Shapes and collectivity of exotic nuclei

The research performed within the project is of fundamental nature. Most of the results obtained are beautiful examples of quantum mechanics at work in atomic nuclei, and as such they contribute to the quest of understanding the interactions between the fundamental building blocks of nature. The overarching goal of nuclear science is to arrive at a comprehensive and unified microscopic description of all nuclei and their reactions with each other. The results obtained in the project add a large amount of new experimental data to this ambitious goal. The new data are significant because they concern so-called exotic nuclei with extreme proton-to-neutron ratios that are not found naturally on Earth, but need to be created in accelerator laboratories. The nuclei studied in this project exhibit dramatic structural changes, making the results particularly suitable as benchmarks for nuclear theory. A particular focus of the research was on atomic nuclei that change their shape by adding or removing protons and neutrons or as a function of excitation energy. Through close collaboration with some of the leading theoreticians in the research field the results contribute to the steady improvement of nuclear models and their predictive power. In this indirect way the results have implications for a wider field of science and technology, for example for the understanding of how heavy elements are formed through nucleosynthesis in stellar environments or to better understand and model the conditions in nuclear power reactors. Experimental techniques were refined and combined with one another in novel ways during the project. The project has been successful at establishing scientists from UiO as leaders of research projects at large international nuclear physics laboratories, significantly enhancing the visibility of the Oslo group internationally. The project has provided opportunities for young researchers to work in international collaborations at the forefront of science and to become future leaders. The research activities provided data and results of high quality for three PhD theses, and has led to a large amount of publications in peer reviewed journals.

The aim of the project is to further our understanding of the nuclear many-body problem by studying shapes and collectivity of exotic, unstable nuclei. Nuclear shapes are very sensitive to the underlying nuclear structure. Experimental measurements of obs ervables related to the nuclear shape represent a stringent test of theoretical models, in particular in regions of the nuclear chart for which rapid shape changes or shape coexistence is expected. The project aims at providing such experimental data by p erforming Coulomb excitation experiments with rare-isotope beams and by measuring the lifetimes of excited nuclear states. Coulomb excitation experiments with rare-isotope beams will be performed at the ISOLDE facility at CERN. Two such experiments led by the University of Oslo have been approved by the CERN Research Board, with beam time awaiting to be scheduled. These experiments will be complemented by lifetime measurements using stable heavy ion beams. Data from a recent lifetime measurement at GANI L is available for analysis, and new proposals for lifetime measurements are in preparation. It is proposed that two PhD candidates be employed in the project, who will assume responsibility for the data analysis of the experiments. The project should fu rthermore be supported by postdoctoral researchers, who should take an active role in preparing the continuation of the research program at the HIE-ISOLDE and SPIRAL2 facilities, which are expected to become operational during the second half of the proje ct. The project offers unique opportunities for a stronger integration of the Oslo nuclear structure group into large-scale European research infrastructures, increasing the visibility of the group internationally. The project exploits synergies between the nuclear physics and nuclear chemistry activities at the University of Oslo and will increase the coherence between the experimental and theoretical nuclear structure programs within the Physics Department