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G
tz, M.*; Yakushev, A.*; Gtz, S.*; Di Nitto, A.*; D
llmann, Ch. E.*; Asai, Masato; Kindler, B.*; Krier, J.*; Lommel, B.*; Nagame, Yuichiro*; et al.
Radiochimica Acta, 110(2), p.75 - 86, 2022/02
Times Cited Count：2 Percentile：20.79(Chemistry, Inorganic & Nuclear)The study of volatile superheavy element carbonyl complexes requires more efficient methods because the yield of transactinide elements decreases with increasing atomic number. This is achieved by using a newly developed double chamber system to separate the recoil chamber and the reaction one, thereby avoiding the decomposition of reactive molecules by the projectile ion beam, which hinders the synthesis of carbonyl complexes. The feasibility of this method was verified by synthesizing 5d metal short-lived isotopes as homologous element isotopes of the light transactinide elements Sg, Bh, Hs, and Mt at the Japan Atomic Energy Agency tandem accelerator and conducting model experiments.
Chiera, N. M.*; Sato, Tetsuya; Eichler, R.*; Tomitsuka, Tomohiro; Asai, Masato; Adachi, Sadia*; Dressler, R.*; Hirose, Kentaro; Inoue, Hiroki*; Ito, Yuta; et al.
Angewandte Chemie; International Edition, 60(33), p.17871 - 17874, 2021/08
Times Cited Count：5 Percentile：25.61(Chemistry, Multidisciplinary)The formation and the chemical characterization of single atoms of dubnium (Db, element 105), in the form of its volatile oxychloride, was investigated using the on-line gas phase chromatography technique, in the temperature range 350 - 600 
C. Under the exact same chemical conditions, comparative studies with the lighter homologs of group-5 in the Periodic Table clearly indicate the volatility sequence being NbOCl
TaOCl
DbOCl. From the obtained experimental results, thermochemical data for DbOCl were derived. The present study delivers reliable experimental information for theoretical calculations on the chemical properties of transactinides.
Chiera, N. M.; Sato, Tetsuya; Tomitsuka, Tomohiro; Asai, Masato; Ito, Yuta; Shirai, Kaori*; Suzuki, Hayato; Tokoi, Katsuyuki; Toyoshima, Atsushi; Tsukada, Kazuaki; et al.
Journal of Radioanalytical and Nuclear Chemistry, 320(3), p.633 - 642, 2019/06
Times Cited Count：2 Percentile：17.45(Chemistry, Analytical)An isothermal gas-chromatographic (IGC) device has been developed and tested for on-line gas phase studies of volatile oxychlorides of short-lived group-5 transition metals. Radioisotopes of niobium and tantalum, produced in nuclear fusion evaporation reactions, are directly flushed into the IGC setup by an inert gas-jet. Oxychloride compounds are formed by the addition of SOCl
and O. Parameters influencing the formation and transport of NbOCl and TaOCl are investigated. For nuclides with half-lives (
) of about 30 s, an overall efficiency of 7% is obtained, rendering the IGC setup suitable for the chemical exploration of 
Db( = 34s).
Chiera, N. M.; Sato, Tetsuya; Tomitsuka, Tomohiro; Asai, Masato; Suzuki, Hayato*; Tokoi, Katsuyuki; Toyoshima, Atsushi; Tsukada, Kazuaki; Nagame, Yuichiro
Inorganica Chimica Acta, 486, p.361 - 366, 2019/02
Times Cited Count：4 Percentile：20.86(Chemistry, Inorganic & Nuclear)The formation of NbOCl and TaOCl and their adsorption behavior on quartz surfaces was explored by applying an isothermal gas-chromatographic method. Trace amounts of short-lived Nb and Ta isotopes were used. Adsorption enthalpy values (
) at zero surface coverage of -(NbOCl) = 102 
4 kJ/mol and -(TaOCl) = 128 5 kJ/mol were determined by analyzing the chromatographic behavior of the Nb andTa complexes with a Monte-Carlo simulation method based on an adsorption-desorption kinetic model.By applying an empirical correlation, the experimental values were successively related to the macroscopic standard sublimation enthalpy, 
, as a measure of the volatility of each substance. The inferred sublimation enthalpies are in agreement with tabulated thermochemical values. Thus, the linear empirical correlation between and for metal-oxychlorides was updated with the inclusion of the present data. According to the predicted (DbOCl), a (DbOCl) value of 135 2 kJ/mol was extrapolated. The future accomplishment of comparative studies with DbOCl under the same experimental conditions will provide valuable information on the volatility trend in Group-5 elements, together with an indication on the magnitude of relativistic effects on the electronic structure of dubnium.
Eichler, R.*; Asai, Masato; Brand, H.*; Chiera, N. M.*; Di Nitto, A.*; Dressler, R.*; Dllmann, Ch. E.*; Even, J.*; Fangli, F.*; Goetz, M.*; et al.
EPJ Web of Conferences, 131, p.07005_1 - 07005_7, 2016/12
Times Cited Count：3 Percentile：71.33(Chemistry, Inorganic & Nuclear)In recent years gas-phase chemical studies assisted by physical pre-separation allowed for the productions and investigations of fragile single molecular species of superheavy elements. The latest highlight is the formation of very volatile hexacarbonyl compound of element 106, Sg(CO)
. Following this success, second-generation experiments were performed to measure the first bond dissociation energy between the central metal atom and the surrounding ligand. The method using a tubular decomposition reactor was developed and successfully applied to short-lived Mo(CO), W(CO), and Sg(CO).
Es targetAsai, Masato; Tsukada, Kazuaki; Hirose, Kentaro; Toyoshima, Atsushi; Tomitsuka, Tomohiro; Chiera, N. M.; Ito, Yuta; Makii, Hiroyuki; Nagame, Yuichiro; Nishio, Katsuhisa; et al.
no journal, ,
Spontaneous fissions of neutron-rich heavy actinide isotopes 
Fm, 
Fm, and 
Lr have been measured at the JAEA Tandem accelerator facility. Fm and Fm were produced in a multinucleon transfer reaction with an 
O beam and an extremely rare Es target with a half-life of 276 days. Reaction products were mass-separated with an on-line isotope separator (ISOL). A transition between the typical asymmetric mass distribution and a very sharp symmetric one was clearly observed between Fm and Fm, while the spontaneous fission of Lr was found to exhibit mixture of three different fission modes.
Asai, Masato; Tsukada, Kazuaki; Hirose, Kentaro; Toyoshima, Atsushi*; Tomitsuka, Tomohiro*; Chiera, N. M.*; Ito, Yuta; Makii, Hiroyuki; Nagame, Yuichiro*; Nishio, Katsuhisa; et al.
no journal, ,
We have studied spontaneous fission of neutron-rich Fm and Lr isotopes. The neutron-rich Fm isotopes were produced with the Es target and the O beam delivered by the JAEA tandem accelerator. The neutron-rich Lr isotope were produced with the 
Cm target and the 
N beam. Reaction products were mass-separated with an on-line isotope separator (ISOL), which enabled us to obtain non-contaminated samples and to measure fission fragments precisely. From the deduced fission-fragment mass and total kinetic energy distributions, we have obtained a new insight into the competition between the symmetric and asymmetric fission which is characteristic in this neutron-rich region.
Np isomer and its decay propertiesAsai, Masato; Suekawa, Yoshihide*; Higashi, Masato*; Kamada, Hiroki*; Tobe, Teruhisa*; Andreyev, A. N.; Hirose, Kentaro; Ito, Yuta; Makii, Hiroyuki; Nishio, Katsuhisa; et al.
no journal, ,
A new isomer 
Np with a half-life of 
9 min has been discovered. It was produced in the reaction of 
U target with 
Li beam at JAEA tandem accelerator, and was identified through characteristic X-ray measurement and mass separation with an on-line isotope separator (ISOL). Gamma-ray singles, gamma-gamma coincidence, and internal-conversion electron measurements were performed. It was revealed that the Np decays mostly through an isomeric E4 transition followed by an M1 transition, and that the spin-parity of the Np should be 5
. The results are introduced in detail, and the nuclear structure of the Np are discussed.
Sato, Tetsuya; Kaneya, Yusuke*; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina*; Osa, Akihiko; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; et al.
no journal, ,
The ground state electronic configuration of lawrencium (Lr, Z =103) is predicted to be [Rn]
, which is different from that of the lanthanide homolog Lu [Xe]
due to strong relativistic effects. According to semi-empirical considerations, volatility of Lr is expected to be higher than that of Lu. We have investigated adsorption behavior of Lr, which was produced in the reaction of 
Cf(
B, 4n), on a tantalum (Ta) metal surface using a surface ion-source installed into the isotope separator on-line (ISOL) at the JAEA tandem accelerator facility. The observed adsorption behavior of Lr was similar to those of Tb and Lu which have relatively higher adsorption enthalpy on Ta surface. It implies that Lr would have low volatility like such as Lu and Tb.
LrAsai, Masato; Kamada, Hiroki*; Shigekawa, Yudai*; Tsukada, Kazuaki; Sato, Tetsuya; Toyoshima, Atsushi; Mitsukai, Akina; Nagame, Yuichiro; Nishio, Katsuhisa; Hirose, Kentaro; et al.
no journal, ,
To clarify the fission mechanism of mass-symmetric spontaneous fissions observed around the neutron-rich Fm region, we have measured kinetic energies and mass distribution of spontaneous-fission fragments in this nuclear region precisely. The experiment was performed at the JAEA tandem accelerator facility using an on-line isotope separator (ISOL). The mass-separated Lr nuclei were implanted into thin foil, and two fragments of their spontaneous fission were coincidently measured with two Si detectors. The spontaneous fission of Lr was found to show a narrow symmetric mass distribution. On the other hand, their total kinetic energy TKE was found to be low, which is apparently different from the high-TKE symmetric fissions observed in the Fm isotopes. This indicates that the fission mechanisms of these two symmetric fissions are different.
Kaneya, Yusuke*; Tomitsuka, Tomohiro; Sato, Tetsuya; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina; Makii, Hiroyuki; Hirose, Kentaro; Osa, Akihiko; et al.
no journal, ,
Tomitsuka, Tomohiro; Kaneya, Yusuke*; Sato, Tetsuya; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina; Osa, Akihiko; Nishio, Katsuhisa; Nagame, Yuichiro; et al.
no journal, ,
In order to investigate the adsorption behavior of Lawrencium (Lr, Z = 103) on a Tantalum (Ta) surface, we measured ionization efficiencies of Lr under several temperature conditions of the surface ionization. We observed ionization efficiencies of Lr which were lower than those calculated by the Saha-Langmuir equation in lower temperature region. Based on a temperature dependence of the obtained ionization efficiencies, we discuss the adsorption behavior of Lr on the Ta surface.
Kaneya, Yusuke*; Asai, Masato; Sato, Tetsuya; Tomitsuka, Tomohiro; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina; Makii, Hiroyuki; Hirose, Kentaro; Osa, Akihiko; et al.
no journal, ,
To study the influence of the valence 7p
electronic orbital on chemical properties of lawrencium, a measurement of the adsorption enthalpy of lawrencium was carried out. A new method using a surface ionization technique coupled to an on-line isotope separator was developed, which enabled one to measure temperature dependence of lawrencium surface adsorption on a metallic tantalum surface at high temperature up to 2800 K. The temperature dependences of adsorption of lawrencium as well as various lanthanide elements were investigated with this method, and the adsorption enthalpy of lawrencium was successfully extracted.
Sato, Tetsuya; Kaneya, Yusuke*; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina*; Osa, Akihiko; Makii, Hiroyuki; Hirose, Kentaro; Nagame, Yuichiro; et al.
no journal, ,
Our experimental results on the first ionization potential measurement of lawrencium (Lr, element 103) have strongly suggested that the Lr atom has a [Rn]
configuration as a result of the influence of strong relativistic effects. The configuration is different from that expected from the lanthanide homologue, lutetium (Lu). According to a semi-empirical consideration, it is expected that the change of the electronic configuration leads higher volatility of Lr than that of Lu. In this work, adsorption behaviors of Lr and various short-lived rare earth isotopes on a tantalum surface were investigated via observation of their surface ionization efficiencies. It was found that Lr would behave like low volatile rare earth elements such as Lu contrary to the semi-empirical expectation.
Np isomerKamada, Hiroki*; Asai, Masato; Tsukada, Kazuaki; Sato, Tetsuya; Toyoshima, Atsushi; Nagame, Yuichiro; Mitsukai, Akina; Tomitsuka, Tomohiro*; Andreyev, A. N.; Nishio, Katsuhisa; et al.
no journal, ,
Existence of the previously unknown isomer Np was discovered for the first time. Np was produced by using the JAEA tandem accelerator. Short-lived reaction products were mass-separated by the on-line isotope separator ISOL, and 
and X rays originating from the decay of Np were observed. The half-life of Np was determined to be approximately 9 min, and Np was found to decay via the EC decay as well as the isomeric transition. On the basis of the observed and X rays and the half-life value, we have evaluated level energy, spin-parity, and proton-neutron configuration of Np.
Md produced in the 
He+Es reactionNishio, Katsuhisa; Hirose, Kentaro; Makii, Hiroyuki; Orlandi, R.; Kean, K. R.*; Tsukada, Kazuaki; Asai, Masato; Toyoshima, Atsushi*; Sato, Tetsuya; Ito, Yuta; et al.
no journal, ,
no abstracts in English
Es targetAsai, Masato; Tsukada, Kazuaki; Hirose, Kentaro; Toyoshima, Atsushi*; Tomitsuka, Tomohiro*; Chiera, N. M.*; Ito, Yuta; Makii, Hiroyuki; Nagame, Yuichiro*; Nishio, Katsuhisa; et al.
no journal, ,
Neutron-rich fermium isotopes Fm and Fm and lawrencium isotope Lr were produced in the multinucleon transfer reaction on Es target with heavy-ion beam and in the heavy-ion fusion reaction on Cm target with N beam, respectively. Reaction products were mass-separated with an on-line isotope separator (ISOL), and spontaneous fission (SF) of these isotopes were measured. It was found that the mass distribution of the SF of Fm was asymmetric, while that of Fm was sharp symmetric, which confirmed the previous experimental results. On the other hand, the SF of Lr seemed to contain both symmetric and asymmetric mass distributions. On the basis of the present results of the mass and total kinetic energy distributions, we discussed the mechanism of fission for these isotopes.
Np isomerAsai, Masato; Suekawa, Yoshihide*; Higashi, Masato*; Kamada, Hiroki*; Tobe, Teruhisa*; Andreyev, A. N.; Hirose, Kentaro; Ito, Yuta; Makii, Hiroyuki; Nishio, Katsuhisa; et al.
no journal, ,
We have carried out experiments to study nuclear structure of the new isomer Np which we discovered recently. The Np was produced in the reaction of U target with Li beam at JAEA tandem accelerator, and was mass-separated with an on-line isotope separator (ISOL). The half-life was determined accurately through LX-ray measurements. The transition emitted by following the isomeric transition was successfully observed through LX- coincidence measurements. Moreover, the multipolarities of the transitions were determined with internal-conversion electron measurements. On the basis of these experimental results, We have clarified excitation energy, spin-parity, and nuclear structure of Np.
Zr and Mo based on solid phase extraction combined with ICP-MS/MS, 2; Spectral interference removal for measurement of Zr and Mo by ICP-MS/MSDo, V. K.; Furuse, Takahiro; Murakami, Erina; Aita, Rena; Ota, Yuki; Tomitsuka, Tomohiro; Sano, Yuichi; Akimoto, Yuji*; Endo, Tsubasa*; Katayama, Atsushi; et al.
no journal, ,
The paper presents removal of possible interferences including from an isobar (Nb) and tailings of adjacent peaks for the quantification of Zr and Mo using an ICP-MS/MS (Agilent 8900). By using ammonia gas (NH
) as a reaction gas, Zr and Mo can be separated from each other and from Nb owing to the different reactions of those elements with the reaction gas. Based on the characterization results, we propose a measurement scheme aiming at quantification of Zr and Mo in environmental samples collected at adjacent location of Fukushima Daiichi Nuclear Power Station.
Zr and Mo based on solid phase extraction combined with ICP-MS/MS, 1; Sequential chemical separation of Zr and Mo from NbFuruse, Takahiro; Do, V. K.; Aita, Rena; Ota, Yuki; Murakami, Erina; Tomitsuka, Tomohiro; Sano, Yuichi; Akimoto, Yuji*; Endo, Tsubasa*; Katayama, Atsushi; et al.
no journal, ,
In order to simplify the analysis of Zr and Mo in radioactive waste from conventional radiation measurement, we have considered analysis method combining solid-phase extraction and ICP-MS/MS. In this presentation, we report the results of a study on sequential chemical separation of Zr and Mo from Nb and sample matrix using ZR resin as a solid-phase extraction resin.
