Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Purpose: The main objective of this study is to propose an alternative parameterization for the empirical relation between mean excitation energies (I-value) and effective atomic numbers (Z(eff)) of human tissues, and to present a simplified formulation (which we called DEEDZ-SPR) for deriving the stopping power ratio (SPR) from dual-energy (DE) CT data via electron density (rho(e)) and Zeff calibration.
Methods: We performed a numerical analysis of this DEEDZ-SPR method for the human-body-equivalent tissues of ICRU Report 46, as objects of interest with unknown SPR and rho(e). The attenuation coefficients of these materials were calculated using the XCOM photon cross-sections database. We also applied the DEEDZ-SPR conversion to experimental DECT data available in the literature, which was measured for the tissue-characterization phantom using a dual-source CT scanner at 80 kV and 140 kV/Sn.
Results: It was found that the DEEDZ-SPR conversion enables the calculation of SPR simply by means of the weighted subtraction of an electron-density image and a low-or high-kV CT image. The simulated SPRs were in excellent agreement with the reference values over the SPR range from 0.258 (lung) to 3.638 (bone mineral-hydroxyapatite). The relative deviations from the reference SPR were within +/- 0.6% for all ICRU-46 human tissues, except for the thyroid that presented a -1.1% deviation. The overall root-mean-square error was 0.21%. Application to experimental DECT data confirmed this agreement within the experimental accuracy, which demonstrates the practical feasibility of the method.
Conclusions: The DEEDZ-SPR conversion method could facilitate the construction of SPR images as accurately as a recent DECT-based calibration procedure of SPR parameterization based directly on the CT numbers in a DECT data set. (C) 2017 American Association of Physicists in Medicine

DOI： 10.1002/mp.12386

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Purpose: The main objective of this study is to propose a simple formulation (which we called DEEDZ) for deriving effective atomic numbers (Zeff) via electron density (qe) calibration from dualenergy (DE) CT data. We carried out numerical analysis of this DEEDZ method for a large variety of materials with known elemental compositions and mass densities using an available photon cross sections database. The new conversion approach was also applied to previously published experimental DECT data to validate its practical feasibility.
Methods: We performed numerical analysis of the DEEDZ conversion method for tissue surrogates that have the same chemical compositions and mass densities as a commercial tissue-characterization phantom in order to determine the parameters necessary for the qe and Zeff calibrations in the DEEDZ conversion. These parameters were then applied to the human-body-equivalent tissues of ICRU Report 46 as objects of interest with unknown qe and Zeff. The attenuation coefficients of these materials were calculated using the XCOM photon cross sections database. We also applied the DEEDZ conversion to experimental DECT data available in the literature, which was measured for two commercial phantoms of different shapes and sizes using a dual-source CT scanner at 80 kV and 140 kV/Sn.
Results: The simulated Zeff ' s were in excellent agreement with the reference values for almost all of the ICRU-46 human tissues over the Zeff range from 5.83 (gallstones-cholesterol) to 16.11 (bone mineral- hydroxyapatite). The relative deviations from the reference Zeff were within 0.3% for all materials, except for one outlier that presented a 3.1% deviation, namely, the thyroid. The reason for this discrepancy is that the thyroid contains a small amount of iodine, an element with a large atomic number (Z = 53). In the experimental case, we confirmed that the simple formulation with less fit parameters enable to calibrate Zeff as accurately as the existing calibration procedure.
Conclusions: The DEEDZ conversion method based on the simple formulation proposed could facilitate the construction of qe and Zeff images from acquired DECT data. (C) 2017 American Association of Physicists in Medicine

DOI： 10.1002/mp.12176

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

Purpose: For accurate tissue inhomogeneity correction in radiotherapy treatment planning, the author previously proposed a simple conversion of the energy-subtracted computed tomography (CT) number to an electron density (Delta HU-rho(e) conversion), which provides a single linear relationship between Delta HU and rho(e) over a wide rho(e) range. The purpose of the present study was to reveal the relation between the Delta HU image for rho(e) calibration and a virtually monochromatic CT image by performing numerical analyses based on the basis material decomposition in dual-energy CT.
Methods: The author determined the weighting factor, alpha(0), of the Delta HU-rho(e) conversion through numerical analyses of the International Commission on Radiation Units and Measurements Report-46 human body tissues using their attenuation coefficients and given rho(e) values. Another weighting factor, alpha(E), for synthesizing a virtual monochromatic CT image from high-and low-kV CT images, was also calculated in the energy range of 0.03 < E < 5 MeV, assuming that cortical bone and water were the basis materials. The mass attenuation coefficients for these materials were obtained using the XCOM photon cross sections database. The effective x-ray energies used to calculate the attenuation were chosen to imitate a dual-source CT scanner operated at 80-140 and 100-140 kV/Sn.
Results: The determined alpha(0) values were 0.455 for 80-140 kV/Sn and 0.743 for 100-140 kV/Sn. These values coincided almost perfectly with the respective maximal points of the calculated a(E) curves located at approximately 1 MeV, in which the photon-matter interaction in human body tissues is exclusively the incoherent (Compton) scattering.
Conclusions: The Delta HU image could be regarded substantially as a CT image acquired with monoenergetic 1-MeV photons, which provides a linear relationship between CT numbers and electron densities. (C) 2015 American Association of Physicists in Medicine.

DOI： 10.1118/1.4921999

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

Purpose: To achieve accurate tissue inhomogeneity corrections in radiotherapy treatment planning, the authors had previously proposed a novel conversion of the energy-subtracted computed tomography (CT) number to an electron density (Delta HU-rho(e) conversion), which provides a single linear relationship between Delta HU and rho(e) over a wide range of rho(e). The purpose of this study is to present an initial implementation of the Delta HU-rho(e) conversion method for a treatment planning system (TPS). In this paper, two example radiotherapy plans are used to evaluate the reliability of dose calculations in the Delta HU-rho(e) conversion method.
Methods: CT images were acquired using a clinical dual-source CT (DSCT) scanner operated in the dual-energy mode with two tube potential pairs and an additional tin (Sn) filter for the high-kV tube (80-140 kV/Sn and 100-140 kV/Sn). Single-energy CT using the same DSCT scanner was also performed at 120 kV to compare the Delta HU-rho(e) conversion method with a conventional conversion from a CT number to rho(e) (Hounsfield units, HU-rho(e) conversion). Lookup tables for.e calibration were obtained from the CT image acquisitions for tissue substitutes in an electron density phantom (EDP). To investigate the beam-hardening effect on dosimetric uncertainties, two EDPs with different sizes (a body EDP and a head EDP) were used for the rho(e) calibration. Each acquired lookup table was applied to two radiotherapy plans designed using the XiO TPS with the superposition algorithm for an anthropomorphic phantom. The first radiotherapy plan was for an oral cavity tumor and the second was for a lung tumor.
Results: In both treatment plans, the performance of the Delta HU-rho(e) conversion was superior to that of the conventional HU-rho(e) conversion in terms of the reliability of dose calculations. Especially, for the oral tumor plan, which dealt with dentition and bony structures, treatment planning with the HU-rho(e) conversion exhibited apparent discrepancies between the dose distributions and dose-volume histograms (DVHs) of the body-EDP and head-EDP calibrations. In contrast, the dose distributions and DVHs of the body-EDP and head-EDP calibrations coincided with each other almost perfectly in the Delta HU-rho(e) conversion for 100-140 kV/Sn. The difference between the V100' s (the mean planning target volume receiving 100% of the prescribed dose; a DVH parameter) of the body-EDP and head-EDP calibrations could be reduced to less than 1% using the H Delta U-rho(e) conversion, but exceeded 11% for the HU-rho(e) conversion.
Conclusions: The Delta HU-rho(e) conversion can be implemented for currently available TPS's without any modifications or extensions. The Delta HU-rho(e) conversion appears to be a promising method for providing an accurate and reliable inhomogeneity correction in treatment planning for any ill-conditioned scans that include (i) the use of a calibration EDP that is nonequivalent to the patient's body tissues, (ii) a mismatch between the size of the patient and the calibration EDP, or (iii) a large quantity of high-density and high-atomic-number tissue structures. (C) 2015 American Association of Physicists in Medicine.

DOI： 10.1118/1.4908207

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

Purpose: For accurate tissue inhomogeneity correction in radiotherapy treatment planning, the authors had previously proposed a novel conversion of the energy-subtracted CT number to an electron density (Delta HU-rho(e) conversion), which provides a single linear relationship between Delta HU and rho(e) over a wide rho(e) range. The purpose of this study is to address the limitations of the conversion method with respect to atomic number (Z) by elucidating the role of partial photon interactions in the Delta HU-rho(e) conversion process.
Methods: The authors performed numerical analyses of the Delta HU-rho(e) conversion for 105 human body tissues, as listed in ICRU Report 46, and elementary substances with Z = 1-40. Total and partial attenuation coefficients for these materials were calculated using the XCOM photon cross section database. The effective x-ray energies used to calculate the attenuation were chosen to imitate a dual-source CT scanner operated at 80-140 kV/Sn under well-calibrated and poorly calibrated conditions.
Results: The accuracy of the resultant calibrated electron density, rho(cal)(e), for the ICRU-46 body tissues fully satisfied the IPEM-81 tolerance levels in radiotherapy treatment planning. If a criterion of rho(cal)(e)/rho(e) - 1 is assumed to be within +/- 2%, the predicted upper limit of Z applicable for the Delta HU-rho(e) conversion under the well-calibrated condition is Z = 27. In the case of the poorly calibrated condition, the upper limit of Z is approximately 16. The deviation from the Delta HU-rho(e) linearity for higher Z substances is mainly caused by the anomalous variation in the photoelectric-absorption component.
Conclusions: Compensation among the three partial components of the photon interactions provides for sufficient linearity of the Delta HU-rho(e) conversion to be applicable for most human tissues even for poorly conditioned scans in which there exists a large variation of effective x-ray energies owing to beam-hardening effects arising from the mismatch between the sizes of the object and the calibration phantom. (C) 2014 American Association of Physicists in Medicine.

DOI： 10.1118/1.4881327

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In radiotherapy treatment planning, the conversion of the computed tomography (CT) number to electron density is one of the main processes that determine the accuracy of patient dose calculations. However, in general, the CT number and electron density of tissues cannot be interrelated using a simple one-to-one correspondence. This study aims to experimentally verify the clinical feasibility of an existing novel conversion method proposed by the author of this note, which converts the energy-subtracted CT number (Delta HU) to the relative electron density (rho(e)) via a single linear relationship by using a dual-energy CT (DECT). The Delta HU-rho(e) conversion was performed using a clinical second-generation dual-source CT scanner operated in the dual-energy mode with tube potentials of 80 kV and 140 kV with and without an additional tin filter. The Delta HU-rho(e) calibration line was obtained from the DECT image acquisition for tissue substitutes in an electron density phantom. In addition, the effect of object size on Delta HU-rho(e) conversion was also experimentally investigated. The plot of the measured Delta HU versus nominal rho(e) values exhibited a single linear relationship over a wide rho(e) range from 0.00 (air) to 2.35 (aluminum). The Delta HU-rho(e) conversion performed with the tin filter yielded a lower dose and more reliable rho(e) values that were less affected by the object-size variation when compared to the corresponding values obtained for the case without the tin filter.

DOI： 10.1088/0031-9155/58/9/N135

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

Purpose: The conversion of the computed tomography (CT) number to electron density is one of the main processes that determine the accuracy of patient dose calculations in radiotherapy treatment planning. However, the CT number and electron density of tissues cannot be generally interrelated via a simple one-to-one correspondence because the CT number depends on the effective atomic number as well as the electron density. The purpose of this study is to present a simple conversion from the energy-subtracted CT number (Delta HU) by means of dual-energy CT (DECT) to the relative electron density (rho(e)) via a single linear relationship.
Methods: The Delta HU-rho(e) conversion method was demonstrated by performing analytical DECT image simulations that were intended to imitate a second-generation dual-source CT (DSCT) scanner with an additional tin filtration for the high-kV tube. The Delta HU-rho(e) calibration line was obtained from the image simulation with a 33 cm-diameter electron density calibration phantom equipped with 16 inserts including polytetrafluoroethylene, polyvinyl chloride, and aluminum; the elemental compositions of these three inserts were quite different to those of body tissues. The Delta HU-rho(e) conversion method was also applied to previously published experimental CT data, which were measured using two different CT scanners, to validate the clinical feasibility of the present approach. In addition, the effect of object size on rho(e)-calibrated images was investigated by image simulations using a 25 cm-diameter virtual phantom for two different filtrations: with and without the tin filter for the high-kV tube.
Results: The simulated Delta HU-rho(e) plot exhibited a predictable linear relationship over a wide range of rho(e) from 0.00 (air) to 2.35 (aluminum). Resultant values of the coefficient of determination, slope, and intercept of the linear function fitted to the data were close to those of the ideal case. The maximum difference between the ideal and simulated rho(e) values was -0.7%. The satisfactory linearity of Delta HU-rho(e) was also confirmed from analyses of the experimental CT data. In the experimental cases, the maximum difference between the nominal and simulated rho(e) values was found to be 2.5% after two outliers were excluded. When compared with the case without the tin filter, the Delta HU-rho(e) conversion performed with the tin filter yielded a lower dose and more reliable rho(e) values that were less affected by the object-size variation.
Conclusions: The Delta HU-rho(e) calibration line with a simple one-to-one correspondence would facilitate the construction of a well-calibrated rho(e) image from acquired dual-kV images, and currently, second generation DSCT may be a feasible modality for the clinical use of the Delta HU-rho(e) conversion method. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.3694111]

DOI： 10.1118/1.3694111

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Ltd  

Purpose: This paper describes the low-kV spectral optimization of dual-energy CT (DECT) equipped with high-kV tin filtration for the quantitative acquisition of electron density information, which is essential for treatment planning in radiotherapy. In addition, an analytical DECT image simulation was preliminarily performed to demonstrate the effectiveness of the optimized DECT with respect to the beam-hardening reduction. Methods: To optimize the low-kV spectrum of DECT, the author calculated the beam-hardening error, CT dose index, and tube loadings for a 50-cm diameter cylindrical water phantom with various combinations of filter materials, a range of thicknesses, and low-kV tube potentials. In addition, a single tube potential of 140 kV filtered by 0.4 mm tin (Sn) was employed for high-kV scanning, as is similar to the commercial implementation of the second-generation dual-source CT scanner. The optimized spectral parameters were then applied to the analytical DECT image simulation using two-dimensional fan-beam geometry for a virtual solid water phantom with 16 bodylike tissue inserts. Results: The author predicts that an optimal low-kV filtration would be 0.144-mm tungsten (W) at 90 kV, as it yields a minimal beam-hardening error with lower tube loadings and dose. The high-kV tube loading and dose obtained using the W filtration were 99 mAs and 2.2 mGy, respectively. These values are nearly equal to those obtained in the case of 2.5 mm Al at 100 kV (100 mAs and 2.3 mGy), which was regarded in this study as a reference filtration
however, the W filtration significantly reduced the beam-hardening error, from 9.5 to 1.4. The corresponding low-kV tube loading (112 mAs) was five times greater than that of the reference case (21 mAs), but it was maintained at a certain practical level since the low-kV tube loading was comparable to the high-kV tube loading of the reference (100 mAs). The superiority of the beam-hardening reduction is reflected in the simulated images
for example, by the use of the W filter, the beam-hardening-induced deviation between the simulated and theoretical electron density values of cortical bone was reduced from 7.4 to 1.2 as compared with the reference filtration, even though no correction for beam hardening was performed. Conclusions: In terms of beam hardening reduction, the DECT with the low-kV W filtration is more effective for the quantitative measurement of electron density within a practical limit of tube loadings and without additional dose. © 2011 American Association of Physicists in Medicine.

DOI： 10.1118/1.3584200

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

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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Other Link： https://jlc.jst.go.jp/DN/JALC/00356579564?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Ltd  

Purpose: This article describes the spectral optimization of dual-energy computed tomography using balanced filters (bf-DECT) to reduce the tube loadings and dose by dedicating to the acquisition of electron density information, which is essential for treatment planning in radiotherapy. Methods: For the spectral optimization of bf-DECT, the author calculated the beam-hardening error and air kerma required to achieve a desired noise level in an electron density image of a 50-cm-diameter cylindrical water phantom. The calculation enables the selection of beam parameters such as tube voltage, balanced filter material, and its thickness. Results: The optimal combination of tube voltages was 80 kV/140 kV in conjunction with Tb/Hf and Bi/Mo filter pairs
this combination agrees with that obtained in a previous study [M. Saito, "Spectral optimization for measuring electron density by the dual-energy computed tomography coupled with balanced filter method," Med. Phys. 36, 3631-3642 (2009)], although the thicknesses of the filters that yielded a minimum tube output were slightly different from those obtained in the previous study. The resultant tube loading of a low-energy scan of the present bf-DECT significantly decreased from 57.5 to 4.5 times that of a high-energy scan for conventional DECT. Furthermore, the air kerma of bf-DECT could be reduced to less than that of conventional DECT, while obtaining the same figure of merit for the measurement of electron density and effective atomic number. Conclusions: The tube-loading and dose efficiencies of bf-DECT were considerably improved by sacrificing the quality of the noise level in the images of effective atomic number. © 2010 American Association of Physicists in Medicine.

DOI： 10.1118/1.3467754

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

The ion-electron structure factor of liquid Ga has been estimated from the anomalous X-ray scattering (AXS) measurements near the Ga K-absorption edge for determining the electron density distribution. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique and the results clearly indicate that the electron density of liquid Ga significantly deviates from spherical distribution with respect to each central Ga ion.

DOI： 10.1515/HTMP.2010.29.5-6.393

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The structural analysis of liquid LiNbO3 near the melting point has been carried out by means of the energy dispersive X-ray diffraction (EDXD). The present EDXD analysis allowed us to give the high-resolution radial distribution function (RDF) of the liquid LiNbO3 at 1550 K by obtaining the experimental interference function in the large wave vector region over 200 nm-1. The rather distorted NbO6 units with a disparity in the first Nb-O atomic pairs were confirmed in liquid LiNbO3. This readily indicates a cluster composed of NbO6 octahedra with the strong cation-cation repulsion. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2008.09.117

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Ltd  

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 article, another DECT technique involving a balanced filter method using a conventional x-ray tube is described. For the spectral optimization of DECT using balanced filters, the author calculates beam-hardening error and air kerma required to achieve a desired noise level in electron density and effective atomic number images of a cylindrical water phantom with 50 cm diameter. The calculation enables the selection of beam parameters such as tube voltage, balanced filter material, and its thickness. The optimized parameters were applied to cases with different phantom diameters ranging from 5 to 50 cm for the calculations. The author predicts that the optimal combination of tube voltages would be 80 and 140 kV with Tb/Hf and Bi/Mo filter pairs for the 50-cm-diameter water phantom. When a single phantom calibration at a diameter of 25 cm was employed to cover all phantom sizes, maximum absolute beam-hardening errors were 0.3% and 0.03% for electron density and effective atomic number, respectively, over a range of diameters of the water phantom. The beam-hardening errors were 1/10 or less as compared to those obtained by conventional DECT, although the dose was twice that of the conventional DECT case. From the viewpoint of beam hardening and the tube-loading efficiency, the present DECT using balanced filters would be significantly more effective in measuring the electron density than the conventional DECT. Nevertheless, further developments of low-exposure imaging technology should be necessary as well as x-ray tubes with higher outputs to apply DECT coupled with the balanced filter method for clinical use. © 2009 American Association of Physicists in Medicine.

DOI： 10.1118/1.3157098

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The inverse dielectric function 1/epsilon(q) is newly obtained in terms of the charge-charge correlation functions S-ZZ(q) by the re-examined theory of dielectric screening in molten salts. The new theory is applied to the molten noble-metal halides, i.e. AgBr and CuBr, in order to obtain S-ZZ(q), and in due course, 1/epsilon(q). The inter-ionic screened potential phi(+-)(SC)(r) is estimated using 1/epsilon(q). The obtained screened potential phi(+-)(SC)(r) is treated as the potential of mean force to obtain the partial pair distribution function between cation and anion g(+-)(r). The results are compared to those obtained by diffraction experiments and molecular dynamics simulation. The deviation from Nernst-Einstein relation in the transport properties is also discussed. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2006.12.161

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

Dual-energy contrast agent-enhanced mammography is a technique of demonstrating breast cancers obscured by a cluttered background resulting from the contrast between soft tissues in the breast. The technique has usually been implemented by exploiting two exposures to different x-ray tube voltages. In this article, another dual-energy approach using the balanced filter method without switching the tube voltages is described. For the spectral optimization of dual-energy mammography using the balanced filters, we applied a theoretical framework reported by Lemacks et al. [Med. Phys. 29, 1739-1751 (2002)] to calculate the signal-to-noise ratio (SNR) in an iodinated contrast agent subtraction image. This permits the selection of beam parameters such as tube voltage and balanced filter material, and the optimization of the latter's thickness with respect to some critical quantity-in this case, mean glandular dose. For an imaging system with a 0.1 mm thick CsI:T1 scintillator, we predict that the optimal tube voltage would be 45 kVp for a tungsten anode using zirconium, iodine, and neodymium balanced filters. A mean glandular dose of 1.0 mGy is required to obtain an SNR of 5 in order to detect 1.0 mg/cm(2) iodine in the resulting clutter-free image of a 5 cm thick breast composed of 50% adipose and 50% glandular tissue. In addition to spectral optimization, we carried out phantom measurements to demonstrate the present dual-energy approach for obtaining a clutter-free image, which preferentially shows iodine, of a breast phantom comprising three major components-acrylic spheres, olive oil, and an iodinated contrast agent. The detection of iodine details on the cluttered background originating from the contrast between acrylic spheres and olive oil is analogous to the task of distinguishing contrast agents in a mixture of glandular and adipose tissues. (C) 2007 American Association of Physicists in Medicine.

DOI： 10.1118/1.2790841

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Language：English   Publishing type：Research paper (international conference proceedings)  

The screened effect in molten AgI-AgBr system is discussed by the inverse dielectric function 1/(q), which is newly obtained in terms of the charge-charge structure factor SZZ(q) by the re-examined theory of dielectric screening in molten salts. SZZ(q) and in due course, 1/(q) are obtained from structural properties of molten AgI-AgBr system by molecular dynamics (MD) simulations. The obtained 1/(q) is multiplied onto the attractive part in the inter-ionic potential between cation and anion to obtain the screened potential. The total screened potential is examined in terms of the potential of mean force.

DOI： 10.1080/08927020601067532

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

The theory of dielectric screening in molten salts is re-examined, using the charge - charge correlation functions S-zz(q). The inverse dielectric function 1/epsilon(q) is newly obtained in terms of Szz( q). This 1/epsilon(q) is multiplied onto the attractive part of the inter-ionic potential between cation and anion, in order to obtain the screened attractive potential phi(+-)(screened attractive)(r). A simplified but effectively screened repulsive potential is added to phi(+-)(screened attractive)(r) get the total screened potential phi(+-)(screened)(r). By using the computer simulation for molten NaCl, Szz( q), and 1/epsilon( q) are obtained. The total screened potential phi(+-)(screened)(r) so as to carry on the above procedure agreed fairly to the potential of mean force defined by the partial pair distribution function between cation and anion, g(+-)( r). A similar calculation was also carried out for molten RbBr, starting from the observed S-zz( q). And results for this system were fairly acceptable. From these, it is considered that the screened inter-ionic potential at a long distance between cation and anion in a molten salt is equivalent to the potential of mean force in it. These facts make it possible to use the potential of mean force obtained experimentally for the calculation of the deviation from the Nernst-Einstein relation in molten salts.

DOI： 10.1080/00319100601106713

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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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Publisher：Japan Association of Mineralogical Sciences  

The structure of disordered materials such as glasses and liquids is usually analyzed by the X-ray diffraction and obtained pair distribution functions are used in the structural discussion. This function corresponds to the probability of finding another atom at a distance r from the origin atom and careful analysis allows us to obtain the local structural image by estimating inter-atomic distances and corresponding coordination numbers at near neighbor region. However, recent structural studies of non-crystalline materials require the information covering middle range structure so as to discuss physico-chemical properties such as crystallization procedure. The reverse Monte Carlo (RMC) simulation technique is one way to obtain such middle range structure and present paper demonstrates a couple of structural studies analyzed by X-ray scattering coupled with RMC simulation method.

DOI： 10.14824/kobutsu.2005.0.86.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS  

A quasi monochromatic x-ray computed tomography (CT) system utilizing balanced filters has recently been developed for acquiring quantitative CT images. This system consisted of basic components such as a conventional x-ray generator for radiography, a stage for mounting and rotating objects, and an x-ray line sensor camera. Metallic sheets of Er and Yb were used as the balanced filters for obtaining quasi monochromatic incident x rays that include the characteristic lines of the W Kalpha doublet from a tungsten target. The mean energy and energy width of the quasimonochromatic x rays were determined to be 59.0 and 1.9 keV, respectively, from x-ray spectroscopic measurements using a high-purity Ge detector. The usefulness of the present x-ray CT system was demonstrated by obtaining spatial distributions of the linear attenuation coefficients of three selected samples-a 20 cm diameter cylindrical water phantom, a 3.5 cm diameter aluminum rod, and a human head phantom. The results clearly indicate that this apparatus is surprisingly effective for estimating, the distribution of the linear attenuation coefficients without any correction of the beam-hardening effect. Thus, implementing the balanced filter method on an x-ray CT scanner has promise in producing highly quantitative CT images. (C) 2004 American Association of Physicists in Medicine.

DOI： 10.1118/1.1819553

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

The three partial structural functions of molten AgBr have been determined by using a combination of the anomalous X-ray scattering (AXS) data and conventional neutron diffraction result. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique. The partial structure factor of αAgAg(Q) in molten AgBr was rather broad than that found in molten alkali halides such as RbBr. The resultant structural parameters suggest that the structure of molten AgBr is quite likely described by disordered close packing of Br ions where Ag ions are distributed in both octahedral and tetrahedral holes.

DOI： 10.1143/JPSJ.68.1932

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DOI： 10.3379/jmsjmag.23.480

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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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Other Link： https://jlc.jst.go.jp/DN/JALC/00049510119?from=CiNii

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

DOI： 10.2320/materia.36.505

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyoj.1996.3.0_283_1

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Language：Japanese   Publisher：広信社  

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

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Language：English   Publisher：WALTER DE GRUYTER GMBH  

A method has been presented for determining a local atomic structure in an amorphous thin film of sub-micron thickness grown on a substrate by the grazing incidence x-ray scattering (GIXS) method. The capability of this method was demonstrated by analyzing amorphous SiO2 and Si3N4 films 200 and 70 nm thick, respectively. A network structure in the amorphous SiO2 film consists of SiO4 tetrahedra connecting each other by oxygen atoms at their vertices. This resembles that in a bulk amorphous SiO2. The local ordering unit structure in the amorphous Si3N4 film was found to be a SiN4 tetrahedron. A significant feature in the present amorphous Si3N4 film is the presence of two types of Si-Si pairs in the near neighbor region while only one type is present in the alpha-Si3N4 crystal. This indicates that a part of the network structure formed by the SiN4 tetrahedra is quite different from that in its crystalline state. According to the coordination number of 3.8 for Si-N pairs, some nitrogen vacancies are quite likely involved in the film. Such nitrogen vacancies, then, are responsible for the modified network structure in the present amorphous Si3N4 film.

DOI： 10.1515/HTMP.1999.18.1-2.99

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Other Link： http://hdl.handle.net/10097/34257

Language：Japanese   Publisher：Tohoku University  

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：Japan Institute of Metals (JIM)  

Two different X-ray scattering experiments of θ-2θ X-ray scattering and grazing incidence X-ray scattering (GIXS) geometries have been done for evaluating the lattice strain anisotropically formed in the Co9Fe/Cu superlattices. The magnitude of lattice strain along Cu [001] and [110] directions which are parallel to the surface was estimated using GIXS geometry. The results confirm that the lattice strain along both directions increases with decreasing Cu thickness and its degree changes with a variation in orientation. On the other hand, the magnitude of lattice strain along two directions of Cu [110] (parallel to the surface) and Cu [110] (perpendicular to the surface) is found to differ from each other by comparing the lattice strain estimated from the measurements for equivalent Cu 220 reflections. The present results clearly suggest that the lattice strain formed in the Co9Fe/Cu superlattices depends upon the lattice orientation.

DOI： 10.2320/matertrans1989.39.557

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Language：English   Publisher：PHYSICAL SOC JAPAN  

An apparatus for controling the glancing angle of incident beam from a synchrotron source has been newly built for structural studies of high temperature liquids by the anomalous X-ray scattering (AXS) method in the reflection mode. The usefulness and capability of this apparatus were demonstrated by obtaining the individual partial structural functions of the liquid Bi30Ga70 alloy using the energies close to the Ga K and Bi L-III absorption edges. The data processing for estimating three partials includes the intensity data, obtained at the energy of 15.0 keV, which is far from both edges and the reverse Monte Carlo (RMC) simulation technique. The resultant partial structural function for Ga-Ga pairs was found to be rather similar to that of pure Ga. On the other hand, partial structural function for Bi-Bi pairs differs from the pure Bi case and the coexistence of more than two species is rather well-recognized in the Bi30Ga70 liquid alloy.

DOI： 10.1143/JPSJ.66.3120

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Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/S1359-6462(96)00466-6

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Language：English   Publisher：PHYSICAL SOC JAPAN  

The individual partial structural functions of molten CuBr have been estimated from the anomalous X-ray scattering (AXS) measurements. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique. The cation-cation structure factor of a(CuCu)(Q) was found to be rather structureless and the closest Cu-Cu distance in molten CuBr was significantly smaller than that for Br-Br, indicating the like-ion penetration into the first unlike-ion coordination shell; similar to the molten CuCl case. It is then suggested that a disordered close packing of Br- ions where Cu+ ions meander so as to take strongly disordered distribution by penetrating through the tetrahedral holes.

DOI： 10.1143/JPSJ.66.633

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Language：Japanese   Publisher：アグネ技術センタ-  

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Language：English   Publisher：JOHN WILEY & SONS LTD  

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Language：English   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

Thin Fe, Fe2O3 and Cr2O3 films deposited on Si wafers have been investigated by grazing incidence X-ray scattering (GIXS) and the results have been compared with microstructural data by atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that changes in density of these films can be estimated from the critical angle in X-ray reflection curves. Measurements in GIXS with two different geometries indicate the preferential orientation of crystalline Fe and Fe2O3 films. AFM and TEM observation shows characteristic features in microstructures of the films, and it is indicate that a ten nanometer order of magnitude of roughness in the surface prevents the oscillations in the X-ray reflection curves.

DOI： 10.1016/S0040-6090(96)08922-5

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Anomalous X-ray scattering (AXS) intensities have been measured at the absorption edges of Fe K and Gd L(III) for amorphous GdM(2) (M = Fe, Co, Ni) alloys prepared by sputtering. The possible atomic arrangements in the near-neighbor region, such as interatomic distances and coordination numbers of amorphous GdM, alloys, were estimated from least-squares analysis so as to reproduce the environmental interference functions as well as the ordinary interference function. The coordination numbers for the Gd-Gd pair increase in the order a-GdNi2, GdCo2 to GdFe2, whereas those for the M-Gd pair vary in the reverse order. Such a variation is also seen in hydrogen-induced amorphous GdM(2)H(x) (M = Fe, Co, Ni) alloys.

DOI： 10.1016/S0022-3093(96)00299-2

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

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Language：English   Publisher：JAPAN INST METALS  

A new method has been proposed for determining the atomic number density of a near-surface element in materials using its grazing X-ray reflection and anomalous dispersion effect. The essential equations for analyzing the measured intensity data and the capability of this anomalous grazing X-ray reflection (AGXR) method have been described by obtaining the atomic number densities of near surface elements in some selected examples of ZrO2-Y2O3 crystal, Cr thin film grown on a glass substrate and passivated stainless steel. The variation of the critical angles of total external reflection through the anomalous dispersion effect was clearly detected and the results suggest the AGXR method is rather surprisingly works well, although there are differences in detail when compared with the values calculated from the bulk density.

DOI： 10.2320/matertrans1989.37.39

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Language：English   Publisher：Elsevier  

X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray scattering (GIXS) have been used for characterizing thin oxide films formed on Fe-10 ∼ 90mass%Cr alloys by heating at 873 K in air. The XPS depth profiles indicate that the oxide film of Fe-10mass%Cr alloy consists of mainly an iron oxide, and a chromium oxide is predominant in the oxide film formed on alloys with chromium more than 50mass%. In Fe-30mass%Cr alloy, the oxide film consists of a two layered structure
iron rich oxide in the outer layer and chromium rich oxide in the inner layer. The thickness of the oxide films appears to be insensitive to the bulk chromium concentration in the range between 30 and 90 mass% under the present oxidation condition. The GIXS results identify the main crystallographic structure of the oxide film with corundum (Fe2O3 or Cr2O3) type structure, although it includes the preferential orientation and depends on the bulk chromium concentration.

DOI： 10.1016/0169-4332(95)00596-X

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Other Link： http://hdl.handle.net/10097/34039

Language：English   Publisher：JAPAN INST METALS  

An in-house grazing incidence X-ray scattering (GIXS) apparatus has been newly developed for characterizing the surface structure at a microscopic level. This system consists of an 18-kW relating anode X-ray generator, a flat or channel-cut Ge(111) single crystal monochromator and crossed double-axis diffractometers. Using this new apparatus, the X-ray reflection profiles of chromium oxide films grown on colored stainless steels were measured. The values of critical angle and thickness of films are estimated and the density variation of chromium oxide films is suggested. Surface diffraction profiles from the SUS304 stainless steel oxidized for 240 s at 1073 K in air were also measured in the vicinity of the critical angle with the GIXS geometry. The observed peaks were identified as Cr2O3, FeCr2O4 and the austenite phase of SUS304. The depth profile has also been discussed from the integrated intensities of both phases of oxide and the stainless steel.

DOI： 10.2320/matertrans1989.36.1

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The anomalous X-ray scattering (AXS) method using Cu and Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (CuI)0.3(Cu2O)0.35(MoO3)0.35. The possible atomic arrangements in near-neighbor region of this glass were estimated by coupling the results with the least-squares analysis so as to reproduce two differential intensity profiles for Cu and Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be 6.1 at the distance of 0.187 nm. This implies that the MoO6 octahedral unit is a more probable structural entity in the glass rather than MoO4 tetrahedra which has been proposed based on infrared spectroscopy. The pre-peak shoulder observed at about 10 nm−1 may be attributed to density fluctuation originating from the MoO6 octahedral units connected with the corner sharing linkage, in which the correlation length is about 0.8 nm. The value of the coordination number of I− around Cu+ is estimated as 4.3 at 0.261 nm, suggesting an arrangement similar to that in molten CuI. © 1995, The Japan Institute of Metals. All rights reserved.

DOI： 10.2320/matertrans1989.36.1434

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Other Link： http://hdl.handle.net/10097/00119461

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Other Link： http://hdl.handle.net/10097/33963

Language：English   Publisher：VERLAG Z NATURFORSCH  

Anomalous X-ray scattering (AXS) has been applied to study the structure of amorphous platinum disulfide, Pt1-xS2, prepared by the precipitation process. The local atomic arrangement in amorphous Pt1-xS2 was determined by the least-squares variational method so as to reproduce the experimental differential interference function at the Pt L(III) absorption edge by the AXS method as well as the ordinary interference function by MoK alpha. The structural unit in amorphous Pt1-xS2 is found to be a PtS6 octahedron, similar to that in crystalline PtS2. These octahedra share both their corners and edges, while only edge-sharing linkages occur in crystalline PtS2.

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Language：English   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

In this paper we discuss some characteristic features of the thermodynamic properties of the Al1-xMnx alloys from which quasi-crystalline phases are generated by rapid quenching. The measurements performed by the Knudsen cell mass spectrometric technique lead to the Gibbs free energy of the alloys at 1570 K. The thermodynamic behaviour indicates a moderate ordering effect due to attractive interactions between aluminium and manganese atoms. The entropy of formation is slightly positive and a compilation of about ten aluminium-based alloys suggests that it could be a significant feature of the quasi-crystal-forming alloys.

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Other Link： http://hdl.handle.net/10097/33895

Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：ELSEVIER SCIENCE BV  

The investigations of the physical properties of solid solution (AgxCu1-x)Br have been reviewed. Structural analysis by X-ray diffraction was given first. The diffraction data were interpreted as an evidence for a massive disorder with cation interstitial concentrations increasing with amounts of Cu+ ions in AgBr. Next the disordered distribution of cations was examined from a thermodynamical point of view. The electrical conductivities and transport numbers of the solid solution (AgxCu1-x) Br have been measured as a function of temperature and composition in order to investigate the contribution of Cu+ dissolved in AgBr to the transport properties. The enthalpies of formation and migration for cations show an exponential decrease with increasing amount of Cu+ into AgBr lattice. The lowering is attributable to the lattice expansion by the occupation of Cu+ at the interstitial sites. The effect of exponential decrease in the formation enthalpy is to allow a rapid growth in the concentration of interstitials around the composition of x=0.85. The creation of massive defects is probably responsible for the high ionic conductivity in the solid solution of this system.

DOI： 10.1016/0167-2738(93)90004-M

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Language：English   Publisher：PHYSICAL SOCIETY JAPAN KIKAI-SHINKO BUILDING  

The electrical conductivities and transport numbers of the solid solution (AgxCu1-x)Br have been measured as a function of temperature and composition. An attempt to determine the partial conductivities and activation energies for mobile ions is made from these results. The estimated enthalpies of formation and migration for Ag+ and Cu+ ions show an exponential decrease with increasing amount of Cu+ into AgBr lattice. The lowering is attributable to the lattice expansion by the occupation of Cu+ at the interstitial sites. The effect of exponential decrease in the formation enthalpy is to allow a rapid growth in the concentration of interstitials around the composition of chi congruent-to 0.85. This result is consistent with structural data derived by X-ray diffraction.

DOI： 10.1143/JPSJ.60.3415

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Language：English   Publisher：PHYSICAL SOCIETY JAPAN KIKAI-SHINKO BUILDING  

The investigations of dilatometry and X-ray diffraction for the polycrystalline of (Ag(x)Cu1-x)Br in the composition range 0.3 less-than-or-equal-to x less-than-or-equal-to 1.0 have been carried out. An abrupt increase of lattice constant a0 was observed at about 230-degrees-C and the composition dependence of a0's showed considerable deviations from the Vegard's law. The observed anomalous expansion of the lattice was caused due to the occupation of Cu+ ions at the interstitial sites which possess relatively small cavity. It is considered that the lattice expansion enables even Ag+ ions having larger ionic radius to migrate to the interstitial sites. The disordered distribution of cations is the reason of high ionic conductivity in the mixed crystals of silver and cuprous bromides.

DOI： 10.1143/JPSJ.60.573

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DOI： 10.1143/JPSJ.58.4041

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DOI： 10.1016/0167-2738(89)90322-6

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Language：English   Publisher：PHYSICAL SOCIETY JAPAN  

DOI： 10.1143/JPSJ.58.527

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