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Journal Articles

Application of a novel gas phase synthesis approach to carbonyl complexes of accelerator-produced 5d transition metals

G$"o$tz, M.*; Yakushev, A.*; G$"o$tz, S.*; Di Nitto, A.*; D$"u$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:34.45(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.

Journal Articles

Chemical characterization of a volatile dubnium compound, DbOCl$$_3$$

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:2 Percentile:16.39(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 $$^circ$$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$$_3 > $$ TaOCl$$_3 geq$$ DbOCl$$_3$$. From the obtained experimental results, thermochemical data for DbOCl$$_3$$ were derived. The present study delivers reliable experimental information for theoretical calculations on the chemical properties of transactinides.

Journal Articles

Optimization of an isothermal gas-chromatographic setup for the chemical exploration of dubnium (Db, Z = 105) oxychlorides

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:1 Percentile:11.65(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$$_2$$ and O$$_2$$. Parameters influencing the formation and transport of NbOCl$$_3$$ and TaOCl$$_3$$ are investigated. For nuclides with half-lives ($$t_{1/2}$$) of about 30 s, an overall efficiency of 7% is obtained, rendering the IGC setup suitable for the chemical exploration of $$^{262}$$Db($$t_{1/2}$$ = 34s).

Journal Articles

Formation and thermochemical properties of oxychlorides of niobium (Nb) and tantalum (Ta); Towards the gas-phase investigation of dubnium (Db) oxychloride

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:3 Percentile:19.16(Chemistry, Inorganic & Nuclear)

The formation of NbOCl$$_3$$ and TaOCl$$_3$$ 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 ($$Delta H_{rm ads}$$) at zero surface coverage of -$$Delta H_{rm ads}$$(NbOCl$$_3$$) = 102 $$pm$$ 4 kJ/mol and -$$Delta H_{rm ads}$$(TaOCl$$_3$$) = 128 $$pm$$ 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 $$Delta H_{rm ads}$$ values were successively related to the macroscopic standard sublimation enthalpy, $$Delta H^circ _{rm subl}$$, 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 $$Delta H_{rm ads}$$ and $$Delta H^circ _{rm subl}$$ for metal-oxychlorides was updated with the inclusion of the present data. According to the predicted $$Delta H^circ _{rm subl}$$(DbOCl$$_3$$), a $$Delta H_{rm ads}$$(DbOCl$$_3$$) value of 135 $$pm$$ 2 kJ/mol was extrapolated. The future accomplishment of comparative studies with DbOCl$$_3$$ 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.

Journal Articles

Complex chemistry with complex compounds

Eichler, R.*; Asai, Masato; Brand, H.*; Chiera, N. M.*; Di Nitto, A.*; Dressler, R.*; D$"u$llmann, 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:2 Percentile:62.08

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)$$_{6}$$. 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)$$_{6}$$, W(CO)$$_{6}$$, and Sg(CO)$$_{6}$$.

Oral presentation

Isothermal gas chromatographic behavior of hafnium isotopes

Tomitsuka, Tomohiro*; Kojima, Takayuki*; Murakami, Masashi*; Goto, Shinichi*; Sato, Tetsuya; Tsukada, Kazuaki; Asai, Masato; Toyoshima, Atsushi; Oe, Kazuhiro; Nagame, Yuichiro; et al.

no journal, , 

In order to study on chemical properties of superheavy element, rutherfordium (Rf, Z=104), we have investigated gas chromatographic behavior of group 4 elements by using an online gas chromatographic technique. Assuming that the gas chromatographic behavior can be described by a typical adsorption-desorption model, an adsorption enthalpy of chemical species of interest on a column surface can be deduced only by comparing the gas chromatographic behavior of isotopes with different half-lives. In this work, we compared gas chromatographic behavior of the short-lived Hf isotopes, $$^{165}$$Hf ($$T_{1/2}$$ = 78 s), $$^{166}$$Hf ($$T_{1/2}$$ = 406 s) and $$^{167}$$Hf ($$T_{1/2}$$ = 123 s). The difference between $$^{165}$$Hf and $$^{167}$$Hf was smaller than that expected from the simple adsorption-desorption model. This result suggests a different process can be expected from the model of adsorption and desorption behavior.

Oral presentation

Adsorption behavior of lawrencium (Lr) on a tantalum surface

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]$$5f^{14}7s^27p_{1/2}$$, which is different from that of the lanthanide homolog Lu [Xe]$$4f^{14}6s^25d$$ 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 $$^{256}$$Lr, which was produced in the reaction of $$^{249}$$Cf($$^{11}$$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 $$^{256}$$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.

Oral presentation

Adsorption behavior of lawrencium (Lr, Z = 103) on a tantalum surface

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]$$7s^25f^{14}7p_{1/2}$$ 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.

Oral presentation

Measurement of mass-symmetric spontaneous fission of $$^{259}$$Lr

Asai, 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 $$^{259}$$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 $$^{259}$$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.

Oral presentation

Adsorption of lawrencium (Lr) on a metallic tantalum (Ta) surface

Kaneya, Yusuke*; Tomitsuka, Tomohiro; Sato, Tetsuya; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Mitsukai, Akina; Makii, Hiroyuki; Hirose, Kentaro; Osa, Akihiko; et al.

no journal, , 

Oral presentation

Adsorption of Lawrencium (Z = 103) on a tantalum surface

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.

Oral presentation

Adsorption of lawrencium on a metallic tantalum surface at high temperature

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$$_{1/2}$$ 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.

Oral presentation

Development of low energy atomic beam extraction technique for determination of valence electronic structure of Lawrencium (Z = 103)

Tomitsuka, Tomohiro; Tokoi, Katsuyuki*; Sato, Tetsuya; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Chiera, N. M.; Kamada, Hiroki; Nagame, Yuichiro; Goto, Shinichi*

no journal, , 

no abstracts in English

Oral presentation

Adsorption behavior of lawrencium on a tantalum surface

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]$$7s^25f^{14}7p_{1/2}$$ 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.

Oral presentation

Discovery of $$^{234m}$$Np isomer

Kamada, 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 $$^{234m}$$Np was discovered for the first time. $$^{234m}$$Np was produced by using the JAEA tandem accelerator. Short-lived reaction products were mass-separated by the on-line isotope separator ISOL, and $$gamma$$ and X rays originating from the decay of $$^{234m}$$Np were observed. The half-life of $$^{234m}$$Np was determined to be approximately 9 min, and $$^{234m}$$Np was found to decay via the EC decay as well as the isomeric transition. On the basis of the observed $$gamma$$ and X rays and the half-life value, we have evaluated level energy, spin-parity, and proton-neutron configuration of $$^{234m}$$Np.

Oral presentation

Development of an atomic beam apparatus for chemistry of the heaviest elements

Tomitsuka, Tomohiro*; Tokoi, Katsuyuki*; Sato, Tetsuya; Asai, Masato; Chiera, N. M.; Goto, Shinichi*; Osa, Akihiko; Toyoshima, Atsushi; Tsukada, Kazuaki; Nagame, Yuichiro

no journal, , 

Oral presentation

Development of a Monte Carlo simulation code for analyses of adsorption and desorption behavior of short-lived isotopes in a surface ion-source

Tokoi, Katsuyuki; Sato, Tetsuya; Eichler, R.*; Ito, Yuta; Tomitsuka, Tomohiro; Suzuki, Hayato*; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi*; Chiera, N. M.; et al.

no journal, , 

We developed a new experimental method combining vacuum chromatography and surface ionization, and applied this to investigate adsorption behavior of lawrencium (Lr, Z =103) on a surface of high temperature metallic tantalum. The adsorption behavior of Lr was similar to that of lutetium having low volatility among lanthanide elements. In this work, a Monte Carlo simulation code has been newly developed to study ionization and chromatographic behavior of short-lived atoms. In the presentation, we will report the details of a developed simulation code and calculation results.

Oral presentation

Spontaneous fission measurements for nuclei around neutron-rich Fm region produced by using an $$^{254}$$Es target

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, , 

Spontaneous fissions of $$^{256}$$Fm, $$^{258}$$Fm, and $$^{259}$$Lr have been measured using an $$^{254}$$Es target at the JAEA Tandem Accelerator Facility. These three nuclei show different fission properties: the asymmetric fission, the high total-kinetic-energy (TKE) symmetric fission, and the low TKE symmetric fission, and the mechanisms of these three fissions should be very different. It is of great interest to elucidate how these differences occur. We have produced $$^{256,258}$$Fm in multinucleon-transfer reactions with a $$^{254}$$Es target and $$^{18}$$O projectiles, and produced $$^{259}$$Lr in the $$^{248}$$Cm($$^{15}$$N,4n) fusion-evaporation reaction. The reaction products were mass-separated with a gas-jet-coupled on-line isotope separator, and were delivered into a rotating wheel alpha- and fission-fragment detection system. By comparing the mass and TKE distributions deduced from the present experimental data, we will discuss the differences in fission mechanism among $$^{256}$$Fm, $$^{258}$$Fm, and $$^{259}$$Lr.

Oral presentation

Development of a slow atomic beam source for superheavy elements

Tomitsuka, Tomohiro; Tokoi, Katsuyuki; Sato, Tetsuya; Ito, Yuta; Suzuki, Hayato*; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Chiera, N. M.; Goto, Shinichi*; et al.

no journal, , 

In order to experimentally determine the ground state electronic configurations of Superheavy element atoms, we have developed a slow Atomic Beam Source (ABS) using a high-temperature nozzle type cavity. In this study, we conducted an off-line experiment using stable isotopes of Cd to examine the extraction of the Cd beams. A symmetrical beam distribution with respect to the atomic beam edge was obtained. The obtained results, together with Monte-Carlo simulations for atomic beam profiles, will be presented.

Oral presentation

Formation and thermochemical properties of oxychlorides of Nb and Ta; Towards the gas-phase investigation of the Superheavy Element dubnium (Db) oxychloride

Chiera, N. M.; Sato, Tetsuya; Asai, Masato; Suzuki, Hayato*; Tokoi, Katsuyuki; Tomitsuka, Tomohiro; Toyoshima, Atsushi; Tsukada, Kazuaki; Nagame, Yuichiro

no journal, , 

30 (Records 1-20 displayed on this page)