SPECIFIC FEATURES OF APPLICATION OF CADMIUM AS A NEUTRON-ABSORBING SCREEN WHILE DOPING SILICON IN A NUCLEAR REACTOR

The gradient of the neutron field in a nuclear reactor and the requirements for the permissible spread of the specific electrical resistance over the volume of the silicon ingot makes it necessary to develop an irradiation device. This is especially true for large silicon ingots. One of the options for reducing the gradient of the neutron flux along the height of the ingot is the use of neutron-absorbing screens in the design of the irradiation device. At the WWR-K reactor, cadmium with a natural isotopic composition is used as a neutron-absorbing screen material. The paper presents the results of a study of an irradiation device with a cadmium screen. The effect of a cadmium screen on the neutron-physical characteristics of an irradiation device for silicon doping is shown.

Laser sintering of oxidized copper nanoparticles deposited by dry aerosol printing

Sintering of oxidized copper nanoparticles arrays in the form of lines by the local treatment of laser radiation with wavelengths of 527 nm and 980 nm was studied. To form lines with a width equal to 40–150 μm and a thickness equal to 0.5–4 μm focused aerosol jets with average nanoparticle sizes of 110 and 65 nm were used. The production of semiconductor arrays from oxidized copper nanoparticles with a specific electrical resistance of 2⋅10−3 Ω⋅m using laser radiation with a wavelength of 980 nm was demonstrated.

Acoustic-electrical testing of defects in the cement-sand and cement-glass model samples

A complex method of acoustic-electrical testing of defects in dielectric samples made from cement-sand and cement-glass mixtures is discussed. The paper reports the results of studies of changes in the parameters of electromagnetic responses and their spectra under pulsed deterministic acoustic excitation of model samples with defects in the form of solid-state inclusions. The results of mathematical calculations of the time variation in the stress-strain state induced in a defective dielectric model sample by deterministic acoustic pulse are presented. The relationship is shown between the parameters of the acoustic excitation and the electromagnetic response to the impact in a magnetic field. The study revealed that the specific electrical resistance of the cement-sand and cement-glass mixtures differs significantly. Excitation of electrical double layers by acoustic pulses causes an electromagnetic signal, parameters of which depend on the parameters of the acoustic impact and acoustic and electrical properties of the material. As a result, a reduced specific electrical resistance of the mixture increases its conductivity. The numerical calculation of the propagation of the deterministic acoustic pulse showed that its parameters change when it passes through a defect with acoustic impedance different from that of the mixture used.

Electrical conductivity of whole and shredded plant tissue

The article gives the electrical conductivity of whole and shredded plant tissue. An experimental study was made of the dependence of the resistivity value and the volume occupied by the pulp on the pressing time and specific pressures on the pulp while taking into account the amount of pressed juice. The electrical resistance (R) of whole and crushed plant tissue was experimentally studied, which, when processing the results, was recalculated to the specific electrical resistance (ρ) of the tissue. The specific pressure (P) on the tissue was determined using a reference manometer, and the deformation (ΔH) of the sample was measured with a dial indicator.

Влияние дискообразных непроводящих включений на электропроводность материала на постоянном токе

The influence of non-conductive disk-like inclusions (fractures) on the conductivity of a conducting medium in direct current is considered. To find the additional specific electrical resistance due to cracks, a self-consistent problem for the current density has been solved. In this case, a hydrodynamic analogy was used between the motion of an ideal incompressible fluid during potential flow around solids and electric current flowing around fractures. The functional dependences of the resulting relative additional specific electrical resistance of the material on the fracturing coefficient for thick and thin samples are found. A graphical visualization of these dependences shows that for a thick specimen, for all real values of the coefficient of fracturing, it is linear and is determined by the shape of the fractures. For a thin sample, the dependence of the relative additional the specific electrical resistance of the material on the fracturing coefficient is proportional to the thickness of the sample and is nonlinear. The obtained dependences of the additional electrical resistivity can be used, in particular, as a non-invasive method for determining the fracturing coefficient of rock samples conducting electric current.

Studies of Changes in the Electrical Resistivity of Rocks of the Tashtagol Mine in a Critical Rock-bump Hazardous State Based on the Kinetic Concept of Solids Destruction

Main hypotheses of the occurrence of seismic events centers, including rock bumps are presented. Equations of kinetic theory of strength are given. A two-stage kinetic model of crack accumulation and catastrophic destruction of rocks is formulated. It consists in the fact that at the first stage of the rock bump preparation there is a diffuse accumulation of cracks, and at the second — merging of cracks, appearance of enlarged cracks and formation of the destruction center. The results are presented concerning the theoretical and laboratory measurements of change of specific electric resistance of the host rocks and ores of iron ore deposit at mechanical loading and destruction. It has been shown that the relative change of specific electrical resistance of the low conductive rocks depends significantly on the ratio of electrical resistance of the rock itself and charged zones near the surface of the incipient cracks during rock loading. With the accumulation of cracks in the process of mechanical loading of the host rocks of the Tashtagol mine, the number of charged point defects of the structure on the crack edges increases. Specific electrical resistance of such rocks decreases with the accumulation of the number of cracks. In the ore bodies and magnetic iron ores, on the contrary, with increasing disturbance, the electrical resistance increases. There is regular change in the electrical resistance of rocks in the intermediate and limit states. For ores and magnetic iron ores, the critical change is 40 %, and for the host rocks with high electrical resistance — 28–37 %. Obtained values of change of the specific electric resistance in the rock critical state can be used for prediction of the rock bumps.