Speaker
Description
Nuclear reactions of astrophysical interest often concern unstable or even exotic species for which no experimental data exist. Although significant efforts have been devoted in the past decades, experimental information only covers a minute fraction of the data set required for nuclear astrophysics. Moreover, the energy range for which experimental data is available is restricted to the small range that present experimental setups can study. Only theoretical predictions can fill the gaps in all unknown cases. In the present study, nucleon capture cross-sections and reaction rates are systematically studied considering the nuclear structure obtained from both microscopic and phenomenological models, using the Hauser-Feshbach statistical model [1]. In particular, the nuclear level density (NLD) derived from the Hartree-Fock-Bogoliuboiv plus combinatorial method and the phenomenological Constant Temperature method, and the gamma-ray strength function determined by the semi-microscopic Gogny D1M interaction plus Quasi Random Phase Approximation and the global empirical Standard Modified Lorentzian are taken into account in the calculation, and the calculated results are compared with the available experimental Maxwellian-averaged cross-sections. It is demonstrated that the experimental data are well reproduced by the nuclear structure models considered here, and the predictive power of these nuclear ingredients is very close. Furthermore, these nuclear structure ingredients are used to investigate the unstable nuclei. Specifically, for eight unstable nuclei for which the NLD has been experimentally determined [2], the calculations show that there are still some gaps between the model predictions.
Meanwhile, the impact of the uncertainties in the NLD on the nucleon-capture cross-sections and astrophysical reaction rates is investigated, and their sensitivity to the variations of NLD in different energy intervals is analyzed. An effective energy window is proposed to describe the effective energy range in which the NLD has great contributions to the cross-section and reaction rate calculations [3]. The results reveal that the 4 - 5 MeV range remains the critical energy interval with the most significant impact on sensitivity for the analyzed nuclei at temperatures of astrophysical interest. All relevant calculations are performed within the statistical Hauser-Feshbach formalism.
[1] S. Goriely, A. C. Larsen, and D. Mücher, Comprehensive test of nuclear level density models, Phys. Rev. C, 106, 044315 (2022)
[2] A. Spyrou, et al., Novel technique for constraining r-process (n, γ) reaction rates, Phys. Rev. Lett., 113, 232502 (2014)
[3] B. Wang et al., Effective energy window of the E1 photon strength function for astrophysical neutron-capture reaction rates, Phys. Rev. C, 108, 065805 (2023)
