An apparatus for studying condensed impurity systems in liquid helium

The design of an apparatus that ensures the injection of gaseous He-4 with water vapor impurities or vapors of other molecular liquids into the experi mental cell, which is filled with superfluid He-II, is described. It is sho wn that, when a He-4 + H2O gas mixture condenses, porous semitransparent sa mples (icebergs) with a characteristic size of similar to1 cm form under th e surface of the superfluid. The volume concentration of water in the sampl es is less than or similar to 10(20) molecules/cm(3). When heated above T-l ambda, icebergs in normal He-I may decompose into ice and He-4. The tempera ture T-d at which intense disintegration begins depends on the pressure of the vapor above the liquid: T-d approximate to 2.5 K at a pressure of 0.2 a tm, and, at a pressure of 1 atm, T-d rises up to 4 K. In an atmosphere of g aseous He-4, icebergs begin disintegrating into parts under warming above 1 .8 K. This indicates the discovery of a new highly porous form of ice in li quid helium-a water gel, the dispersed phase (solid frame) of which is form ed by water clusters surrounded by a solidified helium layer; liquid helium serves as a dispersing medium.