| Project/Area Number |
12640286
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Tokyo Metropolitan University |
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Principal Investigator |
KUMITA Tetsuro Tokyo Metropolitan U. Grad. School of Science, Assistant Professor, 理学研究科, 助手 (30271159)
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| Co-Investigator(Kenkyū-buntansha) |
KAJITA Masatoshi Communications Research Lab., Atomic Standard Section, Senior Researcher, 電磁波計測, 主任研究官 (50359030)
IRAKO Mitsuhiro Tokyo Metropolitan U. Grad. School of Science, Assistant Professor, 理学研究科, 助手 (60087004)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2001: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2000: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Keywords | positron / positronium / Laser excitation / Laser coding / Magnetic quench |
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| Research Abstract |
Aim of the research is to observe laser excitation of positronium (Ps) atom, which is a bound state of an electron and position, by utilizing magnetic quench effect.
Energy gap between 1s and 2p states of a Ps is 5.1eV, corresponding to the wavelength of 243nm.
Ps has two spin states, namely para-Ps U (spin singlet state, lifetime 0.125ns) and ortho-Ps (spin triplet state, lifetime 142ns). A para-Ps dominantly decays into two γ-rays, while an ortho-Ps dominantly decays into three γ-rays.
Since mass of a Ps atom is 1022keV, energy of a γ-ray from a para-Ps decay is 511keV, while energy of γ-rays from ortho-Ps decays continuously distribute between 0keV and 511keV.
The two spin states, para-Ps and ortho-Ps mix to each other in high magnetic field due to Zeeman effect (magnetic quench). Field of a several kGauss is needed to mix the spin states in 1s energy state, while a several hundred Gauss is enough to mix the spin states in 2p energy state.
Laser excitation of positronium atoms can be observed by utilizing the magnetic quench effect. Suppose high intensity laser with the wavelength of 243nm is injected to a positronium cloud under a magnetic field of 500Gauss. Para-Ps and ortho-Ps in the 1s state do not mix because the magnetic field is not high enough but those in 2p states mix to each other once positronium atoms are excited by the laser field. Since lifetime of para-Ps is much shorter than that of ortho-Ps, transition from ortho-Ps to para-Ps dominantly occurs.
We measured decay time and γ-ray energy spectrum of positronium under a magnetic field of 500Gauss with 243nm laser ON and OFF. Significant increase was observed around 511keV in the energy spectrum and at Onsec in the time spectrum, which implied transition from ortho-Ps to para-Ps and thus laser excitation of Ps atoms is observed.
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