Parametric X-ray Radiation Research Articles

Proposal for a Procedure for Measuring the Transverse Dimensions of a Beam of Relativistic Electrons with a Small Longitudinal Size

The possibility of implementing a previously proposed procedure for determining the beam dimensions at a target is analyzed; it includes the measurement of two-dimensional angular distributions of the coherent radiation of fast electrons for two distances between a crystal, where radiation is generated, and a coordinate detector. The use of two mechanisms of parametric X-ray radiation and diffracted transition radiation is considered. The limits of the method sensitivity and the influence of the departure of secondary electrons and photons on them are discussed.

Response to the commentary by X. Artru about the article Interpretation of the results of the experiment on generation of parametric X-radiation by relativistic electrons in a single-crystal target, by S.V. Blazhevich and A.V. Noskov

An analysis of the comment by X. Artru on the results of a theoretical interpretation of the experiment devoted to measuring the angular density of parametric X-ray radiation (PXR) generated by relativistic electrons in a diamond crystal is carried out. We have pointed out the incorrectness of the arguments of the author put forward against the results of the interpretation. It is shown that even in the case of the absorption absence, the sum of angular densities of usual PXR and forward PXR (FPXR) depends on the orientation of the surface of the monocrystalline target relative to a system of diffracting atomic planes, contrary to the opinion of the author of the criticism.

Diffraction of virtual and real photons

Parametric X-ray radiation associated with the diffraction of virtual photons and the diffraction of X-rays described as the diffraction of real photons are studied experimentally. The diffracted radiation was generated by a 7 MeV beam of electrons and an X-ray tube respectively. Both diffraction mechanisms occur in a tungsten powder. The processes have been compared excluding three key parameters: the attenuation in the target, the background of the diffracted signal and the spectrum of the incident radiation. Remarkable differences between the diffraction mechanisms of virtual and real photons are observed. The ratio between the PXR peak and the XRD peak decreases when the peak energy increases.

Incoherent Form Factor in Diffraction and Smith—Purcell Radiations

It has been shown that polarization radiation of charged particle beams generally includes an incoherent form factor caused by a finite transverse size of a beam. Consequently, a widespread opinion that the form factor characterizes only coherent radiation of charge particle bunches is generally invalid. The reason for the existence of incoherent form factor is the interaction of charged particles with the target edge in the direction perpendicular to their trajectory. The incoherent form factor exists for diffraction radiation, Smith-Purcell radiation, and other types of polarization radiation in the case of transversely limited targets: transition radiation, parametric X-ray radiation, and Cherenkov radiation. It has been shown that the difference of the incoherent form factor from unity increases with a decrease in the ratio of the impact parameter to the transverse size of the bunch. Furthermore, it has been shown that the transverse part of the coherent form factor differs from unity to the same extent as the incoherent form factor.

PARAMETRIC X-RAY RADIATION IN THE BACKWARD GEOMETRY

Parametric X-ray Radiation registered in the backward geometry is analysed. The main properties of the radiation for such geometry are discussed. The advantages of the backward geometry over other configurations regarding the intensity, the spectral width and the possibility to discriminate the contributions form different radiation mechanisms to the total radiation yield are presented.

PARAMETRIC X-ray RADIATION IN POLYCRYSTALS

Parametric X-ray radiation produced during the interaction of charged particles with polycrystals is regarded. A review of the existing theories, perspectives of application and performed experiments is presented. The evolution of experimental capabilities as well as the progress in the process comprehension is illustrated. The state of the art of PXR in polycrystals is presented.

Radiation field of an ideal thin Gaussian bunch moving in a periodic conducting wire structure

A theoretical approach for describing the electromagnetic radiation produced by prolonged electron bunch propagating in the lattice of metallic wires of finite length is presented. This approach is based on vibrator antenna theory and involves approximate solving of Hallen's integral equation. For a single wire, it is also supposed that a wire is sufficiently thin and charge motion is relativistic. For many-wire structures, the approximation similar to kinematic approach of parametric X-ray radiation (PXR) theory is additionally applied. The validity of the method is verified by numerical simulations with COMSOL Multiphysics. Possible applications of interaction between charged particle bunches and artificial wire structures are discussed.

Parametric X-ray radiation in the Smith-Purcell geometry for non-destructive beam diagnostics

We investigate parametric X-ray radiation (PXR) under condition of the extremely asymmetric diffraction, when the ultra-relativistic electron bunch is moving in vacuum parallel to the crystal-vacuum interface, close to the crystal surface. This type of geometry coincides with the well known mechanism of generation of radiation, when the self-field of the particle beam interacts with the reflecting metal grating, namely the Smith-Purcell effect. We demonstrate that in this geometry the main contribution is given via a tail region of the beam distribution, which penetrates the crystal and X-rays are radiated along the normal to the crystal surface. We determine the electron beam characteristics, when this phenomenon can be observed. It is essential that in this geometry the majority of electrons does not undergo multiple scattering and consequently the characteristics of the particle beam are not changed, thus allowing the usage of the emitted X-rays for the purpose of non-destructive beam diagnostics, which can complement the traditional knife-edge method.

Performance of K -edge subtraction tomography as an application of parametric x-ray radiation

We developed a novel method for element detection utilizing an x-ray source based on parametric x-ray radiation (PXR), an accelerator-based light source at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University. The method is a type of $K$-edge subtraction (KES) imaging that uses the drastic change of x-ray absorption around the $K$-shell absorption edge of the target element. Using the properties of PXR, simultaneous KES imaging is possible, and can easily be applied to 3-dimensional (3D) computed tomography (CT). We demonstrated the feasibility of simultaneous KES-CT in our previous work. In this study, we investigate the quantitative performance of simultaneous KES imaging for a sample containing the element strontium (Sr) for which the $K$-edge energy is 16.1 keV. Results of a simultaneous KES-CT experiment employing the LEBRA-PXR source confirm that the imaging method can provide a 3D distribution of the element with a value proportional to the Sr concentration. Concerning sensitivity to element concentration, at least in the region of 0.5%-concentration, the sample was successfully distinguished from the region without Sr in the 3D tomographic image obtained using the element-imaging technique.

Coherent X-ray Radiation Excited by a Beam of Relativistic Electrons in a Single Crystal in the Direction of Beam Axis

In the framework of the two-wave approximation of the dynamic diffraction theory, a theory of coherent X-ray radiation of a relativistic electron beam in a single crystal in the direction close to the direction of the beam axis in the Bragg scattering geometry is developed for the general case of asymmetric reflection of the electron field relative to the target surface. Expressions describing the spectral-angular characteristics of parametric X-ray radiation near the velocity direction, transition radiation, and their interference term are obtained and studied.

Interpretation of the results of the experiment on generation of parametric X-radiation by relativistic electrons in a single-crystal target

The coherent X-ray radiation generated by a relativistic electron beam in a monocrystalline target of a limited thickness is investigated in the framework of two-wave approximation of the dynamical theory of diffraction in the conditions of asymmetric reflection of the radiation waves in relation to the target surface. The calculations of the radiation angular density for the conditions of the recent experiment on generation of parametric X-ray radiation (PXR) have been carried out. It has been shown, that adequate description of such experiments is possible only with use of the dynamical theory which takes into account the effects of asymmetric reflection of the radiation.

Parametric X-ray radiation from powders

Parametric X-ray Radiation (PXR) produced in powders has been observed for the first time. PXR spectra were measured under observation angles of 150° and 180° during the interaction of relativistic 7 MeV electrons with a tungsten powder. All the PXR peaks that theoretically can be produced in the studied energy region were registered. The performed absolute comparison of the experiment with the PXR kinematical theory from randomly oriented crystallites showed a good accordance.

X-ray emission by a high-energy electron with a nonequilibrium field in an ultrathin crystal

The process of coherent x-ray emission by an ultrarelativistic electron crossing a system of two targets, thick amorphous upstream and ultrathin crystalline downstream, is considered. It is shown that transformation of the electromagnetic field around the particle after its emission from the upstream target influences upon characteristics of radiation produced by the electron in the downstream target. The considered radiation is an interfering sum of parametric x-ray radiation and diffracted transition radiation. It is demonstrated that in the present case the properties of the x-ray pulse differ both from the ones typical for thick and ultrathin crystals and depend on the distance between the targets. At multi-GeV electron energies, such dependence is observable within macroscopically large values of this distance. Special attention is drawn to the study of the influence of the downstream target finiteness on radiation characteristics. It is shown that it results in the dependence of radiation yield on separation between the targets for macroscopically large values of such separation even at sub-GeV electron energies.

Parametric X-ray radiation and texture of polycrystalline foils

Текстура поликристаллической фольги вольфрама и никеля изучалась с использованием параметрического рентгеновского излучения (PXR), генерируемого электронами с энергией 7 МэВ. Получены кривые качания PXR из кристаллографических плоскостей (200) для вольфрама и (220) для никеля. Приведено сравнение с аналогичными измерениями, полученными с использованием дифракции широкополосных рентгеновских лучей. Сравнение показало хорошее соответствие результатов, касающихся формы кривых качания и положения максимумов. Однако наблюдалось систематическое несоответствие в значении полного максимума полной ширины.

Parametric X-ray radiation and texture of polycrystalline foils

Текстура поликристаллической фольги вольфрама и никеля изучалась с использованием параметрического рентгеновского излучения (PXR), генерируемого электронами с энергией 7 МэВ. Получены кривые качания PXR из кристаллографических плоскостей (200) для вольфрама и (220) для никеля. Приведено сравнение с аналогичными измерениями, полученными с использованием дифракции широкополосных рентгеновских лучей. Сравнение показало хорошее соответствие результатов, касающихся формы кривых качания и положения максимумов. Однако наблюдалось систематическое несоответствие в значении полного максимума полной ширины.

4a-B-7 チャネリング粒子によるパラメトリックX線放射

4a-B-7 チャネリング粒子によるパラメトリックX線放射

4a-B-8 パラメトリックX線放射の動力学的理論

4a-B-8 パラメトリックX線放射の動力学的理論

X-ray radiation generated by a beam of relativistic electrons in composite structure

Abstract The dynamic theory of coherent X-ray radiation generated by a beam of relativistic electrons in the three-layer structure consisting of an amorphous layer, a vacuum (air) layer and a single crystal has been developed. The phenomenon description is based on two main radiation mechanisms, namely, parametric X-ray radiation (PXR) and diffracted transition radiation (DTR). The possibility to increase the spectral-angular density of DTR under the condition of constructive interference of the transition radiation waves from different boundaries of such a structure has been demonstrated. It is shown that little changes in the layers thicknesses should not cause a considerable change in the interference picture, for example, the transition of constructive interference into destructive one. It means that in the considered process the conditions of constructive interference are enough stable to use them for increasing the intensity of X-ray source that can be created based on the interaction of relativistic electrons with such a structure.

Compact and intense parametric x-ray radiation source based on a linear accelerator with cryogenic accelerating and decelerating copper structures

This paper describes a proposal for a compact x-ray source based on parametric x-ray radiation (PXR). The PXR, which is produced when a single crystal is bombarded with relativistic electrons, has good monochromaticity and spatial coherence, and is expected to be well suited for imaging of low-Z materials and medical application. The proposed system employs a pair of copper accelerating structures which are operated at a cryogenic temperature of 20 K and arranged to form a resonant ring configuration. The electron beam is once accelerated up to 75 MeV in one of the structures, being decelerated down to lower than 7 MeV in the other structure after generating PXR at a single crystal, and then dumped. The expected x-ray yield is $1{0}^{9}\text{ }\text{ }\mathrm{photons}/\mathrm{s}$ at a center energy of 15 keV or higher.

Evolution of the characteristics of Parametric X-ray Radiation from textured polycrystals under different observation angles

The Parametric X-Ray radiation (PXR) spectra and yield dependencies on the orientation angle are measured during the interaction of 7 MeV electrons with a tungsten textured polycrystalline foil for different observation angles. The effects of PXR spectral density increase and PXR yield orientation dependence broadening in the backward direction is shown experimentally for the first time. The experimental results are compared with PXR kinematical theories for both mosaic crystals and polycrystals.