Isomeric yield ratio studies in nuclear reactions and alpha-particle induced fission of Thorium

Sammanfattning: Despite decades of research since the initial discovery of nuclear fission, numerous unresolved questions still persist. It is known empirically that fission fragments emerge with high angular momentum. The mechanism responsible for the generation of the large angular momenta observed is one of these open questions. Since the characteristics of fission fragments are not directly measurable, experimentally accessible observables are used to derive the angular momenta using nuclear model codes. One of these observables is the yield ratio between fission products produced in different isomeric states, i.e., metastable energy levels of the same nucleus.In this thesis, a study of the level density models implemented in the nuclear model code TALYS is presented. Simulated and experimental isomeric yield ratios of a large number of nuclear reactions is compared. The results show a bias in the models that favours the population of the high-spin states and that this can be produced by the overestimation of the spin width distribution. The reason for this study is to improve the models then used in the angular momentum calculation. Moreover, the isomeric yield ratio measurement of twenty-one FFs is presented. The measurement was performed using the JYFLTRAP system at the University of Jyväskylä. The fission fragments were produced by the 32 MeV alpha-particle induced fission of 232Th. The analysis process, involving different identification and correction methods, and preliminary results are presented.