Sequential X-Ray Fluorescence Analysis (XRF)
Description of method:
XRF is a nondestructive analytical technique for the identification and determination of the concentration of elements in solids, powder samples and liquids.
When atoms are excited by high-energy X-ray photons, electrons in the form of photoelectrons are knocked out of the zone of the inner electron shells. The instable electron vacancies thus produced in one or several electron shells are replaced by electrons from the outer shells emitting the excess energy in the form of secondary X-ray photons. This phenomenon is known as "fluorescence". The energy of the emitting fluorescence photon is characteristic of the corresponding element (E = hc/l). Moreover, the number of emitting photons is proportional to the concentration of the element in the sample.
Measurement technique and instrumental equipment:
A sequential spectrometer with a 3 kW Rh front window valve, 35 mm beam-Ø (capable of being narrowed to 1mm-Ø in the pentagrid), with its own cooling circuit with conductivity control, 12-fold sample changer is used. The fluorescent radiation is spectrometrically decomposed by different analyser crystals (Bragg's law) and the spectra are recorded by stepwise scanning of the angle of diffraction zone. The detector for "hard X-rays" (Ti-U) is a scintillation counter and for "soft X-rays" (O-Ti) a proportional counter.
A qualitative analysis is performed by comparing the measured spectrum with a stored line library. For the semiquantitative analysis, a fundamental-parameter program using stored element sensitivity libraries is used. Matrix influences and material impurities, such as sample carriers and fixation materials, are also taken into account.