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

https://doi.org/10.1016/j.radphyschem.2022.110590

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.

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

https://doi.org/10.1016/j.cplett.2022.139507

We obtained the temperature dependence up to 150C 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.

Visualizing cation vacancies in Ce:GdAlGaO scintillators by gamma-ray-induced positron annihilation lifetime spectroscopy

Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.

Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08

https://doi.org/10.35848/1882-0786/aba0dd

To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAlO, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.

Positron annihilation in the near surface of room temperature ionic liquids

Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*

Journal of Physics; Conference Series, 791(1), p.012029_1 - 012029_4, 2017/02

https://doi.org/10.1088/1742-6596/791/1/012029

We tried to observe the positron annihilation rates near surface of (room temperature ionic liquids) IL's, such as N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by use of the perpendicular slow positron beamline installed at AIST. The vaper pressure of TMPA-TFSI is very small and hence it is possible to measure the positron annihilation rate in vacuum chamber directly. This represents the first energy variable experimental results of the positron annihilation rate at the near surface of an IL. The triplet positronium annihilation rate seems to be larger at nearer region to the surface of the IL's.

Pressure-temperature-field phase diagram in the ferromagnet UP

Araki, Shingo*; Hayashida, Minami*; Nishiumi, Naoto*; Manabe, Hiroki*; Ikeda, Yoichi*; Kobayashi, Tatsuo*; Murata, Keizo*; Inada, Yoshihiko*; Winiewski, P.*; Aoki, Dai*; et al.

Journal of the Physical Society of Japan, 84(2), p.024705_1 - 024705_8, 2015/02

https://doi.org/10.7566/JPSJ.84.024705

Study on engineering technologies in the Mizunami Underground Research Laboratory; FY2012 (Contract research)

Fukaya, Masaaki*; Noda, Masaru*; Hata, Koji*; Takeda, Yoshinori*; Akiyoshi, Kenji*; Ishizeki, Yoshikazu*; Kaneda, Tsutomu*; Sato, Shin*; Shibata, Chihoko*; Ueda, Tadashi*; et al.

JAEA-Technology 2014-019, 495 Pages, 2014/08

JAEA-Technology-2014-019.pdf:82.23MB

The researches on engineering technology in the Mizunami Underground Research Laboratory (MIU) plan consists of (1) research on engineering technology deep underground, and (2) research on engineering technology as a basis of geological disposal. The former research is mainly aimed in this study, which is categorized in (a) development of design and construction planning technologies, (b) development of construction technologies, (c) development of countermeasure technologies, and (d) development of technologies for security. In this study, the researches on engineering technology are being conducted in these four categories by using data measured during construction as a part of the second phase of the MIU plan.

Improved sensitivity of magnetic measurements under high pressure in miniature ceramic anvil cell for a commercial SQUID magnetometer

Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma*; Fisk, Z.; Ikeda, Shugo*; Kobayashi, Hisao*

Review of Scientific Instruments, 84(4), p.046105_1 - 046105_3, 2013/04

https://doi.org/10.1063/1.4802832

Two modifications have been made to a miniature ceramic anvil high pressure cell (mCAC) designed for magnetic measurements in a commercial superconducting quantum interference (SQUID) magnetometer. Replacing the Cu-Be piston in the former mCAC with a composite piston composed of the Cu-Be and ceramic cylinders reduces the background magnetization significantly smaller at low temperatures. A second modification to the mCAC is the utilization of a ceramic anvil with a hollow in the center of the culet surface.

Effect of sweep gas species on tritium release behavior from lithium titanate packed bed during 14MeV neutron irradiation

Kawamura, Yoshinori; Ochiai, Kentaro; Hoshino, Tsuyoshi; Kondo, Keitaro*; Iwai, Yasunori; Kobayashi, Kazuhiro; Nakamichi, Masaru; Konno, Chikara; Yamanishi, Toshihiko; Hayashi, Takumi; et al.

Fusion Engineering and Design, 87(7-8), p.1253 - 1257, 2012/08

https://doi.org/10.1016/j.fusengdes.2012.02.125

Tritium generation and recovery study on lithium ceramic packed bed was started by use of FNS in JAEA. Lithium titanate was selected as tritium breeding material. In this work, the effect of sweep gas species on tritium release behavior was investigated. In case of sweep by helium with 1% of hydrogen, tritium in water form was released sensitively corresponding to the irradiation. This is due to existence of the water vapor in the sweep gas. On the other hand, in case of sweep by dry helium, tritium in gaseous form was released first, and release of tritium in water form was delayed and was gradually increased.

Radio frequency plasma transition caused by gas puffing and/or direct current biasing using multiturn internal antenna

Yamauchi, Toshihiko; Kobayashi, Seiji*; Sugibayashi, Hideyuki*; Tachibana, Toshiyuki*; Naito, Shunya*; Kanno, Yoshinori*; Hiruta, Toshihito

Japanese Journal of Applied Physics, 51(1), p.01AA02_1 - 01AA02_7, 2012/01

https://doi.org/10.1143/JJAP.51.01AA02

In the beginning of this study, the RF (radio frequency) plasma by the internal antenna which is in contrast to that of the external antenna, was considered for the transition from the charged coupled plasma (CCP) to the inductively coupled plasma (ICP) not to be observed. On the contrary, in our plasma experiment by using the internal multi-turn RF antenna, the transition phenomenon was observed at the extent of 40 W in RF power. In this experiment, the relation between the gas pressure and the RF power on the transition from CCP to ICP indicated almost the same characteristic as Paschen's law. But the transition physics, or the absorption mechanism of RF power based on the collision dumping, was strongly complex. We have experimentally represented the CCP-ICP transition to study the physics using the original physical technique. Firstly, we changed the CCP into the ICP by the gas control. It was considered that the increase of the electron temperature caused the transition. Secondly, the decrease of gas pressure displayed the same meaning with the longer period of the self-pulse transition. Thirdly, the self-bias caused by RF power and the external bias applied between the RF antenna and the stage were described for the transition physics.

Foundations of radiation chemistry; Early processes of radiolysis by V. M. Byakov and S. V. Stepanov, 1

Kobayashi, Yoshinori*; Oka, Toshitaka

Hoshasen Kagaku (Internet), (92), p.39 - 49, 2011/09

Contents of the lecture note by Prof. V. M. Byakov and Dr. S. V. Stepanov (Institute of Theoretical and Experimental Physics, Russia) are described in a series of articles. The first article concerns basic concepts, classification and sources of ionizing radiations.