Superfluid-Helium Converter for Accumulation and Extraction of Ultracold Neutrons
O. Zimmer, K. Baumann, M. Fertl, B. Franke, S. Mironov, C. Plonka,D. Rich, P. Schmidt-Wellenburg, H.F. Wirth and B. van den Brandt
Physical Review Letters 99, 104801 (2007)