Papers by Keyword: Neutron Irradiation

Abstract: The effect of reactor neutron irradiation on the SiC crystals etching rate in KOH melt has been investigated. It is shown that at high doses of irradiation (10¹⁹ - 10²¹ neutrons/cm²) the SiC etching rate sharply increases, especially in the [0001] Si direction, leading to essential reduction of orientation anisotropy of polar {0001} faces etching. The increased rate of irradiated crystals etching remains after high-temperature annealing, up to the temperatures of 1400 – 1600 °C. The results are explained by the presence of meta-stable clusters of radiation defects which are the centers of increased chemical activity in the irradiated crystals.

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.

Abstract: Texture and substructure changes in cladding tubes from Zr-based alloys under neutron irradiation in the atomic reactor during 6 years were investigated by use of X-ray methods. For this aim in the “hot” laboratory the automated X-ray diffractometer was set and the technique to handle with irradiated samples was elaborated. The residual radiation activity of samples correlates with integral texture Kearns parameters of tube, so that the texture weakens as the doze of neutron irradiation grows. Because of the initial substructure inhomogeneity of cladding tubes its changes under neutron irradiation are also inhomogeneous: relatively perfect grains of texture maxima become more distorted, whereas initially distorted grains of texture minima becomes more perfect.

Abstract: The chapter is devoted to a study of the influence of neutron irradiation on the martensitic transformations and shape memory effects in TiNi-based shape memory alloys. Irradiation of the samples was carried out in the low-temperature helium loop of a WWR-M fusion reactor at Petersburg Nuclear Physics Institute in Gatchina (Russia). The experimental data showed that the variation in transformation temperatures depended on the irradiation temperature. The main factors influencing the variation in transformation temperatures during irradiation were disordering of the solid solution at low temperatures, radiation ordering at high temperatures, and thermally activated annealing of radiation damage. All of these mechanisms were taken into account in the differential equation given in the present work for description of the transformation temperature variation during irradiation at different temperatures. It was found that irradiation up to a fluence of 7⋅10¹⁸ cm^-2 did not suppress the transformation plasticity and shape memory effects in TiNi alloy in spite of the variation in transformation temperatures. It was observed that the shape memory effect may be initiated by irradiation up to a fluence of 5⋅10²⁰ cm^-2 at a constant temperature (under isothermal conditions) due to a decrease in transformation temperatures.

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.

Abstract: This paper deals with fracture of neutron irradiated austenitic Ti-stabilized stainless steel 08Ch18N10T. The steel had been tested in air and in water environment (320°C) using several tests representing different stress strain conditions for crack initiation and growth; Slow Strain Rate and Crack Growth Rate tests were performed in the water. Without irradiation the steel did not suffer from stress corrosion cracking in the water, but on irradiated specimens appeared areas of intergranular fracture mixed with transgranular cleavage-like facets and secondary cracks typical for IASCC phenomenon. The differences between fracture of irradiated and non-irradiated specimens in air and in water are documented and discussed.

Abstract: This paper studied the influence of neutron irradiation on the characteristics of 980nm pumped erbium-doped fiber amplifier(EDFA). After 7 days neutron irradiation, with the total fluence of 1.5×1013n/cm2, radiation induced loss changed little compared with pre-irradiation, maximum difference of single signal and WDM signal between pre-irradiation and post- irradiation are 0.5dB and 0.6dB, respectively. EDFA affected by neutron irradiation got less loss when the input signal power is higher.

Abstract: rradiation of ZnO:Al thin film by reactor neutrons with neutron/gamma ratio at 1.44x10⁴ (n.cm^-2.s^-1.mR^-1) leads to a decrease in resistivity in this material. The observed effects in electrical resistivity are attributed to irradiation-induced formation of defects in the ZnO:Al thin film structure.

Abstract: EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100^OC 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.

Abstract: Photoluminescence (PL) spectroscopy has been used to characterize neutron-irradiated cubic silicon carbide crystals. The effects of thermal annealing (600-1100^OC) on the PL bands have been studied. Several PL bands consisting of a sharp line and its phonon replicas have been observed in the 9-80 K temperature range. Certain of them like the D₁ spectrum doublet with 1.975 eV and 1.977 eV zero-phonon lines (ZPL) at 9 K and the L2 spectrum with ZPL at 1.121 eV were reported previously for ion-implanted and electron irradiated 3C-SiC crystals, respectively. Besides, some new bands with ZPL at 2.027, 1.594, 0.989 and 0.844 eV and a broad band at 1.360 eV have been found. A correlation of PL and EPR spectra intensities of these neutron-irradiated and annealed cubic SiC crystals is briefly discussed.