Department №30 Physics of interaction of radiation with matter

The Dept №30 is currently composed of about 12 researchers under the direction of Dr. Sc. Lytvynenko V.V. The department covers a broad range of activities that can roughly be divided into two major focus areas; first on investigation of the interaction of radiation with matter, modification of solids by electron beams, materials behavior in extreme environments. Second focus is on the IR spectrometry methods, thermovision control & diagnostics. The Dept#30 produces novel results that are to the benefit of innovative society. At the current stage, researchers are mainly concentrated on electron beam applications and IR thermography monitoring in industry.

In the recent 20years, radiation technologies industry has developed a great deal. The reasons are as follow:

absence of induced or residual radioactivity (we do not concider the technologies for radionuclides production, we do not use the high-energy particles under the activation threshold);
energy efficiency, significant reduction in energy consumption compared to alternative methods to provide the same technological effect;
green-initiative driving (one of the most important stages in evolution of the radiation technologies was the adoption of the environmental legislation in EU. That initiative induced a rapid growth of the radiation technologies applications based on the e-beam and bremsstrahlung X-ray sources. For instance, radiation-solidifying paints: solidification of 1 m² coating using the thermal method requires 2.7 kWh but the radiation one with a dose 50 kGy requires up to 80 times less and reduces the contribution of these air pollution sources like organic solvents);
e-beam accelerators are the environmentally friendly sources of radiation and safe in operation;
other advantage of these techniques is not generation of disinfection by-products, since the emitted energy is absorbed mainly by the microbial cell (DNA and RNA), causing irreversible and lethal damage.

Fields of applications of electrophysical radiation technologies::

Radiation based sterilization of medical equipment. The main advantage of this treatment is a possibility to destroy pathogenic organisms in the bulk or on the object surface (syringes, catheters, bandages etc.) sensitive to high temperatures or capable to adsorb chemical sterilizing agents.
Radiation-induced modification of polymeric materials. Mechanism of modifying effect is determined by the chemical reactions which can be initiated by radiation at any temperature, under any pressure and in any phase (gas, liquid or solid) without the use of catalysts. The irradiation of polymeric materials with ionizing radiation leads to the formation of very reactive intermediates. These intermediates such as free radicals, ions and excited states can follow several reaction paths, which result in rearrangements and/or formation of new bonds. The ultimate effects of these reactions can be the formation of oxidized products, grafts, degradation or cross-linking. Good control of all of these processing factors facilitates the radiation modification of polymers (polymerization, vulcanization, shape memory polymers, resistance to shrinking,swelling, cracking).
Radiation processing of food. Practical use of the ionizing radiation processes for the production and storage of foodstuffs is based on their ability to slow down or accelerate sprouting and ripening of fruits and vegetables, to induce a partial or complete suppression of vital activity of pathogens to delay food spoilage [1, 5].
Irradiation in agriculture. Prospects for the use of radiation technologies based on the electrophysical radiation sources (X ray, e-beam, UV) in agriculture are very promising due to the opportunity to solve complex problems, such as: removal of nutrients from raw cellulose-containing materials, inactivation of pathogens in wastes (manure etc), pre-sowing treatments to stimulate seed germination and seedling vigour, desinsection of grains, inhibition of sprouting [7].
Environmental cleanup application: clearance of gases from sulfur and nitrogen oxides thermal power stations (above 95% effective), sewage treatment, e-beam wastewater treatment [8].
Radiation modification of characteristics of metals & alloys through the intense e-beam irradiation. It is a kind of the surface and bulk processing techniques affects an increase in the microhardness, corrosion, abrasion, chemical resistance parameters due to induced changes in chemical composition, dislocation structure, grain refinement to the nanoscale dimensions [3] etc.
Powder metallurgy. Irradiation of metals induces the ablation processes which end with production of great amount of powder – removed, crashed, sprayed material (1 nm – 100 mkm particles).
Irradiation of semiconductors to form radiation defects that are the centers for recombination of nonequilibrium charge carriers in the space charge region of a p-n junction. As a result of irradiation, a switch rate of semiconductor elements increases from 10 ^-4 to 10 ^-7 s.
Radiation hardness assurance testing of electronics. Electronic devices can be exposed to a wide range of radiation environments (e.g. naturally-occurring space radiation environment). The types of particles, energies, fluxes, total doses can vary in wide rage of the different radiation environments that electronics devices can be exposed to that lead to large variations in degradation of devices characteristics.
Radiation processing of crude oil. In the 1970’s researchers confused about the use of organically-cooled nuclear reactors and then their activities concentrated on the use of electron beams for processing organic molecules as a way of refining crude and low-cost oil to produce higher value liquid fuels. But a tremendous number of radicals are formed when electrons collide with organic molecules. The key of hydrocarbon enhancement e-beam technology is controlling the generation and propagation of the radicals to minimize polymerization, which produces higher molecular weight materials.
Building products and materials: radiation cross-linked polyethylene foam, electron beam production of portland cement clinker etc.

Development of thermographic diagnostic methods of technological processes and equipment

The Dept#30 studies also the infrared (IR) radiometry, modern thermal imaging techniques for monitoring and diagnostics. Thermography methods are high-tech and rapidly growing applied research based on the theory of heat transfer, interaction of radiation with matter, numerical methods and modern information & computer technologies. In general, the fields in which radiometric instruments and techniques are used are very diverse: from astrophysics to television systems. IR radiometry helps us to solve the problem of spatial visualization of energy characteristics of the radiation fields, the density & exposure distributions of electron flows and gamma-rays in the radiation devices through measuring the radiant IR flux.

Thermal diagnostics, as a highly effective method of non-destructive testing techniques and defectoscopy, permits to detect the defective areas and disrepairs even at an early stage. IR imaging can be used as a good tool to exam and control the equipment, industrial structures and components (for example, nuclear power facilities) that lead to reducing operating and maintenance costs, improving the safety and reliability of the equipment and personnel. In most cases the thermal imaging is the complementary method for conventional NDT but in some cases (equipment and facilities without power outages etc) it is the only effective way to detect specific defects to prevent accidents. The basics of thermovision control methods and defectoscopy technologies rely on the remote infrared radiometry, based on registration of the radiant IR flux emitted from the surface of monitoring objects, and on the following analysis of their thermal images (heat maps, thermograms). The space and time resolved temperature distributions of the target surface describe its physical structure, give us information useful for making the inferences about the location of the hidden or latent defects, defective zones, and for their allowable classification.

Fast development of active thermography methods, infrared correlation radiometry and vibration defectoscopy significantly improved the effectiveness of remote methods of nondestructive testing [2, 4]. The Dept#30 investigates new methods of thermal imaging diagnostics, systems of thermovision operative control of the equipment, facilities and communications. Studies on physics processes of transformation of mechanical vibration energy into heat in the dissipative structures, especially the formation of thermal fields, are conducted depending on the parameters of cyclic loads and stresses in the material, on the characteristics of the energy - absorbing structures (defects zones) and on the measurement conditions of thermograms.