different thermally populated states of the stellar plasma at a given temperature. Such schemes include a number of approximations that have never been tested, such as an approximate width fluctuation correction, the neglect of delayed particle emission during the electromagnetic decay cascade or the absence of the pre-equilibrium contribution at increasing incident energies. New developments have been brought to the reaction code TALYS to estimate the Maxwellian-averaged reaction rates of astrophysics relevance. These new developments give us the possibility to calculate with an improved accuracy the reaction cross sections and the corresponding astrophysics rates. The TALYS predictions for the thermonuclear rates of astrophysics relevance are presented and compared with those obtained with the MOST code on the basis of the same nuclear ingredients for nuclear structure properties, optical model potential, nuclear level densities and γ-ray strength. It is shown that, in particular, the pre-equilibrium process significanly influences the astrophysics rates of exotic neutron-rich nuclei. The reciprocity theorem traditionally used in astrophysics to determine photorates is also shown no to be valid for exotic nuclei. The predictions obtained with different nuclear inputs are also analyzed to provide an estimate of the theoretical uncertainties still affecting the reaction rate prediction far away from the experimentally known regions.

TALYS-1.0

“…New in TALYS-1.0 is the ability to calculate astrophysical reaction rates [14]. For this, a loop over excited target states is made within the WFC compound nucleus model, after which the results are folded with a Maxwellian spectrum.…”

“…Gamma-ray coefficients are modeled with Kopecky-Uhl's generalized Lorentzian and the appropriate giant-dipole resonance parameters. A new option in TALYS-1.0 is the possibility to replace this by HartreeFock-Bogolyubov (HFB) based gamma ray strength functions from Goriely [14]. Besides cross sections, compound angular distributions are calculated using Blatt-Biedenharn coupling factors, again within a full Hauser-Feshbach expression with WFC.…”

New results on proton-induced reactions on Vanadium for $^{47}$Sc production and the impact of level densities on theoretical cross sections

“…Modern nuclear reaction codes are today the best tools to perform theoretical calculations in this field: in this work we have used the TALYS simulation package [34] which is actively developed and maintained. The aim of the authors is to provide a complete and high quality set of models [35] for the different reaction mechanisms that are relevant in the energy range of medical interest, namely nuclear scattering, compound nucleus formation and preequilibrium emission.…”