Distributions Of Parametric X-ray Radiation Research Articles

Use of parametric X-ray radiation of electrons in crystals to determine the parameters of imaging-plates

Good agreement between experimental data and the results of calculations of the yield and angular distributions of parametric X-ray radiation of electrons in crystals within the framework of kinematic theory enables us to use the measurement results to determine the photon energy dependence of the sensitivity of X-ray plates. The results of measurements of the angular distributions of parametric X-ray radiation of electrons with an energy of 255 MeV in a Si crystal using imaging plates of several types were compared with the results of calculations that take into account all currently known experimental factors that influence the measurement results. The spectral dependence of the sensitivity of the studied X-ray plates was determined for photon energies of two orders of reflection and for the (111), (1̅1̅1), and (110) reflection planes.

A proof-of-principle experiment on a new diagnostic tool for determining beam sizes from angular distributions of parametric X-ray radiation

A previously proposed technique for measuring the transverse sizes of an electron beam was verified experimentally by comparing the angular distributions of parametric X-ray radiation in a thin crystal for two distances between the crystal and the detector. The measurements were performed on a 255-MeV electron beam incident on a 20 μm-thick silicon crystal. The angular distributions of parametric X-ray radiation were measured using an imaging plate as a two-dimensional position-sensitive detector. The obtained horizontal and vertical beam sizes were in good agreement with the results of measurements by optical transition radiation. The proposed method would be useful for electron beam diagnostics for recently advanced linear accelerators where optical transition radiation cannot be used as a beam profile monitor owing to the coherent effect.

Observation of parametric X-ray radiation for the asymmetric Laue geometry

Angular distributions of parametric X-ray radiation from 255-MeV electrons in a thin Si crystal have been investigated for asymmetric Laue geometries using an imaging plate as a two-dimensional position-sensitive X-ray detector. The peak intensities of parametric X-ray radiation observed for (111) and (1¯1¯ 1) reflections, normalized by taking into account the effective target thickness and the transmission fraction of X-rays in the crystal, coincided within several percent. A large intensity difference depending on the asymmetry parameter, which is predicted by a dynamical theory dealing with the asymmetric Laue geometry, was not observed under the present experimental conditions. This indicates that the dependence of angular distributions of parametric X-ray radiation on the asymmetry parameter is negligibly weak, i.e., that it can be well explained by the well-established kinematical theory and dynamical theory as well as those for symmetric Laue and Bragg geometries.

Coherent X-ray radiation excited by a beam of relativistic electrons in a layered periodic structure

The dynamic theory of coherent X-ray radiation, excited in a periodic layered medium by a divergent beam of relativistic electrons in the Bragg scattering geometry, is developed. In framework of the two-wave approximation of the dynamic theory of diffraction, expressions describing the spectral-angular and angular distributions of parametric X-ray radiation (PXR) and diffracted transition radiation (DTR) are obtained taking into account the multiple scattering of the relativistic electrons by the atoms of the target. Based on the expressions obtained, the possibilities of the manifestation of the effects of dynamical diffraction in coherent X-rays were investigated. The influence of the asymmetry of the electron Coulomb field reflection with respect to the target surface (the reflecting layers situate nonparallel to target surface) on the spectral-angular characteristics of the PXR and the DTR under conditions of the electron multiple scattering is estimated. It is shown that at a fixed Bragg angle the width of the PXR spectrum increases when the angle of incidence of the electron on the target decreases, which leads to an increase in the PXR angular density. In the same conditions the width of the frequency domain of total external reflection and the amplitude of the DTR spectrum also increase, which leads to a significant increase in the angular density of the DTR. The obtained analytical expressions can be used to determine the optimal parameters of the experiment on confirmation of the predicted dynamic effects.

Angular distributions of parametric X-ray radiation from a diamond crystal

Angular distributions of parametric X-ray radiation (PXR) from 255MeV electrons incident on a 50μm thick diamond crystal are presented. Almost all experiments on the angular distributions of PXR have been performed using Si crystals. The purpose of the present work is to extend this research to diamond crystals. An imaging plate was adopted as a two-dimensional position-sensitive X-ray detector, and high-quality PXR angular distribution data were successfully obtained. The measured PXR angular distributions were compared with those predicted theoretically and good agreement was obtained. The cause of the slight difference observed around the center position (Bragg direction) is also discussed.

Quantum features of the angular distributions of parametric X-ray radiation of channeled relativistic electrons in a crystal

The appearance of sharp stepwise changes (quantum jump) in the angular distribution of parametric X-ray radiation from channeled electrons has been predicted at the appearance of each new quantum state of the channeled electron at the corresponding increase in the energy of an electron beam.

Channeling and parametric X-ray studies at the SAGA Light Source

We present experimental results on channeling and parametric X-ray radiation obtained using a 255-MeV electron beam from an injector linac at the SAGA Light Source. Using a screen monitor, we observed both channeling phenomena and doughnut scattering by measuring the profile of an electron beam transmitted through a 20-μm-thick Si crystal. We also measured the angular distribution of parametric X-ray radiation using an imaging plate as a two-dimensional X-ray detector. The obtained results are in good agreement with theory. The final goal of these studies is the first observation of diffracted channeling radiation, and our strategy for achieving this is discussed.

Quantum effects for parametric X-ray radiation during channeling: Theory and first experimental observation

The theory of X-ray radiation from relativistic channeled electrons at the Bragg angles—parametric X-ray radiation (PXR) during channeling (PXRC)—is developed while accounting for two quantum effects: the initial population of bound states of transverse motion and the transverse “form-factor” of channeled electrons. An experiment was conducted using a 255 MeV electron beam from a linac at the SAGA Light Source. We have identified a difference in the angular distributions of PXR and PXRC and obtained a fairly good agreement between the theoretical and experimental results.

Observation of parametric X-ray radiation by an imaging plate

We have demonstrated experimentally the application of an imaging plate for registering the angular distribution of parametric X-ray radiation. The imaging plate was used as a two-dimensional position-sensitive X-ray detector. High-quality images of the fine structure in the angular distributions of the yield around the reflection of the parametric X-ray radiation produced in a silicon crystal by a 255-MeV electron beam from a linear accelerator have been observed in the Laue geometry. A fairly good agreement between results of measurements and calculations by the kinematic theory of parametric X-ray radiation is shown. Applications of the imaging plates for the observation of the angular distribution of X-rays produced by accelerated particles in a crystal are also discussed.

Parametric X-ray radiation along relativistic electron velocity in asymmetric Laue geometry

An analysis is presented of the parametric X-ray radiation emitted by a relativistic electron at a small angle to its velocity as it passes through a single-crystal plate in asymmetric Laue geometry (including symmetric geometry as a particular case). Expressions describing the spectral-angular distributions of parametric X-ray radiation, transition radiation, and their interference are obtained. The effect of asymmetry on the spectral-angular distributions is examined.

Spectrum broadening effect in coherent x-ray radiation of a relativistic electron crossing a single-crystal plate

Based on the dynamic diffraction theory [1], coherent x-ray radiation of a relativistic electron crossing a single-crystal plate at a constant velocity is considered in the Bragg geometry. In the general case of asymmetric reflection of the radiation from the target, expressions are derived for the spectral-angular distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR). For a fixed angle between the electron trajectory and the system of parallel atomic planes of the crystal (Bragg’s angle) it is shown that a decrease in the angle of electron incidence on the crystal plate gives rise to a significant increase in the PXR and DTR spectra, and the causes for spectral broadening for each of these radiation mechanisms are different.

Effect of anomalous photoabsorption in parametric X-ray radiation under asymmetric reflection conditions

Parametric X-ray radiation (PXR) of a relativistic electron crossing a monocrystalline plate is considered in the Laue scattering geometry. Expressions describing the spectral-angular distributions of PXR and diffracted transient radiation (DTR), which are formed in atomic planes arranged at an arbitrary angle δ to the surface of a crystalline plane (asymmetric reflection), are derived in the two-wave approximation of the dynamic diffraction theory. The conditions under which the effect of anomalously weak photoabsorption (Borman effect) is manifested most clearly are determined. This effect can considerably enhance the intensity of the sources of tunable quasi-monochromatic X rays, which are based on the PXR mechanism.

Parametric x-ray radiation of a relativistic electron under conditions of asymmetric reflection

Coherent x-ray radiation of a relativistic electron crossing a single-crystal plate in the Laue scattering geometry is considered in a two-wave approximation of the dynamic diffraction theory [1]. Analytical expressions describing the spectral-angular distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR) formed on the atomic planes located at an angle δ to the crystal plate surface (asymmetric scattering) are derived. Dependence of the spectral-angular density of PXR, DTR, and their interference term on the angle δ is investigated.

Measurement of the energy distribution of parametric X-ray radiation from a double-crystal system

A parametric X-ray radiation (PXR) generator system was developed at the Laboratory for Electron Beam Research and Applications (LEBRA) at Nihon University; this PXR generator system is a tunable wavelength and quasi-monochromatic X-ray source constructed as one of the advanced applications of the LEBRA 125-MeV electron linear accelerator. The PXR beam which has characteristic of energy distribution.The theoretical values of energy distribution obtained at the output port were calculated to be approximately 300eV and 2keV at the central X-ray energies of 7keV and 20keV, respectively. In order to investigate the energy distribution, several measurements of the X-ray energy were carried out. The X-ray absorption of known materials and that of thin aluminum has been evaluated based on analyses of images taken using an imaging plate.The X-ray energy was deduced base on the identification of the absorption edges, and the energy distribution was estimated based on measurements using aluminum step method. In addition, an X-ray diffraction method using a perfect silicon crystal was employed, and spectra were measured using a solid state detector (SSD). The results of these experiments agreed with the calculated results. In particular, the well-defined absorption edges in the X-ray images and the typical rocking curves obtained by the measurement of the X-ray diffraction indicated that the distribution has a high-energy resolution.

On parametric x-ray radiation

The spectral-angular and angular distributions of parametric x-ray radiation generated in the vicinity of the maximum at small angles to the direction of charged-particle motion are studied under the conditions of Laue and Bragg diffraction geometries. Detector parameters at which the dynamical maxima of parametric x-ray radiation can be observed against the background of transition radiation are indicated. The spectral-angular and angular distributions of parametric x-ray radiation are analyzed for the case of backward geometry. The results of the present theoretical calculations are found to be in good agreement with experimental data.

Collimator-size effect on the parametric-radiation spectrum

It is shown that, by varying the angular size of a collimator, the spectral distribution of parametric x-ray radiation can be split into two isolated peaks and that the center of the spectral distribution of this radiation is shifted in frequency in response to an increase in the collimator size. It is also predicted that an increase in the angular size of the collimator will lead to a substantial modification of the character of the orientation dependence of the radiation spectrum.

Parametric X-ray radiation at a small angle near the velocity direction of the relativistic particle

It is shown, that the angular distribution of parametric X-ray radiation, emitted near the forward direction is essentially narrower than that emitted at large angles. The analytical expressions are obtained for integral PXR intensity near the forward direction.

Multi-wave parametric X-ray production by relativistic particles in crystals: comparison of computations and experimental results

The angular distributions of parametric X-ray radiation (PXR) produced by relativistic particles in crystals under the conditions of 4- and 8-wave Bragg diffraction are computed with the help of the method developed recently by Dubovskaya et al. [J. Phys.: Condens. Matter 5 (1993) 7771]. The computations are qualitatively compared to the experimental data known to date. It is shown that the enhancement of PXR intensity observed in the 8-wave experiment [Sov. Phys. -JETP Lett. (USA) 51 (1990) 242] could indeed be due to the multi-wave Bragg effect. The fine structure of multi-wave PXR peaks is analyzed.

Computation of parametric X-ray production by relativistic particles in crystals under multiple Bragg diffraction

An algorithm for computing spectral-angular and angular distributions of parametric X-ray radiation (PXR) produced by ultrarelativistic particles in crystals under multiple Bragg diffraction is developed. The algorithm is based on the methods applied in the dynamical theory of X-ray multiple diffraction. The angular distribution of three-wave PXR angular distribution into the simulated forbidden reflex (222) in the Ge crystal is computed. It is shown that using multiple PXR generation it is possible to generate X-ray beams with double angular collimation approximately=1 angular s2 and spectral width approximately=10-3.