Sub-boundaries in3He and4He single crystal and their migration below 1K observed by X-ray topography

Abstract

The observation of alterations in crystal structure at ultra-low temperatures by X-ray diffraction, made possible by the realization of synchrotron radiation use after a quarter of this century, plays an important role in obtaining an understanding of the base structure of solids. For that, two types of3He-4He dilution refrigerators with a modified version of the top-loading facilities were installed at the BL-3C2 and 6C1 stations of the Photon Factory. In BL-3C2, the behaviors of lattice defects in solid helium have been studied by X-ray topography. In this note, the migrations of sub-boundaries in3He and4He single-crystals are reported as being the result of an annealing effect. After annealing hcp4He single crystals for 80min at 0.5K, no change in crystallographic orientations could be easily observed from white SR X-ray topographs. In the same type topographs of bcc3He single crystals after annealing for several hours at 03K, migration of sub-boundaries were conspicuously discerned.