Papers by Keyword: Irradiation

Abstract: Radiation stability of ZnO hollow particles under 100 keV proton and electron exposure have been investigated. The experimental data were compared with the calculated ones obtained by modeling in the GEANT4 software package. Hollow particles have better radiation stability compared with bulk microparticles cause by low defects accumulation in the hollow particles, which was confirmed by simulation in GEANT4.

Abstract: The effect of irradiation by protons with an energy of 15 MeV with fluences of (1-40)٠10¹² cm^-2 on the spectral characteristics of UV 4H-SiC photodetectors was considered. Photodiodes with Schottky barriers were formed by thermal vacuum sputtering with a thickness of 20 nm and a diameter of 8 mm on 4H-SiC structures with CVD epitaxial layers with a concentration of uncompensated donors N_d-N_a=(1-4)٠10¹⁴ cm^-3 grown on n⁺-4H-SiC substrates. UV photodetectors withstand irradiation by protons with a fluences of 4٠10¹³ cm^-2 with a photosensitivity improvement due to the gettering of simple radiation defects by localized cluster and amorphous areas, and partial structural improvement of the irradiated material. Irradiation of photodetectors by 15 MeV protons with a fluence of 4٠10¹² cm^-2 at a temperature of 200⁰ C led to an increase in quantum efficiency compared to samples irradiated in similar modes at 25⁰ C due to an additional defective rearrangement.

Abstract: In this paper, by considering the irradiation-enhanced diffusion, a combination of effective free energy model and the thermodynamic model was used for studying the phase relationships in the U-Ti and U-V binary system under irradiation. The steady-state dynamical phase diagrams of U-Ti and U-V binary alloys under different irradiation intensities were calculated and compared with the conventional thermodynamic equilibrium phase diagram. The calculated results show that under irradiation the high-temperature stable (βTi, γU) and (γU,V) phases were stabilized at relatively low temperature resulting in invariant reactions at relatively low temperature. In addition, with the increase of the irradiation intensity, the temperature of the invariant reactions increased, and the phase regions of the (βTi, γU) and (γU,V) also increased.

Abstract: Comparative studies of the structural, electrophysical properties and spectral sensitivity of 4H-SiC photodetectors of ultraviolet radiation in the spectral range of 200-400 nm were carried out before and after electron irradiations. Photodetectors with Cr Schottky barriers with thickness of 20 nm and 8 mm diameter were formed on n-4H-SiC CVD epitaxial layers with a thickness of 5 μm and concentration N_d-N_a= (1-4) х10¹⁴ cm^-3. Cr/4H-SiC photodiodes were irradiated by electrons at 0.9 MeV energy with doses (0.2-1) x10¹⁶ cm^-2.

Abstract: The paper is devoted to studying the effect of the specific surface area (SSA) of SiO₂ nanopowders (3 wt.%) added to BaSO₄ powders of a micron size on grain size distribution and diffuse reflectance spectra (ρ_λ) within the UV, visible, and near IR regions. Additionally, the authors have examined the spectra alteration (Δρ_λ) after irradiating with electrons (E=30 KeV). It has been established that mere mixing of the powders at a low concentration of nanoparticles leads to the post-irradiation decrease in the reflective power and to the subsequent increase in the reflectance coefficient stability.

Abstract: The article discusses the photochemical effects of sunlight on the soil. Under the influence of light energy the amount of mineral and easy hydrolysable nitrogen, as well as labile humus substances increased in the soil. The photochemical destruction of humus substances was accompanied by an increase in their mobility and loss of colour. The article shows that the process of mineral nitrogen formation in the soil during the photochemical destruction of humus substances has two stages. The first stage includes photochemical reactions with the formation of ammonium nitrogen. The second stage is the microbiological oxidation of ammonium nitrogen to the nitrate nitrogen.

Abstract: Experimental studies on the effect of electron irradiation with energy of 4 MeV to the mechanical strength of the film of Mylar type were conducted. It is found that the strain and stress dependences on the radiation dose are satisfactorily described by the proposed exponential models.

Abstract: The effect of protons exposure on the diffuse reflectance spectra of the zinc oxide with different shape particles has been investigated. Particles were micro-, nanocrystals, star and flower shape particles. The synthesis of the particles was carried out by the hydrothermal method using zinc acetate chemicals. The surface morphology, surface area and crystal structure of the particles have been investigated. Evaluating the changes in spectral reflectance it was found that the radiation stability of the micro particles is higher than the radiation stability of the other nanostructured particles. The high stability of the micro particles optical properties is due to the effect of low accumulation of radiation-induced defects.

Abstract: The radiation hardness of two dielectrics, SiO₂ and Al₂O₃, deposited on low doped, n-type 4H-SiC epitaxial layers has been investigated by exposing MOS structures involving these materials to MeV proton irradiation. The samples are examined by capacitance voltage (CV) measurements and, from the flat band voltage shift, it is concluded that positive charge is induced in the exposed structures detectable for fluence above 1×10¹¹ cm^-2. The positive charge increases with proton fluence, but the SiO₂/4H-SiC structures are slightly more sensitive, showing that Al₂O₃ can provide a more radiation hard passivation, or gate dielectric for 4H-SiC devices.

Abstract: Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in film polymer materials (polytetrafluoroethylene and lavsan) have been studied comprehensively. Essential change in material behavior including chain straightening was found in strain (e) – stress (s) curves.