Design considerations for transmission x-ray tubes operated at diagnostic energies

A low-energy expansion of the EGS4 Monte Carlo code system was used in studies that aimed to understand photon production in transmission target x-ray tubes. In each case, foil targets were modelled with incident electrons of a few tens of keV. The production of bremsstrahlung and fluorescence radiation at different depths was studied and the angular distribution of radiation analyzed. The characteristics of x-ray spectra measured along the beam path, for targets of different materials, thicknesses and several beam energies have been determined and the relation between efficiency and the fluorescence-to-bremsstrahlung ratio is shown.