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Hirade, Tetsuya
Materials Science Forum, 607, p.232 - 234, 2009/00
Positron lifetime measurements and age-momentum correlation measurements were performed for several ionic liquids to investigate free electrons through positronium (Ps, a bond state of an electron and a positron) formation. An injected positron forms spurs (cations and excess electrons) and thermalizes at the terminal spur where the positron has a chance to form Ps with one of excess electrons. When positrons and/or electrons are localized somewhere, their mobility becomes much smaller and Ps cannot be formed usually. It means that Ps formation can give information of reactions of mobile electrons and positrons. If the dry electrons can diffuse for long time, Ps formation is quite possible even at the later positron age such as 10
100 ps. The slow Ps formation was observed in the room temperature ionic liquids.
Ito, Kenji*; Oka, Toshitaka*; Kobayashi, Yoshinori*; Shirai, Yasuharu*; Wada, Kenichiro*; Matsumoto, Masataka*; Fujinami, Masanori*; Hirade, Tetsuya; Honda, Yoshihide*; Hosomi, Hiroyuki*; et al.
Materials Science Forum, 607, p.248 - 250, 2009/00
So far no standard procedure for the positron annihilation lifetime (PAL) technique has been established. A lack of the standards has led to difficulty in ensuring the equivalency and reliability of data from different laboratories. As a first, we conducted an interlaboratory comparison of PAL measurements for metal, polymer and silica glass with agreed procedures for data recording and analysis. The PAL data recorded at different laboratories were analyzed with a single lifetime component for the metal sample and with three components for the others, respectively. Based on the results of the reported positron and ortho-positronium lifetimes, the possible sources of the uncertainties in the PAL measurements are discussed. To reduce the effect of scattered 
rays, a lead shield was placed between the detectors. The uncertainty was significantly decreased, signifying that placing lead shields between the detectors effectively reduced the false signals due to the scattered rays.
Kawasuso, Atsuo; Arashima, Hironobu*; Maekawa, Masaki; Ito, Hideaki*; Kabutomori, Toshiki*
Materials Science Forum, 607, p.122 - 124, 2008/11
Using positron lifetime spectroscopy, we examined the evolution of defects in the Ti
Cr
V
alloy prepared by the arc-melting method during hydriding cycles. After one hydriding cycle dislocations were responsible for positron trapping. The dislocation-related lifetime showed no significant change with increasing the hydriding cycle suggesting that the dislocation density is well above the dynamic range of positron trapping rate. After 20 hydriding cycles, prolonged lifetime components (0.4-0.5 ns and 1.9-2 ns) were obtained. These lifetimes were nearly constant during the further hydriding cycles while their intensities increased. Vacancy defects were generated and slowly developed to microvoids during the hydriding cycles. After 200 hydriding cycles the rechargeable hydrogen capacity decreased to 90% relative to the initial amount. It is thus inferred that the reduction of rechargeable hydrogen capacity is partly caused by the formation of microvoids and dislocations.
Kawasuso, Atsuo; Fukaya, Yuki; Hashimoto, Mie; Ichimiya, Ayahiko; Narita, Hisashi*; Matsuda, Iwao*
Materials Science Forum, 607, p.94 - 98, 2008/11
Currently, we are performing the surface study with reflection high-energy positron diffraction (RHEPD). The advantage of this method is the appearance of total reflection of positrons at the first surface layer. In this talk, we will present the recent progress of our research on some unknown surface structures and phase transition mechanisms.
Maekawa, Masaki; Kawasuso, Atsuo; Hirade, Tetsuya; Miwa, Yukio
Materials Science Forum, 607, p.266 - 268, 2008/11
We have developed a positron microbeam using magnetic lenses based on the commercial scanning electron microscope. The minimum beam diameter was 1.9 micron on target. Two-dimensional image of S parameter was successfully obtained. Using this apparatus, S parameter distribution around the crack tip introduced by a stress corrosion cracking of a stainless steel was obtained. S parameter increases at the further region of the tip of the crack. This shows that vacancy type defects may be generated as crack precursor.
Hirade, Tetsuya
no journal, ,
9th International Workshop on Positron and Positronium (Ps) Chemistry (PPC-9) will be held in Wuhan, Chine on May 11-15, 2008. The Summary of the PPC-9, especially the Summary of the researches for production of Ps molecule (Ps
), Ps formation and others will be given.