Limits on the neutron-antineutron oscillation time from the stability of nuclei

We have reexamined the question of what limit may be placed on the free space neutron-antineutron oscillation time nn» from a measured limit T0 on the annihilation lifetime T of a nucleus. Using several recent antinucleon-nucleus optical potentials consistent with both p»-atom and low energy scattering data, we obtain a limit nn»>(10.3)×108 sec if T0=2.4×1031 yr. We consider the effect on our results of nuclear medium corrections such as a renormalization of the effective operator for n n transitions or the presence of additional B=2 decay modes which are absent in free space. It is argued that renormalization effects are not likely to exceed those characteristic of nuclear decay, and that if additional modes are present, the limit on nn» becomes even better.