Vol 51, No 2 (2016)

The thermal physics processes of solid target cooling at proton beam irradiation in С18 cyclotron were calculated. The calculations were made with the help of finite-elements method using ANSYS program for beams with nonuniform density of particle distribution in the beam profile. It was shown that the radiation efficiency and conditions of target cooling essentially depend on distributions of particles in the beam and on efficient size of beam. A principal possibility of the cryocooling of target is shown that would essentially increase the radiation efficiency and the yield of final product–the medical isotope ^99mTc. The developed calculation method may be of use also for other processes of target irradiation with charged particle beams.

Using the Dirac’s method, the formation of metastable molecular states at the resonance scattering of two atoms in the laser radiation field is considered. Expressions for the metastable level populations and the resonance scattering cross sections are obtained. In the case of an exact resonance with the laser radiation, the graphs for populations and resonance scattering cross sections, which have two peaks due to the Autler–Townes effect, are obtained. These results play an important role in the study of the controlled chemical reaction and for the understanding of the processes in the quantum systems of the Bose–Einstein condensate at low temperatures, as well as in the various optical processes in atomic gases.

Gas sensing characteristics of multi-walled carbon nanotubes coated with tin dioxide nanoparticles nanocomposite thick-film structures (MWCNTs/SnO₂) prepared using hydrothermal synthesis, sol–gel technique and their combined process were investigated. Gas response test measurements of all studied nanocomposite structures carried out in air/target gas mixture showed that the most and at one time selective response to butanol vapor exposure in comparison to other mainly toxic and harmful gases such as acetone, toluene, formaldehyde, dimethylformamide, and others is observed for samples obtained by hydrothermal synthesis with 1:4 and 1:200 weight ratios of the nanocomposite components, respectively. These sensors are characterized by relatively short response and recovery times about 12 and 100 s, respectively, as well as low operating temperatures in the range of 150–200°C.

In a uniformly charged prolate spheroidal Thomson hydrogen atom the electron states have been investigated. It has been shown from the mathematical point of view that the problem is equivalent to a spheroidal hydrogen atom in a parabolic potential with the cylindrical symmetry. In the framework of adiabatic approximation, the energy of ground state has been calculated. Comparison with the case of uncharged spheroidal quantum dot has been made, and the analytical form of wave function of electron has been also obtained.

The resistive switching effect in metal–oxide–metal (MOM) structures has been investigated, where the 10% Li-doped ZnO layer was used as an oxide layer, as well as Pt and 20% fluorine doped SnO₂ (SnO₂:F) were used as a bottom electrodes. The current–voltage (I–V) and switching (I–t) characteristics of Ag/ZnO:Li/Pt and Ag/ZnO:Li/SnO₂:F structures were investigated. The unipolar resistive switching is detected in the structures with the Pt, while the use of transparent conductive SnO₂:F electrode instead of Pt, results to the bipolar memory effect.

The results of computer simulation of the processes of heat propagation inside the multilayer sensor of thermoelectric detector after absorbing the single photons with the energies 1 keV and 100 eV are presented. The variants are considered for different geometries of the sensor which consists of the tungsten absorber and of the thermoelectric layer of the cerium hexaboride. The differences of temporal dependence of the signal arising in the thermoelectric layer when the photon is absorbed in the various areas of absorber are studied in details. The energy resolution and the count rate of the sensor are estimated. It is shown that the multilayer sensors have a number of advantages as compared to the single-layered, and their use is promising in the various fields of science and technology.

The reflection of thermal neutron beams from a quartz single crystal was investigated in the Laue geometry under the external influences. The controllability of a neutron beam in space and time is analyzed and its parameters are estimated (relative maximum intensity, the angular and energy distribution of obtained beams etc.).