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In-plane Anisotropy of the Magnetic and the Electric Properties of the Fe Pnictide Ba(Fe1−xCox)2As2
Yoshiaki Kobayashi,Akihiro Ichikawa,Masayuki Toyoda,Masayuki Itoh,Masatoshi Sato 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The anisotropy of the electronic and the magnetic properties within the FeAs planes of Co(2%)-doped BaFe2As2 has been investigated by using 75As nuclear magnetic resonance (NMR) measurementson the As (As0) sites with all four nearest neighbor sites occupied by Fe. Even in thetetragonal phase at temperatures above 100 K, two sets of NMR spectra with twofold symmetry ofin-plane Knight shifts and electronic nuclear quadrupole frequencies are observed. They originatefrom two domains with their symmetry axes lying at right angles to each other. The anisotropies ofthe electronic and the magnetic properties become pronounced at 140 K, below which an in-planeanisotropy is reported to appear in electrical resistivity under a pressure along one of Fe-Fe directions. 75As NMR measurements have also been carried out for the As (As1) sites surrounded byone Co and three Fe. From the data, we conclude that the spin susceptibility of As1 is ~1/3 thatof As0 and that the antiferromagnetic spin fluctuation of As1 is fairly suppressed as compared withthat of As0. We discuss these behaviors of the FeAs layer in connection with the impurity-inducedlocal orbital order model proposed by theoretical studies.
Hiroshi Matsumura,Norikazu Kinoshita,Hiroshi Iwase,Akihiro Toyoda,Yoshimi Kasugai,Norihiro Matsuda,Yukio Sakamoto,Hiroshi Nakashima,Hiroshi Yashima,Nikolai Mokhov,Anthony Leveling,David Boehnlein,Kamr 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
In an antiproton production (Pbar) target station of the Fermi National Accelerator Laboratory (FNAL), the secondary particles produced by bombarding a target with 120-GeV protons are shielded by a thick iron shield. In order to obtain experimental data on high-energy neutron transport at more than 100-GeV-proton accelerator facilities, we indirectly measured more than 100-MeV neutrons at the outside of the iron shield at an angle of 50˚ in the Pbar target station. The measurement was performed by using the Au activation method coupled with a low-background γ-ray counting system. As an indicator for the neutron flux, we determined the production rates of 8 spallation nuclides (^(196)Au, ^(188)Pt, ^(189)Ir, ^(185)Os, ^(175)Hf, ^(173)Lu, ^(171)Lu, and ^(169)Yb) in the Au activation detector. The measured production rates were compared with the theoretical production rates calculated using PHITS. We proved that the Au activation method can serve as a powerful tool for indirect measurements of more than100-MeV neutrons that play a vital role in neutron transport. These results will be important for clarifying the problems in theoretical calculations of high-energy neutron transport.
Masumoto, Kazuyoshi,Matsumura, Hiroshi,Kosako, Kazuaki,Bessho, Kotaro,Toyoda, Akihiro The Korean Association for Radiation Protection 2016 방사선방어학회지 Vol.41 No.3
Background: Activation of air and water in the electron linear accelerator for medical use has not been considered severely. By the new Japanese regulation for protection of radiation hazard, it became indispensable to evaluate of activation of air and water in the accelerator room. The measurement of induced activity in air and water components in the electron energy region of 10 to 20 MeV is very difficult, because this energy region is close to the threshold energy region of photonuclear reactions. Then, we measured the photonuclear reaction yields of $^{13}N$, $^{15}O$, and $^{11}C$ by using the electron linear accelerator. Obtained data were compared with the data calculated by the Monte Carlo method. Materials and Methods: An activation experiment was performed at the Research Center for Electron Photon Science, Tohoku University. Highly purified $SiO_2$, $Si_3N_4$, and carbon disks were irradiated for 10 minutes by bremsstrahlung converted by a tungsten plate. Induced activity from C, N, and O was obtained. Monte Carlo calculation was performed using MCNP5 and AERY (DCHAIN-SP) to simulate the experimental condition. Cross section data were adopted the KAERI dataset. Results and Discussion: In our experiment in hospital, calculated values were not agreed with experimental values. It might be three possible reasons as the cause of this deference, such as irradiation energy, calculation procedure and cross section data. Obtained data of this work, calculated and experimental values were good agreement with each other within one order. In this work, we used KAERI dataset of photonuclear reaction instead of JENDL. Therefore, it was found that the photonuclear cross section data of light elements are most important for yield calculation in these reactions. Conclusion: Further improvement for calculation using a new dataset JENDL/PD-2015 and considering electron energy spreading will be needed.