Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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
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.
Okuma, Ryutaro*; Kofu, Maiko; Asai, Shinichiro*; Avdeev, M.*; Koda, Akihiro*; Okabe, Hirotaka*; Hiraishi, Masatoshi*; Takeshita, Soshi*; Kojima, Kenji*; Kadono, Ryosuke*; et al.
Nature Communications (Internet), 12(1), p.4382_1 - 4382_7, 2021/07
Times Cited Count：0 Percentile：0.01(Multidisciplinary Sciences)Tominaga, Taiki*; Kobayashi, Makoto*; Yamada, Takeshi*; Matsuura, Masato*; Kawakita, Yukinobu; Kasai, Satoshi*
JPS Conference Proceedings (Internet), 33, p.011095_1 - 011095_5, 2021/03
A vertical movement type of sample changer for the neutron spectrometer BL02, J-PARC MLF was developed for our top-loading type cryostat. The sample changer, termed as "PEACE", can control reproducibility of the irradiated position using guides made of polyether ether ketone. The variation between the background scattering profiles of three sample positions was found to be less than plus minus 1.6%. This result is reasonable, considering the deviation of sample position of less than plus minus 0.3 mm from the vertical axis.
) reaction at 12, 20, and 30 MeVPatwary, M. K. A*; Kin, Tadahiro*; Aoki, Katsumi*; Yoshinami, Kosuke*; Yamaguchi, Masaya*; Watanabe, Yukinobu*; Tsukada, Kazuaki; Sato, Nozomi*; Asai, Masato; Sato, Tetsuya; et al.
Journal of Nuclear Science and Technology, 58(2), p.252 - 258, 2021/02
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)While designing deuteron accelerator neutron sources for radioisotopes production, nuclear data for light elements such as Li, Be, and C have been systematically measured in the deuteron energy range from a few MeV to around 50 MeV. Currently, the experimental data available on double-differential thick-target neutron yields (DDTTNYs) is insufficient, especially for deuteron energies between 18 and 33 MeV. In this study, we measured the DDTTNYs of () reactions on 
C target for incident deuteron energies of 12, 20, and 30 MeV using the multiple-foils activation method to improve nuclear data insufficiency. We applied the GRAVEL code for the unfolding process to derive the DDTTNYs. The results were compared with the calculation by DEURACS. The present data were also used to confirm the systematics of the differential neutron yields at 0
and total neutron yield per incident deuteron in the wide range of deuteron energy.
Ikebe, Yurie*; Oshima, Masumi*; Bamba, Shigeru*; Asai, Masato; Tsukada, Kazuaki; Sato, Tetsuya; Toyoshima, Atsushi*; Bi, C.*; Seto, Hirofumi*; Amano, Hikaru*; et al.
Applied Radiation and Isotopes, 164, p.109106_1 - 109106_7, 2020/10
Times Cited Count：0 Percentile：0.01(Chemistry, Inorganic & Nuclear)Boron Neutron Capture Therapy (BNCT) is a radiotherapy for the treatment of intractable cancer. In BNCT precise determination of 
B concentration in whole blood sample before neutron irradiation is crucial for control of the neutron irradiation time and the neutron dosimetry. We have applied the Charged Particle Activation Analysis (CPAA) to non-destructive and accurate determination of B concentration in whole blood sample. The experiment was performed at JAEA Tandem Accelerator using an 8 MeV proton beam. The 478 keV 
ray of 
Be produced in the B(p,
)Be reaction was used to quantify the B, and rays of 
Co originating from the reaction with Fe in blood was used to normalize the -ray intensity. The results demonstrated that the present CPAA method can be applied to the determination of the B concentration in the blood sample.
-ray spectrometryYamada, Takashi*; Asai, Masato; Yonezawa, Chushiro*; Kakita, Kazutoshi*; Hirai, Shoji*
Radioisotopes, 69(9), p.287 - 297, 2020/09
We have confirmed that the commercially available Japanese `standard' gamma-ray analysis programs do not consider the effect of sample volume in calculating true coincidence summing (TCS) corrections, which results in underestimation of 
Cs radioactivity in cylindrical volume samples. In this work, we have developed and examined a practical TCS correction method for general Ge detectors which consider the effect of sample volume properly, and have confirmed that this method can reduce the Cs radioactivity underestimation to less than 1%.
Grund, J.*; Asai, Masato; Blaum, K.*; Block, M.*; Chenmarev, S.*; D
llmann, Ch. E.*; Eberhardt, K.*; Lohse, S.*; Nagame, Yuichiro*; Nagy, Sz.*; et al.
Nuclear Instruments and Methods in Physics Research A, 972, p.164013_1 - 164013_8, 2020/08
Times Cited Count：2 Percentile：66.08(Instruments & Instrumentation)We report on the successful coupling of the Penning-trap mass spectrometry setup TRIGA-TRAP to the research reactor TRIGA Mainz. This offers the possibility to perform direct high-precision mass measurements of short-lived nuclei produced in neutron-induced fission of a 
U target located near the reactor core. An aerosol-based gas-jet system is used for efficient transport of short-lived neutron-rich nuclei from the target chamber to a surface ion source. In conjunction with new ion optics and extended beam monitoring capabilities, the experimental setup has been fully commissioned. The design of the surface ion source, efficiency studies and first results are presented.
and 3
two-proton states in 
Po
populated by two-proton transferDupont, E.*; Astier, A.*; Petrache, C. M.*; Lv, B. F.*; Deloncle, I.*; Kiener, J.*; Orlandi, R.; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; et al.
Physical Review C, 101(1), p.014309_1 - 014309_6, 2020/01
Times Cited Count：0 Percentile：0.02(Physics, Nuclear)Oshima, Masumi*; Yamaguchi, Yurie*; Asai, Masato; Tsukada, Kazuaki; Goto, Jun*; Bamba, Shigeru*; Bi, C.*; Morimoto, Takao*
Journal of Nuclear Science and Technology, 56(9-10), p.866 - 872, 2019/09
Times Cited Count：1 Percentile：24.18(Nuclear Science & Technology)Sensitivity of charged particle activation analysis with 8 MeV proton beam was studied for determination of 35 long-lived radioactive nuclides. Reaction cross sections for those nuclides were estimated with ALICE-91 code and isomer yield ratios were estimated from those of neighboring isotopes by taking into account their spins and parities. It was found that the proposed charged particle activation analysis should show high sensitivity for the determination of several hardly measurable nuclides with long half-lives such as 
Cs, 
Pu, 
I, 
Sn, 
Mo, 
Pd, 
U, 
Cm, and 
Np.
decay of 
Te with a novel recoil-decay scintillation detectorXiao, Y.*; Go, S.*; Grzywacz, R.*; Orlandi, R.; Andreyev, A. N.; Asai, Masato; Bentley, M. A.*; de Angelis, G.*; Gross, C. J.*; Hausladen, P.*; et al.
Physical Review C, 100(3), p.034315_1 - 034315_8, 2019/09
Times Cited Count：10 Percentile：87.18(Physics, Nuclear)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：24.18(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).
Ca+
Bk leading to formation of the element Ts (Z=117)Khuyagbaatar, J.*; Yakushev, A.*; Dllmann, Ch. E.*; Ackermann, D.*; Andersson, L.-L.*; Asai, Masato; Block, M.*; Boll, R. A.*; Brand, H.*; Cox, D. M.*; et al.
Physical Review C, 99(5), p.054306_1 - 054306_16, 2019/05
Times Cited Count：10 Percentile：87.18(Physics, Nuclear)We have performed an experiment to synthesize the element 117 (Ts) with the Ca+Bk fusion reaction. Four -decay chains attributed to the element 117 were observed. Two of them were long decay chains which can be assigned to the one originating from the decay of 
Ts. The other two were short decay chains which are consistent with the one originating from the decay of 
Ts. We have compared the present results with the literature data, and found that our present results mostly confirmed the literature data, leading to the firm confirmation of the synthesis of the element 117.
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：2 Percentile：25.63(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.
Hatsukawa, Yuichi*; Hayakawa, Takehito*; Tsukada, Kazuaki; Hashimoto, Kazuyuki*; Sato, Tetsuya; Asai, Masato; Toyoshima, Atsushi; Tanimori, Toru*; Sonoda, Shinya*; Kabuki, Shigeto*; et al.
PLOS ONE (Internet), 13(12), p.e0208909_1 - e0208909_12, 2018/12
Times Cited Count：0 Percentile：0.01(Multidisciplinary Sciences)Imaging of 
Tc radioisotope was conducted using an electron tracking-Compton camera (ETCC). Tc emits 204, 582, and 835 keV rays, and was produced in the 
Mo(p,n)Tc reaction with a Mo-enriched target. The recycling of the Mo-enriched molybdenum trioxide was investigated, and the recycled yield of Mo was achieved to be 70% - 90%. The images were obtained with each of the three rays. Results showed that the spatial resolution increases with increasing -ray energy, and suggested that the ETCC with high-energy -ray emitters such as Tc is useful for the medical imaging of deep tissue and organs in the human body.
and Au surfaces in preparation for chemical investigations on Cn, Nh, and Fl at TASCALens, L.*; Yakushev, A.*; Dllmann, Ch. E.*; Asai, Masato; Ballof, J.*; Block, M.*; David, H. M.*; Despotopulos, J.*; Di Nitto, A.*; Eberhardt, K.*; et al.
Radiochimica Acta, 106(12), p.949 - 962, 2018/12
Times Cited Count：2 Percentile：33.97(Chemistry, Inorganic & Nuclear)Online gas-solid adsorption studies with single atom quantities of Hg, Tl, and Pb on SiO and Au surfaces were carried out using short-lived radioisotopes with half-lives in the range of 4-49 s. This is a model study to measure adsorption enthalpies of superheavy elements Cn, Nh, and Fl. The short-lived isotopes were produced and separated by the gas-filled recoil separator TASCA at GSI. The products were stopped in He gas, and flushed into gas chromatography columns made of Si detectors whose surfaces were covered by SiO or Au. The short-lived Tl and Pb were successfully measured by the Si detectors with the SiO surface at room temperature. On the other hand, the Hg did not adsorb on the SiO surface, but adsorbed on the Au surface. The results demonstrated that the adsorption properties of short-lived Hg, Tl, and Pb could be studied with this setup, and that this method is applicable to the experiment for Cn, Nh, and Fl.
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：16 Percentile：71.05(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.
Asai, Masato
Radioisotopes, 67(6), p.291 - 298, 2018/06
Stability and limit of existence essentially depend on nuclear shell structure. It is theoretically predicted that stable doubly-closed-shell spherical superheavy nuclei should exist around the region of the proton number 114 to 126 and the neutron number 172 to 184, although their locations and degree of stability have not been established because of large variety of theoretical predictions. On the other hand, recent advances on experimental techniques have made it possible to accumulate experimental data concerning the shell structure of superheavy nuclei, such as half-lives and nuclear masses. In addition, some pioneering experiments have been performed to directly establish the level structure of superheavy nuclei through spectroscopic methods. This paper introduces the current status of experimental studies on nuclear shell structure of superheavy nuclei.
Tanaka, Taiki*; Narikiyo, Yoshihiro*; Morita, Kosuke*; Fujita, Kunihiro*; Kaji, Daiya*; Morimoto, Koji*; Yamaki, Sayaka*; Wakabayashi, Yasuo*; Tanaka, Kengo*; Takeyama, Mirei*; et al.
Journal of the Physical Society of Japan, 87(1), p.014201_1 - 014201_9, 2018/01
Times Cited Count：10 Percentile：73.02(Physics, Multidisciplinary)Excitation functions of quasielastic scattering cross sections for the Ca + 
Pb, 
Ti + Pb, and Ca + Cm reactions were successfully measured by using the gas-filled recoil-ion separator GARIS. Fusion barrier distributions were extracted from these data, and compared with the coupled-channels calculations. It was found that the peak energies of the barrier distributions for the Ca + Pb and Ti + Pb systems coincide with those of the 2n evaporation channel cross sections for the systems, while that of the Ca + Cm is located slightly below the 4n evaporation ones. This results provide us helpful information to predict the optimum beam energy to synthesize superheavy nuclei.
Nishio, Katsuhisa; Hirose, Kentaro; Vermeulen, M. J.; Makii, Hiroyuki; Orlandi, R.; Tsukada, Kazuaki; Asai, Masato; Toyoshima, Atsushi; Sato, Tetsuya; Nagame, Yuichiro; et al.
EPJ Web of Conferences, 163, p.00041_1 - 00041_6, 2017/11
Times Cited Count：1 Percentile：69.79Ca + Cm 
Lv
at RIKEN-GARISKaji, Daiya*; Morita, Kosuke*; Morimoto, Koji*; Haba, Hiromitsu*; Asai, Masato; Fujita, Kunihiro*; Gan, Z.*; Geissel, H.*; Hasebe, Hiroo*; Hofmann, S.*; et al.
Journal of the Physical Society of Japan, 86(3), p.034201_1 - 034201_7, 2017/03
Times Cited Count：16 Percentile：79.91(Physics, Multidisciplinary)The fusion reaction of Ca + Cm Lv was studied using the gas-filled recoil-ion separator GARIS at RIKEN. A total of seven and spontaneous-fission decay chains were observed, which would originate from the reaction products of the element 116, 
Lv and Lv. Decay properties observed in the chains are in good agreement with the previously published ones. However, one of the chains showed a discrepancy, indicating the new spontaneous-fission branch in 
Cn or the production of the new isotope Lv.
