  Parity nonconservation due to the nuclear weak charge is considered. We
demonstrate that the radiative corrections to this effect due to the vacuum
fluctuations of the characteristic size larger than the nuclear radius $r_0$
and smaller than the electron Compton wave-length $\lambda_C$ are enhanced
because of the strong electric field of the nucleus. The parameter that allows
one to classify the corrections is the large logarithm $\ln(\lambda_C/r_0)$.
The vacuum polarization contribution is enhanced by the second power of the
logarithm. Although the self-energy and the vertex corrections do not vanish,
they contain only the first power of the logarithm. The value of the radiative
correction is 0.4% for Cs and 0.9% for Tl, Pb, and Bi. We discuss also how the
correction affects the interpretation of the experimental data on parity
nonconservation in atoms.
