University of the West of Scotland Nuclear Physics Group Consolidated Grant

It is almost exactly 100 years since Ernest Rutherford's pioneering experiments which demonstrated the existence of the atomic nucleus. In the century that has followed, landmark developments, such as the inception of the nuclear shell model in the 1940s, the construction of heavy-ion accelerators in the 1960s, and major advances in nuclear-detector techniques, have firmly established nuclear physics as an international activity at the forefront of scientific research. In the past few decades, the quest to understand the properties of exotic nuclei ever further from the valley of stability has led to considerable experimental progress. The programme of research described in this Consolidated Grant application covers research into the structure and properties of atomic nuclei that lie far from stability. One of the main aims of our research programme is to achieve a better understanding of the structure and behaviour of exotic nuclei on both the neutron-rich and proton-rich sides of the valley of stability. Recent experimental observations, supported by theoretical calculations, have begun to suggest that the structure of neutron-rich nuclei may be different from those near stability. For example, the well known sequence of magic numbers, corresponding to energy gaps in nuclear shell structure, is now thought to change in nuclei with an extreme excess of neutrons. The evidence for such a change is already convincing around neutron number N=20, and similar effects are expected for the other shell gaps at N=28, 50, and 82. We will study the evolution of shell gaps in neutron-rich nuclei using both gamma-ray and charged-particle spectroscopy techniques. Above mass number A~100, electrostatic repulsion causes stable nuclei to have more neutrons than protons. Proton-rich nuclei just above the doubly-magic Sn100 nucleus are those with near equal numbers of neutrons and protons. These nuclei are known to decay by exotic decay modes such as proton emission. Spectroscopic study of the properties of these decays can give invaluable information about the properties of the nucleus in its ground state and in the first few excited states. Our research programme will include studies of proton-rich nuclei around A~110 by investigating their particle decays and by gamma-ray spectroscopy. Another aspect of our research programme will be devoted to studying fission of the nucleus. Fission is a collective mode of decay most commonly associated with heavy nuclei in the uranium region, but in our research we will study the beta-delayed fission of exotic nuclei in the lead region that lie very far from stability (by ~20-25 neutrons) and which have only recently become experimentally accessible with the development of radioactive beams. A study of the properties of beta-delayed fission, such as the mass distributions of the fission fragments, will give important information about nuclear structure and shell effects at low excitation energy. In a related part of our research programme, we will use radioactive At beams to study other nuclear-structure effects such as shape coexistence. Our research programme has several themes which will use different methodologies. Primarily, our experiments will be carried out using state-of-the-art apparatus at large international facilities. Gamma-ray spectroscopy offers one of the best methods of studying the structure of exotic nuclei, and here we will exploit the new AGATA gamma-ray tracking spectrometer at Legnaro National Laboratory, GSI and GANIL. Another part of our research will make use of the Jurogam gamma-ray spectrometer with the RITU recoil separator at Jyväskylä in Finland. Our programme to study beta-delayed fission will make use of beams of radioactive isotopes from the ISOLDE facility at CERN and at the JAEA laboratory in Japan. Furthermore, we will exploit the development of new radioactive beams of astatine at ISOLDE.