Research Interests
David O'Donnell
My current research is focused on the spectroscopy of extremely neutron-deficient atomic nuclei. Specifically, my most recent work has concentrated on nuclei in the vicinity of N=82 and Z=82 shell closures. This region is particularly interesting because the competition between collective and single-particle excitations manifests itself in the form of shape-coexistence where the nucleus can adopt different shapes at different energies. Another of my interests is the investigation of the limits of existence, beyond which nuclear matter cannot exist. As the number of neutrons in a given isotopic chain is reduced, a point is reached at which the nucleus has too few neutrons and is no longer bound.
The nuclei in the region discussed above can only be populated using fusion-evaporation reactions. This process involves the fusion of projectile and target nuclei and the subsequent evaporation of nucleons. Many of the nuclei of interest are populated via the evaporation of neutrons which, in this region of the nuclear chart, competes unfavourably with other processes. Therefore, highly-selective techniques exploiting specially-designed apparatus are required. Much of this work is conducted at JYFL of the University of Jyvaskyla in Finland where the unique combination of the JUROGAM - RITU - GREAT devices provides the ideal tool for this research.
I have been involved in the design and construction of the LISA spectrometer which is another device recently installed at JYFL. Consisting of sixteen position sensitive silicon strip detectors and two silicon annular detectors it is designed to complement the existing JYFL apparatus. By detecting the emission of prompt (at the target position) charged particles the device will primarily be used to study the ground-state decay of extremely short-lived nuclei. It is anticipated that LISA will be used to investigate exotic decay modes such as prompt charged particle decay in which the emission of protons and a particles competes with g-ray emission in the decay of discrete excited states. The device could also be used to veto reaction exit channels involving the evaporation of charged particles, thus increasing the sensitivity of the JYFL apparatus.
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