Polarization Bremsstrahlung Research Articles

Studies of polarization bremsstrahlung and ordinary bremsstrahlung from 89Sr beta particles in metallic targets in the photon energy region of 1–100 keV

Abstract Studies of polarization bremsstrahlung (PB) and ordinary bremsstrahlung (OB) produced by the 89Sr beta emitter in Al, Ti, Sn and Pb targets were undertaken at photon energies of 1–100 keV. The experimental results are compared with the Elwert corrected (non-relativistic) Bethe–Heitler (EBH) theory and the modified Elwert factor (relativistic) Bethe–Heitler ( F mod BH) theory for OB and with the Avdonina and Pratt ( F mod BH + PB) theory for total bremsstrahlung (BS). These results are in agreement with the F mod BH + PB theory up to 13 keV, 16 keV, 22 keV and 28 keV energies for Al, Ti, Sn and Pb targets, respectively; F mod BH theory is more accurate at higher energies.

Polarization Bremsstrahlung by Relativistic Electrons in Backscattering Geometry for Diagnosing Atomic Structure of Polycrystals

The measurements of X-ray polarization’s bremsstrahlung in the back scattering geometry (PBBS) generated during the interaction of 7 MeV electrons with polycrystalline foils of copper and niobium were performed. The analysis has shown a good agreement of the spectral width and position of the peaks with the theoretical calculations. The obtained results confirm the availability to develop a new method based on the PBBS peaks measurements for diagnostics of materials with a polycrystalline atomic structure.

Research of the polarization bremsstrahlung of relativistic electrons in polycrystalline targets

The collimated spectra of polarization bremsstrahlung (PB) produced by 7MeV electrons in Al, Ni, Cu, Mo and W poly crystalline foils are measured and the angular dependences of the PB characteristics are studied. A comparison of the experimental results with theoretical predictions is performed. Polarization bremsstrahlung sensitivity to texture and grain size of the target in the backscattering geometry is shown. The possibility of developing a new method based on the characteristics measurement of the coherent PB component for the diagnostics of polycrystalline materials is considered.

Polarization bremsstrahlung process in quantum plasmas including electron-exchange and shielding effects

Abstract The electron-exchange and quantum shielding effects on the polarization bremsstrahlung spectrum due to the electron-shielding sphere encounters are investigated in quantum plasmas. From this work, it is found that the electron-exchange effect strongly suppresses the polarization bremsstrahlung radiation cross section. Additionally, it is found that the polarization bremsstrahlung radiation cross section increases with increasing plasmon energy and, however, decreases with increasing Fermi energy. The variation of the influence of electron-exchange and quantum shielding on the polarization bremsstrahlung spectrum is also discussed.

Bremsstrahlung polarization correlations and their application for polarimetry of electron beams

The correlation between electron spin and photon linear polarization in atomic-field bremsstrahlung was measured with a polarized electron beam. The angle of photon polarization and the photon emission intensity were found to be correlated with the spin orientation. These effects are interpreted in terms of spin-orbit interaction. They lead to a new technique of electron beam polarimetry.

Diagnostics of nanodisperse polycrystals based on the polarization bremsstrahlung of relativistic electrons

The spectra of polarization bremsstrahlung are measured in the backscattering geometry during the interaction of 7-MeV electrons with a polycrystalline Ni foil. Measurement is conducted under conditions such that the size of the region of coherent X-ray radiation scattering in a target is on the order of 10 nm. The obtained results make it possible to suggest that using polarization bremsstrahlung as a new method for the diagnostics of the atomic structures of nanodisperse polycrystals is effective.

An apparatus to study the energy and angular distributions of electron-bremsstrahlung photons from gaseous targets

An apparatus is developed to measure the energy- and angular distributions of bremsstrahlung generated from collisions of energetic electrons with isolated atoms and molecules. A considerable reduction of thick target bremsstrahlung (TTB) background produced by scattered electrons from the chamber wall is achieved. Details of the experimental setup with regard to design of its components, experimental technique, data acquisition and analysis etc. are given and discussed. The reliability and performance of the setup are demonstrated by obtaining some test results on angular- and energy distributions of bremsstrahlung produced in collisions of 4.0keV electrons with free argon atoms. These results are compared with the theoretical predictions of the ordinary- and the polarization bremsstrahlung emissions. In this comparison, the experimental data for energy distributions of BS photons are found to be in reasonable agreement while they are found to have noticeable differences in shape of angular distributions.

Polarization bremsstrahlung at collisions of fast ions with multiatomic targets

The processes of polarization bremsstrahlung at collisions of fast ions with linear chains consisting of isolated atoms have been considered. The intensities and angular distributions of radiation spectra have been obtained for an arbitrary number of atoms in a chain. It has been shown that the interference of the photon emission amplitudes leads to a noticeable change in the spectral angular distributions of polarization bremsstrahlung as compared to the distributions at collisions with an isolated atom. The results allow standard generalization to the cases of polarization bremsstrahlung at channeling of fast ions over surfaces and in solid lattices.

Experimental study of polarization bremsstrahlung from small-grained polycrystals

The spectrum of polarization Bremsstrahlung is measured in backscattering geometry for 7-MeV electrons and a polycrystalline Ni foil without texture. The average size of grains in the foil is 300 nm. The results show the possibility of using a new method in the diagnostics of the atomic structure of polycrystalline materials with nanosized grains. The method is based on measuring the coherent component of polarization Bremsstrahlung.

Radiation Emission of Fast Electrons in Collisions with “Ion‐Sphere” in Dense Plasmas

AbstractRadiative emission of fast electrons in collision with an “ion‐sphere” electron distribution in dense plasmas is under consideration. The electron structure of the ion sphere is calculated ab initio using self‐consistent solution of both bound and free electron distribution inside the sphere. Two radiation channels are included: emission of the colliding electron itself in static potential (conventional or static Bremsstrahlung) and the emission of “ion sphere” medium due to its polarization by the colliding electron (polarization Bremsstrahlung). The last one is calculated in the frame of local plasma density approximation. Interference between conventional and polarization Bremsstrahlung is taken into account. It is shown that spectral cross section of the process has characteristic features depending on plasma density and ionization stage of plasma ions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bremsstrahlung polarization correlations and their application for polarimetry of electron beams

Linear polarization of hard x rays emitted in the process of atomic-field electron bremsstrahlung has been measured with a polarized electron beam. The correlation between the initial orientation of the electron spin and the angle of photon polarization has been systematically studied by means of Compton and Rayleigh polarimetry techniques applied to a segmented germanium detector. The results are in good agreement with those of fully relativistic calculations. The observed correlations are also explained classically and in a unique way manifest that due to the spin-orbit interaction the electron scattering trajectory is not confined to a single scattering plane. The developed photon polarimetry technique with a passive scatterer is very efficient and accurate and thus allows for additional applications. Bremsstrahlung polarization correlations lead to an alternative method of polarimetry of electron beams. Such a method is sensitive to all three components of the electron spin. It can be applied in a broad range of the electron beam energies from $\ensuremath{\approx}$100 keV up to a few tens of MeV. The results of a measurement at 100 keV are shown. The optimum scheme for electron polarimetry is analyzed and the relevant theoretical predictions are presented.

Polarization bremsstrahlung study of the surface of xenon clusters: The pseudocrystalline state

The half width of the polarization bremsstrahlung profile is measured as a function of the number W(N) of atoms in free clusters of xenon. The clusters are excited by electrons with energies of 0.7 and 0.3 keV, which preferentially probe the core and surface, respectively, of the clusters. It turns out the W(N) curves are entirely different for electrons with energies of 0.7 and 0.3 keV. An analysis of this difference indicates that the crystalline fcc core of clusters with sizes N ≈ 2000/8000 atoms/cluster (R ≈ 30–50 Å) is covered with a noncrystalline shell. This layer is examined in terms of the possible formation of glassy and pseudocrystalline states. For the first time a pseudocrystalline state is found in inert gas clusters. In this state the system is structurally unstable and constantly fluctuates between the liquid and solid phases.

Linear Polarization of the High-Energy End of Bremsstrahlung in Electron-Atom Collisions

We report on the effects of electron spin polarization on the bremsstrahlung polarization properties occuring in collisions of polarized electrons with thin target foils.

Bremsstrahlung of fast electron on graphene

Polarization Bremsstrahlung (PB) [1] and Static (ordinary) Bremsstrahlung (SB) [2] of fast electron scattered on graphene are investigated theoretically for relativistic and non-relativistic projectile velocities. In the framework of the first Born approximation spectral, angular and velocity dependences of PB and SB are calculated and analyzed for various incident electron angles. Coherent and incoherent interactions between electron and two-dimensional graphene are taken into account in the calculations.

Diagnostics of atoms encapsulated into fullerenes by the polarization bremsstrahlung from accelerated electrons

It is shown that the polarization bremsstrahlung (PB), which arises during scattering of coherent electromagnetic fields of fast charged particles by atomic electrons and resonantly reacts to changes of the density of a substance, allows one to diagnose the states of atoms that are encapsulated in fullerene. As a result of modeling, by comparing the spectra of an empty fullerene and fullerene with an encapsulated atom and using difference fitting, it is possible to detect compressions or expansions of an electron shell of the atom that is encapsulated in a fullerene. The calculations are fulfilled for the model approximation of the P@C60 endohedral compound.

Atomic analogue of photonuclear configurational splitting

It is shown that the polarized bremsstrahlung (PB) emitted upon the scattering of a relativistic charged particle’s Coulomb field by atomic electrons yields direct information on the electronic structure of a medium. Indeed, in the X-ray photon energy range 1–10 keV, PB exhibits collective features and the PB intensity sharply increases. At higher photon energies, the coherence of shell electrons rapidly collapses, which is accompanied by a drastic decrease in the PB intensity; hence, the position of the PB spectrum kink allows estimation of the atomic size.

Measuring coherent peaks of polarization bremsstrahlung from relativistic electrons in polycrystalline targets in backscattering geometry

The spectra of polarization bremsstrahlung (PB) in the X-ray range induced by 7-MeV electrons in a polycrystalline copper target have been measured in the backscattering geometry for various orientations of the target relative to the electron beam. It is shown that the PB backscattering is sensitive to the texture of a target. The possibility of developing a new method based on the measurement of characteristics of the coherent PB component for the diagnostics of polycrystalline materials is considered.

Role of polarization Bremsstrahlung in the formation of thick target Bremsstrahlung spectra in the energy range of 5–10 keV

Role of polarization Bremsstrahlung in the formation of total Bremsstrahlung (BS) spectra in thick targets of Al, Ti, Sn and Pb, produced by complete absorption of 90Sr beta particles having an energy range of 0–546 keV, are studied in the photon energy region of 5 to 10 keV. The theoretical BS spectral photon distributions, obtained from Elwert corrected (nonrelativistic) Bethe–Heitler theory, a modified Elwert factor (relativistic) Bethe–Heitler theory that describe ordinary Bremsstrahlung (OB) and a modified Elwert factor (relativistic) Bethe–Heitler theory for BS spectra that includes the polarization Bremsstrahlung (PB) into OB in stripped atom approximation, were compared with the experimentally measured BS spectral photon distributions. It has been observed that the experimental results are in agreement with the modified Elwert factor (relativistic) Bethe–Heitler theory at photon energy from 5 to 10 keV. It has been also observed that the contribution of PB into OB decreases with increase in end‐point energy of beta emitter and the energy of the emitted photon. Further, it has been found that the contribution of PB into OB increases with increase in atomic number of the target atom. This indicates the importance of PB in the formation of BS produced by continuous beta particle. Copyright © 2012 John Wiley & Sons, Ltd.

Dependence of spectral shape of bremsstrahlung spectra on atomic number of target materials in the photon energy range of 5–30 keV

Dependence of spectral shape of total bremsstrahlung spectra i.e. the sum of ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB), on the atomic number ( Z) of target materials (Al, Ti, Sn and Pb), produced by continuous beta particles of 90Sr and 204Tl, has been investigated in the photon energy region of 5–30 keV. It has been found that the spectral shape of total bremsstrahlung spectra, in terms of S ( k, Z) i.e. the number of photons of energy k per m o c 2 per beta disintegration, is not linearly dependent on the atomic number ( Z) of the target material and rather it is proportional to Z n . At lower photon energies, the index values ‘ n’ of Z-dependence are much higher than unity, which is due to the larger contribution of PB into OB. The decrease in ‘ n’ values with increase of photon energy is due to the decrease in contribution of PB into OB. It is clear that the index ‘ n’ values obtained from the modified Elwert factor (relativistic) Bethe–Heitler theory, which include the contribution PB into OB, are in agreement with the experimentally measured results using X-PIPS Si(Li) detector. Hence the contribution of PB into the formation of a spectral shape of total bremsstrahlung spectra plays a vital role.

Polarization Bremsstrahlung radiation on a nanosphere in a dielectric

Within the limits of a new approach based on the Mie scattering theory, polarization bremsstrahlung radiation (PBR), arising during electron scattering on a metallic nanosphere with radius from 10 to 100 nm placed in a dielectric medium is theoretically investigated. The spectral range close to the plasmon resonance is considered, where the contribution of the polarized channel to bremsstrahlung radiation dominates. Spectral, velocity, and angular PBR characteristics are calculated. The sensitivity of the PBR spectrum to the dielectric permittivity of the medium surrounding the nanosphere is demonstrated.