Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-ToF MS) enhanced in-gas-jet Laser Spectroscopy of the Heavy Actinides
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Abstract
Laser spectroscopy is a versatile tool to study the atomic structure and properties of exotic nuclei with high effciency and sensitivity. Electronic states of atoms can be excited via illumination with monochromatic, resonant laser light. In this work, the identifcation of excited atoms is done by either observation of their fluorescence emitted when relaxing back to an energetically lower state (light induced fluorescence, LIF), or by ionization of the atom via multi-step excitation (resonant ionization spectroscopy, RIS). This thesis presents some recent developments and applications of the JetRIS setup, a setup designed for laser spectroscopy in a gas jet. Within the context of this work, laser spectroscopy was utilized to characterize its spectral resolution, an atomic transition of 254No, multiple resonances of natSm, hyperfne components and isotope shifts and to test multiple technical developments necessary for studying on-line produced nuclides with the JetRIS setup.
A crucial part of the JetRIS setup is the nozzle and the corresponding gas jet formation. Here, the performance in terms of spectral linewidth was characterized utilizing LIF via laser excitation of Dy I using a 4f 106s2 → 4f106s6p transition at λ = 404.5nm. The spatially resolved fluorescence in dependence of the laser excitation frequency was recorded and a maximum average resolution of Δν = 212(30)MHz was obtained. JetRIS was then used in on-line experiments at the GSI facility in Darmstadt, utilizing two-step RIS and α-decay based detection measuring the 1S0→ 1P1 transition of 254No. The centroid of the transition was determined with ν = 29 961.480(12) cm−1 while a resolution of Δν = 770(300)MHz was achieved.
The last part of the thesis is dedicated towards RIS of samarium using ToF based detection utilizing and characterizing a Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-ToF MS). Here six different First Excitation Step (FES) transitions were characterized, determining their mass and field shifts, as well as the hyperfine parameter A for the isotopes 147Sm and 149Sm. For five FES transitions, two Auto-Ionizing (AI) transitions were identified each, while for the remaining FES transition, only one AI transition was found. Utilizing the isotope 154Sm, the mass resolving power R, the relative effciency ϵ and the capability of in-trap-deflection of the MR-ToF MS was characterized. The MR-ToF MS will be integrated into the JetRIS setup, to enhance its detection capabilities for future on-line studies using a linear Paul trap as a radiofrequency (RF) cooler buncher. The cooler buncher and merging of both setups are planned for future work.