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Journal Articles

Quasielastic neutron scattering of brucite to analyse hydrogen transport on the atomic scale

Okuchi, Takuo*; Tomioka, Naotaka*; Purevjav, N.*; Shibata, Kaoru

Journal of Applied Crystallography, 51, p.1564 - 1570, 2018/12

It is demonstrated that quasielastic neutron scattering (QENS) is a novel and effective method to analyse atomic scale hydrogen transport processes occurring within a mineral crystal lattice. The method was previously characterized as sensitive for analysing the transport frequency and distance of highly diffusive hydrogen atoms or water molecules in condensed matter. Here are shown the results of its application to analyse the transport of much slower hydrogen atoms which are bonded into a crystal lattice as hydroxyls. Two types of hydrogen transport process were observed in brucite, Mg(OH)$$_{2}$$ : a jump within a single two-dimensional layer of the hydrogen lattice and a jump into the next nearest layer of it. These transport processes observed within the prototypical structure of brucite have direct implications for hydrogen transport phenomena occurring within various types of oxides and minerals having layered structures.

Journal Articles

Evaluation of residual stress relaxation in a rolled joint by neutron diffraction

Hayashi, Makoto*; Root, J. H.*; Rogge, R. B.*; Xu, P. G.

Quantum Beam Science (Internet), 2(4), p.21_1 - 21_16, 2018/12

The rolled joint of pressure tube, consisting of three axial symmetric parts, modified SUS403 stainless steel, Zr-2.5Nb pressure tube and Inconel-718, has been examined by neutron diffraction for residual stresses. It was heat treated at 350$$^{circ}$$C for 30, 130 and 635 hours to simulate the thermal aging of the rolled joint over the lifetime of the advanced thermal reactor at 288$$^{circ}$$C for 1, 5 and 30 years. The crystal lattice strains at various locations in the rolled joint before and after the aging treatments were measured by neutron diffraction and the residual stress distribution in the rolled joint was evaluated by using the Kroner elastic model and the generalized Hooke's law. In the crimp region of the rolled joint, it was found that the aging treatment had weak effect on the residual stresses in the Inconel and the SUS403. In the non-aged Zr-2.5Nb, the highest residual stresses were found near its interface with the SUS430. In the Zr-2.5Nb in the crimp region near its interface with the SUS430, the average compressive axial stress was -440 MPa, having no evident change during the long-time aging. In the Zr-2.5Nb outside closest to the crimp region, the tensile axial and hoop stresses were relieved during the 30 hours aging. The hoop stresses in the crimp region evolved from an average tensile stress of 80 MPa to an average compressive stress of 230 MPa after the 635 hours aging, suggesting that the rolled joint had a good long-term sealing ability against the leakage of high temperature water.

Journal Articles

Neutron transport

Tamura, Itaru

Hamon, 28(4), p.204 - 207, 2018/11

A Neutron guide is one of the devices to transport neutron beam for long distance without sacrificing much neutrons; therefore, it can supply neutrons to many experimental instruments distributed in a large experimental hall. Also, by using a curved guide, only the neutrons in a required energy range can be transported, and $$gamma$$ rays and fast neutrons can be effectively eliminated, therefore the signal to background ratio is improved. In addition, a neutron beam can be branched by applying curved guides. Neutron guides are also used to control the divergence angle and intensity of the neutron beam supplied to the neutron instrument.

Journal Articles

Shielding

Maekawa, Fujio

Hamon, 28(4), p.208 - 211, 2018/11

Adequate shielding of neutrons and associated $$gamma$$-rays is of importance from viewpoints of the radiation safety of researchers and good experimental data taking by reducing the background. This article introduces basics of neutron shielding, physics and suitable materials for neutron and $$gamma$$-ray shielding, and an example of conceptual shielding design for the 1-MW spallation neutron source of J-PARC MLF.

Journal Articles

Effect of the interface roughness correlation on the reflectivity in a neutron multilayer mirror

Maruyama, Ryuji; Yamazaki, Dai; Soyama, Kazuhiko

JPS Conference Proceedings (Internet), 22, p.011011_1 - 011011_5, 2018/11

Neutron multilayer mirrors are one of the most important optical elements for neutron scattering experiments. Good interface quality in terms of sharpness and smoothness plays a critical role in determining the performance of optical elements. We have shown that a multilayer with a large vertical correlation length and small lateral correlation length effectively suppresses the diffuse scattering intensity. In this study, the effect of the interface roughness correlation on the neutron reflectivity of the multilayer mirror is investigated using the reflectivity calculation based on the distorted wave Born approximation.

Journal Articles

Localized 5$$f^2$$ states in UPd$$_5$$Al$$_2$$ and valence crossover in the Vicinity of Heavy-Fermion superconductivity

Metoki, Naoto; Haga, Yoshinori; Yamamoto, Etsuji; Matsuda, Masaaki*

Journal of the Physical Society of Japan, 87(11), p.114712_1 - 114712_9, 2018/11

The localized 5$$f$$ states with 5$$f^2$$ ($$^3H_4$$) configuration of U$$^{4+}$$ ion have been revealed in UPd$$_5$$Al$$_2$$. We found that the low-lying states are the same as PrPd$$_5$$Al$$_2$$ flat orbitals with large $$J_z$$ are stabilized by a two-dimensional CEF potential in the unique crystal structure. The present study involves the valence crossover from tetravalent to trivalent in a series of AnPd$$_5$$Al$$_2$$, demonstrated by lattice and/or transport anomaly as well as many body effects in the vicinity of the boundary. The valence instability plays important role for the unusual heavy fermion superconductivity in NpPd$$_5$$Al$$_2$$.

Journal Articles

Gapless magnetic excitation in a heavily electron-doped antiferromagnetic phase of LaFeAsO$$_{0.5}$$D$$_{0.5}$$

Tamatsukuri, Hiromu*; Hiraka, Haruhiro*; Ikeuchi, Kazuhiko*; Iimura, Soshi*; Muraba, Yoshinori*; Nakamura, Mitsutaka; Sagayama, Hajime*; Yamaura, Junichi*; Murakami, Yoichi*; Kuramoto, Yoshio*; et al.

Physical Review B, 98(17), p.174415_1 - 174415_6, 2018/11

Magnetic excitations in a heavily electron-doped antiferromagnet, LaFeAsO$$_{0.5}$$D$$_{0.5}$$, have been investigated using powder inelastic neutron scattering. Unlike other parent compounds of the iron-based superconductors, the magnetic excitation gap in LaFeAsO$$_{0.5}$$D$$_{0.5}$$ was not detected down to the lowest measured temperature of 4 K. This result can be understood as a result of quasi-isotropy within the ab plane, which is consistent with the band calculation result that the $$d_{xy}$$ orbital plays the dominant role in the magnetism of LaFeAsO$$_{0.5}$$H$$_{0.5}$$. In addition, the intensities of the magnetic excitations in this phase are much stronger than those in nondoped LaFeAsO. Even in the paramagnetic phase, the magnetic excitation in LaFeAsO$$_{0.5}$$D$$_{0.5}$$ persists. These results corroborate recent studies showing that the electron doping enhances the localized nature in this system.

Journal Articles

Al-impurity-induced magnetic excitations in heavily over-doped La$$_{1.7}$$Sr$$_{0.3}$$Cu$$_{0.95}$$Al$$_{0.05}$$O$$_{4}$$

Ikeuchi, Kazuhiko*; Nakajima, Kenji; Kawamura, Seiko; Kajimoto, Ryoichi; Wakimoto, Shuichi; Suzuki, Kensuke*; Fujita, Masaki*

AIP Advances (Internet), 8(10), p.101318_1 - 101318_5, 2018/10

By means of inelastic neutron scattering, we measured magnetic excitations in a sizable single crystal of La$$_{1.7}$$Sr$$_{0.3}$$Cu$$_{0.95}$$Al$$_{0.05}$$O$$_{4}$$, which is an Al-substituted system of the heavily hole-doped cuprate system La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ with an effective concentration of holes of $$X_{rm eff}$$ = 0.25.

Journal Articles

Schottky specific heat of the lightly Mn-substituted electron-doped SrTiO$$_3$$

Okuda, Tetsuji*; Kajimoto, Ryoichi; Noda, Masaaki*; Kuwahara, Hideki*

AIP Advances (Internet), 8(10), p.101339_1 - 101339_5, 2018/10

Large changes in the low-temperature specific heat (low-$$TC$$) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr$$_{1-x}$$La$$_{x}$$TiO$$_{3}$$. The changes in the low-$$TC$$ are qualitatively well explained by the Schottky specific heat ($$C_mathrm{Sch}$$) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn$$^{4+}$$ ($$S$$ = 3/2) ions, but are Jahn-Teller active Mn$$^{3+}$$ ($$S$$ = 2) ions or mixtures of Mn$$^{3+}$$ and Mn$$^{2+}$$ ions. However, the actual numbers of localized spins estimated from $$C_mathrm{Sch}$$ are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.

Journal Articles

Reduction of the kicker impedance maintaining the performance of present kicker magnet at RCS in J-PARC

Shobuda, Yoshihiro; Irie, Yoshiro*; Takayanagi, Tomohiro; Togashi, Tomohito; Yamamoto, Masanobu; Yamamoto, Kazami

Journal of Physics; Conference Series, 1067, p.062007_1 - 062007_8, 2018/10

The present four-terminal kicker at the Rapid Cycling Synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) has the power-saving benefit due to the doubled excitation currents by shorting two-terminals. On the other hand, beam instabilities are excited by the kicker impedances. In this report, we describe a scheme to reduce the kicker impedances using diodes (nonlinear devices) with resistors, while retaining the benefit of the doubled kicker excitation currents.

Journal Articles

Baseband simulation model of the vector rf voltage control system for the J-PARC RCS

Tamura, Fumihiko; Sugiyama, Yasuyuki*; Yoshii, Masahito*; Omori, Chihiro*; Yamamoto, Masanobu; Shimada, Taihei; Nomura, Masahiro; Hasegawa, Katsushi*; Hara, Keigo*; Furusawa, Masashi*

Journal of Physics; Conference Series, 1067, p.072030_1 - 072030_6, 2018/10

Vector RF voltage feedback control for the wideband magnetic alloy cavity of the J-PARC RCS is considered to be employed to compensate the heavy beam loading caused by high intensity proton beams. A prototype system of multiharmonic RF vector voltage control has been developed and is under testing. To characterize the system performance, full RF simulations could be performed by software like Simulink, while the software is proprietary and expensive. Also, it requires much computing power and time. We performed the simplified baseband simulations of the system in z-domain by using free software, Scilab and Python control library. It seems to be beneficial for searching the parameters that the baseband simulation can be performed quickly. In this presentation, we present the setup and results of the simulations. The simulations well reproduce the open and closed loop responses of the prototype system.

Journal Articles

Development of a new modular switch using a next-generation semiconductor

Takayanagi, Tomohiro; Ueno, Tomoaki*; Horino, Koki*

Journal of Physics; Conference Series, 1067, p.082019_1 - 082019_6, 2018/10

Semiconductor switches using SiC-MOSFETs are expected to substitute the thyratron, and they are designed by connecting many semiconductor switches in parallel-series for high power operation. In order to suppress the common-mode noise caused by switching, it is common to form a symmetrical circuit. However, as the number of parallel connections in the horizontal direction increases, the length of the parallel circuit becomes longer, and the output waveform is distorted due to time lag between the circuits. Therefore, we propose a radially-symmetrical type module switch which can equalize the circuit length regardless of the number of parallel circuit. Even in circuit fabrication, it was easy for the radially-symmetrical type to make the distances of the parallel circuits equal, shorten the circuit length, and make the circuit impedance lower than the line-symmetrical type. It was confirmed that the radially-symmetrical type circuit is very useful for constructing multiple circuits. The design and preliminary test results of two types of switch circuits, radially-symmetrical type and general line-symmetrical type are presented here.

Journal Articles

Evaluation of deformation and fracture behavior of reinforced concrete using neutron beam technique

Ueno, Kazuki*; Suzuki, Hiroshi; Koyama, Taku*; Nishio, Yuhei*; Kanematsu, Manabu*

Konkurito Kozobutsu No Hoshu, Hokyo, Appuguredo Rombun Hokokushu, 18, p.647 - 650, 2018/10

本研究では、中性子イメージング技術と画像処理技術を組み合わせることで、コンクリート内部に分散したガドリニウムマーカの動きを精度よく評価できる技術を開発した。次に、中性子イメージング技術と中性子回折法を組み合わせて、鉄筋コンクリートの引張載荷時の付着劣化挙動を評価した。その結果、中性子イメージング技術により得られるコンクリートの変形挙動と、中性子回折により得られる鉄筋の応力分布を比較・検討することで、鉄筋コンクリートの付着劣化挙動の評価が可能になることを示した。

Journal Articles

Convergence behavior in line profile analysis using convolutional multiple whole-profile software

Kumagai, Masayoshi*; Uchida, Tomohiro*; Murasawa, Kodai*; Takamura, Masato*; Ikeda, Yoshimasa*; Suzuki, Hiroshi; Otake, Yoshie*; Hama, Takayuki*; Suzuki, Shinsuke*

Materials Research Proceedings, Vol.6, p.57 - 62, 2018/10

The convergence behavior of the parameters related to microstructural characteristics $$a$$-$$e$$ was studied during optimizations in a common line profile analysis software program based on the convolutional multiple whole profile (CMWP) method. The weighted sums of squared residual (WSSR) was a criterion of the optimization. The parameters $$b$$ and $$d$$, which are related to the dislocation density and to the crystallite size, respectively, strongly affect the line profile shape. Therefore, the distributions of WSSRs on the space parameters $$b$$ and $$d$$ were first observed. The variation trajectory of parameters $$b$$ and $$d$$ during iterative calculations with several values of parameter $$e$$ was then observed, along with the variations when all of the parameters were variable. In the case where only three parameters were variable, we found that a smaller initial value of $$e$$ should be chosen to ensure stability of the calculations. In the case where all parameters were variable, although all of the results converged to similar values, they did not precisely agree. To attain accurate optimum values, a two-step procedure is recommended.

Journal Articles

Spherical neutron polarimetry under high pressure for a multiferroic delafossite ferrite

Terada, Noriki*; Qureshi, N.*; Chapon, L. C.*; Osakabe, Toyotaka

Nature Communications, 9, p.4368_1 - 4368_9, 2018/10

We have succeeded in carrying out the first spherical neutron polarimetry (SNP) experiments in conjunction with the application of pressure, working with the multiferroic delafossite CuFeO$$_{2}$$ and using the newly developed nonmagnetic hybrid anvil high pressure cell (HAC). This work determined the detailed magnetic structures in the pressure-induced ferroelectric phases of this material, as well as nonpolar phases at ambient pressure. The present study provides evidence that SNP measurements are viable even in combination with high pressure conditions.

Journal Articles

Two inherent crossovers of the diffusion process in glass-forming liquids

Kofu, Maiko; Faraone, A.*; Tyagi, M.*; Nagao, Michihiro*; Yamamuro, Osamu*

Physical Review E, 98(4), p.042601_1 - 042601_6, 2018/10

We report on incoherent quasielastic neutron scattering measurements examining a self-diffusion process in two types of glass-forming liquids, namely a molecular liquid (3-methylpentane) and an ionic liquid (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide). We have experimentally demonstrated that both liquids exhibit two crossovers in the momentum transfer ($$Q$$) dependence of the self-correlation function, which is basically described by the stretched exponential function, $$exp [-(t/tau)^beta]$$. The first crossover point ($$Q approx 0.2$$~$AA$^{-1}$$) corresponds to a crossover from Fickian ($$beta = 1$$) to non-Fckian ($$beta ne 1$$) diffusion attributed to dynamical correlation. On the other hand, the second one at $$Q approx 0.8$$~$AA$^{-1}$$ is associated with the crossover from Gaussian to non-Gaussian behavior. It is remarkable that the stretching exponent $$beta$$ gradually changes in between the two crossover points. We consider that the two crossovers are the universal feature for glass-forming liquids.

Journal Articles

Present status of the J-PARC cesiated rf-driven H$$^-$$ ion source

Shinto, Katsuhiro; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Takagi, Akira*; Shibata, Takanori*; Nammo, Kesao*; Namekawa, Yuya*; Ueno, Akira; Oguri, Hidetomo

AIP Conference Proceedings 2011, p.050018_1 - 050018_3, 2018/09

Operation of a cesiated RF-driven negative hydrogen ion source was initiated in September 2014 in response to the requirements of beam current upgrade in J-PARC linac. Delivery of the required beam current from the ion source to the J-PARC accelerators has been successfully performed. In 2016-2017 campaign, continuous operation of the ion source for approximately 1,840 hours (RUN#75 from April to July 2017) was achieved with beam current, macro pulse width and repetition of 45 mA, 500 $$mu$$s and 25 Hz, respectively. We present the operation status of the ion source and a high current H$$^-$$ beam with 70 mA extracted from the ion source for the further high-power upgrade in J-PARC accelerators.

Journal Articles

Observation of beam current fluctuation extracted from an RF-driven H$$^-$$ ion source

Shinto, Katsuhiro; Shibata, Takanori*; Miura, Akihiko; Miyao, Tomoaki*; Wada, Motoi*

AIP Conference Proceedings 2011, p.080016_1 - 080016_3, 2018/09

In J-PARC, peak H$$^-$$ current of several tens mA is produced from a cesiated hydrogen plasma generated by a solid-state RF amplifier with the frequency of 2 MHz. In case of the high-intensity H$$^-$$ beam extracted from the ion source, the plasma density in the source chamber is so high that the ion sheath around the beam extraction area follows the RF oscillation. Because the ion plasma frequency defined by the ion density is much higher than the driving frequency. The potential fluctuation of the plasma is combined with the driving RF electric field and causes motion of charged particles in the plasma some changes. As a result, the H$$^-$$ beam extracted from the source plasma also fluctuates. The beam current signal from a Faraday cup was measured by a spectrum analyzer. A powerful frequency component at 2 MHz which is as same as that of the RF amplifier was also observed after the acceleration of RFQ linac located at the downstream of the ion source.

Journal Articles

Observation of plasma density oscillation with doubled value of RF frequency in J-PARC RF ion source

Shibata, Takanori*; Shinto, Katsuhiro; Takagi, Akira*; Oguri, Hidetomo; Ikegami, Kiyoshi*; Okoshi, Kiyonori; Nammo, Kesao*; Naito, Fujio*

AIP Conference Proceedings 2011, p.020008_1 - 020008_3, 2018/09

Balmer alpha line intensity in J-PARC Radio Frequency (RF) negative hydrogen ion source has been measured by photometry measurement. The line intensity shows several interesting time characteristics in different phases; (1) 2 MHz (RF frequency) oscillation just after plasma ignition and (2) 4 MHz (doubled RF frequency) and 2 MHz coupled oscillation in the steady-state. From the comparison between numerical analysis, it has been explained that electron acceleration in inductively coupled electromagnetic field takes place with 4 MHz frequency which results in the 4 MHz line intensity oscillation. From the understandings of the background physics, we can conclude that this fast photometry measurement is a good diagnosis tool to understand whether RF plasma is in E-mode or H-mode in general RF ion sources.

Journal Articles

Thermal behavior, structure, dynamic properties of aqueous glycine solutions confined in mesoporous silica MCM-41 investigated by X-ray diffraction and quasi-elastic neutron scattering

Yoshida, Koji*; Inoue, Takuya*; Torigoe, Motokatsu*; Yamada, Takeshi*; Shibata, Kaoru; Yamaguchi, Toshio*

Journal of Chemical Physics, 149(12), p.124502_1 - 124502_10, 2018/09

Differential scanning calorimetry, X-ray diffraction, and quasi-elastic neutron scattering (QENS) measurements of aqueous glycine solutions confined in mesoporous silica (MCM-41) were performed at different glycine concentrations, pH, and loading ratio (= mass of glycine solution / mass of dry MCM-41) in the temperature range from 305 to 180 K to discuss the confinement effect on the thermal behavior, the structure, and the dynamic properties of the solutions.

17935 (Records 1-20 displayed on this page)