Search for low-energy upscattering of ultracold neutrons from a beryllium surface

We present results of a search for anomalous low-energy upscattering of ult racold neutrons from a beryllium surface. This upscattering is considered o ne for the possible reasons for UCN "disappearance'' from very cold berylli um bottles, as observed in experiments. The indium foil activation method w as used to measure a very low intensity flux of upscattered UCN. The (15-30 0) m/ s velocity range of upscattered UCN is ruled out by these measurement s at a confidence level of 90%. (C) 1999 American Institute of Physics. [S1 063-7761(99)01301-3].