Understanding the physics of low-energy nuclear reactions is essential for explaining the chemical evolution of the Universe.
At the heart of this cosmic transformation are nuclear reactions, acting as the central “engine” propelling stellar phenomena. These reactions not only control the synthesis of elements but also imprint distinct signatures on the various stages of stellar evolution. An accurate estimate of the corresponding cross-sections is thus needed to reliably model stars and correctly explain the abundance of the elements observed in the universe.
Precise determination of cross-section values also plays an important role in cosmology. Central to this is the Big Bang Nucleosynthesis (BBN), the standard model theory for the production of light nuclides during the early stages of the Universe. The abundance of these nuclides serves as a sensitive test for the conditions in the early Universe.
Reactions induced by neutrons are also essential to model various stages of a star’s life. In particular, they play a crucial role during the s- and r-processes, which explain the formation of the heaviest elements.
However, direct measurements of these reactions are possible only for stable or long-lived isotopes and are very difficult, if not impossible, when involving strongly radioactive nuclei.
An alternative approach is the use of indirect methods. The idea is to consider another reaction, which is easier to measure and/or which exhibits significantly higher cross-sections. Most of the reactions that take place in stars are radiative captures, i.e. reactions in which a nucleon or a light cluster of nucleons, such as an α particle, is captured by a heavier nucleus, which then emits a γ for energy and angular-momentum conservation.
The new MESA accelerator, in combination with the high resolution spectrometers of the MAGIX experiment, offers unique opportunities to make substantial contributions to this field. The idea is to perform the photo-dissociation of the final nucleus using the high-intensity electron beam delivered by MESA. This innovative approach can be utilized to investigate neutron capture through the inverse (e, e′n) channels. This enables the measurement of neutron cross-sections for s-process studies, an area currently limited to direct measurements on stable or long-lived nuclei for neutron capture reactions.