Nuclear astrophysics

Abstract

Nuclear astrophysics is that branch of astrophysics which helps understanding the Universe, or at least some of its many faces, through the knowledge of the microcosm of the atomic nucleus. It attempts to find as many nuclear physics imprints as possible in the macrocosm, and to decipher what those messages are telling us about the varied constituent objects in the Universe at present and in the past. In the last decades much advance has been made in nuclear astrophysics thanks to the sometimes spectacular progress made in the modelling of the structure and evolution of the stars, in the quality and diversity of the astronomical observations, as well as in the experimental and theoretical understanding of the atomic nucleus and of its spontaneous or induced transformations. Developments in other sub-fields of physics and chemistry have also contributed to that advance. Notwithstanding the accomplishment, many longstanding problems remain to be solved, and the theoretical understanding of a large variety of observational facts needs to be put on safer grounds. In addition, new questions are continuously emerging, and new facts endangering old ideas.This review shows that astrophysics has been, and still is, highly demanding to nuclear physics in both its experimental and theoretical components. On top of the fact that large varieties of nuclei have to be dealt with, these nuclei are immersed in highly unusual environments which may have a significant impact on their static properties, the diversity of their transmutation modes, and on the probabilities of these modes. In order to have a chance of solving some of the problems nuclear astrophysics is facing, the astrophysicists and nuclear physicists are obviously bound to put their competence in common, and have sometimes to benefit from the help of other fields of physics, like particle physics, plasma physics or solid-state physics. Given the highly varied and complex aspects, we pick here some specific nuclear physics topics which largely pervade nuclear astrophysics. Direct cross-section measurements 7.3.2. Indirect cross-section measurements 7.4. Neutron capture reactions: Experiments 7.5. Thermonuclear reaction rates: Models 7.5.1. Microscopic models 7.5.2. The potential and DWBA models 7.5.3. Parameter fits 7.5.4. The statistical models 8. Selected topics 8.1. Heavy-element nucleosynthesis by the s-and r-processes of neutron captures 8.1.1. Defining the s-process 8.1.2. Defining the r-process 8.1.3. The s-and r-process contributions to the solar-system composition 8.1.4. Astrophysical sites for the s-and r-processes 8.1.5. Heavy elements in low-metallicity stars 8.2. Cosmochronometry 8.2.1. Nucleo-cosmochronology: generalities 8.2.2. The trans-actinide clocks 8.2.3. The 187 Re -187 Os chronometry 8.3. Type-II supernovae 8.3.1. Evolution of massive stars leading to neutrino-driven supernovae 8.3.2. Nucleosynthesis in the hot bubble: Can the r-process occur ? 8.3.3. Signatures of a large-scale mixing of nucleosynthesis products 9. Summary References * The situ...

From the microcosm of the atomic nuclei to the macrocosm of the stars

“…The non-explosive nuclear history of a star is made of the burnings of H, He, C, Ne, O, and Si, at least if the stellar mass exceeds about 10 M , where M is the solar mass (see e.g., [1]). These burnings involve essentially stable nuclides only.…”

“…Indirect approaches are a very important complement to direct measurements. From experiments on reactions of no astrophysical relevance, information (e.g., resonance characteristics) can be gained on reactions of interest ( [1] for a brief overview). Theorists are thus requested to supply reliable extrapolations from the experimental data obtained at the lowest possible energies, or to evaluate cross sections from indirectly gained information.…”

“…Theorists are thus requested to supply reliable extrapolations from the experimental data obtained at the lowest possible energies, or to evaluate cross sections from indirectly gained information. Electron screening effects in laboratory conditions, or the contribution to the reaction rates of the target excited states, bring their share of additional difficulties (e.g., [1]). …”

“…From this sensitivity, and from a comparison between solar and predicted r-abundances, some are tempted to evaluate the relative virtues of different mass models. This is quite risky, especially as the proper site(s) for the r-process remain(s) unknown, as recently reviewed by [18]. In fact, figures 5-7 are based on models that have been parametrised in one way or another to obtain a well-developed r-process.…”

Neutron physics of the Re/Os clock. III. Resonance analyses and stellar (n,γ) cross sections ofOs186,187,1

“…Apart from the astrophysical question for the production rate of 187 Re with time [10][11][12][13], other key problems refer to several nuclear physics issues. Takahashi and Yokoi [14] pointed out that the β-decay rate of 187 Re is drastically enhanced at stellar temperatures in excess of about 10 8 K, * Kaori.Fujii@ts.infn.it when the increasing degree of ionization opens additional decay channels to unoccupied atomic orbits (bound state decay).…”