Laser and decay spectroscopy studies in the neutron-rich lead region

The phenomenon of low-energy shape coexistence is unique to atomic nuclei, and arises when a strong competition between structures with deformed and spherical shapes exists at low excitation energies. This behaviour has been observed in almost every region of the nuclear chart, with its occurrence providing valuable insight into the underlying interactions between protons and neutrons within the nucleus that govern its properties. However, a consistent model description remains a major challenge to nuclear theory, with further progress only possible through the collection of additional experimental data to constrain our models.

Over the past decade, York has spearheaded an extensive campaign of laser and decay spectroscopy experiments conducted at CERN's ISOLDE facility, revealing a wide range of behaviours related to shape coexistence in the neutron-deficient isotopes near the Z=82 shell closure. However, comparatively little is known about the neutron-rich isotopes in this region, which until now have been inaccessible to experiment due to the presence of strong, surface-ionised contamination and low production rates. Recent breakthroughs in ion source designs involving quartz lines and ion traps means it is now possible to access these isotopes in the lab. Of particular interest are isotopes just below Z=82 and near the N=126 shell closure, such as the neutron-rich mercury isotopes. Very little data on the structures of these isotopes exists, which are expected to be "textbook" examples of spherical shell-model nuclei.

In this project, the spins, parities, masses, decay properties, charge radii and electromagnetic moments of neutron-rich mercury isotopes will be studied through a combination of decay and laser spectroscopy, providing a rich dataset that will serve as a critical testbench for our nuclear models. The thesis of the student working on this project will be based on this data collected at ISOLDE using the ISOLDE Decay Station (IDS). The IDS system has recently undergone a significant upgrade led by York, improving the sensitivity of the device by a factor >4. The student will make a strong contribution to the running and further development of IDS for the work of this proposal, as well as the wide-ranging scientific programme undertaken by the IDS collaboration. In doing so, they will gain invaluable experience in the cutting-edge of nuclear experimental techniques.