Investigating the Structure of Exotic Nuclei with Lifetime Measurements of Excited Nuclear States

• Applicant: Dr. Christoph Fransen
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539294151

The focus of this follow-up project lies on the appearance of collective phenomena in atomic nuclei with special emphasis to shape coexistence, i.e., the coexistence of two or more nuclear shapes at low excitation energies, and the evolution of the shell structure of nuclei far from the valley of stability. Our preceding work already gave detailed information on the evolution of nuclear structure, but also revealed that further investigations are needed to allow unique structural interpretations for such nuclei. Here, we want to address the following subjects: (i) shell structure of neutron-rich nuclei with charge Z<20 close to doubly-magic 48Ca with respect to a likely weakening of the N=28 neutron shell closure, and to clarify a possible valence proton symmetry relative to the Z=20 shell closure. (ii) nuclear structure in mid-shell Te and Xe isotopes. The aim is a clarification of the reason for (possible) anomalous E2 transition strengths between the lowest excited states, where existing data are partly ambiguous so far, and the search for shape coexistence, as there exist signatures for such in this region. (iii) Structure of neutron deficient nuclei in the A=170-180 region. In this framework, we aim to investigate especially different effects that are peculiar in this region: the evolution of shape coexistence of weakly deformed and prolate shapes, a possible development toward configuration mixing, and evolution of the properties of extremely neutron deficient nuclei that are not understood so far even with state-of-the-art models. Besides from the level schemes, absolute transition strengths between excited states yield fundamental information on nuclear structure and will be used to address the aforementioned subjects. The latter observables and their determination from level lifetimes has been in the focus of our group since many years. For the measurement of level lifetimes, our group intensively uses the recoil distance Doppler-shift technique of gamma-rays emitted after nuclear reactions ("plunger technique") and we continue to develop it. This includes the construction of sophisticated so-called plunger devices for new experimental conditions, also during the last funding period, where the latter were already used successfully in experiments. In such experiments the nuclei of interest are produced in a nuclear reaction in a thin target foil and stopped or degraded in a degrader foil placed at a precisely and well defined distance from the target. Our group has many years of detailed experience with this method in very different kinematic regimes and is acknowledged worldwide.

• DFG Programme: Research Grants