Applications to Nuclear Structure and Astrophysics

Half of the elements with mass greater than 70 is created by the astrophysical r process, which proceeds via unstable very neutron-rich nuclei in stellar explosions or other violent astrophysical events such as the coalescence of neutron stars. The identification of the location of the r-process remains one of the major challenges of nuclear astrophysics. Recent advances in the description of the interaction of neutrinos with matter and its implementation in the modelling of supernovae explosions tend to show that supernovae explosions only contribute to the production of Z elements below 50. Compact star coalescences are currently considered to be the best candidates for determining the site of the main r-process. Observational confirmation of the occurrence of the r-process in such an astrophysical event was given at the end of 2017 with the multi-messenger detection of the merging of two neutron stars and the measurement of the emitted electromagnetic radiation. Beta decay of nuclei is among the important processes that influence r-element abundances along with neutron capture reactions, photo-dissociation, temperature and density. In particular, measurements of radioactive periods of the progenitors of stable nuclei help to determine their abundance and are thus important ingredients in nucleosynthesis calculations that attempt to reproduce them. With the exception of a few key nuclei that are relatively close to the valley of stability, half-lives must be calculated using theoretical models. In this type of calculation, the strength distribution associated with beta decay as a function of energy must be calculated for all possible end states. This involves determining what proportion of the strength resides in the energy window opened by the beta decay. The TAGS technique is the preferred technique to perform these measurements, and can also be used to study the presence of low-energy collective modes that influence the paths of the nucleosynthesis process r. The TAGS measurements proposed by the Subatech team, in international collaboration with the IFIC in Valencia, Spain, CIEMAT in Madrid, the University of Surrey in England (and other international laboratories that are coming to participate in the experiments), at state-of-the-art facilities for the production of exotic nuclei such as JYFL in Finland, or ISOLDE at CERN (among others) will provide the necessary tests for the theoretical models.