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

To examine the collectivity of the previously proposed K-pi = 4(+) gamma gamma-two-phonon state in Er-168 at an excitation energy of 2056 keV and of the first excited K-pi = 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(gamma gamma)(+) state to the gamma-band was remeasured to be B(E2, 4(gamma gamma)(+) --> 2(gamma)(+)) = (600 +/- 130) e(2)fm(4), 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(gamma)(+) states were measured to be B(E2, 2(g)(+) -->0(b)(+)) = 4.4 +/- 0.6) e(2) fm(4) and B(E2, 2(gamma)(+) --> 0(b)(+)) = (30.4 +/- 4.6) e(2) fm(4); the latter is almost a factor of 10 smaller than the B(E2, 2(gamma)(+) --> 0(g)(+)) value, which shows that the 0(b)(+) band head has no significant contribution of the K-pi = 0(+) gamma gamma-two-phonon state in its wave function.