Parametric X-ray Research Articles

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.

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.

Comment 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

The strong dependence of the PXR yield on the orientation of the crystal surface, claimed in a recent article by S. Blazhevich and A. Noskov, is questioned. It is argued that, if absorption is neglected, the sum of the ordinary and forward PXR yields does not depend of the surface orientation.

Coherent parametric X-radiation by the train of charged particles bunches: Conditions of observation

The problem of coherent parametric X-radiation (PXR) by the electron bunch is considered. The PXR by different electrons could be coherent at small bunch dimensions. Conditions for this kind of radiation – coherent PXR (CPXR) – were considered. Features of CPXR by the bunch as well as by the train of bunches are demonstrated.

Coherent X-Radiation Excited by a Beam of Multiply Scattered Relativistic Electrons in a Single Crystal in the Bragg Scattering Geometry

A dynamic theory of coherent x-radiation emitted by a divergent beam of relativistic electrons traversing a thin single-crystal plate is developed which takes into account multiple scattering of the electrons on the target atoms. The case is considered in which the target is quite thin, so that it is not necessary to take absorption of radiation into account, but the electron path in the target is quite long, so that it is necessary to take multiple scattering into account. Expressions are obtained which describe the spectral–angular characteristics of parametric x-radiation and diffracted transient radiation under these conditions. Conditions are described under which diffracted bremsstrahlung radiation can be neglected. The possibility of manifesting the effects of dynamic diffraction is investigated.

Project on the superposition of beamlines for parametric X-ray radiation and coherent transition radiation in the THz region at LEBRA

A new project to develop a terahertz (THz)-wave light source is in progress at the parametric X-ray (PXR) beamline of the Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University. The THz-wave source is based on coherent transition radiation (CTR) emitted from a metal foil inserted downstream from a crystal target that is the PXR radiator. Beryllium or titanium foil is the most promising candidate for a THz-wave radiator. Since the electron linac of LEBRA was developed for a free electron laser (FEL), electron beam with bunch length of 1 ps (rms) can be provided by magnetic bunching at the bending magnet section. Thus, very intense coherent transition radiation (CTR) can be obtained in the frequency region around 1 THz. The results of preliminary experiments for CTR production suggested that sufficiently intense THz-CTR can be obtained using the LEBRA linac. In order to realize a THz-wave source for practical application studies, we have a plan to add the extraction feature for THz waves to the PXR beamline.

Quantum Features of PXRC Angular Distributions From Relativistic Channeled Electrons in a Crystal

We predict quantum features in angular distributions of parametric X-radiation from channeled relativistic electrons (PXRC). The effect is connected with the number of quantum states of channeled electrons, form-factors of the transverse quantum channeling states and initial populations of these quantum states. The main motivation of this work is theoretical prediction for the future experiment at the SAGA-LS facility.

Influence of real photons diffraction contribution on parametric X-ray observed characteristics

It is proposed and implemented a simple method of calculating of the output of the diffracted real photons of bremsstrahlung and transition radiation from perfect crystals of arbitrary thickness up to a primary extinction lengths. It is shown that for small thickness of crystals and observation angles concerning the center of the diffraction of reflex, contribution of diffraction of real photon is comparable with the output of parametric X-radiation. Influence of experimental equipment characteristic on observed characteristics of radiation is discussed.

Experimental and theoretical study of PXRC (Parametric X-Radiation at Channeling) from 255 MeV electrons in Si

The X-radiation from relativistic channeled electrons at the Bragg angles – Parametric X-Radiation at Channeling (PXRC) – is studied both experimentally and theoretically. The experiment was carried out using a 255MeV electron beam from a Linac at newly constructed beam line for the study of interactions between a relativistic electron beam and crystals at the SAGA Light Source. The observed asymmetry of PXRC angular distribution at (220) planar channeling in a 20μm Si is explained taking account of two quantum effects: initial populations and transverse form-factors of the quantum states of planar channeled electrons. Further perspectives for PXRC studies at SAGA-LS are analyzed.

Coherent X-radiation along the velocity of a relativistic electron in a bounded periodic multilayer medium

In the present work a theory of the coherent X-radiation generated by the relativistic electron crossing an artificial periodic layered structure in Laue scattering geometry is built. The expressions are derived for spectral-angular distribution of the radiation in direction of the particle velocity. The comparative analysis of the spectral-angular density of the radiation is carried out for an artificial periodic structure and a single crystal in similar conditions. It is shown, that the spectral peak of the parametric X-radiation in the artificial periodic layered structure in the forward direction (FPXR) will be considerably wider than the one in a single crystal target which can make its experimental detection and investigation appreciably easier.

Asymmetric wave reflection in kinematic and dynamic approaches to description of parametric X-radiation of a relativistic electron in the crystal

Parametric X-radiation (PXR) of a relativistic electron travelling through a monocrystalline plate is examined in the Laue scattering geometry under the assumption of asymmetric and symmetric reflections of the particle field with respect to a target surface. The formulas of the kinematic and dynamic approaches to PXR characterization are analyzed and compared. The results of the experiment on relativistic electron PXR implemented at the Mainz microtron are interpreted using an expression derived for its angular distribution. It has been revealed for the first time that the dynamic effect of anomalous photoabsorption (the Bormann effect) of PXR has taken place in this experiment.

Ratio of the parametric X-radiation yields in the Bragg direction and along the relativistic electron velocity in the Bragg geometry

Parametric X-radiation (PXR) and parametric radiation at a small angle to the relativistic electron velocity (FPXR) that arises from electron motion through a monocrystalline plate in Bragg scattering geometry are analyzed on the basis of the dynamic diffraction theory. The expressions for spectral-angular densities of these radiations have been derived in the general case of asymmetric field reflections from a target surface. They make it possible to reveal the noticeable dependence of the ratio of the PXR and FPXR yields on the angle between reflecting atomic planes and the surface of a monocrystalline plate, i.e., reflection asymmetry.

Influence of crystal mosaicity on the X-radiation characteristics observed at a small angle to the particle velocity direction

The experimentally measured yields of X-rays generated by 500-MeV electrons (the X-ray energies are ω ∼ γωp) in oriented tungsten single crystals are analyzed. A series of experiments have been performed at the Tomsk synchrotron with the use of crystal-diffraction spectrometers based on mosaic pyrolytic graphite crystals. The measured results are shown to be explained by competition between parametric X-radiation and bremsstrahlung diffraction in mosaic crystals of the aα class. The characteristic sizes of microblocks of refractory metal crystals are discussed from the standpoint of their influence on the positron yield in designed positron sources. A method for determining the characteristic sizes of microblocks in mosaic crystals of the aα class is proposed.

A Preliminary Study on Low-dose X-ray Imaging Using Parametric X-ray

Parametric X-ray (PXR) is a new type of radiography with variable monochrome wavelength and high coherent characteristics. The Laboratory for Electron Beam Research and Application (LEBRA) at Quantum Science Institute, Nihon University generated LEBRA-PXR, a system that irradiates Si crystal with electron accelerated by linear accelerator (LINAC). LEBRA-PXR is uniquely developed for world-wide application experiment. X-ray images of tooth samples were taken with flat panel detector using LEBRA-PXR. As a result, images were captured as short as 1 sec. LEBRA-PXR uses LINAC with micro-macro pulse electron beam structure. Imaging time of 1 sec is equivalent to about 0.025 msec when x-ray is converted to actual radiation exposure. The effective dose point estimates of x-rays were about 1 μ Sv/5 sec. Results show that LEBRA-PXR can be used to generate low dose x-ray imaging advocating the possibility of its application in biological studies and medical treatment.

Effect of acoustic wave on the parametric X-ray generation by relativistic electrons in a crystal

An exhaustive description of the parametric X-ray (PXR) generation by relativistic electrons in a crystal excited by an acoustic wave is proposed. A principal question as to whether it is possible to enhance the PXR yield under these conditions is considered.

Radiation from relativistic electrons in a thin crystal target as complementary X-ray and gamma source at synchrotron light facilities

Concept of using crystal targets as complementary X-ray and gamma ray sources at synchrotron light facilities is considered. Calculations of channeling radiation, parametric X-radiation and bremsstrahlung from relativistic electrons in the crystal targets are performed for parameters of synchrotrons operating in Moscow (Kurchatov Center for Synchrotron Radiation, KCSR) and Karlsruhe (ANKA).

Relativistic electron PXR and FPXR yield ratio

The parametric X-radiation of relativistic electron crossing a single crystal plate is considered on the basis of dynamic diffraction theory in Laue geometry both in Bragg (PXR) and forward (FPXR) directions. Analytical expressions for spectral-angular density of these radiations in indicated directions are derived in general case of electron coulomb field asymmetric reflection from the target surface. The ratio of contributions of these radiation mechanisms into the total yield of the radiation is investigated. It is shown that the ratio of contributions of these radiation mechanisms can change sharply depending on the value of the reflection asymmetry.

Appropriateness of kinematical approach in description of parametric X-radiation of relativistic electron in a single crystal

Contrastive analysis of the formulas for parametric x-ray radiation (PXR) in the dynamic and kinematic approximation is made in the present work. The criteria for the usage of the kinematic formulas are determined on the basis of the dynamic theory. Specifically it was shown that the dynamic effects of PXR must be taken into account even in case of a thin non-absorptive crystal. The published results of the experiment on relativistic electron PXR on Mainz microtron MAMI are discussed. The manifestation of the effect of abnormal photo absorption (the Borrmann effect) in PXR is demonstrated in the experiment.

Contributions of transition and parametric X-ray radiation along the relativistic electron velocity in the Laue geometry

Parametric X-radiation along the velocity of a relativistic electron (FPXR) moving through a single crystal plate is analyzed in the Laue scattering geometry. It is shown that the ratio between the contributions of these radiation mechanisms strongly depends on the degree of reflection asymmetry. The presented theoretical results can be used for experimental investigations of FPXR.

Manifestation of dynamic effects in coherent X-radiation from relativistic electron in Bragg scattering geometry

Analytic expressions describing the spectral-angular distribution of parametric X-radiation (PXR) and diffracted transient radiation (DTR) of a relativistic electron traversing a single-crystal plate in the Bragg scattering geometry are derived on the basis of the two-wave approximation of the dynamic diffraction theory. The expressions are obtained in the general case of asymmetric reflection of a particle’s field relative to the surface of the crystal plate. It is shown that in the given geometry, a significant increase of the PXR angular density is possible due to the dynamic effect of PXR spectral broadening. The conditions for an increase in the DTR spectrum width, which causes a considerable increase of the DTR angular density, are derived. The possibility of the most pronounced manifestation of the Bormann dynamic effect in PXR is demonstrated for a thick absorptive crystal.