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Argunova, Tatiana S.,Gutkin, Mikhail Yu.,Kazarova, O.P.,Mokhov, E.N.,Nagalyuk, Sergey S.,Je, Jung H. Trans Tech Publications, Ltd. 2015 Materials science forum Vol.821 No.-
<P>We report on the growth method and the structural characterization of freestanding AlN crystals. An AlN layer is grown on a gradually decomposing SiC substrate yielding a freestanding crack free 2H single crystal with dislocation density 5×10<SUP>4</SUP>cm<SUP>-2</SUP>and without grain boundaries as confirmed by synchrotron radiation phase contrast imaging and topography data. Wafers of 600-1000 μm thick and up to 15 mm in diameter are obtained. The thermal stress distribution in a conventional AlN/SiC structure is discussed. Theoretical estimates show that cracking of AlN layers is a natural result of their growth on undecomposed SiC substrates.</P>
N. Matsuda,Y. Kasugai,Y. Sakamoto,H. Nakashima,H. Matsumura,H. Iwase,N. Kinoshitay,H. Hirayama,H. Yashima,N. Mokhov,A. Levering,D. Boehnlein,K. Vazili,L. Gary,S. Wayne,K. Oishi,T. Nakamura,K. Ishibash 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
Neutron spectra in high-energy region between 1 and 100 MeV in the shield configuration of the anti-proton target station and a 120-GeV proton beam at Fermi National Accelerator Laboratory (Fermilab) were determined using the reaction rate data obtained with the multi-foil activation method. Two kinds of methods were employed for the determination of neutron spectra: one is the fitting method which is newly developed in this work, another is the unfolding method with SAND-II code. The calculations were performed using the PHITS. From the comparison between the calculated and experimental neutron spectra, it concluded that the PHITS can be used for shielding design of highenergy proton accelerators.
Microstructure and strength of AlN–SiC interface studied by synchrotron X-rays
Argunova, T. S.,Gutkin, M. Y.,Shcherbachev, K. D.,Je, J. H.,Lim, J. H.,Kazarova, O. P.,Mokhov, E. N. Springer Science + Business Media 2017 JOURNAL OF MATERIALS SCIENCE - Vol.52 No.8
<P>Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (<= 1.5 mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. TheAlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between similar to 0.02 degrees misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested.</P>
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.
Shielding Experiments under JASMIN Collaboration at Fermilab (I) Overview of the Research Activities
Y. Kasugai,N. Matsuda,Y. Iwamoto,Y. Sakamoto,H. Nakashima,H. Matsumura,N. Kinoshitay,H. Iwase,T. Sanami,M. Hagiwara,H. Hirayama,H. Yashima,N. Sigyo,H. Arakawa,K. Ishibashi,N. Mokhov,A. Leveling,D. Boe 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
Shielding experiments were started on 2007 using high-energy proton accelerator at Fermi National Accelerator Laboratory (Fermilab) under the collaborative study program of JASMIN: Japanese and American Study of Muon Interaction and Neutron Detection. In this series of papers entitled "Shielding experiments under JASMIN collaboration at Fermilab", the part of the results regarding neutron detection has been reported. This paper, as a first paper of the series, overview of the research activities are described, and experimental results on high-energy neutron transportation are presented in a viewpoint of neutron attenuation in steel shield and applicability of Moyer's model. In addition, deductions of a neutron spectrum in wide energy range between 1 eV and 100 MeV by means of the hybrid method using the current-readout Bonner sphere together with foil-activation technique are presented.
Kajimoto, T.,Shigyo, N.,Sanami, T.,Iwamoto, Y.,Hagiwara, M.,Lee, H.S.,Soha, A.,Ramberg, E.,Coleman, R.,Jensen, D.,Leveling, A.,Mokhov, N.V.,Boehnlein, D.,Vaziri, K.,Sakamoto, Y.,Ishibashi, K.,Nakashim North-Holland Physics Pub 2014 Nuclear instruments & methods in physics research. Vol.337 No.-
The energy spectra of neutrons were measured by a time-of-flight method for 120GeV protons on thick graphite, aluminum, copper, and tungsten targets with an NE213 scintillator at the Fermilab Test Beam Facility. Neutron energy spectra were obtained between 25 and 3000MeV at emission angles of 30<SUP>o</SUP>, 45<SUP>o</SUP>, 120<SUP>o</SUP>, and 150<SUP>o</SUP>. The spectra were parameterized as neutron emissions from three moving sources and then compared with theoretical spectra calculated by PHITS and FLUKA codes. The yields of the theoretical spectra were substantially underestimated compared with the yields of measured spectra. The integrated neutron yields from 25 to 3000MeV calculated with PHITS code were 16-36% of the experimental yields and those calculated with FLUKA code were 26-57% of the experimental yields for all targets and emission angles.
Hiroshi Yashima,Norihiro Matsuda,Yoshimi Kasugai,Hiroshi Nakashima,Yukio Sakamoto,Hiroshi Matsumura,Hiroshi Iwase,Norikazu Kinoshita,David Boehnlein,Gary Lautenschlager,Anthony Leveling,Nikolai Mokhov 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23
The JASMIN Collaboration has performed an experiment to conduct measurements of nuclear reaction rates around the anti-proton production (Pbar) target at the Fermi National Accelerator Laboratory (FNAL). At the Pbar target station, the target, consisting an Inconel 600 cylinder, was irradiated by a 120 GeV/c proton beam from the FNAL Main Injector. The beam intensity was 3.6 X 10^(12) protons per second. Samples of Al, Nb, Cu, and Au were placed near the target to investigate the spatial and energy distribution of secondary particles emitted from it. After irradiation, the induced activities of the samples were measured by studying their gamma ray spectra using HPGe detectors. The production rates of 30 nuclides induced in Al, Nb, Cu, Au samples were obtained. These rates increase for samples placed in a forward (small angle) position relative to the target. The angular dependence of these reaction rates becomes larger for increasing threshold energy. These experimental results are compared with Monte Carlo calculations. The calculated results generally agree with the experimental results to within a factor of 2 to 3.