IN-BEAM SPECTROSCOPY IN THE ACTINIDE REGION USING AN EVAPORATION RESIDUE DETECTOR ∗

The evaporation-residue counter HERCULES, an auxiliary detector for GAMMASPHERE to perform spectroscopy in the presence of a large fission background, is described. Results from a typical experiment using the Mg + Pt → Th∗ reaction at 128 MeV are discussed. The discussion focuses on the new Th level scheme. The simplex feature (alternatingparity levels) persists up to the highest spins observed. However, Th exhibits a more vibrational-like behavior than the heavier Th isotopes. A novel interpretation for Th based on a picture of tidal waves on a reflection-asymmetric nuclear surface is briefly reviewed. Finally, the identification of excited states in Th is discussed.