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Journal Articles

Formation of nanoscale protrusions on polymer films after atomic oxygen exposure; Observations with positron annihilation lifetime spectroscopy

Goto, Aki*; Michishio, Koji*; Oka, Toshitaka; Tagawa, Masahito*; Yamashita, Shinichi*

Langmuir, 39(34), p.11954 - 11963, 2023/08

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.

Journal Articles

Positrons and positronium in macromolecules; Consequences of different charge states

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:1 Percentile:71.05(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.

Journal Articles

Positron annihilation study of tungsten exposed to low-energy deuterium plasma

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 $$^{22}$$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.

Journal Articles

Energy dissipation of para-positronium in polymers and silica glass

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:1 Percentile:37.1(Physics, Applied)

We discuss the energy dissipation of short-lived $textit{para}$-positronium ($textit{p}$-Ps) in polymers and silica glass. The $$S$$ parameter characterizing the Doppler broadening of $textit{p}$-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 $$S$$ parameter with that expected for thermalized $textit{p}$-Ps trapped in a free volume reveals that $textit{p}$-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.

Journal Articles

Temperature dependence of positron annihilation lifetime in near-surface and bulk of room-temperature ionic liquid observed by a slow positron beam

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$$^{circ}$$C of the triplet positronium ($$ortho$$-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 150$$^{circ}$$C, 120$$^{circ}$$C above the melting temperature. The $$ortho$$-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 $$ortho$$-Ps and radiolysis products such as the OH radicals. The temperature dependence observed for TMPA-TFSI suggested that the chemical reaction of $$ortho$$-Ps occurred.

Journal Articles

Temperature dependence of ortho-positronium annihilation 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 ($$ortho$$-Ps) pick-off annihilation lifetime indicated that there was a nano-meter structure remained by ionic interactions even at high temperatures. The $$ortho$$-Ps pick-off annihilation lifetime will be a strong tool to study nano-structure in RTILs.

Journal Articles

Research progress at the Slow Positron Facility in the Institute of Materials Structure Science, KEK

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:74.47

no abstracts in English

Journal Articles

Increase in the beam intensity of the linac-based slow positron beam and its application at the Slow Positron Facility, KEK

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:38 Percentile:85.41(Optics)

no abstracts in English

Oral presentation

Recent development of the slow positron facility at institute of materials structure science, KEK

Wada, Ken*; Hyodo, Toshio*; Yagishita, Akira*; Ikeda, Mitsuo*; Osawa, Satoshi*; Shidara, Tetsuo*; Michishio, Koji*; Suzuki, Ryohei*; Tachibana, Takayuki*; Nagashima, Yasuyuki*; et al.

no journal, , 

no abstracts in English

Oral presentation

The New experiment stations at KEK Slow Positron Facility

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

Oral presentation

Increase in the intensity and brightness enhancement of the slow positron beam and its application at the Slow Positron Facility, KEK

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

Oral presentation

Beam-line improvement and new experiment stations of KEK-IMSS slow-positron facility

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

Oral presentation

Beam-line improvement and recent results of KEK-IMSS slow-positron facility

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

Oral presentation

Present status of the KEK-IMSS Slow Positron Facility; A New beam-line branch and a rearrangement of the experiment stations

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

Oral presentation

Recent developments and results of the KEK slow positron facility

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

Oral presentation

Materials science at the KEK slow positron facility

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

Oral presentation

Introduction to the slow positron facility at KEK

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

Oral presentation

Application of a linac-based intense slow-positron beam to diffraction experiments

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

Oral presentation

Temperature dependence of ortho-positronium lifetime in a room temperature ionic liquid

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.

Oral presentation

Microstructure formation on polymer surfaces induced by atomic oxygen irradiation; Free volumes of polymer surfaces

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 $$10^{18}$$ atoms/cm$$^{2}$$ - $$10^{19}$$ atoms/cm$$^{2}$$. The free volumes in the surfaces within 40 nm - 50 nm decreased due to the AO irradiations.

22 (Records 1-20 displayed on this page)