2-PHOTON EMISSION PROCESSES IN ELECTRON-ATOM INTERACTIONS

We will describe the experimental techniques and preliminary results of an on-going three-parameter coincidence experiment in which two-photon spectra are obtained by electron bombardment of target foils of selected thicknesses. The atomic number of the foils ranges from Z = 26 to 82. Incident electrons have been provided both by the beta spectrum of a Pm-147 source and by a 50-150 keV electron beam from an accelerator. Processes considered to date include: double bremsstrahlung, double innershell ionization, and coherent emission of both a characteristic and a continuum X-ray. The cross sections for these two-photon processes are much smaller than the processes that produce single photons in the target. This can lead typically to a large accidental rate in the accelerator experiment, or accentuate the need for a target thickness study of the real rate in the source experiment where thicker targets have been used to increase the statistics.