Imgram, Phillip (2023)
High-precision laser spectroscopy of helium-like carbon 12C4+.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00023082
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

The size of an atomic nucleus is a fundamental observable and defined by the distribution of the neutrons and protons composing the nucleus and the respective mean-square radii. The precise investigation of the nuclear size across the chart of nuclides delivers important benchmarks for nuclear structure theory and tests our fundamental knowledge of matter. In contrast to matter and neutron radii, the nuclear charge radius can be probed through the well-known electromagnetic interaction. Different techniques have been developed over time to measure nuclear charge radii such as elastic electron scattering or muonic atom spectroscopy. While these techniques are typically limited to stable nuclei, collinear laser spectroscopy and resonant ionization spectroscopy are used to determine nuclear charge radii of short-lived radioactive isotopes relative to a reference charge radius of a stable isotope. In some cases, this can limit the uncertainty of the obtained charge radii of radioactive nuclei to the uncertainty of the reference measurements from elastic electron scattering or muonic atom spectroscopy. To overcome this limit in light mass nuclei like 10, 11B, an all-optical approach for the charge radius determination purely from laser spectroscopy measurements and non-relativistic QED calculations was tested in this work with the well-known nucleus of 12C through laser excitation of helium-like 12C4+ from the metastable 1s2s 3S1 state with a lifetime of 21 ms to the 1s2p 3PJ states. The high-precision collinear laser spectroscopy was performed at the Collinear Apparatus for Laser Spectroscopy and Applied Science (COALA), situated at the Institute for Nuclear Physics at the Technical University Darmstadt. In order to produce the the highly charged C4+ ions, a new electron beam ion source including a Wien filter for charge/mass separation was installed and commissioned at COALA. Additionally, a new switchyard and beam diagnostics were designed, built and installed. The 1s2s 3S1 → 1s2p 3PJ rest-frame transition frequencies were determined with less than 2 MHz uncertainty through quasi-simultaneous collinear and anticollinear laser spectroscopy. These transition frequencies are in excellent agreement with state-of-the-art ab initio atomic structure calculations and an all-optical nuclear charge radius of 12C was extracted. Its accuracy is limited by theory, which must be improved by two orders of magnitude before the experimental uncertainty becomes significant again. At that point, the accuracy of the extracted charge radius would have already outperformed all previous measurements of this observable. Furthermore, the high precision of this work enabled the estimation of the next missing order in the atomic structure calculations and the transition frequencies from this work can be used together with ongoing measurements in 13C4+ for a conventional determination of the mean-square charge radius difference δ⟨r2⟩12,13 between 12C and 13C which has not been measured so far by laser spectroscopy.

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