The Magnetic Exchange Current and the Spin-Orbit Interaction

It is shown that model independent local isoscalar and isovector exchange current operators associated with the spin-orbit component of the nucleon-nucleon interaction may be constructed from such nucleon-nucleon interactions that have been derived from relativistic models (e.g. boson exchange) for the scattering amplitude. The resulting magnetic moment operators contain terms that cannot be obtained by direct gauging of the conventional spin-orbit interaction. It is shown that the model independent isoscalar exchange current associated with the spin-orbit interaction causes a quenching of the order 10% of the effective isoscalar magnetic moment operator in heavy nuclei. The corresponding isovector exchange current operator causes a somewhat smaller enhancement of the effective isovector magnetic moment operator, which counteracts the much larger quenching effect caused by isobar-hole screening of the nucleons. The isoscalar exchange current operator leads to a small modification of the calculated magnetic formfactor of deuterium, which counteracts the contribution from typical model dependent exchange current contributions.