Mössbauer-Effect Observations of Recoil Radiation Damage Following Coulomb Excitation in Various Hf Compounds

Mössbauer-effect experiments following Coulomb excitation have been performed involving Hf nuclei in Hf metal, Hf${\mathrm{B}}_2$ HfC, HfN, and Hf${\mathrm{O}}_2$. The first excited states of ${\mathrm{Hf}}^{178}$, ${\mathrm{Hf}}^{180}$, and ${\mathrm{Hf}}^{177}$ were populated via Coulomb excitation by 6-MeV $\alpha$ particles. The majority of the experiments were performed with both targets and absorbers near liquid-nitrogen temperature. Anomalous hyperfine interactions are found in all of the compounds when they are used as targets, compared to the hyperfine interactions observed when they are used as absorbers. The anomalous interactions are interpreted in terms of lattice distortions resulting from vacancies produced in the locale of the decaying recoil Mössbauer nuclei following Coulomb excitation. The degree of lattice distortion is found to be dependent upon the bonding characteristics of the compounds.