Alpha-gamma Angular Correlation and Hyperfine Interaction in the Decay of²⁴⁹₉₈Cf

The angular correlation between the main α-transition (5.81 MeV) and the following 388 KeV E 1 gamma transition (and in one case also the 333 KeV E 1 transition branching from the same level) in the decay of 249 98 Cf to 245 96 Cm has been studied. Thin sources were used. The recoiling daughter ions were allowed to escape into vacuum. The strong hyperfine interaction perturbing the correlation in this case was neutralized by a longitudinal decoupling field with a strength of some kilogauss. The unperturbed values of the A 22 -coefficients do not support the mixing ratios ( L =0, L =2, L =4) from the Bohr-Fröman-Mottelson theory. The correlation was also studied, in silver and nickel surroundings where it was found to be almost unperturbed. In an insulator a strong perturbation was found which was not influenced by the longitudinal field.