Birmingham Nuclear Physics Consolidated Grant

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The project is an exploration of the nature of strongly interacting matter. The research will probe the nature of matter at extreme temperature and density where the nucleons inside a nucleus loose their individual identity and dissolve into their constituents of quarks and gluons - the state of matter which it is believed existed an instant after the Big Bang. Using the ALICE experiment at CERN (in which the Birmingham group have played a leading role building the trigger electronics), and collisions between Lead nuclei, the nature of this state of strongly interacting matter will be characterised in detail for the first time. The study of this exotic state of matter, known as a quark-gluon plasma, will help physicists understand more about the nature of the strong force and the evolution of the very early Universe. Nucleons in nuclei are bound via the strong interaction. On the nuclear scale, the interaction is complex and has yet to be fully characterised. Nevertheless, despite the complexity rather simple patterns emerge, such as shell structure and magic numbers or geometric arrangements of nucleons as clusters within nuclei. Due to the very high stability of the alpha-particle it is most often alpha-clusters that precipitate within the nucleus. The role of clusterisation in nuclei is central to understanding the structure of light-nuclei. For example, the famous Hoyle-state in 12C, through which carbon is synthesised in stars, has a structure which is composed of three alpha-particle. The characterisation of such systems forms a key element of the programme. As one adds more and more neutrons to a nucleus the limit of stability is reached where the last neutron no-longer 'sticks' to the nucleus, a point called the neutron drip-line. Studying nuclei close to this limit provides a unique test of our understanding of the nature of the strong interaction. One rather interesting possibility is that nuclei at the drip-line will have a rather exotic structure and behave as clusters embedded in a sea of neutrons. Part of the current programme will study how clusterisation changes as the drip-line approaches. One of the most precise tests of the structure of nuclei comes from an indirect technique. The energy levels of the electrons in an atom are largely determined by the properties of the nucleus; its overall charge, the nuclear shape and radius, the charge distribution and the magnetic moment of the nucleus. Hence, rather fundamental properties of a nucleus may be determined through an interrogation of the electronic energy levels using laser techniques. The Birmingham group has nearly 20 years accumulated experience in using laser-spectroscopy techniques to determine nuclear properties with high precision. The current work will focus on the cerium isotopes which lie at the edge of a region of shape transition due to the weakening of the Z=64 proton sub shell. To measure these isotopes new transitions using a metastable state populated by optical pumping will be needed as well as a more efficient light collection region.