Investigation of light exotic isotopes with ultra-sensitive laser spectroscopic methods

• Applicant: Dr. Bernhard Maaß
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447367248

The scientific goal of this application is the measurement of the nuclear charge radius of the isotope boron-8. The large excess of protons and their low separation energy indicate the existence of a proton-halo nucleus. Such a system is characterized by a central core with the least bound proton orbiting in a large mean distance. While neutron-halo nuclei can be found in several light systems that have been investigated thoroughly, an independent test of the exotic structure of boron-8 is still outstanding. A determination of the nuclear charge radius could provide such a test, since it allowed calculating the distance between core and halo proton in a model-independent way.To measure this nuclear charge radius, laser spectroscopy is the method of choice. Here, the atomic levels are probed with high-resolution laser systems. The size of the nucleus influences the energy of these levels slightly, and by measuring the transition energy difference between different isotopes, it is possible to calculate the magnitude of this tiny effect. This requires advanced atomic physics calculations, which just recently became available for the boron system. Also, the experimental precision is crucial which is mostly limited by the preparation of the short-lived boron-8 in the right atomic state and in sufficient amounts.While such techniques are well-established for heavier isotopes, the low mass and the high reactivity of the lightest elements are particularly challenging. In the scope of this project, the production rate of boron-8 at Argonne National Laboratory (Chicago, IL, USA) will be optimized. Also, two segments will be implemented which allow to prepare the radioactive boron in the correct state which is accessible with laser spectroscopy. At the same time, I plan to update the fluorescence detection region to provide a higher sensitivity, determining the total amount of boron-8 needed in an experiment. The new segments can also be tested at ANL to investigate the nuclear structure in the palladium isotopic chain by laser spectroscopy.The setup and the experiments will be performed in collaboration with the group “Laboratory of Exotic Molecules and Atoms” at the Massachusetts Institute of Technology (MA, USA), led by Dr. Ronald Fernando Garcia Ruiz. They are also focused on studying light, exotic nuclei and will provide the necessary scientific platform and know-how to perform the challenging experiments at ANL.

• DFG Programme: WBP Fellowship
• International Connection: USA
• Hosts: Dr. Ronald Fernando Garcia Ruiz; Professor Dr. Peter Mueller