Radiative neutron capture cross sections measurement of 70Ge at n_TOF CERN facility and its relevance for stellar nucleosynthesis

Abstract

Stellar nucleosynthesis is the name given to the nuclear reactions taking place in stars to create the nuclei of the chemical elements. Elements heavier than iron/nickel are dominantly created by neutron capture reactions. Neutron capture reactions are responsible for forming about 99% of the elements of mass number >56. When neutron densities are rather small and radioactive decay is generally faster than subsequent neutron capture on radionuclides, it is the so called s process (slow). In environments with high neutron densities nuclei can capture many neutrons, increasing rapidly their mass number, and then decay by beta cascade - the r process. This work is dedicated to the study of the radiative neutron capture reaction of the 70Ge isotope. The isotope 70Ge plays a special role, it is an “s-only” nuclide, which cannot be produced by the r process since it is shielded from beta decays coming from the neutron rich side by its stable isobar 70Zn. Neutron capture on germanium has a significant influence on the production of the elements from germanium to strontium in stars. For that reason information on the stellar cross sections of the Ge(n,gamma) reactions has an influence on the abundances of these elements. The main goal of this work is the determination of the neutron capture cross section of 70Ge in the neutron energy range from thermal up to hundreds of keV. Measurements were performed at the n_TOF facility via the time-of-flight technique, enabling neutron spectrometry, with a detection system constituted of liquid scintillators.