Studies of Certain Nuclear Processes in Stars. Part I. Neutron Capture Chains in Heavy Element Synthesis. Part II. A Search for Excited States in N¹⁴ Pertaining to the Synthesis of C¹³

Citation

Clayton, Donald Delbert (1962) Studies of Certain Nuclear Processes in Stars. Part I. Neutron Capture Chains in Heavy Element Synthesis. Part II. A Search for Excited States in N¹⁴ Pertaining to the Synthesis of C¹³. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8QPZ-5656. https://resolver.caltech.edu/CaltechTHESIS:07282011-092105755

Abstract

Part I. A. An analysis of the abundance distributions resulting from a chain of successive neutron captures is presented in considerable generality. The solutions are applied to the stellar problem of neutron capture at a rate slow compared to beta-decay, the so-called s-process. Theoretically al abundance distributions are correlated with present knowledge of element and isotope abundances in order to draw inferences about the "history” of stellar neutron capture. A semiempirical analysis of isotopic neutron capture cross sections is appended. This work was carried out in conjunction with W. A. Fowler, T. E. Hull, and B. A. Zimmerman. The presentation is in the form of a reprint of an article from the Annals of Physics by the same authors. B. The studies described in Section A have been independently extended in this thesis. A theoretical table of solar abundances is presented for the stable heavy nuclei whose formation is attributable to the operation of the r- and s-processes. The importance of the normalization of these two theories to certain key abundance determinations is emphasized. The table facilitates a comparison of these theories of nucleosynthesis with current observations on the abundances of the elements and their isotopes. Part II. Experimental nuclear studies relevant to astrophysical situations constitute the second part of this thesis research. Alpha particle groups from the reactions N^(15) (He^3, α) N^(14) and N^(14) (He^3, α) N^(13) leading to states in the 7-8 Mev excitation range of the two nitrogen isotopes are reported. States were observed in N^(14) at excitations of 8.06, 7.97, and 7.034 ± .008 Mev and in N^(13) at excitations of 7.388 ± .008 and 7.166 ± .008 Mev. Differential cross sections are evaluated for these reactions at laboratory angles of 90° and 150° and a bombarding energy of 2.76 Mev. No other states in this range of excitation were observed. In particular, a state does not appear near 7.6 Mev excitation in N^(14), indicating that the reaction C^(13) (p, γ) N^(14) in the CNO-cycle at stellar temperatures is nonresonant.

Thesis Files