The Application of Proton induced Characteristic X-Rays to Radiography and Fluorescence Analysis

Abstract

This work investigates the feasibility of employing proton induced X-rays for radiography and fluorescence analysis. High purity characteristic X-rays, produced by bombarding metallic targets with 2.6MeV protons, were used either to take radiographs or to fluoresce biomedical samples. High contrast has been obtained by using characteristic Ag X-rays for radiographing Cd and Mo foils placed adjacently. A comparison of this contrast with the low contrast obtainable using different energy characteristic radiation or broad X-ray spectra was made. A radiography table containing parameters for the range of perspex thickness that can be radiographed using these X-rays is presented. A water-cooled rotary anode chamber has been constructed allowing manual or remote positioning of metallic targets of Ag, Mo, Zr, Cu, Fe and Ti at 45° with respect to the incident proton beam. Specimens to be analysed were sandwiched between two pieces of Kimfoil and mounted in standard 35mm slide mounts. The fluorescent X-rays from specimens were detected with a standard Si(Li) detector coupled to a multichannel analyser. Fluorescent K X-ray yields from thin calibration foils of KCl, Ti, Mn, Co, Cu, Ge, Y and Mo were employed to calibrate the system. Repeated measurements on these calibrators and using thin Ti wire as X-ray beam monitor verified the system reproducibility. A system detection limit of (10-6-10-8) g.cm2 has been obtained for elements with Z numbers between 22 and 39, present in a 30mg.cm-2 biological matrix irradiated for 20 minutes. The accuracy of the system has been evaluated by comparing the measured elemental concentration of NBS bovine liver with the certified values. The versatility of this technique was demonstrated by analysing blood samples and hair samples of hyperactive children. Suggestions for improving the analytical capabilities of the present system are discussed.