Updated on 2025/09/01

写真a

 
SAITO Masatoshi
 
Organization
Academic Assembly Institute of Medicine and Dentistry Health Sciences Professor
Faculty of Medicine School of Health Sciences Professor
Graduate School of Health Sciences Health Sciences Professor
Title
Professor
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Degree

  • 博士(理学) ( 1992.3   新潟大学 )

Research Interests

  • 物質構造科学

  • 医用物理学

  • 固体物性

Research Areas

  • Life Science / Radiological sciences

  • Natural Science / Semiconductors, optical properties of condensed matter and atomic physics

  • Nanotechnology/Materials / Metallic material properties

Research History (researchmap)

  • Niigata University   Professor

    2010.4

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  • Niigata University   Associate Professor

    2000.4 - 2010.3

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  • Tohoku University   Lecturer

    1999.4 - 2000.3

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  • Tohoku University   Research Assistant

    1992.4 - 1999.3

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Research History

  • Niigata University   Faculty of Medicine School of Health Sciences   Professor

    2010.4

  • Niigata University   Graduate School of Health Sciences Health Sciences   Professor

    2010.4

  • Niigata University   Graduate School of Health Sciences Health Sciences   Professor

    2010.4

  • Niigata University   Faculty of Medicine School of Health Sciences   Associate Professor

    2007.4 - 2010.3

  • Niigata University   Faculty of Medicine School of Health Sciences   Associate Professor (as old post name)

    2000.4 - 2007.3

Education

  • Niigata University   Graduate School of Science and Technology   物質科学専攻

    1989.4 - 1992.3

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    Country: Japan

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  • Niigata University   理学研究科   物理学専攻

    1987.4 - 1989.3

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    Country: Japan

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  • Niigata University   Faculty of Science   Department of Physics

    - 1987.3

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    Country: Japan

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Professional Memberships

 

Papers

  • A simple algorithm to derive virtual non‐contrast electron density from dual‐energy computed tomography data for radiotherapy treatment planning Reviewed

    Masatoshi Saito, Tatsuki Saito

    Medical Physics   52 ( 5 )   3107 - 3116   2025.1

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    Authorship:Lead author, Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    Abstract

    Background

    The use of iodinated contrast‐enhancing agents in computed tomography (CT) improves the visualization of relevant structures for radiotherapy treatment planning (RTP). However, it can lead to dose calculation errors by incorrectly converting a CT number to electron density.

    Purpose

    This study aimed to propose an algorithm for deriving virtual non‐contrast (VNC) electron density from dual‐energy CT (DECT) data. This algorithm was developed by extending the formula previously developed by Saito, which enables the calculation of the electron density of human tissue through weighted subtraction of CT numbers acquired from DECT scans.

    Methods

    To investigate the feasibility of the proposed VNC algorithm, we performed analytical DECT image simulations at 90 and 150 kV/Sn on virtual phantoms consisting of various tissue/iodine surrogates with known mass densities and elemental compositions. Two different shapes of phantoms made of water‐mimicking surrogates were generated as inputs: a circular phantom (33 cm diameter) for calibration and an elliptical phantom (33 cm width and 28 cm height) for validation. The circular phantom was equipped with inserts of human‐tissue‐mimicking substitutes, pure water, and iodine‐enhanced soft‐tissue substitutes (2, 5, 10, and 15 mg/mL iodine). The elliptical phantom contained inserts of reference human tissues, iodine‐enhanced soft‐tissue substitutes (2, 2.5, 5, 7.5, 10, 15, and 20 mg/mL iodine), and a 10‐mm‐diameter core of 4 mg/mL iodine surrounded by a blood‐mimicking base material. The performance of the proposed algorithm was evaluated by comparing the accuracy of VNC electron densities with those of non‐contrast (NC) base materials (water‐ or blood‐mimicking surrogates).

    Results

    The derived algorithm enabled the calculation of VNC electron density in a manner similar to that of unenhanced human tissues by adapting a VNC‐specific weighting factor, thereby eliminating the intermediate step of converting CT numbers to electron density. The simulated results showed that the VNC algorithm could almost completely remove the contrast in the electron density image between iodine‐enhanced and base materials. The relative deviations of simulated VNC electron density values from the corresponding pre‐contrast value were within ± 0.4% for all tested materials, with a root‐mean‐square error (RMSE) of 0.2%.

    Conclusions

    Within the limits of the analytical DECT image simulation used in this study, the simple VNC algorithm could effectively provide accurate VNC electron densities for iodine‐enhanced materials. This may allow the contrast agent to be used for CT scans during RTP without compromising dose calculation accuracy.

    DOI: 10.1002/mp.17648

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  • Technical note: Implementing MRI/CT‐based elemental concentration data to Monte Carlo simulation for yielding positron emitters in proton therapy Reviewed

    Masatoshi Saito, Ryuga Matsumoto

    Medical Physics   51 ( 4 )   2861 - 2870   2023.12

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    Abstract

    Background

    The elemental concentration (especially oxygen and carbon) and mass density must be accurately assigned to perform Monte Carlo (MC) simulations for predicting proton‐induced nuclear reactions in the human body. We recently proposed an approach to quantify elemental concentrations and mass densities of human soft tissues from water content (WC) data obtained by quantitative magnetic resonance (MR) imaging (which we called “MRWC”).

    Purpose

    This study presents the first implementation of MRWC‐derived elemental concentrations and mass densities as complementary inputs into MC simulations on a virtual head phantom, and demonstrates the simulation of positron emitter production yields in proton therapy.

    Methods

    An MC code, PHITS, was used to simulate proton therapy with a monoenergetic 140 MeV beam for a digital head phantom provided by BrainWeb. Three different head images were synthesized as inputs: a conventional CT image, an ideal CT image as a reference, and a WC image coupled with the bone‐only CT image for a hybrid approach (MRWC/CT). Thereafter, the performance of the MRWC/CT method was evaluated by comparing its accuracy in predicting the production yields of positron emitters (<sup>11</sup>C and <sup>15</sup>O) with the gold‐standard CT‐only method.

    Results

    The MRWC/CT method could predict <sup>11</sup>C and <sup>15</sup>O production yield maps that closely resembled the corresponding reference maps, while the CT‐only method failed. The structural similarity index measures between the reference and CT‐ or MRWC/CT‐derived maps were improved from 0.67 (CT‐only) to 0.87 (MRWC/CT) for <sup>11</sup>C and 0.76 (CT‐only) to 0.93 (MRWC/CT) for <sup>15</sup>O. Furthermore, applying post‐processing normalizations to account for elemental density variations in the production yields of positron emitters facilitated the determination of distal fall‐off positions in depth activity profiles.

    Conclusion

    At least in the head area, the MRWC/CT method demonstrated potential for more precise predictions of proton‐induced positron emitter distributions via MC simulations than that of the CT‐only method.

    DOI: 10.1002/mp.16896

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  • MRI‐based quantification of carbon and oxygen concentrations in human soft tissues for range verification in proton therapy Reviewed

    Masatoshi Saito

    Medical Physics   50 ( 9 )   5671 - 5681   2023.3

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    ABSTRACT

    Background

    In‐situ range verification of particle therapy based on the detection of secondary emitted radiation requires highly accurate assignment of elemental concentrations (particularly carbon and oxygen) in the human body.

    Purpose

    A method for quantitatively predicting carbon and oxygen concentrations in human soft tissues is proposed. This method relies on an empirical one‐to‐one correspondence between the mass fraction and water content (WC), which is a measurable tissue quantity based on magnetic resonance (MR) imaging (referred to as “MRWC‐based method”).

    Methods

    A numerical analysis of the MRWC‐based method was performed for 47 standard human soft tissues tabulated in the literature as objects of interest with unknown mass fractions of the four main elements—C, O, H, and N. Thereafter, the method was evaluated in terms of the mass‐fraction quantification accuracy by comparing it with the gold‐standard CT‐based method developed by Schneider et al. The MRWC‐based method was also applied to the MR imaging data of a virtual head phantom obtained from a three‐dimensional MRI‐simulated brain database.

    Results

    The predicted mass fractions in a range of human soft tissues were in better agreement with the reference values than those predicted by the CT‐based method. The mean absolute errors of the predicted mass% values for the overall standard soft tissues could be reduced from 4.8 percentage points (pp) (CT‐based) to 0.5 pp (MRWC‐based) for carbon and from 5.2 pp (CT‐based) to 0.4 pp (MRWC‐based) for oxygen. The application to the simulated MRI data confirmed the capability of the sufficient recognition of the boundaries between the white matter and gray matter in the brain that could not be realized by the CT‐based method. Thus, the MRWC‐based method exhibits superior performance in the prediction of carbon and oxygen concentrations in soft tissues.

    Conclusions

    This study is limited to a proof‐of‐concept scope but demonstrates the feasibility of the MRWC‐based method for the generation of elemental images of human soft tissues from MRI‐derived water‐content images.

    DOI: 10.1002/mp.16353

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.16353

  • Quadratic relation for mass density calibration in human body using dual‐energy CT data Reviewed

    Masatoshi Saito

    Medical Physics   48 ( 6 )   3065 - 3073   2021.6

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    DOI: 10.1002/mp.14899

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.14899

  • Proton dose calculation based on converting dual-energy CT data to stopping power ratio (DEEDZ-SPR): a beam-hardening assessment Reviewed International journal

    Sodai Tanaka, Yoshiyuki Noto, Satoru Utsunomiya, Takaaki Yoshimura, Taeko Matsuura, Masatoshi Saito

    Physics in Medicine & Biology   65 ( 23 )   235046 - 235046   2020.12

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    To achieve an accurate stopping power ratio (SPR) prediction in particle therapy treatment planning, we previously proposed a simple conversion to the SPR from dual-energy (DE) computed tomography (CT) data via electron density and effective atomic number (Z eff) calibration (DEEDZ-SPR). This study was conducted to carry out an initial implementation of the DEEDZ-SPR conversion method with a clinical treatment planning system (TPS; VQA, Hitachi Ltd., Tokyo) for proton beam therapy. Consequently, this paper presents a proton therapy plan for an anthropomorphic phantom to evaluate the stability of the dose calculations obtained by the DEEDZ-SPR conversion against the variation of the calibration phantom size. Dual-energy x-ray CT images were acquired using a dual-source CT (DSCT) scanner. A single-energy CT (SECT) scan using the same DSCT scanner was also performed to compare the DEEDZ-SPR conversion with the SECT-based SPR (SECT-SPR) conversion. The scanner-specific parameters necessary for the SPR calibration were obtained from the CT images of tissue substitutes in a calibration phantom. Two calibration phantoms with different sizes (a 33 cm diameter phantom and an 18 cm diameter phantom) were used for the SPR calibrations to investigate the beam-hardening effect on dosimetric uncertainties. Each set of calibrated SPR data was applied to the proton therapy plan designed using the VQA TPS with a pencil beam algorithm for the anthropomorphic phantom. The treatment plans with the SECT-SPR conversion exhibited discrepancies between the dose distributions and the dose-volume histograms (DVHs) of the 33 cm and 18 cm phantom calibrations. In contrast, the corresponding dose distributions and the DVHs obtained using the DEEDZ-SPR conversion method coincided almost perfectly with each other. The DEEDZ-SPR conversion appears to be a promising method for providing proton dose plans that are stable against the size variations of the calibration phantom and the patient.

    DOI: 10.1088/1361-6560/abae09

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    Other Link: https://iopscience.iop.org/article/10.1088/1361-6560/abae09/pdf

  • Simulation of photon-counting detectors for conversion of dual-energy-subtracted computed tomography number to electron density Reviewed

    Masatoshi Saito

    Radiological Physics and Technology   12 ( 1 )   105 - 117   2019.3

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:Springer Science and Business Media LLC  

    DOI: 10.1007/s12194-018-00497-0

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    Other Link: http://link.springer.com/article/10.1007/s12194-018-00497-0/fulltext.html

  • Comment on: Methodological accuracy of image‐based electron density assessment using dual‐energy computed tomography [Med. Phys. 44(6), 2429–2437 (2017)] Reviewed

    Masatoshi Saito

    Medical Physics   46 ( 2 )   1075 - 1076   2019.2

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    DOI: 10.1002/mp.13052

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    Other Link: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.13052

  • Comment on: Dual-energy CT quantitative imaging: A comparison study between twin-beam and dual-source CT scanners [Med. Phys. 44(1), 171-179] Reviewed

    Masatoshi Saito

    Medical Physics   45 ( 8 )   3996 - 3996   2018.8

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  • Simplified derivation of stopping power ratio in the human body from dual-energy CT data Reviewed

    Masatoshi Saito, Shota Sagara

    MEDICAL PHYSICS   44 ( 8 )   4179 - 4187   2017.8

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    DOI: 10.1002/mp.12386

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  • A simple formulation for deriving effective atomic numbers via electron density calibration from dual-energy CT data in the human body Reviewed

    Masatoshi Saito, Shota Sagara

    MEDICAL PHYSICS   44 ( 6 )   2293 - 2303   2017.6

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    DOI: 10.1002/mp.12176

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  • Technical Note: Relation between dual-energy subtraction of CT images for electron density calibration and virtual monochromatic imaging Reviewed

    Masatoshi Saito

    MEDICAL PHYSICS   42 ( 7 )   4088 - 4093   2015.7

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    DOI: 10.1118/1.4921999

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  • Initial implementation of the conversion from the energy-subtracted CT number to electron density in tissue inhomogeneity corrections: An anthropomorphic phantom study of radiotherapy treatment planning Reviewed

    Masayoshi Tsukihara, Yoshiyuki Noto, Ryuta Sasamoto, Takahide Hayakawa, Masatoshi Saito

    MEDICAL PHYSICS   42 ( 3 )   1378 - 1388   2015.3

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    DOI: 10.1118/1.4908207

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  • Technical Note: Exploring the limit for the conversion of energy-subtracted CT number to electron density for high-atomic-number materials Reviewed

    Masatoshi Saito, Masayoshi Tsukihara

    MEDICAL PHYSICS   41 ( 7 )   071701   2014.7

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    DOI: 10.1118/1.4881327

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  • Conversion of the energy-subtracted CT number to electron density based on a single linear relationship: an experimental verification using a clinical dual-source CT scanner Reviewed

    Masayoshi Tsukihara, Yoshiyuki Noto, Takahide Hayakawa, Masatoshi Saito

    PHYSICS IN MEDICINE AND BIOLOGY   58 ( 9 )   N135 - N144   2013.5

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    DOI: 10.1088/0031-9155/58/9/N135

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  • Potential of dual-energy subtraction for converting CT numbers to electron density based on a single linear relationship Reviewed

    Masatoshi Saito

    MEDICAL PHYSICS   39 ( 4 )   2021 - 2030   2012.4

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    DOI: 10.1118/1.3694111

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  • Optimized low-kV spectrum of dual-energy CT equipped with high-kV tin filtration for electron density measurements Reviewed

    Masatoshi Saito

    Medical Physics   38 ( 6 )   2850 - 2858   2011

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    DOI: 10.1118/1.3584200

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  • Structural Study of Zr_<50>Cu_<50> Amorphous Alloy by Anomalous X-ray Scattering Coupled with Reverse Monte-Carlo Simulation

    KAWAMATA T., YOKOYAMA Y., SAITO M., SUGIYAMA K., WASEDA Y.

    Materials Transactions, JIM   51 ( 10 )   1796 - 1801   2010.10

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    Anomalous X-ray scattering (AXS) analysis was applied for the structural analysis of a rapidly quenched Zr<SUB>50</SUB>Cu<SUB>50</SUB> amorphous alloy. The present AXS analysis provided the environmental structural information round Cu and Zr, and the subsequent reverse Monte Carlo (RMC) simulation allowed us to obtain three partial pair distribution functions together with a three-dimensional structural model. The Voronoi polyhedral analysis of the nearest-neighbor region confirms that the structural features are similar to those of the dense random packing of hard spheres (DRPHS) model. The chemical oscillatory structure composed of alternating Cu-rich and Zr-rich coordination shells was realized in the middle range, up to 0.8 nm. The shell structure is suggested to be one of the fundamental structural features of medium-range ordering in the Zr<SUB>50</SUB>Cu<SUB>50</SUB> amorphous alloy.

    DOI: 10.2320/matertrans.MAW201016

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  • Technical note: Optimization for improved tube-loading efficiency in the dual-energy computed tomography coupled with balanced filter method Reviewed

    Masatoshi Saito

    Medical Physics   37 ( 8 )   4182 - 4185   2010

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    DOI: 10.1118/1.3467754

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  • Electron density distribution in liquid Ga estimated from the anomalous X-ray scattering measurements Reviewed

    Masatoshi Saito, Kazumasa Sugiyama, Yoshio Waseda

    High Temperature Materials and Processes   29 ( 5-6 )   393 - 403   2010

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Walter de Gruyter GmbH and Co. KG  

    DOI: 10.1515/HTMP.2010.29.5-6.393

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  • Structural study of liquid LiNbO3 by the high-temperature energy dispersive X-ray diffraction coupled with reverse Monte Carlo simulation Reviewed

    K. Sugiyama, M. Saito, Y. Waseda

    Journal of Crystal Growth   311 ( 3 )   966 - 969   2009.1

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    DOI: 10.1016/j.jcrysgro.2008.09.117

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  • Spectral optimization for measuring electron density by the dual-energy computed tomography coupled with balanced filter method Reviewed

    Masatoshi Saito

    Medical Physics   36 ( 8 )   3631 - 3642   2009

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    DOI: 10.1118/1.3157098

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  • Dielectric screening properties in molten noble-metal halides Reviewed

    Shigeki Matsunaga, Masatoshi Saito, Takahiro Koishi, Shigeru Tamaki

    JOURNAL OF ALLOYS AND COMPOUNDS   452 ( 1 )   182 - 187   2008.3

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    DOI: 10.1016/j.jallcom.2006.12.161

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  • Dual-energy approach to contrast-enhanced mammography using the balanced filter method: Spectral optimization and preliminary phantom measurement Reviewed

    Masatoshi Saito

    MEDICAL PHYSICS   34 ( 11 )   4236 - 4246   2007.11

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    DOI: 10.1118/1.2790841

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  • Dielectric screening effects in molten AgI-AgBr system Reviewed

    S. Matsunaga, M. Saito, T. Koishi, S. Tamaki

    Molecular Simulation   33 ( 1-2 )   153 - 158   2007.1

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    DOI: 10.1080/08927020601067532

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  • Dielectric screening properties in molten salts Reviewed

    Takahiro Koishi, Masatoshi Saito, Shigeki Matsunaga, Shigeru Tamaki

    PHYSICS AND CHEMISTRY OF LIQUIDS   45 ( 2 )   181 - 196   2007

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    DOI: 10.1080/00319100601106713

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  • The Structural Analysis of Non-crystalline Materials by the Anomalous X-ray Scattering Coupled with Reverse Monte Carlo Simulation Reviewed

    SUGIYAMA Kazumasa, SAITO Masatoshi

    Nihon Kessho Gakkaishi   48 ( 1 )   81 - 85   2006.2

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    Language:Japanese   Publisher:The Crystallographic Society of Japan  

    The anomalous X-ray scattering (AXS) coupled with model calculation using reverse Monte Carlo (RMC) simulation, has recently received much attention for analyzing the middlerange ordering for non-crystalline materials. The usefulness of this new method was demonstrated with some selected examples of a Bi<SUB>30</SUB>Ga<SUB>70</SUB>high temperature liquid alloy and an amorphous ZrO<SUB>2</SUB>.

    DOI: 10.5940/jcrsj.48.81

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  • Structural characterization for a complex system by obtaining middle-range ordering Reviewed

    Yoshio Waseda, Shigeru Suzuki, Masatoshi Saito

    Characterization of Corrosion Products on Steel Surfaces   7   77 - 104   2006

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    Language:English   Publishing type:Part of collection (book)   Publisher:Springer Berlin Heidelberg  

    DOI: 10.1007/978-3-540-35178-8_5

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  • Quasimonochromatic x-ray computed tomography by the balanced filter method using a conventional x-ray source Reviewed

    M Saito

    MEDICAL PHYSICS   31 ( 12 )   3436 - 3443   2004.12

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    DOI: 10.1118/1.1819553

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  • Fe (O, OH)(6) network structure of rusts formed on weathering steel surfaces

    M Kimura, T Suzuki, G Sigesato, M Saito, S Suzuki, H Kihira, K Tanabe, Y Waseda

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   66 ( 3 )   166 - 175   2002.3

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    DOI: 10.2320/jinstmet1952.66.3_166

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  • Effective Pair Potentials of Molten AgBr Estimated from Experimental Partial Structure Factors

    MITEV Pavlin Dakev, SAITO Masatoshi, WASEDA Yoshio

    MATERIALS TRANSACTIONS   42 ( 5 )   829 - 832   2001.5

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    Language:English   Publisher:The Japan Institute of Metals and Materials  

    Three effective pair potentials of Ag&ndash;Br, Br&ndash;Br and Ag&ndash;Ag pairs in molten AgBr have been calculated from measured partial structural data by applying the modified hypernetted-chain equation coupled with a predictor-corrector method. The present results of pair potentials were also compared with model potentials originally proposed by Vashishta and Rahman. The resultant potentials suggest two characteristic features. One is the relatively shallow minimum in the interaction of Ag&ndash;Br pair in the first nearest neighbor region at 0.27&thinsp;nm, in comparison with the model potential case. The other is both positive and negative deviation from the simple asymptotic form detected in the interaction of Br&ndash;Br pair in the range of 0.3&sim;1.1&thinsp;nm. These results may be attributed to a particular structural feature of molten AgBr, suggesting not only the purely ionic character.

    DOI: 10.2320/matertrans.42.829

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  • Transport Properties of Superionic Conducting Glasses (AgX)_<0.4>(Ag_2O)_<0.3>(GeO_2)_<0.3> (X=I, Br, Cl)

    KANG Shinchul, SAITO Masatoshi, JACOB K. Thomas, WASEDA Yoshio

    Materials Transactions, JIM   41 ( 12 )   1670 - 1674   2000.12

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    Language:English   Publisher:The Japan Institute of Metals  

    In order to identify the dominant mechanism of ionic conduction, the electrical conductivity and ionic mobility of the glasses (AgX)<SUB>0.4</SUB>(Ag<SUB>2</SUB>O)<SUB>0.3</SUB>(GeO<SUB>2</SUB>)<SUB>0.3</SUB> (X=I, Br, Cl) were measured separately in the temperature range from 293 to 393 K by coupling the AC technique with the TIC method. Electronic conductivity was also measured at 293 K by the Wagner polarization method. The total electrical conductivity of these glasses was found to be as high as 10<SUP>&minus;1</SUP> &Omega;<SUP>&minus;1</SUP> m<SUP>&minus;1</SUP>, and the mobility about 10<SUP>&minus;6</SUP> m<SUP>2</SUP> V<SUP>&minus;1</SUP> s<SUP>&minus;1</SUP>. The variation of total electrical conductivity and mobility at constant temperature and composition with the type of halide occurred in the sequence, Cl<Br<I. For each composition, both conductivity and mobility increased with temperature. The mobile ion concentration was found to be about 10<SUP>23</SUP> m<SUP>&minus;3</SUP> at 293 K, and it was insensitive to the type of halide as well as temperature. The results suggest that the change in ionic conductivity with the temperature and the type of halide present is mainly attributable to the change in ionic mobility rather than carrier concentration. Moreover, the electronic conductivity was found to be about 10<SUP>&minus;6</SUP> &Omega;<SUP>&minus;1</SUP> m<SUP>&minus;1</SUP> at 293 K. Thus, the electronic contribution to the total conductivity is negligibly small.

    DOI: 10.2320/matertrans1989.41.1670

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  • Partial structural functions of molten copper halides CuX (X = Br, I) estimated from the anomalous x-ray scattering measurements

    Y. Waseda, S. Kang, K. Sugiyama, M. Kimura, M. Saito

    Journal of Physics Condensed Matter   12   2000.12

  • Structural Study of Amorphous Ge 50Al 40Cr 10 Alloy

    Louzguine Dmitri, Saito Masatoshi, Waseda Yoshio, Inoue Akihisa

    J Phys Soc Jpn   68 ( 7 )   2298 - 2303   1999.7

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    Language:English   Publisher:The Physical Society of Japan (JPS)  

    The structure of an amorphous Ge50Al40Cr10 alloy was studied by conventional X-ray diffraction, anomalous X-ray scattering and transmission electron microscopy including high-resolution imaging. The anomalous X-ray scattering profiles were obtained at Ge and Cr K-absorption edges. Structural information in the form of interference function obtained by the experimental methods was checked for its correctness by using the reverse Monte Carlo simulation method. The structure of the alloy studied is discussed on the basis of transmission electron microscopy images, an ordinary radial distribution function, partial structure functions and partial pair distribution functions.

    DOI: 10.1143/JPSJ.68.2298

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  • Partial structural functions of molten AgBr estimated from the anomalous X-ray scattering data coupled with neutron diffraction

    Masatoshi Saito, Shinchul Kang, Kazumasa Sugiyama, Yoshio Waseda

    Journal of the Physical Society of Japan   68 ( 6 )   1932 - 1938   1999.1

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    Language:English   Publisher:The Physical Society of Japan (JPS)  

    DOI: 10.1143/JPSJ.68.1932

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  • Structure and Magnetic Properties of La(Co<SUB>1-x</SUB>Mn<SUB>x</SUB>)<SUB>13</SUB> Crystlline and Amorphous Alloys

    K. Asada, A. Fujita, S.G. Kim, K. Fukamichi, E. Matsubara, M. Saito, Y. Waseda

    J. Magn. Soc. Jpn.   23   480 - 482   1999

  • Structural Study of Pd-Based Amorphous Alloys with Wide Supercooled Liquid Region by Anomalous X-ray Scattering

    Park Changyong, Saito Masatoshi, Waseda Yoshio, Nishiyama Nobuyuki, Inoue Akihisa

    Materials Transactions, JIM   40 ( 6 )   491 - 497   1999

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    Language:English   Publisher:The Japan Institute of Metals  

    The anomalous X-ray scattering (AXS) measurements have been made to determine the local ordering structures around Ni and Cu in Pd<SUB>40</SUB>Ni<SUB>10</SUB>Cu<SUB>30</SUB>P<SUB>20</SUB> and Pd<SUB>40</SUB>Ni<SUB>40</SUB>P<SUB>20</SUB> alloys in both the liquid and amorphous state using the synchrotron radiation at incident X-ray energies close to the <I>K</I>-absorption edges of Ni and Cu. A characteristic small hump was clearly found at <I>r</I>=0.37 nm in the environmental radial distribution function (RDF) around Cu in liquid and amorphous Pd<SUB>40</SUB>Ni<SUB>10</SUB>Cu<SUB>30</SUB>P<SUB>20</SUB> alloy. Such peak was not detected in the environmental RDF around Ni, and the local atomic arrangement around Ni was found to be similar to the Pd<SUB>40</SUB>Ni<SUB>40</SUB>P<SUB>20</SUB> case. These experimental facts can be described when considering the trigonal prismatic packing related to Ni and the tetragonal dodecahedral packing related to Cu. This is in a sense a necessary condition at best, although it might not be the sufficient condition. However, the effect of elemental substitution with Cu for Ni in the Pd&ndash;Ni&ndash;Cu&ndash;P alloy is thought to induce the particular atomic association related to Cu, which is an important factor for exhibiting its wide supercooled liquid region and high reduced glass transition temperature.

    DOI: 10.2320/matertrans1989.40.491

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  • Effective Pair Potentials of Liquid CuBr Estimated from the Anomalous X-Ray Scattering Data

    Omote Kazuhiko, Saito Masatoshi, Waseda Yoshio

    J Phys Soc Jpn   66 ( 10 )   3097 - 3101   1997.10

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    Language:English   Publisher:The Physical Society of Japan (JPS)  

    We have proposed a method for calculating the effective pair potentials of molten salt from measured structural data in which a long-range Coulombic interaction is important [K. Omote and Y. Waseda: J. Phys. Soc. Jpn. 66 (1997)]. By applying this method, the effective pair potentials of liquid CuBr have been successfully estimated from the experimental partial structure factors obtained by anomalous X-ray scattering. The resultant potentials show two characteristic features. One is remarkable shielding for the Cu–Cu Coulomb repulsion in its nearest neighbor region. This might be a possible origin for the absence of marked structure in the Cu–Cu correlation and the penetration of Cu ions into the first like-ion coordination shell. The other is the deviation from the Coulomb potential in the range of 0.4∼0.9 nm in the interactions of Cu–Cu and Cu–Br pairs, suggesting a certain correlation to a pre-peak found in the Cu–Cu structure factor at about 10 nm-1.

    DOI: 10.1143/JPSJ.66.3097

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  • Structure Analysis of Disordered Materials by the Anomalous X-ray Scattering(AXS) Method. Reviewed

    SUGIYAMA Kazumasa, SAITO Masatoshi, WASEDA Yoshio, MATSUBARA Eiichiro

    Nihon Kessho Gakkaishi   39 ( 1 )   20 - 25   1997.2

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    Language:Japanese   Publisher:The Crystallographic Society of Japan  

    The anomalous X-ray scattering method has recently received much attention for obtaining the fine structure of disordered materials, coupled with the synchrotron radiation source. This paper demonstrates the usefulness of the AXS method for determining the local environmental structure around a specific element as a function of distance, by providing fundamentals with some selected examples of high temperature CuBr liquid, 70GeO<SUB>2</SUB>30Bi<SUB>2</SUB>O<SUB>3</SUB> oxide glass and Zr-Y-Al-Ni metallic glasses.

    DOI: 10.5940/jcrsj.39.20

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  • Development of grazing incidence X-ray scattering apparatus for structural analysis of liquid surface and liquid/liquid interface.

    Sato Shigeo, Saito Masatoshi, Matsubara Eiichiro, Waseda Yoshio, Omote Kazuhiko

    Bulletin of the Japan Institute of Metals   36 ( 5 )   505 - 507   1997

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    DOI: 10.2320/materia.36.505

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Awards

  • AFOMP Journal Prize, 2020

    2020.12   Asia-Oceania Federation of Organizations for Medical Physics:AFOMP  

    Masatoshi Saito

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  • 2019年度Radiological Physics and Technology誌・土井賞(診断物理分野・最優秀論文)

    2020.4   日本放射線技術学会&日本医学物理学会   「Simulation of photon-counting detectors for conversion of dual-energy-subtracted computed tomography number to electron density」

    齋藤正敏

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  • 第59回日本金属学会論文賞(第14回若手講演論文)

    2011.3   日本金属学会   「Structural Study of Zr50Cu50 Amorphous Alloy by Anomalous X-ray Scattering Coupled with Reverse Monte-Carlo Simulation」

    川又透, 横山嘉彦, 杉山和正, 早稲田嘉夫, 齋藤正敏

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  • 第54回日本金属学会論文賞(材料化学部門)

    2006.9   日本金属学会   「Influence of Sulfate Ions on the Atomic-Scale Structure of β-FeOOH」

    權相九, 鈴木茂, 齋藤正敏, 上村隆之, 幸英昭, 早稲田嘉夫

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  • 第51回日本金属学会論文賞(物性部門)

    2003.10   日本金属学会   「耐候性鋼に形成されるさびのFe(O,OH)6ネットワーク構造」

    木村正雄, 鈴木環輝, 重里元一, 齋藤正敏, 鈴木茂, 紀平寛, 田辺康児, 早稲田嘉夫

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  • 第47回日本金属学会論文賞(物性部門)

    1999.11   日本金属学会   「Evaluation of Anisotropic Lattice Strain of Co9Fe/Cu Superlattice by Grazing Incidence X-ray Scattering Method」

    佐藤成男, 齋藤正敏, 松原英一郎, 早稲田嘉夫, 猪俣浩一郎

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  • 第19回村上奨励賞

    1999.5   財団法人村上記念会   「先端的X線構造解析法による各種機能性材料の微視的構造解明」

    齋藤正敏

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  • 第45回日本金属学会論文賞(物性部門)

    1997.9   日本金属学会   「Anomalous Grazing X-ray Reflectometry for Determining the Number Density of Atoms in the Near-Surface Region」

    齋藤正敏, 松原英一郎, 早稲田嘉夫

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  • 第35回原田研究奨励賞

    1995.11   財団法人金属研究助成会   「高導電性固体電解質の局所構造とイオン伝導現象に関する基礎的研究」

    齋藤正敏

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Research Projects

  • 高精度モンテカルロ線量計算のためのデュアルエナジーCT値-物理密度変換法の開発

    Grant number:23K07079

    2023.4 - 2026.3

    System name:科学研究費助成事業

    Research category:基盤研究(C)

    Awarding organization:日本学術振興会

    齋藤 正敏

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    Authorship:Principal investigator 

    Grant amount:\2600000 ( Direct Cost: \2000000 、 Indirect Cost:\600000 )

    モンテカルロ法は、がんの放射線治療を高い精度で実現できる次世代の線量計算アルゴリズムとして期待されている。しかし、線量計算に必要な入力パラメータ「生体の物理密度」は、旧態依然としてCT画像(シングルエナジーCTで撮影)から密度を推測する『CT値-物理密度変換』が使われており、その変換過程の不確かさのため、特に高い精度を必要とするリスク臓器近傍における線量計算の潜在的な誤差となっている。本研究の目的は、モンテカルロ線量計算の高精度化を可能とするデュアルエナジーを用いた新しい『CT値-物理密度変換』の開発である。本目的達成のため研究期間内に、デュアルエナジーCT装置を用いた撮影を通して本手法の物理密度の計算精度を調べると共に、得られる線量分布の精度やロバスト性を検証する。本年度の研究計画に基づき、物理密度イメージングのための『デュアルエネルギーCT値-物理密度変換』による数値解析を行った結果、広範なヒト組織において、原子番号/質量比と実効原子番号の間に単純な2次の線形関係があることが明らかになった。シミュレーションされた物理密度値は、0.260(肺)から3.225(ハイドロキシアパタイト)までの密度範囲において、参照値と非常によく一致した。参照値からの相対的な偏差は、眼の水晶体(約-1.0%)を除いて、すべての基準ヒト組織で±0.6%以内に留まっていた。さらに本手法を臨床用dual-source CT装置(Somatom FORCE, Siemens)を使って管電圧条件90-150 kV/Snで行った。CT撮影する被写体として電子密度校正用ファントム(Gammex RMI 467, Gammex)を用いた。解析の結果、Gammexファントムのすべてのロッドにおいて、物理密度の計算値と参照値の間に良好な一致が見られ、本手法の実用可能性が示された。

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  • A simple derivation of stopping power ratio in the human body from dual-energy CT data

    Grant number:19K08168

    2019.4 - 2022.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Saito Masatoshi

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    Grant amount:\3120000 ( Direct Cost: \2400000 、 Indirect Cost:\720000 )

    The objective of this study is to present a simple method for deriving the stopping power ratio (SPR) from dual-energy (DE) CT data via electron density and effective atomic number calibration. It is found that the DECT-SPR conversion with excellent SPR agreement can be achieved at the cost of increased image noise due to the subtraction process of the method. Guided filtering effectively reduced the image noise to a third of the original value or less without significant loss of subtle structures in the SPR images.

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  • Simplified phantom for electron density calibration by dual-energy CT

    Grant number:16K09011

    2016.4 - 2019.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Saito Masatoshi

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    Grant amount:\2860000 ( Direct Cost: \2200000 、 Indirect Cost:\660000 )

    The purpose of this research is to develop a simple phantom for electron density calibration necessary to calculating dose distribution in a radiation treatment plan of cancer using dual-energy CT. The basic performance of this simple phantom built in the study was checked through electron density calibration of a known standard substance. It was found that an excellent linear relationship is formed between the energy-subtracted CT values and the electron densities. The obtained electron density values could be determined within 1-2% errors.

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  • Conversion of the energy-subtracted CT number to electron density based on a single linear relationship

    Grant number:25461908

    2013.4 - 2016.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Saito Masatoshi

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    Grant amount:\2080000 ( Direct Cost: \1600000 、 Indirect Cost:\480000 )

    To achieve accurate tissue inhomogeneity corrections in radiotherapy treatment planning, we have previously proposed a novel conversion of the energy-subtracted CT number to an electron density (ΔHU-ρe conversion). In the present study, we investigate an initial implementation of the ΔHU-ρe conversion method for a treatment planning system. Two radiotherapy plans were used to compare the reliabilities of dose calculations based on the novel ΔHU-ρe conversion and the conventional method. The ΔHU-ρe conversion generally offered superior reliability. Based on our results, ΔHU-ρe conversion appears to be a promising method of providing a reliable inhomogeneity correction in treatment planning for ill-conditioned scans.

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  • Dual-energy CT for electron density measurements using clinical x-ray source

    Grant number:22611007

    2010.4 - 2012.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    SAITO Masatoshi

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    Grant amount:\1950000 ( Direct Cost: \1500000 、 Indirect Cost:\450000 )

    Dual-energy computed tomography (DECT) has the potential for measuring electron density distribution in a human body to predict the range of particle beams for treatment planning in proton or heavy-ion radiotherapy. However, thus far, a practical dual-energy method that can be used to precisely determine electron density for treatment planning in particle radiotherapy has not been developed. In this study, another DECT technique involving a balanced filter method using a conventional x-ray tube has been proposed. From the viewpoint of beam hardening and the tube-loading efficiency, the DECT using balanced filters would be significantly more effective in measuring the electron density than the conventional DECT.

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  • Short-range and Middle-range Ordering

    Grant number:17206075

    2005.4 - 2007.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    Research category:Grant-in-Aid for Scientific Research (A)

    Awarding organization:Japan Society for the Promotion of Science

    WASEDA Yoshio, SUZUKI Shigeru, SAITO Masatoshi, KANIE Kiyoshi, SHINODA Kozo

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    Grant amount:\49140000 ( Direct Cost: \37800000 、 Indirect Cost:\11340000 )

    Ferrous Fe(II) ions and ferric Fe(III) ions dissolved in aqueous solution are precipitated as polycations during corrosion of metallic iron, by which corrosion products are formed. In these processes, iron oxyhydroxides and oxides with complicated structure are formed. In this work, the EXAFS and quantitative X-ray diffraction methods were systematically used for characterizing influences of foreign ions on the short range and middle range ordering of their iron compounds. In addition to these experiments, reaction conditions of the aqueous solution were also analyzed using electrochemical potential and pH measurements, in order to clarifying the formation conditions of these iron compounds. In this works, green rust containing ferrous ions was specially synthesized, which was oxidized to iron oxyhydroxides and oxides under controlled conditions such as temperature. The results showed that the transformation from green rust to different iron oxides and oxyhydroxides strongly depend on reaction conditions such as temperature rate and pH of aqueous solution. In addition, X-ray anomalous scattering measurement of solid particles was carried out in order to investigate an influence of foreign cations such as manganese on the structure of iron oxides. This result indicated that manganese was almost equally distributed to different sites in the spinel structure of magnetite. Furthermore, the short range and middle range ordering the atomic arrangements of iron oxyhydroxides, which were oxidized with foreign anions was also characterized. Foreign ions like silicate ions were considered to be incorporated into the solid particles during structural changes of GR, by which the structure was distorted. As a result, foreign anions are likely to induce the distortion of the atomic arrangement by their incorporation, and this appears to cause not only the morphological changes and also properties of particles such as ion selectivity.

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  • FeO_6八面体をユニットとするオキシ水酸化物の自己組織化と構造相移転

    Grant number:15656152

    2003.4 - 2004.3

    System name:科学研究費助成事業 萌芽研究

    Research category:萌芽研究

    Awarding organization:日本学術振興会

    早稲田 嘉夫, 鈴木 茂, 齋藤 正敏

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    Grant amount:\3300000 ( Direct Cost: \3300000 )

    本研究では、オキシ水酸化鉄の形成段階において、異種原子を含む多面体ユニットの置換などによりFeO_6八面体ユニットの自己組織化過程を制御し、原子レベルの構造と特性との相関を定量的に評価するための研究を行った。研究においては、いくつかのオキシ水酸化鉄の局所構造における原子相関に関する情報(干渉関数)を、実験室X線および放射光による定量的散乱強度解析により評価した。これらの実験的に得られる平均的あるいは特定原子に関する干渉関数から、リバースモンテカルロシミュレーションにより二体分布関数を見積もった。これにより、クロムを含むオキシ水酸化鉄中の原子レベルの不完全性などを示し、FeO_6八面体ユニットの連結構造が異種カチオンを含む多面体ユニットやアニオンによって変化することを明らかにした。
    一方、湿式反応セル中における異種元素を添加した鉄合金のその場腐食過程を利用して、水溶液の種類や繰り返し反応条件を変えたときに形成するオキシ水酸化物(α-、β-、γ-FeOOHなど)の種類を調べた。これらの実験においては、実験室X線回折法やシンクロトロン放射光によるその場構造解析を用いた。これらの実験から、合金表面から酸素分圧の高い大気側へのオキシ水酸化鉄の自己組織化過程に関する情報を得て、不均一な腐食系におけるオキシ水酸化物の自己組織化過程の全体像について検討した。さらに、二次イオン質量分析法により、オキシ水酸化物を構成する元素、特に水素と酸素の挙動を調べ、その形成過程に関する情報を得た。これらの一連の結果から、様々な環境下でのオキシ水酸化鉄の形成過程を明らかにすることにより、それらの構造御のための知見を提示した。

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  • X線異常散乱を利用する液体金属の価電子密度分布の実験的導出

    Grant number:14655228

    2002.4 - 2003.3

    System name:科学研究費助成事業 萌芽研究

    Research category:萌芽研究

    Awarding organization:日本学術振興会

    齋藤 正敏

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    Authorship:Principal investigator 

    Grant amount:\3300000 ( Direct Cost: \3300000 )

    今日まで、液体金属の原子配列に関する構造研究は、放射光利用を含めてX線構造解析結果が大部分を占めている。しかし、液体状態に限らずX線構造解析により求めた物質の原子配列はあくまでも電子(主として価電子)を媒介とした有効イオン間の相関を反映したものである。したがって、液体金属の原子分布と電子構造との関連性をより本質的に解明するためには、価電子密度分布を実験的に求めることが重要課題の一つと考えられる。この課題に対して、中性子とX線の散乱機構の違いを利用した(以下、「中性子-X線法」と略す)液体金属の価電子密度分布を実験的に導出する試みが幾つか報告されている。しかし、この中性子-X線法の場合、2種類の試料は全く同じ状態に保持されていることが前提であること、また各散乱実験の角度分解能等の精度を統一しなければならないといった実験上の隘路のために、解析結果に基づく電子分布の議論よりも、散乱実験データ間の差の有意性に関する検討に重点が置かれているのが現状であった。本研究代表者は、上記のような研究上の支障を打破するため、中性子-X線法とは全く原理の異なった実験法として、「X線異常散乱」を利用する液体の価電子密度分布の導出法を新たに考案した。本年度は、剛体球モデルでは近似できない原子分布を有する液体Geと同様に長周期構造を持たないが、結晶状態と同じ半導体的性質を示す非晶質Geに対して本手法を適用した。導出した価電子分布の結果から、構造不規則状態にある非晶質Geの共有的な結合様式についての新たな知見を得ることができ、また、得られた結果と理論計算との比較を通して、本手法の信頼性や問題点を検証した。

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  • Structural Study of Reversible Phase Change Recording Materials by Anomalous Garzing Incidence X-ray Scattering

    Grant number:12650654

    2000.4 - 2001.3

    System name:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    SAITO Masatoshi, TAKAHASHI Hideyuki, WASEDA Yoshio

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    Authorship:Principal investigator 

    Grant amount:\3600000 ( Direct Cost: \3600000 )

    The purpose of this research is to analyze precisely the reversible structural change in phase change recording materials represented for CD-RW by the anomalous X-ray scattering (AXS) method under the grazing incidence condition. The phase change recording materials, using the variation of optical reflectivity between crystalline and non-crystalline phases, attract much attention as a storaging medium of digital information. These materials have already been commercialized and their upgrading such as capacity enlargement and high reliability will advance in future more and more. As showing this tendency to increase, it is anticipated that the structural control greatly influences their characteristics. Therefore, the structural analysis of phase change recording materials in the atomic level might be one of important subjects for developing steadily these fields. The AXS method by using the anomalous dispersion effect may be one of powerful tools for obtaining the structural information in the atomic level.
    In 2000, the local structural information of amorphous Ag-Br-Ge-O system has been estimated from the AXS measurements using Ge and Br K absorption edges. The resultant structural parameters suggest mat GeO_4 tetrahedral unit is the probable structural entity in this glass and the arrangement of Ag and Br ions is similar to that in crystalline AgBr. From these results, effectiveness of the AXS method for characterizing amorphous materials could be confirmed.
    In 2001, the usefulness and validity of energy dispersive grazing incidence X-ray reflectometry have been demonstrated for characterizing the multilayer interfaces. The method appears to hold promise in reducing difficulty of conventional angular dispersive method due to absorption with an upper layer by enabling the use of high energy white X-ray radiation and obtaining much higher reflected intensity. Taken from all results in this research, it would be very interesting to extend the present method to other systems.

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  • 斜入射X線異常反射率法による液体金属表面・界面の深さ方向密度分布の精密決定

    Grant number:09750727

    1997.4 - 1998.3

    System name:科学研究費助成事業 奨励研究(A)

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    齋藤 正敏

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    Authorship:Principal investigator 

    Grant amount:\2200000 ( Direct Cost: \2200000 )

    液体の表面や界面の構造に関する情報は、表面近傍における成分比がバルクの値から著しくずれる表面分離や相分離現象を科学的に解明する上で不可欠である。また、電気化学反応や触媒作用を制御する技術的課題にとっても重要な基礎情報である。液体の表面や界面の構造を調べる実験的手段の1つとして、X線の全反射現象を利用した斜入射X線反射率法がある。表面に対してX線を平行に近いきわめて浅い角度で入射すると全反射が起き、この様な全反射条件下ではX線の物質への侵入深さは数nm程度に抑えられ、また観測される反射強度プロファイルはその深さ領域の密度分布を反映する。しかし、斜入射X線反射率法による液体/電極界面の評価は上層の液体によるX線の吸収が非常に大きいという理由から実際には殆ど行われていない。本研究では、この問題を克服する新たな方法として、エネルギー分散型による斜入射X線反射率測定法の開発を試みた。液体/電極界面での反射率測定として、0.01mol/l NiSO_4水溶液/Fe電極界面について測定を行った。この測定により,水溶液/電極界面での反射率測定がエネルギー分散型を利用することで十分に可能になることが立証できた。また、Fe電極およびSUS304上に真空蒸着により金を積層させたAu電極上にNiを電析させた界面での反射率測定を実施した。Fe電極の場合、通電時間の増加と共に密度の増加が認められた。この理由としては、Fe電極上にFeよりも重元素であるNiを析出させた結果、電極表面の密度は増加したと考えられる。一方、Au電極の場合はAuよりも軽いNiを析出させたにもかかわらず電極表面密度の増加が観測された。これは、Au電極表面には多数の空間的な欠陥が存在し、電気めっきによりその部分にNiが優先的に析出したために密度の増加が起きたと考えられる。

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  • 先端的X線解折手法によるセラミックスのガラス相誘起超塑性変形の解明

    Grant number:09228202

    1997

    System name:科学研究費助成事業 重点領域研究

    Research category:重点領域研究

    Awarding organization:日本学術振興会

    早稲田 嘉夫, 齋藤 正敏

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    Authorship:Coinvestigator(s) 

    Grant amount:\2600000 ( Direct Cost: \2600000 )

    セラミックスの超塑性現象において粒界すべり、粘性流動、結晶粒界におけるガラス相の存在などが重要な役割を果たすことが指摘されつつあるが、その本性の解明および制御のためには巨視的特性と微視的構造を関連付ける情報の蓄積が不可欠である。本研究では、バルクとは異なることが予想される材料表面の構造や結晶粒の配向性の変化等の超塑性変形機構に関する新しい知見を得ることを目的として、全反射X線回折法を超塑性セラミックスに適用し、超塑性材料表面の構造評価を行った。
    本実験で使用したバルク3Y-TZPはほぼ単一のtetragonal相であるが、しかし、Seemann-Bohlin(S-B)法およびGrazing Incidence X-ray Scattering(GIXS)法の全反射X線回折法により得られた3Y-TZPの回折パターンにはmonoclinic相も認められ、また測定法の違いによる強度比の変化が生じていることから各相の表面構造に配向性があることが分かった。例えば、GIXS法ではtetragonal相002反射のピークは検出されず、200反射のピークが明瞭に観察された。一方、S-B法では、相対的に002反射の反射強度の増加が認められることから3Y-TZP材料表面の構造は、[001]選択配向の傾向が強いことを示唆している。また、赤外線イメージ炉で試料を大気中で加熱して3Y-TZPのX線反射率を測定し、その温度依存性を調べた。臨界波長の入射角依存性から表面密度を見積もった結果、文献値とほば一致した値が得られた。

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  • 広角及び小角X線異常散乱法による沃化銀系超イオン伝導ガラスの構造解析

    Grant number:08229201

    1996.4 - 1997.3

    System name:科学研究費助成事業 重点領域研究

    Research category:重点領域研究

    Awarding organization:日本学術振興会

    早稲田 嘉夫, 齋藤 正敏

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    Authorship:Coinvestigator(s) 

    Grant amount:\2200000 ( Direct Cost: \2200000 )

    室温で電解質溶液に匹敵するイオン伝導度を有するガラスが沃化銀-酸素酸銀系で見出され、高イオン伝導性はもちろんのこと、その透明性、等方均質性、薄膜化が容易であることからニューガラスと呼ばれる機能性材料の一つとして注目を集めている。今日まで、主にその電気的特性に関する研究が国内外で活発に展開されてきたが、イオン伝導機構を議論する上で基礎となるガラス構造に関しては、多元系非晶質のため従来のX線あるいは粒子線回折法による定量的解析は事実上不可能であり、赤外吸収スペクトル等の観測に基いて提唱されている構造モデルの検証は非常に難しく未解決の部分が多い。この様な研究上の支障を克服するため、目的元素の環境構造を距離の関数として導出できるX線異常散乱(AXS)法を用いて(AgI)_<0.6>(Ag_2MoO_4)_<0.4>超イオン伝導ガラスの詳細な構造解析を実施した。得られた平均動径分布関数に見られる第1ピークと第2ピークは、結晶Ag_2MoO_4における各種原子対間の距離および液体Ag_2MoO_4の動径分布との対応からそれぞれMo-OとAg-Oペア相関と同定できた。このことはMoの環境動径分布関数にAg-O原子ペア相関がほとんど観測されないことからも支持される。また、Ag-Iのペア相関と予想されるピークもMoの環境動径分布関数には観測されず、期待された通りMo-O原子ペアが分離し観測できた。更に詳細な動径分布関数の定量的解析の結果から以下のことが判明した。(1)Moは0.18nmの原子間距離で約4個の酸素原子に囲まれている。この結果はガラス構造中の基本構造単位はMoO_4四面体が支配的であることを示し、赤外分光実験等による指摘と対応する。(2)Agは距離0.287nmで平均1.9個のIイオンに囲まれており、この配位数は結晶および溶融AgI(配位数4)よりも少ない。しかし、AgIとして添加されたAgイオン1個あたりのIイオンの配位数は約4.4と換算できる。したがってガラス構造中のAgイオンは、結晶あるいは溶融AgIと類似の環境下に置かれており、この種のAgがイオン伝導に寄与するものと理解できる。

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  • 斜入射X線異常反射率法による基板上薄膜の深さ方向密度プロファイル決定

    Grant number:08750760

    1996

    System name:科学研究費助成事業

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    齋藤 正敏

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    Grant amount:\1100000 ( Direct Cost: \1100000 )

    各種薄膜の特徴ある物性を支配すると考えられるのと同程度、あるいはそれ以下の厚さ領域における薄膜の原子構造に関する情報を得ることは、新機能性素材を開発する上で工業的に重要であり,また、バルクとは異なる物質表面近傍および界面における特性発現のメカニズムを解明する上で基礎科学的にも切望されている。未知の物質表面近傍の構造解析を行うには物質構成元素の絶対量(原子数密度)を知る必要がある。物質表面近傍の組成についてはSIMS, XPS等の表面分析手法により比較的容易に決定できるが,密度はバルク材料に用いる手法の表面への応用は事実上不可能であり,実験的に求めることは極めて困難な状況にある。この研究上の支障を打破する手段として,X線異常散乱と全反射現象を組み合わせた斜入射X線異常反射法(Anomalous Grazing X-ray Reflectometry : AGXR)を開発し,その解析法を確立した。入射X線のエネルギーが物質を構成する元素の吸収端に近い場合,異常分散効果によって原子のX線に対する前方への散乱能が減少し,その結果、全反射臨界散乱ベクトルは小さくなる。その変化量は異常散乱を起こしている原子数に依存する。この異常分散効果が顕著となる吸収端近傍での全反射臨界散乱ベクトルの大きな変化を利用する手法が、AGXR法である。応用例として、ステンレス鋼表面上に薄く形成しているクロム酸化膜について,CrK吸収端およびFeK吸収端近傍の入射X線を用いて斜入射X線異常反射率を測定した。解析の結果得られたステンレス鋼表面酸化膜中のCrとFe原子の数密度値はAuger電子分光法で得られた結果と矛盾しないことが確認された。AGXR法は,臨界散乱ベクトルの差を計算する過程で角度の誤差が相殺されるので,角度の絶対値の厳密な決定が必要でないことが利点であり,また、結晶・非結晶を問わず種々の物質に対して適用可能であることが分かった。

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  • X線異常小角散乱装置の試作および巨大磁気抵抗効果の解明

    Grant number:07555475

    1995

    System name:科学研究費助成事業 試験研究(B)

    Research category:試験研究(B)

    Awarding organization:日本学術振興会

    早稲田 嘉夫, 表 和彦, 杉山 和正, 齋藤 正敏

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    Authorship:Coinvestigator(s) 

    本研究のキ-ポイントは、たとえ原子番号が近接する元素が共存する場合でも夫々の元素を的確に識別し、数十ナノメートルの微細構造を解明するX線異常小角散乱装置を世界に先駆け試作し、Co/Cu合金からなる巨大磁気抵抗効果の解明をすることにある。
    当初の研究計画に基づき、まず本研究補助金を持ちいて入射X線のエネルギーを自由に選択できるヨハン型あるいは2結晶モノクロメータを搭載する分光部、角度分解能の優れた小角ゴニオメータおよび位置敏感型検出器を装備した計測部を設計・製作し、既設の高輝度X線源と組み合わせたX線異常小角散乱装置を試作した。また本年度は、原子番号が近接するCoおよびCuから構成される多層膜の構造解析を実施した。X線異常小角散乱を応用した結果、CoおよびCu元素の原子番号が5番近く離れている場合に相当する小角散乱強度が測定できた。フーリエ変換法によって解析した結果、本実験で解析した多層膜は2.05nm周期であり、Cuが0.46nm,Coが0.50nm堆積し境界界面構1.09nmであることが判明した。この解析結果は、X線異常小角散乱法を用いて初めて得られた結果であり、今後はこの新しい手法を用いた各種機能性素材の系統的かつ精密な微細構造の解明が十分期待できる。

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  • 広角および小角X線異常散乱法によるハロゲン化銀およびハロゲン化銅系超イオン伝導ガラスの構造解析

    Grant number:07239202

    1995

    System name:科学研究費助成事業 重点領域研究

    Research category:重点領域研究

    Awarding organization:日本学術振興会

    早稲田 嘉夫, 斎藤 正敏

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    Authorship:Coinvestigator(s) 

    Grant amount:\2700000 ( Direct Cost: \2700000 )

    室温で電解質溶液に匹敵するイオン伝導度を有するガラスが沃化銀-酸素酸銀系で見出され、高イオン伝導性はもちろんのこと、その透明性、等方均質性、薄膜化が容易であることからニューガラスと呼ばれる機能性材料の一つとして注目を集め、薄膜電池等への応用が始まっている。今日まで、銀イオン伝導ガラスを中心に、主にその電気的特性に関する研究が国内外で活発に展開されてきたが、イオン伝導機構を議論する上での基礎となるガラス構造に関しては、赤外吸収スペクトルや電気伝導度の組成依存性等の観測に基く構造モデルが提唱されてはいるが、多元系非晶質のため従来のX線あるいは粒子線回折法による定量的解析は事実上不可能であり、モデルの検証は非常に難しく未解決の部分が多い。
    本研究では、この様な研究上の支障を克服するため、目的元素の環境構造を距離の関数として導出できるX線異常散乱(AXS)法を用いて、(Cul)_<0.3>(Cu_2O)_<0.35>(MoO_3)_<0.35>の詳細な構造解析を実施し、最近接領域のみならず、第二、第三近接等の短範囲規則領域を含むガラス構成元素の環境構造の決定を行った。その結果、以下のことが判明した。(1)Moは0.187nmの原子間距離で6.1個の酸素原子に囲まれている。この事実はガラス構造中の基本構造単位が赤外分光実験等により示唆されてきたMoO_4四面体よりもMoO_6八面体であることを示唆する。(2)Cuは距離0.261nmで平均1.3個の沃素イオンに囲まれており、この配位数は結晶および溶融CuI(配位数4)よりも少ない。しかし、CuIとして添加されたCuイオン1個あたりの沃素イオンの配位数は約4.3と換算でき、結晶および溶融CuIの値とほぼ一致する。また、溶融CuIに見られる約0.34nmの最近接Cu-Cuペア相関が本ガラス中にも見出されることから、溶融CuI類似の環境下に置かれたCuイオンがガラス構造中に存在し、この種のCuがイオン伝導に寄与するものと理解できる。

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  • Structural Analysis of Al_2O_3 Based High Temperature Melts

    Grant number:06452308

    1994 - 1995

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for General Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    WASEDA Yoshio, SAITO Masatoshi

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    Grant amount:\8500000 ( Direct Cost: \8500000 )

    The structural information on the melt containing Al_2O_3 is important for the better understanding of solid-melt reactions of the crystal and steel making process. However, such information is not enough because in-situ X-ray diffraction measurement at high temperature is very difficult. The main purpose of the present research project is to obtain the systematic structural data of high temperature melts containing Al_2O_3
    Basing on the structural data of pure Al_2O_3 (Waseda et al, 1994), the melt structure in the Al_2O_3-SiO_2-Na_2O system was systematically analyzed by the common angular dispersive X-ray diffraction (ADXD) and the energy dispersive X-ray diffraction (EDXD) techniques. The EDXD technique is known to be one of the powerful techniques which allow to get wide interference function Qi(Q) of over 250nm^<-1> and this enables us to obtain precise radial distribution functions (RDF). The experimental RDFs clearly indicate that the local structural unit of AlO_6 in the Al_2O_3 melt changes into that of AlO_4 with the addition of SiO_2 and Na_2O.These useful results are obtained only by the combination of ADXD and EDXD analyzes, presently developed. The present analysis are expected to be applied to the wider field of structural analyzes.

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  • 層構造白金族ダイカルコゲナイドの2次元的電気伝導及び磁気的性質に関する研究

    Grant number:05750591

    1993

    System name:科学研究費助成事業 奨励研究(A)

    Research category:奨励研究(A)

    Awarding organization:日本学術振興会

    斎藤 正敏

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    Authorship:Principal investigator 

    Grant amount:\900000 ( Direct Cost: \900000 )

    遷移金属ダイカルコゲナイドMX_2(X=S,Se,Te)の多くは層状構造を持ち、電荷密度波、インターカレーション化合物の生成など数多くの興味を提起し、今日迄広く研究がなされてきた。一方、その非晶質化合物は、電気化学的性能や触媒作用が、結晶状態よりも優れた特性を有することで注目されているが、その原子構造解析や物性データの蓄積は未だ十分なされていない。本研究では、沈殿法により合成した非晶質白金硫化物(Pt_<1-X>S_2)の局所的な原子構造をX線異常散乱法(AXS)を用いて調べ、、結晶構造と比較し、電気化学的特性との関係を検討した。試料はH_2PtCl_6水溶液にH_2Sガスを吹き込むことにより合成した。この試料について高エネルギー物理学研究所の放射光X線源を利用し、PtのL_<III>吸収端(11.562keV)の30及び300eV低エネルギー側のX線を用いて散乱測定を行った。散乱強度のエネルギー依存性からPt周囲の環境干渉関数求め、フーリエ変換によりPtの環境動径分布関数を得た。これとMo Kalpha線を用いて得られた全動径分布関数と比較することによって、CdI_2構造型PtS_2における八面体ユニット(PtS_6)を基本構造としたランダム連結モデルを想定し、最小自乗法を用いて干渉関数にフィッティングを行うことで原子間距離および配位数の精密化を行った。精密化された構造パラメターから非晶質硫化白金の組成はPt過少であって、熱重量分析から算出された組成および密度と一致し、Pt過少による空孔体積の増加、つまり微視的な表面積の増加により電気化学的活性が高められていることが分かった。

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  • 窒化ウラン燃料とFP金属との反応生成物に関する結晶学的ならびに熱力学的研究

    Grant number:05680409

    1993

    System name:科学研究費助成事業

    Research category:一般研究(C)

    Awarding organization:日本学術振興会

    藤野 威男, 斎藤 正敏, 佐藤 修彰

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    Grant amount:\2100000 ( Direct Cost: \2100000 )

    窒化ウラン燃料とFP金属との反応性を調べるために,窒化ウランと類似性のある硫化ウランを合成し,FP金属との反応性を熱力学的に調べるとともに,生成物の構造変化について調べた.また,アクチノイドと類似性をもつ希土類元素を用いて,硫酸塩の炭硫化反応やFP金属との反応性について検討した.以下の結果が得られた.
    1)U切削片を約280℃で水素と反応させ,UH_3を得た後,H_2SあるいはCS_2と1000℃で反応させるとβ-US_2が得られた.H_2Sを用いた場合には少量ながらUOSが生成することがわかった.
    2)硫酸ウラニル(UO_2SO_4)とCS_2との炭硫化反応により,1200℃ではβ-US_2を,1270℃ではα-US_2を合成することができ,これらの結果は熱力学的考察とよく対応していた.特にα-US_2は硫黄の不定比性を示し,この不定比性はウラン原子の占有率により生じることをX線粉末回折の結果より明らかにした.
    3)CS_2を用いるネオジム硫酸塩(Nd_2(SO_4)_3)の炭硫化反応について,熱重量分析(TG)を行った結果,Nd_2(SO_4)_3はまず,Nd_2O_2SO_4を経てNd_2O_2Sを生成し,このNd_2O_2Sの硫化によりNd_2S_3を生成する.そしてこの硫化の段階においては,直接Nd_2S_3を生成する反応と,一旦NdS_2を生成し,このNdS_2の熱分解によりNd_2S_3を生成する反応とが合成条件により競合しながら,最終的にNd_2S_3を生成することを明らかにした.
    4)CS_2を用いてウランとマグネシウムの混合硫酸塩の炭硫化反応を行ったところ,Mgはα-およびβ-US_2に固溶せず,また複硫化物も生成しないことがわかった.また,CS_2を用いるウランとバリウムの混合硫酸塩の炭硫化反応を行い,U:Ba比が1:1の場合には複硫化物BaUS_3を,また1:2の場合にはBaU_2S_5を生成することを明らかにした.

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Teaching Experience

  • 放射線理工学演習

    2024
    Institution name:新潟大学

  • 放射線計測学演習

    2024
    Institution name:新潟大学

  • 放射線物理学

    2023
    Institution name:新潟大学

  • 放射線物理学演習

    2023
    Institution name:新潟大学

  • 放射線計測学

    2023
    Institution name:新潟大学

  • 放射線撮影技術学演習

    2022
    -
    2023
    Institution name:新潟大学

  • 医療英語ベーシック(放射)

    2021
    Institution name:新潟大学

  • 応用数理解析学概論

    2021
    Institution name:新潟大学

  • 放射線物質科学演習

    2021
    Institution name:新潟大学

  • 医学物理学特講

    2021
    Institution name:新潟大学

  • 放射線科学セミナー

    2021
    Institution name:新潟大学

  • 保健学特定研究(放射線技術科学)

    2021
    Institution name:新潟大学

  • 保健学特別研究(放射線技術科学)

    2021
    Institution name:新潟大学

  • 卒業研究

    2021
    Institution name:新潟大学

  • 放射線計測学実験

    2021
    Institution name:新潟大学

  • 医学物理学特講演習

    2021
    Institution name:新潟大学

  • 放射線物理学II及び演習

    2021
    -
    2023
    Institution name:新潟大学

  • 放射線物理学I演習

    2021
    -
    2023
    Institution name:新潟大学

  • 放射線計測学I及び演習

    2021
    -
    2023
    Institution name:新潟大学

  • 放射線撮影技術学実習

    2020
    Institution name:新潟大学

  • 保健学特別研究(放射線技術科学)

    2014
    -
    2018
    Institution name:新潟大学

  • 医学物理学特講演習

    2014
    Institution name:新潟大学

  • 医学物理学特講

    2014
    Institution name:新潟大学

  • 放射線物理学Ⅱ及び演習

    2012
    -
    2018
    Institution name:新潟大学

  • 医療英語(放射)

    2011
    Institution name:新潟大学

  • 放射線物理学Ⅰ

    2011
    -
    2023
    Institution name:新潟大学

  • 卒業研究

    2011
    -
    2018
    Institution name:新潟大学

  • 放射線物理学Ⅰ演習

    2011
    -
    2018
    Institution name:新潟大学

  • 保健学特定研究(放射線技術科学)

    2011
    -
    2014
    Institution name:新潟大学

  • スタディスキルズ (放射)

    2008
    -
    2023
    Institution name:新潟大学

  • 放射線計測学Ⅱ

    2008
    -
    2023
    Institution name:新潟大学

  • 放射線計測学Ⅰ及び演習

    2008
    -
    2018
    Institution name:新潟大学

  • 放射線科学セミナー

    2008
    -
    2018
    Institution name:新潟大学

  • 物理学基礎実験

    2007
    Institution name:新潟大学

  • 放射線物質科学特論

    2007
    Institution name:新潟大学

  • 放射線計測学I及び演習

    2007
    -
    2023
    Institution name:新潟大学

  • 入門医療英語

    2007
    -
    2018
    Institution name:新潟大学

  • 放射線物質科学演習

    2007
    -
    2018
    Institution name:新潟大学

  • 放射線計測学実験

    2007
    -
    2018
    Institution name:新潟大学

  • 応用数理解析学概論

    2007
    -
    2018
    Institution name:新潟大学

  • 医用放射線科学特別研究

    2007
    -
    2013
    Institution name:新潟大学

  • 医用物理学特講演習

    2007
    -
    2013
    Institution name:新潟大学

  • 医用物理学特講

    2007
    -
    2013
    Institution name:新潟大学

  • 原子力施設見学

    2007
    Institution name:新潟大学

  • 放射線計測学II

    2007
    Institution name:新潟大学

  • 粒子線物理学

    2007
    Institution name:新潟大学

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