SOLIDIFICATION OF HELIUM IN CONFINED GEOMETRIES

Solidification and melting of helium in confined geometries has been s tudied in a series of in situ pressure measurements, using both He-3 a nd He-4, in porous glass with pore sizes from 12 to 191 Angstrom in ra dius. These measurements covered the temperature range from 0.04 to 2 K and pressures up to 6 MPa. In He-3, a pressure minimum is observed i n the pores at the same temperature as for the bulk. At large pore siz es the elevation in pressure in He-3 is inversely proportional to the pore radius as predicted by the model based on homogeneous nucleation of solid as a result of density fluctuations. However, the magnitude o f the pressure elevation does not agree with this model. In He-4, comp arison with the model is complicated by the strong temperature-depende nce of the pressure elevation.