Yields and spectroscopy of radioactive isotopes at LOHENGRIN and ISOLDE

Yields of radioactive nuclei were measured at two facilities: the recoil separator LOHENGRIN at the Institut Laue Langevin in Grenoble and the on-line isotope separator ISOLDE at CERN in Geneva. At LOHENGRIN the yields of light charged particles were measured from thermal neutron induced ternary fission of several actinide targets: 233U, 235U, 239Pu, 241Pu and 245Cm. Thin targets are brought into a high neutron flux. The produced nuclei leave these with the recoil obtained in the fission reaction. They are measured at different energies and ionic charge states. After corrections for the experimental acceptance, the time behaviour of the fission rate and the ionic charge fraction, the yields are integrated over the kinetic energy distribution. Comparing these yields with the predictions of various ternary fission models shows that the most abundant nuclides are well reproduced. On the other hand the models overestimate significantly the production of more "exotic" nuclides with an extreme N/Z ratio. Therefore a refinement of the models is required. The collected yields provide a good database to test improved versions. In the second part yields of various radioactive nuclei were determined at the ISOL (isotope separation on-line) facility ISOLDE. Here, high energy protons (1.0 or 1.4 GeV) hit targets from different materials and cause various nuclear reactions. The produced radioactive nuclei are stopped in the thick target, diffuse and effuse out at high temperatures, are ionized, electrostatically accelerated to 60 keV and mass separated. Subsequently they are delivered to different beam ports for various applications. The measurement of these beam intensities is less used to study the mechanism of the production reaction (fission, spallation or fragmentation), but to understand and reduce the losses occuring on the way from production to detection. In contrast to a recoil separator these losses vary strongly from isotope to isotope. To increase the final yields a careful optimization of many parameters is required: the chemical composition and the microscopic structure of the target material, the temperature of the target and ion source system, the type and operation conditions of the ion source, etc. The obtained yields and possible improvements are discussed at the example of some elements: Be, Al, Mn, Ni, Cu, Ga, Cd, In, Sn, Cs and Fr. An important contribution to the efficient and selective separation of many metallic elements gives the RILIS (resonance ionization laser ion source) technique. Its applications can be further extended to provide even isomeric selectivity or to perform atomic spectroscopy with radioactive isotopes. With these intense and pure radioactive ion beams several new nuclear physics results were obtained. The span reaches nearly over the full periodic system, including a new determination of the lifetime and the beta-delayed neutron emission probability of 12Be (T(1/2) = 21.34(23)ms, Pn=0.48(+0.12-0.10)%), a rough measurement of the magnetic moments of 70gCu (mu = (+)1.8(3) mu_N) and 70mCu (|mu| = 1.2(3) mu_N), the study of beta-delayed neutron emission of the neutron-rich copper isotopes 73-78Cu with the first detection of beta-delayed neutrons from 73Cu, the first measurement of the lifetimes of 149Cs (T(1/2) = 112(3)ms) and 150Cs (T(1/2) = 82(7)ms) and the observation of new gamma lines in the decay of 232Fr.