The isotope shifts and hyperfine-structure-splitting constants of the $6s^2{}^{1}S_0-5d6p{}^{3}D_1(\lambda =538.2\text{nm})$ and $5d^2{}^{3}P_2-5d6p{}^{1}D_2(\lambda =548.4\text{nm})$ transitions of $\text{La}\mathrm{II}$ have been measured by collinear laser-ion-beam spectroscopy for the accelerator-produced isotopes ${}^{135}\text{La}$ and ${}^{137}\text{La}$, and for the naturally occurring isotopes ${}^{138}\text{La}$ and ${}^{139}\text{La}$. The magnetic moments of the ground states of the isotopes ${}^{135}\text{La}$ and ${}^{137}\text{La}$ have been determined to be $\mu \left(135\right)=+3.70\left(9\right){\mu }_N$ and $\mu \left(137\right)=+2.700\left(15\right){\mu }_N$, respectively, and the quadrupole moments to be $Q\left(135\right)=-0.4\left(4\right)e\mathrm{b}$ and $Q\left(137\right)=+0.21\left(3\right)e\mathrm{b}$. The ratio of the magnetic dipole coupling constants $A\left(138\right)∕A\left(139\right)$ of the level $5d6p{}^{3}D_1$ has shown a $-0.35\left(23\right)\%$ hyperfine anomaly with respect to the NMR ratio of the nuclear $g$ factors. The change in the mean-square nuclear charge radius determined from the isotope shift between ${}^{139}\text{La}$ and ${}^{135}\text{La}$ is $\delta {⟨r^2⟩}^{135,139}=0.08\left(3\right){\text{fm}}^2$. This value is smaller than the predictions made by the finite-range droplet model or by the Hartree-Fock plus BCS calculation.

• Received 15 August 2003

DOI:https://doi.org/10.1103/PhysRevC.68.054328