Coincident Emission of Two Photons in Electron - Collisions: Double Bremsstrahlung and Radiative Inner - Ionization.

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 +/- 45^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 Deltak_1 = Deltak_2 = 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.