Coincident emission of two photons in electron-atom collisions: double Bremsstrahlung and radiative inner-shell ionization

Abstract

The differential cross section for the coincident emission of two x-ray photons induced in the collision of electrons with target atoms has been measured. A two-photon emission process may be defined as any process which can produce the correlated emission of two photons simultaneously. A measurement of the differential cross sections for the two-photon processes of double bremsstrahlung and separately, double bremsstrahlung combined with radiative inner-shell ionization, has been performed using a coincidence technique in which thin-film targets are bombarded by a 70 keV electron beam and coincident photons are detected at $\pm$45$\sp\circ$ to the incident beam direction. Data are presented for Al, Cu, Ag, Tb and U for the process of double bremsstrahlung for a photon energy window of $\Delta$k$\sb1$ = $\Delta$k$\sb2$ = 10-30 keV. For the processes of double bremsstrahlung and radiative inner-shell ionization combined, data are presented for Fe, Cu, Y and Ag for one photon within a narrow energy window (a few keV) centered on the characteristic K x-ray of the target atom and the second photon in a window from 15 to 25 keV.