Limits on n n̄ oscillations from nuclear stability

The relationship between the lower limit on the nuclear stability lifetime as derived from the nondisappearance of "stable" nuclei (T_d≳5.4× 10³¹ yr), and the lower limit thus implied on the oscillation time (τ_nn̄) of a possibly underlying neutron-antineutron oscillation process, is clarified by studying the time evolution of the nuclear decay within a simple model which respects unitarity. The order-of-magnitude result τ_nn̄ ≈2(T_d/Γ_n̄)^1/2>2× 10⁸ s, where Γ_n̄ is a typical n̄ nuclear annihilation width, agrees as expected with the limit on T_nn̄ established by several detailed nuclear physics calculations, but disagreeing by 15 orders of magnitude with a claim published recently [V. I. Nazaruk, Phys. Rev. C 58, R1884 (1998)].