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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.
1)-OTakahashi, Shin*; Fujimoto, Yosuke*; Teraoka, Yuden; Yoshigoe, Akitaka; Okuyama, Hiroshi*; Aruga, Tetsuya*
Surface Science, 601(18), p.3809 - 3812, 2007/09
Times Cited Count：4 Percentile：22.69(Chemistry, Physical)Supersonic molecular beam techniques with 0.5-1.0eV and high resolution X-ray photoelectron spectroscopy using synchrotron radiation were applied to the dynamics study for oxygen dissociative adsorption on Ru(0001). Increase of adsorption probability and saturation coverage with increasing translational energy suggests a direct dissociation mechanism. We measured uptake curves with and without heating a molecular beam source to verify internal energy effects. We found drastic enhancement of dissociative adsorption. In comparison with rotational and translational cooling during beam expansion, vibrational populations are known to be almost unrelaxed. Then, we concluded that adsorption enhancement was mainly caused by vibrational excitation, indicating that dissociation barrier was located in the exit channel on the potential energy surface. Such vibrational effect was also found on oxygen pre-covered Ru(0001) surface with a 0.5 monolayer corresponding to a p(21) structure.
Shirai, Toshiyuki*; Tanabe, Mikio*; Soda, Hikaru*; Ikegami, Masahiro*; Fujimoto, Shinji*; Tongu, Hiromu*; Noda, Akira*; Noda, Koji*; Shibuya, Shinji*; Fujimoto, Tetsuya*; et al.
Proceedings of 9th Symposium on Accelerator and Related Technology for Application, p.19 - 22, 2007/06
Takahashi, Shin*; Fujimoto, Yosuke*; Teraoka, Yuden; Yoshigoe, Akitaka; Aruga, Tetsuya*
Chemical Physics Letters, 433(1-3), p.58 - 61, 2006/12
Times Cited Count：3 Percentile：8.82(Chemistry, Physical)Dissociative adsorption of oxygen on Ru(0001) surface was investigated by supersonic molecular beam method combined with high resolution X-ray photoelectron spectroscopy (XPS) using synchrotron radiation. We examined effects of the molecular vibrational excitation as well as translational energy on dissociative adsorption of oxygen in the direct adsorption regime. We found an enhancement of dissociative oxygen adsorption on Ru(0001) by molecular vibrational excitation, indicating that potential energy surface has late barrier for this system.
Takahashi, Shin*; Fujimoto, Yosuke*; Teraoka, Yuden; Yoshigoe, Akitaka; Moritani, Kosuke*; Aruga, Tetsuya*
KEK Proceedings 2006-3, p.80 - 82, 2006/08
Growth of oxygen adlayer on a Ru(0001) surface with high energy supersonic oxygen molecular beam was studied using high energy resolution X-ray photoelectron spectroscopy. The Ru 3
core level was used to monitor the growth of oxygen adlayer in the coverage region from 0.5 to 0.6 monolayer (ML) and the photoelectron spectrum was resolved into bulk and two surface components denoted as S1(2O) and S1(3O), which were first layer Ru atoms bonded to two and three oxygen atoms, respectively. The intensity change of each component as a function of oxygen dosage suggests the possibility of partial island formation on Ru(0001).
Kashiwagi, Hirotsugu; Fukuda, Mitsuhiro; Okamura, Masahiro*; Jameson, R. A.*; Hattori, Toshiyuki*; Hayashizaki, Noriyosu*; Sakakibara, Kazuhiko*; Takano, Jumpei*; Yamamoto, Kazuo*; Iwata, Yoshiyuki*; et al.
Review of Scientific Instruments, 77(3), p.03B305_1 - 03B305_4, 2006/03
Times Cited Count：12 Percentile：52.29(Instruments & Instrumentation)Acceleration of a 17mA 100keV/u C
ion beam has been successfully achieved with an RFQ linac by means of "Direct injection scheme". The Direct injection scheme is a new scheme for injecting an ion beam from a laser ion source to the RFQ linac without a low energy beam transport line to avoid a beam loss due to the space charge effect. The high current C beam is required for single turn injection to a synchrotron to reduce the size of synchrotron magnets. The high current C beam produced by an ion source with a Nd-YAG laser was injected to the RFQ linac by the Direct injection scheme. It has been proved experimentally that the fully-stripped carbon ion beam with a current more than 10mA can be accelerated by the RFQ linac.
Kashiwagi, Hirotsugu; Okamura, Masahiro*; Hattori, Toshiyuki*; Jameson, R. A.*; Yamamoto, Kazuo*; Fujimoto, Tetsuya*; Kamiya, Tomihiro
Proceedings of 3rd Annual Meeting of Particle Accelerator Society of Japan and 31st Linear Accelerator Meeting in Japan (CD-ROM), p.570 - 572, 2006/00
no abstracts in English
Kashiwagi, Hirotsugu; Okamura, Masahiro*; Jameson, R. A.*; Hattori, Toshiyuki*; Hayashizaki, Noriyosu*; Sakakibara, Kazuhiko*; Takano, Jumpei*; Yamamoto, Kazuo*; Iwata, Yoshiyuki*; Fujimoto, Tetsuya*
Proceedings of 2nd Annual Meeting of Particle Accelerator Society of Japan and 30th Linear Accelerator Meeting in Japan, p.182 - 184, 2005/07
The carbon beam from a Nd-YAG laser ion source was accelerated successfully by an RFQ linac using Direct injection scheme. The "Direct injection scheme" is the way to inject an ion beam to the RFQ linac without a low energy beam transport line to avoid space charge effect due to a high intensity beam from the laser ion source. About 30mA of a carbon beam was detected by a faraday cup just behind the RFQ linac.
Kim, J.*; Kim, D. E.*; Kawachi, Tetsuya; Hasegawa, Noboru; Sukegawa, Kota*; Iwamae, Atsushi*; Fujimoto, Takashi*
Journal of the Optical Society of Korea, 7(3), p.145 - 149, 2003/09
The anistropy of electron energy distribution in oxygen plasmas produced by a high intensinty laser was investigated by using polarization spectroscopy. An ultra-short pulsed laser with a pulse duration of 66.5 fs and a power density of 110
W/cm
was used. At this power density and pulse duration, the plasma was generated predominantly by optical field ionization. The degree of polarization of OVI 1s2p P-1s4d D
(J=1/2-3/2 and J=3/2-5/2) transition line at 129.92 
の1s 2pP-1s4sS (J=1/2-1/2 and J=3/2-1/2) transition line at 132.26 AA was used to calibrate the sensitivity of the optical system. The dependencies of the degree of polarization on the initial gas density and on the laser polarization were investigated. When the laser polarization was changed from a linear to a circlar polarization was decreased. When the initial gas density was increased, the degree of polarization was decreased.
Takahashi, Shin*; Fujimoto, Yoichi*; Aruga, Tetsuya*; Teraoka, Yuden; Yoshigoe, Akitaka; Moritani, Kosuke
no journal, ,
Ru(0001) surface was oxidized by supersonic oxygen molecular beams. Chemical bonding states of O and Ru atoms at the surface were analized by photoemission spectroscopy with synchrotron radiation. First, the Ru(0001) surface was exposed to oxygen gas to be formed oxygen-saturated surface with 0.5 ML. The oxidized Ru surface was irradiated by supersonic oxygen molecular beams. Adsorption characterictics of oxygen molecules were investigated. The translational kinetic energy of oxygen molecular beam was 0.5eV. Differences of oxygen uptake curves were investigated for a nozzle temperature of 300K and 1400K. In the case of 300K, saturated oxygen amount increased up to 0.58ML. The oxygen coverage increased up to 0.61ML in the case of 1400K. The difference was interpreted as a large adsorption probability of vibrationally-excited oxygen molecules.
Takahashi, Shin*; Fujimoto, Yosuke*; Teraoka, Yuden; Yoshigoe, Akitaka; Aruga, Tetsuya*
no journal, ,
Oxygen adsorption processes at a Ru(0001) surface were investigated in an oxygen coverage region larger than 0.5ML via supersonic oxygen nmolecular beam techniques and high resolution photoemission spectroscopy with synchrotron radiation. It was found that vibrationally-excited oxygen molecules enhanced their adsorption in such a coverage region. This indicates that a trapping-mediated adsorption mechanism via a precursor state is dominant under such experimental conditions.
Takahashi, Shin*; Fujimoto, Yosuke*; Teraoka, Yuden; Yoshigoe, Akitaka; Aruga, Tetsuya*
no journal, ,
no abstracts in English
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.
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(GdAlGaO), 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.
AlGaO crystals revealed by gamma-ray induced positron annihilation lifetime spectroscopyFujimori, 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(GdAlGaO), 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*; 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.
Taira, Yoshitaka*; Fujimoto, Masaki*; Okano, Yasuaki*; Kitaura, Mamoru*; Hirade, Tetsuya
no journal, ,
Laser Thomson/Compton scattering is a unique technique to generate gamma-rays with features such as quasi-monochromatic and tunable energy, highly polarized, low divergence angle, and low background. We have developed GiPALS using an ultra-short pulsed gamma-ray generated at the synchrotron radiation facility UVSOR-III. The gamma-rays are generated via laser Thomson scattering with 90 degree collisions between a 750-MeV electron beam and a Ti:Sa laser. The pulse width of the gamma-rays is calculated to be 5 ps (FWHM). The gamma-ray induced positron annihilation lifetime spectroscopy (GiPALS) is currently available for users. In addition to GiPALS, we develop gamma-ray induced age-momentum correlation (GiAMOC), which measures the lifetime and Doppler broadening of annihilation gamma-rays simultaneously. In this conference, we will present a generation method of the ultra-short pulsed gamma-rays and details of GiPALS and GiAMOC.
