A COMPUTER SOFTWARE PACKAGE FOR THICK TARGET PIXE ANALYSIS

Abstract

A computer software package has been developed for quantitative PIXE (Proton-Induced X-ray Emission) analysis of thick samples. It consists of four main programs and a number of auxiliary programs for data acquisition, X-ray yield calculation and evaluation of elemental concentrations. The package is designed for use in IBM personal computers or their compatibles and written in Turbo Pascal. One of the main programs is for data acquisition. It controls the functions of a pulse height analyser which accepts signals from the X-ray detection system. The data acquisition can be executed in cyclic mode starting with data collection followed by data transfer from the analyser to the host computer and then storing of data on the hard disk. An input file containing information such as data collection time and file names for the spectra to be stored in the hard disk needs to be planned and prepared prior to an experiment. When the program is executed, it reads this information from the input file before signaling the pulse height analyser to start data collection. The auxiliary programs associated with this main program include the input file preparation routine and the spectrum display routine. Another main program is for X-ray yields calculations. It outputs the X-ray yields for a given target composition and a specified proton energy. When invoked, the program reads the information about target composition, proton energy, geometrical factors, etc. from an input file or keyboard. It then computes the yields with a set of basic parameters, such as ionisation cross-sections, stopping powers and X-ray absorption coefficients. This program can also be used to obtain thin targets yields from measured yields of thick standards and to calculate detector efficiencies from experimental yields of standards. It can be executed in batch mode or interactive mode. The third main program is for analysing thick specimens with multi-layer compositions. This program was used to determine the phosphorus contents in silica layers which were deposited on silicon substrates. The results were compared with those obtained using the technique of RBS (Rutherford Backscattering Spectrometry) and SIMS (Secondary Ions Mass Spectrometry). PIXE is found to be a better technique for this type of analysis. The fourth program is for analysing homogeneous thick specimens of known constituents. The application of this program in the analysis of high Tc Y-Ba-Cu-O superconductors was demonstrated. For this type of specimens, the contents of Y, Ba and Cu can be directly determined from their X-ray yields. Since Oxygen is the only component whose X-rays cannot be measured, its content can be deduced indirectly. A serious drawback of this technique is that the uncertainty in the oxygen stoichiometry is relatively high.