Two-phonon γ-vibrational states in 166Er

The nucleus 166Er has been Coulomb excited using a beam of 58Ni. In addition to the ground-and γ-vibrational bands three states were observed, a new state at 1943 keV, a previously known 4+ state at 1978 keV and a new state at 2029 keV suggested to have also spin and parity 4+. The two 4+ states decay to the 2+ and 3+ states of the one-phonon γ-vibrational band, and their B(E2) values to the 2γ+ state are measured to 49−25+20 and 267−100+100 e2 fm4, respectively. It is suggested that the 1978 keV state has a small and the 2029 keV state a large component of the Kπ = 4+ two-phonon γ vibrational configuration in their wave functions.