Hyperfine Structure in Europium Metal

M\"ossbauer resonance experiments were performed on europium metal, using the 21.7-keV gamma ray in Eu¹⁵¹. The N\'eel 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 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 Eu₂{O}₃$. This is consistent with an electronic level $4{f}⁷6{s}²$, $⁸S7/2$ for the europium atom. The effect of nuclear deformation on isomeric chemical shifts is considered, and it is concluded that ${Eu}¹⁵¹$, with a moderately deformed ground state, has a less deformed excited state at 21.7 keV.