Nuclear orientation of160Hog+mGd: Sign change ofE2/M1mixing ratios inΔK=2transitions of160Dy

Abstract

Directional distribution of \ensuremath{\gamma} rays following the decay of ${}^{160}{\mathrm{Ho}}^{g+m}$ oriented in a gadolinium host at low temperature has been studied. The \ensuremath{\gamma}-ray anisotropies of transitions from the levels below 3 MeV in ${}^{160}\mathrm{Dy}$ were measured and multipole mixing ratios \ensuremath{\delta} were determined. The variations in both sign and magnitude of \ensuremath{\delta} for the $M1+E2$ transitions between the \ensuremath{\gamma}-vibrational ${(K}^{\ensuremath{\pi}}{=2}^{+})$ and ground-state ${(K}^{\ensuremath{\pi}}{=0}^{+})$ bands were observed. The $E2/M1$ mixing ratios for the $\stackrel{\ensuremath{\rightarrow}}{2}2$ and $\stackrel{\ensuremath{\rightarrow}}{4}4$ transitions from the \ensuremath{\beta}-vibrational ${(K}^{\ensuremath{\pi}}{=0}^{+})$ band to the ground-state band were determined, and the $E0/E2$ probability ratios obtained are consistent with the values for the \ensuremath{\beta}-vibrational bands. The $E2/M1$ mixing ratios of the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}g$ transitions in ${}^{160}\mathrm{Dy}$ obtained previously by the nuclear orientation of ${}^{160}\mathrm{Tb}$ are compared with the present results. The dynamic deformation model is employed to calculate the collective bands, electromagnetic moments, transition probabilities, and mixing ratios in ${}^{160}\mathrm{Dy}.$ A sign change of the $E2/M1$ mixing ratio is predicted for the ${10}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{10}_{g}$ transition. Our experimental results give such a sign change for the ${4}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{4}_{g}$ and ${6}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{6}_{g}$ transitions. Comparison with the presently determined experimental values of $X(E0/E2)$ for $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}g$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\beta}}g$ transitions is also given.