E0decay from the first0+state inDy156andEr160

Excited states in $^{160}\mathrm{Er}$ and $^{156}\mathrm{Dy}$ were populated via ${\ensuremath{\beta}}^{+}/\mathrm{EC}$ decay and were studied via conversion electrons and $\ensuremath{\gamma}$-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 $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ 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.