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Recent measurements have found non-classical rotational inertia (NCRI) insolid 4He starting at T ~ 200 mK, leading to speculation that a supersolidstate may exist in these materials. Differences in the NCRI fraction due to thegrowth method and annealing history imply that defects play an important rolein the effect. Using x-ray synchrotron radiation, we have studied the nature ofthe crystals and the properties of the defects in solid 4He at temperaturesdown to 50 mK. Measurements of peak intensities and lattice parameters do notshow indications of the supersolid transition. Using growth methods similar tothose of groups measuring the NCRI we find that large crystals form. Scanningwith a small (down to 10 x 10 um2) beam, we resolve a mosaic structure withinthese crystals consistent with numerous small angle grain boundaries. Themosaic shows significant shifts over time even at temperatures far frommelting. We discuss the relevance of these defects to the NCRI observations.

X-ray Studies of Structure and Defects in Solid 4He from 50 mK to Melting