Papers by Keyword: Neutron Irradiation

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Authors: Jakub Čížek, František Bečvář, Ivan Procházka, Jan Kocik
Authors: Charalamos A. Londos, M. Potsidou, Andrzej Misiuk, I.V. Antonova
Authors: Victor Bratus', Roman Melnyk, Sergii Okulov, Bela Shanina, Volodymyr Golub, Iryna Makeeva
Abstract: EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100OC temperature range. Three new paramagnetic defects named Ky6, Ky7 and Ky8 have been revealed. Based on the present results, these defects have been tentatively attributed to the negatively charged carbon vacancy-carbon antisite pair, negatively charged divacancy and neutral carbon <100> split interstitial, respectively. Furthermore, the finding of practically isotropic hyperfine splitting for EPR lines of the T6 center confirms its assignment as a carbon vacancy-interstitial pair.
Authors: Charalamos A. Londos, N.V. Sarlis, L.G. Fytros
Authors: Stanislav Popelka, Pavel Hazdra, Vít Záhlava
Abstract: The effect of radiation damage produced by fast neutrons on characteristics of JBS diodes produced on 4HSiC epilayers was investigated. 1200V JBS diodes from Cree were irradiated in nuclear reactor by fast neutrons with fluences ranging from 1.3x1013 to 4x1014 cm-2 (1MeV NIEL equivalent in Si). Evolution of radiation damage was studied by deep level transient spectroscopy. New characterization method based on dynamic measurement of current to voltage characteristics in the kV range then allowed precise analysis of blocking characteristics and observation of free charge carrier removal with increasing neutron fluence. Results show that irradiation with fast neutrons introduces different point defect giving rise to acceptor like deep levels in SiC bandgap. These levels have a negligible effect on dynamic and blocking characteristics of irradiated JBS diodes, however, acceptor character of introduced deep levels accompanied by deactivation of donor dopants deteriorates diodes ON-state resistance already at low irradiation fluences. This degradation is then manifested by increasing values of the series resistance and the emission coefficient in the SPICE model of the JBS diode.
Authors: Aleksandr R. Gokhman, F. Bergner, Andreas Ulbricht, Uwe Birkenheuer
Abstract: The coupling between copper rich precipitates (CRP) and point defects in neutron irradiated iron alloys and VVER steels was investigated by means of cluster dynamics (CD) simulations. The consideration of the strain energy effect on CRP kinetics as well as the application of the regular solution model for the case of different fixed copper contents of CRP provides a good agreement between the simulation results and experimental data for complex iron based alloys with small (0.015 wt%) and high (0.42 wt%) copper content. It was found that the CD simulation is applicable to irradiated VVER steel with 0.07 wt% of copper.
Authors: Aleksandr R. Gokhman, Andreas Ulbricht, Uwe Birkenheuer, Frank Bergner
Abstract: Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr precipitates in neutron irradiated Fe-12.5at%Cr alloys at T = 573 K with irradiation doses up to 12 dpa and a flux of 140 ndpa/s. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data on the defect structure of this material irradiated at doses of 0.6 and 1.5 dpa are used to calibrate the model. A saturation behavior was found by CD for the free vacancy and free SIA concentrations as well as for the number density of the SIAC and the volume fraction of the Cr precipitates for neutron exposures above 0.006 dpa. The CD simulations also indicate the presence of VC with radii less than 0.5 nm and a strong SIAC peak with a mean diameter of about 0.5 nm, both invisible in SANS and TEM experiments. A specific surface tension of about 0.028 J/m2 between the a matrix and the Cr-rich a' precipitate was found as best fit value for reproducing the long-term Cr evolution in the irradiated Fe-12.5%Cr alloys observed by SANS.
Authors: Anatoly M. Strel'chuk, V.T. Gromov, Viktor V. Zelenin, A.N. Kuznetsov, Alexander A. Lebedev, N.G. Orlov, N.S. Savkina, V.P. Shukailo
Abstract: Neutron irradiation (~1 MeV, dose 1014-5.6∙1015 neutron/cm2) of packaged diodes based on 6H-SiC pn structures (with the base n-layer doped to ~5∙1016 cm-3) has been studied. In addition to the well-known rise in the series resistance of the diodes, the effect of a partial suppression of the excess current in both forward-and reverse-biased diodes and that of an increase in the recombination current, probably associated with the decrease in the nonequilibrium carrier lifetime, were discovered and discussed. These effects are common to 6H-and 4H-SiC pn structures.
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