A study of the low-energy level structure of 165Dy

Thermal and average resonance neutron capture studies on targets of enriched 164Dy2O3 have been performed. The secondary gamma-ray spectra after thermal neutron capture were studied with bent-crystal diffraction spectrometers while the primary gamma-rays were measured with pair spectrometers. As a result, a detailed level scheme for 165Dy comprising 50 levels below 1.5 MeV has been established. The level scheme construction was based on the Ritz combination principle using the very precise secondary gamma-ray energies. The neutron separation energy was found to be 5715.76(30) keV. Up to about 1.4 MeV, the level scheme is believed to be essentially complete in I=1/2 and 3/2 levels of both parities. In this energy range, the levels have been grouped into 14 rotational bands. The intrinsic structure of these bands is interpreted on the basis of the present (n, γ) results in combination with previously published (d, p) data. It is shown that as a consequence of the quasiparticle-phonon interaction most low-lying levels have a strongly mixed intrinsic structure with both a one-quasiparticle and a collective vibrational character. Between 500 keV and 1300 keV, as much as six rotational bands with a predominantly vibrational structure have been observed. (orig.)