Observations are reported on the appearance of frustrated total reflec
tion, i.e. the tunnelling phenomenon, with cold neutron wave-particles
. This tunnelling resonance was observed in a thin film Ni-V-Ni Fabry-
Perot cavity by time of flight grazing angle neutron reflectometry. Th
is frustrated total reflection phenomenon was used to estimate the neu
tron lifetime, which varies from approximately 0.1 to 1 mu s.