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978-3-8439-0660-9, Reihe Physik

Kerstin Geibel
Search for Proton Emission in Ni-54 and Multi-Nucleon Transfer Reactions in the Actinide Region

190 Seiten, Dissertation Universität Köln (2012), Softcover, A5

Zusammenfassung / Abstract

The first part of the thesis presents the investigation of fusion-evaporation reactions in order to verify one-proton emission from the isomeric 10+ state in the proton rich nucleus 54Ni. Between the years 2006 and 2009 a series of experimental studies were performed at the Tandem accelerator in the Institut für Kernphysik (IKP), University of Cologne. These experiments used fusion-evaporation reactions to populate 54Ni via the two-neutron-evaporation channel of the compound nucleus 56Ni. The cross section for the population of the ground state of 54Ni was predicted to be in orders of microbarn. This required special care with respect to the sensitivity of the experimental setup, which consisted of a double-sided silicon-strip detector (DSSSD), a neutron-detector array and HPGe detectors. In two experiments the excitation functions of the reactions (32S+24Mg) and (28Si+28Si) were determined to find the optimal experimental conditions for the population of 54Ni. A final experiment employed a 28Si beam at an energy of 70MeV, impinging on a 28Si target. With a complex analysis it is possible to obtain a background-free energy spectrum of the DSSSD. An upper cross section limit for the population of the 10+ state in 54Ni is established at σ(54Ni(10+)) ≤ (13.9 ± 7.8) nbarn.

In the second part of the thesis the population of actinide nuclei by multi-nucleon transfer reactions is investigated. Two experiments, performed in 2007 and 2008 at the CLARA-PRISMA setup at the Laboratori Nazionali di Legnaro, are analyzed with respect to the target-like reaction products. In both experiments 238U was used as target. A 70Zn beam with 460MeV and a 136Xe beam with 926MeV, respectively, impinged on the target, inducing transfer reactions. Kinematic correlations between the reaction partners are used to obtain information on the unobserved target-like reaction products by the analysis of the beam-like particles identified with the PRISMA spectrometer. γ spectra from neutron-rich actinide nuclei are obtained with the CLARA array. An extension of the ground-state rotational band in 240U up to the 18+ state is achieved. The level and transition energies as well as the moments of inertia are compared with theoretical predictions. Based on cross section distributions for various reaction channels the perspectives and limitations for in-beam γ spectroscopy with this experimental method in the actinide region are discussed.