Polarization Of Bremsstrahlung Research Articles

CdTe Timepix detectors for single-photon spectroscopy and linear polarimetry of high-flux hard x-ray radiation.

Single-photon spectroscopy of pulsed, high-intensity sources of hard X-rays - such as laser-generated plasmas - is often hampered by the pileup of several photons absorbed by the unsegmented, large-volume sensors routinely used for the detection of high-energy radiation. Detectors based on the Timepix chip, with a segmentation pitch of 55 μm and the possibility to be equipped with high-Z sensor chips, constitute an attractive alternative to commonly used passive solutions such as image plates. In this report, we present energy calibration and characterization measurements of such devices. The achievable energy resolution is comparable to that of scintillators for γ spectroscopy. Moreover, we also introduce a simple two-detector Compton polarimeter setup with a polarimeter quality of (98 ± 1)%. Finally, a proof-of-principle polarimetry experiment is discussed, where we studied the linear polarization of bremsstrahlung emitted by a laser-driven plasma and found an indication of the X-ray polarization direction depending on the polarization state of the incident laser pulse.

Suprathermal electrons in a vacuum spark discharge

Results of experiments on the detection of suprathermal electron beams in the plasma of a highcurrent low-inductance vacuum spark by means of space-resolved spectral X-ray polarimetry are presented. It is shown that the observed polarization of bremsstrahlung may be caused by an ~100-keV electron beam propagating along the discharge axis from the pinching region toward the anode. The influence of the discharge initiation conditions on the parameters of the generated electron beams is analyzed.

Spin-orbit interaction in bremsstrahlung and its effect on the electron motion in a strong Coulomb field

Linear polarization of bremsstrahlung x rays produced in collisions of longitudinally polarized 2.1-MeV electrons with gold atoms was studied using the Compton scattering technique. We observed that the angle of x-ray polarization is strongly correlated with the incoming electron polarization. This correlation reveals the dominance of the spin-orbit interaction in bremsstrahlung and indicates a striking effect of the electron spin on the electron motion in a strong Coulomb field. The results confirm the validity of the theoretical predictions in a computationally challenging energy regime.

Polarization of atomic bremsstrahlung in coincidence studies

We present a theoretical study of bremsstrahlung produced by high-energy electrons scattered by heavy atomic targets. Considering coincident observation of the emitted photons and the scattered electrons, we pay special attention to the polarization degree and direction of the outgoing light. To investigate these properties of atomic bremsstrahlung, we apply the density matrix approach and solutions of the Dirac equation. Detailed calculations are performed for initial electron energies ranging from 100 to 500 keV and different fixed electron scattering angles. The results of these calculations are compared with predictions obtained under the assumption that the scattered electrons remain unobserved. This comparison reveals that both the degree and the direction of linear polarization of bremsstrahlung are very sensitive to the direction of the scattered electron.

Observation of the spin–orbit interaction in bremsstrahlung

The effects of the spin–orbit interaction are pronounced for an electron scattered in a Coulomb field of the nucleus. They cause the electron scattering plane to turn or precess as the electron moves. This precession is visible through linear polarization of bremsstrahlung. The first experiment to observe it is described in this contribution.

PEBSI – A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets

We present a Monte Carlo code dedicated to the simulation of bremsstrahlung arising in collisions of polarized electrons with thin target foils. The program consists of an electron transport algorithm taking into account elastic electron-nucleus scattering and inelastic collisions with target electrons as well as a treatment of polarized-electron bremsstrahlung emission. Good agreement is found between the predictions of the electron transport code and data stemming from other simulation programs and experiments. In addition, we present first results from the bremsstrahlung simulation which indicate a significant decrease in the degree of linear polarization of bremsstrahlung even for the thinnest gold targets considered.

Polarization of bremsstrahlung at electron scattering in an anisotropic medium

Bremsstrahlung from relativistic electrons is considered under conditions when some transverse direction of momentum transfer is statistically preferred. It is shown that in the dipole approximation all the medium anisotropy effects can be accumulated into a special modulus-bound transverse vector, $\bm N$. To exemplify a target with $N^2\sim1$, we calculate radiation from electron incident at a small angle on an atomic row in oriented crystal. Radiation intensity and polarization dependence on the emission angle and frequency for constant $\bm N$ is investigated. Net polarization for the angle-integral cross-section is evaluated, which appears to be proportional to $N^2/2$, and decreases with the increase of the photon energy fraction. A prominent feature of the radiation angular distribution is the existence of an angle at which the radiation may be completely polarized, in spite of the target complete or partial isotropy -- that owes to existence of an origin-centered tangential circle for polarization in the fully differential radiation probability kernel. Possibilities for utilizing various properties of the polarized bremsstrahlung flux for preparation of polarized photon beams and for probing intrinsic anisotropy of the medium are analyzed.

The polarization of bremsstrahlung from radiative ionization induced by relativistic highly charged projectiles

Based on inverse kinematics the close relation between radiative electron capture to the projectile continuum, calculated within the impulse approximation, and electron–nucleus bremsstrahlung is shown. Particular emphasis is laid on the short-wavelength limit corresponding to cusp-electron emission in the target frame of reference. Differential cross sections and the degree of photon polarization are calculated for the coincident emission of electron and photon. Coplanar and non-coplanar geometries are considered, and the polarization is compared with that obtained from experiments on the elementary bremsstrahlung process and on radiative electron capture to bound states.

Photon polarization effects in inverse photoemission from Cu(001)

A study of the polarization of Bremsstrahlung emitted from a Cu(001) single crystal surface helps to identify surface states and allows to determine the parity of bulk final states involved in a particular radiative transition if the angle of electron incidence is varied in a mirror plane of the crystal. In case of overlapping peaks with different polarization, a polarization dependent light detection increases in addition the apparent experimental resolution considerably.

Information on neutral weak currents from circular polarization of bremsstrahlung

Bremsstrahlung of unpolarized electrons is analysed for information on neutral weak interactions. The coupling of axial lepton and polar hadron neutral currents should cause a circular polarization of about 10 −6 at electron and photon energies of a few hundred MeV and forward angles. The specific nuclear structure is of modest importance.

Neutral currents and the circular polarization of bremsstrahlung

Bremsstrahlung from lepton-nucleus scattering has a small circular polarization if the weak neutral currents are vector and axial vector. The magnitude of the effect is calculated for low incident lepton energies where the nuclear excitation may be neglected.

Polarization of Free-Free Bremsstrahlung from Magnetically Confined Plasmas

The polarization of bremsstrahlung from electron-ion collisions is calculated for magnetically confined electrons in the Born approximation. The polarization at high temperature is found to be of opposite sign to the low-temperature result and of smaller magnitude.

Linear Polarization of Low-Energy-Electron Bremsstrahlung

The linear polarization of bremsstrahlung from thin targets (\ensuremath{\sim} 50 ${\mathrm{\ensuremath{\mu}}\mathrm{g}/\mathrm{c}\mathrm{m}}^{2}$) of Al, Cu, Ag, and Au was measured for incident electron energies of 50, 75, and 100 keV. The polarization was measured as a function of photon energy at four emission angles ($\ensuremath{\theta}={22.5}^{\ensuremath{\circ}},{45}^{\ensuremath{\circ}},{90}^{\ensuremath{\circ}}, \mathrm{and} {135}^{\ensuremath{\circ}}$). Data presented were obtained with a Compton polarimeter having a large asymmetry ratio (from 35 to 150) and high resolution. The results have been found to be in general agreement with the predictions of various bremsstrahlung calculations.

On the polarization and anisotropy of solar X-radiation during flares

Starting from the idea that the electrons accelerated during a solar flare have originally a preferred direction, the angular distribution and the polarization of bremsstrahlung below 10 A is calculated taking into account the influence of the magnetic field. The energy distribution of the nonthermal electrons is based on X-ray spectra measured by the Leicester group during flares in 1962 and 1967. In addition to the case of a fixed angle α between the electron velocity and the magnetic field, an angular distribution of the form sin n α is considered. The results may be used to test flare models. Recent measurements of the polarization of solar X-radiation yield the expected order of magnitude.

Angular Asymmetry in Pair Production by Polarized Bremsstrahlung at Intermediate Energies

Method of measuring linear polarization of bremsstrahlung at intermediate energies is discussed. The polarization is determined from the angular distribution of electron positron pairs produced in an amorphous converter. The vertical distribution of electrons is detected by a wire spark chamber or a counter hodoscope and positrons by a large counter. The cross section is a counter hodoscope and positrons by a large counter. The cross section is obtained analytically. The maximum asymmetry ratio of the cross section is 11∼13% for photons with the energies higher than ∼100 MeV.

Polarization of Bremsstrahlung at the Short-Wavelength Limit

Polarization of Bremsstrahlung at the Short-Wavelength Limit

Coherent Bremsstrahlung and Pair Production in the Diamond Crystal in Graphical Representation between 1 and 40 GeV

The paper supplies numerical information on coherent effects of bremsstrahlung and electron pair production in diamond crystals in the energy range from 1 to 40 GeV. The information is collected in a number of graphs and tables showing the intensity and polarization of bremsstrahlung and the cross section and asymmetry ratio for pair production as a function of crystal orientation. The basic formulas for the interpretation of the diagrams are given. The experimental problem of a precise orientation of the crystal, which is closely connected with the production of coherent radiation, is discussed on the basis of these formulas.

Messung der zirkularen polarisation der bremsstrahlung unter berücksichtigung der elektronendiffusion in dicken absorbern

The circular polarization of bremsstrahlung produced in thick absorbers by β-particles is a function of the atomic number of the absorber. Some authors report that the EB polarization is also dependent on the magnitude of the electric or magnetic fields within the absorber. It is shown here that the Z dependence of EB polarization is a second-order effect of electron diffusion in thick absorbers in contrast to other explanations which require a modification of the primary EB production process. The electric field dependence of the EB polarization was not found within an error of ±2%.

Circular polarization of bremsstrahlung produced in high-energy collisions of electrons with polarized protons

The purpose of this paper is to calculate the circular polarization of bremsstrahlung emitted in the high-energy collision of an unpolarized electron with a proton which is initially polarized in an arbitrary direction. We have taken into account the effect of the anomalous magnetic moment and the recoil of the proton but have neglected the matrix element for the bremsstrahlung of the proton and so our formula is valid when the angle between the directions of the electron and the photon is of the order ofmc2/E (m andE being the mass and energy of the electron, respectively).

Circular polarization of bremsstrahlung emitted by a longitudinally polarized electron in WeizsÄcker-Williams method

The method of WeizsAcker and Williams is applied here to calculate the circular polarization of bremsstrahlung produced in the field of nucleus by a longitudinally polarized electron. This method, valid only for extremely high energy of the electron, simplifies the calculations by reducing the problem to one of Compton scattering in a suitable Lorentz frame.