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Ding, H.*; Ito, Keita*; Endo, Yasushi*; Takanashi, Koki; Seki, Takeshi*
Journal of Physics D; Applied Physics, 57(38), p.385002_1 - 385002_10, 2024/09
gamma-ray imager using detector response patternsKitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*
Japanese Journal of Applied Physics, 63(7), p.076502_1 - 076502_8, 2024/07
We constructed a gamma-ray imager that estimates the distribution of gamma-ray sources based on the response patterns of multiple gamma-ray detectors randomly positioned in three-dimensional space. The Coded Cube Camera for Gamma-ray (C3G), comprising eight GAGG (Ce) scintillator and eighteen lead cubes is housed in a cubical casing with an 86 mm edge length and weighs approximately 600 g. Results of the 4 imaging experiment confirmed the feasibility of imaging a 10 MBq 
Cs source located 3 m away with an angular uncertainty of 5
within a 10 min measurement. C3G operates with only eight channels, instead of the hundreds needed by a typical imager, offering a simplified circuit and reconstruction algorithm, thereby achieving a cost-effective and reliable system. With its compact and lightweight design, 4 field of view, and high angular uncertainty, this technology is expected to find extensive applications in astronomy, medicine, nuclear security, and decommissioning projects.
Zhang, Z.*; Hattori, Takanori; Song, R.*; Yu, D.*; Mole, R.*; Chen, J.*; He, L.*; Zhang, Z.*; Li, B.*
Journal of Applied Physics, 136(3), p.035105_1 - 035105_8, 2024/07
Solid-state refrigeration using barocaloric materials is environmentally friendly and highly efficient, making it a subject of global interest over the past decade. Here, we report giant barocaloric effects in sodium hexafluorophosphate (NaPF
) and sodium hexafluoroarsenate (NaAsF) that both undergo a cubic-to-rhombohedral phase transition near room temperature. We have determined that the low-temperature phase structure of NaPF is a rhombohedral structure with space group R
and NaAsF, i.e., F
, E
, and A
. The phase transition temperature varies with pressure at a rate of dT
/dP = 250 and 310 K/GPa for NaPF and NaAsF. The pressure-induced entropy changes of NaPF and NaAsF are determined to be around 45.2 and 35.6J kg
K, respectively. The saturation driving pressure is about 40 MPa. The pressure-dependent neutron powder diffraction suggests that the barocaloric effects are related to the pressure-induced cubic-to-rhombohedral phase transitions.
Kubota, Masato; Kato, Seiichi*
Journal of Applied Physics, 136(2), p.025102_1 - 025102_5, 2024/07
Watanabe, Kenichi*; Oshima, Yuya*; Shigyo, Nobuhiro*; Hirata, Yuho
Japanese Journal of Applied Physics, 63(5), p.056001_1 - 056001_5, 2024/05
Lithium-containing scintillators are used for neutron detection; Li-containing scintillators detect tritons and alpha rays produced by neutrons. Since these particles deposit higher energy than gamma rays, Li-containing scintillators can separate gamma rays and neutrons. However, the luminescence efficiency of scintillator decreases for ion beams due to a phenomenon called the quenching effect. Evaluation of the quenching effect is necessary to accurately separate neutrons and gamma rays. The Birks equation is used to predict the scintillation efficiency change due to the quenching effect, but it is necessary to determine the quenching coefficient in the Birks equation. In this study, we used PHITS to calculate the luminescence of Li-containing scintillators considering the quenching effect based on Birks' equation with the quenching coefficient as a free parameter. Then, by comparing the simulated results with the experimentally obtained luminescence, the extinction coefficients of Li glass, Ce:LiCaAlF
, and Eu:LiCaAlF scintillators were determined.
Omer, M.; Shizuma, Toshiyuki*; Hajima, Ryoichi*; Koizumi, Mitsuo
Journal of Applied Physics, 135(18), p.184903_1 - 184903_10, 2024/05
-Ga
O
(001)Tsai, Y. H.*; Kobata, Masaaki; Fukuda, Tatsuo; Tanida, Hajime; Kobayashi, Toru; Yamashita, Yoshiyuki*
Applied Physics Letters, 124(11), p.112105_1 - 112105_5, 2024/03
Times Cited Count：0 Percentile：0.00Shamoto, Shinichi; Akatsu, Mitsuhiro*; Chang, L.-J.*; Nemoto, Yuichi*; Ieda, Junichi
Applied Physics Letters, 124(11), p.112402_1 - 112402_5, 2024/03
Times Cited Count：0 Percentile：0.00The magnon excitation by ultrasound injection in Y
Fe
O
is studied by inelastic neutron scattering. Both longitudinal and transverse ultrasound injections enhanced the inelastic neutron scattering intensity.
-MgAgSbLi, J.*; Li, X.*; Zhang, Y.*; Zhu, J.*; Zhao, E.*; Kofu, Maiko; Nakajima, Kenji; Avdeev, M.*; Liu, P.-F.*; Sui, J.*; et al.
Applied Physics Reviews (Internet), 11(1), p.011406_1 - 011406_8, 2024/03
Times Cited Count：0 Percentile：0.00(Physics, Applied)Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*
Japanese Journal of Applied Physics, 63(3), p.032005_1 - 032005_6, 2024/03
Times Cited Count：0 Percentile：0.00(Physics, Applied)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
Times Cited Count：0 Percentile：0.00Fracture 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.
NaTiO?BaTiO solid solutionsYoneda, Yasuhiro; Kobayashi, Toru; Tsuji, Takuya; Matsumura, Daiju; Saito, Yuji; Noguchi, Yuji*
Japanese Journal of Applied Physics, 62(SM), p.SM1006_1 - SM1006_8, 2023/11
In niobium-based perovskite oxides(
NbO), the alkali metal occupying the site is considered to be highly ionic, and therefore, changes in ion size are generally thought to control the phase transition. Since the change in ion size alters the chemical bonding state, we considered it necessary to understand the electronic structure in conjunction with the structure. Therefore, we analyzed the local structure of Nb-based perovskite oxide ferroelectrics NaNbO, KNbO, and AgNbO and compared it with the electronic structure of oxygen using spectroscopic techniques to reveal the chemical bonding state, and observed the electronic structure as varied as the local structure.
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：66.71(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.
Yamazaki, Takumi*; Seki, Takeshi*; Kubota, Takahide*; Takanashi, Koki
Applied Physics Express, 16(8), p.083003_1 - 083003_4, 2023/08
Kawabori, Tatsuru*; Watanabe, Masashi; Imai, Yoshiyuki; Ueta, Shohei; Yan, X.; Mizoshiri, Mizue*
Applied Physics A, 129(7), p.498_1 - 498_9, 2023/07
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)We investigated a potential of femtosecond laser sintering of silicon carbide (SiC) using the nanoparticles in air. A SiC nanoparticle ink including polyvinylpyrrolidone and ethylene glycol exhibited intense absorption by SiC nanoparticles at the wavelength of 780 nm. The whole of the sintered film patterns from the surface to the bottom underwent significant oxidation at a scanning speed of 1 mm/s, suggesting that the excessive energy irradiation generated silicon oxides. In contrast, the patterns fabricated by laser scanning at a raster pitch of 30 
m at which a sintered area was observed at a scanning speed of 5 mm/s, exhibited no significant difference in oxidation of the raw SiC nanoparticles except for the surfaces from 1.72 m. These results indicate that the irradiation of femtosecond laser pulses generated the sintered SiC patterns without additional atmospheric oxidation of the raw materials because of its low heat accumulation. In additions, the dispersant of polyvinylpyrrolidone and ethylene glycol did not affect the sintering by an X-ray photoelectron spectroscopy. This vacuum-free direct printing technique has the potential for additive manufacturing.
Horibe, Sohei*; Shimizu, Hiroki*; Hoshi, Kojiro*; Makiuchi, Takahiko*; Hioki, Tomosato*; Saito, Eiji
Applied Physics Express, 16(7), p.073001_1 - 073001_4, 2023/07
Times Cited Count：0 Percentile：0.00(Physics, Applied)Sakakibara, Ryotaro*; Bao, J.*; Yuhara, Keisuke*; Matsuda, Keita*; Terasawa, Tomoo; Kusunoki, Michiko*; Norimatsu, Wataru*
Applied Physics Letters, 123(3), p.031603_1 - 031603_4, 2023/07
Times Cited Count：1 Percentile：44.21(Physics, Applied)We here report a step unbunching phenomenon, which is the inverse of the phenomenon of step bunching. When a 4H-SiC (0001) surface is annealed at a high temperature, step bunching arises due to the different velocities of the step motion in adjacent steps, resulting in steps with a height of more than several nanometers. We found that the bunched steps, thus, obtained by hydrogen etching in an Ar/H atmosphere were "unbunched" into lower height steps when annealed subsequently at lower temperatures. This unbunching phenomenon can be well explained by the consequence of the competition between energetics and kinetics. Our findings provide another approach for the surface smoothing of SiC by hydrogen etching and may give significant insight into the application of SiC power devices and two-dimensional materials growth techniques in general.
neutron diffraction study on the deformation behavior of the plastic inorganic semiconductor AgSWang, Y.*; Gong, W.; Kawasaki, Takuro; Harjo, S.; Zhang, K.*; Zhang, Z. D.*; Li, B.*
Applied Physics Letters, 123(1), p.011903_1 - 011903_6, 2023/07
Times Cited Count：1 Percentile：44.21(Physics, Applied)Yamanoi, Kazuto*; Sakakibara, Yuri*; Fujimoto, Junji*; Matsuo, Mamoru; Nozaki, Yukio*
Applied Physics Express, 16(6), p.063004_1 - 063004_6, 2023/06
Times Cited Count：0 Percentile：0.00(Physics, Applied)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.
