Optical determination of the nuclear moments of137La

Using the reactor-produced lanthanum isotope ₅₇ ¹³⁷ La, the hyperfine structure (hfs) of the transition La I, 5d ² 6p z ⁴ G ₁₁ ^2/0 ?5d ² 6s a ⁴ F _9/2, λ=6250 Å and La I, 5d ² 6p z ² H ₁₁ ^2/0 ? 5d ² 6s a ²G_9/2, λ=6266 Å were measured by means of a Fabry-Pérot interferometer. The nuclear spin I (¹³⁷La)=7/2, already theoretically estimated by earlier authors, was confirmed. The nuclear magnetic dipole moment μ_I(¹³⁷La)=+ 2.690 (6) n.m. and the electric quadrupole momentQ(¹³⁷La)=+ 0.26 (8) · 10^?24 cm² were determined from the ratios of the hfs interaction constantsA andB of¹³⁷La and the natural¹³⁹La.