Time Reversal in Nuclear Interactions

The limitations imposed by time-reversal invariance of nuclear forces have been examined for nuclear reactions, elastic double scattering (polarization) experiments, and angular correlations of gamma rays emitted from unoriented nuclei. For each of these, we have found that certain experiments, which may superficially appear to be sensitive tests of time-reversal invariance, are actually completely or partially insensitive to this symmetry. For example, in certain cases, the unitarity of the $S$ matrix is sufficient to assure detailed balance. Such insensitivity to time-reversal invariance operates in some of the experimentally best-investigated problems. Those experiments which may be expected to be sensitive tests yield an upper limit of about 10% for that fraction of the Hamiltonian which is odd with respect to a time inversion. We have suggested experiments which may lower this limit.