Rotational bands and fast el transitions in 163Ho

Abstract

The level scheme of the deformed odd-proton nucleus 163Ho has been investigated by in-beam and decay spectroscopic methods. Single γ-ray spectra, conversion electron spectra, γ-γ coincidences and angular distributions of the γ-rays were measured in the reaction 163Dy(d, 2nγ) at a deuteron energy of about 13.5 MeV. Single γ-ray spectra were also taken in the 163Dy(p, nγ) reaction with 6.7 MeV protons. Additional information on the 163Ho level scheme was obtained by re-investigating the γ-radiation in the electron capture decay of 163Er. The proposed level scheme of 163Ho contains in addition to the ground state band 7 2 − [523] the rotational bands built on the intrinsic states 7 2 + [404], 3 2 + [411], 1 2 + [411] and 7 2 − [541] (band heads at 439.94, 360.36, 297.88 and 471.25 keV, respectively). Further levels at 1113.5, 876.0 and 614.3 keV are interpreted as being mainly the quasiparticle excitations 5 2 − [532], 5 2 + [413] and possibly the ground state γ-vibration, respectively. A comparison of the quasiparticle excitations in the Ho isotopes is performed on the basis of the Nilsson model including pairing corrections. Discontinuities in the rotational bands are described by Coriolis coupling effects. Several fast E1 interband transitions were observed in 163Ho. Some of them connect levels of the 1 2 + [411] band with the ground state band 7 2 − [523]. The appearance of these K-forbidden transitions is explained by a weak mixing between states of the bands 7 2 + [411] and 7 2 + [404] caused by Coriolis interaction.