Various collective states in the i 124 nucleus

The level structure of I124 (Z=53, N=71) has been studied via the Sn122(Li7,5n)I124 reaction with a beam energy of 54 MeV. Through in-beam and out-of-beam ?-ray spectroscopy, the sophisticated low-lying levels including isomeric states and numerous collective states have been established for the first time. A positive-parity collective band built on the 10+ state at 1297 keV is interpreted as being associated with the combination of a proton and a neutron in the same intruder h11/2 orbital, namely the ph11/2?h11/2 configuration. This band shows a typical quadrupole vibrational character. In contrast, the negative parity bands based on the pg7/2?h11/2 configuration show a soft triaxial rotation. An isomeric 8- state at 689 keV with a half-life of 14 ns can be explained as a K isomer due to a proton with an ?p=9/2 in the g9/2 orbital coupled to a neutron with an ?n=7/2 in the h11/2 orbital. The excited states based on this pg9/2?h11/2 configuration show a coupled rotational structure. Another coupled rotational band built on the 6+ state at 714 keV is thought to be based on the pg9/2?d3/2 configuration.