Interaction Contribution to Nuclear Isomerism

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Abstract
A number of observed magnetic multipole isomeric transitions are forbidden on a strict Mayer model of the nucleus, and even on a number of variations thereof, if the ordinary magnetic moment operator is used. Possible explanations include modifications of the nuclear model, of the magnetic moment operator, or of both. Modifications of the operator involve consideration of the currents due to the exchange of mesons between nucleons which give rise to interaction contributions to the magnetic moment operator. An exploratory investigation has been carried out to see to what extent these interaction effects by themselves can account for these so-called forbidden transitions. Using certain simplicity arguments the operators were chosen from the set which can be written down, phenomenologically, with the radial functions arbitrary. The dipole calculations were performed on both the Fermi model and the shell model. On the Fermi model, the transition matrix element involves the unknown radial function only in an integral which is identical for all transitions. By an appropriate but arbitrary choice of the numerical value of this integral, the data can be accounted for, though somewhat crudely; the difference between transitions in odd-proton and odd-neutron nuclei is not explained. There are very few data on "forbidden" octupole transitions; the data that do exist can be more or less understood in terms of the interaction moments.