Linear polarization of photons produced by the electron plane channeling in a silicon crystal

Abstract

We present the results of the polarization and intensity measurements versus photon energy ¿ MeV for the photon beam produced by the electron plane channeling with the energies 1.2 and 1.5 GeV in silicon crystals 500 m and 290 m thick along the (110) plane. The comparison with results of another research group and theoretical calculations indicate a qualitative agreement. The correlation between the shape of the radiation intensity spectrum and its polarization energy dependence is observed. I IntroductionRecent achievements and progress of x-ray and gamma ray microtomography, x-ray and gamma ray optics and their imaging properties [1,2], especially in the case of material studies and non destructive tests, as well as classical studies of polarization phenomena of nuclear reactions near the threshold, which give extremely important information about the structure of nuclear matter and nuclear forces, stimulated this attempt to review the experimental methods of polarized monochromatic photon production, specifically the photon beam produced by electron channeling in crystals.There is a relatively small number of methods of polarized photon production in the energy range of 1 -100 MeV. Considering the physical principles they are based on, these methods could be classified as following: 1) angular selection of electron bremsstrahlung radiation; 2) Compton scattering of laser beam on ultrarelativistic electrons; 3) coherent bremsstrahlung radiation of electrons in monocrystals. Each of these methods has its own disadvantages. The first one gives very small polarization degree and not monochromatic intensity spectrum. The second method has good monochromaticity and practically 100% polarization, but low intensity and, in order to obtain with this method a beam suitable for practical work, one needs a storage ring, where electron beam frequently cross the region of interaction during the time of laser outburst. The third method gives higher intensity of photons than the others, a its quasimonochromatic spectrum has the polarization of approximately 50%.Twenty years ago the high polarization degree was found for photon beams produced by high-energy electron plane channelling in crystals [3]. Such photon beam has the intensity several times higher than ever produced with the mentioned above method No. 3. The maximum of this spectrum is located in the giant resonance region of atomic nuclei. These specific characteristics make such photon beam very suitable for the study of atomic nuclear structure as well as dynamic characteristics of nuclear reactions induced by polarized photons. It is clear that in this case one has to know very precisely the intensity and the polarization for the given photon beam energy. The beam intensity was actively investigated by the theoreticians and experimentalists during the last years, but the study of photon polarization has been started recently. Only few experiments were dedicated to the measurements of photon beam polarization [4,5]. The high polarization degree P = 0,6 -0,9 near th...