Periodic Reporting for period 4 - MAIDEN (Masses, isomers and decay studies for elemental nucleosynthesis)
Reporting period: 2022-12-01 to 2023-11-30
The origin of chemical elements heavier than iron, such as gold, has been a long-standing puzzle. About half of the heavy-element abundances are expected to be produced by the astrophysical rapid neutron capture process, the r process. Its astrophysical site has been one of the biggest outstanding questions in physics. The observation of the binary neutron-star merger GW170817 and the associated kilonova in August 2017 gave the first direct evidence that the r process takes place at least in such neutron-star mergers. However, there are still several open questions related to the r process. Can neutron-star mergers explain all observed r-process abundances? What is the role of supernovae in the production of heavier elements? How to interpret the observed kilonova? In order to better model the r process, accurate nuclear physics input data are needed. Nuclear masses are one of the most important nuclear physics inputs for the r process and for studying the chemical evolution in the Cosmos. In this project, we have performed around 170 high-precision atomic mass measurements that serve as important inputs for modelling the r process. Around 55 long-living isomeric states, which can also play a role in the r process, were resolved from the ground states and measured using novel measurement techniques. New isomeric states were discovered during the project. Around 40 atomic masses were experimentally determined for the first time, thus extending the knowledge of neutron-rich nuclei and reducing the mass-related uncertainties in the r-process calculations. Post-trap decay spectroscopy was employed to identify which state was measured in order to avoid systematic uncertainties in the mass values, and also to provide further information on beta-decay properties and nuclear structure which also affect the r-process calculations. A new gas cell and target platform have been designed, manufactured and successfully commissioned to produce heavier neutron-rich nuclei via multinucleon-transfer reactions at IGISOL. The new data gathered in this project have been compared with theoretical nuclear models and included in the astrophysical calculations. The improved r-process calculations are essential to fully benefit from the anticipated new multimessenger observations from neutron-star mergers. This project has advanced our knowledge of nuclear structure far from stability and reduced nuclear data uncertainties in the r-process calculations, which can potentially constrain the astrophysical site for the r process and help to understand the origin of heavier elements.
In this project we have performed around 170 high-precision atomic mass measurements for neutron-rich radioactive nuclides, including around 55 isomeric states, with the JYFLTRAP Penning trap at the IGISOL facility in the JYFL accelerator laboratory at the University of Jyväskylä. The measurements have provided crucial data for the r-process calculations. For example the rare-earth mass measurements have yielded a better agreement between the r-process calculations and the observed r-process abundances. In addition to nuclear astrophysics, the measurements have provided important information on nuclear structure far from stability. With the more than 40 new atomic masses measured, and with the total of around 170 high-precision mass measurements, we have significantly extended the knowledge of nuclear binding energies and tested state-of-the-art nuclear models. We have also discovered new isomeric states during the project.
A new gas cell and target platform have been designed, manufactured and successfully commissioned to produce heavier neutron-rich nuclei via multinucleon-transfer reactions at IGISOL. These nuclei are particularly relevant for the heaviest r-process abundance peak and the origin of heavy elements, such as gold. Decay properties of radioactive nuclei have been studied for nuclear structure and astrophysics using various detector setups. In addition, ion-trapping techniques have been further developed for faster measurements and to obtain a higher resolving power, both for the mass measurements and decay spectroscopy. The technical developments will advance the possibilities for studies of exotic nuclei and isomeric states and enable new types of measurements also after the project. The project and its results have been widely disseminated to the scientific community as well as for the general public.
A new gas cell and target platform have been designed, manufactured and successfully commissioned to produce heavier neutron-rich nuclei via multinucleon-transfer reactions at IGISOL. These nuclei are particularly relevant for the heaviest r-process abundance peak and the origin of heavy elements, such as gold. Decay properties of radioactive nuclei have been studied for nuclear structure and astrophysics using various detector setups. In addition, ion-trapping techniques have been further developed for faster measurements and to obtain a higher resolving power, both for the mass measurements and decay spectroscopy. The technical developments will advance the possibilities for studies of exotic nuclei and isomeric states and enable new types of measurements also after the project. The project and its results have been widely disseminated to the scientific community as well as for the general public.
The project was extremely successful with many new technical developments done and experimental results obtained. The stopping cell and target platform for the multinucleon-transfer reactions can be utilised in the forthcoming experiments. The project has already produced around 60 publications and many publications will follow. The obtained mass values will provide more accurate input data for the r-process calculations and therefore reduce the nuclear-physics related uncertainties. This is essential to better interpret the anticipated new multimessenger observations from neutron star mergers. In addition, the project has advanced our understanding of nuclear structure far from stability and helped to develop nuclear models in the long run.