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Endo, Shunsuke; Abe, Ryota*; Fujioka, Hiroyuki*; Ino, Takashi*; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kawamura, Shiori*; Kimura, Atsushi; Kitaguchi, Masaaki*; Kobayashi, Ryuju*; et al.
European Physical Journal A, 60(8), p.166_1 - 166_10, 2024/08
Times Cited Count:0 Percentile:0.00(Physics, Nuclear)Omer, M.; Shizuma, Toshiyuki*; Koizumi, Mitsuo; Taira, Yoshitaka*; Zen, H.*; Ogaki, Hideaki*; Hajima, Ryoichi
UVSOR-50, P. 37, 2023/08
no abstracts in English
Taira, Yoshitaka*; Endo, Shunsuke; Kawamura, Shiori*; Nambu, Taro*; Okuizumi, Mao*; Shizuma, Toshiyuki*; Omer, M.; Zen, H.*; Okano, Yasuaki*; Kitaguchi, Masaaki*
Physical Review A, 107(6), p.063503_1 - 063503_10, 2023/06
Times Cited Count:5 Percentile:75.86(Optics)no abstracts in English
Endo, Shunsuke; Shizuma, Toshiyuki*; Zen, H.*; Taira, Yoshitaka*; Omer, M.; Kawamura, Shiori*; Abe, Ryota*; Okudaira, Takuya*; Kitaguchi, Masaaki*; Shimizu, Hirohiko*
UVSOR-49, P. 38, 2022/08
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
Times Cited Count:6 Percentile:32.40(Physics, Applied)To clarify the existence of cation vacancies in Ce-doped GdAl
Ga
O
(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:Y
Al
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.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90
collision laser Compton scattering at UVSOR.
Kitaura, Mamoru*; Fujimori, Kosuke*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Hirade, Tetsuya; Kamada, Kei*; Watanabe, Shinta*; Onishi, Akimasa*
no journal, ,
Positron annihilation spectroscopy is the only way to investigate the properties of cation vacancies because they are negatively charged. We generated high-energy pulsed gamma rays by the vertical collision of an ultrashort pulse laser and electron beam. In this study, we investigated the vacancy-type defects present in the crystals of GAGG(GdAl
Ga
O
), GAGG: Ce and GAGG: Ce, Mg by positron annihilation lifetime spectroscopy using the high-energy gamma rays. 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.
Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Hirade, Tetsuya; Kamada, Kei*; Watanabe, Shinta*; Onishi, Akimasa*
no journal, ,
We generated high-energy pulsed gamma rays by the vertical collision of an ultrashort pulse laser and electron beam. In this study, we investigated the vacancy-type defects present in the crystals of GAGG(GdAl
Ga
O
), GAGG: Ce and GAGG: Ce, Mg by positron annihilation lifetime spectroscopy using the high-energy gamma rays. The lifetime of the defect-related component was significantly changed by Mg co-doping. This indicates that the Al/Ga vacancies disappear. This fact corresponds well with the suppression of the phosphorescence component and is an important result showing that the Mg co-doping is effective in suppressing the shallow electron capture center.
Taira, Yoshitaka*; Sugita, Kento*; Yamamoto, Ryohei*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
We are developing gamma-ray-induced positron annihilation spectroscopy at UVSOR-III. This method enables defect analysis of the entire bulk sample with a thickness of several cm, which was difficult to measure with the conventional method using a positron radiation source. Currently, the user use of the positron lifetime measurement method is being developed, and in parallel with this, the coincidence Doppler broadening method, the age-momentum correlation measurement method, and the spin-polarized positron spectroscopy are being developed. Here, we will describe the development status of them.
Yamamoto, Ryohei*; Taira, Yoshitaka*; Sugita, Kento*; Hirade, Tetsuya; Takashima, Yoshifumi*; Kato, Masahiro*
no journal, ,
Positron annihilation spectroscopy is a powerful analytical method that can observe single-atom vacant defects in crystals and microvoids in insulating materials. UVSOR-III installed at the Institute of Molecular Science is promoting the development and user use of Gamma-ray induced positron annihilation spectroscopy (GiPAS) by ultrashort pulse gamma rays. We have succeeded in positron lifetime measurement and lifetime momentum correlation measurement. This time, we succeeded in detecting the process of defect capture in the positron age-momentum correlation measurement of strained steel materials.
Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
We applied the ultra-short pulsed gamma rays to positron annihilation spectroscopy (PAS). PAS using high energy gamma-rays, called gamma induced PAS (GiPAS), has several advantages compared with PAS using radioisotopes. (i) It enables defect analysis of thick material in a few centimetres because positrons are created throughout a bulk material via pair production by irradiation with gamma-rays having high penetration into the material. (ii) There is no contribution of positrons annihilated in the covering material of the shield sources, making the data analysis easy and accurate.
Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
We have developed the gamma-ray induced positron annihilation lifetime spectroscopy (GiPALS) with a time resolution of 140 ps. It has eight BaF detectors and two digital oscilloscopes currently available for users. In addition to GiPALS, we have developed gamma-ray induced age-momentum correlation (GiAMOC). We will present a generation method of the ultra-short pulsed gamma-rays, details of GiPALS and GiAMOC, and future plans, including the development of a spin-polarized positron source generated from circularly polarized gamma rays.
Yabuuchi, Atsushi*; Hirade, Tetsuya; Fujinami, Masanori*; Awaji, Ryo*; Oshima, Nagayasu*; Takai, Kenichi*; Taira, Yoshitaka*; Sugita, Kento*
no journal, ,
In situ measurements of positron annihilation lifetimes have been performed at the UVSOR synchrotron radiation facility to characterise defects formed during tensile deformation of pure iron using the gamma-ray induced positron annihilation spectroscopy (GiPAS) technique. A dumbbell-shaped specimen was attached to a small tensile tester and stretched to a nominal strain of 7 or more at a strain rate of 2.210
/s. Positron lifetime changes during tensile deformation of a pure iron specimen were observed using positrons generated in the sample by irradiating the centre of the sample with a 66MeV gamma-ray pulse beam of 3mm in diameter. Unlike the results reported so far, the change in the positron lifetime, especially at the early deformation stage, was very small, making clear the importance of in-situ measurement.
Taira, Yoshitaka*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
BL1U is a beamline that researches the development of new light sources and the exploration of usage methods. We are generating 6.6 MeV ultrashort pulse gamma rays using a Ti: Sa laser with a wavelength of 800 nm and are researching gamma ray-induced positron annihilation spectroscopy (GiPALS). GiPALS is a method that measures the lifetime of positrons by measuring the emission time distribution of annihilation gamma rays and can analyze the type and size of defects inside a sample. GiPALS is available to users for in-situ measurements of defect formation in metallic materials during stress loading and measurements of bulk samples such as ferrous materials, catalytic materials, and scintillators.
Doshi, Satoru*; Maeda, Kazuki*; Taira, Yoshitaka*; Watanabe, Shinta*; Hirade, Tetsuya
no journal, ,
Gamma-ray-induced positron annihilation lifetime measurement (GiPALS), which utilizes the generation of positrons inside a sample by pair generation with gamma rays, has a significantly smaller background component than conventional measurement methods. It can perform measurements in harsh environments such as high temperature and high pressure because there is no positron source inside the sample. It has been reported that the positron annihilation lifetime spectrum of CeO can be fitted with two components. However, in reality, it is thought that there are at least three components: a component of annihilation in the bulk, a component of annihilation trapped in lattice defects, a component of annihilation trapped on the surface. Therefore, in this study, we tried to fit three components and assigned each by changing the particle size. In addition, we theoretically investigated the bulk, defect, and surface components in the positron annihilation lifetime of CeO
using first-principles calculations.
Taira, Yoshitaka*; Fujimoto, Masaki*; Fujimori, Kosuke*; Kitaura, Mamoru*; Zen, H.*; Okano, Yasuaki*; Hosaka, Masahito*; Yamazaki, Junichiro*; Kato, Masahiro*; Hirade, Tetsuya; et al.
no journal, ,
For general positron sources, radioisotopes such as Na are often used. However, there is a problem that positrons cannot probe the deep region of metal materials with a thickness of 1 mm or more. Gamma-ray induced positron annihilation lifetime measurement (GiPALS) is a method for generating positrons in bulk samples with a thickness of several centimeters and samples placed in vessels such as high temperature and/or pressure furnaces. The annihilation lifetime of positrons is about 200 ps for metal materials, so it is important to use gamma rays with a shorter pulse width for GiPALS in order to accurately measure the positron lifetime. We have succeeded in the proof-of-principle experiment for GiPALS of ultra-short pulse gamma rays with a pulse width of 2 ps, which was originally developed using 90
collision laser Compton scattering at UVSOR.
Yamamoto, Ryohei*; Sugita, Kento*; Taira, Yoshitaka*; Hirade, Tetsuya
no journal, ,
Age-Momentum Correlation (AMOC) can observe the Doppler broadening of time-resolved annihilation gamma rays. The annihilation rate depends on the positron state, and it is possible to know if positrons are trapped in structural defects in a sample. Moreover, the Doppler broadening gives the information of impurities around the defects. Positrons from radioactive isotopes cannot penetrate a deep region of bulk material. The application of radioisotopes is difficult for the measurements under severe conditions such as in high pressure or a high temperature. Therefore, we have developed a GiAMOC (Gamma-ray induced AMOC) system, which is a measurement method for generating positrons in a sample using inverse Thomson scattered gamma rays in UVSOR-III. In addition, the developed measurement system was used to measure the reference material for positron lifetime measurement.
Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Fujimoto, Masaki*; Hirade, Tetsuya
no journal, ,
Positron annihilation spectroscopy is a powerful analytical method that can observe single-atom vacant defects in crystals and micro voids in insulating materials. UVSOR-III installed at the Institute of Molecular Science is promoting the development and user use of Gamma-ray induced positron annihilation spectroscopy (GiPAS) by ultrashort pulse gamma rays. Since the ultrashort pulse gamma rays generate positrons inside the material by pair production, positron annihilation experiments of bulk materials with a thickness of several cm can be performed non-destructively. We have succeeded in the generation of ultrashort pulse gamma rays and positron annihilation experiments such as the lifetime measurement and the positron age-momentum correlation measurement.
Omer, M.; Shizuma, Toshiyuki*; Hajima, Ryoichi*; Koizumi, Mitsuo; Taira, Yoshitaka*
no journal, ,
Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
We have developed ultra-short, pulsed gamma rays at the synchrotron radiation facility UVSOR-III by a 90-degree collision between a 750-MeV electron beam and a Ti:Sa laser pulse. The maximum energy of the gamma rays is 6.6 MeV and the pulse width is calculated to be sub-ps to ps ranges. We applied this ultra-short, pulsed gamma rays to positron annihilation spectroscopy (PAS). A positron is an excellent probe of atomic-scale defects in solids such as vacancies, dislocations, and clusters and of free volumes in polymers. PAS using a high energy gamma-ray, which is called gamma induced PAS (GiPAS), has several advantages compared with PAS using Na-22. We will present a generation method of the ultra-short, pulsed gamma rays and details of GiPAS.