Nuclear Physics Consolidated Grant

The atomic nucleus, which forms the tiny massive core at the centre of the atom, is composed of protons and neutrons and each of these particles are themselves comprised of quarks. However, this knowledge does not allow us to make a complete prediction of the behaviour of any given nucleus or isotope. The system is too complex, involving three of the four fundamental forces: the electromagnetic, weak and strong nuclear forces. The behaviour of the nucleus is often described as an emergent phenomenon as it cannot be readily predicted from its component parts. This drives theoretical effort and the need to benchmark theory with precision measurements. Our research is aimed at studying the funadamental properties of atomic nuclei, the origin of elements in the cosmos and applications of nuclear technology. We study nuclei on the very limits of stability, in particular those with an excess of protons, and those which have the same number of protons and neutrons (N=Z nuclei). The N=Z nuclei exhibit special symmetries and deviations from these symmetries tell us very detailed information on the validity of competing nuclear models. Such measurements are very challenging as these nuclei are very difficult to produce in any quantity to perform experiments on. Our programme uses some of the principal facilities for nuclear physics worldwide where such exotic nuclei can be produced. Our work involves studies of how protons and neutrons interact in N=Z nuclei and to what extent the clustering of nucleons (eg into alpha particles) occurs in such nuclei. In our work we aim to addess specific questions related to nuclei residing in three of these regions, (i) N=Z nuclei around mass 70, (ii) deformed nuclei around mass 150 and (iii) nuclei around the neutron deficient lead region, where one of the best examples of nuclear shape co-existence has been observed to date at very low excitation energy. A further aspect of our research into the structure of nuclei concerns their shape. It is a remarkable property of the nucleus that it can adopt different shapes: spherical, oblate (smartie-shaped) and prolate (rugby-ball shaped) often for a small costs in energy. Predicting the shape of a nucleus and how this shape evolves as the nucleus is excited (given more energy) is extremely challenging from a theoretical perspective. Determining nuclear shape experimentally can help to discriminate between competing models of the nucleus and pin down our theoretical understanding. Nuclear structure effects relating to nuclear shapes and the phenomenon of shape co-existence are found in many regions of the chart of the nuclides. A third strand of our research is into the origin of the chemical elements in stars, and the role played by nuclear physics in this question. Some elements and isotopes are only produced in very hot and exotic events such as exploding stars: novae and supernovae. In these events, a rapid series of nuclear reactions takes place. We seek to understand how rapidly such reactions take place by reproducing them in the laboratory. This is very challenging as many of the nuclei involved in these studies are themselves radioactive and difficult to produce. Nevertheless, we are able to advance our understanding of how the chemical elements are created. The final area of research is into the mechanisms of nuclear fission, with emphasis on exploring how these develop in nuclei that reside away from the well known transactinide region of nuclei which can undergo induced fisson or in the case of the heaviest nuclei even spontaneous fission following their creation. Our data on these new regions of fission, such as in the light mercury isotopes around mass 180, are presenting challenges to the present models of the nuclear fission process. Our proposed work in this area will provide new data on extremely exotic nuclei to help develop the models of the fission process further.