Rapport de stage effets du milieu stellaire sur les phénomènes nucléaires, tutoriel & rapport PDF.

ELEMENTS OF NUCLEAR ASTROPHYSICS
INTRODUCTION
Nuclear Astrophysics is the study of the nuclear processes which drive the birth, evolution and death of stars. The current cosmological belief is that the nuclei which make up the majority of matter were first made from nucleons created a short time after the beginning of the Universe, in the expanding fireball we call the Big-bang, and later forged in the interiors of stars and stellar explosions [Arn00].
It is of significant and enduring interest to Mankind to piece together the picture of our evolution from the very first times. In particular, we now know that almost all of the material from which our planet was created was made in a vast series of nuclear reactions inside stars, and spread throughout the interstellar medium via stellar outbursts and energetic explosions. Astrophysicists have modeled these processes in the hope of explaining the isotopic abundances we see today on our Earth, around the Solar system, in meteoric remount and in astronomical observations of other stellar systems and the interstellar medium, in the hope of tying together a comprehensive understanding of the series of events leading to our present condition. Also of interest are the physical constraints placed on the energy generation and lifetimes of stars resulting from the detailed study of the realm of nuclear interactions, leading to predictive models and observational tools useful in cosmology, the study of the large-scale evolution of the Universe [Arn00].
Currently, much research is being done into the reaction rates of various nuclear processes in low energy stellar environments, such as Hydrogen burning in Main sequence stars and red giants. Nuclear cross-sections are measured at the lowest possible experimental energy, and then extrapolations are made to stellar energies, which tend to be still lower. Also subjects of active research are the higher energy processes of hydrogen burning in the hot CNO cycles and their breakout.
The breakout reactions from the hot CNO cycle are currently being paid much experimental attention. Of particular importance in Nuclear Astrophysics however, is the study of the specifics of the rapid proton process. Questions which need to be answered are: What are the key contributing reactions in the rp-process at various temperatures? What are typical r p-process sites:
does it occur in X-ray busters only, and if so does the envelope escape into the interstellar medium providing a nucleosynthesis source? Do rp-process reactions occur in novae, where we know the envelope escapes? How much of the nucleosynthesis of proton-rich nuclei can be accounted for by these rp-process scenarios?

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