Detailed spectroscopy in the superdeformed second minimum of Pu-240

Spectroscopic studies in the superdeformed shape isomer of Pu-240 using gam ma -spectroscopy, conversion electron spectroscopy and transmission resonan ce spectroscopy have been performed. In a high-resolution and high-efficien cy gamma -spectroscopy experiment the out-of-band decays of several excited superdeformed rotational sequences with K = 2(-) and 1(-) could be identif ied together with evidence for a weakly populated 0(-) octupole band. Surpr isingly, no low-lying collective quadrupole excitations could be observed. Complementary information could be obtained in conversion electron measurem ents in coincidence with isomeric fission, resulting in the first identific ation of the lowest beta -vibrational K = 0(+) band. For all rotational ban ds the variation of the moment of inertia with spin could be studied. A pre dominant population of negative parity states in the second well could be o bserved, which can be explained by the selective population and depopulatio n of the second minimum. Complementary transmission resonance measurements have been performed, yielding new information on the fine structure of high -lying (beta-)vibrational multi-phonon states. A new method could be establ ished to determine the excitation energy of the fission isomer ground state from measured level densities.