University of the West of Scotland Nuclear Physics Group Consolidated Grant

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It is just over 100 years since Ernest Rutherford's pioneering experiments which demonstrated the existence of the atomic nucleus. In the century that has followed, landmark developments, such as the inception of the nuclear shell model in the 1940s, the construction of heavy-ion accelerators in the 1960s, and major ongoing advances in nuclear-detector techniques, have firmly established nuclear physics as an international activity at the forefront of scientific research. In the past few decades, the quest to understand the properties of exotic nuclei ever further from the valley of stability has led to considerable experimental progress. The programme of research described in this Consolidated Grant application covers research into the structure and properties of atomic nuclei that lie far from stability. The overarching aim of our research programme is to achieve a better understanding of the structure and behaviour of exotic nuclei, on both the neutron-rich and proton-rich sides of the valley of stability, and for heavy nuclei. Recent experimental observations, supported by theoretical calculations, have begun to suggest that the structure of exotic nuclei may be different from nuclei near stability. For example, the well-known sequence of magic numbers, corresponding to energy gaps in nuclear shell structure, is now thought to change in nuclei with an extreme excess of neutrons. The evidence for such a change is already convincing around neutron number N=20, and similar effects are expected for the other shell gaps at N=28, 50, and 82. In order to provide a test of nuclear models, experimental data are needed. In this respect, we will primarily focus our research on two areas of the nuclear chart, close to two doubly-magic nuclei: the proton-rich nuclei around Sn100 (N=Z=50) and the neutron-rich nuclei close to Sn132 (Z=50, N=82). An important consideration in the description of an atomic nucleus is its shape. It is well established that nuclei with filled shells of neutrons and protons are spherical, and nuclei with partially-filled shells can become deformed. Indeed, it is the deformation of the nucleus into a prolate (rugby ball) shape, that leads to rotational excitations. A more exotic form of deformation is when the nucleus takes on a reflection-asymmetric "pear shape". The so-called "octupole deformation" is most prominent in localized regions of the nuclear chart, such as the light actinide region (radium, thorium, uranium nuclei with A~224) and the neutron-rich lanthanides (such as the A~144 barium and cerium nuclei). Although octupole correlations in nuclei have been studied for a number of years, recent developments in accelerator and detector technology will now allow experiments to be performed to provide new insights into this type of deformation. In our research programme, we will make a comprehensive study of octupole correlations in nuclei, focusing on the actinide and lanthanide regions, as well as the proton-rich nuclei near N=Z=56. The mirror-symmetry-violating pear shape allows for the search for physics that is responsible for the existent matter-antimatter symmetry violation. Our research will primarily proceed using different methods of gamma-ray spectroscopy. We will use the best facilities available for the physics goals of the project. For example, we will carry out Coulomb excitation experiments at ISOLDE at CERN, fission-fragment spectroscopy at Institut Laue Langevin in Grenoble, and gamma-ray plus conversion electron spectroscopy with SAGE at JYFL in Jyväskylä, Finland. The funds requested here will provide support for postdoctoral research associates and PhD Students to help carry out this work, as well as funds for travel and subsistence. We have also requested funds to enable world leading theoretical nuclear physicists to visit our group to help with the interpretation of our results, and to provide important theoretical input into our experimental research programme.