Scattering of alpha particles by oxygen. II. Bombarding energy range 10 to 19 MeV

Mehta, Madhukar Kapilrai ; Hunt, W. E. ; Davis, R. H. (1967) Scattering of alpha particles by oxygen. II. Bombarding energy range 10 to 19 MeV Physical Review Letters, 160 (4). pp. 791-802. ISSN 0031-9007

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The O16(α, α)O16 and O16(α, α'γ)O16 reactions have been studied in the bombarding energy range from 10.0 to 19.0 MeV. Elastic-scattering differential cross sections were measured at eight angles as a function of energy, and a total of thirty-five levels in the compound nucleus Ne20 have been observed in the excitation curves. Angular distributions of the elastically scattered a particles have been measured at seven energies and each shows a strong dependence of the differential cross section on angle. These were analyzed in terms of the Ackhiezer-Pomeranchuk-Blair-McIntyre (APBM) model and the nuclear optical model. Good theoretical fits to the experimental data were obtained only when contributions from resonances were included explicitly in the APBM-model calculations. Excitation curves for the γ rays emitted from nuclei excited in inelastic-scattering events have been measured, and the Ne20 energy levels found in the γ-ray excitation curves confirm most of the levels found in the elastic-scattering experiment. Thin- and thick-target angular distributions for the 6.13-MeV γ rays were measured at 15 energies. Thick-target γ-ray angular distributions which average over many resonances could not be simply interpreted in terms of broad levels in Ne20. Twenty spin-and-parity assignments to states in Ne20 have been made in the analysis of the elastic- and inelastic-scattering data, and of these, 14 are tentative. The levels in Ne20 observed here have broader widths, larger spacings, and greater spins than the majority of those reported in the literature for the same excitation energy range. These differences are discussed and a possible explanation is offered. The incorporation of several of the levels found in this work in Ne20 rotational bands has been included in Paper I.

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