Hyperfine Structure of the Spectrum of Gadolinium

The hyperfine structures of 32 lines of Gd I and 2 lines of Gd II in the visible region were measured. They could be interpreted as due to the isotope displacement effect of the even isotopes (156, 158 and 160) and the splittings due to the nuclear magnetic moments of the odd isotopes (155 and 157). The ratio of the isotope displacements Δ (158-156)/ Δ (160-158)=0.97±0.06 was determined. The relative isotope displacement Δ (160-158) in some 30 terms of Gd I is tabulated.