Laser spectroscopy of nobelium isotopes

Precision measurements of optical transitions of the heaviest elements validate state-of-the-art atomic calculations describing relativistic effects and electron correlations which affect physical and chemical properties of these elements. Isotope shift and hyperfine structure of an optical transition furthermore reveal nuclear ground state properties such as deformation, magnetic moment, and spin of the investigated isotopes. Elements beyond fermium (Z=100) are produced in complete fusion-evaporation reactions at accelerator facilities on-line, resulting in production rates of at most a few ions per second. The sensitive Radiation Detected Resonance Ionization Spectroscopy (RADRIS) technique was developed for laser spectroscopy on nobelium (Z=102) in a buffer-gas filled stopping cell. Nobelium ions are separated from the primary beam by the velocity filter SHIP at GSI, Darmstadt. Subsequently, they are thermalized in high-purity argon gas, accumulated on a filament, thermally evaporated as neutrals from the filament, and eventually laser ionized, which is detected by their characteristic alpha-decay.
The ¹S₀ → ¹P₁ ground state optical transition in nobelium was identified for the first time along with several high lying Rydberg levels. This allowed the deduction of the upper-limit of the first ionization potential (IP) of nobelium. In this year’s beamtime, the studies in nobelium were extended and the IP of No was extracted with high precision. In addition, the isotope shift in the ¹S₀ → ¹P₁ transition was studied for ^252-254No, as well as the hyperfine splitting in ²⁵³No. In this talk, a report on the recent achievements will be given.