Obtaining systematics of (n, α) reaction cross section and description of Hauser-Feshbach model definition

Data analysis on neutron-induced reactions has continued an important research topic in nuclear astrophysics and nuclear technology applications. In particular, cross section data on (n, α) reactions are required in many energy generation and nucleosynthesis processes in the stellar environment, as well as in many applications in nuclear engineering and medicine. Cross sections can be obtained from experimental, nuclear models and systematics. Experimental cross sections of (n, α) reactions for many target nuclei and incident energies are either not available or a limited number of measurements are available. In addition, in the measurements made for some target nuclei, quite different cross sections were obtained from each other. When experimental data for any reaction channel are inconsistent, limited, or when there are no measurements in the full energy range, either nuclear model calculations or cross-section systematics need to be used to obtain cross sections for these reactions. In the light of this thought, empirical and semi-empirical formulas based on compound statistical reaction theory for (n, α) reaction cross sections are obtained in this thesis. In addition, nuclear model calculations were carried out for the (n, α) reaction channel. Nuclear model calculations were performed within the framework of statistical Hauser-Feshbach theory using TALYS 1.95 and NON-SMOKER reaction codes. The effects of nuclear mass and level density models on cross sections were analyzed using the TALYS 1.95 code. Besides, evaluations of isotopic effects on (n, α) cross sections were made by performing cross section calculations on 47−74F e and 100−132Sn isotopes. In addition, (n, α) reaction cross section calculations were employed for 12 nuclei contributing to the weak s-process. In addition to the analysis of the properties of the calculated (n, α) cross sections, Maxwellian average cross sections were determined for the temperature range in the stellar environment. With the model calculations, the astrophysically relevant energy windows in which the (n, α) reactions occur in the stars have been determined. The results obtained from this study were compared with the experimental data from the literature. The results presented for cross sections of (n, α) reactions in current work provide a guide for priority energy ranges in future experimental studies. Key Words:(n, α) Reaction Cross Section, Empirical Formula, Hauser-Feshbach Model, Nucleosynthesis, Weak s-Process. February, 2022; 125 pages