  Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.
