Nuclear Physics at the Extremes: Theory & Experiment

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 these 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 these 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 these 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 and understanding. The radiation-detector advances that our work drives can be incorporated in medical diagnosis and treatment and in environmental management. We engage strongly with the National Physical Laboratory on these topics. In addition, we provide an excellent training environment 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 have a keen interest in sharing our specialist knowledge with a wide audience, and actively pursue a public engagement agenda.