# Physics of atomic nucleus and elementary particles

## Minimal Quark-Lepton Symmetry Model and Its Manifestations at Low Energies

**Background and Objectives:** The four color symmetry of quarks and leptons predicts scalar leptoquarks along with vector leptoquarks. If the scale of the violation of four-color symmetry is associated with the masses of vector leptoquarks and, as recently shown, can be about 100 TeV, the mass of scalar leptoquarks can be much smaller. Numerical values of additional fermionic mixing matrices were obtained in the study of restrictions on the mass of vector leptoquarks from leptonic decays K_{L}^{0} and B^{0}, B_{S}^{0} bosons.

## Calculation and Approximation of Radial Dose Function of Iridium Sources

**Background and Objectives:** The purpose of this paper is to investigate optimal fitting parameters for approximating radial dose function of Iridium sources. Calculations were performed using written by authors source code based on GEANT4 library package designed to simulate particle transport processes using Monte–Carlo method. **Results:** Following parameters of the source were determined: dose rate constant, radial dose function and anisotropy function. Obtained satisfactory coherence with other researchers’ data.

## Effect of Secondary Particles with High Linear Energy Transfer on Photon Beam Quality Factor

The energy dependence is investigated for a monoenergetic photon radiation quality factor with energies up to 40 MeV, while passing through a thin layer. The conditions of irradiation simulate radiobiological experiments to determine the relative biological eectiveness. The quality factor is calculated on the basis of data on linear energy transfer of all the particles in the irradiated layer, which are calculated using the Monte–Carlo method using GEANT4 code.