Nuclear dipole, quadrupole and octupole moments of 155Gd by atomic beam magnetic resonance

Hyperfine structure measurements have been made by atomic beam magnetic resonance in weak fields on the J = 2, 3, 4, 5 and 6 states of the 4f 7 5d6s 2 9 D ground fine-structure multiplets in 155 Gd and 157 Gd. These reveal a 2:1 ratio in the effective radial integrals <( r 5d -3 > associated with the l. I and ( sC (2) ) (1) . I parts of the magnetic dipole interaction as a result of configuration mixing. Significant relativistic effects are found in the quadrupole interaction, and the ratios 157 A / 155 A = 1·311 43(23) and 157 B / 155 B = 1·065 34(3) are established. Further measurements in kilogauss magnetic fields by triple resonance on the state J = 3 give the dipole moment 155 μ I = -0·2584(5) n.m. (after diamagnetic correction), the electric quadrupole moment 155 Q = 1·59(16) × 10 -24 cm 2 , and show the existence of a measurable octupole interaction. After making second-order hyperfine structure corrections, an unusually large octupole moment 155 Ω = -1·6(6) × 10 -24 n.m. cm -2 is deduced.