Isomer Shifts and Mössbauer-Effect Efficiencies in Intermetallic Compounds of Europium

Recoilless absorption measurements of the 97- and 103-keV $\gamma$ rays of ${\mathrm{Eu}}^{153}$ in variuos intermetallic compounds of Eu were carried out. The results obtained for the isomer shifts were compared with those obtained previously for the 21.7-keV transition of ${\mathrm{Eu}}^{151}$ and found to be consistent with the existing theories, according to which, $\Delta E$ can be expressed as a product of a nuclear factor and an electronic factor. Anomalies found in the isomer shifts in Eu metal are very probably a result of the very low Debye temperature of the metal and the existence of impurities in the metal. The Debye temperatures of the intermetallic compounds of Eu estimated from the size of the recoilless absorption effects lie in the range between 160 and 200°K. From the analysis of the absorption spectrum of the 103-keV $\gamma$ rays of ${\mathrm{Eu}}^{153}$ in Eu metal, the Debye temperature of Eu metal at 4° was estimated to be (94±6)°K.