Collective states fed by weak α-transitions in the 230U chain

Abstract

The 230U decay chain has been investigated using Ge(Li) spectrometers in singles and coincidence measurements. The internal-conversion spectra have been studied in a β-spectrometer with a Si(Li) detector placed in a homogeneous magnetic field. A total of 31 γ-ray transitions, 14 of which have not been reported before, have been observed in the decay of 230U and its descendants. All transitions could be unambiguously placed in the individual level schemes. The new band-heads at 805 and 914 keV in 226Th and 222Ra, respectively, are proposed as 0+ quadrupole-pairing vibrations. No evidence has been found for the existence of 0+ two-phonon harmonic octupole states in these nuclei. A possible anharmonicity of the octupole vibrations is discussed.