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    November 2017

    23.11.2017 - FLNR Scientific Seminar "Measurements of the first ionization potentials of heavy actinide elements", 11-00, Flerov Lab Conference Hall

    Speakers: T. K. SATO, Advanced Science Research Center, Japan Atomic Energy Agency

    The first ionization potential (IP1), a measure of the energy required to remove one valence electron from a neutral atom, yields information on the valence electronic structure. Recently, we successfully determined the IP1 value of the heaviest actinide element, lawrencium (Lr, Z = 103) for the first time in an atom-at-a-time scale using a surface ionization method [1]. The experimental result has shown that the IP1 of Lr is distinctly low among actinide elements owing to the configuration of closed 5f14 and 7s2 shells with an additional weakly-bound electron in the valence orbital.
    As a next step, for a confirmation of completing the closed shells at nobelium (No, Z = 102), we have applied this method to IP1 measurements of other heavy actinide elements, No, mendelevium (Md, Z = 101) and fermium (Fm, Z = 100).
    The experimental results of the three elements are in good agreement with the predicted ones obtained by theoretical and/or semi-empirical calculations. The IP1 value increased with an atomic number up to No and fell dramatically at Lr, indicating the similar trend with that of heavy lanthanide elements. This behavior clearly indicates that the 5f orbital is filled up at No. Details of the experiments and the results will be given in the presentation.

    [1] T. K. Sato et al. Nature 520, 209-211 (2015).

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