Intermediate Structure and the Photodisintegration of O16

Wayne L. Wang and C. M. Shakin
Phys. Rev. C 5, 1898 – Published 1 June 1972
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Abstract

A theory of photonuclear reactions is formulated using a projection-operator formalism. We obtain a T matrix describing a direct photoeffect and a resonance reaction. By introducing doorway and secondary-doorway states, we can conveniently study the structure and energy dependence of the T matrix.

The formalism is applied to the analysis of the photonuclear cross sections of O16. The (γ,n) and (γ,p) cross sections are calculated. We consider those channels in which the residual nucleus is left in the ground state (Jπ=12) or the third excited state (Jπ=32). In the shell-model formulation, the doorways are taken to be mixtures of 1p-1h states, which are constructed in the Tamm-Dancoff approximation. The secondary doorways are assumed to be 3p-3h states, which are constructed in the interacting-boson approximation of Iachello and Feshbach. By mixing the doorways and the secondary doorways, we obtain a microscopic description of the compound states formed in the reactions. The doorways are shown to be responsible for the gross structure of the giant dipole resonances, while their couplings to the secondary doorways give rise to intermediate structure. A particular model of the 3p-3h states, together with certain simplifications in the description of the reaction, reproduces some of the experimental data (the photodisintegration to the Jπ=12 ground state) to a surprising degree of accuracy.

The calculation evidently shows the importance of the 3p-3h admixture in the low-lying odd-parity states of O16. Our results also give strong support to assigning E1 nature to the resonances at 21.0, 22.3, 23.1, 24.2, 25.2, and 25.6 MeV.

  • Received 28 October 1971

DOI:https://doi.org/10.1103/PhysRevC.5.1898

©1972 American Physical Society

Authors & Affiliations

Wayne L. Wang*

  • Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

C. M. Shakin

  • Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106

  • *Present address: Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213.

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Issue

Vol. 5, Iss. 6 — June 1972

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