The cross sections (sigma(in) and sigma(el)) of low energy (n) over ba
r interaction with different nuclei are calculated. The optical-cascad
e model of slow (n) over bar annihilation on nuclear target is develop
ed with the aim to use it as an event generator for n --> (n) over bar
search experiment. New limit for the n --> (n) over bar oscillation p
eriod in vacuum is obtained from the stability of O-16.