Investigating pear-shaped nuclei with radioactive ion beams
Most atomic nuclei are not spherical as envisaged in the simplistic picture, but they are in fact deformed. The lowest order and most common deformation observed is the quadrupole shapes of prolate and oblate nature, i.e. the shape of a rugby ball or a discus. The next order is the asymmetric octupole mode that produces pear-shaped nuclei and examples of this are much rarer across the chart of nuclei and occur away from the line of stability.
Enhanced octupole correlations in the nucleon-nucleon interaction are what lead to the asymmetric contribution to the nuclear shape. The pear shape can manifest dynamically with the appearance of excited vibrational states, whilst a static deformation produces rotational bands of states with opposite parity and odd spin. Key to characterising these nuclei are the energies of the low-lying Iπ = 3- states and their transition strength from the ground state.
Two particular regions of the chart of isotopes, around 224Ra and 144Ba, provide the best candidates for statically octupole-deformed, or pear-shaped, nuclei. The nuclei in both of these regions are radioactive and as such have remained elusive to complete spectroscopic studies. The former region is of interest for potential candidates in the search for atomic electric dipole moments (EDMs), which if observed to be non-zero would need to be described with new physics beyond the standard model. Nuclear structure input to this problem is paramount to the planning and eventual success of future experiments as well as the interpretation of the results.
This project aims to investigate the nuclear octupole degree of freedom with different spectroscopic techniques, primarily γ-ray and conversion electron spectroscopy following β-decay. Experiments have been and will be performed at the radioactive ion beam facilities of ISAC (TRIUMF, Canada) and ISOLDE (CERN, Switzerland). In addition, a new technique of inelastic scattering with deuterons in inverse kinematics will be exploited using post-accelerated beams at the HIE-ISOLDE facility, taking advantage of the recently commissioned ISOLDE Solenoidal Spectrometer (ISS).
During the studentship, the student will be primarily based within the Nuclear Physics Research group at the University of Liverpool. The project will consist initially of data analysis of β-decay experiments already performed at TRIUMF and contribute to the planning and implementation of future experiments at ISOLDE. They will gain hands-on experience working with the new ISS device, setting up electronics, learning to handle vacuum and gas systems, data acquisition and system monitoring/maintenance. It is expected that the student will publish their results in peer-reviewed journals and work in an enthusiastic, international team towards the realisation of the first inelastic scattering measurements with ISS.
Overseas travel to international laboratories will be required during the studentship and support will be provided for participation in international conferences to present the results of the project. Opportunities will be available to participate in the nuclear physics group’s other research activities, as well as the potential to spend an extended period at ISOLDE during the studentship.
To apply, please visit: https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/ and quote Studentship Reference: PPPR007 in the Finance Section of the Application Form.
Upon acceptance of a student, this project will be funded by the University of Liverpool for 3.5 years and cover fees and a stipend for living expenses. Funding for travel expenses incurred while undertaking the research will also be provided. UK and other EU citizens are eligible to apply. A full package of training and support will be provided by the Physics Department’s Nuclear Physics group. An IELTS score of at least 6.5 is required.