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Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*
Japanese Journal of Applied Physics, 63(3), p.032005_1 - 032005_6, 2024/03
We introduce a novel gamma-ray imaging technique that uses detector response patterns. This method employs multiple shielding cubes randomly positioned in a three-dimensional configuration. Within the volume defined by these cubes, a unique gamma-ray flux pattern is formed based on the incidence direction of the gamma rays. This pattern can be measured using the responses of several scintillator cubes. By pre-measuring the detector response pattern and incidence direction of the gamma rays, the incidence direction can be estimated using an unfolding technique. Simulations were performed using a 
Cs point source. Our results show that a 10 MBq Cs source, located 3 m away from the imager, can be imaged with an angular resolution close to 10
. These findings suggest that our new method is comparable to existing gamma-ray imaging techniques. Potential applications of this imaging method include nuclear power plant decommissioning, nuclear medicine, security, and astronomy.
-FeSuzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*
Journal of Applied Physics, 135(7), p.075102_1 - 075102_7, 2024/02
Fracture of body centred cubic (bcc) metals and alloys below the ductile-to-brittle transition temperature is brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plasticdeformation; hence, brittle fracture is chosen over plastic deformation. Although this view is true from a macroscopic point of view, such brittle fracture is always accompanied by small-scale plastic deformation in the vicinity of the crack tip, i.e. crack tip plasticity. This short paper investigates the origin of this plasticity using atomistic modeling with a recently developed machine-learning interatomic potential of -Fe. The computational results identified the precursor of crack tip plasticity, i.e. the group of activated atoms dynamically nucleated by fast crack propagation.
Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke*; Sato, Tatsuhiko
Japanese Journal of Applied Physics, 62(10), p.106001_1 - 106001_6, 2023/10
Times Cited Count：2 Percentile：75.57(Physics, Applied)Optimization of semiconductor detector design requires theoretical analysis of the process of radiation conversion to carriers (excited electrons) in semiconductor materials. We, therefore, developed an electron track-structure code that can trace an incident electron trajectory down to a few eV and simulate many excited electron productions in semiconductors, named ETSART, and implemented it into PHITS. The accuracy of ETSART was validated by comparing calculated electron ranges in semiconductor materials with the corresponding data recommended in ICRU Report 37 and obtained from another simulation code. The average energy required to produce a single excited electron (epsilon value) is an important value that describes the characteristics of semiconductor detectors. Using ETSART, we computed the epsilon values in various semiconductors and found that the calculated epsilon values cannot be fitted well with a linear model of the band-gap energy. ETSART is expected to be useful for initial and mechanistic evaluations of electron-hole generation in undiscovered materials.
Ogawa, Hiroki; Asamori, Koichi; Negi, Tateyuki*; Ueda, Takumi*
Journal of Applied Geophysics, 213, p.105012_1 - 105012_17, 2023/06
Times Cited Count：0 Percentile：0.02(Geosciences, Multidisciplinary)A number of schemes for processing magnetotelluric (MT) data have been reported aiming at suppressing the strong effect of artificial electromagnetic noise, especially coherent noise that is correlated between electric and magnetic time series. Many of the recent denoising schemes are based on decomposing MT data into the responses of the natural signal and noise. Meanwhile, it is crucial to distinguish the natural signal from noise stably without depending on any empirical choice of parameter setting. In addition, improper subtraction of values from the separated signal can lead to the loss of useful values of the natural signal or missing noise-affected values, which may result in failure in deriving the true MT responses. We propose a novel data-processing method that applies frequency-domain independent component analysis (FDICA) to both the local MT data and the reference magnetic data. Among the separated signal, the proposed method can quantitatively distinguish the natural signal from the noise-affected components by calculating the ratio of cross-power spectrum with the reference data to the auto-power spectrum for each component. When determining which values to subtract from the separated signal, we introduce an evaluation index with respect to two characteristics of the MT response function: stationary in the time domain and smoothness in the frequency domain. We conduct the experiments both with MT time series severely contaminated by synthetic coherent noises and with MT field data interfered with DC (direct current) railways. Consequently, we confirm the superiority of the proposed method in the noise-suppression performance over the conventional methods of MT data processing.
/GaN interfaces with suppressed Ga-oxide interlayer via sputter deposition of SiOOnishi, Kentaro*; Kobayashi, Takuma*; Mizobata, Hidetoshi*; Nozaki, Mikito*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*
Japanese Journal of Applied Physics, 62(5), p.050903_1 - 050903_4, 2023/05
While the formation of an GaO
interlayer is key to achieving SiO/GaN interfaces with low defect density, it can affect the reliability and stability of metal-oxide-semiconductor (MOS) devices if the annealing conditions are not properly designed. In the present study, we aimed to minimize the growth of the GaO layer on the basis of the sputter deposition of SiO on GaN. Synchrotron radiation X-ray photoelectron spectrometry measurements confirmed the suppressed growth of the GaO layer compared with a SiO/GaN structure formed by plasma-enhanced chemical vapor deposition. Negligible GaO growth was also observed when subsequent oxygen annealing up to 600C was performed. A MOS device with negligible capacitance-voltage hysteresis, nearly ideal flat-band voltage, and low leakage current was demonstrated by performing oxygen and forming gas annealing at temperatures of 600C and 400C, respectively.
Maekawa, Sadamichi; Kikkawa, Takashi*; Chudo, Hiroyuki; Ieda, Junichi; Saito, Eiji
Journal of Applied Physics, 133(2), p.020902_1 - 020902_24, 2023/01
Times Cited Count：9 Percentile：96.84(Physics, Applied)
Np and 
Am gamma ray regionsFukuda, Tatsuo; Kobata, Masaaki; Shobu, Takahisa; Yoshii, Kenji; Kamiya, Junichiro; Iwamoto, Yosuke; Makino, Takahiro*; Yamazaki, Yuichi*; Oshima, Takeshi*; Shirai, Yasuhiro*; et al.
Journal of Applied Physics, 132(24), p.245102_1 - 245102_8, 2022/12
Times Cited Count：1 Percentile：17.38(Physics, Applied)Direct energy conversion has been investigated using Ni/SiC Schottky junctions with the irradiation of monochromatized synchrotron X-rays simulating the gamma rays of Np (30 keV) and Am (60 keV). From current-voltage measurements, electrical energies were obtained for both kinds of gamma rays. The energy conversion efficiencies were found to reach up to 
1.6%, which is comparable to those of a few other semiconducting systems reported thus far. This result shows a possibility of energy recovery from nuclear wastes using the present system, judging from the radiation tolerant nature of SiC. Also, we found different conversion efficiencies between the two samples. This could be understandable from hard X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements, suggesting the formation of Ni-Si compounds at the interface in the sample with a poor performance. Hence, such combined measurements are useful to provide information that cannot be obtained by electrical measurements alone.
-BaTiO solid solutionsYoneda, Yasuhiro; Kim, S.*; Mori, Shigeo*; Wada, Satoshi*
Japanese Journal of Applied Physics, 61(SN), p.SN1022_1 - SN1022_10, 2022/11
Times Cited Count：1 Percentile：17.38(Physics, Applied)Local structural analysis of the (1-
) BiFeO-BaTiO solid solution was performed by PDF analysis of the data obtained in the synchrotron radiation high-energy X-ray diffraction experiment. First, when XAFS experiments were performed and sample screening was performed, it was found that structural fluctuations were large in the BiFeO-rich composition. Therefore, PDF analysis of a sample with BiFeO-rich composition was performed. As a result, it was found that although the average structure is a cubic structure, the local structure can be reproduced with a rhombohedral crystal structure, and there is a displacement that breaks the symmetry of the rhombohedral structure in a composition with a large fluctuation.
Hirata, Yuho; Kai, Takeshi; Ogawa, Tatsuhiko; Matsuya, Yusuke; Sato, Tatsuhiko
Japanese Journal of Applied Physics, 61(10), p.106004_1 - 106004_6, 2022/10
Times Cited Count：5 Percentile：67.2(Physics, Applied)Some radiation effects such as pulse-height defects and soft errors can cause problems in silicon (Si) devices. Local energy deposition in microscopic scales is essential information to elucidate the mechanism of these radiation effects. We, therefore, developed an electron track-structure model, which can simulate local energy deposition down to nano-scales, dedicated to Si and implemented it into PHITS. Then, we verified the accuracy of our developed model by comparing the ranges and depth-dose distributions of electrons obtained from this study with the corresponding experimental values and other simulated results. As an application of the model, we calculated the mean energies required to create an electron-hole pair, the so-called epsilon value. We found that the threshold energy for generating secondary electrons reproducing the epsilon value is 2.75 eV, consistent with the corresponding data deduced from past theoretical and computational studies. Since the magnitudes of the radiation effects on Si devices largely depend on the epsilon value, the developed code is expected to contribute to precisely understanding the mechanisms of pulse-height defects and semiconductor soft errors.
Iwase, Akihiro*; Fukuda, Kengo*; Saito, Yuichi*; Okamoto, Yoshihiro; Semboshi, Satoshi*; Amekura, Hiroshi*; Matsui, Toshiyuki*
Journal of Applied Physics, 132(16), p.163902_1 - 163902_10, 2022/10
Times Cited Count：0 Percentile：0(Physics, Applied)Amorphous SiO samples were implanted with 380 keV Fe ions at room temperature. After implantation, some of the samples were irradiated with 16 MeV Au ions. magnetic properties were investigated using a SQUID magnetometer, and the morphology of the Fe-implanted SiO samples was examined using transmission electron microscopy and X-ray absorption spectroscopy (EXAFS and XANES), which showed that the size of Fe nanoparticles was increasing The size of Fe nanoparticles increased with increasing Fe implantation amount; some of the Fe nanoparticles consisted of Fe oxides, and the valence and structure of Fe atoms became closer to that of metallic -Fe with increasing Fe injection amount. The magnetization-field curve of the sample implanted with a small amount of Fe was reproduced by Langevin's equation, suggesting that the Fe nanoparticles behave in a superparamagnetic manner. In addition, when a large amount of Fe was implanted, the magnetization-magnetic field curve shows a ferromagnetic state. These magnetic property results are consistent with the X-ray absorption results. Subsequent 16 MeV Au irradiation crushed the Fe nanoparticles, resulting in a decrease in magnetization.
Yoshida, Masayuki*; Nishihata, Itsuki*; Matsuda, Tomoki*; Ito, Yusuke*; Sugita, Naohiko*; Shiro, Ayumi*; Shobu, Takahisa; Arakawa, Kazuto*; Hirose, Akio*; Sano, Tomokazu*
Journal of Applied Physics, 132(7), p.075101_1 - 075101_9, 2022/08
Times Cited Count：5 Percentile：67.2(Physics, Applied)/4H-SiC(11
0) interfacesNakanuma, Takato*; Iwakata, Yu*; Watanabe, Arisa*; Hosoi, Takuji*; Kobayashi, Takuma*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*
Japanese Journal of Applied Physics, 61(SC), p.SC1065_1 - SC1065_8, 2022/05
Times Cited Count：7 Percentile：77.62(Physics, Applied)Nitridation of SiO/4H-SiC(110) interfaces with post-oxidation annealing in an NO ambient (NO-POA) and its impact on the electrical properties were investigated. Sub-nm-resolution nitrogen depth profiling at the interfaces was conducted by using a scanning X-ray photoelectron spectroscopy microprobe. The results showed that nitrogen atoms were incorporated just at the interface and that interface nitridation proceeded much faster than at SiO/SiC(0001) interfaces, resulting in a 2.3 times higher nitrogen concentration. Electrical characterizations of metal-oxide-semiconductor capacitors were conducted through capacitance-voltage (
) measurements in the dark and under illumination with ultraviolet light to evaluate the electrical defects near the conduction and valence band edges and those causing hysteresis and shifting of the curves. While all of these defects were passivated with the progress of the interface nitridation, excessive nitridation resulted in degradation of the MOS capacitors. The optimal conditions for NO-POA are discussed on the basis of these experimental findings.
He cryostat and a closed-cycle He gas handling system installed in a SQUID magnetometer without continuous-cooling functionalityShimamura, Kazutoshi*; Wajima, Hiroki*; Makino, Hayato*; Abe, Satoshi*; Haga, Yoshinori; Sato, Yoshiaki*; Kawae, Tatsuya*; Yoshida, Yasuo*
Japanese Journal of Applied Physics, 61(5), p.056502_1 - 056502_7, 2022/05
Times Cited Count：1 Percentile：17.38(Physics, Applied)
structure observation of pyroelectric ceramics during power generation cycleKawasaki, Takuro; Fukuda, Tatsuo; Yamanaka, Satoru*; Sakamoto, Tomokazu*; Murayama, Ichiro*; Kato, Takanori*; Baba, Masaaki*; Hashimoto, Hideki*; Harjo, S.; Aizawa, Kazuya; et al.
Journal of Applied Physics, 131(13), p.134103_1 - 134103_7, 2022/04
Times Cited Count：1 Percentile：17.38(Physics, Applied)Sasada, Seiji*; Takahashi, Yoshihito*; Takeuchi, Keisuke*; Hiroi, Kosuke; Su, Y. H.; Shinohara, Takenao; Watanabe, Kenichi*; Uritani, Akira*
Japanese Journal of Applied Physics, 61(4), p.046004_1 - 046004_8, 2022/03
Times Cited Count：0 Percentile：0(Physics, Applied)Sasada, Seiji*; Hiroi, Kosuke; Osanai, Kenta*; Shinohara, Takenao; Watanabe, K.*; Uritani, Akira*
Japanese Journal of Applied Physics, 60(12), p.126003_1 - 126003_6, 2021/12
Times Cited Count：1 Percentile：7.86(Physics, Applied)
NaTiO in high-temperature phasesYoneda, Yasuhiro; Noguchi, Yuji*
Japanese Journal of Applied Physics, 60(SF), p.SFFA08_1 - SFFA08_10, 2021/11
Times Cited Count：4 Percentile：36.85(Physics, Applied)BiNaTiO (abbreviated as BNT) is a lead-free material but exhibits relatively large piezoelectric properties, a lot of researches have been conducted. We performed local structural analysis using high-quality BNT with a stoichiometrically correct composition, and found a chemical order structure of Bi/Na in locally. BNT undergoes a phase transition to a cubic phase at 400C. We estimated that a new disorder structure will appear in the high-temperature phase. In the high temperature phase, pair distribution function (PDF) analysis using synchrotron radiation high-energy X-rays was performed. As a result, we found that Bi shifts from 200C, and this shift becomes an order parameter for the phase transition.
Kurita, Keisuke; Sakai, Takuro; Suzui, Nobuo*; Yin, Y.-G.*; Sugita, Ryohei*; Kobayashi, Natsuko*; Tanoi, Keitaro*; Kawachi, Naoki*
Japanese Journal of Applied Physics, 60(11), p.116501_1 - 116501_4, 2021/11
Times Cited Count：1 Percentile：7.86(Physics, Applied)Radioisotope tracer imaging is useful for studying plant physiological phenomena. In this study, we developed an autoradiography system with phosphor powder (ZnS:Ag), "Live-autoradiography", for imaging radioisotope dynamics in a living plant. This system visualizes the element migration and accumulation in intact plants continuously under a light environment. An imaging test was performed on point sources of Cs, with a radioactivity of 10-100 kBq of being observed; this indicates satisfactory system linearity between the image intensity and the radioactivity of Cs. Moreover, dynamics imaging of Cs was performed on an intact soybean plant for four days. The serial images indicated Cs accumulation in the node, vein, and growing point of the plant. The developed system can be used for studying plant physiological phenomena and can be employed for quantitative measurement of radionuclides.
Nakamura, Jumpei*; Kawakita, Yukinobu; Shimomura, Koichiro*; Suemasu, Takashi*
Journal of Applied Physics, 130(19), p.195701_1 - 195701_7, 2021/11
Times Cited Count：1 Percentile：7.86(Physics, Applied)Maruyama, Ryuji; Yamazaki, Dai; Aoki, Hiroyuki; Akutsu, Kazuhiro*; Hanashima, Takayasu*; Miyata, Noboru*; Soyama, Kazuhiko; Bigault, T.*; Saerbeck, T.*; Courtois, P.*
Journal of Applied Physics, 130(8), p.083904_1 - 083904_10, 2021/08
Times Cited Count：3 Percentile：27.71(Physics, Applied)