Elsevier

Nuclear Physics A

Volume 108, Issue 1, 29 January 1968, Pages 94-112
Nuclear Physics A

A shell-model study of the isotopes of O, F and Ne

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Abstract

The nuclei 18,19,20O, 18,19,20F and 20Ne are described in terms of the shell model within the configurations (1d52, 2s12)n, n = 2–4. The residual nucleon-nucleon interaction is parametrized in terms of its two-body matrix elements, which are varied until a best fit to the spectra is obtained. The resulting wave functions are used to compute static and dynamic nuclear properties. In general, the model fits the known experimental data on spectra, transition rates and static multipole moments quite satisfactorily. In particular, good agreement with experiment is obtained for the rotational spectrum of 20Ne and for the lifetimes of several of the states of its ground-state rotational band. Fitting the level properties of 20Ne, however, is found to impose on the interaction parameters few restrictions beyond those already implied by a successful treatment of the O and F spectra. Although 36 states are fitted with a 16-parameter potential, it is found that several of the two-body matrix elements are not very well determined. Those interaction parameters that are well determined are compared with the results of a recent reaction-matrix calculation. It is found that satisfactory over-all agreement with experiment can be obtained only if the 1+ excited state of 18F at 1.7 MeV is omitted from the fitting procedure. Rough estimates suggest that a core-excited 1+ state should occur at about this energy. Thus although the shell model with effective interaction can absorb large amounts of configuration impurity, it cannot do so successfully when the degree of configuration impurity in one of the states under consideration differs radically from that in its neighbors.

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    †††

    Work performed under the auspices of the U. S. Atomic Energy Commission.

    Permanent address: Department of Physics, University of Tokyo, Tokyo, Japan.

    ††

    John Simon Guggenheim fellow, on leave of absence during 1966–1967 at the Department of Theoretical Physics, Oxford University, England.

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