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Yoshida, Kenta*; Toyama, Takeshi*; Inoue, Koji*; Nagai, Yasuyoshi*; Shimodaira, Masaki
Materia, 62(3), p.154 - 158, 2023/03
no abstracts in English
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.
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.
Hirade, Tetsuya
Yodenshi Kagaku; Kiso Kara Oyo Made, p.127 - 132, 2021/08
Positron annihilation Age-MOmentum Correlation (AMOC) measurement is the coincidence measurement method of positron injection time, positron annihilation time and positron annihilation-rays energy. The methods for measurement and analysis of AMOC will be introduced briefly. Some of the interesting researches also will be introduced.
Al
GaO
scintillators by gamma-ray-induced positron annihilation lifetime spectroscopyFujimori, 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
Times Cited Count：5 Percentile：33.01(Physics, Applied)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:YAl
O, 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.
Saito, Kei*; Hirade, Tetsuya; Takai, Kenichi*
Metallurgical and Materials Transactions A, 50(11), p.5091 - 5102, 2019/11
Times Cited Count：29 Percentile：84.62(Materials Science, Multidisciplinary)An attempt was made to separate and identify hydrogen peaks desorbed from lattice defects formed by plastic-strain in the presence of hydrogen in tempered martensitic steel showing quasi-cleavage fracture using thermal desorption spectroscopy from a low temperature (L-TDS) and positron annihilation spectroscopy (PAS). The L-TDS results made it possible to separate two peaks, namely, that of the original desorption and also that of new desorption. The PAS results revealed that the new desorption obtained by L-TDS corresponded to vacancy-type defects. Hydrogen enhanced vacancy-type defect concentration, approximately 10
order in terms of atomic ratio, formed within 1.5 mm from the fracture surface, These results indicate that the accumulation of excess vacancy-type defects enhanced by hydrogen in the local region can lead to nanovoid nucleation and coalescence in plastic deformation, resulting in quasi-cleavage fracture of tempered martensitic steel.
Hirade, Tetsuya; Ando, Hirokazu*; Manabe, Kensuke*; Ueda, Daisuke*
Nuclear Instruments and Methods in Physics Research A, 931, p.100 - 104, 2019/07
Times Cited Count：8 Percentile：66.68(Instruments & Instrumentation)A detector identification method using waveform-shape analysis is proposed. A method for enabling discrimination of detectors by making a characteristic waveform shape for every detector by each own loop circuit on the detector is shown as an example. This method can be applied in many experimental contexts with detectors, making a high counting rate possible. Moreover, detector identification can be used for other important questions such as detector position. As an example, this detector identification method is used to perform positron-annihilation age-momentum correlation measurement with a high temporal resolution and a high counting rate.
-gas exposure at high temperaturesTakeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya
JPS Conference Proceedings (Internet), 25, p.011023_1 - 011023_3, 2019/03
In this study, we prepared samples under two different conditions, (1) 810C, for 600 min, and (2) 850C, for 720 min. A depth-profile analysis of the surfaces of the samples is conducted through Doppler broadening (DB) measurements of positron annihilation 
rays using a slow positron beam. It was indicated that many of positrons annihilated in defects near the surface. According to the TEM image, there are nano-crystal grains near the surface and then positrons can diffuse in the grains and annihilate in defects at the grain boundaries. Furthermore, DB measurements indicated that there is a depth dependence on the chemical composition where positrons annihilate. EDS spectroscopy measurements also indicated that there is a depth dependence of impurities such as Vanadium. These results indicated change of the chemical composition at the grain boundaries.
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
Kagaku To Kogyo, 92(2), p.44 - 54, 2018/02
A positron, an anti-particle of an electron, annihilates with an electron and emits energy that is proportional to mass energy as annihilation -rays. Positron annihilation methods are applied by detecting these -rays. The information of annihilation time, energy of -rays, and direction of -rays emission has been used for materials science. Here, positron annihilation lifetime, doppler broadening of annihilation -rays and positron annihilation age-momentum correlation are mainly explained by use of research examples for metals and polymers, etc.
Hirade, Tetsuya
Radioisotopes, 66(11), p.587 - 593, 2017/11
Positron, anti-particle of electron, annihilates with the lifetime of 100ps to several ns in condensed matter. The energy of the mass of both particles emits as two -rays. The annihilation rate of energy of -rays indicate information just before the annihilation. Positrons have some possibility of reaction with excess electrons to form Positronium (Ps). Ps formation occur within ~ps, therefore Ps formation can be a probe of very fast reactions. Moreover, long lived triplet Ps can have reaction with reactive species until the lifetime of ~ns. Here, methods of positron annihilation research for radiation chemistry and some researches done by positron annihilation methods are introduced.
Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*
Journal of Physics; Conference Series, 791(1), p.012029_1 - 012029_4, 2017/02
Times Cited Count：2 Percentile：62.67(Physics, Multidisciplinary)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.
-gas exposure at high temperaturesTakeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya
Journal of Physics; Conference Series, 791(1), p.012022_1 - 012022_4, 2017/02
Times Cited Count：1 Percentile：42.05(Physics, Multidisciplinary)Titanium alloy is widely used for applications such as golf club heads and structural materials for aircrafts. The surface can be exceedingly hardened by nitriding treatment that initiates defects, but there are some difficulties on use of titanium nitride because the layer can be exfoliated by stress. Therefore, we prepared samples in two different treatment conditions, (1) 810C 600 min and (2) 850C 720 min and performed depth profile analysis of Doppler broadening of positron annihilation -rays (DB) for these samples. According to a calculation of nitrogen diffusion depth, the nitride layer should be only about 0.05-0.1
m. However, the depth profile analysis of the DB measurement indicated that the defects introduced by nitriding treatment extended to a depth of 0.5m.
Hirade, Tetsuya
Hoshasen To Sangyo, (139), p.23 - 28, 2015/12
The researches and the applications of the Positronium Chemistry were introduced. The mechanism of Ps formation in low temperature insulators was clarified by Hirade and it is almost the end of the long, more than half century, period for arguments on Ps formation. Hence almost all of the researchers have been accepting the Spur Reaction Model proposed by Mogensen. Therefore, radiation chemistry researches by use of the Spur Reaction Model, especially the study of excess electrons at the time range of pico-to-nano second and electron mobility, were introduced. It was also introduced that the Free Volume Model is not correct and then the sub-nano meter vacant space, such as the microscopic free volume in polymers, can be studied by just the triplet Ps lifetime. As the latest research for the application, it was introduced that Ps bubble shows oscillation especially in ionic liquids and is expected to be a strong tool to investigate nano-scale properties of ionic liquids.
Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Hirade, Tetsuya; Oshima, Nagayasu*
NanotechJapan Bulletin (Internet), 8(3), 5 Pages, 2015/07
Studying the creation and time evolution of defects is an important issue for interpreting the hydrogen embrittlement mechanism of steels. We have been studied the relationship between hydrogen embrittlement of high strength steel and lattice defects associated with hydrogen by thermal desorption analysis (TDA) and positron probe microanalyzer (PPMA).
Hirade, Tetsuya
Yodenshi Kagaku, (4), p.3 - 8, 2015/02
Positron annihilation Age-MOmentum Correlation (AMOC) measurement is the coincidence measurement method of positron injection time, positron annihilation time and positron annihilation -rays energy. The methods for measurement and analysis of AMOC will be introduced briefly. Some of the interesting researches also will be introduced.
Kawasuso, Atsuo; Yoshikawa, Masahito; Ito, Hisayoshi; Krause-Rehberg, R.*; Redmann, F.*; Higuchi, Takatoshi*; Betsuyaku, Kiyoshi*
Physica B; Condensed Matter, 376-377, p.350 - 353, 2006/04
Times Cited Count：13 Percentile：52.05(Physics, Condensed Matter)In this presentation, we report identification of vacancy defects in cubic and hexagonal SiC irradiated with fast electrons through electron-pisitron momentum distribution measurements and theoretical analyses. In cubic SiC isolated silicon vacancies are responsible for positron trapping. The lifetime of positrons trapped at silicon vacancies is prolonged due to the outward lattice relaxation. Because of the local tetrahedral symmetry of silicon vacancies, the observed momentum distributions are consistently explained. In the case of hexagonal SiC, one particular vacancy defects appearing after annealing of isolated silicon vacancies have dangling bonds along the c-axis. From the enhancement of positron annihilation probability with carbon 1s electrons, the above defects are attributed to carbon-vacancy-antisite-carbon complexes.
Chen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Sakai, Seiji; Naramoto, Hiroshi*
JAEA-Review 2005-001, TIARA Annual Report 2004, p.232 - 234, 2006/01
no abstracts in English
-implanted ZnO studied using a slow positron beamChen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Suzuki, Ryoichi*; Odaira, Toshiyuki*
Applied Physics Letters, 87(9), p.091910_1 - 091910_3, 2005/08
Times Cited Count：31 Percentile：71.4(Physics, Applied)Zinc oxide crystals were implanted with N
, O, and co-implanted with O/N ions. Positron annihilation measurements show the introduction of vacancy clusters upon implantation. In the N-implanted sample, these vacancy clusters are only partially annealed at 800C as compared to their full recovery in the O-implanted sample, suggesting a strong interaction between nitrogen and vacancy clusters. At 1000-1100C, nitrogen also forms stable complexes with thermally generated vacancies. To remove all the detectable vacancy defects, a high temperature annealing at 1250C is needed. Furthermore, Hall measurements of this sample show n-type conductivity though nitrogen is expected as acceptors. On the contrary, in the O/N co-implanted sample, most vacancy clusters disappear at 800C. Probably oxygen scavenges nitrogen to form N-O complexes and hence enhance the annealing of vacancy clusters. A highly compensated semi-insulating layer is formed in the co-implanted sample.
Chen, Z. Q.; Yamamoto, Shunya; Kawasuso, Atsuo; Xu, Y. H.; Sekiguchi, Takashi*
Applied Surface Science, 244(1-4), p.377 - 380, 2005/05
Times Cited Count：16 Percentile：55.78(Chemistry, Physical)Homo- and heteroepitaxial ZnO films were grown by pulsed laser deposition on single crystal ZnO substrate and Al
O
substrate, respectively. The surface roughness probed by atomic force microscope (AFM) depends strongly on the substrate, which is much larger for the heteroepitaxial layer. Doppler broadening of positron annihilation measurements show existence of defects in both of the films, with a higher concentration in the homoepitaxial film. Raman scattering measurements reveal the E2 phonon vibration mode at 437 cm
, which is characteristic of the wurtzite structure. These films show strong ultraviolet (UV) emission at 3.3 eV from the cathodoluminescence measurements, which indicates good optical properties.
