Nuclear Physics A559 (1993) 543-578 North-Holland NUCLEAR PHYSICS A The electromagnetic exchange current, the nucleon-nucleon interaction, and nuclear magnetic moments K. Tsushima, D.O. Riska zyxwvutsrqponmlkjihgfedcbaZYXW Department of Physics and Research Institute for Theoretical Physics, P.O. Box 9, ~UOl4 University of Helsinki, Helsinki, Finland P.G. Blunden Department of Physics, University of ~a?lito~a, W innipeg, MB, R3T 2N2 Canada Received 16 July 1992 (Revised 23 November 1992) zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Abstract: A method of constructing the electromagnetic exchange-current density operator from a given complete, energy-independent model for the nucleon-nucleon interaction, which satisfies the continuity equation to order (r;/cf2, is developed. The resulting current operator is then used to derive the general expression for the two-nucleon part of the nuclear magnetic moment operator that is associated with the nucleon-nucleon interaction. The utility of this method is illustrated by a derivation of the general expression for this exchange-current contribution to the effective magnetic moment operator of a valence nucleon outside a closed shell in the Fermi-gas model. Numerical values for the g-factors of the valence nucleon are calculated using two realistic models for the nucleon-nucleon interaction. The calculated exchange-current correc- tions are finally combined with the corrections from the most important model-dependent currents to give the net exchange-current correction to the g-factors. 1. Introduction A problem of great practical importance in the theoretical description of electromagnetic nuclear properties and reactions is that of constructing a nuclear current (density) operator which is consistent with the model for the nuclear interaction used to construct the wave functions [l-11]. The problem does not in fact have a unique solution, as the continuity equation only determines the longitudinal component of the current operator. In spite of this, a procedure for Correspondence to: Dr. D.O. Riska, Department of Physics, P.O. Box 9, 00014 University of Helsinki, Helsinki, Finland. 0375-9474/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved