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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：69.23(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.
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：20.28(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.
Yamawaki, Masato*; Uesugi, Naoya*; Oka, Toshitaka; Nagasawa, Naotsugu*; Ando, Hirokazu*; O'Rourke, B. E.*; Kobayashi, Yoshinori*
Japanese Journal of Applied Physics, 59(11), p.116504_1 - 116504_5, 2020/11
Positron annihilation lifetime measurements were performed on polyethylene films with thickness of 15
m - 2000m using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.
-irradiated ultra high molecular weight polyethyleneKobayashi, Yoshinori*; Yamawaki, Masato*; Oka, Toshitaka; Saiki, Seiichi; Mohamed, H.*; Hattori, Kanehisa*; Watanabe, Yoshihiro*
Materials Science Forum, 733, p.147 - 150, 2013/00
Times Cited Count：3 Percentile：79.46(Materials Science, Multidisciplinary)Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to -irradiation. Correlations were found between the mechanical properties and o-Ps lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of -irradiation on positronium formation is discussed.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron lifetime measurement (PALS) is a useful tool for evaluating nanometer-sized defects in materials such as metals and semiconductors. However, PALS measurement required two flat specimens placed at both sides of the positron source therefore it was difficult to apply PALS for one complicated shaped small specimen. Purpose of this research is developing a PALS method that can be applied for one small specimen having complicated shape. We succeeded to measure PALS spectra with just one specimen.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
The positron lifetime measurement method (PALS) is a useful tool for evaluating nanometer-sized vacancy defects in metals and semiconductors. Especially in the material development for nuclear fusion reactors or nuclear reactors, elucidation of damage behavior by radiation is an important subject. However, PALS always needs to have large enough two specimens. At present, miniaturization of sample is strongly required to reduce radioactivity, but this restriction is a big hindrance to the application of PALS. In this research, we developed a measurement system that can measure positron lifetime with one specimen of arbitrary shape. Positron surrounding the specimen with a scintillator and not incident on the specimen was detected by the light emission of the scintillator, and PALS measurement in the sample was attempted by excluding treatment (anti-coincidence). As a result, we succeeded in obtaining a spectrum which is roughly in agreement with the conventional measurement method.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron annihilation lifetime spectroscopy (PALS) is very strong tool to investigate sab-nanometer scale defects in metals and semiconductors. PALS is based on the -ray measurement techniques and it is difficult to measure radioactive samples such as Neutron irradiated samples. Therefore we are creating a method by which you can measure PALS for one very small radioactive sample. It is needed to reject events that positrons annihilate at outside of the sample. We placed the sample at a small space between scintillators and used signals from the scintillators for the anti-coincidence method to reject the events. We succeeded to reject 20% of the events.
Sumiya, Masato; Ikeda, Koki; Sonoda, Takashi; Niizato, Tadafumi; Mikake, Shinichiro; Abe, Hironobu; Inoue, Makoto; Eguchi, Kazutoshi; Kozawa, Masachiyo; Terunuma, Akihiro; et al.
no journal, ,
no abstracts in English
