Electromagnetic transition probabilities in odd-mass erbium isotopes

Abstract

Nanosecond lifetimes of 163, 165Er excited states have been measured by means of delayed γ-γ coincidences in the (α, 2n) reaction on enriched Dy targets and delayed γ-ce coincidences in the 163,165Tm decay. The following half-lives unknown so far were obtained: T 1 2 (84.3 keV) = 0.92 ± 0.08 ns , T 1 2 (104.3 keV) = 0.52 ± 0.05 ns and T 1 2 (443.8 keV) = 0.58 ± 0.10 μ s for 163Er levels as well as T 1 2 (296.1 keV) ≦ 0.24 ns, T 1 2 (297.3 keV) = 0.70 ± 0.08 ns, T 1 2 (356.5 keV) = 0.35 ± 0.06 ns, T 1 2 (507.3 keV) = 0.70 ± 0.12 ns, T 1 2 (551.0 keV) = 0.25 ± 0.03 μ s, T 1 2 . (589.7 keV) ≦ 0.6 ns and T 1 2 (745.7 keV) = 1.00 ± 0.15 ns for 165Er levels. From the investigation of γ-ray spectra populating the 11 2 −[505] isomer, the rotational levels at 1024.0 keV (J π = 17 2 −) and 1259.8 keV (J π = 19 2 −) in 163Er could be confirmed as well as the level at 1078.1 keV with J π = 17 2 − in 165Er could be established. In order to obtain the wave functions of K-mixed nuclear levels, Coriolis coupling calculations taking into account the δN = 2 mixing in 165Er are performed for 161, 163, 165Er including in the fit all the experimentally known band-head and rotational energies of positive-parity and negative-parity states, respectively. Partial γ-ray half-lives of E1, M1 and E2 transitions in 161,163,165,167,169Er are deduced from the present results and earlier data. Electromagnetic transition probabilities are calculated within a non-adiabatic approach and compared with the experimental values. The influence of pairing correlations and configuration admixtures on the transition probabilities is demonstrated using hindrance factors and numerical values of transition matrix elements.