SIGNAL-TO-BACKGROUND IN EPMA - MEASUREMENT AND MONTE-CARLO CALCULATION

By the method of Monte Carlo calculation, the dependence of the signal-to-background ratio of detected X-rays on the energy of electrons as well as on the thickness of the sample was calculated. The range of energy was 40 divided-by 120 keV, the range of thickness was approximately 8 divided-by 80 mug/cm2 (40 divided-by 400 nm at density rho = 2 g/cm3). The results were compared with measurements in electron microscope on thin resin standard for biological microanalysis. The measured dependence of signal-to-background ratio on the energy of electrons has the maximum at 80 keV, the calculated one changes at increased thickness from a monotonic form to one with a maximum at a particular thickness. The absolute values (Hall correction procedure was used for measured values) differs mainly at the highest energy used (120 keV); the difference is probably caused by unproper correction of measured value of background at this energy. Simultaneously, the source distribution of emitted X-ray photons is calculated. Its knowledge gives the possibility to estimate simply the interaction volume diameter and, by this way, to determine the spatial resolution of electron probe X-ray microanalysis.