Neutron - Antineutron Oscillations in a Trap Revisited

We have reexamined the problem of $n-\bar n$ oscillations for ultra-cold neutrons (UCN) confined within a trap. It is shown that for up to $10^3$ collisions with the walls the process can be described in terms of wave packets. The exact equation is derived describing the time-evolution of the $\bar n$-component for an arbitrary number of collisions with the trap walls. The $\bar n$-component grows linearly with time with enhancement factor depending on the reflection properties of the walls.