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Sato, Tetsuya; Asai, Masato; Borschevsky, A.*; Beerwerth, R.*; Kaneya, Yusuke*; Makii, Hiroyuki; Mitsukai, Akina*; Nagame, Yuichiro; Osa, Akihiko; Toyoshima, Atsushi; et al.
Journal of the American Chemical Society, 140(44), p.14609 - 14613, 2018/11
Times Cited Count:29 Percentile:69.01(Chemistry, Multidisciplinary)The first ionization potential (IP) yields information on valence electronic structure of an atom. IP values of heavy actinides beyond einsteinium (Es, Z = 99), however, have not been determined experimentally so far due to the difficulty in obtaining these elements on scales of more than one atom at a time. Recently, we successfully measured IP of lawrencium (Lr, Z = 103) using a surface ionization method. The result suggests that Lr has a loosely-bound electron in the outermost orbital. In contrast to Lr, nobelium (No, Z = 102) is expected to have the highest IP among the actinide elements owing to its full-filled 5f and the 7s orbitals. In the present study, we have successfully determined IP values of No as well as fermium (Fm, Z = 100) and mendelevium (Md, Z = 101) using the surface ionization method. The obtained results indicate that the IP value of heavy actinoids would increase monotonically with filling electrons up in the 5f orbital like heavy lanthanoids.
Henning, G.*; Khoo, T. L.*; Lopez-Martens, A.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.
Physical Review Letters, 113(26), p.262505_1 - 262505_6, 2014/12
Times Cited Count:34 Percentile:83.02(Physics, Multidisciplinary)Fission barrier heights of a shell-stabilized superheavy nucleus No have been determined as a function of spin up to 19 through the measured distribution of entry points of deexcitations in the excitation energy vs. spin plane. The fission barrier height of No was determined to be 6.0 MeV at spin 15, and 6.6 MeV at spin 0 by extrapolation. This demonstrates that the shell effect actually enlarges the fission barrier in such heavy nuclei and keeps the barrier high even at high spin.
Henning, G.*; Lopez-Martens, A.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; Asai, Masato; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.
EPJ Web of Conferences, 66, p.02046_1 - 02046_8, 2014/03
Times Cited Count:3 Percentile:69.7(Physics, Nuclear)Fission barrier heights of No have been determined through the entry distribution method. The entry distribution is the initial distribution of excitation energy and spin from which the deexcitation starts in the fusion-evaporation reaction. The initial distribution is extracted from measured -ray multiplicity and total -ray energy. This paper describes the details of the entry distribution method, and reports the first determination of the fission barrier heights of No, which is the heaviest nucleus whose fission barrier has been measured.
Sato, Tetsuya; Asai, Masato; Kaneya, Yusuke; Tsukada, Kazuaki; Toyoshima, Atsushi; Vascon, A.; Takeda, Shinsaku; Mitsukai, Akina*; Nagame, Yuichiro; Ichikawa, Shinichi; et al.
no journal, ,
In order to determine the IP of the heavy elements, we have developed a novel measurement method based on a surface ionization technique by using a surface ionization ion source coupled to a He/CdI gas-jet transport system for an Isotope Separator On-Line (ISOL) at the JAEA tandem accelerator facility. In this work, we have determined IP value of No by using the method. In a surface ionization process, an ionization efficiency of an atom depends on its IP. To obtain a relationship between IP and ionization efficiency in present system, we measured ionization efficiencies of various short-lived isotopes. Ionization efficiency of No produced in the Cm(C, 4n) reaction was also measured. Measured ionization efficiency of No was 0.8%, which yields IP value of No to be 6.6 eV. This value is in a good agreement with the value which has been evaluated by extrapolation from those of the lighter actinide elements, 6.65 eV.
Sato, Tetsuya; Asai, Masato; Kaneya, Yusuke; Tsukada, Kazuaki; Toyoshima, Atsushi; Takeda, Shinsaku; Mitsukai, Akina*; Nagame, Yuichiro; Ichikawa, Shinichi; Makii, Hiroyuki; et al.
no journal, ,
We successfully determined the first ionization energy (IE) of nobelium (No, = 102) using a short-lived No isotope, No produced in theCm(C, 4n) reaction, based on the IE dependence of the ionization efficiency in a surface ionization process. The IE value of No was evaluated to be 6.6 eV. This value is in a good agreement with the value which has been estimated by an extrapolation from those of the lighter actinide elements, 6.65 eV.
Sato, Tetsuya
no journal, ,
It is known that an ionization efficiency of an element in surface ionization process depends on temperature and a work function of the surface, and the first ionization energy of the atom of the element to be ionized. We determined the first ionization energies of nobelium (No) and lawrencium (Lr) by using the newly developed method based on surface ionization process. The ionization energies have not been measured owing to its low production rate and short half-lives. Concerning Lr, the experimental value of the ionization energy is in good agreement of the theoretical one which calculated using the state-of-the-art relativistic calculation. The value of No is consistent with the value obtained by an extrapolation from lighter actinide elements.
Sato, Tetsuya
no journal, ,
The experimental determination of the first ionization potential (IP) yields information on the electronic structure of the element. We successfully ionized and mass-separated No and Lr with efficiencies () of (0.5 0.1)% and (36 7)% at 2800 K, respectively. From these values, IP values of No and Lr were determined based on the relationship between and IP. Our values are in good agreement with the predicted ones by theoretical calculations.
Sato, Tetsuya
no journal, ,
We measured the first ionization energy (IE) of nobelium (No, Z = 102) and lawrencium (Lr, Z =103) by exploiting the dependence of the ionization efficiency () on the IE in a surface ionization process. The isotopes No ( = 24.5s) and Lr ( = 27 s), produced in the reaction Cm (C, 4n) and Cf (B, 4n), respectively, were used for studying their ionization. The reaction products recoiling from the targets were transported to a surface ion-source by a He/CdI gas-jet transport system. The products ionized in the ion-source were mass-separated with JAEA-ISOL. The number of ions collected at the end of the ISOL was determined by -particle measurements and was used to evaluate values. With the present system, we successfully ionized and mass-separated No and Lr with efficiencies of (0.5 0.1)% and (36 7)% at 2800 K, respectively. From these values, IE values of No and Lr were determined based on the relationship between and IE. Our values are in good agreement with the predicted ones by theoretical calculations.
Sato, Tetsuya; Asai, Masato; Kaneya, Yusuke*; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina*; Takeda, Shinsaku*; Vascon, A.*; Sakama, Minoru*; Sato, Daisuke*; et al.
no journal, ,
The first ionization potential (IP) yields information on valence electronic structure of an atom. IP values of heavy actinides beyond einsteinium (Es, Z = 99), however, have not been determined experimentally so far due to the difficulty in obtaining these elements on scales of more than one atom at a time. Recently, we successfully measured IP of lawrencium (Lr, Z = 103) using a surface ionization method. The result suggests that Lr has a loosely-bound electron in the outermost orbital. In contrast to Lr, nobelium (No, Z = 102) is expected to have the highest IP among the actinide elements owing to its full-filled 5f and the 7s orbitals. In the present study, we have successfully determined IP values of No as well as fermium (Fm, Z = 100) and mendelevium (Md, Z = 101) using the surface ionization method. The obtained results indicate that the IP value of heavy actinoids would increase monotonically with filling electrons up in the 5f orbital like heavy lanthanoids.
Sato, Tetsuya
no journal, ,
The first ionization potential (IP) yields information on valence electronic structure of an atom. IP values of heavy actinides beyond einsteinium (Es, Z = 99), however, have not been determined experimentally so far due to the difficulty in obtaining these elements on scales of more than one atom at a time. Recently, we successfully measured IP of lawrencium (Lr, Z = 103) using a surface ionization method. In the present study, we have successfully determined IP values of No as well as fermium (Fm, Z = 100) and mendelevium (Md, Z = 101) using the surface ionization method. The obtained results indicate that the IP value of heavy actinoids would increase monotonically with filling electrons up in the 5f orbital like heavy lanthanoids.
Sato, Tetsuya; Asai, Masato; Kaneya, Yusuke*; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina*; Takeda, Shinsaku*; Vascon, A.*; Sakama, Minoru*; Sato, Daisuke*; et al.
no journal, ,
The first ionization potential (IP) yields information on valence electronic structure of an atom. IP values of heavy actinides beyond einsteinium (Es, Z = 99), however, have not been determined experimentally so far due to the difficulty in obtaining these elements on scales of more than one atom at a time. Recently, we successfully measured IP of lawrencium (Lr, Z = 103) using a surface ionization method. The result suggests that Lr has a loosely-bound electron in the outermost orbital. In contrast to Lr, nobelium (No, Z = 102) is expected to have the highest IP among the actinide elements owing to its full-filled 5f and the 7s orbitals. In the present study, we have successfully determined IP values of No as well as fermium (Fm, Z = 100) and mendelevium (Md, Z = 101) using the surface ionization method. The obtained results indicate that the IP value of heavy actinoids would increase monotonically with filling electrons up in the 5f orbital like heavy lanthanoids.
Sato, Tetsuya
no journal, ,
The first ionization potential (IP), 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 IP value of the heaviest actinide element, lawrencium (Lr, ) for the first time in an atom-at-a-time scale using a surface ionization method. The experimental result has shown that the IP of Lr is distinctly low among actinide elements owing to the configuration of closed and shells with an additional weakly-bound electron in the valence orbital. As a next step, we have applied this method to IP measurements of other heavy actinide elements, No, mendelevium (Md, ) and fermium (Fm, ). The experimental results of the three elements are in good agreement with the predicted ones obtained by theoretical and/or semi-empirical calculations. The IP 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 orbital is filled up at No.