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Volume 42, Issue 8
Displaying 1-5 of 5 articles from this issue
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Preface
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Yoshinori UCHIKAWA2007 Volume 42 Issue 8 Pages 243
Published: August 25, 2007
Released on J-STAGE: October 27, 2008
JOURNAL FREE ACCESSDownload PDF (579K)
Review Articles
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Takashi KATO, Tomokazu ASO, Hideki TATSUMOTO, Shoichi HASEGAWA, Kiichi ...2007 Volume 42 Issue 8 Pages 244-254
Published: August 25, 2007
Released on J-STAGE: October 27, 2008
JOURNAL FREE ACCESSThe Japan Atomic Energy Agency and the High-Energy Accelerator Research Organization are collaborating in the construction of the Japan Proton Accelerator Research Complex, a high-intensity proton accelerator complex with MW beam power. The use of various secondary particle beams (neutrons, mesons, antiprotons, etc.) that are produced in proton-nucleus reactions is the prime purpose of the project. Accordingly, four science experimental facilities are being constructed, including a materials and life science experimental facility, a nuclear and particle experimental facility, a neutrino experimental facility, and a nuclear transmutation facility (planned for the future). At the materials and life science experimental facility, where materials or biological structures are analyzed by neutron beam scattering experiments, a spallation neutron source has been constructed to provide experiment users with neutron beams that have the world's highest pulse intensity. Neutrons produced using spallation reaction should possess a high energy of MeV order, but neutrons used for experiments should have energy of a low meV order. Therefore, an effective material that is capable of moderating neutron energy by approximately nine orders is required. That material is supercritical hydrogen; and the spallation neutron source should therefore be equipped with a cryogenic hydrogen system that provides supercritical hydrogen to the neutron energy moderating system. This paper discusses the spallation neutron source and introduces the cryogenic hydrogen system that is used for constructing the neutron source.View full abstractDownload PDF (1374K) -
Takashi KATO, Tomokazu ASO, Hideki TATSUMOTO, Shoichi HASEGAWA, Kiichi ...2007 Volume 42 Issue 8 Pages 255-264
Published: August 25, 2007
Released on J-STAGE: October 27, 2008
JOURNAL FREE ACCESSThe Japan Atomic Energy Agency has been constructing the Japan Proton Accelerator Research Complex (J-PARC), a high intensity proton accelerator complex with MW beam power, in collaboration with the High-Energy Accelerator Research Organization. The materials and life science experimental facility (MLF), where materials and biological structures are analyzed using neutron beam-scattering experiment, has been constructed as one of the experimental science facilities at J-PARC. A spallation neutron source that produces neutrons through nuclear spallation reaction using high-energy proton beam injection and provides neutron beams for experimental users has been installed at the MLF. Hydrogen nuclei are used as a neutron moderating material (moderator) to reduce the neutron energy from MeV to meV order. Therefore, a cryogenic hydrogen system should be installed at the spallation neutron source to provide supercritical hydrogen to moderators. This paper describes the safety design of the cryogenic hydrogen system. Especially, the system is subject to high-pressure gas safety laws, and refrigeration safety regulations are applied to the system for the first time. We also discuss the technical contents that were argued through this application.View full abstractDownload PDF (1217K)
Originals
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Myoungjoo PARK, Takaya TERADA, Yoko AKIYAMA, Yoshinobu IZUMI, Shigehir ...2007 Volume 42 Issue 8 Pages 265-269
Published: August 25, 2007
Released on J-STAGE: October 27, 2008
JOURNAL FREE ACCESSTo examine the mechanism of cell death, it is important to design a temperature program for cryoablation. In this study, the cause of cell death is discussed based on the correlation between cell survival rate and cell morphology. Cell survival rate after freezing and thawing was evaluated using the MTT (3-(4,5-dimethyl-2-thiazoly)-2,5-diphenyltetrazolium Bromide) method. We also observed change in cell morphology during the freezing-thawing process using an optical microscope. The survival rate decreased, and the percentage of cell diameter change rate increased as the freezing-thawing speed increased. This result suggests that a large change in the ratio of cell diameter causes cell death. It is believed that the osmosis phenomenon during freezing and thawing is one of the factors that causes changes in cell morphology and it results in the cell death.View full abstractDownload PDF (1132K) -
Yui ISHII, Yoshiaki TAZAKI, Takayoshi NAKASHIMA, Hiraku OGINO, Shigeru ...2007 Volume 42 Issue 8 Pages 270-277
Published: August 25, 2007
Released on J-STAGE: October 27, 2008
JOURNAL FREE ACCESSEffects of RE mixing and dilute impurity doping for the CuO chain on the critical current properties for RE123 melt-solidified bulks were investigated. Low level Lu or Tb mixing to the RE site of Y123 or Dy123 melt-solidified bulks showed high Jc characteristics compared to the undoped bulks. Especially in the a-growth region of Tb mixed bulks, Jc in the low magnetic field was largely improved up to ∼ 105 A cm-2 at 77 K. Through microstructural observation, X-ray diffraction and local compositional analysis, the formation of finely dispersed BaTbO3 precipitates was confirmed in the Dy123 matrix, suggesting that these precipitates acted as effective pinning centers. The addition of fine BaTbO3 powder was also effective for enhancement of Jc. Furthermore, Tb4O7 added Dy123 melt-solidified bulks exhibited remarkably improved Jc due to the generation of fine BaTbO3 precipitates with 0.1 ∼ 0.2 μm in size in the Dy123 matrix without decreasing Tc. This result means Tb4O7 is a more effective additive than CeO2, which slightly decreases Tc. On the other hand, effects of dilute impurity doping to the CuO chain of Y123 melt-solidified bulks on their flux pinning properties were also studied. All the Fe-, Co-, and Ga-doped samples maintained high Tc above 90 K and exhibited dramatically improved Jc characteristics accompanying huge second peaks in Jc-H curves. This result suggests that the introduction of local disorders in the CuO chain by dilute impurity doping is more excellent way to improve the critical current properties of the RE123 system than direct impurity substitution for Cu in the CuO2 plane, which always decreases Tc.View full abstractDownload PDF (3725K)
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