Coulomb excitation of 182, 184, 186W and 166Er with 4He and 16O ions

Abstract

The Coulomb excitation reaction induced by 4He ions selectively excites 2 + and 3 − states by direct E2 and E3 Coulomb excitation. In this paper, we present new results from γ-ray spectroscopy with 15 MeV 4He ions on a natural abundance target of W. In particular, a 3 − state in each isotope, 182, 184, 196W, was observed by direct E3 excitation. In addition to obtaining B(Eλ, 0 → J = λ) for excitation of each state, information on the reduced transition probabilities for the different decay modes of these states is given. The Coulomb excitation probabilities of the 2' + states at 786 keV in 166Er and at 737 keV in 186W were measured with 16O and 4He ions by the backscattered particle-gamma coincidence method in order to determine the static electric quadrupole moment Q 2'. We obtain for 166Er Q 2' = 2.11 ± 0.37 e· b which is in agreement with ( Q 2') rot and for 186W Q 2' = 1.17 ± 0.30 e · b which is in agreement with Kumar-Baranger model calculations and is significantly smaller than ( Q 2') rot. This deviation of the measured Q 2' from ( Q 2' rot implies in the framework of the Kumar-Baranger calculations a strong coupling between β- and γ-vibrational bands. On the other hand, our observed upper limit for B(E2,2″ → 2′) does not confirm this implication.