Consolidated nuclear physics grant 2011

The majority of the visible mass of the universe is made up of atomic nuclei that lie at the centre of the atom. Nuclear physics seeks to answer fundamental questions such as: 'What are the limits of nuclear existence, at the proton drip-line and for the heaviest masses?'; 'How do simple patterns emerge in complex nuclei?'; 'Can nuclei be described in terms of our understanding of the underlying fundamental interactions?'; 'What is the equation-of-state of nuclear matter, including compact matter in neutron stars?'; 'How does the ordering of quantum states change in extremely unstable nuclei?; 'Are there new forms of structure and symmetry at the limits of nuclear existence?'. The aim of this research proposal is to try to answer these questions. No one yet knows how heavy a nucleus can be; in other words, just how many neutrons and protons can be made to bind together. We will study the heaviest nuclei that can be made in the laboratory and determine their properties which will allow better predictions to be made for the 'superheavies'. For lighter nuclei we will explore in the region of the proton and neutron drip lines, which are the borders between bound and unbound nuclei. We will determine more precisely than ever before the location of these drip lines. Nuclei beyond the proton drip line have so much electrical charge that they are highly unstable and try to achieve greater stability through the process of proton emission. We will investigate how nuclear behaviour is affected when protons become unbound. For these exotic systems we will also explore how the nucleus prefers to rearrange its shape, which can be a sphere, rugby ball, pear, etc. and how it stores its energy among the possible degrees of freedom. We will also investigate how the properties of these nuclei develop as we make them spin faster and faster. We will try to determine the precise nature of ultra high spin states in heavy nuclei, just before the nucleus breaks up due to fission. We will study whether a nucleon looks the same when it is inside the nucleus or when it is in free space. By violently removing the nucleon from the nucleus in a nuclear reaction at high energies and measuring its properties, we can investigate to what extent the nucleon 'feels' the influence of its neighbouring nucleons, whether it is correlated with them. Such information tells us about the nuclear force inside the nucleus at different inter-nucleon distances. Nuclear matter can exist in different phases, analogous to the solid, liquid, gas and plasma phases in ordinary substances. By varying the temperature, density, pressure and isospin asymmetry (the relative number of neutrons and protons in the matter), nuclear matter can undergo a transition from one phase to another. The thermodynamic properties of the matter and its phase transitions can be summarised by the equation of state. By colliding nuclei together at high energies, we will study how nuclear matter behaves as the isospin asymmetry and density vary. Such information is not only important for nuclear physics but also to understand neutron stars and other compact astrophysical objects. This programme of research will employ a large variety of experimental methods to probe many aspects of nuclear structure and the phases of strongly interacting matter, mostly using instrumentation that we have constructed at several world-leading accelerator laboratories. The work will require a series of related experiments at a range of facilities in order for us to gain an insight into the answers to the questions posed above. These experiments will help theorists to refine and test their calculations that have attempted to predict the properties of nuclei and the phases of strongly interacting matter, often with widely differing results. The resolution of this problem will help us to describe complex many-body nuclear systems.