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Journal Articles

Comparison of heavy-ion transport simulations; Collision integral with pions and $$Delta$$ resonances in a box

Ono, Akira*; Xu, J.*; Colonna, M.*; Danielewicz, P.*; Ko, C. M.*; Tsang, M. B.*; Wang, Y,-J.*; Wolter, H.*; Zhang, Y.-X.*; Chen, L.-W.*; et al.

Physical Review C, 100(4), p.044617_1 - 044617_35, 2019/10

 Times Cited Count:4 Percentile:13.58(Physics, Nuclear)

International comparison of heavy-ion induced reaction models were discussed in the international conference "Transport2017" held in April 2017. Owing to their importance for safety assessment of heavy-ion accelerators and dosimetry of astronauts, various models to simulate heavy-ion induced reaction models are developed. This study is intended to clarify the difference among them to pinpoint their problems. In the comparison study, 320 protons and neutrons were packed in a 20-fm-large cube to calculate the number and energies of collisions during the time evolution. The author contributed to this study by running calculation using JQMD (JAERI Quantum Molecular Dynamics). This study showed that time step in the calculation is one of the biggest causes of the discrepancies. For example, the calculation by JQMD comprises 1-fm/c time steps, each of which is composed of transport, scattering and decay phases. Therefore a sequence of scattering, and decay followed by another scattering in 1 fm/c cannot be considered. Moreover, in JQMD particles are labeled by sequential numbers and scattering reactions are simulated by the order. Therefore scattering between low ID numbers, that between high ID numbers and that between the first (low ID) pair is overlooked in JQMD. Above indications obtained in this study must be kept in our mind for future JQMD upgrades.

Journal Articles

Proton shell evolution below $$^{132}$$Sn; First measurement of low-lying $$beta$$-emitting isomers in $$^{123,125}$$Ag

Chen, Z. Q.*; Li, Z. H.*; Hua, H.*; Watanabe, Hiroshi*; Yuan, C. X.*; Zhang, S. Q.*; Lorusso, G.*; Orlandi, R.; 60 of others*

Physical Review Letters, 122(21), p.212502_1 - 212502_6, 2019/05

 Times Cited Count:1 Percentile:47.32(Physics, Multidisciplinary)

Journal Articles

Comparison of heavy-ion transport simulations; Collision integral in a box

Zhang, Y.-X.*; Wang, Y,-J.*; Colonna, M.*; Danielewicz, P.*; Ono, Akira*; Tsang, M. B.*; Wolter, H.*; Xu, J.*; Chen, L.-W.*; Cozma, D.*; et al.

Physical Review C, 97(3), p.034625_1 - 034625_20, 2018/03

 Times Cited Count:33 Percentile:0.81(Physics, Nuclear)

International comparison of heavy-ion induced reaction models were discussed in the international conference "Transport2017" held in April 2017. Owing to their importance for safety assessment of heavy-ion accelerators and dosimetry of astronauts, various models to simulate heavy-ion induced reaction models are developed. This study is intended to clarify the difference among them to pinpoint their problems. In the comparison study, 320 protons and 320 neutrons were packed in a 20-fm-large cube to calculate the number of particle-particle collisions as well as the energies of collisions during the time evolution. In addition to the calculation, their algorithms were compared. The author contributed to this study by running calculation using JQMD (JAERI Quantum Molecular Dynamics). The results were compared with those calculated by the other 15 codes from over the world. Algorithm comparison showed that JQMD calculates collision probabilities from protons at first and collisions by neutrons are simulated later, which might be unreasonable. On the other hand, it was clarified that the calculation by JQMD agrees with those by the others. Despite the fact that some codes deviate from the average by a factor of 2, JQMD exhibited stable performance.

Journal Articles

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr cross section from the surrogate ratio method and its effect on $$s$$-process nucleosynthesis

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; Nishio, Katsuhisa; Lugaro, M.*; Karakas, A. I.*; Makii, Hiroyuki; Mohr, P.*; Su, J.*; Li, Y. J.*; et al.

Astrophysical Journal, 848(2), p.98_1 - 98_8, 2017/10

 Times Cited Count:0 Percentile:100(Astronomy & Astrophysics)

Journal Articles

Examination of the surrogate ratio method for the determination of the $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr cross section with $$^{90,92}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{92,94}$$Zr reactions

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; Nishio, Katsuhisa; Makii, Hiroyuki; Su, J.*; Li, Y. J.*; Nishinaka, Ichiro; Hirose, Kentaro; Han, Y. L.*; et al.

Physical Review C, 94(1), p.015804_1 - 015804_5, 2016/07

 Times Cited Count:3 Percentile:60.28(Physics, Nuclear)

Journal Articles

Enhanced damage buildup in C$$^{+}$$-implanted GaN film studied by a monoenergetic positron beam

Li, X. F.*; Chen, Z. Q.*; Liu, C.*; Zhang, H.; Kawasuso, Atsuo

Journal of Applied Physics, 117(8), p.085706_1 - 085706_6, 2015/02

 Times Cited Count:20 Percentile:21.91(Physics, Applied)

Vacancy-type defects in C$$^{+}$$-implanted GaN were probed using a slow positron beam. The increase of Doppler broadening S parameter indicates introduction of arge vacancy clusters. Post-implantation annealing at temperatures up to 800$$^{circ}$$C makes these vacancy clusters to agglomerate into microvoids. The vacancy clusters or microvoids show high thermal stability, and they are only partially removed after annealing up to 1000$$^{circ}$$C. Amorphous regions are observed by high resolution transmission electron microscopy measurement, which directly confirms that amorphization is induced by C$$^{+}$$-implantation. The disordered GaN lattice is possibly due to special feature of carbon impurities, which enhance the damage buildup during implantation.

Journal Articles

Li(Zn,Mn)As as a new generation ferromagnet based on a I-II-V semiconductor

Deng, Z.*; Jin, C. Q.*; Liu, Q. Q.*; Wang, X. C.*; Zhu, J. L.*; Feng, S. M.*; Chen, L. C.*; Yu, R. C.*; Arguello, C.*; Goko, Tatsuo*; et al.

Nature Communications (Internet), 2, p.1425_1 - 1425_5, 2011/08

 Times Cited Count:112 Percentile:6.28(Multidisciplinary Sciences)

In a prototypical ferromagnet (Ga,Mn)As based on a III-V semiconductor, substitution of divalent Mn atoms into trivalent Ga sites leads to severely limited chemical solubility and metastable specimens available only as thin films. The doping of hole carriers via (Ga,Mn) substitution also prohibits electron doping. To overcome these difficulties, Masek et al. theoretically proposed systems based on a I-II-V semiconductor LiZnAs, where isovalent (Zn,Mn) substitution is decoupled from carrier doping with excess/deficient Li concentrations. Here we show successful synthesis of Li$$_{1+y}$$(Zn$$_{1-x}$$Mn$$_x$$)As in bulk materials. We reported that ferromagnetism with a critical temperature of up to 50 K is observed in nominally Li-excess compounds, which have p-type carriers.

Journal Articles

Spin conversion of positronium in NiO/Al$$_{2}$$O$$_{3}$$ catalysts observed by coincidence Doppler broadening technique

Zhang, H. J.*; Chen, Z. Q.*; Wang, S. J.*; Kawasuso, Atsuo; Morishita, Norio

Physical Review B, 82(3), p.035439_1 - 035439_8, 2010/07

 Times Cited Count:17 Percentile:35.67(Materials Science, Multidisciplinary)

Positronannihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/Al$$_{2}$$O$$_{3}$$ catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetime components correspond to ortho-positronium (o-Ps) annihilated in microvoids and large pores, respectively. With increasing NiO content, both the latter lifetime and intensity show continuous decrease. Meanwhile, the para-positronium (p-Ps) intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of Ps in NiO/Al$$_{2}$$O$$_{3}$$ catalysts. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.

Journal Articles

Ferromagnetism and microstructure in Fe$$^{+}$$-implanted ZnO

Wang, D.*; Chen, Z. Q.*; Zhou, F.*; Lu, W.*; Maekawa, Masaki; Kawasuso, Atsuo

Applied Surface Science, 255(23), p.9371 - 9375, 2009/09

 Times Cited Count:12 Percentile:47.48(Chemistry, Physical)

We investigated iron-implanted ZnO by various methods. Photoluminescence measurements showed the introduction of non-radiative recombination centers. Raman scattering measurements showed the introduction of damages that distor the crystal symmetry. These defects were annealed out at 700$$^{circ}$$C. X-ray diffraction and magnetization measurements revealed the formation of iron nano-crystal and appearance of ferromagnetism accompanying the above heat treatment.

Journal Articles

Vacancy defects in electron-irradiated ZnO studied by Doppler broadening of annihilation radiation

Chen, Z. Q.*; Betsuyaku, Kiyoshi*; Kawasuso, Atsuo

Physical Review B, 77(11), p.113204_1 - 113204_4, 2008/03

 Times Cited Count:25 Percentile:26.9(Materials Science, Multidisciplinary)

Vacancy defects in ZnO induced by electron irradiation were characterized by the Doppler broadening of annihilation radiation measurements together with the local density approximation calculations. Zinc vacancies ($$V_{rm Zn}$$) are responsible for positron trapping in the as-irradiated state. These are annealed out below 200$$^{circ}$$C. The further annealing at 400$$^{circ}$$C results in the formation of secondary defects attributed to the complexes composed of zinc vacancies and zinc antisites ($$V_{rm Zn}$$-Zn$$_{rm O}$$).

Journal Articles

Study of X-ray emission enhancement via a high-contrast femtosecond laser interacting with a solid foil

Chen, L.-M.; Kando, Masaki; Xu, M. H.*; Li, Y.-T.*; Koga, J. K.; Chen, M.*; Xu, H.*; Yuan, X.-H.*; Dong, Q. L.*; Sheng, Z. M.*; et al.

Physical Review Letters, 100(4), p.045004_1 - 045004_4, 2008/02

 Times Cited Count:74 Percentile:7.56(Physics, Multidisciplinary)

We observed the increase of the K-$$alpha$$ X-ray conversion efficiency (hK) produced by a 60 fs frequency doubled high contrast laser pulse focused on Cu foil, compared to the case of the fundamental laser pulse. hK shows a strong dependence on the nonlinearly skewed shape of the laser pulse. It reaches a maximum for a 100 fs negatively skewed pulse. The electron spectrum shaping contributes to the enhancement of hK. Simulations demonstrate that high contrast lasers are an effective tool for optimizing the X-ray emission, via the enhanced Vacuum Heating mechanism.

Journal Articles

The H-Invitational Database (H-InvDB); A Comprehensive annotation resource for human genes and transcripts

Yamasaki, Chisato*; Murakami, Katsuhiko*; Fujii, Yasuyuki*; Sato, Yoshiharu*; Harada, Erimi*; Takeda, Junichi*; Taniya, Takayuki*; Sakate, Ryuichi*; Kikugawa, Shingo*; Shimada, Makoto*; et al.

Nucleic Acids Research, 36(Database), p.D793 - D799, 2008/01

 Times Cited Count:50 Percentile:23.37(Biochemistry & Molecular Biology)

Here we report the new features and improvements in our latest release of the H-Invitational Database, a comprehensive annotation resource for human genes and transcripts. H-InvDB, originally developed as an integrated database of the human transcriptome based on extensive annotation of large sets of fulllength cDNA (FLcDNA) clones, now provides annotation for 120 558 human mRNAs extracted from the International Nucleotide Sequence Databases (INSD), in addition to 54 978 human FLcDNAs, in the latest release H-InvDB. We mapped those human transcripts onto the human genome sequences (NCBI build 36.1) and determined 34 699 human gene clusters, which could define 34 057 protein-coding and 642 non-protein-coding loci; 858 transcribed loci overlapped with predicted pseudogenes.

Journal Articles

Ion species dependence of the implantation-induced defects in ZnO studied by a slow positron beam

Chen, Z. Q.*; Maekawa, Masaki; Kawasuso, Atsuo; Naramoto, Hiroshi

Physica Status Solidi (C), 4(10), p.3646 - 3649, 2007/09

 Times Cited Count:2 Percentile:41

We implanted B$$^{+}$$, O$$^{+}$$, Al$$^{+}$$, and P$$^{+}$$ ions into ZnO (Dose: 4E+15/cm$$^{2}$$). The thermal recovery of implantation-induced defects were studied using a slow positron beam. S parameters show much increase after ion implantation, indication introduction of vacancy defects. The thermal recovery of these vacancies induced by different ions shows much difference. For O$$^{+}$$ implantation, vacancy clusters disappear rapidly after annealing up to about 700$$^{circ}$$C. For the lighter ion B$$^{+}$$ implantation, however, vacancy clusters grow to a larger size at 500$$^{circ}$$C. The vacancies begin to recover and disappear after further annealing up to 900$$^{circ}$$C. For the Al$$^{+}$$ implantation, the vacancies grow into even a much larger size after annealing at 600$$^{circ}$$C, and they are annealed out at 900$$^{circ}$$C. However, for the P$$^{+}$$ -implanted sample, it was shown that a much weaker agglomeration process of the vacancy clusters compared with Al$$^{+}$$ implantation. A higher annealing temperature of 1100$$^{circ}$$C is needed to fully remove these vacancies.

Journal Articles

Thermal evolution of defects in as-grown and electron-irradiated ZnO studied by positron annihilation

Chen, Z. Q.*; Wang, S. J.*; Maekawa, Masaki; Kawasuso, Atsuo; Naramoto, Hiroshi*; Yuan, X. L.*; Sekiguchi, Takashi*

Physical Review B, 75(24), p.245206_1 - 24520_9, 2007/06

 Times Cited Count:60 Percentile:10.37(Materials Science, Multidisciplinary)

Vacancy-type defects in as-grown ZnO single crystals have been identified using positron annihilation spectroscopy. The grown-in defects are supposed to be zinc vacancy V$$_{Zn}$$-related defects, and can be easily removed by annealing above 600$$^{circ}$$C. V$$_{Zn}$$-related defects are also introduced in ZnO when subjected to 3 MeV electron irradiation with a dose of 5.5$$times$$10$$^{18}$$ cm$$^{-2}$$. Most of these irradiation-induced V$$_{Zn}$$ are annealed at temperatures below 200$$^{circ}$$C through recombination with the close interstitials. However, after annealing at around 400$$^{circ}$$C, secondary defects are generated. A detailed analysis of the Doppler broadening measurements indicates that the irradiation introduced defects and the annealing induced secondary defects belong to different species. It is also found that positron trapping by these two defects has different temperature dependences. The probable candidates for the secondary defects are tentatively discussed in combination with Raman scattering studies. After annealing at 700$$^{circ}$$C, all the vacancy defects are annealed out. Cathodoluminescence measurements show that V$$_{Zn}$$ is not related to the visible emission at 2.3 eV in ZnO, but would rather act as nonradiative recombination centers.

Journal Articles

Self-guiding of 100 TW femtosecond laser pulses in centimeter-scale underdense plasma

Chen, L.-M.; Kotaki, Hideyuki; Nakajima, Kazuhisa*; Koga, J. K.; Bulanov, S. V.; Tajima, Toshiki; Gu, Y. Q.*; Peng, H. S.*; Wang, X. X.*; Wen, T. S.*; et al.

Physics of Plasmas, 14(4), p.040703_1 - 040703_4, 2007/04

 Times Cited Count:35 Percentile:19.73(Physics, Fluids & Plasmas)

An experiment for the laser self-guiding studies has been carried out with 100 TW laser pulse interaction with the long underdense plasma. Formation of extremely long plasma channel with its length, about 10 mm, 20 times above the Rayleigh length is observed. The self-focusing channel features such as the laser pulse significant bending and the electron cavity formation are demonstrated experimentally for the first time.

Journal Articles

Experimental study on $$K$$$$_{alpha}$$ X-ray emission from intense femtosecond laser-solid interactions

Xu, M. H.*; Chen, L.-M.; Li, Y.-T.*; Yuan, X.-H.*; Liu, Y.-Q.*; Nakajima, Kazuhisa; Tajima, Toshiki; Wang, Z.-H.*; Wei, Z.-Y.*; Zhao, W.*; et al.

Acta Physica Sinica, 56(1), p.353 - 358, 2007/01

The characteristics of $$K$$$$_{alpha}$$ X-ray sources generated by p-polarized femtosecond laser-solid interactions are experimentally studied in the relativistic regime. By use of knife-edge image technique and a single-photon-counting X-ray CCD camera, we obtain the source size, the spectrum and the conversion efficiency of the $$K$$$$_{alpha}$$ X-ray sources. The experimental results show that the conversion efficiency of $$K$$$$_{alpha}$$ photons reaches an optimum value 7.08$$times$$10$$^{-6}$$/sr at the laser intensity of 1.6$$times$$10$$^{18}$$W/cm$$^{2}$$, which is different from the Reich's simulation results. We find that about 10% of laser energy is converted into the forward hot electrons at the laser intensity of 1.6$$times$$10$$^{18}$$W/cm$$^{2}$$.

Journal Articles

Vacancy-type defects induced by He-implantation in ZnO studied by a slow positron beam

Chen, Z. Q.*; Kawasuso, Atsuo

Acta Physica Sinica, 55(8), p.4535 - 4540, 2006/08

ZnO single crystals were implanted with with He ions with energies of 20-100keV to a dose of 4E+15 cm$$^{-3}$$. To study, implantation-induced defects, the Doppler broadeing measurements of positron-electron annihilation radiation were performed using a positron beam. As a result, it was found that divacancies and further vacancy clusters were generated due to implantation. It was found that upon annealing at 400 $$^{circ}$$C He atoms start to occupy vacancy clusters. After further annealing at 600 $$^{circ}$$C, vacancy cluster sizes increased. At 800 $$^{circ}$$C, He atoms desorbed from vacancy clusters and vacancy clusters also disappeared.

Journal Articles

Annealing process of ion-implantation-induced defects in ZnO; Chemical effect of the ion species

Chen, Z. Q.*; Maekawa, Masaki; Kawasuso, Atsuo; Sakai, Seiji; Naramoto, Hiroshi

Journal of Applied Physics, 99(9), p.093507_1 - 093507_5, 2006/05

 Times Cited Count:60 Percentile:11(Physics, Applied)

no abstracts in English

Journal Articles

Electron irradiation-induced defects in ZnO studied by positron annihilation

Chen, Z. Q.*; Maekawa, Masaki; Kawasuso, Atsuo; Sakai, Seiji; Naramoto, Hiroshi

Physica B; Condensed Matter, 376-377, p.722 - 725, 2006/04

 Times Cited Count:16 Percentile:38.45(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Energy variable slow positron beam study of Li$$^{+}$$ -implantation-induced defects in ZnO

Chen, Z. Q.*; Maekawa, Masaki; Kawasuso, Atsuo

Chinese Physics Letters, 23(3), p.675 - 677, 2006/03

no abstracts in English

42 (Records 1-20 displayed on this page)