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Journal Articles

Numerical interpretation of hydrogen thermal desorption spectra for iron with hydrogen-enhanced strain-induced vacancies

Ebihara, Kenichi; Sugiyama, Yuri*; Matsumoto, Ryosuke*; Takai, Kenichi*; Suzudo, Tomoaki

Metallurgical and Materials Transactions A, 52(1), p.257 - 269, 2021/01

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We simulated the thermal desorption spectra of a small-size iron specimen to which was applied during charging with hydrogen atoms using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy clusters $$V_9$$, which is composed of nine vacancies and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduced the experimental spectra except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of $$V_2$$ and $$V_3$$ is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.

Journal Articles

Negatively charged muonium and related centers in solids

Ito, Takashi; Higemoto, Wataru; Shimomura, Koichiro*

Journal of the Physical Society of Japan, 89(5), p.051007_1 - 051007_8, 2020/05

 Times Cited Count:1 Percentile:34.07(Physics, Multidisciplinary)

Journal Articles

Ice I$$_{rm c}$$ without stacking disorder by evacuating hydrogen from hydrogen hydrate

Komatsu, Kazuki*; Machida, Shinichi*; Noritake, Fumiya*; Hattori, Takanori; Sano, Asami; Yamane, Ryo*; Yamashita, Keishiro*; Kagi, Hiroyuki*

Nature Communications (Internet), 11(1), p.464_1 - 464_5, 2020/02

 Times Cited Count:5 Percentile:18.68(Multidisciplinary Sciences)

Water freezes below 0$$^{circ}$$C at ambient pressure ordinarily to ice I$$_{rm h}$$, with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice I$$_{rm c}$$ without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice I$$_{rm c}$$ without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C$$_{2}$$, which has a host framework isostructural with ice I$$_{rm c}$$. The stacking-disorder free ice I$$_{rm c}$$ is formed from C$$_{2}$$ via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations occurring in ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice I$$_{rm c}$$ shows remarkable thermal stability, until the phase transition to ice I$$_{rm h}$$ at 250 K, originating from the lack of dislocations. This discovery of ideal ice I$$_{rm c}$$ will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice I$$_{rm h}$$.

Journal Articles

Stacking fault energy analyses of additively manufactured stainless steel 316L and CrCoNi medium entropy alloy using in situ neutron diffraction

Woo, W.*; Jeong, J. S.*; Kim, D.-K.*; Lee, C. M.*; Choi, S.-H.*; Suh, J.-Y.*; Lee, S. Y.*; Harjo, S.; Kawasaki, Takuro

Scientific Reports (Internet), 10(1), p.1350_1 - 1350_15, 2020/01

 Times Cited Count:1 Percentile:41(Multidisciplinary Sciences)

Journal Articles

Ultrasonic inspection technique for weld part of mercury target vessel for spallation neutron source

Wakui, Takashi; Wakai, Eiichi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Takada, Hiroshi; Shintaku, Yohei*; Li, T.*; Kanomata, Kenichi*

Choompa Techno, 30(5), p.16 - 20, 2018/10

A mercury target vessel has been used for the spallation neutron source at J-PARC. It has a complicated multi-layered structure composed of a mercury target and a surrounding double-walled water shroud, which is assembled with thin plates (minimum thickness of 3 mm) by welding. Thus, welding inspection during the manufacturing process is important. We investigated the applicability of new ultrasonic inspections using specimens (thickness of 3 mm) with defects to improve the accuracy of welding inspection for the mercury target vessel. Immersion ultrasonic testing using a probe (frequency of 50 MHz) could detect a spherical defect with a diameter of 0.2 mm. The size was smaller than target value of 0.4 mm. The length of unwelded region estimated using the phased array ultrasonic testing corresponded with the actual length (0.8 - 1.5 mm).

Journal Articles

Prediction for plastic collapse stresses for pipes with inner and outer circumferential flaws

Hasegawa, Kunio; Li, Y.; Mares, V.*; Lacroix, V.*

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 5 Pages, 2018/07

Appendix C-5320 of ASME Code Section XI provides a formula of bending stress at the plastic collapse, where the formula is applicable for both inner and outer surface flaws. Authors considered the separated pipe mean radii at the flawed ligament and at the un-flawed ligament and formulas of plastic collapse stresses for each inner and outer flawed pipe were obtained. It is found that the collapse stress for inner flawed pipe is slightly higher than that calculated by Appendix C-5320 formula, and the collapse stress for outer flawed pipe is slightly lower than that by Appendix C-5320 formula. The collapse stresses derived from the three formulas are almost the same in most instances. For less common case where the flaw angle and depth are very large for thick wall pipes, the differences among the three collapse stresses become large.

Journal Articles

Irradiation induced reactivity in Monju zero power operation

Takano, Kazuya; Maruyama, Shuhei; Hazama, Taira; Usami, Shin

Proceedings of Reactor Physics Paving the Way Towards More Efficient Systems (PHYSOR 2018) (USB Flash Drive), p.1725 - 1735, 2018/04

Irradiation dependence of the core excess reactivity was investigated for the Monju system startup tests at zero-power carried out in 2010. The excess reactivity basically decreases with the $$beta$$ decay of $$^{241}$$Pu in zero-power operation. However, the excess reactivity little changed in the two month period of the startup tests, which suggests a positive reactivity insertion during the period. The investigated irradiation dependence shows that the positive reactivity increases with reactor operation and mostly saturates by the fission-dose attained during the Monju zero-power operation in a month ($$sim$$10$$^{17}$$ fissions/cm$$^{3}$$). The saturated positive reactivity is equivalent to approximately 47% of the initially accumulated self-irradiation damage recovery assuming the defects were recovered by the fission-fragment irradiation in the reactor operation.

Journal Articles

Introduction of subsurface proximity criteria in the world and stress intensity factors for transformed surface flaws

Hasegawa, Kunio; Li, Y.; Katsumata, Genshichiro*; Dulieu, P.*; Lacroix, V.*

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 6 Pages, 2017/07

Net-section stress at the ligament between component free surface and subsurface flaw increases when the ligament distance is short. It can be easily expected that stress intensity factors increase when the subsurface flaw locates near the free surface. To avoid catastrophic failures caused by ligament failure, fitness-for-service (FFS) codes provide flaw-to-surface proximity rules. The proximity rules are used to determine whether the flaws should be treated as subsurface flaws as-is, or transformed to surface flaws. The stress intensity factor for the transformed surface flaw increases furthermore. The increment of the stress intensity factor before and after transformation depends on the location of the subsurface flaw. Although the concept of the proximity rules are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws differ amongst FFS codes. Particularly, the criteria are different amongst the same organizations of ASME (American Society of Mechanical Engineers). The proximity criteria of the FFS codes in the world were introduced in this paper. In addition, the stress intensity factors based on the different criteria used in the ASME Codes are compared.

Journal Articles

High flux pinning efficiency by columnar defects dispersed in three directions in YBCO thin films

Sueyoshi, Tetsuro*; Nishimura, Takahiro*; Fujiyoshi, Takanori*; Mitsugi, Fumiaki*; Ikegami, Tomoaki*; Ishikawa, Norito

Superconductor Science and Technology, 29(10), p.105006_1 - 105006_7, 2016/10

 Times Cited Count:6 Percentile:57.99(Physics, Applied)

A systematic investigation of flux pinning by widely direction-dispersed columnar defects (CDs) in YBa$$_{2}$$Cu$$_{3}$$Oy thin films was carried out by using heavy-ion irradiation: a parallel configuration of CDs aligned along the $$c$$-axis, and two trimodal splay configurations composed of crossing CDs; relative to the $$c$$-axis, where the splay plane defined by the three irradiation angles is perpendicular (trimodal-A) or parallel (trimodal-B) to the transport current direction. The trimodal configurations show high pinning efficiency over a wide range of magnetic field orientations compared to the parallel one at low magnetic field. In particular, trimodal-B shows the higher critical current density of the two trimodal configurations.

Journal Articles

Study on modeling of thermal desorption spectra of hydrogen including variation of vacancy-type trap sites

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

"Suiso Zeika No Kihon Yoin To Tokusei Hyoka Kenkyukai Chukan Hokokukai" Shimposium Yokoshu (USB Flash Drive), p.30 - 35, 2016/09

no abstracts in English

Journal Articles

High speed inspection of the defect inside concrete by using laser technologies

Hasegawa, Noboru

Kagaku, 71(3), p.72 - 73, 2016/02

In Japan, the deterioration of the infrastructure built in the high economic growth period (1954-1979) becomes big social problem. We have developed the inspection method of the defect in the concrete by using the laser technologies. We have succeeded to demonstrate the high-speed inspection of a mock-defect in concrete by using the high repetition rate impact laser and laser vibrograph. The repetition rate of inspection was improved to be 25 Hz. We commented about this measurement technique.

Journal Articles

Proximity factor on transformation from subsurface to surface flaw

Hasegawa, Kunio*; Li, Y.; Serizawa, Ryosuke*; Kikuchi, Masanori*; Lacroix, V.*

Procedia Materials Science, 12, p.36 - 41, 2016/00

 Times Cited Count:0 Percentile:100

If subsurface flaws are detected that are close to component free surfaces, flaw-to-surface proximity rule is used to determine whether the flaws should be treated as subsurface flaws as is, or transformed to surface flaws. However, specific factors for the proximity rules on transforming subsurface to surface flaws differ among fitness-for-service codes. The objective of the paper is to reveal the proximity factor from the stress intensity factor interaction between the subsurface flaw and the free surface.

Journal Articles

Study on flaw-to-surface proximity rule for transforming subsurface flaws to surface flaws based on fatigue crack growth experiments

Hasegawa, Kunio; Li, Y.; Saito, Koichi*

Journal of Pressure Vessel Technology, 137(4), p.041101_1 - 041101_7, 2015/08

 Times Cited Count:3 Percentile:75.81(Engineering, Mechanical)

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a flaw-to-surface proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the concrete criteria of the re-characterizations are different among the FFS codes. Cyclic tensile experiment was conducted on a carbon steel flat plate with a subsurface flaw at ambient temperature. The objective of the paper is to compare the experiment and calculation of fatigue crack growth behavior for a subsurface flaw and the transformed surface flaw, and to describe the validity of the flaw-to-surface proximity rule defined by ASME Code Section XI, JSME S NA1 Code and other codes.

Journal Articles

Influence of discontinuous columnar defects on flux pinning properties in GdBCO coated conductors

Sueyoshi, Tetsuro*; Kotaki, Tetsuya*; Furuki, Yuichi*; Uraguchi, Yusei*; Kai, Takashi*; Fujiyoshi, Takanori*; Shimada, Yusuke*; Yasuda, Kazuhiro*; Ishikawa, Norito

IEEE Transactions on Applied Superconductivity, 25(3), p.6603004_1 - 6603004_4, 2015/06

 Times Cited Count:6 Percentile:56.82(Engineering, Electrical & Electronic)

To investigate the effect of discontinuity of 1-D pinning centers on the flux pinning in a wide range of magnetic field directions, discontinuous columnar defects (CDs) and continuous CDs were formed in GdBCO coated conductors using Xe-ion irradiations with 80 and 270 MeV, respectively. An overall shift upward in Jc, for the 80-MeV-irradiated sample compared to the 270-MeV-irradiated one, can be observed in every direction of magnetic field, which is more remarkable as temperature decreases. This implies a synergetic effect of the pinning interaction between the linearity and the discontinuity for the discontinuous CDs.

Journal Articles

Radiation hardness of n-type SiC Schottky barrier diodes irradiated with MeV He ion microbeam

Pastuovi$'c$, $v{Z}$*; Capan, I.*; Cohen, D.*; Forneris, J.*; Iwamoto, Naoya*; Oshima, Takeshi; Siegele, R.*; Hoshino, Norihiro*; Tsuchida, Hidekazu*

Nuclear Instruments and Methods in Physics Research B, 348, p.233 - 239, 2015/04

 Times Cited Count:6 Percentile:40.42(Instruments & Instrumentation)

Journal Articles

Swift heavy ion irradiation effects in nanocrystalline gold

Chimi, Yasuhiro; Iwase, Akihiro*; Ishikawa, Norito; Kobiyama, Mamoru*; Inami, Takashi*; Kambara, Tadashi*; Okuda, Shigeo*

Nuclear Instruments and Methods in Physics Research B, 245(1), p.171 - 175, 2006/04

 Times Cited Count:13 Percentile:30.08(Instruments & Instrumentation)

We have studied effects of irradiation with energetic particles on defect accumulation in nanocrystalline gold (nano-Au). The specimens of nano-Au foil (3-5 $$mu$$m thickness) with various grain sizes (23-156 nm) are prepared by the gas deposition method and subsequent thermal annealings. Irradiations of the specimens with 60-MeV $$^{12}$$C ions, 3.54-GeV $$^{136}$$Xe ions or 2.0-MeV electrons are performed at low temperature. The defect accumulation behavior is observed by measuring the electrical resistivity change during irradiation. Through an analysis of defect accumulation behavior, cross-sections for defect production, $$sigma$$$$_{d}$$, and annihilation, $$sigma$$$$_{r}$$, in nano-Au increase monotonically as the grain size decreases. These results are considered to be caused by the existence of a large volume fraction of the regions near grain boundaries in nano-Au where the threshold energy for atomic displacements, E$$_{d}$$, becomes lower than in polycrystalline gold. The possibility of electronic excitation effects in nano-Au is also discussed.

Journal Articles

Defect layer in SiO$$_2$$-SiC interface proved by a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Miyashita, Atsumi; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physica B; Condensed Matter, 376-377, p.354 - 357, 2006/04

 Times Cited Count:2 Percentile:86.39(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Identification of divacancies in 4H-SiC

Son, N. T.*; Umeda, Takahide*; Isoya, Junichi*; Gali, A.*; Bockstedte, M.*; Magnusson, B.*; Ellison, A.*; Morishita, Norio; Oshima, Takeshi; Ito, Hisayoshi; et al.

Physica B; Condensed Matter, 376-377, p.334 - 337, 2006/04

 Times Cited Count:3 Percentile:80.82(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Relationship between defects induced by irradiation and reduction of hole concentration in Al-doped 4H-SiC

Matsuura, Hideharu*; Kagamihara, So*; Ito, Yuji*; Oshima, Takeshi; Ito, Hisayoshi

Physica B; Condensed Matter, 376-377, p.342 - 345, 2006/04

 Times Cited Count:8 Percentile:59.17(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Effects of ion irradiation on hydriding rate of Mm based hydrogen storage alloy

Abe, Hiroshi; Morimoto, Ryo*; Sato, Fumiatsu*; Azuma, Yorito*; Uchida, Hirohisa*

Journal of Alloys and Compounds, 408-412, p.348 - 350, 2006/02

 Times Cited Count:10 Percentile:41.88(Chemistry, Physical)

Mm(misch metal) based hydrogen storage alloys are applied to the negative electrode of the Ni-H battery and other hydrogen storage systems. In such pratical applications, various surface processes of hydrogen molecules often become rate contolling. Therefore, the improvement of the alloy surface is of great importance to promote the initial activation and hydriding rate. We have reported that the alkaline pretreatment of an alloy surfece exhibits a high durability against CO attack. Since low energy ion irradiation is quite useful for surface modification of materials, the hydriding proerties of a Mm is expected on electrochemical hydriding rate of the alloy. As a result, the ion irradiation Mm was found to induce a higher hydriding rate than that of the un-irradiation one.

259 (Records 1-20 displayed on this page)