Bulletin of the Russian Academy of Sciences: Physics最新文献

Results from modernizing the BR-K1M nuclear research facility (a cascade-type booster reactor) are presented. Research performed at the startup of the facility’s second stage is discussed, and the measuring and processing techniques used to obtain the main characteristics of the reactor core, the operating parameters, and the limit values for the facility’s safe operation are described.

Theoretical approaches proposed by A. Bulgac et al. (Washington University, Seattle) and J. Randrup et al. (Lawrence Berkeley National Laboratory (LBNL)) for studying correlations of angles between the spins of double spontaneous fragments and low-energy fission fragments are considered and compared. The idea of J. Randrup’s theoretical team (Lawrence Berkeley National Laboratory (LBNL)) on 2D and 3D spin is analyzed. Angular distributions for actinide nuclei ({}^{{232}}{text{Th}}(n,f),,,{}^{{252}}{text{Cf}}(sf),,,{}^{{238}}{text{U}}(n,f)) are derived with allowance for the special geometry of fissioning nuclei (2D) and compared to results from A. Bulgac et al. (Washington University, Seattle).

The surfaces of homoepitaxial 4H-SiC layers were studied using a nuclear scanning microprobe in the Rutherford backscattering mode. Analysis of the state of the sample surfaces and the synthesis conditions showed that an increase in the silicon (Si) content in the upper layers of some samples precedes the formation of highly defective 4H-SiC layers.

Correctly measuring of the moments of inertia of fragments of binary fission of actinide nuclei helps solve the important problem in nuclear physics of determining the spins of such fragments. The moments of inertia are calculated using the solid rotation, hydrodynamic, and superfluid models. The best agreement with experimental data is obtained using the superfluid model with an oscillatory potential.

ALICE-3 is a future upgrade of the current ALICE experiment to be operated at the high-luminosity Large Hadron Collider at CERN after 2030. One of the physics objectives of the experiment is to probe the hot and dense QCD matter produced in heavy-ion collisions by measuring the production of open charm hadrons. The ALICE-3 detector is equipped to measure the production of ground and excited states of D‑mesons in decay channels with charged particles in the final state. Results are presented from feasibility studies of recording of open charm hadrons in decay channels with neutral photons or mesons in the final state using the large acceptance electromagnetic calorimeter.

The features of nonlinear excitation of photoluminescence of wide-gap crystals by femtosecond laser radiation were studied. It was determined that, during multiphoton ionization of the proper substance of crystals, the excitation of intrinsic 2pO^2– valence-band photoluminescence has a long-wavelength threshold. The yield of the impurity photoluminescence excited by the capture of the band electrons and holes induced during the nonlinear ionization of the proper substance reaches saturation with increasing intensity of femtosecond laser pulses.

Square planar nickel microparticles deposited on the surface of single crystals of lithium niobate in the hexagonal phase and potassium titanyl phosphate were studied. Because the thermal expansion coefficients of these single crystals strongly differ, the uniaxial anisotropy is induced in the microparticles by heating or cooling relative to the deposition temperature. The phenomenon of the induction of anisotropy was explored using magnetic force microscopy and ferromagnetic resonance spectroscopy. Data obtained from ferromagnetic resonance spectra show that, in the ensemble of microparticles, with increasing temperature of the samples from –10 to 60°C, the axis of anisotropy rotates by 90°. This agrees well with the data about the domain structure of an individual microparticle, obtained by magnetic force microscopy.

The electron paramagnetic resonance (EPR) spectra of oxygen-deficient rutile TiO_{2 – δ} under photoexcitation at low temperatures in the range of 15–40 K were measured. Excluding the early described Ti³⁺ centers, concentration of which is independent of photoexcitation, new EPR signals appear at various wavelengths (λ) of photoexcitation taken in the range 400–460 nm. From the analysis of the EPR data we conclude that the observed EPR signals can be attributed to either the positive-charged oxygen vacancies (({text{V}}_{{text{O}}}^{ + })) with S = 1/2 (upon photoexcitation with λ ≤ 420 nm only), or more complex defects such as positively-charged [Ti³⁺–V_O]⁺ pairs with S = 1/2 and neutral complexes of (Ti³⁺–V_O–Ti³⁺) with S = 1. The latter is observed upon photoexcitation with a wavelength above 420 nm.

A model was developed for laser cooling of alkali atoms in a polychromatic field, considering the real structure of atomic levels. The model was tested by the example of the ⁶Li atom. The minimum achievable temperatures of laser cooling of light alkali atoms were studied for different polarizations of the light field components, and the possibility of cooling below the Doppler limit was shown.

An epitaxial film of a Pd–Fe alloy with a thickness of 202 nm was synthesized with an iron concentration varying in depth from 2 to 10 at %. The temperature dependence of the spin-wave resonance spectra in the film was measured. The spectra of standing spin waves were simulated. From the correlation of the theoretical spectra with the experimental data, the temperature dependences of the normalized exchange stiffness, the ratio of effective magnetization to saturation magnetization, and the surface spin pinning coefficients were obtained.