Diffracted transition radiation of relativistic electrons in an artificial periodic structure

A theory concerning the coherent X-ray radiation of relativistic electrons crossing an artificial periodic medium in Laue scattering geometry has been constructed. Expressions describing the spectralangular characteristics of radiation in the Bragg scattering direction have been obtained and studied. Radiation is considered in analogy with that in the crystal medium as a result of the coherent summation of the contributions of two radiation mechanisms, in particular, parametric X-ray radiation (PXR) and diffracted transition radiation (DTR). It is shown that the DTR yield from a layered target can exceed the particle radiation yield in a single-crystal radiator by one order or more under similar conditions.     

Transition radiation of fast electrons as a broadband vacuum-ultraviolet radiation source

The characteristics of a possible radiation source in the vacuum-ultraviolet and soft X-ray range based on the transition radiation of electrons with an energy of about 100 keV are calculated. The possibilities of enhancing the radiation yield in the geometry of the glancing interaction of electrons with a target are analyzed. The possibility of creating a source with a yield on the order of 10^?5 photon/(eV sr) per electron is demonstrated.     

Ionization yield of two-step photoionization process in an optically thick atomic medium of barium

The kinetics of a two-step photoionization process in optically thick atomic medium of barium (Ba) is studied using the rate equation approach. In the first step, Ba atoms get resonantly excited by laser radiation from their ground state to an intermediate excited state and subsequently are ionized in the second step by another laser radiation. The absorption of exciting radiation is taken into account along its propagation direction (optically thick). However, the medium is assumed to be optically thin for the ionizing radiation. A numerical simulation is done to estimate the ionization yield for time-varying Gaussian shaped laser pulses. The required energy density of the laser pulse to saturate the excitation transition throughout the thick medium is calculated. The effect of optical delay between the laser beams on the ionization yield is simulated. The calculated ionization yield from the simulation is compared with the measured values.     

Borrmann effect in parametric X-ray radiation

The suppression of the photoabsorption in parametric X-ray radiation by relativistic particles in a crystal is predicted. This dynamical effect caused by the contribution of emitting particle transition radiation to parametric X-ray radiation yield is possible in a crystal with a finite thickness only.     

Correlation effects of multiple charged accelerated ions in Cherenkov radiation

The correlation effects in Cherenkov radiation associated with fluctuations of multiple charged accelerated ions in the medium are considered. The contribution of additional correlation into the radiation is determined by the ion charge mean-square deviation from its equilibrium value and defines the non-zero radiation yield as the threshold conditions are not fulfilled. The numerical estimations of the yield of Au ion radiation in the optical and X-ray frequency range in carbon are presented.     

Correlation phenomena in the Cherenkov radiation of accelerated multiply charged ions

Correlation phenomena occurring in Cherenkov radiation are considered which are related to fluctuations of the charge states of multiply charged accelerated ions in a medium. The additional correlation contribution to the radiation is determined by the root-mean-square deviation of the ion charge from its equilibrium value and is responsible for the nonzero radiation yield in the event that the threshold condition is not fulfilled. Numerical estimates of the radiation yield of heavy ions in the optical and X-ray frequency ranges are given. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 41–46, January, 2009.     

The factor of suppression of Cherenkov radiation from electron-positron pairs produced by a hard γ photon

Cherenkov radiation from electron-positron pairs produced by hard γ photons is considered. The radiation yield is shown to be suppressed when the distance between an electron and a positron is less than the wavelength. This effect depends on the γ-photon energy and radiation intensity.     

Coherent diffraction radiation as a source of radiation in far-infrared and terahertz range

The results of measurements of the coherent diffraction radiation yield generated by femtosecond electron beam are presented. It is shown that the simulated and experimental data agreed quite well. The coherent diffraction radiation can be considered as a real candidate to develop a source of radiation in far-infrared and terahertz range.     

Effect of anomalous photoabsorption on parametric X-ray radiation from relativistic electrons

Parametric x-ray radiation from relativistic electrons moving in a crystal is theoretically investigated in Bragg geometry. It is shown that the effect of anomalous photoabsorption can manifest itself within this geometry of the scattering of the pseudophoton field of a fast particle. In this case, the angular distribution of the radiation changes significantly, while the total radiation yield can increase by a factor of 3.     

Light radiation from sodium films bombarded with slow electrons

Optical radiation from Na films by slow electron bombardment and the energy dependence of the radiative yield over the range 0–40 eV is investigated. In general the radiation is due to surface plasmons radiative decay. For the electron energy higher than 5.2 eV and lower than energy of surface plasmons (3.6 eV), the radiative yield is found to increase.     

利用康普顿散射实现太赫兹皮秒脉冲的分析

 研究了利用微波与电子束团的康普顿散射实现太赫兹的方法、光子产额和辐射功率。推导出了单个电子产生的太赫兹的光子产额和辐射功率表达式,也推导出了电子束团产生的太赫兹的光子总产额和辐射总功率表达式。结果发现：利用微波与电子束团发生康普顿垂直散射,可以产生太赫兹皮秒脉冲;单个电子产生的太赫兹光子产额与微波功率、微波波长成正比,与微波束截面积成反比;单个电子产生的太赫兹辐射功率与微波功率、电子Lorentz因子的平方成正比,与微波束截面积成反比;电子束团产生的太赫兹光子总产额与微波功率的平方、微波波长的平方成正比,与微波束截面积的平方成反比;电子束团产生的太赫兹辐射总功率与微波功率的平方、微波波长以及电子Lorentz因子的平方成正比,与微波束截面积的平方成反比。     

超热电子产生Kα辐射的参数影响

 超短超强激光与固体靶相互作用,可以产生大量的Kα特征谱线发射。这种Kα线光源在背光照相、医学成像和超快诊断等方面具有显著优势。为了寻求获得Kα线高产额的方法,利用ITS蒙卡模拟程序,对超短超强激光产生的超热电子在固体靶中产生的Kα线发射进行了模拟。系统研究了Kα线发射强度随出射角度、靶厚度和超热电子温度等参数的变化情况。研究发现在恒定的激光功率密度或超热电子温度下,存在最佳的靶厚度,使得Kα线光子产额最大,并用模拟结果对已有实验数据进行了解释。     

Effect of heavy ion charge fluctuations on Cherenkov radiation

Correlation effects in the Cherenkov radiation due to ions charge fluctuations in the matter are considered. Stochastic process of charge exchange leads to the washout of a radiation wave front and to the transformation of spectral-angular density. The effect is determined by a root-mean-square deviation of an ion charge. The additional radiation yield gives the nonzero contribution at the violation of the Cherenkov threshold condition. The interference of an electromagnetic field generated in the matter by the different ion's charge states along the trajectory is the cause of the additional radiation.     

Vacuum Cherenkov effect in logarithmic nonlinear quantum theory

We describe the radiation phenomena which can take place in the physical vacuum such as Cherenkov-type shock waves. Their macroscopical characteristics - cone angle, flash duration, radiation yield and spectral distribution - are computed. It turns out that the radiation yield is proportional to the square of the proper energy scale of the vacuum which serves also as the vacuum instability threshold and the natural ultraviolet cutoff. While the analysis is mainly based on the theory engaging the logarithmic nonlinear quantum wave equation, some of the obtained results must be valid for any Lorentz-invariance violating theory describing the vacuum by (effectively) continuous medium in the long-wavelength approximation.     

Formation of tight plasma pinches and generation of high-power soft x-ray radiation pulses in fast Z-pinch implosions

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field. Original Text ? Astro, Ltd., 2006.     

Generation of large-scale radiative vortex structures at stagnation of pulsed plasma jets in air

Large-scale vortex structures forming when pulsed plasma jets of the capillary discharge stagnate in atmospheric air are investigated. It is shown that injection of high-enthalpy plasma jets into air may effectively generate electromagnetic radiation from the optical range: the energy yield of radiation reaches 20–37% of the total energy content of the plasma. The radiation pulse has a complex time waveform including micro-and nanosecond components.     

Photochemical Reactions of Protein Tryptophanyls in the Eye Lenses of Rats in the Presence of Chloroform

The modifying action of chloroform on photochemical reactions induced in the eye lenses of rats by UVB radiation is revealed. In anesthetic concentrations, halogenmethane increases the quantum yield of photodisintegration of protein tryptophanyls with formation of a new photochemical product that absorbs radiation in the UVA range and possesses the photosensitizing activity.     

Dependence of F-center accumulation in NaCl crystals on the proton beam intensity

The manifold of dependences of the radiation defect yield on the radiation intensify is explained from a single viewpoint. It is assumed that the form of such dependences is determined by the relationship between the relaxation times of processes in the particle tracks and the time of overlapping of the tracks. The existence of an optimal intensity at which the defect yield is a maximum is predicted. It is shown that processes having a relaxation time of the order of 10 sec play an essential part in F-center accumulation in the slow stage at 295 °K.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 27–31, November, 1971.     

Femtosecond laser plasma in CaF<Subscript>2</Subscript> crystal microchannel and effective generation of characteristic X-ray radiation

The dependence of the characteristic X-ray radiation yield from CaF₂ crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 10¹⁵ W/cm²) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic X-ray radiation increased from 6 × 10⁻⁸ for the surface up to 10⁻⁷ in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source of X-ray radiation was located near the surface inside the microchannel.     

Nanophosphors and outlooks for their use in ionizing radiation detection

The fundamental properties of nanophosphors determined by their structural state are discussed. The influence of a high concentration of surface trapping centers and quantum confinement effect on the nanophosphor luminescence characteristics is noted. These features determine some new properties, which are important for radiation detection. They include the increase in the luminescence yield under high-dose irradiation and improvement of radiation resistance. The luminescence and dosimetric properties of nanophosphors of different compositions are described. It is noted that nanophosphors show promise as high-dose detectors of ionizing radiation.