Nuclear Physics Consolidated Grant 2023

Now well into its second century, the science of nuclear physics remains vibrant and active. Over the past 100 years, there has been a wealth of experimental and theoretical research that has led to milestone results and discoveries, such as the discovery of the neutron, the development of successful models of the nucleus, and the identification of numerous novel decay modes. Progress in nuclear physics has gone hand-in-hand with the development of particle accelerators, which started with modest electrostatic machines, capable of accelerating light ions, and resulting in modern day accelerators capable of accelerating any nucleus up to uranium-238, with energies of 10 MeV per nucleon or more. Facilities now exist that can accelerate radioactive ions, and there is effort being put into improving the intensities, energies, and purity of radioactive beams. Despite the wealth of research activity in nuclear physics, and the maturity of the subject, a complete understanding of the atomic nucleus has still not been achieved. There are still many open questions that need to be answered, which we will address in our research programme. Technological and scientific developments in nuclear physics are leading to applications outside of the areas of fundamental science - nuclear-related concepts are now used in many areas of industry, medicine, and society leading to new areas of applied research. Our programme of research in this Consolidated Grant application covers research into the structure, behaviour and properties of atomic nuclei that lie far from stability as well as collective behaviour in stable nuclei, which remains poorly understood.

One of the main parts of our programme of research is the study of the shapes of atomic nuclei. It is well established that nuclei with filled shells of neutrons and protons are spherical, and nuclei with partially-filled shells can become deformed. One of the themes within our research programme will study quadrupole shaped nuclei, where the nucleus takes on a rugby-ball shape. This type of nuclear deformation is prevalent and occurs in many different regions of the nuclear chart. A more exotic form of deformation is when the nucleus takes on a reflection-asymmetric "pear" shape. Such 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 lanthanides near barium-144. In our research programme, we will make a comprehensive study of octupole deformation in nuclei, focusing on the actinide and lanthanide regions, as well as the proton-rich nuclei near N=Z=56. There is significant attention on these nuclei from outside of nuclear physics since atoms containing pear-shaped nuclei are excellent candidates in which to search for an atomic electric dipole moment.

Over the past 20 years, experimental observations, supported by theoretical calculations, have suggested that the structure of exotic nuclei may be different from those near stability. The well-known sequence of magic numbers, corresponding to energy gaps in nuclear shell structure, are thought to change depending on the proton-neutron ratio, known as type-I shell evolution. Indeed, the recent development of type-II shell evolution suggests such a change happens in a nucleus when exciting nucleons from one shell to another. In our programme, we will study the shell evolution in a range of nuclei across the nuclear chart, including the nuclei close to the doubly-magic nuclei Sn-100 and Pb-208. Another aspect of our research programme is a study of high-energy collective modes in nuclei, in multi-messenger approaches. The latter feeds into our research studying reactions relevant to nuclear astrophysics, which will include a focus on hydrogen burning that occurs in stars or nuclear structure determining processes in explosive astrophysical scenarios, like a type-II supernovae.