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Study of positronium-gas molecule interaction using silica aerogel

Research Project

Project/Area Number 63460037
Research Category

Grant-in-Aid for General Scientific Research (B)

Allocation TypeSingle-year Grants
Research Field 物理学一般
Research InstitutionUniversity of Tokyo

Principal Investigator

FUJIWARA Kunio  Coll. of Arts & Sciences, Univ. Tokyo, Professor, 教養学部, 教授 (40012314)

Co-Investigator(Kenkyū-buntansha) NAGASHIMA Yasuyuki  Coll. of Arts & Sciences, Univ. Tokyo, Research Assoc., 教養学部, 助手 (60198322)
HYODO Toshio  Coll. of Arts & Sciences, Univ. Tokyo, Assoc. Professor, 教養学部, 助教授 (90012484)
Project Period (FY) 1988 – 1989
Project Status Completed (Fiscal Year 1989)
Budget Amount *help
¥7,300,000 (Direct Cost: ¥7,300,000)
Fiscal Year 1989: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1988: ¥6,600,000 (Direct Cost: ¥6,600,000)
KeywordsSilica aerogel / Positronium / Positron / Gas molecule
Research Abstract

Silica aerogel is a porous material composed of a random three-dimensional network of SiO_2 fine grains whose mean diameter is about 50A. When energetic positrons are injected into this material, the grains function as positron-moderation and positronium (Ps)-formation medium, and large free space outside the grains provides a micro chamber for free motions of the Ps atoms. By introducing a gas into this space, therefore, one can investigate Ps-gas molecule for the first time in a systematic way. This possibility was recently pointed out by Hyodo et al. of our group, and verified by their pioneering experiments on Ps-O_2 scattering and so on.
In the present wori, we have applied the same method to the study of Ps scattering by various gas molecules after improving our apparatus by equipping it with an electromagnet to control ortho-para conversion process of the Ps atoms. Our main results are as follows:
1. Formation cross section of para-Ps in Xenon was found to be consistent with the prediction of the Ore model, thus solving a long puzzle concerning the Ps formation in rare gases.
2. It has been concluded from the careful observation of Ps slowing down in gases that the Ps kinetic energy is transferred only to the translational motion of the gas molecules via elastic collisions, and that the excitations of vibrations and rotations of the molecules are negligibly small. This result is understandable if one noticesthat Ps atoms are electrically neutral, and hence the interaction between Ps and gas molecules cannot be a long-ranged one.

Report

(3 results)
  • 1989 Annual Research Report   Final Research Report Summary
  • 1988 Annual Research Report
  • Research Products

    (19 results)

All Other

All Publications (19 results)

  • [Publications] 柿元満: "Evidence for normal formation of positronium in gaseous Xe" J.Phys.B:At.Mol.Opt.Phys.21. 2977-2987 (1988)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 柿元満: "Slowing-down of positronium in gases" Positron Annihilation,edited by L.Dorikens-Vanbaet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 737-739 (1989)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 柿元満: "Angular correlation study of positronium formation in Xenon" Positron Annihilation,edited by L.Dorikens-Vanbaet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 746-748 (1989)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 柿元満: "Ortho-para conversion of positronium in oxygen studied by the angular correlation method" Positron Annihilation,edited by L.Dorikens-Vanbaet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 755-757 (1989)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 兵頭俊夫: "Relaxation of the momentum distribution of free positronium atoms interacting with silica fine particle" Positron Annihilation,edited by L.Dorikens-Vanbaet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 878-880 (1989)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 兵頭俊夫: "Evidence for nonexistence of self-trapped positronium in KI at very low temperatures" Physical Review B. 40. 8037-8040 (1989)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Kakimoto M. et al.: "Evidence for normal formation of positronium in gaseous Xe" J. Phys. B: At. Mol. Opt. Phys. 21 (1988) 2977-2987.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Kakimoto M. et al.: "Slowing-down of positronium in gases" Positron Annihilation, edited by L. Dorikens-Vanbraet, M. Dorikens and D. Segers (World Scientific, Singapore, 1989) p.737-739.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Kakimoto M. et al.: "Angular correlation study of positronium formation in Xenon" ibid. p.746-748.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Kakimoto M. et al.: "Ortho-para conversion of positronium in oxygen studied by teh angular correlation method" ibid. p.755-757.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Hyodo T. et al.: "Relaxation of the momentum distribution of free positronium atoms interacting with silica fine particle" ibid. p.878-880.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] Hyodo T. et al.: "Evidence for nonexistence of self-trapped positronium in KI at very low temperatures" Physical Review B40 (1989) 8037-8040.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1989 Final Research Report Summary
  • [Publications] 柿元満: "Slowing-down of positronium in gases" Positron Annihilation,edited by L.Dorikens-Vanbraet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 737-739 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 柿元満: "Angular correlation study of positronium formation in Xenon." Positron Annihilation,edited by L.Dorikens-Vanbraet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 746-748 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 柿本満: "Ortho-para conversion of positronium in oxygen studied by the angular correlation method" Positron Annihilation,edited by L.Dorikens-Vanbraet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 755-757 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 兵頭俊夫: "Study of positronium states in KI by using magnetic field" Positron Annihilation,edited by L.Dorikens-Vanbraet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 845-847 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 兵頭俊夫: "Relaxation of the momentum distribution of free positronium atoms interacting with silica fine particles" Positron Annihilation,edited by L.Dorikens-Vanbraet,M.Dorikens and D.Segers(World Scientific,Singapore,1989). 878-880 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 兵頭俊夫: "Evidence for nonexistence of self-trapped positronium in KI at very low temperatures" Physical Review B. 40. 8037-8040 (1989)

    • Related Report
      1989 Annual Research Report
  • [Publications] 柿元 満: J.Phys.B:At.Mol.Opt.Phys.21. 2977-2987 (1988)

    • Related Report
      1988 Annual Research Report

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Published: 1988-04-01   Modified: 2016-04-21  

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