  It has been proposed that the observed nonclassical rotational inertia (NCRI)
in solid helium results from the superflow of thin liquid films along
interconnected grain boundaries within the sample. We have carried out new
torsional oscillator measurements on large helium crystals grown under constant
temperature and pressure. We observe NCRI in all samples, indicating that the
phenomenon cannot be explained by a superfluid film flowing along grain
boundaries.
