Radiochemical studies of nuclear reactions and nuclear decay

The neutron-induced fission of Th-233 (TRIGA Mainz), Pu-239, Am-242 and Cf-249 (ILL) was studied. The yields in the very asymmetric fission show extreme odd-even and shell effects. In the fission of Cf-249 strong deviations of the experimental mass yields from predictions were observed. With a detection system based on Rutherford backscattering of heavy ions a search for supermassive nuclei in nature was performed. Upper limits between 10-10 and 10-15 relative to the number of nucleons were found for the abundance of strange supermassive nuclei with masses A=500 to 107 amu. An on-line separation system was developed for studies on neutron-rich isotopes of the heaviest elements. The coexistence of deformed intruder states and spherical states in odd-mass nuclei in the mass region A=100-120 was investigated. Furthermore experiments were performed in order to study the β- decay of Rn-223, Rn-225 and Rn-227. The sharing excitation energy in binary reactions at the barrier is dominated by shape fluctuations at scission. Quasielastic transfer reactions show a complex behaviour at the barrier. Inclusive measurements of cross sections for the excitation of giant resonances at 1 GeV/u gave hints for a strong excitation of 2-phonon states. With LAND, the 2-phonon GDR was detected exclusively. In central Au+Au collisions the 'squeeze-out' of neutrons was detected for the first time. At CERN-ISOLDE 18 neutron-rich isotopes in the vicinity of 78Ni have been measured among them the two r-process 'waiting-point' nuclei 79Cu and 80Zn. QRPA calculations have been performed for exotic Fe-Ni isotopes. Detailed spectroscopic investigations of neutron-rich Kr isotopes indicate sphericity up to N=58 as in their Sr isotones. For 89,91Kr and 91,93Sr an I=j-1 (j=νd5/2) anomaly has been observed. Shape coexistence has been verified in the N=58,59 isotones of Sr and Zr. In 98,100Sr and 99,101Sr band-twinning has been shown at maximum possible ground-state deformation. In these nuclei, the usual A5/3 mass dependence of the moment of inertia is cancelled. (orig.)