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

Absolute values of the Mössbauer fraction $f$ of zero-phonon gamma rays from dilute ${\mathrm{Co}}^{57}$ 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, $f=0.81\mathrm{}$; for Cu at 297°K, $f=0.71\mathrm{}$. Systematic errors are estimated to be less than 2%. The Mössbauer spectrum of Be shows a quadrupole splitting $\Delta E=0.56\mathrm{}\pm 0.03$ mm/sec and a chemical shift $\delta =-0.11\mathrm{}\pm 0.03$ mm/sec with respect to an Fe absorber.