Παραγωγη Μονοχρωματικων Δεσμων Ακτινων Χ Απο Πρωτονια Και Χρηση Τους Σε Αναλυτικες Εφαρμογες

Abstract

The possibility of using protons with energy of a few MeV for the production of monoenergetic x-ray beams with application to the x-ray fluorescence analysis (XRF), was investigated theoretically and experi mentally. The yield of the characteristic x-rays, produced when a pure target is bombarded by protons, was calculated (at reflection or trans mission geometry) and its dependence on various experimental param eters (proton energy, angle of incidence) was studied. An experimen tal arrangement with small intercomponent diastances (source-sampledetector) and suitable for sample irradiation and detection of the fluo rescent x-rays in vacuum, was constructed. The background produced in the Si(Li) detector by the γ-rays, originating from the primary target, was studied as a function of the proton energy, for the purpose of finding an optimum energy. For calibration purposes, a number of thin targets were made and their thickness was measured employing independent methods. Also, in order to improve the accuracy of the calibration pro cedure, the exact theoretical calculation of the enhancement of the XRF intensity, due to the scattering inside the sample of either the exciting or the characteristic radiation, was performed. A software program for the quantitative analysis of homogeneous samples was developed, which take into account all second order corrections to the XRF intensity and also having the advantage of using simultaneously data from many x-ray sources. The concentrations of various elements contained in standard samples (biological, clays, steels) were measured with good agreement with the certified values. Also, the sensitivity of the method in the anal ysis of trace elements contained in biological samples was investigated with the final conclusion that minimum detection limits lower than 1 ppm can be achieved.