Matrix elements between nuclear compound states and dynamical enhancement of the weak interaction

A method to calculate the mean squared matrix element of the 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 ${}_{}{}^{233}{}_{}{}^{}\mathrm{Th}$ are in 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 unnecessary to assume a value of the weak constant bigger than standard one (g≃${10}^8$ε∼1–4).