r-Process Simulation and Heavy-Element Nucleosynthesis.

Sammanfattning: r-process, short for rapid neutron capture process, is a nucleosynthesis process taking place on short time scales. Rapid neutron captures produce less and less stable neutron-rich nuclei which in turn beta minus decays when the probability for beta decay is higher than the probability for neutron captures, upon which more neutrons are captured and the process repeats itself, creating r-process paths. Very neutron-rich heavy elements are the product of this process taking place at explosive astrophysical sites with high neutron flux. Simulations of r-processes are important for finding out the exact sites, something that is yet not known. To get more accurate simulation results leading to a better understanding of r-processes, the initial parameter dependence of the simulations is important to understand. This report discusses the dependence on three important initial parameters; temperature, density and electron fraction. Furthermore, the dependence on nuclear masses is covered, which is important since no exact model for nuclear masses exists for the neutron-rich nuclei involved. Finally, different stopping criteria are simulated, representing different physical environments in which r-processes may occur. Results from the simulations, carried out using r-Java 2.0, show that r-process simulations are sensitive to all parameters discussed; further research can tell to which extent. A better understanding of the dependence on the parameters will hopefully extend our knowledge of r-processes and where in the universe they occur.