Matrix Elements between Nuclear Compound States and Dynamical Enhancement of the Weak Interaction

A method to calculate the mean squared matrix element of weak interaction between compound states is developed. The result is expressed in terms of matrix elements of the nucleon-nucleon strong and weak interactions times the Fermi distribution functions at finite temperature. Numerical calculations for $^{233}$Th are in excellent agreement with recent measurements of parity nonconservation effects in neutron capture. In fact, our calculations prove that the factor of dynamical enhancement (ratio of compound-nucleus effect to single-particle one) really exceeds 100, thus making it unnesessary to assume a value of the weak constant bigger than standard one ($g\simeq 10^{8} \epsilon \sim 1\div 4$).