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Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Ichimiya, Ayahiko
Materials Science Forum, 445-446, p.144 - 146, 2004/05
no abstracts in English
Hirade, Tetsuya
Materials Science Forum, 445-446, p.234 - 238, 2004/02
Positronium (Ps) formation mechanism by shallowly localized long-lived electrons and positrons at low temperatures explained successfully the Ps formation enhancement at low temperatures observed in polymers and molecular solids. The expected phenomena by this Ps formation mechanism, such as effects by visible light exposure, beautiful relation between the density of shallowly localized electrons and the Ps formation and delayed Ps formation were observed. Some possibilities of application of this new Ps formation, such as a new idea of observing spin polarized positrons by this Ps formation, will be given. The shallowly localized long-lived electrons can be polarized when they are placed in magnetic field at very low temperatures. It is probably possible to see the polarity of positrons by the Ps formation with these polarized electrons. The detail of the idea will be introduced. It will be given as an invited talk.
-rays produced in laser-induced compton-backscatteringHirade, Tetsuya; Toyokawa, Hiroyuki*; Odaira, Toshiyuki*; Suzuki, Ryoichi*; Ogaki, Hideaki*
Materials Science Forum, 445-446, p.474 - 476, 2004/02
Positron annihilation methods are very unique and strong tools to investigate materials. However, positrons are usually injected from outside of the samples. Therefore the samples should be in a vacuum or radioisotopes should be attached. Recently, Selim et al. applied high-energy g-rays (2MeV) produced by use of 6MeV electron linac to create positrons in thick materials. We have also been trying a similar method. In our case, high-energy -rays (
20MeV) produced in laser-induced Compton-backscattering are applied for positron creation in samples. The -rays do not spread and penetrate straightly in air. When you place a sample on the path of -rays, positrons are created in the sample and usual positron annihilation methods can be applied. Moreover, It is not needed to place the samples in vacuum and radioisotopes are not necessary. It means that the measurements of very high temperature materials such as metals near/over melting points will be possible. The detail of this method and some examples of experimental results will be introduced.
7 surfaceKawasuso, Atsuo; Fukaya, Yuki; Hayashi, Kazuhiko; Maekawa, Masaki; Ishimoto, Takayuki*; Okada, Sohei; Ichimiya, Ayahiko*
Materials Science Forum, 445-446, p.385 - 389, 2004/02
We so far discovered the total reflection and the first Bragg peak in reflection high-energy positron diffraction (RHEPD). However, the fractional order diffractions from reconstructed surfaces have been eluded from the observation. We therefore attempted to get RHEPD patterns from a Si-77 surface. Consequently, the 1/7, 2/7 and 3/7 diffraction rings due to Si(111)-77 reconstruction were clearly found in addition to the zeroth and the first Laue zones. The specular intensity was measured as a function of glancing angle. A small structure was found in the total reflection region. The small structure was attributed to the interference of positron wavefunction because of adatoms. However, the overall intensity profile was not well reproduced using a model already determined in the electron diffraction studies. To reproduce the obtained intensity profile, we may need to modify the vertical positions of the topmost surface and/or the absorption potential due to inelastic scattering processes.
Hirade, Tetsuya; Kumada, Takayuki
Materials Science Forum, 445-446, p.301 - 303, 2004/02
Positrons injected in molecular solids or polymers will have the positronium formation around a terminal spur of positron track, so-called positron spur, with active species in the positron spur, such as excess electrons. In this case, the electrons are not polarized. At low enough temperatures, long-lived shallowly localized electrons are accumulated by irradiation in darkness, and positrons will have a next chance to form positronium with these long-lived shallowly localized electrons. For these electrons, it is possible to make them to be polarized by applying magnetic field at very low temperatures. We successfully observed the effect of the positronium formation reaction of polarized positron and polarized electrons.
Chen, Z. Q.; Maekawa, Masaki; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Kawasuso, Atsuo
Materials Science Forum, 445-446, p.57 - 59, 2004/00
no abstracts in English