The thickness of the thin native oxygen layers on Al, Fe, Co, Ni and Gd metals have been determined by making use of the 3.05 MeV resonance in the elastic scattering reaction 16O (α, α) 16O. The surfaces of iron have been studied specially for different ways of preparation, e.g., evaporation, sputtering, passivation. The advantageous application of the method to interfaces is shown in an investigation of an iron-aluminium sample.

The angular correlation between the main α-transition (5.81 MeV) and the following 388 KeV E1 gamma transition (and in one case also the 333 KeV E1 transition branching from the same level) in the decay of 249 98Cf to 245 96Cm 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.

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Institute ql' Ph)tsit's, 75I 21 Uppsala, Sweden The nuclear resonance in the l6O(a, a)l6O elastic scattering reaction at 3.045 MeV has been used in concentration profile measurements ol oxygen in thin-film structuresThe concentration profile can be deduced lrom an energy scan ol the incoming a-particies, thus shifting the resonance to different depths in the sample. The methocl has been applie

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