Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Goto, Aki*; Michishio, Koji*; Oka, Toshitaka; Tagawa, Masahito*; Yamashita, Shinichi*
Langmuir, 39(34), p.11954 - 11963, 2023/08
Times Cited Count：1 Percentile：0.00(Chemistry, Multidisciplinary)Atomic oxygen (AO) is one of the dominant components of the residual atmosphere in low Earth orbit. AO collides with spacecraft with translational energy of 5 eV, forming nanoscale protrusions on polymeric materials. This study investigated the size of free-volume holes and the layer thickness that interacted with AO for polyethylene (PE), polypropylene (PP), and polystyrene (PS) by positron annihilation lifetime spectroscopy. By the AO irradiation, oxidized layer formed in the surface, and the maximum depth of the oxidized layer for PE and PP were deeper than for PS. The different sizes of free-volume holes would affect the injection depths of AO, resulting in the oxidized layers' thicknesses and surface morphologies.
Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Radiation Physics and Chemistry, 202, p.110590_1 - 110590_6, 2023/01
Times Cited Count：5 Percentile：72.25(Chemistry, Physical)Because of their different charge states, positrons and positronium (Ps) behave quite differently in macromolecules. The behavior of positively charged positrons is strongly influenced by electrostatic interactions. In nonpolar macromolecules such as polyethylene, energetic positrons, if not incorporated into Ps, fall into a delocalized state. These positrons are sensitively trapped by polar groups, if any. On the other hand, charge-neutral Ps is localized in a free volume regardless of the macromolecule's chemical structure. In this study, we discuss the behavior and annihilation characteristics of positrons and Ps in various macromolecules, emphasizing their differences.
Hirade, Tetsuya; Furuta, Hikaru*; Torikai, Yuji*; Fujimura, Yuki; Michishio, Koji*
JJAP Conference Proceedings (Internet), 9, p.011106_1 - 011106_7, 2023/00
Positron annihilation lifetime (PAL) measurements by use of a positron source of 
Na were performed for polycrystalline ITER-grade tungsten samples exposed to low-energy deuterium plasma. The energy of deuterium plasma was low and then it was expected that it would affect just near-surface region. However, we obtained the longer mean positron annihilation lifetime in the tungsten samples exposed to the low-energy deuterium plasma than the virgin tungsten samples. Moreover, almost same longer values were obtained even on the other (no exposed) side of the samples, although the thickness of the samples were about 2 mm. Although, there has been no report of observation of defect formation by existence of hydrogen or deuterium in tungsten, the results indicated that deuterium existence in tungsten can be one of reasons of defects formation.
Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Applied Physics Express, 15(7), p.076001_1 - 076001_4, 2022/07
Times Cited Count：2 Percentile：22.29(Physics, Applied)We discuss the energy dissipation of short-lived 
-positronium (
-Ps) in polymers and silica glass. The 
parameter characterizing the Doppler broadening of -Ps annihilation is determined from the previously reported systematic data of positron annihilation age momentum correlation for various polymers and silica glass. A comparison of the parameter with that expected for thermalized -Ps trapped in a free volume reveals that -Ps is not thermalized and possesses excess energy in fluorinated polymers and silica glass, indicating that it is difficult for Ps to lose energy in substances containing heavy elements such as fluorine and silicon.
Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*
Chemical Physics Letters, 795, p.139507_1 - 139507_4, 2022/05
Times Cited Count：1 Percentile：0.00(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.
Hirade, Tetsuya; Michishio, Koji*; Kobayashi, Yoshinori*; Oshima, Nagayasu*
Acta Physica Polonica A, 137(2), p.109 - 112, 2020/02
Times Cited Count：0 Percentile：0.00(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.
Hyodo, Toshio*; Wada, Ken*; Mochizuki, Izumi*; Kimura, Masao*; Toge, Nobukazu*; Shidara, Tetsuo*; Fukaya, Yuki; Maekawa, Masaki*; Kawasuso, Atsuo*; Iida, Shimpei*; et al.
Journal of Physics; Conference Series, 791(1), p.012003_1 - 012003_8, 2017/02
Times Cited Count：3 Percentile：72.71(Physics, Multidisciplinary)no abstracts in English
Wada, Ken*; Hyodo, Toshio*; Yagishita, Akira*; Ikeda, Mitsuo*; Osawa, Satoshi*; Shidara, Tetsuo*; Michishio, Koji*; Tachibana, Takayuki*; Nagashima, Yasuyuki*; Fukaya, Yuki; et al.
European Physical Journal D, 66(2), p.37 - 40, 2012/02
Times Cited Count：39 Percentile：84.53(Optics)no abstracts in English
Goto, Aki*; Tagawa, Masahito*; Michishio, Koji*; Oka, Toshitaka; Yamashita, Shinichi*
no journal, ,
Films of polyethylene, polypropylene and polystyrene were irradiated with AO, and their surface morphologies and free volumes were investigated. Nanoscale protrusions were formed for all sample surfaces with the AO fluences of 
atoms/cm
- 
atoms/cm. The free volumes in the surfaces within 40 nm - 50 nm decreased due to the AO irradiations.
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Shidara, Tetsuo*; Osawa, Satoshi*; Ikeda, Mitsuo*; Shirakawa, Akihiro*; Furukawa, Kazuro*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Shidara, Tetsuo*; Osawa, Satoshi*; Ikeda, Mitsuo*; Shirakawa, Akihiro*; Furukawa, Kazuro*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Shidara, Tetsuo*; Fukaya, Yuki; Maekawa, Masaki; Kawasuso, Atsuo; Michishio, Koji*; Terabe, Hiroki*; Iida, Shimpei*; et al.
no journal, ,
no abstracts in English
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.
Goto, Aki*; Tanji, Takashi*; Tagawa, Masahito*; Michishio, Koji*; Oka, Toshitaka; Yamashita, Shinichi*
no journal, ,
Atomic oxygen (AO) is a dominant constituent of residual atmosphere in low Earth orbit, it is necessary to evaluate materials' durability against AO before launching but the mechanism for the microstructure formation has not been understood. In this study, we irradiated AO to polymer surface and investigated the change of surface morphologies. The mass losses of irradiated polymers were similar regardless of polymer's type and temperature, however, the formed protrusions became larger and fewer with increasing temperature. This shows that the polymer chains' thermal motions affected the surface morphologies.
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Shidara, Tetsuo*; Osawa, Satoshi*; Ikeda, Mitsuo*; Michishio, Koji*; Terabe, Hiroki*; Iida, Shimpei*; Nagashima, Yasuyuki*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Ikeda, Mitsuo*; Osawa, Satoshi*; Shidara, Tetsuo*; Michishio, Koji*; Tachibana, Takayuki*; Nagashima, Yasuyuki*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Yagishita, Akira*; Ikeda, Mitsuo*; Osawa, Satoshi*; Suwada, Tsuyoshi*; Furukawa, Kazuro*; Shirakawa, Akihiro*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Nigorikawa, Kazuyuki*; Shidara, Tetsuo*; Osawa, Satoshi*; Ikeda, Mitsuo*; Shirakawa, Akihiro*; et al.
no journal, ,
no abstracts in English
Wada, Ken*; Mochizuki, Izumi*; Hyodo, Toshio*; Kosuge, Takashi*; Saito, Yuki*; Nigorikawa, Kazuyuki*; Shidara, Tetsuo*; Osawa, Satoshi*; Ikeda, Mitsuo*; Shirakawa, Akihiro*; et al.
no journal, ,
no abstracts in English
Goto, Aki*; Tanji, Takashi*; Tagawa, Masahito*; Michishio, Koji*; Oka, Toshitaka; Yamashita, Shinichi*
no journal, ,
Crystallinity and thermal property were evaluated for polyethylene, polypropylene, polystyrene films, then, they were irradiated with atomic oxygen (AO) and observed by a scanning electron microscope and positron annihilation lifetime spectroscopy. Free-volume holes and thermal motions affected spatial scales for the reactions with AO, determining the sizes and numerical density of formed protrusions.
