On the properties of low-lying states in Ho odd-odd nuclei with A=156, 158 and 160 populated in beta decay of Er isotopes

Radioactive decays of neutron-deficient isotopes 156Er (Tsub(1/2)=19.5 min), 158Er (Tsub(1/2)=2.24 h) and 160Er (Tsub(1/2)=30 h) have been investigated. Gamma-radiation has been measured by means of spectrometers with Ge (Li) detectors. Internal conversion electron spectra have been measured by means of iron-free beta-spectrometer with toroidal magnetic field and beta-spectrograph with constant homogeneous magnetic field. To confirm schemes of the studied isotope decay the measurements of e-γ-coincidences have been performed at the installation created on the base of a beta- spectrometer with toroidal magnetic field and gamma-spectrometer with Ge(Li) detector. Mass differences ΔM(156Er→156Ho)=1670-L-55+105 keV, ΔM(158Er→158Ho)=1706-L-35+55 keV and ΔM(160Er→160Ho)=370-L-90+190 keV have been defined. First forbidden beta-transitions of the type 0+→1- have been confidently identified in the decay of 156Er and 158Er with anomalously small values lgft=5.2 and 5.4, respectively. One does not observe in the 158Ho nucleus the population from the 158Er decay of the level 1+, [p523 excitation n523 de-excitation ] expected in accordance with theories. Reliable arguments have been obtained in favour of excitation of the state 160Ho with I=1+ of the above indicated type from 160Er decay. Using as an example the beta-decay 156Er→156Ho there has been demonstrated experimentally there are no delayed beta-transitions which have been expected to occur due to sharp differencies in the nuclei shapes