Ultracold neutrons extracted from a superfluid-helium converter coated with fluorinated greaseO. Zimmer, P. Schmidt-Wellenburg, M. Fertl, H.-F. Wirth, M. Assmann, J. Klenke and B. van den BrandtEur. Phys. J. C, 67 3-4 (2010) 589-599DOI: https://doi.org/10.1140/epjc/s10052-010-1327-1