DEVELOPMENT OF A COMPUTER CONTROLLED PIXE SYSTEM AND A SOFTWARE PACKAGE FOR X-RAY SPECTRUM ANALYSIS

Abstract

A project to automate the system for Particle-Induced X-ray Emission (PIXE) analysis at the National University of Singapore (NUS) is being undertaken. The ultimate aim of the project is to have a PIXE system which is capable of changing samples automatically and performing on-line analysis of data. The project involves the design and development of both hardware components and software packages. The work reported in this thesis is part of the joint effort of the PIXE group to automate the PIXE system.

A computer controlled sample positioning system has been constructed. Sample positioning is attained by means of a stepper motor. The stepper motor· can be controlled by using either three contact switches attacched to the stepper motor holder or the computer keyboard.

An important part of the work done in this project is the development of a novel background fitting method for PIXE spectrum background estimation. The main merit of this method is that no input of approximated parameter values is required for the iterative fitting process. The initial values of these parameters are estimated from the spectrum data in the peak-free regions which are automatically located by a peak search technique we have developed.Both the background fitting and the peak search routines constitute part of the software package APAS (Automatic PIXE Analysis Software) being developed for on-line analysis of PIXE spectra and for controlling the operation of the data acquisition electronics.

APAS is developed to run on an IBM AT compatible microcomputer, the host computer of the automated system. The host computer is linked to a multi-channel analyzer (MCA) which is used for data acquisition. The development of the modules for the transfer of spectrum data between the host computer and the MCA, for displaying a spectrum on the computer monitor screen and for plotting a spectrum on the plotter are parts of the work reported in this thesis.

An ancillary package to APAS has also been developed for the preliminary study of the oxygen content in high-Tc superconductors using the technique of PIXE and the 16O(d, p ?) 170 nuclear reaction.

This package controls the timing of the data acquisition, initiates data transfer from the MCAs to the host computer upon the completion of the data collection process and triggers the data analysis process at the end of data transfer.