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Probing Sizes and Shapes of Nobelium Isotopes by Laser Spectroscopy

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)]. 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.

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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.

Voir en ligne : PHYS. REV. LETT. 120, 232503 (2018)



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