Mean-Square Displacement of Dilute Iron Impurity Atoms in High-Purity Beryllium and Copper

Absolute values of the M\"ossbauer fraction f of zero-phonon gamma rays from dilute Co⁵⁷ in Be and Cu were obtained for several temperatures between liquid helium and room temperature using the technique of the "black absorber." For Be at 297^∘{}K, $f=0.81$; for Cu at 297^∘{}K, $f=0.71$. Systematic errors are estimated to be less than 2%. The M\"ossbauer spectrum of Be shows a quadrupole splitting ΔE=0.56±0.03 mm/sec and a chemical shift δ=-0.11±0.03 mm/sec with respect to an Fe absorber.