Signal-to-background in EPMA: Measurement and Monte Carlo calculation

Abstract

Abstract. 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 -120 keV, the range of thickness was approximately 8 -80 #g/cm 2 (40 -400 nm at density p = 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.Key words: electron probe, X-ray microanalysis, electron scattering simulation, X-ray production, biological thin sections.In electron probe X-ray microanalysis (EPMA) Monte Carlo methods (MCC) are currently used for calculation of electron scattering [1,2] as well as of intensity of emitted X-ray radiation [3,4]. MCC gives the possibility to calculate and estimate the non-or hardly measurable parameters, influencing the results of analyses (e.g., the size of interaction volume, the X-ray lateral and depth distribution, the backscatter coefficient, etc). Usually, the correctness of the model and the accuracy of calculations of some parameters, at least those easily measurable, would be checked by experiment.