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Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*
Chemical Physics Letters, 795, p.139507_1 - 139507_4, 2022/05
Times Cited Count：0 Percentile：0.01(Chemistry, Physical)We obtained the temperature dependence up to 150
C of the triplet positronium (
-Ps) lifetime in N,N,N-Trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by the vertical slow positron beamline installed at AIST. Positrons penetrate into the liquid surface of TMPA-TFSI with the positron energies of 2 keV and 12 keV to investigate at the near-surface and the balk. The surface structure was visible at 150C, 120C above the melting temperature. The -Ps lifetime became shorter at higher temperatures for both positron energies. Similar temperature dependence had appeared just in water as the result of the reaction of -Ps and radiolysis products such as the OH radicals. The temperature dependence observed for TMPA-TFSI suggested that the chemical reaction of -Ps occurred.
-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
AIP Conference Proceedings 2182, p.030007_1 - 030007_5, 2019/12
Times Cited Count：2 Percentile：84.78(Nuclear Science & Technology)There are many new application of room temperature ionic liquids (RTILs) for many different fields. One of them is reprocessing spent nuclear fuels and then research of irradiation effects on RTILs are very important. The positron annihilation techniques are very strong tool to investigate fast reactions of excess electrons. Positron annihilation age-momentum correlation (AMOC) experiment was applied to deepen understanding the phenomena occurred at very young positron ages. We clarified that Ps bubble formation in RTILs was very slow and, finally, oscillation of Ps bubble was observed just after the Ps formation at near melting temperatures. These results can indicate that Ps formation occurred in very short time in RTILs. The phenomena observed by Ps just in RTILs will be discussed.
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
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
no journal, ,
The Ps bubble oscillations in N,N,N-trimethyl-N-propylammonium bis(trifluoro-methanesulfonyl)imide (TMPA-TFSI), N-Methyl-N-propylpiperidinium bis(trifluoromethane-sulfonyl) imide (PP13-TFSI) and 1-Ethyl-3-methylimidazolium thiocyanate (EMIM-SCN) were successfully observed. It is almost impossible to see this kind of phenomenon in usual molecular liquids. Even though the Ps bubble size is smaller for EMIM-SCN, the oscillation frequency of the Ps bubble at 10C above the melting temperatures were quite similar for the other RTILs. Hence, the Ps bubble oscillation is, probably, caused by the repulsive force initiated by the ionic structures in RTILs that can remain at 10-15C above the melting temperatures.
Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*
no journal, ,
Positronium (Ps) forms bubbles in liquids, and the bubbles become larger due to the lower surface tension at higher temperatures, resulting in longer o-Ps lifetimes. In room-temperature ionic liquids, it has been shown that the structure of Ps bubble is different and depends on the structure formed by the Coulomb force of the ions. We successfully obtained that the o-Ps lifetime did not increase at high temperatures. The existence of new state of Ps bubble was further clarified.
Hirade, Tetsuya
no journal, ,
It has been clarified that the annihilation lifetime of triplet positronium in room temperature ionic liquid is shortened at high temperature. This is a phenomenon that has been observed only in water, and is caused by the reaction of triplet positronium and radicals formed at the end part of the incident positron track. Then it is considered that the reaction of triplet positronium also occurs in the room temperature ionic liquid, and the reaction of the spin correlated pair of the triplet positronium and the radical will give the quantum beats as observed in water. Therefore, we performed positron age-momentum correlation (AMOC) measurements on bis(trifluoro-methanesulfonyl)imide (TMPA-TFSI) and successfully observed quantum beats as the energy distribution change of annihilation gamma rays. As a result, it was clarified that radicals formed in room temperature ionic liquids can be detected by positron annihilation method.
Hirade, Tetsuya
no journal, ,
-positronium (-Ps) has the longest positron annihilation lifetime in the insulators. This lifetime becomes shorter at higher temperatures in room temperature ionic liquids (RTIL). This phenomenon is different from many other liquids. Only water showed the same tendency, suggesting the -Ps reaction as in water. Therefore, quantum beats were expected and observed in RTIL as well as in water. Quantum beats are the result of a reaction with the spin-correlated radical, indicating that the formed radical can be probed by the quantum beats.
