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 75d6s2 9D ground fine-structure multiplets in 155Gd and 157Gd. These reveal a 2:1 ratio in the effective radial integrals <(r5d-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 157A/155A = 1·311 43(23) and 157B/155B = 1·065 34(3) are established. Further measurements in kilogauss magnetic fields by triple resonance on the state J = 3 give the dipole moment 155μ I = -0·2584(5) n.m. (after diamagnetic correction), the electric quadrupole moment 155Q = 1·59(16) × 10 -24 cm2, and show the existence of a measurable octupole interaction. After making second-order hyperfine structure corrections, an unusually large octupole moment 155Ω = -1·6(6) × 10-24 n.m. cm-2 is deduced.