MeV Electrons In Silicon Research Articles

Spectral-angular and polarization properties of near-axis channeling radiation of 31 MeV electrons in silicon

The spectral-angular and the linear polarization properties of channeling radiation emitted by 30.8 MeV electrons incident on a 13 μm thick silicon crystal at small angles with respect to various major crystal axes have been investigated. The transition from axial to planar channeling radiation properties is well described by a two-dimensional many-beam calculation based on a periodic string potential. At energies above the strongest planar channeling radiation lines coherent bremsstrahlung linearly polarized perpendicular to the polarization of the corresponding planar channeling radiation is observed and found to be well reproduced by the model calculations. Axial channeling radiation of the 〈1 1 0〉 axis shows a small amount of linear polarization due to the `double-well' potential in agreement with the calculations.

Measurement of the linear polarization of channeling radiation in silicon and diamond.

Utilizing 90{degree} Compton scattering the linear polarization of channeling radiation produced at the superconducting accelerator S-DALINAC with 62 MeV electrons in silicon and diamond has been measured in the energy range between 50 and 400 keV. Planar channeling radiation due to transitions involving transversal bound as well as unbound states is completely linearly polarized perpendicular to the channeling plane. Axial channeling radiation does not show linear polarization.

Toward a three-dimensional treatment of channeling radiation

Abstract Many authors have studied channeling radiation theoretically by means of the so called many beam approach. For axial channeling this approach tends to involve rather large eigenvalue problems if high accuracy is desired. With the extension to three-dimensional problems in mind we have therefore investigated the possibilities for a more efficient solution of these eigenvalue problems. The Lanczos algorithm [2] used in the preparation of Fig. 1 provides a substantial reduction of the numerical effort. We have also obtained some preliminary results for three-dimensional corrections to the tranverse problem. These corrections were found to be three-dimensional rather than longitudinal in character and tend to reduce the photon energy. The corrections are smaller than 1 percent for 4 MeV electrons in silicon. A more thorough investigation of these effects for the low energy part of the spectrum and a study of their impact on the high energy radiation [3] is now in progress. The conventional transverse many beam approach based on the Lindhard continuum approximation does not describe the latter effect.

Measurement of the linear polarization of channeling radiation

Using a Compton polarimeter, the linear polarization of channeling radiation of 63 MeV electrons in silicon has been measured at the superconducting electron linear accelerator S-DALINAC. Planar channeling radiation due to transitions between transversal bound states as well as for free-bound transitions is completely linear polarized. Axial channeling radiation has no component of linear polarization.

Measurement of the polarization of channeling radiation from 65 MeV electrons in silicon

At the new superconducting electron linear accelerator S-DALINAC polarization of channeling radiation from 65 MeV electrons in silicon has been measured for transitions between discrete transversal bound states for the first time. Using a Compton-polarimeter the linear polarization was determined for the (100) and the (110) plane. Within errors the channeling radiation is completely polarized in agreement with theoretical expectation.

Measurement of Planar Channeling Radiation from 19.2 MeV Electrons in Silicon Using a Microtron

AbstractAn experimental set‐up for studying radiation of channeled relativistie electrons in single crystals is designed. The source of electrons is a 19.2 MeV microtron. With the help of a mirror‐symmetric achromatic magnetic system a beam of electrons wih an angular divergence less than 0.3 mrad is transported to a single crystal target. The measured radiation spectra at planar channeling of 19.2 MeV electrons in silicon single crystals 3, 7, and 18 μm thick are presented and compared with the calculated spectra. Theoretical calculations are based on a newly developed method using a complex potential for describing the line broadening.

Channeling radiation from 72 MeV electrons in silicon: transition from planar to axial channeling

Channeling radiation from 72 MeV electrons was measured using the new superconducting electron accelerator at Darmstadt (S-DALINAC). Radiation spectra were obtained for electrons channeled along the main axes and planes in a 13 μm thick silicon crystal. Good agreement between theory, i.e. many-beam calculations, and experiment can be reported for planar channeling radiation. The radiation at the transition from planar channeling in the (110) plane and the (111) plane to channeling along the 〈110〉 axis was also investigated. The spectra show a continuous change from pure planar radiation to the more intense axial channeling radiation, with new lines occurring in the (110) spectra for angles between the electron direction and the 〈110〉 axis smaller than about 10 mrad. The line energies depend on the angle to the axis and range from about 50 to several hundred keV.

Planar-Channeling Radiation and Coherent Bremsstrahlung for MeV Electrons

The radiation from MeV electrons penetrating a single crystal has been studied. Coherent bremsstrahlung and channeling radiation are discussed theoretically with particular emphasis on the relation between the two phenomena. The close connection becomes clear when the coherent bremsstrahlung is interpreted as radiation from transitions between free states of motion relative to a set of planes, while the planar-channeling radiation is due to transitions between bound states in the planar averaged potential. Detailed calculations of the one-dimensional band structure for such states have been carried out for the case of 4 MeV electrons in silicon, which has also been studied experimentally. In the measured forward-radiation spectra, free-to-free, bound-to-bound, and also free-to-bound transitions have been identified, and the observed energies and intensities are in good agreement with the predictions.

Coherent bremsstrahlung and channeling radiation from MeV electrons in silicon and gold

We report the observation of coherent bremsstrahlung in the range 1-25 keV from electrons incident at small angles to prominent crystal planes of thin silicon and gold crystals. We also find x radiation produced by electrons making transitions between bound quantized axial-channeling orbits in silicon and gold. We find no radiation above 1 keV from any bound planar-channeling states for either silicon or gold at electron energies up to 3.0 MeV.

Axial bloch wave channeling of 15 MeV electrons in silicon

Experimental transmission profiles of 15 MeV electrons in silicon [111] have been measured. They show a fine structure which is not reproduced by a classical calculation. On the basis of the dynamical theory of diffraction a 331-beam calculation has been performed to interpret the experimental curves.