The primary tool for investigating the structure of exotic nuclei is time-correlated gamma-coincidence spectroscopy, where cascades of gamma rays that de-excite highly excited states are resolved and identified with high-resolution gamma-ray detectors. Typically, these are high-purity germanium (HPGe) detectors surrounded by Compton-suppression shields (such as bismuth germanate scintillator) that are used to ensure that only full-energy events are collected for each detected gamma ray. The Nuclear Structure research group in the Department of Nuclear Physics has a strong research program involving experiments performed locally and at international facilities across the world.
Our local research is conducted at ANU’s Heavy Ion Accelerator Facility using ion beams delivered by the 14UD particle accelerator. The CAESAR array of HPGe detectors is optimised for high-resolution gamma-ray spectroscopy of metastable states in atomic nuclei. There are several ongoing research programs to investigate different regions of the nuclear chart and to probe aspects of nuclear behaviour. For example, the shell-model structure of nuclei near 208Pb and the transition from spherical to collective behaviour, and the nature of the K quantum number and related high-K isomers in well-deformed nuclei.
Our group also performs experiments at international facilities such as Argonne National Laboratory (USA), RIKEN (Japan) and CERN (Switzerland). These projects are often focused on trying to understand the evolution of nuclear structure in neutron-rich exotic nuclei and tests of nuclear models moving away from stability.
A typical project might involve an experiment using the 14UD particle accelerator to initiate nuclear reactions and make exotic nuclei that don’t normally exist in nature. Observation of the emitted gamma-rays can enable the construction of new level schemes never before seen, followed by interpretation of the new structures in terms of nuclear models.