Periodic Reporting for period 6 - DoRES (Direct measurements of key nuclear Reactions for the creation of Elements in Stars)
Reporting period: 2023-12-01 to 2024-09-30
The chemical elements from carbon onwards have all been produced in stars. The elemental abundances we observe in our solar system, meteorites and distant stars provide us with clues of how these elements were produced in a variety of astrophysical sites and processes. However, many open questions remain, and a key to finding the answers is to study the nuclear reactions occuring in stars and stellar explosions which are responsible for element formation. These reactions often involve unstable nuclei which do not naturally occur on earth - this provides a challenge to make these nuclei accessible experimentally. This ERC project addressed major open questions in the field, related to the origin of elements heavier than iron, the origin of cosmic gamma ray emitters, and the source of neutrons in low mass stars. Our team performed experiments to measure key nuclear reactions involving unstable particles, using upgraded and new world-leading international accelerator facilites, combined with advanced, sensitive detection systems, purpose-built within the ERC project. Our team has used the results obtained in experiments to improve the modelling of stellar interiors and stellar evolution, for example related to the production of Ge and Se isotopes in massive stars, the production of the cosmic gamma ray emitter Al-26 in Red Giant stars, and the neutron budget available for heavy element production in the slow neutron capture process.
High precision measurements of neutron capture reactions have been performed on intermediate mass nuclei (germanium, selenium and zinc) at the neutron time-of-flight facility n_TOF at CERN. These data are essential to model the production of the heavy elements in massive stars, which at the end of their lives explode as a core-collapse supernova. Our results provide a better match to observed abundances. We have studied key neutron destruction reactions of the cosmic gamma ray emitter 26Al, an important tracer of nucleosynthesis in our galaxy, using the new ultra-high flux beamline EAR-2 at n_TOF. For this experiment, we designed and built an advanced silicon strip detection system to detect the particles produced in the reaction of 26Al with neutrons. The experiment resolved long-standing discrepancies in previous experimental results, and allowed us to study Al-26 production in Red Giant stars in detail. Towards the end of the grant, we have performed an additional study focussing on Al-26 production in massive stars and results are expected soon. We have used our new detection system to investiagte reactions important for the neutron balance in stars, which has impact on the stellar structure and neutron capture nucleosynthesis in low mass stars. We have studied the origin of nature's rarest stable isotope 180mTa, by producing a radioactive 179Ta target, which was produced in collaboration with the UK Birmingham Cyclotron and PSI Villigen laboratory and subsequent measurement at the Mainz research reactor.
New detection systems are combined with advanced accelerator facilities to study nuclear reactions of key importance for elemental synthesis in stars and stellar explosions. This project allowed to address several open questions by directly measuring certain key reactions for the first time, which will provides important information on nucleosynthesis processes and helps to unravel the mysteries of element formation in the cosmos.