Radiative neutron capture is a nuclear reaction forming a compound nucleus which decays by emitting gamma-rays at excitation energy around the neutron binding energy. This well-known reaction which we known how to accurately measure its cross section at low incident neutron energies for most stable and few unstable nuclei close the stability valley, remains difficult to measure for exotic nuclei like fission fragments. Nuclear reaction models based essentially on stable nuclei, also struggle to provide reliable predictions of cross sections for these exotic nuclei. However, in the recent years, progress made related to the models and the measurements for the radiative capture show that significant improvements in including microscopic ingredients studies. These micoscopic ingredients: gamma strength function and nuclear level density, remain accesible to the experiment. These ingredients which respectively manage the way of how the gamma cascade occurs and the nuclear structure at high excitation energy can also be measured and calculated to be compared and suggest ways to improve the predictability of models. This kind of improvements have a direct impact for instance on the cross sections for these exotic nuclei which are produced in the stellar nucleosynthesis. The subject of thie thesis is to measure these quantities for a nucleus involved in the nucleosythesis using a new setup called SFyNCS.
This PhD project is concerned with the numerical and theoretical modeling of the ultra-relativistic plasmas encountered in a variety of astrophysical environments such as gamma-ray bursts or pulsar wind nebulae, as well as in future laboratory experiments on extreme laser-plasma, beam-plasma or gamma-plasma interactions. The latter experiments are envisioned at the multi-petawatt laser facilities currently under development worldwide (e.g. the European ELI project), or at next-generation high-energy particle accelerators (e.g. the SLAC/FACET-II facility).
The plasma systems under scrutiny have in common a strong coupling between energetic particles, photons and quantum electrodynamic effects. They will be simulated numerically using a particle-in-cell (PIC) code developed at CEA/DAM over the past years. Besides the collective effects characteristic of plasmas, this code describes a number of gamma-ray photon emission and electron-positron pair creation processes. The purpose of this PhD project is to treat additional photon-particle and photon-photon interaction processes, and then to examine thoroughly their impact and interplay in various experimental and astrophysical configurations.