The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries

Abstract

The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system.A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. Fission probabilities of very neutron-rich actinides have also to be known in order to determine the most massive nuclei that have a chance to be involved in the r-process. Even the properties of asymmetric nuclear matter may enter the problem. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented.Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. The ultimate goal of r-process studies is clearly to identify realistic sites for the development of the r-process. Here too, the challenge is enormous, and the solution still eludes us. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one-or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed.Given the uncertainties remaining on the astrophysical r-process site and on the involved nuclear physics, any confrontation between predicted r-process yields and observed abundances is clearly risky. A comparison dealing with observed r-nuclide abundances in very metal-poor stars and in the solar system is attempted on grounds of r-process models based on parametrised astrophysics conditions. The virtues of the r-process product actinides for dating old stars or the solar system are also

Origin of r-Process Elements and Galactic Chemodynamical Evolution

“…Observations [6] showing the appearance of heavy-element r-process abundances early in the history of the Galaxy seem to favor the short stellar lifetime of CCSNe as the r-process site. However, identifying the r-process site in models of CCSNe has been difficult [20,21].…”

Studies of exotic nuclei with advanced radiation detectors

“…(ii) production of heavy elements: Half of the nuclei heavier than iron are believed to be synthesised in the rapid neutron-capture process, the so called r-process (Arnould et al, 2007). No comprehensive model for the r-process exists.…”

Systematic Studies on the β-decay Half-lives of r-process Nuclei

“…The rapid neutron-capture process (r-process) of stellar nucleosynthesis is believed to explain the production of about half of the nuclides heavier than iron in the universe [1,2]. A large amount of nuclear data, such as mass, decay and reaction rates, are necessary in the studies of r-process.…”