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A Monte Carlo model has been developed, using the EGS4 code, to aid the design and optimization of a polarized source for in vivox-ray fluorescence(XRF) analysis of platinum (Pt). The modeled code is based on a 300 kV clinical x-ray therapy unit at Singleton Hospital. The code handles five individual components (x-ray tube, filter, polarizer, sample, and detector) which the user assembles as needed, thus allowing the facility for simulation of a wide variety of XRF systems. For each component, all the physical dimensions and materials involved are set by the user. The model includes polarized photon transport modification, K-edge fluorescent photon transport modification and K-edge sampling method for mixtures (a facility previously available only for simple compounds). It incorporates a variance reduction technique (forcing photon interaction) and uses random number generator called RANMAR. Also EGS4PICT (The EGS4 Shower Display System for PC) is built in to display a shower picture at every stage of simulation. The selected polarizermaterials tested are C, Al, Fe, Cu, Sn, and Pb. The material shape and thickness are investigated. The secondary beam collimator diameter, length, and material are also studied. Results are compared with analytical models and experiment.

Samples in the form of metallic disc are grequently used in the analysis of cast iron by x-ray emission spectrometry and give good results for common analyses (determination of carbon, suplhur, phosphorus, silicon, manganese, copper, etc.) because of the uniform distribution of the analyte in the sample. However, the results of the analysis of metallic disc samples of cast iron to which cerium had bbeen added werw poor, wich could be attributed to a non-uniform distribution of compounds which cerium formed with sulphur and oxygen. A more detailed investigation of cerium distribution in relation to its content in the sample gave evidence of the presumed non-uniform distribution. Scanning electron microscopy confirmed the presence of unequally distributed aggregates of different size containing cerium, sulphur and oxygen. On the basis of an examination and comparison of published pretreatment procedures, a modified procedure including cerium precipitation with oxalate without transformation into the oxide form is proposed. Using this method, greater reliability of the results was obtained than in the analysis of cast iron samples without pretreatment, i.e. in the disc form.