Hyperfine Structure in Europium Metal

Abstract

M\"ossbauer resonance experiments were performed on europium metal, using the 21.7-keV gamma ray in ${\mathrm{Eu}}^{151}$. The N\'eel point of 87\ifmmode^\circ\else\textdegree\fi{}K was confirmed. Above this temperature a single line was observed and attributed to paramagnetic relaxation. At 4.2\ifmmode^\circ\else\textdegree\fi{}K a six-line spectrum was found. Analysis yielded a spin of $\frac{7}{2}$ and a moment of +2.53\ifmmode\pm\else\textpm\fi{}0.03 nm for the 21.7 keV excited state, an internal field of 264\ifmmode\pm\else\textpm\fi{}8 kG, and an isomeric chemical shift of -0.81\ifmmode\pm\else\textpm\fi{}0.03 cm/sec, relative to ${\mathrm{Eu}}_{2}$${\mathrm{O}}_{3}$. This is consistent with an electronic level $4{f}^{7}6{s}^{2}$, $^{8}S_{\frac{7}{2}}$ 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.