Neutron Radiography Of Helium Ii

We have used a neutron radiography technique to investigate the spatial distribution of He-3 atoms in very dilute liquid He-3-He-4 mixtures at temperatures below the superfluid transition temperature. By imposing heat currents and monitoring the subsequent redistribution of He-3 within the sample volume we obtain a direct measurement of the relevant mass diffusion coefficient. Data from these experiments provides a striking demonstration of the manner in which the distribution of impurity atoms within the liquid can be influenced by the presence of a free surface. (C) 2003 Elsevier Science B.V. All rights reserved.