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UBC Theses and Dissertations

Direct capture reactions O16 (p,[gamma])F17 and D (p,[gamma])He3 Lal, Mohan


This thesis is concerned with two nuclear reactions which have astrophysical significance. First, for the reaction O¹⁶(p, γ)F¹⁷ a theoretical analysis of the currently available data has been made. Second, for the reaction D(p, γ)He³, experimental results have been obtained at lower energies than previously reported and a crude theoretical analysis of the data is presented. The analysis of the reaction O¹⁶(p, γ)F¹⁷ is based on a relatively simple nuclear model. The system, O¹⁶+p, is described in terms of a single particle wave function for the odd proton, moving in a potential provided by the O¹⁶ core. The proton is assumed to be captured directly from the continuum to one of the final bound states of F¹⁷ with the emission of gamma rays. A square well plus, coulomb potential is assumed to represent the interaction between the O¹⁶ core and the odd proton. A check on the bound state wave functions produced by the model was made by calculating the lifetime for the quadrupole transition between the 2s[subscript ½] first excited state and 1d[subscript 5/2] ground state. A similar check on the validity of the continuum wave functions given by the present model was made by comparing the O¹⁶(p,p)O¹⁶ scattering cross section predicted by the model with the experimental data of Eppling. For direct capture, the radial integrals for electric dipole transitions from continuum P-states to final 2s[subscript ½] and 1d[subscript 5/2] states were evaluated numerically for radii of 4.8 and 3.65 fermis. For 4.8 fermi radius, the absolute cross section, energy dependence and ratio of the transitions to the first excited and to the ground states are in good agreement with the experimental data. The cross sections for the 3.65 fermi radius are a factor of two low. For energies lower than 0.5 Mev, there is a considerable increase in the astrophysical S factor contributed by S[subscript s], corresponding to the first excited state transition, while S[subscript d], corresponding to the ground state transition remains practically constant over the whole energy range. [ ... ]

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