Angular Correlations of Gamma Rays inTa181

Abstract

The directional angular correlation of three different gamma-ray cascades in ${\mathrm{Ta}}^{181}$ have been measured with a fast delayed-coincidence scintillation spectrometer employing NaI phosphors as detectors. An interpretation of the results, in combination with measured $K$-shell internal-conversion coefficients, indicates that an unambiguous assignment of the angular momenta of three excited states in ${\mathrm{Ta}}^{181}$ and a classification of the gamma rays are possible. The spin sequences are as follows: for the 132-480 kev gamma-ray cascade $\frac{5}{2}(E2)\frac{9}{2}(E2+M1)\frac{7}{2}$ with ${\ensuremath{\delta}}_{480}$, the square root of the intensity ratio of electric quadrupole to magnetic dipole radiation, equal to ---1.25; for the 132-345 kev gamma-ray cascade $\frac{5}{2}(E2)\frac{9}{2}(E2+M1)\frac{9}{2}$ with ${\ensuremath{\delta}}_{345}=1.0\ifmmode\pm\else\textpm\fi{}0.2$; and for the 345-135 kev gamma-ray cascade $\frac{9}{2}(E2+M1)\frac{9}{2}(E2+M1)\frac{7}{2}$ with ${\ensuremath{\delta}}_{345}=0.95\ifmmode\pm\else\textpm\fi{}0.10$ and ${\ensuremath{\delta}}_{135}=0.5\ifmmode\pm\else\textpm\fi{}0.05$. The observed angular correlation functions for the 132-480 kev and 132-345 kev cascades indicate an appreciable attenuation by perturbing interactions in the intermediate state of the nucleus by its surroundings, even in the liquid state. For polycrystalline hafnium metal and hafnium compounds, the attenuation coefficients are smaller than the "hard core" values for a static electric quadrupole interaction.