Atsushi YABUUCHI - Academia.edu (original) (raw)
Papers by Atsushi YABUUCHI
金属箔からの低エネルギーΜプラス粒子の測定[J‐PARC:2015A0324]
KEK Progress Report, 2016
JJAP Conference Proceedings
A desktop positron beam apparatus combined with a β +-γ coincidence positron annihilation lifetim... more A desktop positron beam apparatus combined with a β +-γ coincidence positron annihilation lifetime spectrometer was used for investigating thermal equilibrium vacancies in a TiAl intermetallic compound which is expected to find uses as a lightweight, heat-resistant structural material. The vacancy formation energy of the TiAl was derived from high-temperature in-situ measurements of positron lifetimes, and its value is in good agreement with a previously-reported value measured using a sophisticated internal positron source method. The measurement method used in this study makes it possible to investigate the vacancy formation energies in any material at high temperatures easily, even in unweldable ceramics, semiconductors, and brittle intermetallics for which conventional internal positron source methods cannot be applied.
Investigation of defect states in light-irradiated single-crystal ZnO by low-temperature positron annihilation lifetime spectroscopy
Japanese Journal of Applied Physics
Positron annihilation lifetime spectroscopy of single crystalline ZnO during light illumination h... more Positron annihilation lifetime spectroscopy of single crystalline ZnO during light illumination has been performed in conjunction with electron spin resonance (ESR) to investigate defects related to persistent photoconductivity. The intensity of the ESR signal changes depending on the light wavelengths and the apparent positron lifetime during red-light illumination is approximately 6 ps lower on average than that during blue-light illumination. The results suggest that the excitation of V O during blue-light illumination increases positively ionized V O, while the relaxation of V O during red-light illumination decreases positively ionized V O, leading to a decrease in the apparent positron lifetime.
Journal of Physics: Conference Series, 2014
Molecular-beam-epitaxy-grown Ga 1−x Gd x N films were investigated by Xray diffraction and slow p... more Molecular-beam-epitaxy-grown Ga 1−x Gd x N films were investigated by Xray diffraction and slow positron beams. From the positron lifetime results, N-vacancyrelated defects may be expected in the Ga 0.9 Gd 0.1 N film grown under Ga-rich conditions which exhibits a lattice expansion in the c-axis direction. In contrast, Ga vacancies more than 10 19 cm −3 were detected in the Ga 0.9 Gd 0.1 N film grown under N-rich conditions which does not exhibit the lattice expansion, implying that the highly-concentrated Ga vacancies contribute to a relaxation of the lattice distortion caused by incorporating oversized Gd atoms.
JJAP Conference Proceedings
We have developed a positron moderator annealing system with a handmade electron gun which allows... more We have developed a positron moderator annealing system with a handmade electron gun which allows the pre-assembled moderator temperature to be monitored directly during heating. The moderator, composed of strips of tungsten arranged in a regular lattice, was heated by bombarding electrons emitted from a hot tungsten filament. Moderator annealing was successfully achieved up to a temperature of 2600 • C in the central region of the moderator with a thermionic power of about 1200 W. Positron annihilation lifetime measurements of as-received and annealed tungsten foils were performed using a pulsed slow positron beam. As a result, it was confirmed that residual defects contained in the as-received tungsten foil were eliminated by conducting the annealing process.
Characterization of Ion-Beam-Synthesized β-FeSi 2 Films Using a Slow Positron Beam
The Japan Society of Applied Physics, 2018
Short positron lifetime at vacancies observed in electron-irradiated tungsten: Experiments and first-principles calculations
Journal of Nuclear Materials, 2020
Abstract A positron lifetime component of ∼ 170 ps has been reported for irradiated tungsten (W)... more Abstract A positron lifetime component of ∼ 170 ps has been reported for irradiated tungsten (W) in some studies. This value is considerably shorter than that calculated for isolated monovacancies ( ∼ 200 ps). In this study, positron annihilation lifetime spectroscopy was used to investigate the recovery behavior of the defects with a short positron lifetime of ∼ 170 ps in electron-irradiated W. The binding energies and positron lifetimes of vacancy-impurity complexes decorated with impurity atoms were calculated. A positron lifetime of 169 ps, which was similar to the experimentally observed lifetime of 171 ± 1 ps, was calculated for defect complexes comprising a monovacancy decorated with two hydrogen atoms (V-2H complexes). In addition, a value of 1.42 eV was calculated for the dissociation energy of a hydrogen atom from the V-H and V-2H complexes, and the defects with a positron lifetime of ∼ 170 ps were experimentally observed to migrate at 623 K. These were consistent with previously reported dissociation energy and desorption temperature of deuterium from vacancies in W studied by thermal desorption spectroscopy. These results suggested that the vacancies observed in the electron-irradiated W were hydrogen-decorated V-nH complexes.
Journal of Nuclear Materials, 2020
Irradiation damage and its evolution in noble gas ion-irradiated tungsten have not been investiga... more Irradiation damage and its evolution in noble gas ion-irradiated tungsten have not been investigated in detail other than in the case of helium ion irradiation. In this study, irradiation-induced vacancy-type defects in helium ion-and neon ion-irradiated tungsten were investigated by using a slow positron beam, and their annealing behavior in the temperature range of 20 + C-900 + C was compared by characterizing the Doppler broadening of positron annihilation radiation spectra. In helium ion-irradiated tungsten, slight aggregation of irradiation-induced vacancy-type defects was observed upon annealing, but eventually, a large portion of the vacancy clusters was eliminated after annealing at 900 + C. In contrast, in neon ion-irradiated tungsten, irradiation-induced vacancy-type defects were observed to aggregate significantly at 300 + C and 600 + C. In addition, the large vacancy clusters formed by the aggregation survived even after annealing at 900 + C.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019
Reactor (KUR) were measured during reactor operation and solenoid-coil excitation. During KUR ope... more Reactor (KUR) were measured during reactor operation and solenoid-coil excitation. During KUR operation at 5 MW, the temperature of the top of the beamline reached 300°C. This temperature which is close to the melting point (321°C) of Cd was used to enhance positron generation. On the other hand, the temperature of the flange supporting the beamline was approximately 50°C and it was sufficiently low in terms of the strength of the beamline. The temperature of the top of the beamline was successfully reduced to 240°C by introducing a He gas flow around the vacuum duct of the beamline. Beamline temperatures calculated using a finite element method were in agreement with measured temperatures. Such calculation is useful for future experiments with longer or irregular KUR operation.
Physics Procedia, 2012
Fe48-at.%Al alloy were implanted with 50 keV H + ions to the fluence of 3× 10 16 and 1× 10 18 /cm... more Fe48-at.%Al alloy were implanted with 50 keV H + ions to the fluence of 3× 10 16 and 1× 10 18 /cm 2 at room temperature. Positron annihilation Doppler broadening and lifetime measurements for these alloys have been carried out using slow positron beam apparatus with an energy range of 0.2 to 30.2 keV. The positron annihilation S-parameter decreased by H + ion irradiation. Also the positron lifetimes for hydrogen deposited region in the alloy decreased by the irradiation. These results show that implanted H atoms were trapped by vacancy type defects.
Journal of Nuclear Materials, 2012
To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L ... more To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L stainless steels, vacancy recovery processes were investigated by means of positron annihilation spectroscopy. Although vacancies in additive-free 316L stainless steels were mobile at 300°C, which is a typical nuclear reactor operating temperature, vacancies in oversized elements doped 316L were stable up to 300-350°C. This result indicates that oversized elements stabilize vacancies in stainless steels. Stability of vacancies inhibits the radiation-induced grain boundary segregation and may also lead to suppression of high-temperature water stress corrosion cracking that is observed in nuclear materials.
Proceedings of the 14th International Workshop on Spallation Materials Technology
For validation of the number of displacements per atom (DPA) of tungsten, we measured the defect-... more For validation of the number of displacements per atom (DPA) of tungsten, we measured the defect-induced electrical resistivity change of the wire sample of tungsten related to the displacement cross section under irradiation with 389-MeV protons at 10 K. The Gifford-McMahon (GM) cryocooler cooled the sample by means of a conduction coolant via the aluminum plate and the oxygen-free high-conductivity copper (OFHC) block. After irradiation with 1.36 × 10 19 protons/m 2 , the damage rate of the wire sample was 4.35 × 10 −30 Ωm 3 /proton. In comparison with experimental data under 1.1 and 1.9 GeV proton irradiation, we found that damage rate of tungsten increases with proton energy due to increase the number of secondary particles produced by nuclear reactions.
Change of free volume in hydrogenated DLC film by the irradiation of soft X-rays
The Japan Society of Applied Physics, Jan 26, 2021
Evaluation of nanostructures and hydrogen effects in DLC films by slow positron beams
The Japan Society of Applied Physics, Jul 9, 2020
25aSA-4 Direct detection of spin-Hall effect using spin-polarized positron annihilation
Meeting Abstracts of the Physical Society of Japan, 2012
Recovery behavior of irradiation-induced vacancies in dilute impurity doped stainless steels
Recovery behavior under tensile stress of 2MeV electron beam irradiation defects in austenitic stainless steels
Positron microscopy study of vacancies close to SCC crack tips in stainless steels
Lattice defects distribution measurements around SCC cracks in Type 304 stainless steels
9pAE-4 J-PARC MLFにおける超低速ミュオンビームラインのチューニング(9pAE X線・粒子線(ミュオン),領域10(構造物性(誘電体,格子欠陥,X線・粒子線,フォノン)))
Meeting Abstracts of the Physical Society of Japan (Nihon Butsuri Gakkai koen gaiyoshu), 2014
金属箔からの低エネルギーΜプラス粒子の測定[J‐PARC:2015A0324]
KEK Progress Report, 2016
JJAP Conference Proceedings
A desktop positron beam apparatus combined with a β +-γ coincidence positron annihilation lifetim... more A desktop positron beam apparatus combined with a β +-γ coincidence positron annihilation lifetime spectrometer was used for investigating thermal equilibrium vacancies in a TiAl intermetallic compound which is expected to find uses as a lightweight, heat-resistant structural material. The vacancy formation energy of the TiAl was derived from high-temperature in-situ measurements of positron lifetimes, and its value is in good agreement with a previously-reported value measured using a sophisticated internal positron source method. The measurement method used in this study makes it possible to investigate the vacancy formation energies in any material at high temperatures easily, even in unweldable ceramics, semiconductors, and brittle intermetallics for which conventional internal positron source methods cannot be applied.
Investigation of defect states in light-irradiated single-crystal ZnO by low-temperature positron annihilation lifetime spectroscopy
Japanese Journal of Applied Physics
Positron annihilation lifetime spectroscopy of single crystalline ZnO during light illumination h... more Positron annihilation lifetime spectroscopy of single crystalline ZnO during light illumination has been performed in conjunction with electron spin resonance (ESR) to investigate defects related to persistent photoconductivity. The intensity of the ESR signal changes depending on the light wavelengths and the apparent positron lifetime during red-light illumination is approximately 6 ps lower on average than that during blue-light illumination. The results suggest that the excitation of V O during blue-light illumination increases positively ionized V O, while the relaxation of V O during red-light illumination decreases positively ionized V O, leading to a decrease in the apparent positron lifetime.
Journal of Physics: Conference Series, 2014
Molecular-beam-epitaxy-grown Ga 1−x Gd x N films were investigated by Xray diffraction and slow p... more Molecular-beam-epitaxy-grown Ga 1−x Gd x N films were investigated by Xray diffraction and slow positron beams. From the positron lifetime results, N-vacancyrelated defects may be expected in the Ga 0.9 Gd 0.1 N film grown under Ga-rich conditions which exhibits a lattice expansion in the c-axis direction. In contrast, Ga vacancies more than 10 19 cm −3 were detected in the Ga 0.9 Gd 0.1 N film grown under N-rich conditions which does not exhibit the lattice expansion, implying that the highly-concentrated Ga vacancies contribute to a relaxation of the lattice distortion caused by incorporating oversized Gd atoms.
JJAP Conference Proceedings
We have developed a positron moderator annealing system with a handmade electron gun which allows... more We have developed a positron moderator annealing system with a handmade electron gun which allows the pre-assembled moderator temperature to be monitored directly during heating. The moderator, composed of strips of tungsten arranged in a regular lattice, was heated by bombarding electrons emitted from a hot tungsten filament. Moderator annealing was successfully achieved up to a temperature of 2600 • C in the central region of the moderator with a thermionic power of about 1200 W. Positron annihilation lifetime measurements of as-received and annealed tungsten foils were performed using a pulsed slow positron beam. As a result, it was confirmed that residual defects contained in the as-received tungsten foil were eliminated by conducting the annealing process.
Characterization of Ion-Beam-Synthesized β-FeSi 2 Films Using a Slow Positron Beam
The Japan Society of Applied Physics, 2018
Short positron lifetime at vacancies observed in electron-irradiated tungsten: Experiments and first-principles calculations
Journal of Nuclear Materials, 2020
Abstract A positron lifetime component of ∼ 170 ps has been reported for irradiated tungsten (W)... more Abstract A positron lifetime component of ∼ 170 ps has been reported for irradiated tungsten (W) in some studies. This value is considerably shorter than that calculated for isolated monovacancies ( ∼ 200 ps). In this study, positron annihilation lifetime spectroscopy was used to investigate the recovery behavior of the defects with a short positron lifetime of ∼ 170 ps in electron-irradiated W. The binding energies and positron lifetimes of vacancy-impurity complexes decorated with impurity atoms were calculated. A positron lifetime of 169 ps, which was similar to the experimentally observed lifetime of 171 ± 1 ps, was calculated for defect complexes comprising a monovacancy decorated with two hydrogen atoms (V-2H complexes). In addition, a value of 1.42 eV was calculated for the dissociation energy of a hydrogen atom from the V-H and V-2H complexes, and the defects with a positron lifetime of ∼ 170 ps were experimentally observed to migrate at 623 K. These were consistent with previously reported dissociation energy and desorption temperature of deuterium from vacancies in W studied by thermal desorption spectroscopy. These results suggested that the vacancies observed in the electron-irradiated W were hydrogen-decorated V-nH complexes.
Journal of Nuclear Materials, 2020
Irradiation damage and its evolution in noble gas ion-irradiated tungsten have not been investiga... more Irradiation damage and its evolution in noble gas ion-irradiated tungsten have not been investigated in detail other than in the case of helium ion irradiation. In this study, irradiation-induced vacancy-type defects in helium ion-and neon ion-irradiated tungsten were investigated by using a slow positron beam, and their annealing behavior in the temperature range of 20 + C-900 + C was compared by characterizing the Doppler broadening of positron annihilation radiation spectra. In helium ion-irradiated tungsten, slight aggregation of irradiation-induced vacancy-type defects was observed upon annealing, but eventually, a large portion of the vacancy clusters was eliminated after annealing at 900 + C. In contrast, in neon ion-irradiated tungsten, irradiation-induced vacancy-type defects were observed to aggregate significantly at 300 + C and 600 + C. In addition, the large vacancy clusters formed by the aggregation survived even after annealing at 900 + C.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2019
Reactor (KUR) were measured during reactor operation and solenoid-coil excitation. During KUR ope... more Reactor (KUR) were measured during reactor operation and solenoid-coil excitation. During KUR operation at 5 MW, the temperature of the top of the beamline reached 300°C. This temperature which is close to the melting point (321°C) of Cd was used to enhance positron generation. On the other hand, the temperature of the flange supporting the beamline was approximately 50°C and it was sufficiently low in terms of the strength of the beamline. The temperature of the top of the beamline was successfully reduced to 240°C by introducing a He gas flow around the vacuum duct of the beamline. Beamline temperatures calculated using a finite element method were in agreement with measured temperatures. Such calculation is useful for future experiments with longer or irregular KUR operation.
Physics Procedia, 2012
Fe48-at.%Al alloy were implanted with 50 keV H + ions to the fluence of 3× 10 16 and 1× 10 18 /cm... more Fe48-at.%Al alloy were implanted with 50 keV H + ions to the fluence of 3× 10 16 and 1× 10 18 /cm 2 at room temperature. Positron annihilation Doppler broadening and lifetime measurements for these alloys have been carried out using slow positron beam apparatus with an energy range of 0.2 to 30.2 keV. The positron annihilation S-parameter decreased by H + ion irradiation. Also the positron lifetimes for hydrogen deposited region in the alloy decreased by the irradiation. These results show that implanted H atoms were trapped by vacancy type defects.
Journal of Nuclear Materials, 2012
To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L ... more To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L stainless steels, vacancy recovery processes were investigated by means of positron annihilation spectroscopy. Although vacancies in additive-free 316L stainless steels were mobile at 300°C, which is a typical nuclear reactor operating temperature, vacancies in oversized elements doped 316L were stable up to 300-350°C. This result indicates that oversized elements stabilize vacancies in stainless steels. Stability of vacancies inhibits the radiation-induced grain boundary segregation and may also lead to suppression of high-temperature water stress corrosion cracking that is observed in nuclear materials.
Proceedings of the 14th International Workshop on Spallation Materials Technology
For validation of the number of displacements per atom (DPA) of tungsten, we measured the defect-... more For validation of the number of displacements per atom (DPA) of tungsten, we measured the defect-induced electrical resistivity change of the wire sample of tungsten related to the displacement cross section under irradiation with 389-MeV protons at 10 K. The Gifford-McMahon (GM) cryocooler cooled the sample by means of a conduction coolant via the aluminum plate and the oxygen-free high-conductivity copper (OFHC) block. After irradiation with 1.36 × 10 19 protons/m 2 , the damage rate of the wire sample was 4.35 × 10 −30 Ωm 3 /proton. In comparison with experimental data under 1.1 and 1.9 GeV proton irradiation, we found that damage rate of tungsten increases with proton energy due to increase the number of secondary particles produced by nuclear reactions.
Change of free volume in hydrogenated DLC film by the irradiation of soft X-rays
The Japan Society of Applied Physics, Jan 26, 2021
Evaluation of nanostructures and hydrogen effects in DLC films by slow positron beams
The Japan Society of Applied Physics, Jul 9, 2020
25aSA-4 Direct detection of spin-Hall effect using spin-polarized positron annihilation
Meeting Abstracts of the Physical Society of Japan, 2012
Recovery behavior of irradiation-induced vacancies in dilute impurity doped stainless steels
Recovery behavior under tensile stress of 2MeV electron beam irradiation defects in austenitic stainless steels
Positron microscopy study of vacancies close to SCC crack tips in stainless steels
Lattice defects distribution measurements around SCC cracks in Type 304 stainless steels
9pAE-4 J-PARC MLFにおける超低速ミュオンビームラインのチューニング(9pAE X線・粒子線(ミュオン),領域10(構造物性(誘電体,格子欠陥,X線・粒子線,フォノン)))
Meeting Abstracts of the Physical Society of Japan (Nihon Butsuri Gakkai koen gaiyoshu), 2014