2004 Fiscal Year Final Research Report Summary
| Project/Area Number |
14204025
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | Osaka University |
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Principal Investigator |
NAGAI Yasuki Osaka Univ., Research Center for Nuclear Physics, Professor, 核物理研究センター, 教授 (80028240)
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| Co-Investigator(Kenkyū-buntansha) |
ITAHASHI Takahisa Osaka Univ., Research Center for Nuclear Physics, Asoc.Prof., 核物理研究センター, 助教授 (20112071)
SHIMA Tatsushi Osaka Univ., Research Center for Nuclear Physics, Res.Assist., 核物理研究センター, 助手 (10222035)
TAKAHISA Keiji Osaka Univ., Research Center for Nuclear Physics, Res.Assist., 核物理研究センター, 助手 (30263338)
IGASHIRA Masayuki Tokyo Inst.Tech., Research Lab.For Nucl.Reactors, Asso.Prof., 原子炉工学研究所, 助教授 (10114852)
大崎 敏郎 東京工業大学, 原子炉工学研究所, 助手 (80262327)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Cosmo chronology / Nuclear Cosmo Clock / rapid process / slow process / nucleosynthesis / neutron capture reaction / Re-Os pair |
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| Research Abstract |
^<187>Re-^<187>Os pair is known as one of cosmochronometers, since ^<187>Re is produced by only r-process and its half life is quite long 42.3±1.3Gyr. ^<187>Os is produced by s-process of ^<186>Os. In addition, there is a problem originating from the excited state at 10 keV in ^<187>Os, which could be populated at stellar temperature, and therefore ^<187>Os is depleted by the (n,γ)process the through the state. In order to correct for the loss rate we measured both the (n,γ) cross sections and neutron inelastic cross sections of ^<186>Os, ^<187>Os and ^<189>Os using a newly developed experimental method. Pulsed neutrons were bombarded on enriched samples of ^<186>Os, ^<187>Os and ^<189>Os and ^<197>Au. The (n,γ)cross section of Os isotopes was measured using an anti-Compton NaI(Tl) spectrometers by detecting prompt gamma rays feeding from a neutron capture state of Os to low lying states. For the measurement of the ^<189>Os(n,n')^<189>Os reaction cross section we have developed a new detection system with use of four Li-glass detectors with a diameter of 50 mm and a thickness of 10 mm. Neutron energy scattered elastically and/or inelastically by ^<189>Os is determined by employing a TOF method. The discrimination between scattered neuron by ^<189>Os and gamma ray background can be made by their pulse heights. In order to obtain the inelastic scattering cross section of ^<189>Os accurately, it was crucial to prevent direct neutrons from the ^7Li(p,n) ^7Be reaction entering into the Li-glass detector. To find proper arrangement of these shield materials of borated polyethylene, cadmium and Boron, an extensive calculation has been made using a Monte Carlo Code. In addition, through many R & D works we have finally succeeded to construct a high sensitive measuring system of the inelastic scattering cross section of a nucleus. We succeeded to measure the ^<187>Os(n,n')^<187>Os cross section with high accuracy.
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