PRECISE - Production of RadioactivE siliCon-32 In Stars and stellar Explosions

• Applicant: Professor Dr. Rene Reifarth, since 9/2019
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Astrophysics and Astronomy
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 414982478

This project PRECISE deals with the origin of heavy elements in stars and stellar explosions. In particular, it concentrates on stellar environments exposed to moderate neutron densities. Recent model calculations stress their importance for element synthesis especially in the early galaxy. Within this project, nuclear processes will be experimentally probed and a method for extracting cross sections of key neutron-induced reactions will be further developed. Neutron-induced reactions are dominantly contributing to the synthesis of heavy elements. Two major processes are known and are constantly constrained experimentally (if possible): the s-process takes place in low neutron density environments, whereas the r-process proceeds in highest neutron densities and shortest timescales. In both processes, free neutrons get captured on seed nuclei at different stellar sites producing a heavier isotope. If this is radioactive, it decays via beta-decay to create a heavier new chemical element.However, most recent observations of very old stars and on presolar grains, which have been formed in stars and stellar explosions and are implanted in primitive meteorites far before the creation of our solar system, show that the s- and r-process are not sufficient to explain the observed abundance distributions. When adding environments exposed to moderate neutron densities to the models, these peculiar observations can be explained. These neutron densities are in between the s- and the r-process; consequently, this process is called the intermediate neutron capture process (i process). It has also been confirmed in recent extended and detailed 3D fluid dynamic simulations.Certain presolar grains carry another important fingerprint of these processes: they are formed in core-collapse supernovae and reveal a unique possibility to extract data from a particular well-defined position in the star during the explosion. This is extremely valuable information for core-collapse supernova models and is urgently required. Observations show that radioactive Si-32 must be formed, which decays to S-32 after 150 years. This signature has been extracted on these special grains. Current astrophysical models, however, are not precise enough to extract relevant data: the neutron-capture cross section of Si-32 is not constrained and differs in theoretical models by a factor of 100. This is by far too uncertain. Consequently, within this project, this cross section will be measured for the first time using the above mentioned further developed method. This will highly constrain core-collapse supernovae models as well as i-process models, since Si-32 is also produced in i-process calculations. In the future, this method can be used for similar isotopes produced in moderate neutron density environments.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Christoph Langer, until 8/2019