Vol 51, No 3 (2016)

Nuclear reactions at the interaction of particles with heavy targets were studied using the method of induced activity. This method permits an investigation of the mechanism of residual nuclei formation in a wide range of nuclear masses beginning from light nuclei up to the nuclei with masses near to the target mass. The results of investigations of nuclear reactions on separated isotopes of lead (²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) and tin (¹¹⁸Sn) isotope performed using the method of induced activity are given.

The system of qubits interacting with the perturbation field of an arbitrary envelope in the Furry representation based on the Magnus expansion in quantum electrodynamics is investigated. The general expressions for quantum transitions for probabilities between the states of a qubit are derived. The generalizations of this approach to the system of two interacting qubits are presented.

It is shown that the possibility to create the free electron laser without inversion (FELWI) has a threshold behavior on the field of intensity of amplified wave. In the collective approach, the description of threshold conditions is given. It is shown that the threshold of observation of amplification without inversion is sufficiently high, which hampers essentially the possibility of experimental realization of the FELWI.

The influence of the nonzero four-photon detuning on the adiabatic transfer of population in five-level system has been studied both analytically and numerically. The estimations determining the permissible variation of the four-photon detuning have been obtained, which are well confirmed by numerical calculations.

A fluorescence enhancement phenomenon, which is realized as a result of a sharp increase in the radiative decay rate of a quantum dipole emitter (QDE) is investigated theoretically in the vicinity of a conical metal tip. The QDE relaxation process is considered as a self-stimulated transition from an excited state into the ground state due to the feedback field formation from the tip. The dynamics of the system shows a stepped relaxation behavior that differs significantly from the conventional exponential decay. This effect can be observed in a small region of the resonance frequency, which is defined by an angle of conical tip. The increase of fluorescence when approaching of molecule to the metal tip on the surface enables one to determine its location.

Based on an analysis of absorption spectra from ⁴I_9/2 ground state to the excited states of Nd³⁺ ions in Pb(MoO₄)_x(WO₄)_1–x crystals, the main spectroscopic characteristics, including the probabilities of intermultiplet transitions and radiative lifetimes, are determined with the help of Judd–Ofelt method. The values of Judd–Ofelt parameters Ω₂ = 8.91 × 10^–20 cm², Ω₄ = 4.50 × 10^–20 cm², and Ω₆ = 3.89 × 10^–20 cm² are obtained for Nd³⁺ ions in Pb(MoO₄)_x(WO₄)_1–x crystals. The calculated radiative lifetime is compared with experimentally measured luminescence decay time.

An X-ray interferometric Fourier holography was proposed and theoretically investigated. X-ray Interferometric Young fringes and the reconstruction of an object image were investigated by the Fourier transform method. It was shown that on the output surface of the analyzer crystal (the third plate of the interferometer) the interference pattern of two slits gives X-ray interferometric Young fringes. An expression for the period of X-ray interferometric Young fringes was obtained. The subsequent reconstruction of the slit image as an object is conducted by means of the Fourier transform method of intensity distribution on the hologram. Three methods for reconstruction of the function of complex transmission of the object are presented: an analytical one–the approximate method, the iteration method and the step-by-step approach. As examples a recording of X-ray interferometric Fourier hologram and the reconstruction of the function of complex amplitude transmission of a beryllium circular cylinder are given.