Neutron-Induced Reactions in Nuclear Astrophysics

The quest for the origin of the chemical elements, which we find in our body, in our planet (Earth), in our star (Sun) or in our galaxy (Milky Way), could only be resolved with a thorough understanding of the nuclear physics properties of stable and unstable atomic nuclei. While the elements until iron are either created during the big bang or during fusion reactions in stars, most of the elements heavier than iron are produced via neutron-induced reactions. Therefore, neutron capture cross-sections of stable and unstable isotopes are important. So far, time-of-flight or activation methods have been applied very successfully, but these methods reach their limits once the isotopes with half-lives shorter than a few months are of interest. A combination of a radioactive beam facility, an ion-storage ring and a high-flux reactor or a spallation source would allow a direct measurement of neutron-induced reactions over a wide energy range of isotopes with half-lives down to minutes. The idea is to measure neutron-induced reactions on radioactive ions in inverse kinematics. This means that the radioactive ions will pass through a neutron target. In order to efficiently use the rare nuclides as well as to enhance the luminosity, the exotic nuclides can be stored in an ion-storage ring. The neutron target can be the core of a research reactor, where one of the central fuel elements is replaced by the evacuated beam pipe of the storage ring. Alternatively, a large moderator surrounding a spallation source can be intersected by the beam pipe of an ion-storage ring. Using particle detectors and Schottky spectroscopy, most of the important neutron-induced reactions, such as (n, gamma), (n, p), (n, alpha), (n, 2n) or (n, f), could be investigated.