Date of Original Version
Quasistationary states of ultracold neutrons have been observed in a double-hump potential barrier. This potential barrier was created by sandwiching a thin film of aluminum between two thin copper films. Measurements of reflection from and transmission through such composite films displayed clear resonances. The resonance positions and widths are in agreement with calculations.
K. -A. Steinhauser, A. Steyerl, H. Scheckenhofer, and S. S. Malik. (1980). "Observation of Quasibound States of the Neutron in Matter." Physical Review Letters, 44(20), 1306. Available at: http://dx.doi.org/10.1103/PhysRevLett.44.1306