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Hirade, Tetsuya; Suzuki, Naoki*; Saito, Fuminori*; Hyodo, Toshio*
no journal, ,
The electrons formed by ionization can be localized with 0.5-3eV at low temperatures (below -50
C) in some materials for long time. Positrons injected in liquids and molecular solids have a chance to form positronium with one of the excess electrons in the spur. However some of the positrons can escape from the positronium formation and they will annihilates from free positron state, usually. If there are weakly localized electrons in the materials at low temperatures, positrons will have the next chance to form positronium with these electrons. We showed that this positornium formation was slower than the positoronium formation in the spur. We have analyzed the data with considering the positron localization time and obtained several 10 ps as the localization time of positrons in polyethylene at 20K.
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and digital methodsHashi, Yohei; Hirade, Tetsuya; Suzuki, Takenori*
no journal, ,
Positron Annihilation Lifetime was measured by - coincidence method with a digital storage cscilloscope(DSO). A photodiode was used to detect the positron injected into a sample from a source. Two sets of a photomultiplier tube and a scintillator were used to detect annihilation rays emitting to opposite directions from the sample. This - coincidence lifetime measurement was first attempt and the signal-to-noise ratio became better than the conventional lifetime measurement by - coincidence method.
Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*; Suzuki, Takenori*
no journal, ,
Many ions and the excess electrons are formed by the injected positron just before the thermalization of that positron in a small area (it is called spur or blob) in condensed matter. The positron has a chance to form positronium (Ps) with one of the excess electrons. According to the model of Ps formation in the spur (blob), the initial encounter pairs of an electron and a positron will form Ps in short time. Some of the positrons have some possibility to form Ps after diffusion in several hundreds pico-seconds. There were experimental results that were interpreted as a Ps thermalization by a group in Germany more than 10 years ago. However, we have believed that some of the results were caused by the delayed Ps formation and have successfully obtained the experimental evidence of the delayed Ps formation by applying electric fields on the sample, fused quartz.
layer and its interface formed by implantation of O into SiCMaekawa, Masaki; Kawasuso, Atsuo
no journal, ,
no abstracts in English
Yu, R.; Kawasuso, Atsuo; Maekawa, Masaki
no journal, ,
In this work, we present our ongoing effort to focus a positron beam to tens of micrometer in diameter. The beam was obtained by using the optics for conventional scanning electron microscopy (SEM), in which a projection lens, a middle lens and an objective lens are combined. As long as we use relatively high energy (keV) positron beam and small enough source, a microbeam can be formed. At present stage, the beam diameter was determined by scanning the beam across a 200 micrometer metal grid and found to be about 70 micrometer. Both one and two dimensional scanning measurements were performed on test samples. A line scan through the center of a 130 micrometer hole in a stainless steel mesh indicated a 30 micrometer beam lateral resolution.
Yachi, Hironari; Hashi, Yohei; Hirade, Tetsuya; Suzuki, Takenori*
no journal, ,
Recently, it is becoming possible to apply digital oscilloscopes for positron annihilation lifetime measurement instead of use of analogue circuit (NIM modules). More than 1 million sets of wave signals from -ray detectors constructed by scintillaters and photomultiplier tubes are recorded by a digital oscilloscope and analyzed afterward by a personal computer. More than 1 million events of positron annihilation are accumulated on a multi channel analyzer (MCA) for 2-4 hours to construct one lifetime spectrum in the case of the conventional analogue lifetime measurement system. However, it is possible to measure 100 times longer time, i.e. to accumulate 100 times more counts, because of the much better stability of the positron annihilation lifetime measurement system by digital oscilloscopes. Although it is clear that the system by digital oscilloscopes is very stable, There is no indication how much it is stable and how we can construct stabler and better systems. We studied these things and can conclude that we should apply one electric power supply for all detectors and higher voltage to the detectors and full range measurement (8bit) can give better time resolution.
Maekawa, Masaki; Kawasuso, Atsuo
no journal, ,
no abstracts in English
Fukaya, Yuki; Kawasuso, Atsuo; Ichimiya, Ayahiko
no journal, ,
no abstracts in English
Hori, Fuminobu*; Fukuzumi, Masafumi*; Kawasuso, Atsuo; Iwase, Akihiro*
no journal, ,
no abstracts in English
Hashimoto, Mie; Fukaya, Yuki; Kawasuso, Atsuo; Ichimiya, Ayahiko
no journal, ,
no abstracts in English
Zgardzinska, B.*; Hirade, Tetsuya; Goworek, T.*
no journal, ,
Injecting positrons that are use for positron annihilation lifetime measurement is also the ionizing radiation and the trapped electrons are formed in low temperature n-heptadecane during measurement. Positrons can pick off these trapped electrons to form positronium and there is a good correlation between density of trapped electrons and positronium formation. It was reported that the densities of trapped electrons to have same positronium formation in polyethylene and polymethylematacrylate are different and it was explained with difference of diffusion length of positrons. In low temperature n-heptadecane, we have tested the effect of positron diffusion length by measuring at different temperatures where there is no change of the density of trapped electrons. We succeeded to obtain a reasonable change of positronium formation by changing the temperature. It is a clear indication that positron diffusion affects the yield of positronium formation.
Kobayashi, Yoshinori*; Ito, Kenji*; Oka, Toshitaka*; Sakaki, Koji*; Shirai, Yasuharu*; Honda, Yoshihide*; Shimazu, Akira*; Fujinami, Masanori*; Hirade, Tetsuya; Saito, Haruo*; et al.
no journal, ,
For making a standard sample of positron annihilation measurement, quartz glass and polycarbonate were measured with 12 apparatus at AIST, Chiba Univ., Tokyo Univ., Tsukuba Univ., Touhoku Univ., Tokyo Gakugei Univ. JAEA, Nitto Denko, and Toray Research Center. By regulating procedure for the measurement and data analysis the uncertainties of the positron annihilation lifetime obtained at different laboratories were significantly reduced.
Kawasuso, Atsuo; Chen, Z. Q.*; Maekawa, Masaki
no journal, ,
no abstracts in English
Maekawa, Masaki; Kawasuso, Atsuo
no journal, ,
A positron microbeam was developed for the elucidation of a destructive mechanism of nuclear reactor materials. Positron beam was generated by a small positron source developed by us and the solid neon moderator. It succeeded in formation of the positron microbeam of 1.9 micrometers of diameters by combining an object lens of large magnification. A test pattern was used for the performance test. It was confirmed that the shape of the test pattern with a line width of 12 micrometers is clearly observed as change of positron annihilation parameters. This positron microbeam has a sufficient performance for the measurement of the distribution of the vacancy-type defects of selected areas, such as a crack tip of metal material.
Fukaya, Yuki; Hashimoto, Mie; Kawasuso, Atsuo; Ichimiya, Ayahiko
no journal, ,
no abstracts in English
Hirade, Tetsuya; Lee, J.*; Nakamura, Takemi
no journal, ,
The positronium (Ps), a bond state of an electron and a positron, is formed at the terminal spur of injected positron and annihilates with the lifetimes of 100 pico-seconds to several nano-seconds. The triplet Ps, ortho-Ps, has the longest lifetime that depends on the sub-nano meter hole size where the Ps is captured. The lifetime is longer in a larger hole. In liquids, Ps creates a bubble by itself and the size of the bubble is larger at higher temperature. Therefore the lifetime of ortho-Ps is usually longer at higher temperatures. However, the ortho-Ps lifetime in water showed opposite temperature dependence and the reason has not been clarified. If there are reactions of ortho-Ps and reactants formed by the injected positron, it is possible to explain the temperature dependence of ortho-Ps lifetime in water. We have successfully obtained spin exchange reaction between ortho-Ps and radicals in water by use of the positron annihilation age-momentum correlation measurement (AMOC).
Kawasuso, Atsuo; Maekawa, Masaki
no journal, ,
no abstracts in English
Fukaya, Yuki; Kawasuso, Atsuo; Ichimiya, Ayahiko
no journal, ,
no abstracts in English
Maekawa, Masaki; Kawasuso, Atsuo
no journal, ,
We have developed the positron microbeam apparatus. With the present equipment, the Doppler broadening measurement is possible. In order to collect more information about vacancy-type defects, it is necessary to perform positron annihilation lifetime spectroscopy measurement. For this purpose, the beam pulsing section inserting in the existing beam line was developed. This consists of a coaxial cylinder type pre-buncher, a deflection type chopper, and a resonator type buncher. When pulsing system was operated, it was confirmed that a pulsed beam with the pulse width of 140ps can be formed and that PALS measurement is possible.