Differential measurements of the angular correlation of the 133-482 ke V cascade in the decay of 181Hf have been performed. The source was prepared by an irradiation of a Hafnium single crystal by thermal neutrons. The analysis of the data proved that the electric field gradient at the position of the nucleus has axial symmetry. The strength of the electric field gradient was derived as: 17 2 Vzz = (5,5 ± 0,3) . 10 Vjcm This calculation is based on the electric quadrupole moment 24 2 Q(I = ~) = (2,5 ± 0,1) ·10- cm By combining the internal field with an external magnetic field the reso nance between the electric and magnetic Larmor precession could be observed. The amplitude of the observed spin rotation curve diminishes with increasing time-delay. The reason for this effect is not yet understood. Resume Nous avons effectue des mesures differentielles de la correlation directio nelle entre les cascades 133-482 keV du lSlHafnium. La source etait con stituee par un monocristal de Hafnium, ayant ete irradie par des neutrons thermiques. L'analyse des mesures montre que le gradient du champ magnetique aupres du noyeau a la symmetrie axiale. Sa valeur est: 17 2 V = (5,5 ± 0,3) .10 Vjcm zz Ce calcul repose sur un moment quadripolaire de 24 2 Q(I = ~) = (2,5 ± 0,1) .10- cm La superposition d'un champ magnetique externe nous a permis d'ob server la resonance entre la precession de Larmor electrique et magnetique.

Inhalt
Beobachtung der Resonanz zwischen elektrischer und magnetischer Hyperfeinstrukturwechselwirkung.- Probleme der Zeitmessung.