Excited states in ${}^{160}\mathrm{Er}$ and ${}^{156}\mathrm{Dy}$ were populated via ${\beta }^{+}/\mathrm{EC}$ decay and were studied via conversion electrons and $\gamma$-ray spectroscopy at the Tandem Accelerator in the INFN Laboratori Nazionali del Sud in Catania, Italy. Conversion electrons were detected by a mini-orange spectrometer with a transmission energy window that ranged from 500 to 1000 keV for ${}^{160}\mathrm{Er}$ and from 350 keV to 750 keV for ${}^{156}\mathrm{Dy}$. The $E0$ decays of the first excited state at 893 keV in ${}^{160}\mathrm{Er}$ and at 676 keV in ${}^{156}\mathrm{Dy}$ were observed, and $X(E0/E2)$ ratios of reduced transition probabilities were deduced. Furthermore, for both nuclei $E0$ admixtures in transitions from the lower members of the $\beta$ and $\gamma$ bands to the ground-state band were observed, and $X(E0/E2)$ values were deduced. The values of the $X(E0/E2)$ for the $0_2^{+}$ decays are compared to IBA-1 calculations that use the full Hamiltonian in multipole expansion. Properties related to the nuclear shape seem to be sensitive to higher-order terms of the expansion.

• Received 9 September 2014

DOI:https://doi.org/10.1103/PhysRevC.90.044317