1990 Fiscal Year Final Research Report Summary
Study of Positronium by High Resolution AgeーMomentum Correlation Measurements
| Project/Area Number |
01460031
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性
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| Research Institution | The University of Tokyo |
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Principal Investigator |
HYODO Toshio The University of Tokyo, The College of Arts and Sciences, Associate Professor, 教養学部, 助教授 (90012484)
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| Co-Investigator(Kenkyū-buntansha) |
NAGASHIMA Yasuyuki The University of Tokyo, The College of Arts and Sciences, Research Associate, 教養学部, 助手 (60198322)
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| Project Period (FY) |
1989 – 1990
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| Keywords | positron annihilation / positronium / gamma-ray detector / position sensitive detector |
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| Research Abstract |
The positronium is a unique "atom" whose information can be obtained by investigating the angular correlation or the Doppler broadened energy spectrum of its annihilation gamma rays. In this work, we combine the positron lifetime method with the angular-correlation or energy-spectrum method to get more detailed information on positronium. A planer-type high purity Ge detector is used to get high resolution energy spectrum. Position sensitive photomultilipers are used to increase efficiency of the angular correlation system. The following new results are obtained.
(1) The pickoff annihilation cross section of positronium-oxygen collisions has been determined for the first time : Because the ground state of the oxygen molecule is triplet, the ortho-positronium colliding with oxygen is converted into para-positronium at a very high rate. Because of this, it has been believed impossible to measure the ordinary pickoff annihilation cross section. This is made possible in the present work by using the difference between the momentum distributions for the ortho-para conversion and the pickoff annihilation.
(2) Methods to measure the positron spin polarization by the energy spectrum and the angular correlation are established : High precision measurements of positron spin polarization are made by using the asymmetry of the ortho- and para-positronium formation probabilities in a magnetic field.
(3) The momentum transfer crosssection for the positronium-helium collisionin is determined for the first time : This is performed by measuring the time dependence of the momentum distribution of positronium in helium.
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