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[en] Using our relativistic-configuration-interaction methodology, we report multireference calculations of energy differences and magnetic-dipole and electric-quadrupole hyperfine structure constants of all five levels in the (5d+6s)² J=2 manifold of singly ionized ¹³⁹La. The errors in the splittings of the bottom four levels are no more than 0.02 eV, while the separation of the two highest levels has an error of 0.11 eV due to an incomplete description of the correlation in the levels belonging to higher manifolds. The hyperfine-structure constants show strong sensitivity to many-body effects, resulting in striking improvements over the multiconfiguration Dirac-Fock values. Seven of the ten hyperfine constants are accurate within 2--12 %. For the rest of the constants we have identified the primary cause of the errors as an incorrect description of many-body effects in the high-lying levels and have discussed possible remedies

[en] We report on zero-field nuclear spin-lattice relaxation measurements of ¹³⁹La in La_1.8Sr_0.2CuO_4-δ in the normal and the superconducting state. Below the superconducting transition temperature T_c the relaxation rate behaves like 1/T₁ ∼ exp[-Δ/kT] with activation energy Δ = 11.5 MeV leading to a gap energy of 2Δ = 23 MeV. With T_c = 38 K the ratio 2Δ/kT_c = 7.1 is obtained, which is twice as large as the weak-coupling value of 3.5

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[en] A lead target which resonantly scatters the 7.279 MeV line of neutron capture γ rays of iron was used as a source of variable energy γ-radiation. Variation of the angle of the resonantly scattered beam between 60⁰ and 120⁰ permits an energy variation, ΔE = 275 eV, below the resonant energy. In ¹³⁹La, a transmission experiment using a ¹³⁹La absorber has yielded 3 dips in the above angular range. The values of g GAMMA₀ of these levels, and the nuclear level spacing in ¹³⁹La are deduced. (Auth.)

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[en] Optogalvanic laser spectroscopy has been applied to measure the hyperfine structure of 19 spectral lines of La I in the wavelength regions from 570 to 590 nm and 700 to 825 nm. Experimental hyperfine structure constants A and B of the isotope ¹³⁹La have been measured for 16 levels of odd parity. From those values six magnetic dipole and ten electric quadrupole constants have been determined for the first time. Some disagreements with previously obtained values are discussed