Computer method for qualitative and semicuantitative x-ray fluorescence analysis of geological samples

Abstract

The X-ray fluorescence spectrometry is a well known techniq1.1e for the quantitative analysis of large series of geological samples. Moreover, this technique is extremely well suite_d to qualitative and semiquantitative analysis'. of them, but its systematic application is rather limited, mainly in the wavelength-dispersive X-ray spectrometry,· because. of the long time required for the Spectra interpretation step. This process can be simplified and accelerated. by means of microcomputers. In this paper we describe the preparation of a s~t of programs which might allow the use of srriall-capaci ty computers for this type of analysis without being on line with the spectrometer .. In this method, the analyses are carried out starting from the spectra taken either from the spectrometer recorder or directly by the computer if this option .is available. The programs have been written in GWBA~IC for an Olivetti M-24 personal computer (with .MS-DOS operating system and may also be runned in an IBM compatible personal computer), and their main functions are: Input the spectra data. The data corresponding to the sample to be analysed are stored in a sequential "Sample Data File" and associated Subfiles. In the Sample Data File, the sample identification, X-ray tube used, number of recorded spectra and analysing crystals used, order of spectra analysis, etc., are stored. In the Subfiles, all data corresponding to each recorded spectrum and the results obtained in its qualitative analysis are stored. The X-ray data (peak posj.tion and intensity) can be loaded manually or automatical}Y (only if the computer can receive the intensity values obtained in the spectrum scanning). The FXAI program allows the automatic loading of intensity values of any X-ray spectrometer directly by means of a DT2805 analog and digital I/0 board; this board allows analog inputs (i.e. the electric pulses that arrive to recorder) with no other interface. Preparation of an X-ray emission lines and absorption edges table. The FXT program allows to prepare and use the FXTAB.DAT file. In this data file, the Ka, Kal, Ka2, Kb, Kbl, Kb2, La, Lal, La2, Lbl, Lb2, Lb3, Lb4, Lb5, Lb6, Lgl, Lg2, Lg3, Ll, Ln, Mal, Ma2, Ma and Mb emission lines (of orders 1 to 5, and rel~tive intensity ~ 1) and the AK, ALl, AL2 and 0 AL3 absorption edges, whose wavelengths range between 0.2 and 25 A, have been stored for the elements of atomic numbers 9 to 83, 90 and 92. The lines (emission lines and absorption edges) are arranged at increasing wavelength values. Qualitative analysis. The FXQUAt program is designed for the qualitative analysis of fluorescence spectr'a recorded with any analysing crystal and using any wavelength-dispersive X-ray spectrometer. The analysis is carried out in four stages: (1) peak line assignment; (2) identification of the elements; (3) setting up the selection criteria for each identified element; and (4) final results list. Semi quantitative analysis. The; FXSQ program permits to compare,' in the computer display, the recorded wa\(elength spectra of the unknown sample and prospective known materials.