Thermal Defects in BCC ³He Crystals Determined by X-Ray Diffraction

Abstract

Information about thermally created defects in a solid can be obtained by comparing the change of macroscopic volume V and of X-ray cell volume Ω for different temperatures by means of the relation

$$ \frac{{\Delta V}} {V} - \frac{{\Delta \Omega }} {\Omega } = c $$

((1))

where c is the net concentration of vacancy-type defects.¹ Solid bcc ³He can be investigated at essentially constant volume, thus reducing Eq. (1) to

$$ - \Delta \Omega /\Omega = - 3\Delta a/a = c $$

((2))

where a is the lattice parameter. Thus in a constant-volume experiment, observation of a single lattice parameter change with change of temperature can be directly related to the creation of vacancy-type defects.

Work supported in part by the U. S. Atomic Energy Commission.