s-process Nuclear Reaction Rates

¹ Physics Department of the University of Naples "Federico II" and National Institute for Nuclear Physics (INFN) - Naples division, Complesso Universitario di Monte Sant’Angelo, viale Cintia 80126 Naples, Italy

^* e-mail: david.rapagnani@unina.it

Published online: 8 December 2023

Abstract

In stars the ¹³C(α, n)¹⁶O and ²²Ne(α, n)²⁵Mg reactions are the two main sources of neutrons for the so-called slow neutron capture process (s-process), which is one of the main mechanisms for the stellar synthesis of heavy elements. About ¹³C(α, n)¹⁶O, in despite of many efforts in measuring its cross section at the lower energies, only high uncertainty data above the s-process Gamow window (150 keV < E_cm < 230 keV) were available, due mostly to the difficulties on suppress the natural background. Indeed, only recently the LUNA collaboration performed high precision underground measurements of the reaction cross section inside the Gamow window, improving the accuracy of its extrapolation at the lower energies. Again due to natural background, only upper limits for the ²²Ne(α, n)²⁵Mg reaction cross section are currently known in the s-process Gamow window (450 keV < E_cm < 750 keV). For this, the ERC founded project SHADES (Unina/INFN) aims to perform high precision and high sensitivity measurements of the ²²Ne(α, n)²⁵Mg reaction cross section down to the neutron threshold. A sensitivity improvement of at least two orders of magnitude over the state of the art is expected thanks to the low natural background environment of the INFN-LNGS laboratory in Italy, the high beam current of the new LUNAMV accelerator and the Beam Induced Background events suppression performed by SHADES hybrid detectors array. In this paper I will present the LUNA efforts to estimate nuclear reaction rates for ¹³C(α, n)¹⁶O, with a focus on the R-Matrix analysis performed with the code AZURE2 to extrapolate nuclear reaction rates at stellar energies and the estimate of their uncertainty through Monte Carlo methods. I will also present an overview of the SHADES project to measure ²²Ne(α, n)²⁵Mg in the Gamow window and the first results on the setup commissioning.