Isospin breaking matrix elements in compound nuclei

The study of compound-nucleus reactions that are isospin forbidden yields information on the average Coulomb matrix element, that mixes states of different isospin in the domain of highly excited overlapping levels. A prerequisite for this is, however, the calculation and subtraction of 'external' mixing. In the present work, an approximate calculation is carried through. It is based on a transport theory of statistical nuclear reactions developed in recent years. Coulomb matrix elements are derived in 18 cases for which experimental data are available. (orig.)