Production of isomers in compound and transfer reactions with 4He ions

A well-known island of nuclear isomerism appears near A=175–180 due to the deformation alignment of single-particle orbits at high angular momentum. This sometimes results in the formation of multi-quasiparticle states with record spin that are long-lived because of “K-hindrance”, i.e. symmetry re-arrangement. Production methods and spectroscopic studies of these isomers remain a challenge for modern nuclear reaction and nuclear structure physics. In the present work, activities were produced by irradiation of 176Yb (97.6% enriched) and natLu targets with 35 MeV 4He ions from the internal beam of the U-200 cyclotron. Induced activities were analyzed by applying the methods of radiochemistry and gamma spectroscopy. Yields of the compound and nucleon-transfer reactions were measured and the isomer-to-ground state ratios were deduced. Calculated results were obtained using standard procedures to reproduce the (α, xn) cross-sections, and the systematic behavior of the nucleon-transfer yields was established. The isomer-to-ground-state ratios for direct reactions with 4He ions were examined, resulting in a new characterization of the reaction mechanism.