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-positronium and radical in liquidsHirade, Tetsuya
Proceedings of 8th Asia Pacific Symposium on Radiation Chemistry (APSRC 2020) (Internet), 2 Pages, 2020/04
The positrons injected in insulating materials make ionization at the end part of the track, forming excess electrons and radicals. When one of the excess electrons and the incident positron form positronium, the electron in the positronium and the unpaired electron in the radical have a spin correlation. By using this spin correlation, a quantum beat phenomenon that depends on the hyperfine coupling constant of the radical appears in the spin conversion reaction with the positronium. The spin-correlated radical and other radicals can be distinguished by a reaction using the positronium as a probe. It is possible to study the behavior of OH radicals in water and the state of cation radicals in room temperature ionic liquids.
Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*
Acta Physica Polonica A, 137(2), p.109 - 112, 2020/02
Times Cited Count：0 Percentile：0(Physics, Multidisciplinary)Recently, it was reported that the positronium (Ps) bubble in Room Temperature Ionic Liquids (RTILs) showed some phenomena that were very different from them observed in other molecular liquids. Now the reason of these interesting phenomena is being understood. The structure caused by the ionic interaction between anions and cations can exist even at the higher temperatures than the melting temperatures. It was the reason why the oscillation of Ps bubble was observed at the temperatures near the melting temperatures in RTILs. The temperature dependence of the Ps bubble size estimated by the triplet Ps (
-Ps) pick-off annihilation lifetime indicated that there was a nano-meter structure remained by ionic interactions even at high temperatures. The -Ps pick-off annihilation lifetime will be a strong tool to study nano-structure in RTILs.
Hirade, Tetsuya
Yodenshi Kagaku, (11), p.33 - 40, 2018/09
The positron injected in insulating materials thermalizes at the end part of its track and forms Positronium (Ps) with one of excess electrons within 
1 ps. Therefore, Ps formation can be a tool to investigate very fast processes like excess electron solvation in liquids. Many phenomena appeared in radiation chemistry researches for room temperature ionic liquids (ILs) are interesting and important for the application. Positron annihilation lifetime (PAL) measurements in ILs were carried out and anomalously long lifetime values of the shortest lifetime component were found in ILs. PAL and positron annihilation age-momentum correlation (AMOC) measurements were performed to clarify the reason of these anomalously long lifetime values and Ps bubble oscillation was finally discovered. Recent progresses are introduced with showing some results.
Hirade, Tetsuya
Hoshasen To Sangyo, (139), p.23 - 28, 2015/12
The researches and the applications of the Positronium Chemistry were introduced. The mechanism of Ps formation in low temperature insulators was clarified by Hirade and it is almost the end of the long, more than half century, period for arguments on Ps formation. Hence almost all of the researchers have been accepting the Spur Reaction Model proposed by Mogensen. Therefore, radiation chemistry researches by use of the Spur Reaction Model, especially the study of excess electrons at the time range of pico-to-nano second and electron mobility, were introduced. It was also introduced that the Free Volume Model is not correct and then the sub-nano meter vacant space, such as the microscopic free volume in polymers, can be studied by just the triplet Ps lifetime. As the latest research for the application, it was introduced that Ps bubble shows oscillation especially in ionic liquids and is expected to be a strong tool to investigate nano-scale properties of ionic liquids.
Hirade, Tetsuya
Journal of Physics; Conference Series, 618(1), p.012004_1 - 012004_5, 2015/06
Times Cited Count：5 Percentile：84.22(Physics, Applied)Positronium (Ps; a bound state of positron and electron) has a negative work function in materials and forms a bubble state in liquids. On the way of stable bubble state, the bubble grows and probably oscillates. The usual fast bubble formation has not been observed with the time resolution of the positron annihilation methods that is usually 100-200 pico-seconds. There had been many anomalous phenomena observed in the room temperature ionic liquids (RTIL). Recently it was found that very slow bubble formation caused these anomalous phenomena. And hence the oscillation of the Ps bubble was successfully observed by the change of the annihilation rate of the triplet Ps that is affected by the size of the bubble. The oscillation and the decay of the bubble give the information of the viscoelastic properties at the sub-nano scale. The temperature dependence of the oscillation has been also successfully indicated.
Hirade, Tetsuya
Radiation Physics and Chemistry, 76(2), p.84 - 89, 2007/02
Times Cited Count：3 Percentile：25.51(Chemistry, Physical)There are many connections between radiation and positronium chemistry. The Spur Reaction model proposed by Mogensen needs much radiation chemistry knowledge. On the other hand, the Spur Reaction model could give new ideas to radiation chemists. Positronium formation reaction is very fast and hence there is a good relationship between reactions observed by a pulse radiolysis measurement and positronium formation, which was shown by Dupratre et al. Enhancement of positronium formation at low temperatures was successfully explained by the reaction of trapped electrons and positrons. The trapped electrons have been studied well by radiation chemists. That knowledge was needed to propose a new idea to explain the positronium formation at low temperatures. And now, probably it is becoming possible to use the positronum formation reaction to study the trapped electrons. Positron methods will be able to be used for the radiation chemistry research.
Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*
Radiation Physics and Chemistry, 76(2), p.330 - 332, 2007/02
Times Cited Count：3 Percentile：25.51(Chemistry, Physical)Recently, positronium (Ps) formation mechanism in the spur is becoming clarified. Blob model, the modified Spur model, proposed by Stepanov can give information of Ps formation time. Dauwe et al. showed that S(t) curve of PMMA observed by AMOC measurement could be fitted by the blob model. The young-age broadening was found and explained with the delayed slowing down of Ps by Stuttgart group. The delayed Ps formation was shown by Suzuki et al. especially at low temperatures, because positrons can diffuse long distance to find trapped electrons. According to the blob model, Ps formation even after long diffusion of positrons might be possible even at the room temperature. Now we are trying to obtain the experimental evidence of delayed Ps formation in spur process.
Hirade, Tetsuya
Acta Physica Polonica A, 107(4), p.615 - 622, 2005/00
Positronium (Ps) formation by weakly localized long-lived electrons (trapped electrons or anions) and positrons at low temperatures successfully explained the Ps formation enhancement at low temperatures observed in polymers and molecular solids. This Ps formation is completely different from Ps formations by Ore process or spur process. The phenomena expected by this Ps formation mechanism, such as an effect due to visible light exposure, the density effect of weakly localized electrons and the delayed Ps formation were successfully observed as the experimental evidence of this Ps formation process. Some possibilities for application of this new Ps formation were also given. One is a new idea for estimation of spin polarity positrons. Another is the possibility of application to study the local molecular motion by observing the decay of Ps formation possibility by this Ps formation process.
Stepanov, S. V.*; Byakov, V. M.*; He, C.*; Hirade, Tetsuya; Mikhin, K. V.*
Acta Physica Polonica A, 107(4), p.642 - 650, 2005/00
Role of trapped and solvated electrons in Ps formation is discussed. Combination of thermalized positron with such electrons is energetically possible and may contribute to Ps formation. Contrary to the positron reaction with a quasi-free electron, this process is not limited to picosecond times, but proceeds on a timescale of nanoseconds. In this case conventional exponential deconvolution of row lifetime positron annihilation spectra becomes questionable. Rigorous treatment of the data needs nonexponential deconvolution, based on an adequate physical input. Such an approach is suggested here. Its reduced form is used for interpretation of the Ps formation data in polyethylene, EMMA and PMMA in dark and in light vs. time of the measurement and temperature. Parameters characterized accumulation of trapped electrons and their recombination with counter ions and positrons are obtained.
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.
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.
Hirade, Tetsuya
Radiation Physics and Chemistry, 68(3-4), p.375 - 379, 2003/10
Times Cited Count：17 Percentile：72.74(Chemistry, Physical)The trapped electrons or anions in molecular solids and polymers cause the enhancement of positronium formation at low temperatures during positron annihilation lifetime (PAL) measurement. This method can be applied to investigate trapped electrons and anions in polymers. The advantage of the method is that the any kinds of trapped electrons or anions can be observed. We clarified that the glow peak appeared around 240K was caused by the trapped electrons on -CH- radicals by PAL experiment.
Suzuki, Naoki*; Hirade, Tetsuya; Saito, Fuminori*; Hyodo, Toshio*
Radiation Physics and Chemistry, 68(3-4), p.647 - 649, 2003/10
Times Cited Count：23 Percentile：80.7(Chemistry, Physical)no abstracts in English
Hirade, Tetsuya
Hoshasen Kagaku, (75), p.46 - 51, 2003/03
Enhancement of positronium (Ps) formation at low temperatures has been observed in many materials since 1980's. There were some interpretations. However, none of them explained the phenomena successfully. In 1998, a new idea of the Ps formation was proposed and the expected phenomena were successfully observed. This new Ps formation process will be explained with those experimental results and the possibility of usage of Ps formation for radiation chemistry researches will be also discussed.
-irradiation on positronium formation in polymers at low temperaturesShantarovich, V. S.*; Hirade, Tetsuya; Kevdina, I. B.*; Gustov, V. W.*; Oleinik, E. F.*
Acta Physica Polonica A, 99(3-4), p.497 - 501, 2001/03
no abstracts in English
-irradiation on positronium formation in polyethyleneHirade, Tetsuya; Kumada, Takayuki
Radiation Physics and Chemistry, 60(4-5), p.541 - 544, 2001/03
Times Cited Count：17 Percentile：74.85(Chemistry, Physical)no abstracts in English
Hirade, Tetsuya; Maurer, F. H. J.*; Eldrup, M.*
Radiation Physics and Chemistry, 58(5-6), p.465 - 471, 2000/06
Times Cited Count：130 Percentile：99.13(Chemistry, Physical)no abstracts in English
Hirade, Tetsuya
JAERI-Conf 2000-001, p.306 - 309, 2000/03
no abstracts in English
C.L.Wang*; Hirade, Tetsuya; Maurer, F. H. J.*; Eldrup, M.*; N.J.Pedersen*
Journal of Chemical Physics, 108(11), p.4654 - 4661, 1998/03
Times Cited Count：153 Percentile：97.11(Chemistry, Physical)no abstracts in English
Hirade, Tetsuya
Journal of Radioanalytical and Nuclear Chemistry, 211(1), p.15 - 22, 1996/11
Times Cited Count：0 Percentile：0.01(Chemistry, Analytical)no abstracts in English
