Journal of Contemporary Physics (Armenian Academy of Sciences)最新文献

The vacuum expectation value of the current density for a massive scalar field in a (D + 1)-dimensional flat space-time with compact dimension is investigated. Along a compact dimension, the field operator obeys the helical quasiperiodicity condition with a constant phase. The results previously studied in the literature are obtained in the special case of a zero helicity parameter. In contrast to this case, the vacuum current, in addition to the component along the compact dimension, has a non-zero component in the direction of the non-compact dimension along which the field operator is shifted. A simple relation between these components is obtained. They are odd periodic functions of magnetic flux penetrating the compact dimension, with the period equal to the magnetic flux quantum. For a given non-zero value of the helicity parameter, the component of the vacuum current along the compact dimension tends to zero in the limit when the length of that dimension tends to zero. In the problem considered earlier with the usual quasiperiodic condition, the vacuum current diverges in that limit.

This article provides data on the development and creation of a vacuum window module, which will bring out the proton beam of the C18 cyclotron (IBA, Belgium) with energy of 18 MeV from a vacuum environment into the atmosphere. The module is made of aluminum and consists of a flange with a collimator and a helium (He) chamber of foil plates cooling. The module was installed at the end of the cyclotron’s beam line. Profile measurements were made for various current values of proton beam from 1 to 30 µA. The vacuum window showed its functionality.

The use of a drone as an aerial vehicle to realize the antenna measurement method is considered. The drone is controlled by software, using unified radio-electronic equipment containing a transmitter, a half-wave vibrator, and a GPS navigator. The parameters of the directional properties of the antenna system are the result of software processing of the output signals of the radar receiver synchronized with the coordinates of the drone flight path points.

Using computer simulation, the processes of heat propagation were studied and noise was determined in a three-layer detection pixel of a thermoelectric single-photon detector, consisting of an absorber (Pt), a thermoelectric sensor (La_0.99Ce_0.01B₆) and a heat sink (Pt, Mo). The absorption of photons with energies of 0.8–7.1 eV (1550–175 nm) in absorbers of various thicknesses, providing high absorption efficiency, was studied. The simulation was based on the heat propagation equations from a limited volume. The temporal dependencies of the signal appearing on the sensor were studied. Signal power, noise equivalent power, and signal-to-noise ratio were determined. It was shown that a detection pixel with a platinum absorber can reliably detect single photons with the energy of 3.1–7.1 eV.

Briefly presented the scientific and technical state of the linear accelerator complex of the A. Alikhanyan National Scientific Laboratory. LUE-75 after renovation work carried out in recent years. The need for further modernization of the accelerator’s main systems to ensure its long scientific life is substantiated. An analysis of the state of individual nodes and systems of the accelerator and calculations have been carried out, based on which modernization is proposed by the introduction of modern technology. The use of new-generation power electronics, vacuum equipment with a modern interface, and a thermostabilization system is offered.

A somewhat partial pair-interacting gas of heavy holes localized in a highly elongated ellipsoidal Ge/Si quantum dot has been studied in the adiabatic approximation. The interparticle interaction potential is considered within the one-dimensional Moshinsky atom model when the interaction depends on the square of the distance between particles. Within the framework of the Boltzmann approximation, the statistical sum of a somewhat partial hole gas is analytically calculated. The main thermodynamic parameters of the system, such as average energy, free energy, entropy, and heat capacity have been investigated. It is shown that taking into account interparticle interaction results in the ordering of the system, which, in particular, affects the entropy of the gas.

The spectral features and structural factors influencing the formation of luminescence bands of Ce³⁺ ions in YAG:Ce crystals are considered. The energy levels of the 4f shell of Ce³⁺ ions occupying both dodecahedral and octahedral sites of the crystal lattice have been determined. The participation of Ce³⁺ ions and ({text{Ce}}_{{{text{Al}}}}^{{3 + }}) ions in the structure of the luminescence band was shown and the multicenter structure of Ce³⁺ ions in the 4f ↔ 5d transitions of the activator was determined.

Peculiarities of X-ray beam diffraction from potassium and rubidium bi-phthalate piezo crystals under the condition of excitation of transverse ultrasonic vibrations are investigated. Previously, under a similar influence in quartz crystals, the effect of X-ray acoustic redistribution was observed, in which the intensity of diffracted radiation in the exact Bragg position increases significantly with a simultaneous decrease in the intensity of the transmitted beam, down to zero for certain parameters for reflecting atomic planes, called the full pumping effect. This effect can be used for controlled tuning of the diffracted beam intensity. In this work, to search for new materials for the creation of elements that allow such a rearrangement, we studied the dependences of the degree of amplification of diffracted radiation on the amplitude of the control signal for potassium and rubidium bi-phthalates crystals. The actual possibility of X-ray intensity modulation using transverse vibrations in these crystals is demonstrated.

A new type of atomic interferometer in which the registration is carried out by absorption spectroscopy of probing radiation is theoretically presented. To split the input atomic beam, the interaction with counterpropagating resonant waves is used. In addition, the atom also acquires equal populations at internal energy levels. The interaction with the subsequent traveling wave results in the interference between neighboring momentum states of the atom, and the distribution periodically varies with a strong asymmetry relative to the input momentum value. At the measurement stage, the result of the interference of matter waves is reproduced by the spectral distribution of the probing electromagnetic wave.

The article describes a new detector, a volume filled with hexane at low pressure (3 Torr), containing multi-wire proportional chambers and a silicon semiconductor detector. Using this setup, alpha particles emitted during the decay of the radioactive isotope ²²⁶Ra were detected. The device has an energy resolution of ≤ 5% and allows measuring the ionization energy losses of alpha particles as well. Thus, the LPMWPC and SSD-based experimental setup is a good tool for studying both binary and ternary fission of heavy nuclei, in which the third fragment is a high-energy alpha particle.