Low Temperature Physics: 34, 316 (2008); https://doi.org/10.1063/1.2908893 (4 pages)
Neutron reflection from a liquid helium surface
T.R. Charlton1, R.M. Dalgliesh1, A. Ganshin2, O. Kirichek1, S. Langridge1, and P.V.E. McClintock2
1ISIS, STFC, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, OX11 0QX, UK
2Physics Department, Lancaster University, Lancaster, LA1 4YB, UK
Received November 6, 2007
The reflection of neutrons from a helium surface has been observed for the first time. The 4He surface is smoother in the superfluid state at 1.54 K than in the case of the normal liquid at 2.3 K. In the superfluid state we also observe a surface layer ~200 Å thick which has a subtly different neutron scattering cross-section, which may be explained by an enhanced Bose–Einstein condensate fraction close to the helium surface. The application of neutron reflectometry described in this paper creates new and exciting opportunities for the surface and interfacial study of quantum fluids.
PACS: 68.03.–g Gas–liquid and vacuum–liquid interfaces;
Key words: neutron reflection, liquid helium, surface, Bose–Einstein condensate.