For a century, physicists have studied atomic nuclei almost exclusively by smashing stable beams into stable targets—but this has left roughly half of all predicted nuclei completely unobserved. This project uses short-lived radioactive beams to explore the exotic, neutron-rich nuclei that have never been seen before, particularly those forged inside stars and supernovae. Understanding these nuclei matters because their unexpected shapes and stability trends directly affect the reaction rates that govern how stars explode and how all the elements are made. The Surrey group combines experimental equipment at world-leading facilities with new theoretical models that can handle the delicate, unusual behaviour of these extreme nuclei. This is primarily fundamental science, driven by the big questions about the limits of nuclear existence—how many neutrons can bind to a given number of protons before the nucleus falls apart. The work also drives advances in radiation detectors, which can feed into medical imaging and environmental monitoring, and it trains researchers who go on to fill critical skills gaps in the UK’s nuclear power industry.
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For a hundred years, atomic nuclei have been probed more or less exclusively by studying collisions between stable beams and stable targets. This restricted the nuclei that could be studied to just a just a small fraction of those that are thought to exist. Most of the nuclei important to making all of the elements (in various stellar processes) have for example been inaccessible to experiment. The major thrust in nuclear physics worldwide, and a key priority in the UK's programme, is to reach out and study these exotic nuclei by using beams produced from short-lived radioactive isotopes. This in turn reveals that nuclear structure is not always like it seems to be for the stable nuclei, and nuclei are found to have surprising trends in stability and to have different shapes that will affect reaction rates inside stars and supernovae. At Surrey we take the UK priorities and the new opportunities very much to heart, and we seek out and lead programmes at the world's best facilities for making radioactive beams. To make the beams is difficult and the facilities - as well as the research effort - are international in scale. Surrey builds and runs innovative experimental equipment at these facilities. The present grant request is focused on the exploitation of the best capabilities at the best laboratories. Experimental progress is intimately linked with theory, and the development of novel and better theoretical approaches are a hallmark of the Surrey group. An outstanding feature of the group as a whole, which is key to our research plans and acknowledged as a rare and valuable strength, is our powerful blend of theoretical and experimental capability. Our science goals are aligned with current STFC strategy for nuclear physics, as expressed in detail through the Nuclear Physics Advisory Panel's road map. We wish to understand the boundaries of nuclear existence, i.e. the limiting conditions that enable neutrons and protons to bind together to form nuclei. Under such conditions, the nuclear system is in a delicate state and shows unusual phenomena. It is very sensitive to the properties of the nuclear force. It is unknown whether, and to what extent, the neutrons and protons can show different collective behaviour or even how many neutrons can bind to a given number of protons. It is features such as these that determine how stars explode. To tackle these problems, we need a more sophisticated understanding of the nuclear force, we need more powerful theories that can build this understanding into the calculations, and we need experimental information about nuclei with unusual numbers of neutrons relative to protons so that we can test our theoretical ideas. Therefore, theory and experiment go hand-in-hand as we push forward towards the nuclear limits. An overview of nuclear binding reveals that about one half of predicted nuclei have never been observed, and the vast majority of this unknown territory involves nuclei with an excess of neutrons. Much of our activity addresses this "neutron rich" territory, exploiting the new capabilities made possible with radioactive beams and exploiting advances in computational power and analytical theories to bring superior new theoretical tools to bear on the latest observations. Our principal motivation is the basic science and the STFC "big questions", and we contribute strongly to the world sum of knowledge. The radiation-detector advances that our work drives can be incorporated in medical diagnosis and in environmental management. We engage strongly with the National Physical Laboratory on these topics. Our work also relates to national nuclear security and we have strong links in this area with AWE. We provide excellent training for our research students and staff, many of whom go on to work in the nuclear power industry, helping to fill the current skills gap. Furthermore, we are enthusiastic about sharing our research, and actively pursue a public engagement agenda
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