Parity Mixing and Nuclear Structure in the Decays from OrientedGd153,159andTb161

Abstract

Measurement of the angular distribution of the 363-keV $\ensuremath{\gamma}$ radiation following the decay of $^{159}\mathrm{Gd}$ oriented in Gd${\mathrm{Fe}}_{2}$ at low temperatures has yielded a vanishing value of the parity-non-conserving forward-backward asymmetry, indicating in this transition no large effect resulting from the parity-violating weak nucleon-nucleon interaction. Vanishing asymmetries were observed for other strongly hindered transitions in $^{159}\mathrm{Tb}$ and in $^{161}\mathrm{Dy}$. The 0-90\ifmmode^\circ\else\textdegree\fi{} anisotropy of the 363-keV angular distribution has yielded a value for the magnetic moment of the $^{159}\mathrm{Gd}$ ground state of $\ensuremath{\mu}=(\ensuremath{-}0.44\ifmmode\pm\else\textpm\fi{}0.03){\ensuremath{\mu}}_{N}$. The magnitude of the hyperfine field of Tb in Gd${\mathrm{Fe}}_{2}$ has been estimated to be 370 \ifmmode\pm\else\textpm\fi{} 80 kG, based on observation of the 0-90\ifmmode^\circ\else\textdegree\fi{} anisotropy of $\ensuremath{\gamma}$ transitions in $^{161}\mathrm{Dy}$. The multipole characters of various $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ transitions following the decay of oriented $^{153,159}\mathrm{Gd}$ and $^{161}\mathrm{Tb}$ have been deduced.