Fundamental physical features of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in strong laser fields

Theoretically predicted fundamental features in the process of resonant spontaneous bremsstrahlung radiation during the scattering of ultrarelativistic electrons with energies of the order ∼ 100 GeV by the nuclei in strong laser fields with intensities up to I ∼ 1024 W cm−2. Under resonant conditions, an intermediate electron in the wave field enters the mass shell. As a result, the initial second-order process by the fine structure constant is effectively reduced to two first-order processes: laser-stimulated Compton effect and laser-assisted Mott process. The resonant kinematics for two reaction channels (A and B) is studied in detail. An analytical resonant differential cross-section with simultaneous registration of the frequency and the outgoing angle of a spontaneous gamma-quantum for channels A and B is obtained. The resonant differential cross section takes the largest value with a small number of absorbed laser photons. In this case, the resonant cross-section is determined by one parameter, depending on the small transmitted momenta, as well as the resonance width. In strong fields, spontaneous gamma quanta of small energies are most likely to be emitted compared to the energy of the initial electrons. At the same time, the angular width of the radiation of such gamma quanta is the largest. With an increase in the number of absorbed laser photons, the resonant cross-section decreases quite quickly, and the resonant frequency of spontaneous gamma quanta increases. It is shown that the resonant differential cross-section has the largest value in the region of average laser fields (I ∼ 1018 W cm−2) and can be of the order of ∼ 1 0 19 in units Z 2 α r e 2 . With an increase in the intensity of the laser wave, the value of the resonant differential cross-section R r e s max decreases and for the intensity I ∼ 1024 W cm−2 is R r e s max ≲ 1 0 7 in units Z 2 α r e 2 . The obtained results reveal new features of spontaneous emission of ultrarelativistic electrons on nuclei in strong laser fields and can be tested at international laser installations.

MODELING AND EXPERIMENTAL RESEARCH OF THE PROCESSES OF FORMATION OF RADIATION DAMAGE IN THE INTERACTION OF GAMMA QUANTUM FLOWS AND RELATIVISTIC ELECTRON BEAMS WITH SOLUTIONS OF ORGANIC DYES

The processes of interaction of an aqueous solution of an organic dye: methylene blue (MB)  C16H18N3SCl with gamma quanta and electrons were investigated. A model has been developed and the passage of electrons with an energy of 15 MeV through tungsten layers with a thickness of 1…8 mm has been simulated. Based on the simula-tion results, a number of experiments were carried out. Analysis of the calculated and experimental data showed that one incident electron destroys 4 times more dye molecules than one incident gamma quantum.

The effect of gamma quanta absorption due to interaction with thermal bremsstrahlung photons of hot gas in galaxy clusters

The interaction of gamma quantum from distant sources with thermal bremsstrahlung photons of hot intracluster gas with producing electron-positron pair in case of 10 galaxy clusters is considered. It is supposed that intracluster gas in considered clusters is isothermal and electron number density may be described by β distribution with β = 2/3. It is presented that the optical depth due to considered interaction is about 10−8 — 10−.

Analytical model for determining the leakage albedo component for a direct cylindrical channel passing through the nuclear reactor protective layer

The task of determining the radiation situation, including neutron and gamma-quantum flux density, radiation spectrum, specific volumetric activity of radioactive gases in the air, etc. behind the protective composition having inhomogeneities, has always been important in matters of radiation safety. One of the ways to solve the problem of determining gamma radiation fluxes was to divide the total ionizing radiation flux into four components: line-of-sight (LOS), leakage, line-of-sight albedo, and leakage albedo, and obtain an analytical solution for each component. The first three components have been studied in detail in relation to simple geometries and there are analytical solutions for them, but there is no such a solution for the last component. The authors of this work have derived an analytical representation for the leakage albedo component, which, in contrast to numerical methods (such as Monte Carlo methods), makes it possible to analyze the effect of inhomogeneities in protective compositions on the radiation environment as well as to quickly obtain estimated values of fluxes and dose rates. Performing a component-by-component comparison, it becomes possible to single out the most significant mechanisms of the dose load formation behind the nuclear reactor protection, to draw conclusions about the effectiveness of design solutions in the protection design and to improve the protection at significantly lower computational costs. Finally, the authors present calculations for the four components of the total ionizing radiation flux for various parameters of the cylindrical inhomogeneity in the reactor protection. Based on the obtained values, conclusions are made about the importance of taking into account the leakage albedo component in the formation of the radiation situation behind the core vessel.

Resonant Production of an Ultrarelativistic Electron–Positron Pair at the Gamma Quantum Scattering by a Field of the X-ray Pulsar

The process of a resonant production of an ultrarelativistic electron–positron pair in the process of gamma-quantum scattering in the X-ray field of a pulsar is theoretically studied. This process has two reaction channels. Under resonant conditions, an intermediate electron (for a channel A) or a positron (for a channel B) enters the mass shell. As a result, the initial second-order process of the fine-structure constant in the X-ray field effectively splits into two first-order processes: the X-ray field-stimulated Breit–Wheeler process and the the X-ray field-stimulated Compton effect on an intermediate electron or a positron. The resonant kinematics of the process is studied in detail. It is shown that for the initial gamma quantum there is a threshold energy, which for the X-ray photon energy (1–102) keV has the order of magnitude (103–10) MeV. In this case, all the final particles (electron, positron, and final gamma quantum) fly in a narrow cone along the direction of the initial gamma quantum momentum. It is important to note that the energies of the electron–positron pair and the final gamma quantum depend significantly on their outgoing angles. The obtained resonant probability significantly exceeds the non-resonant one. The obtained results can be used to explain the spectrum of positrons near pulsars.

MODELING THE RESPONSE OF A PLANAR SILICON DETECTOR WHEN MEASURING THE EXPOSURE DOSE RATE IN THE ENERGY RANGE FROM 5keV TO 10MeV

The main advantages of using silicon semiconductor detectors in dosimetry in comparison with traditional detectors are considered. The shortcomings are analyzed and possible methods for their elimination are proposed. One of the proposed methods makes it possible to increase the efficiency of detecting gamma quantum in the energy range 0.1...10MeV . The requirements are formulated to optimize the design of detectors operating in a wide range of dose rates and gamma radiation energies by computer simulation. Mathematical calculations and computer simulations determine the dosimeter design, materials and thicknesses γ-converter. The mechanisms of modeling the absorbed dose in air and ambient dose in silicon detectors with a thickness of 300µm, sizes (5×5)mm2 and (1.8×1.8)mm2, in the range of incident γ-ray energies from 5keV to 10MeV are presented.

The Resonant Bremsstrahlung of Ultrarelativistic Electrons on a Nucleus with Radiation of Hard Gamma-Quanta in the Presence of a Pulsed Field of the X-ray Pulsar

The investigation scrutinizes the circulation of the large-scaled fluxes of ultrarelativistic electrons near the neutron stars. This work focuses on the effects that occur during the adjustment of the strong electromagnetic field near the X-ray pulsars. Particularly, this study analyzes the resonant high-energy spontaneous bremsstrahlung of ultrarelativistic electrons in the pulsed fields of a nucleus and X-ray pulsar. Specific attention is given to the pulsed character of the field model. Under the resonant conditions the intermediate virtual electron within the electromagnetic field transforms into a real particle. As a result, the initial second-order process with accordance to the fine structure constant effectively splits into two first-order effects: the stimulated Compton process and the field-assisted scattering of an electron on a nucleus. In this research we obtain the resonant differential cross-sections with registration of frequency and radiation angle of a hard gamma-quantum. To summarize, the resonant differential cross-section of the effect within the external pulsed electromagnetic field of X-ray pulsar significantly exceeds the corresponding cross-section without an external field.

Resonant Effects in a Photoproduction of Ultrarelativistic Electron-Positron Pairs on a Nucleus in the Field of the X-ray Pulsar

The resonant photoproduction of the electron-positron pairs on a nucleus near a surface of the X-ray pulsar was studied theoretically. The main feature of the processes, which are responsible for the formation of the electron-positron fluxes, is a capability to occur in a resonant way in the electromagnetic field of the X-ray pulsar. One of the properties of the resonant case is that the initial process of second order in the fine structure constant in an external field effectively reduces into two successive processes of the first order due to the fact that in the resonant conditions intermediate virtual electron (positron) becomes a real particle. It is shown that the resonances are possible only when the initial gamma quantum energy is more than the threshold energy, which significantly depends on the number of absorbed photons of an external electromagnetic field. Additionally, in the resonant conditions, the energies of the particles depend on the outgoing angle of a positron (channel A) or an electron (channel B). It is shown that the resonant differential cross section has an extremely large magnitude in units αZ2re2. A mechanism to explain the presence of anomalous fluxes of ultrarelativistic positrons near the surface of an X-ray pulsar was proposed.