Microscopic Theory of Effective Operators for Electromagnetic Interactions in Nuclei

Abstract

Effective operators for valence (open-shell) nucleons only are constructed, for electromagnetic interactions in nuclei. Such operators are calculated in terms of excitations and deexcitations of particle-hole pairs of the oore nucleons. The nuclear force involved is a realistic; nucleon-nucleon potential (Yale-Shakin). The theory is applied to the Sn region described in terms of five valence neutron subshells and of all the core and open subshells of both the neutrons and protons between the magic numbers 8 and 126. The effective quadrupole charge matrix has all the elements of about the same order of magnitude,thus giving a first partial support to the concept of a oonstant neutron effective charge. Calculations of observables are performed with the states of the even tin isotopes described in terms of the twoand fourquasiparticle Tamm-Dancoff theories involving explicitly only the valence neutrons. Results are presented for the B(E2, 2, * 0 . ) t the quadrupole moment Q ( 2 ) , the gyromagnetic factor g and the inelastic electron-scattering form factors for the 2+ and 3r 116 — XI states of Sn . Except for the last (3-* ) form factor, a good seraiquantitative agreement with all the corresponding experimental data is obtained. The reported calculations involve no ad hoc adjustable parameter.