Isomeric States in the Rapid Neutron Capture Process

Abstract

The rapid neutron capture process, the r-process, is responsible for creating around a half of the nuclei above A ≈ 60. The r-process nucleosynthesis is simulated with a nuclear reaction network that evolves the system according to the given parameters. The nuclear reaction networks involve thousands of different nuclides, but in general, they only utilise the ground state nuclei, and not isomeric states, i.e. the metastable states of the nuclei. However, in recent years, there has been research on isomers and their effect on the r-process nucleosynthesis. The so-called astromers are isomers that potentially have the greatest effect on the outcome of the r-process nucleosynthesis. In this thesis, for the first time, a wide selection of isomers were added to a nuclear reaction network. The original code was modified to include isomeric states, and the results obtained with isomers were compared with the results without isomers. The nucleosynthesis code was run with five different initial conditions. Abundances of elements were compared at t = 1 Ga, and the total heating was compared during the first 1000 days after the r-process. The obtained results show not only that the code works with the added isomers but also that the results with the added isomers show some expected differences to the reference results without isomers. The differences are subtle, and especially the location of the added isomers with respect to the r-process path determine, what is the effectiveness of the isomers to the results.