Collective excitations built on the 2+ γ state in 168Er

Abstract

To examine the collectivity of the previously proposed K π=4+γγ-two-phonon state in 168Er at an excitation energy of 2056 keV and of the first excited K π=0+ band at 1217 keV (b-band), a Coulomb excitation experiment has been carried out at the Heidelberg-Darmstadt Crystal Ball spectrometer. The B(E2) value connecting the 4+ γγ state to the γ-band was remeasured to be B(E)2,4+ γγ→ 2+ γ)=(600± 130) e2fm4, which almost exhausts the harmonic expectation. In addition, the B(E2) values connecting the band head of the lowest lying excited 0+ b band to the 2+ g and 2+ γ states were measured to be B(E2,2+ g→ 0+ b)=(4.4±0.6) e2fm4 and B(E2, 2+ γ→ 0+ b)=(30.4±4.6) e2fm4; the latter is almost a factor of 10 smaller than the B(E2,2+ γ→ 0+ g) value, which shows that the 0+ b band head has no significant contribution of the K π= 0+γγ-two-phonon state in its wave function.