Nuclear quadrupole precession after recoil implantation into single crystals for Hf180 in Hf and W186 in Gd

Coulomb excitation with O16 and S32 beams was used to excite, polarize, and implant Hf180(2+) in Hf single crystals and W186(2+) in Gd single crystals. Particle-γ correlations for different crystal orientations were measured. The general features of the perturbed correlations were consistent with the prediction for a static axially symmetric quadrupole interaction in a single crystal, but additional perturbations had to be taken into account to explain the results quantitatively. Special experimental geometries were employed to separate these perturbations. In the Hf180 in Hf experiment the sign of the quadrupole interaction could be unambiguously determined as negative using the known polarization of the excited nucleus. In the W186 in Gd case unknown perturbation mechanisms reduced the terms linear in the quadrupole interaction frequency to such an extent that the negative sign indicated is less certain. Control experiments with implantation of W186 in Cu foils were used to check the experimental technique for systematic errors. NUCLEAR REACTIONS (HI Coulomb excitation) W186, E(O16)=40 MeV, E(S32)=80 MeV, recoil Gd single crystal; measured O16γ(θ), S32γ(θ); deduced sign W186(2+) quadrupole interaction. Hf180, E(O16)=40 MeV, recoil Hf single crystal; measured O16γ(θ); deduced sign Hf180(2+) quadrupole interaction.