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Tomiyasu, Keisuke*; Ito, Naoko*; Okazaki, Ryuji*; Takahashi, Yuki*; Onodera, Mitsugi*; Iwasa, Kazuaki*; Nojima, Tsutomu*; Aoyama, Takuya*; Ogushi, Kenya*; Ishikawa, Yoshihisa*; et al.
Advanced Quantum Technologies (Internet), 1(3), p.1800057_1 - 1800057_7, 2018/12
Spin-state transition, also known as spin crossover, plays a key role in diverse systems. In theory, the boundary range between the low- and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that the Sc substitution in LaCoO3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co-O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low- and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition.
Cs in seabed sediment off the Fukushima coast; Implications from numerical simulationsMisumi, Kazuhiro*; Tsumune, Daisuke*; Tsubono, Takaki*; Tateda, Yutaka*; Aoyama, Michio*; Kobayashi, Takuya; Hirose, Katsumi*
Journal of Environmental Radioactivity, 136, p.218 - 228, 2014/10
Times Cited Count：22 Percentile：54.1(Environmental Sciences)Major controls on spatiotemporal variations of Cs activity in seabed sediments derived from the Fukushima Dai-ichi Nuclear Power Plant accident during the first year after the accident were investigated by using numerical simulations. The model successfully reproduced major features of the observed spatiotemporal variations of Cs activity in sediments. The spatial pattern of Cs in sediments, which mainly reflected the history of Cs activity in the bottom water overlying the sediment and the sediment particle size distribution, became established during the first several months after the accident. Taking Cs activities in sediments in the coastal area and in the vicinity of the power plant into account, increased the simulated total inventory of Cs in sediments off the Fukushima coast to a value on the order of 10
Bq.
Maeda, Shigetaka; Saikawa, Takuya*; Aoyama, Takafumi
JNC TN9410 2001-005, 219 Pages, 2001/03
JNC-TN9410-2001-005.pdf:4.92MB
Neutron fluence and related spectral information are key parameters in post-irradiation test analysis so they need to be evaluated accuracy. Nuclear calculations and a number of reactor dosimetry tests have been conducted in the JOYO experimental fast reactor to assure reliable and accurate neutron fluence for fuel and material irradiation tests. This paper describes the multiple activation foil dosimetry technique for neutron fluence evaluation. Neutron fluence was determined with neutron spectrum adjustment using measured reaction rates of a set of activation foils. Dosimetry results from individual fuel and material irradiation tests and a surveillance test characterized the neutron field of the JOYO MK-II core. Neutron flux in the JOYO core region was calculated using diffusion theory in a three-dimensional Hex-Z geometry. Flux in the stainless steel reflector region, which is outside the core, was calculated using the DORT two-dimensional transport calculation code. It is essential to correct the dosimetry results for locations far outside the core region. With corrected values, the calculated to experimental value (C/E) was approximately 1.05 in the core region and 1.1
1.5 in the reflector region.
Ito, Chikara; Aoyama, Takafumi; Masui, Tomohiko*; Saikawa, Takuya*
JNC TN9400 99-029, 26 Pages, 1999/03
The material dosimetry using the multiple foil activation method has been carried out in order to assure the accuracy and reliability of neutron fluences for the irradiation tests in the experimental fast reactor "JOYO". In this study, the neutron fluences were calculated by the JOYO core management code system "MAGI" for the subassemblies which were irradiated at the positions around control rods or reflector boundary in the JOYO Mk-II core. Improvement of neutron fluence was evaluated when the "MAGI" calculation was corrected with the dosimetry results. The difference of the neutron spectrum adjustment was also investigated between ENDF/B-V and JENDL-3 dosimetry files. The major results obtained are summarized as follows; (1)The reaction rates of the dosimeters calculated by the adjusted neutron spectrum agreed well with the measured values, and its error was reduced. (2)The neutron spectrum adjusted using JENDL-3 dosimetry file was significantly improved than that by ENDF/B-V in the energy range of 10100 keV, because of the less error of the neutron capture cross sections of Co and Sc. (3)It showed that the correction rate of the "MAGI" calculation by the dosimetry results ranged 1030% for the subassemblies of the JOYO irradiation test.
Aoyama, Takafumi; *; Sumino, Kozo; Saikawa, Takuya*
PNC TN9410 98-004, 74 Pages, 1997/12
The Corrosion Product (CP) is the major radiation source in the primary cooling system of an LNFBR plant. It is important to characterize and predict the CP behavior to reduce the personnel exposure dose due to CP deposition. The CP measurement was carried out in the Experimental Fast Reactor JOYO during the 11th annual inspection period when the accumulated reactor thermal power reached about l43GWd. The CP deposition density was measured using a pure germanium detector. The plastic scintillation fiber (PSF) was applied for the gamma-ray dose rate distri bution measurement and compared with the thermoluminescence dosimeter (TLD). The major results obtained by the CP measurements in JOYO are the follows: (1)The major CP nuclides deposited in the primary cooling system are 
Mn and 
CO. Mn is the dominant isotope and it tends to deposit in the cold leg region. On the other hand, Co deposits mainly in the hot leg region. The deposition density of Mn is about seven times as much as that of Co in the cold leg region and twice in the hot leg region. (2)The deposition densities of Mn and Co, and the gamma-dose rate were decreased from the last data in the previous annual inspection period mainly due to the short operation time and the longer cooling time. (3)The continuous gamma-ray dose rate distribution up to 10m can be measured by using the PSF in a few minutes. The PSF is suitable to measure the gamma-ray dose rate distribution in the maintenance work area where it is narrow and the mixture of gamma-ray sources from primary pipings and components. The data base of detailed gamma-ray dose rate distribution was greatly extended by the PSF.
Maeda, Shigetaka; Ito, Chikara; Aoyama, Takafumi; Saikawa, Takuya*; Masui, Tomohiko*
no journal, ,
In 2003, Joyo MK-III core was upgraded to increase the irradiation testing capability. This paper describes the details of distributions of neutron flux and reaction rate in the MK-III core that was measured by characterization tests during the first two operating cycles. The calculation accuracy of the core management codes HESTIA, TORT and MCNP, was also evaluated by the measured data. The calculated fission rates of 
U by HESTIA agreed well with the measured one within approximately 4% in the fuel region. MCNP could simulate within 6% in the central non-fuel irradiation test subassembly and the radial reflector region, while large discrepancies were obtained in TORT results. Hence, the precise geometry model was effective in evaluating the neutron spectrum and the flux at such locations.
