Quantum Evaporation from Superfluid 4He

The quantum evaporation experiments of Brown and Wyatt have been re-analysed in the light of a recent measurement of the high-energy phonon spectrum created by a pulse-heated thin film. Two sources of systematic error become significant at the level of the precision required by this new analysis: firstly, in the detector position which is recalibrated by using large-angle roton evaporation; and secondly, in the liquid height due to capillary action affecting the level-detectors. These effects have been included in an improved simulation of the experiment which has brought the angular dependence of the measured and theoretical phonon-atom evaporation results into agreement within the mechanical tolerances of the apparatus. The reanalysis suggests that the roton-atom evaporation probability increases with wave vector. PACS numbers: 67.40.Db, 68.45.Da, 67.40.-w