Comparative study of the electron-atom and positron-atom bremsstrahlung

Abstract

Fully relativistic treatment of the electron-atom and positron-atom bremsstrahlung is reported. The calculation is based on the partial-wave expansion of the Dirac scattering states in an external atomic field. A comparison of the electron and positron bremsstrahlung is presented for the single and double differential cross sections and the Stokes parameters of the emitted photon. It is demonstrated that the electron-positron symmetry of the bremsstrahlung spectra, which is nearly exact in the nonrelativistic regime, is to a large extent removed by the relativistic effects. 78.70.En When a charged particle traverses an atomic field, a part of its energy may be converted into radiation. This is the atomic bremsstrahlung, one of the fundamental collision processes. It is one of the important mechanisms of the energy loss in hot plasmas and in particle beams traversing thick targets. The process of the electron-atom bremsstrahlung has been extensively studied in the literature. The single and double differential cross sections of this process were tabulated [1, 2] and the polarization properties of the emitted radiation were calculated [3][4][5][6].Much less is known on the positron-atom bremsstrahlung.Several reported investigations of this process [7-9] were dealing primarily with the bremsstrahlung energy loss. It was shown that, for high energies of the incident and final projectile, the cross sections of the electron and positron bremsstrahlung are very much similar. However, when the energy of the final projectile decreases, the cross section of the positron bremsstrahlung becomes increasingly suppressed as compared to the electron one, because of the strong Coulomb repulsion between the positron and nucleus at short distances. The ratio of the positron-to-electron bremsstrahlung stopping power was the main subject of those early works.To the best of our knowledge, the angular dependence of the cross section and the polarization properties of the relativistic positron-atom bremsstrahlung have never been studied. They are becoming subjects of experimental interest today, with the advent of techniques for the production of highly polarized positrons beams [10] and the detection of polarization correlations in the bremsstrahlung radiation [11,12].In the present investigation, we make a comparative study of the positron-and electron-atom bremsstrahlung, by analyzing the double differential cross section and the polarization correlations between the incident projectile and the emitted photon. The calculation is performed within the fully relativistic approach based on the partialwave representation of the Dirac continuum states with a fixed value of the asymptotic momentum. This work extends our previous calculations of the electron-atom bremsstrahlung [5,13].

Relativistic configuration-interaction calculations of the energy levels of the 1s22l and 1s2l2l′Yerokhin1, Surzhykov2, Müller3 2017Phys. Rev. ASelf Cite3410333View full textAdd to dashboardCite

“…The dependence of the calculated results on the parameters n a , ǫ, and L max was carefully studied in order to provide estimates of the numerical uncertainty (see Tables I and II of Ref. [12] for examples of the analysis of the basis convergence).…”

“…Partly motivated by the needs described above, the goal of the present work was to extend our previous calculation of the n = 2 valence and core-excited states of Li-like ions [12] to the lower-Z region. This task turned out to be less straightforward than it seemed and required significant alterations of our original computational approach, for two reasons.…”

“…Second, the computation of the QED effects for the nuclear charges as low as Z = 6 in the same way as it was done in Ref. [12] turned out to be not possible because of technical difficulties and numerical cancellations, which grow fast as Z is decreased. Our ways for overcoming these problems are discussed in the next two sections.…”

“…In our previous investigation [12] we obtained predictive results for energies of the 1s2l2l ′ core-excited states of Li-like ions in the nuclear charge region Z = 18 − 36. By combining results obtained by the relativistic configuration-interaction method with the one-loop QED effects calculated in effective screening potentials, we were able to produce theoretical predictions with an accuracy better than what is presently achievable in experiments, see, e.g., the recent measurement of the Kα transitions in iron [13].…”

“…[12], possible calibrations are restricted to the X-ray energies beyond 3 keV. The energy range of most third-and fourth-generation synchrotron light sources, however, lies in the region of smaller X-ray energies [14].…”