Hyperfine Structure in Europium Metal

Abstract

Mössbauer resonance experiments were performed on europium metal, using the 21.7-keV gamma ray in ${\mathrm{Eu}}^{151}$. The Néel point of 87°K was confirmed. Above this temperature a single line was observed and attributed to paramagnetic relaxation. At 4.2°K a six-line spectrum was found. Analysis yielded a spin of $\frac{7}{2}$ and a moment of +2.53±0.03 nm for the 21.7 keV excited state, an internal field of 264±8 kG, and an isomeric chemical shift of -0.81±0.03 cm/sec, relative to ${\mathrm{Eu}}_2$ ${\mathrm{O}}_3$. This is consistent with an electronic level $4f^{7}6s^2$, ${}_{}{}^8{}_{}{}^{}S_{\frac{7}{2}}^{}{}_{}{}^{}$ for the europium atom. The effect of nuclear deformation on isomeric chemical shifts is considered, and it is concluded that ${\mathrm{Eu}}^{151}$, with a moderately deformed ground state, has a less deformed excited state at 21.7 keV.