Measurement of the asymmetry in the emission of bremsstrahlung by transversely polarized electrons

Mergl, E.; Nakel, W.

doi:10.1007/bf01437366

Cited by 14 publications

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“…An important observable is the angular asymmetry of bremsstrahlung emitted by a transversely polarized electron beam where the spin direction is perpendicular to the photon emission plane, defined by the momenta of the incoming electron and the emitted photon. Disregarding the decelerated outgoing electrons such left-right photon emission asymmetries have been measured by several groups [1,2] and recently in our laboratory [3] in order to clear up discrepancies with calculations which appeared in previous work [2]. We found good agreement with the theoretical predictions of a partial wave calculation of Tseng and Pratt [4].…”

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“…They solved the Dirac equation numerically by means of partial wave expansion using a relativistic local self-consistent screened central potential. This theory, the best currently available for bremsstrahlung, yields doubly differential cross sections we used for comparison with our noncoincident asymmetry measurements [3]. However, this theory does not yet yield numerical results for the triply differential cross section needed for electron-photon coincidence experiments.…”

Section: Photon Emission Asymmetry In the Elementary Process Of Bremsmentioning

confidence: 99%

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Photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons

et al. 1992

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By using an electron-photon coincidence method the photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons was measured for fixed directions of the outgoing electrons and coplanar geometry. For an electron beam of 300 keV incident on a gold target, emission asymmetries up to 35% were found. Even in the case of no deflection of the decelerated outgoing electrons a nonzero photon emission asymmetry was observed. The measurements are a proper test for theories going beyond the first Born approximation.PACS numbers: 34.80.-i Bremsstrahlung emitted by an electron scattered in the Coulomb field of an atomic nucleus is a process suitable to study the coupling of radiation with matter. The aim of our experiment is to investigate the role of spin-orbit interaction in this fundamental radiation process. An important observable is the angular asymmetry of bremsstrahlung emitted by a transversely polarized electron beam where the spin direction is perpendicular to the photon emission plane, defined by the momenta of the incoming electron and the emitted photon. Disregarding the decelerated outgoing electrons such left-right photon emission asymmetries have been measured by several groups [1,2] and recently in our laboratory [3] in order to clear up discrepancies with calculations which appeared in previous work [2]. We found good agreement with the theoretical predictions of a partial wave calculation of Tseng and Pratt [4]. However, since in all these experiments only the emitted photons have been observed, the results are necessarily averaged over all electron scattering angles. Therefore the test of theoretical predictions is not as strong as it could be. To get detailed information on the elementary collision process we performed a coincidence measurement between outgoing electrons and photons emitted by a transversely polarized beam. The results of the measurement are presented in this Letter.Using unpolarized electrons such an electron-photon coincidence experiment was first performed in our laboratory in 1966 [5]. Its continuation and the work of other groups were reviewed by Nakel [6]. In all these (coplanar) coincidence measurements it proved that there is a strong angular correlation with the photons being predominantly emitted on the same side relative to the primary beam as the decelerated electrons. This feature can be used to illustrate in a very simple way the photon emission asymmetry from transversely polarized electrons observed in noncoincidence experiments by additionally taking into account the asymmetric scattering of the radiating electrons due to spin-orbit coupling (analogous to Mott scattering). However, to interpret the results of our present electron-photon coincidence experiment revealing the structure of the elementary bremsstrahlung process, the simple picture does not suffice. This becomes particularly clear in the special case where the electron detector is put into the 0° position, i.e., in the direction of the primary beam. Here the outgoi...

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confidence: 80%

Section: Photon Emission Asymmetry In the Elementary Process Of Bremsmentioning

confidence: 99%

Photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons

et al. 1992

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“…Disregarding the decelerated outgoing electrons such left-right photon emission asymmetries were measured by several groups (see, e.g., Mergl and Nakel, 1990 and references therein). However, since in all these experiments only the emitted photons were observed, the results are necessarily averaged over all electron scattering angles, implying small values of the asymmetry.…”

Section: Photon Emission Asymmetry Of Bremsstrahlung From Transverselmentioning

confidence: 99%

Photon polarization and spin asymmetry in the elementary process of bremsstrahlung

Nakel

2006

Radiation Physics and Chemistry

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“…Disregarding the decelerated outgoing electrons such left-right photon emission asymmetries have been measured by several groups [1][2][3]. However, since in all these experiments only the emitted photons have been observed, the results are necessarily averaged over all electron scattering angles.…”

Section: Pacsmentioning

confidence: 99%

“…Therefore either approximate analytic solutions or numerical methods have to be used. Tseng and Pratt [9] solved the Dirac equation numerically by means of a partial wave expansion using a relativistic local self-consistent screened central potential and calculated doubly differential cross sections that we used for comparison with our noncoincident asymmetry measurements [3]. However, this theory does not yet yield numerical results for the triply differential cross section needed for electron-photon coincidence experiments.…”

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Asymmetry of bremsstrahlung from transversely polarized electrons

Geisenhofer

Nakel

1996

Z Phys D - Atoms, Molecules and Clusters

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By using an electron-photon coincidence method the photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons was measured. For an electron beam of 300 keV incident on a gold target the asymmetry for spin up and down of the primary beam was measured for fixed directions of the outgoing electrons and photons as a function of the energy split. Asymmetries up to 30% were found. The measurements are a proper test for theories going beyond the first Born approximation. : 34.80.-i; 34.90. #q Bremsstrahlung emitted by a beam of transversely polarized electrons in the Coulomb field of an atomic nucleus shows a left-right asymmetry in the angular distribution when the spin direction is perpendicular to the photon emission plane defined by the momenta of the incoming electron and the emitted photon. PACSDisregarding the decelerated outgoing electrons such left-right photon emission asymmetries have been measured by several groups [1][2][3]. However, since in all these experiments only the emitted photons have been observed, the results are necessarily averaged over all electron scattering angles. Therefore the test of theoretical predictions is not as strong as it could be. To get detailed information on the elementary collision process [4] Mergl et al.[5] performed a coincidence measurement between outgoing electrons and photons emitted by a transversely polarized beam. The authors measured the photon emission asymmetry for spin up and down of the primary beam as a function of the photon emission angle for fixed directions of the outgoing electrons and for fixed energy split between photons and electrons.In the present paper we report on a measurement of the photon emission asymmetry for spin up and down of the primary beam as a function of the energy split between outgoing electrons and photons for fixed directions of the outgoing electrons and photons. That means the goal of the measurement is the same as in our first experiment [5], but now the theory is checked by varying different variables. For this a two-parameter energy-sharing coincidence experiment was built up.A sketch of the experimental arrangement is shown in Fig. 1. The source of the polarized electron beam (the same as in [5] and described in detail elsewhere [6]) used the photoemission of electrons from a GaAsP crystal irradiated by circularly polarized light of a helium-neon laser. After being deflected by a 90°cylindrical deflector, the extracted electrons are transversely polarized. The spin flip of the electron beam can be easily achieved by reversing the helicity of the laser light. The source is installed in a high voltage terminal of a 300-kV accelerator tube and produces a continuous transversely polarized beam with a polarization degree in the range of 35% to 40%. The degree of spin polarization was measured by a Mott analyzer put into the beam line in front of the entrance of the scattering chamber.In the Mott analyzer the electrons scattered through 120°by a gold foil were detected by a pair o...

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Measurement of the asymmetry in the emission of bremsstrahlung by transversely polarized electrons

Cited by 14 publications

References 4 publications

Photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons

Photon emission asymmetry in the elementary process of bremsstrahlung from transversely polarized electrons

Photon polarization and spin asymmetry in the elementary process of bremsstrahlung

Asymmetry of bremsstrahlung from transversely polarized electrons

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