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Journal Articles

Imaging of radiocesium dynamics in soybean by using a high-resolution gamma camera

Yin, Y.-G.; Kawachi, Naoki; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 112, 2016/02

Journal Articles

Development of a gamma camera system for high-energy gamma photon for quantitative observation of $$^{137}$$Cs movement in a plant body

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 94, 2016/02

Journal Articles

Imaging of radiocesium uptake dynamics in a plant body by using a newly developed high-resolution gamma camera

Kawachi, Naoki; Yin, Y.-G.; Suzui, Nobuo; Ishii, Satomi; Yoshihara, Toshihiro*; Watabe, Hiroshi*; Yamamoto, Seiichi*; Fujimaki, Shu

Journal of Environmental Radioactivity, 151(Part 2), p.461 - 467, 2016/01

 Times Cited Count:5 Percentile:55.17(Environmental Sciences)

Journal Articles

Magnetic and electronic properties of URu$$_2$$Si$$_2$$ revealed by comparison with nonmagnetic references ThRu$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$

Emi, Naoya*; Hamabata, Ryosuke*; Nakayama, Daisuke*; Miki, Toshihiro*; Koyama, Takehide*; Ueda, Koichi*; Mito, Takeshi*; Kohori, Yo*; Matsumoto, Yuji*; Haga, Yoshinori; et al.

Journal of the Physical Society of Japan, 84(6), p.063702_1 - 063702_4, 2015/06

 Times Cited Count:9 Percentile:31.29(Physics, Multidisciplinary)

Journal Articles

Size and dopant-concentration dependence of photoluminescence properties of ion-implanted phosphorus- and boron-codoped Si nanocrystals

Nakamura, Toshihiro*; Adachi, Sadao*; Fujii, Minoru*; Sugimoto, Hiroshi*; Miura, Kenta*; Yamamoto, Shunya

Physical Review B, 91(16), p.165424_1 - 165424_8, 2015/04

 Times Cited Count:10 Percentile:36.72(Materials Science, Multidisciplinary)

Semiconductor nanocrystals have unique electrical and optical properties, because of the quantum confinement effect, and the doping of impurities into nanocrystals. In this study, we investigated the photoluminescence (PL) properties of phosphorus- (P) and boron- (B) co-doped Si nanocrystals (Si NCs), which was synthesized using an ion implantation technique. The Si-NC size (average diameter: 3.5, 4.4, 5.2 nm) and the P and B ion doses (0.1-4.5$$times$$10$$^{16}$$ cm$$^{-2}$$)values were systematically varied. We find that the PL peak energy shifts to lower values with increasing the average diameters of Si NCs and PB ion dose. The results of PL measurements indicate that the PL spectra are due to the band-to-band transition at the reduced Si-NC band gap caused by the formation of impurity and the radiative transitions between defect- and/or impurity-related localized states. It was found that the PL properties can be controlled by varying the Si-NC size as well as the dopant concentration.

Journal Articles

Phosphorus and boron codoping of silicon nanocrystals by ion implantation; Photoluminescence properties

Nakamura, Toshihiro*; Adachi, Sadao*; Fujii, Minoru*; Miura, Kenta*; Yamamoto, Shunya

Physical Review B, 85(4), p.045441_1 - 045441_7, 2012/01

 Times Cited Count:20 Percentile:25.42(Materials Science, Multidisciplinary)

Silicon nanocrystals (Si-nc's) such as nanometer-sized Si dots embedded in a SiO$$_{2}$$ matrix and porous Si have been intensively investigated because of their interesting photoluminescence (PL) properties. Si-nc's exhibit strong and visible emission at room temperature. Because of their compatibility with Si-based technology, light-emitting Si-nc's are an attractive candidate for materials used in various optoelectronic device applications. In this study, the PL properties of n- and p-type dopants phosphorus (P) and boron (B) co-doped Si-nc's prepared by the ion implantation were studied. For (P, B) co-doped Si-nc's, the donor-acceptor (D-A)-pair recombination emission was clearly observed on the long-wavelength side of the intrinsic Si-nc emission. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc's.

Journal Articles

Recent progress in the energy recovery linac project in Japan

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

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

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

Journal Articles

Study on double heterogeneity effect of Pu-rich agglomerates in mixed oxide fuel using cross section homogenization method for particle-dispersed media

Yamamoto, Toshihiro

Annals of Nuclear Energy, 37(3), p.398 - 405, 2010/03

 Times Cited Count:5 Percentile:56.14(Nuclear Science & Technology)

A cross section homogenization method for media containing randomly and uniformly dispersed particles has been applied to MOX fuels containing Pu-rich agglomerates. This method (Shmakov method), which is incorporated into a Monte Carlo code MCNP, has been applied to lattice calculations of an infinite MOX fuel rod array. Shmakov method can accurately reproduce the calculation results for a heterogeneous arrangement of Pu-rich agglomerates. A correction factor used to define an effective microscopic cross section provides a quantitative indication of the double heterogeneity of Pu-rich agglomerates. The correction factors exhibit an obvious double heterogeneity effect. However, the double heterogeneity effect of Pu-rich agglomerates on k-eff seems to be unexpectedly minor because the underestimate of the reaction rates in the resonance energy range is offset by the overestimate of the reaction rates in the thermal energy range.

JAEA Reports

Second version of data collection part of nuclear criticality safety handbook (Contract research)

Okuno, Hiroshi; Suyama, Kenya; Tonoike, Kotaro; Yamane, Yuichi; Yamamoto, Toshihiro; Miyoshi, Yoshinori; Uchiyama, Gunzo

JAEA-Data/Code 2009-010, 175 Pages, 2009/08

JAEA-Data-Code-2009-010.pdf:13.1MB
JAEA-Data-Code-2009-010(errata).pdf:0.11MB

The report revised the Data Collection part of Nuclear Criticality Safety Handbook, which was published in 1988. This second version provided criticality data on homogeneous U-H$$_{2}$$O and UF$$_{6}$$-HF, which were not cited in the previous version, and increased those data on the medium-enriched uranium fuels. Calculations were performed mainly with the Continuous-Energy Monte Carlo Criticality Calculation Code, MVP, and the Japanese Evaluated Nuclear Data Library, JENDL-3 Revision 2, JENDL-3.2, both of which were developed at the late Japan Atomic Energy Research Institute (JAERI). Data on atomic number densities of actinide metal and oxide were additionally supplied, and nuclide compositions of irradiated fuels were improved from the first version. One million histories of neutrons were followed in benchmark calculations of critical experiments and in calculations of single-unit criticality data, i.e., critical mass, volume, dimensions, etc., to attain almost ten times higher precision than the first version.

Journal Articles

Benchmark critical experiments and FP worth evaluation for a heterogeneous system of uranium fuel rods and uranium solution poisoned with pseudo-fission-product elements

Tonoike, Kotaro; Yamamoto, Toshihiro; Miyoshi, Yoshinori; Uchiyama, Gunzo; Watanabe, Shoichi*

Journal of Nuclear Science and Technology, 46(4), p.354 - 365, 2009/04

A series of critical experiments were performed using heterogeneous cores at the Static Experiment Critical Facility in Japan Atomic Energy Agency in order to obtain systematic benchmark data concerning dissolving process in a reprocessing plant. Focusing on the introduction of the burn-up credit, critical mass measurement was conducted for a combination of uranium dioxide fuel rods (5wt% $$^{235}$$U) and uranyl nitrate solution (6wt% $$^{235}$$U) poisoned with pseudo fission product (FP) elements - samarium, cesium, rhodium, and europium. Fuel rods were arrayed with an 1.5-cm lattice interval in the poisoned fuel solution in a 60-cm diameter cylindrical tank. The uranium concentrations of the solution was roughly kept at about 320gU/L, and the FP element concentrations were adjusted to be equivalent to a burn-up of about 30GWd/t. The result provides basic experimental data for validation of computational methods to evaluate a reactivity effect of each FP element, as well as benchmark criticality data for validation of neutron multiplication factor calculation of heterogeneous systems of spent fuel. In the report, detail of the experiments and its benchmark models will be presented as well as the procedure and the result of separate reactivity worth evaluation for each FP element. The experimental result and the computational evaluation will also be compared.

Journal Articles

Convergence of the second eigenfunction in Monte Carlo power iteration

Yamamoto, Toshihiro

Annals of Nuclear Energy, 36(1), p.7 - 14, 2009/01

 Times Cited Count:17 Percentile:18.39(Nuclear Science & Technology)

The conditions of convergence in a modified Monte Carlo power iteration method to generate the eigenfunction with the second largest criticality eigenvalue, which was originally proposed by Booth, have been defined with a different approach. In this work, the first and second eigenvectors composed of two volume-integrated fission source intensities defined in two-partitioned regions are used for deriving the convergence conditions. The conditions of convergence as shown by Booth are found to be true in the limit of a small amplitude of the first eigenfunction. Following the method that uses two estimates of the second eigenvalue defined in two-partitioned regions, a new method for removing the fundamental mode eigenfunction from the fission source distributions has been shown. Because of the explicit removal of the first eigenfunction, the validity of this method is convincing as a technique for obtaining the second eigenfunction. Although this method needs the first eigenfunction and eigenvalue, and the subtraction of the first eigenfunction from the fission source distribution, it has the advantage in that the adjoint mode calculation that is in general difficult for continuous energy Monte Carlo codes is not required.

Journal Articles

Progress in R&D efforts on the energy recovery linac in Japan

Sakanaka, Shogo*; Ago, Tomonori*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; Harada, Kentaro*; Hiramatsu, Shigenori*; Honda, Toru*; et al.

Proceedings of 11th European Particle Accelerator Conference (EPAC '08) (CD-ROM), p.205 - 207, 2008/06

Future synchrotron light sources based on the energy-recovery linacs (ERLs) are expected to be capable of producing super-brilliant and/or ultra-short pulses of synchrotron radiation. Our Japanese collaboration team is making efforts for realizing an ERL-based hard X-ray source. We report recent progress in our R&D efforts.

Journal Articles

Benchmark critical experiments and FP worth evaluation for a heterogeneous system of uranium fuel rods and pseudo FP doped uranium solution

Tonoike, Kotaro; Miyoshi, Yoshinori; Uchiyama, Gunzo; Watanabe, Shoichi*; Yamamoto, Toshihiro*

Proceedings of 8th International Conference on Nuclear Criticality Safety (ICNC 2007), p.222 - 227, 2007/05

In order to obtain systematic benchmark criticality data concerning dissolving process in a reprocessing plant for LWR spent fuel, a series of critical experiments were performed using heterogeneous cores at the Static Experiment Critical Facility (STACY) in Japan Atomic Energy Agency (JAEA). Focusing on the introduction of the burn-up credit to the process, critical mass measurement was conducted for a combination of uranium fuel rods and uranium solution where pseudo fission product (FP) materials were doped. In this report, the "pseudo FP materials" means elements such as Sm, Cs, Rh and Eu whose isotopic composition is natural but which contains some FP nuclide(s). The result is going to provide basic experimental data for validation of computational methods to evaluate a reactivity effect of each FP material, as well as benchmark criticality data for validation of neutron multiplication factor calculation of heterogeneous systems of spent fuel. In the report, detail of the experiments including a differential reactivity worth curve over the solution level variation is going to be provided as well as the procedure and the result of separate reactivity worth evaluation of each pseudo FP material. Comparison of the experimental result and the computational evaluation will also be presented.

JAEA Reports

Material data for criticality transient phenomena analysis of MOX powder system; Data of MOX and zinc stearate powders (Contract research)

Yamane, Yuichi; Sakai, Mikio*; Abe, Hitoshi; Yamamoto, Toshihiro*; Okuno, Hiroshi; Miyoshi, Yoshinori

JAEA-Data/Code 2006-021, 75 Pages, 2006/10

JAEA-Data-Code-2006-021.pdf:24.75MB

Propety data of MOX, Zinc Stearate, etc. were investigated and examined as part of the development for criticality accident evaluation method for MOX fuel fabrication facility. Property data gathered for the powders of MOX, UO$$_{2}$$, Zinc Stearate, Tungsten and their mixture were density, specific heat, thermal conductivity and etc. as well as the data concerning fluidization or degree of mixing.

Journal Articles

Extension of cross section homogenization method for particle-dispersed media to layered particles

Yamamoto, Toshihiro

Annals of Nuclear Energy, 33(9), p.804 - 812, 2006/06

 Times Cited Count:2 Percentile:79.37(Nuclear Science & Technology)

A cross section homogenization method for media containing randomly dispersed particles, which was originally developed by Shmakov et al., and then was improved by Yamamoto et al., is extended to layered particles, such as coated fuel particles of gas-cooled reactors. A new extended formulation is derived for concentric double-layered spherical particles. This formulation is successfully implemented into a continuous energy Monte Carlo code MCNP, and is applied to some examples including a simplified gas-cooled reactor core. The extended method for double-layered spherical particles provides as accurate results as the previously developed method for mono-layered particles does. For the simple gas-cooled reactor core, the new method reproduces keff within several hundreds of pcm as compared to the direct heterogeneous calculation in which double-layered spherical particles are explicitly distributed in the fuel compact. Whereas the previously developed method for mono-layered particles can be performed analytically, this new technique requires numerical integration, making the computation efficiency of the new method deteriorate. However, this method allows one to perform Monte Carlo criticality calculations for double-layered particle-dispersed media with much less computing time than direct heterogeneous calculations.

Journal Articles

Extension of effective cross section calculation method for neutron transport calculations in particle-dispersed media

Yamamoto, Toshihiro; Miyoshi, Yoshinori; Takeda, Toshikazu*

Journal of Nuclear Science and Technology, 43(1), p.77 - 87, 2006/01

 Times Cited Count:5 Percentile:57.94(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Education method on Monte Carlo Analysis in atomic energy

Sakurai, Kiyoshi; Yamamoto, Toshihiro

Nippon Genshiryoku Gakkai Wabun Rombunshi, 4(4), p.248 - 258, 2005/12

no abstracts in English

Journal Articles

Concerned items on variance reduction method of Monte Carlo calculation written in published literatures; A Logic of Monte Carlo calculation = from experience to science

Sakurai, Kiyoshi; Yamamoto, Toshihiro

Nippon Genshiryoku Gakkai Wabun Rombunshi, 4(3), p.219 - 226, 2005/09

no abstracts in English

Journal Articles

A Estimation methods of lower weight bound on neutron deep penetration problem with Monte Carlo method

Sakurai, Kiyoshi; Yamamoto, Toshihiro

Nippon Genshiryoku Gakkai Wabun Rombunshi, 4(2), p.172 - 176, 2005/06

Typical weight estimation methods with Monte Carlo method such as MCNP default, empirical formula, mono-energy neutron attenuation curve, MCNP wwg and adjoint flux are described. The mono-energy neutron attenuation curve method is proposed by authors. Weights estimated by methods except MCNP default and adjoint flux methods are compared with those calculated by MCNP wwg method.

Journal Articles

Highly polarized electrons from GaAs-GaAsP and InGaAs-AlGaAs strained-layer superlattice photocathodes

Nishitani, Tomohiro; Nakanishi, Tsutomu*; Yamamoto, Masahiro*; Okumi, Shoji*; Furuta, Fumio*; Miyamoto, Masaharu*; Kuwahara, Makoto*; Yamamoto, Naoto*; Naniwa, Kenichi*; Watanabe, Osamu*; et al.

Journal of Applied Physics, 97(9), p.094907_1 - 094907_6, 2005/05

 Times Cited Count:45 Percentile:15.72(Physics, Applied)

no abstracts in English

94 (Records 1-20 displayed on this page)