Search for anomalous transmission of ultracold neutrons through metal foils

Results are presented on the search for anomalous transmission of ultracold neutrons (UCNs) through beryllium (thickness ∼0.14 mm), stainless steel (0.05 and 0.015 mm), and copper (0.01 and 0.018 mm) foils. This anomalous transmission is considered to be a possible reason for the disappearance of UCNs from beryllium bottles, an effect which was discovered in experiments at the St. Petersburg Nuclear Physics Institute and which was recently observed in the experiment of V. E. Varlamov et al., JETP Lett. 66, 336 (1997). No transmission was found in our measurements at the 10⁻⁷ level except in the case of copper foils, which we attribute to the presence in the UCN flux of an admixture of neutrons with energies higher than the boundary energy for copper. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 440–444 (10 April 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.