  We study the contribution of two-body meson-exchange processes to axial
charge transitions for nuclei in the lead, tin and oxygen regions. We conduct
calculations in the Dirac-Hartree (the Walecka model) and the relativistic
Hartree (where the full one-nucleon-loop effects are included) approximations.
We present results indicating that one- and two-body processes enhance the
matrix elements of the axial-charge operator by some (100+-20)% in all three
regions studied. This agrees well with the fit of eighteen first-forbidden
beta-decay transitions conducted by Warburton in the lead region. We also
discuss some sensitivities present in the calculation.
