Physical and chemical properties of the transfermium elements (Z > 100) are influenced by relativistic effects altering the configuration of the electron shell. Laser spectroscopy allows probing precisely atomic properties and thus gives access to a better understanding of relativistic effects and highly correlated systems. These studies are hampered by low production rates and the fact that atomic information is only available from theoretical predictions. Only recently, optical transitions in nobelium (Z = 102) were identified in a pioneering experiment employing the RADRIS (RAdiation Detected Resonance Ionization Spectroscopy) technique in a buffer gas cell at the SHIP velocity filter in GSI [Nature 538, 495 (2016) https://www.nature.com/articles/nature19345]. The nobelium ions are subsequently stopped in high purity argon gas and collected onto a thin tantalum filament. After an appropriate collection time the accumulated ions are re-evaporated as neutral atoms, laser ionized and finally detected by their characteristic α-decay. The ¹S₀è¹P₁ ground-state transition and several high- lying Rydberg states were identified in ²⁵⁴No for the first time. Furthermore, the isotopic shifts of the 1S₀è¹P₁ transition for the isotopes ^252-254No were measured as well as the hyperfine splitting in ²⁵³No. These observables in combination with state-of-the-art atomic calculations, allow determining the evolution of the deformation of the nobelium isotopes in the vicinity of the deformed shell closure at neutron number N = 152 and extracting the magnetic moment and the spectroscopic quadrupole moment of ²⁵³No.

Read the publication at : https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.232503 
Read the Physics focus at : https://physics.aps.org/articles/v11/58

Upper panel : Deformation parameter β2 for different even-even isotopes of Th, U, Pu, Cm, and No obtained from the DFT calculations with the UNEDF1 functional. The inset figure shows the calculated proton distribution of ²⁵⁴No from highest density (red) to low density (blue). Lower panel : Relative depth of the central depression.