Nuclear Physics Rolling Grant

Scientists are beginning to understand the intimate connections between science on the most microscopic scales and spectacular large scale events in the cosmos. It is an astonishing fact that most of the chemical elements we observe today were created from the ashes of ancient stellar explosions. The most spectacular events of this type are supernovae. With very high sensitivity telescopes we can study the chemical abundances of material ejected from distant supernovae and compare with those abundances found in our own solar system. Understanding abundances from spectacular explosive astrophysical events like these crucially depends on nuclear reaction processes involving so-called exotic nuclei. Exotic nuclei are unstable to radioactive decay, and have different ratios of constituent neutron and proton particles compared to the naturally occuring stable isotopes. Only now have scientists developed the technology whereby we can actually produce beams of radioactive nuclei to reproduce nuclear reactions here on earth driving these large explosions occuring out in the cosmos. These exotic nuclei can exhibit remarkable properties such as halos, and neutron skins which also turn out to be important in understanding astrophysical objects like neutron stars, one of the possible end points of supernovae explosions, another alternative being black holes. It turns out that exotic nuclei don't behave like stable nuclei, and we need to study what their properties are, in some cases going to the very limits of nuclear existence, the drip-lines, to connect the microscopic physics of nuclear reactions to the matter we observe in the cosmos. Nuclei used to be thought of as liquid drops and then it was realised that certain numbers of neutrons and protons, known as magic numbers, were much more stable due to the quantum mechanical nature of these systems. A good analogy is the stability of chemical systems such as the inert gases where all the electrons fill a single shell. Our studies will explore whether these shell structures found in stable isotopes persist all the way to the the drip lines. There is great theoretical uncertainty in predicting what happens at these extreme limits, where rare decay phenomena occur. For example, these nuclei can decay by emitting constituent single protons or pairs of protons. These processes occur by quantum tunneling, and it turns out the rate of tunneling critically depends on the nuclear shells and the shape of the nuclei - some can be highly deformed and this can speed up quantum tunneling rates by orders of magnitude! In some regions such as near shell closures exotic quasi-stable states exist high above above the ground-state, which have a very high spin. These states are particularly revealing about shell structures, and provide a wonderful new laboratory to study these exotic decay processes. While assemblies of nucleons in nuclei behave in remarkable ways, it is also not fully understood the ways in which the nucleons themselves can be excited, and how they behave inside nuclei, and influence nuclear properties. This is a very exciting field that naturally leads to consideration of the roles of quarks inside the nucleons themselves, and how we can connect our models of nuclei and their interactions, with a more fundamental understanding based on modern theories such as Quantum Chromo Dynamics (QCD). Such theories suggest the existence of remarkable, undiscovered, particles called glueballs and quark-gluon hybrids; we will search for these in future experiments. All these experiments are performed at atom smashers all over the world, where the Edinburgh Group takes its equipment and performs these fundamental measurements. A lot of the hard work is done back in Edinburgh where we build highly advanced detector and electronics systems based on silicon technology using products jointly developed with UK firms, and with large UK laboratories supported by the STFC.