Effect of isotopic composition on the lattice parameter of germanium measured by x-ray backscattering

We have measured, by x-ray backscattering, the lattice constant of four highly enriched Ge isotopes: A = 70, 73, 74, and 76 at temperatures ranging from 8 to 300 K. Comparing with {sup 70}Ge, values of {Delta}a/a ranged from -10 to -46 p.p.m. A good quantitative agreement over the whole temperature range (8-300 K) was found with values calculated from a theory that takes into account the zero point motion and the anharmonicity of the lattice.