THE AXIAL EXCHANGE CHARGE OPERATOR AND THE NUCLEON NUCLEON-INTERACTION

The short-range contributions to the effective axial charge operator of a nucleon in a nuclear medium that are implied by realistic nucleon-nucleon interaction models cause an enhancement of approximately 40% at nuclear-matter density of the single-nucleon value, the numerical value depending on the potential model. Combined with the approximately 45-60% enhancement caused by pion exchange, this yields a net enhancement of approximately 85-100%, in good agreement with the approximately 100% implied by first forbidden beta-decay transitions in the lead region.