Study of the K=8 and K=16 isomeric states in 178Hf

In 178Hf it has been found that some 2- and 4-quasiparticle states can occur lower in energy than members of the collective ground state rotational band with corresponding spin. Recent studies of these high-K isomers in the Lu, Hf, Ta, region have uncovered the existence of surprisingly large transition probabilities between the K = 0 ground state band and the high-K bands which should be forbidden if the K selection rule is valid. For the population of the Kπ=8- isomer in 178Hf a 2-band K-mixing model is presented which reproduces both the long lifetime of the isomer and the strong Coulomb excitation. In two scattering experiments at the Munich tandem accelerator and at the UNILAC in Darmstadt we searched for excited states built on the Kπ=16+ isomer. Micro weight quantities of 1015 atoms in the isomeric state have been produced by a Dubna-Orsay-GSI collaboration in order to prepare a radioactive target. In both measurements the first excited state built on the Kπ=16+ isomer has been observed at an excitation energy of 357 keV with respect to the isomeric state. The intrinsic electric quadrupole moment of Q0 = 8.2±1.1 b has been derived from the experimental data within the rigid rotor model. (author)