Quantum Evaporation from Superfluid 4He

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The quantum evaporation experiments of Brown and Wyatt2 have been re-analysed in the light of a recent measurement of the high-energy phonon spectrum created by a pulse-heated thin film10. 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.

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