AbstractsPhysics

The effect of a static quadrupole interaction on the 133-482 Kev gamma-gamma angular correlation in Ta-181 has been studied by the delayed coincidence method. Using a source of Hf-181 in polycrystalline hafnium metal, the anisotropy was measured as a function of time between the formation and decay of the 482 Key state with a fast-slow coincidence spectrometer. The anisotropy as a function of time revealed clearly the periodic fluctuations arising from the reorientation of the nuclear spin due to coupling of the quadrupole moment of the 482 Kev state with the electric field gradients of the hafnium crystals. The interaction strength evaluated on the basis of the theory of Abragam and Pound for axially-symmetric gradients was 317 ± 8 Mc/sec. Evidence for the presence of a rhombic (non-axial symmetric) electric interaction was observed in the departure of the results from the predictions of the axially-symmetric theory. The results are, however, in agreement with the theory for rhombic interactions if the electric field gradient in the hafnium crystals used is assumed to have an asymmetry parameter η = (V[subscript xx] - V[subscript yy])/V[subscript zz] = 0.3. A similar study of the 133-345 Key gamma-ray cascade did not permit a direct observation of the quadrupole coupling due to interference from the 133-482 and 345-137 Key cascades; however, when the contributions of the interfering cascades were removed from the composite data, the results were consistent with those of the 133-482 experiment as well as with existing theory. An indirect determination of the anisotropy of the 345-137 Key cascade gave the value 0.32 ± 0.02 in agreement with a previous measurement. In addition, the half-life of the 482 Key excited state was remeasured to be 10.4 ± 0.2 nanoseconds consistent with prior determinations.