An experiment on penetration of sub-barrier ultra-cold neutrons (UCN) through beryllium foils and coatings

The results of measurements of penetration of the sub-barrier ultracold neutrons through beryllium foils and coatings are discussed. The scheme of the installation used for measurements is shown. The observed penetration probability value is revealed to be much higher than that expected for the quantum-mechanic tunneling effect. It is concluded that the phenomenon detected is very likely to have the same nature as the effect of the so-called anomalous losses of ultracold neutrons during their storage in traps. The 56 μm thick Be foil produced by rolling Be metal prepared by hot-pressing of Be powder is placed so as to span the entire section of the 9 cm in-diameter neutron guide which connects the storage volume to the ultracold neutron detector. The flux of ultracold neutrons at the level of the Be foil is equal to 500 n/sec/cm2. The flux of ultracold neutrons penetrating through the Be foil is measured to be (1.16 ± 0.20) x 10-2 sec-1 for an initial energy range E0 ≅ 0.52 - 1.8 m. The probability of penetration is (5.0 ± 1.0) x 10-7 per collision. The statistical reliability of the measurement is of the order of 6 standard deviations