COMPRESSIBILITY OF HE-4 LIQUID CONFINED IN NUCLEPORE

Adding and removing He-4 from an experimental cell which contains the porous material Nuclepore results in capillary condensation, hysteresi s and avalanches. The volume of liquid in the nearly cylindrical pores in monitored with a capacitance technique. For the situation when all of the pores are full, the initial removal of He-4 from the cell resu lts in a slight non-hysteretic decrease int he capacitance which we at tribute to the isothermal compressibility of He-4. As He-4 atoms are r emoved, the surface tension at the meniscus applies a negative pressur e to the liquid in the filled pores, which results in a reduction of t he density and a decrease in the capacitance. We present results for H e-4 capillary condensed in 2000 Angstrom pore diameter Nuclepore.