First ionization energies of heavy actinides

Nagame, Yuichiro ; Sato, Tetsuya   ; Asai, Masato  ; Kaneya, Yusuke*; Makii, Hiroyuki   ; Mitsukai, Akina; Osa, Akihiko  ; Schdel, M.*; Toyoshima, Atsushi; Tsukada, Kazuaki  ; Vascon, A.*; Borschevsky, A.*; Stora, T.*; Ichikawa, Shinichi*; Sato, Nozomi*; Sato, Daisuke*; Oe, Kazuhiro*; Miyashita, Sunao*; Takeda, Shinsaku*; Sakama, Minoru*; Shigekawa, Yudai*; Dllmann, Ch. E.*; Eberhardt, K.*; Kratz, J. V.*; Renisch, D.*; Runke, J.*; Thrle-Pospiech, P.*; Trautmann, N.*; Eliav, E.*; Kaldor, U.*

The first ionization potential (IP) is one of the most sensitive atomic properties which reflect the outermost electron configuration. Precise and accurate determination of IP of heavy elements allows us to give significant information on valence electronic configuration affected by relativistic effects. The IP values of heavy elements up to einsteinium (Es, = 99), produced in a nuclear reactor in macroscopic quantities, were successfully measured by resonance ionization mass spectroscopy (RIMS). IP values of heavy elements with Z 100, however, have not been determined experimentally, because both half-lives and production rates of nuclides of still heavier elements are rapidly decreasing, which forces us to manage elements on an atom-at-a-time scale. Here we report the determination of IP of the heavy actinides, fermium (Fm, atomic number = 100) through lawrencium (Lr, = 103), by using a novel technique based on a surface ionization process.