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Journal Articles

Sparse modeling approach for quasiclassical theory of superconductivity

Nagai, Yuki; Shinaoka, Hiroshi*

Journal of the Physical Society of Japan, 92(3), p.034703_1 - 034703_8, 2023/03

https://doi.org/10.7566/JPSJ.92.034703
 Times Cited Count：0 Percentile：0(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

sparse-ir; Optimal compression and sparse sampling of many-body propagators

Wallerberger, M.*; Badr, S.*; Hoshino, Shintaro*; Huber, S.*; Kakizawa, Fumiya*; Koretsune, Takashi*; Nagai, Yuki; Nogaki, Kosuke*; Nomoto, Takuya*; Mori, Hitoshi*; et al.

Software X (Internet), 21, p.101266_1 - 101266_7, 2023/02

https://doi.org/10.1016/j.softx.2022.101266
 Times Cited Count：10 Percentile：87.16(Computer Science, Software Engineering)

no abstracts in English

Journal Articles

Sparse modeling of large-scale quantum impurity models with low symmetries

Shinaoka, Hiroshi*; Nagai, Yuki

Physical Review B, 103(4), p.045120_1 - 045120_8, 2021/01

https://doi.org/10.1103/PhysRevB.103.045120
 Times Cited Count：3 Percentile：26.56(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Structural change of borosilicate glass by boron isotope composition

Nagai, Takayuki; Okamoto, Yoshihiro; Akiyama, Daisuke*; Uehara, Akihiro*; Fujii, Toshiyuki*; Sekimoto, Shun*

KURNS Progress Report 2019, P. 257, 2020/08

https://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep2019/ProgressReport2019_online.pdf

To understand the influence of glass structural change by neutron irradiation and boron isotope composition, glass samples were made from enrichment boric acid reagents and neutron irradiation of those samples was carried out in Pn-2 of KUR. The structural change of glass sample after the irradiation will be estimated in 2020FY. Before neutron irradiation test of glass samples, the Si-O bridging structure difference by boron isotope composition compared by using a Raman spectrometry.

Journal Articles

Structural change of borosilicate glass by neutron irradiation

Nagai, Takayuki; Kobayashi, Hidekazu; Okamoto, Yoshihiro; Akiyama, Daisuke*; Sato, Nobuaki*; Uehara, Akihiro*; Fujii, Toshiyuki*; Sekimoto, Shun*

KURNS Progress Report 2018, P. 105, 2019/08

https://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep2018/KURNS_Progress_Report2018_web.pdf

To understand this structural change of a borosilicate glass by a neutron irradiation in detail, the irradiation test was carried out in KUR in 2017FY. The glass structure was estimated by using Raman spectrometry in 2018FY. Comparing with the Raman spectra of glass samples before and after irradiation, it could be observed the change of peak height of Si-O bridging structure by the irradiation.

Journal Articles

Smooth self-energy in the exact-diagonalization-based dynamical mean-field theory; Intermediate-representation filtering approach

Nagai, Yuki; Shinaoka, Hiroshi*

Journal of the Physical Society of Japan, 88(6), p.064004_1 - 064004_5, 2019/06

https://doi.org/10.7566/JPSJ.88.064004
 Times Cited Count：11 Percentile：64.45(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Selection of borosilicate glass composition for neutron irradiation test

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*

KURRI Progress Report 2017, P. 128, 2018/08

https://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep2017/CO4.pdf

In this study, to understand the structural change of a borosilicate glass by a neutron irradiation in detail, the neutron irradiation test was carried out for 50 min in the Pn-2 of the Kyoto University Research Reactor (KUR). The structural change of glass sample after the irradiation will be estimated in 2018FY. Before the irradiation test, the glass composition was selected to estimate a structural change accurately by Raman spectrometry and 2 kinds of Li free borosilicate glass for the irradiation test samples were prepared.

Journal Articles

Electronic structure and magnetic properties of the half-metallic ferrimagnet Mn$$_{2}$$VAl probed by soft X-ray spectroscopies

Nagai, Kodai*; Fujiwara, Hidenori*; Aratani, Hidekazu*; Fujioka, Shuhei*; Yomosa, Hiroshi*; Nakatani, Yasuhiro*; Kiss, Takayuki*; Sekiyama, Akira*; Kuroda, Fumiaki*; Fujii, Hitoshi*; et al.

Physical Review B, 97(3), p.035143_1 - 035143_8, 2018/01

AA2017-0644.pdf:1.01MB

https://doi.org/10.1103/PhysRevB.97.035143
 Times Cited Count：22 Percentile：69.75(Materials Science, Multidisciplinary)

We have studied the electronic structure of ferrimagnetic Mn$$_{2}$$VAl single crystals by means of soft X-ray absorption spectroscopy (XAS), X-ray absorption magnetic circular dichroism (XMCD), and resonant soft X-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all the constituent elements. The Mn L$$_{2,3}$$ XAS and XMCD spectra are reproduced by spectral simulations based on density-functional theory, indicating the itinerant character of the Mn 3$$d$$ states. On the other hand, the V 3$$d$$ electrons are rather localized since the ionic model can qualitatively explain the V L$$_{2,3}$$ XAS and XMCD spectra. This picture is consistent with local $$dd$$ excitations revealed by the V L$$_{3}$$ RIXS.

Journal Articles

Influence of borosilicate glass by neutron irradiation

Nagai, Takayuki; Kobayashi, Hidekazu; Okamoto, Yoshihiro; Uehara, Akihiro*; Fujii, Toshiyuki*

Photon Factory Activity Report 2015, Part B, 2 Pages, 2016/00

http://pfwww.kek.jp/acr/2015pdf/part_b/pf15b0070.pdf

To investigate the characterization damage of a borosilicate glass by a neutron irradiation, the glass sample after neutron irradiation was estimated by using the Raman spectrophotometry and the synchrotron XAFS measurement. As a result, we confirmed that the Si-O bridge structure of a borosilicate glass and the containing element valence in the glass were changed by the neutron irradiation.

Journal Articles

Design and performance of high-pressure PLANET beamline at pulsed neutron source at J-PARC

Hattori, Takanori; Sano, Asami; Arima, Hiroshi*; Komatsu, Kazuki*; Yamada, Akihiro*; Inamura, Yasuhiro; Nakatani, Takeshi; Seto, Yusuke*; Nagai, Takaya*; Utsumi, Wataru; et al.

Nuclear Instruments and Methods in Physics Research A, 780, p.55 - 67, 2015/04

https://doi.org/10.1016/j.nima.2015.01.059
 Times Cited Count：75 Percentile：98.98(Instruments & Instrumentation)

PLANET is a time-of-flight (ToF) neutron beamline dedicated to high-pressure and high-temperature experiments. The large six-axis multi-anvil high-pressure press designed for ToF neutron diffraction experiments enables routine data collection at high pressures and high temperatures up to 10 GPa and 2000 K, respectively. To obtain clean data, the beamline is equipped with the incident slits and receiving collimators to eliminate parasitic scattering from the high-pressure cell assembly. The high performance of the diffractometer for the resolution ($$Delta$$ $$d$$/$$d$$ $$sim$$ 0.6%) and the accessible $$d$$-spacing range (0.2-8.4 ${AA}$) together with low-parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions.

Journal Articles

Production of $$^{rm 95m}$$Tc for Compton camera imaging

Hatsukawa, Yuichi; Hashimoto, Kazuyuki; Tsukada, Kazuaki; Sato, Tetsuya; Asai, Masato; Toyoshima, Atsushi; Nagai, Yasuki; Tanimori, Toru*; Sonoda, Shinya*; Kabuki, Shigeto*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1283 - 1285, 2015/02

https://doi.org/10.1007/s10967-014-3508-0
 Times Cited Count：2 Percentile：17.52(Chemistry, Analytical)

Technetium-99m ($$^{rm 99m}$$Tc) is used in radioactive medical diagonostic tests, for example as a radioactive tracer that medical equipment can detect in the human body. It is well suited to the role because it emits readily detectable 141 keV $$gamma$$ rays, and its half-life is 6.01 hours (meaning that about 94% of it decays to technetium-99 in 24 hours). There are at least 31 commonly used radiopharmaceuticals based on technetium-99m for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors. Recent years, with the develop-ment of the Compton camera which can realize high position resolution, technetium isotopes emitting high energy $$gamma$$-rays are required. In this study, technetium-95m which emits some $$gamma$$ rays around 800 keV was produced by the $$^{95}$$Mo(p,n)$$^{rm 95m}$$Tc reaction.

Journal Articles

Redox equilibrium of the UO$$_2^{2+}$$/UO$$_2^{+}$$ couple in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Sato, Nobuaki*; Kofuji, Hirohide; Myochin, Munetaka; Yamana, Hajimu*

Journal of Nuclear Materials, 454(1-3), p.159 - 163, 2014/11

https://doi.org/10.1016/j.jnucmat.2014.07.070
 Times Cited Count：1 Percentile：8.82(Materials Science, Multidisciplinary)

The redox equilibrium of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was measured in Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt at 550$$^{circ}$$C by cyclic voltammetry and absorption spectrophotometry. The standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was approximately evaluated by cyclic voltammetry. Further, the absorption spectrum and equilibrium potential were measured, repeatedly adding UO$$_2^{2+}$$ source material into the melt containing UO$$_2^{+}$$. From the correlation between the equilibrium potential of the melt and the concentration ratio [UO$$_2^{2+}$$]/[UO$$_2^{+}$$] spectrophotometrically evaluated, the standard redox potential of UO$$_2^{2+}$$/UO$$_2^{+}$$ couple was determined to be -0.847$$pm$$0.010 V vs. O$$_{2}$$/O$$^{2-}$$.

Journal Articles

Reduction behavior of UO$$_{2}$$$$^{2+}$$ in molten LiCl-RbCl and LiCl-KCl eutectics by using tungsten

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*

Journal of Nuclear Materials, 439(1-3), p.1 - 6, 2013/08

https://doi.org/10.1016/j.jnucmat.2013.03.078
 Times Cited Count：9 Percentile：53.27(Materials Science, Multidisciplinary)

The reduction of uranium from UO$$_{2}$$$$^{2+}$$ to UO$$_{2}$$$$^{+}$$ or U$$^{4+}$$ in molten LiCl-RbCl and LiCl-KCl eutectics was examined by using tungsten and chlorine gas. Spectrophotometric technique was adopted to determine the concentration of uranium species. When tungsten was immersed into the LiCl-RbCl eutectic melt at 400$$^{circ}$$C without supplying chlorine gas, 36% of the total weight of the hexavalent of UO$$_{2}$$$$^{2+}$$ was reduced to the pentavalent of UO$$_{2}$$$$^{+}$$. Under purging chlorine gas into the melt, 96% of UO$$_{2}$$$$^{2+}$$ was reduced to the tetravalent of U$$^{4+}$$. Tungsten oxy-chloride of WOCl$$_{4}$$ was produced via the reductions of UO$$_{2}$$$$^{2+}$$, which was volatized from the melt and adsorbed on the upper part of experimental cell. On the other hand, 84% of UO$$_{2}$$$$^{2+}$$ in the LiCl-KCl eutectic melt at 500$$^{circ}$$C was reduced to U$$^{4+}$$ by using tungsten and chlorine gas.

Journal Articles

Synthesis and investigation of uranyl molybdate UO$$_{2}$$MoO$$_{4}$$

Nagai, Takayuki; Sato, Nobuaki*; Kitawaki, Shinichi; Uehara, Akihiro*; Fujii, Toshiyuki*; Yamana, Hajimu*; Myochin, Munetaka

Journal of Nuclear Materials, 433(1-3), p.397 - 403, 2013/02

https://doi.org/10.1016/j.jnucmat.2012.10.010
 Times Cited Count：10 Percentile：60.97(Materials Science, Multidisciplinary)

In order to examine easily synthetic conditions of uranyl molybdate, UO$$_{2}$$MoO$$_{4}$$, used for the reprocessing process study of spent nuclear oxide fuels in alkaline molybdate melts, the uranium molybdate compounds were produced from U$$_{3}$$O$$_{8}$$ powder and anhydrous MoO$$_{3}$$ reagent. The results of having investigated them in solid state by using X-ray diffractometry and Raman spectrometry, it was confirmed that UO$$_{2}$$MoO$$_{4}$$ could be synthesized by heating mixed powder of U$$_{3}$$O$$_{8}$$ and MoO$$_{3}$$ with stoichiometric mole ratio at 770$$^{circ}$$C for 4 h under air atmosphere. Moreover, adding this UO$$_{2}$$MoO$$_{4}$$ into Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic melt, most of the dissolved uranium species in the melt were observed as hexa-valent uranyl ions by absorption spectrophotometry.

Journal Articles

Absorption spectra and cyclic voltammograms of uranium species in molten lithium molybdate-sodium molybdate eutectic at 550 $$^{circ}$$C

Nagai, Takayuki; Uehara, Akihiro*; Fukushima, Mineo; Myochin, Munetaka; Fujii, Toshiyuki*; Sato, Nobuaki*; Yamana, Hajimu*

Proceedings in Radiochemistry, 1(1), p.151 - 155, 2011/09

http://www.oldenbourg-link.com/doi/abs/10.1524/rcpr.2011.0012

Absorption spectra of dissolved uranium species in molten Li$$_{2}$$MoO$$_{4}$$-Na$$_{2}$$MoO$$_{4}$$ eutectic at 550 $$^{circ}$$C were measured by spectrophotometry, and their redox reactions were also investigated by cyclic voltammetry. Observed absorption spectra of uranium species were similar to those of UO$$_{2}$$$$^{+}$$ in molten chlorides. After purging oxygen into the melt, the absorption peaks of UO$$_{2}$$$$^{+}$$ decreased and UO$$_{2}$$$$^{+}$$ was thought to be oxidized to UO$$_{2}$$$$^{2+}$$. When the uranium species were not contained in the melt, we confirmed that alkali metals deposited at -0.7 V and a small reduction of this melt was observed at -0.3 V. When UO$$_{2}$$ was dissolved into the melt, the reduction of the uranium species was observed at -0.2 V. It was suggested that the dissolved uranium species are recovered as mixed uranium-molybdenum oxides by electrolysis.

Journal Articles

EXAFS analysis of uranium(IV) and thorium(IV) complexes in concentrated CaCl$$_{2}$$ solutions

Uehara, Akihiro*; Fujii, Toshiyuki*; Matsuura, Haruaki*; Sato, Nobuaki*; Nagai, Takayuki; Minato, Kazuo; Yamana, Hajimu*; Okamoto, Yoshihiro

Proceedings in Radiochemistry, 1(1), p.161 - 165, 2011/09

http://www.oldenbourg-link.com/doi/abs/10.1524/rcpr.2011.0030

Journal Articles

Electrochemical behavior and electronic absorption spectra of uranium trivalent ions in molten LiCl-CsCl mixtures

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Sato, Nobuaki*; Yamana, Hajimu*

Journal of Nuclear Materials, 414(2), p.226 - 231, 2011/07

https://doi.org/10.1016/j.jnucmat.2011.03.048
 Times Cited Count：11 Percentile：63.92(Materials Science, Multidisciplinary)

Journal Articles

Recent progress in the energy recovery linac project in Japan

Sakanaka, Shogo*; Akemoto, Mitsuo*; Aoto, Tomohiro*; Arakawa, Dai*; Asaoka, Seiji*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.2338 - 2340, 2010/05

http://accelconf.web.cern.ch/AccelConf/IPAC10/papers/tupe091.pdf

Future synchrotron light source using a 5-GeV energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting R&D efforts for that. We are developing high-brightness DC photocathode guns, two types of cryomodules for both injector and main superconducting (SC) linacs, and 1.3 GHz high CW-power RF sources. We are also constructing the Compact ERL (cERL) for demonstrating the recirculation of low-emittance, high-current beams using above-mentioned critical technologies.

Journal Articles

Redox equilibria of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Sato, Nobuaki*; Yamana, Hajimu*

Denki Kagaku Oyobi Kogyo Butsuri Kagaku, 77(8), p.614 - 616, 2009/08

https://doi.org/10.5796/electrochemistry.77.614
 Times Cited Count：15 Percentile：32.97(Electrochemistry)

Formal redox potentials of the U$$^{4+}$$/U$$^{3+}$$ and U$$^{3+}$$/U couples in molten LiCl-RbCl eutectic were determined by cyclic voltammetry. These redox potentials were more negative than those in the LiCl-KCl eutectic but positive comparing to those in the NaCl-CsCl eutectic. This relation would be correlated with the averaged alkali cation radius.

Journal Articles

Redox equilibria of Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in molten NaCl-CsCl eutectic as measured by absorption spectrophotometry

Nagai, Takayuki; Uehara, Akihiro*; Fujii, Toshiyuki*; Shirai, Osamu*; Myochin, Munetaka; Yamana, Hajimu*

Radiochimica Acta, 97(4-5), p.209 - 212, 2009/05

https://doi.org/10.1524/ract.2009.1596
 Times Cited Count：3 Percentile：24.47(Chemistry, Inorganic & Nuclear)

Redox behavior of uranium and plutonium in molten salts is the essential information for establishing an effective reprocessing process with spent MOX fuel. In an oxide electro-winning reprocessing process, the spent nuclear fuel is dissolved into the molten NaCl-CsCl eutectic, and the dissolved U(VI) and Pu(VI) species are reduced to be dioxides by electrolysis. In the present study, formal redox potentials of the Pu$$^{4+}$$/Pu$$^{3+}$$ and PuO$$_{2}$$$$^{2+}$$/Pu$$^{4+}$$ couples in the molten NaCl-CsCl eutectic at 923 K were determined. The fractions of Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$ were determined by UV/Vis/NIR absorption spectrophotometry. PuO$$_{2}$$ was dissolved into the molten NaCl-CsCl eutectic by Cl$$_{2}$$$$_{2}$$ gas purging. Valences of plutonium (Pu$$^{0}$$, Pu$$^{3+}$$, Pu$$^{4+}$$, and PuO$$_{2}$$$$^{2+}$$) were controlled by changing the flow rates of Cl$$_{2}$$, O$$_{2}$$, and Ar gases.

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