Isotope-selective Spectroscopy: Fast Timing R&D and fp-Shell Mirror Isomers

This thesis highlights the research and development of a new plastic-scintillator detector for time-of-flight measurements in relativistic heavy-ion beam experiments. The detector makes possible the identification of different ion species on flight distances as short as a few meters. The novelty lies in the design approach of using many moderately fast, independent measurements of every physical event to combine the statistics into extremely precise and reliable timing information. In the case of the tested prototype, a circular, 2 cm thick acrylic-glass frame hosts 32 photomultiplier tubes at about 3 mm distance from the 0.5 to 3.0 mm thick scintillator with a diameter of 27 cm. This concept yields a detector performance of approximately 10 ps root mean square.

Details are discussed in the context of simulations, bench tests on prototype detectors in the laboratory, as well as in-beam tests. Read-out electronics and their effects are discussed and generally shown to be an advantageous aspect of this detector design. Several methods for raw-data handling are described and their effects shown in simulated scenarios as well as for data from experiments.

The thesis also gives an overview of the experimental setup and experimental results of an experiment dedicated to investigating the nuclear structure of the radioisotope 54Ni. This experiment was carried out as part of the RISING campaign at GSI in March 2006. In this experiment a 550 MeV/u primary beam of 58Ni was fragmented on a 1 g/cm² 9Be target to subsequently select and unambiguously identify the isotope 54Ni. The 54Ni ions were stopped in a passive 9Be stopper to investigate the gamma-decay of isomeric states produced in the initial fragmentation, as well as those produced in the stopping process.