FUNDAMENTAL PARAMETER METHOD FOR THE LOW ENERGY REGION INCLUDING THE CASCADE EFFECT AND THE PHOTOELECTRON EXCITATION, N. Kawahara, T. Shoji, T. Yamada, Y. Kataoka, B. Beckhoff, G. Ulm, M. Mantler, pp. 511-516

We have demonstrated the cascade effect and the secondary photoelectron excitation effect by means of Cr-L line measurements by using monochromatic radiation of high spectral purity and well-known flux provided by two beamlines of the Physikalisch-Technische Bundesanstalt (PTB), Germany's national institute of metrology at the electron storage ring BESSY II. The plane grating monochromator beamline for undulator radiation covers the energy range from 30 eV to 1.9 keV, and the four-crystal monochromator beamline for synchrotron radiation from 1.75 keV to 10.5 keV. The Cr-L fluorescence intensities show a considerable jump at Cr-K edge energy as the source photon energy rises, indicating the magnitude of the cascade effect. The fundamental parameter method including the cascade effect and the secondary photoelectron excitation effect shows good agreement with the measurement. The evaluation of this computation method for the measurement carried out with a conventional XRF spectrometer also shows good performance of the calculation. INTRODUCTION Low-energy characteristic X-ray measurements play a key role in X-ray fluorescence (XRF) analysis of light elements and of thin layer materials. Besides primary excitation by incident Xrays and secondary excitation by fluorescent X-rays, there are other secondary processes which contribute to low-energy characteristic X-ray emissions. One of them is the excitation by photoelectrons, which has been introduced into a fundamental parameter method 1 and evaluated experimentally . Another process is the emission of L-series X-rays following radiative and nonradiative relaxations of the K-shell ionization. This “cascade” effect on L-series X-ray emission occurs when the energy of source X-rays is higher than the K-shell binding energy, i.e. in a measurement of L-lines of low energy using an XRF spectrometer with, for example, a Rh-target end-window tube. The contribution of the cascade effect exceeds that of direct excitation in these situations. Obviously, this effect can contribute also to M-series X-ray emission. Although this cascade effect was studied already , neither a recent implementation in a fundamental parameter software nor experimental evaluation have been reported. The extension of XRF application, however, requires measurements of Lor M-lines, in which the cascade effect arises. Copyright (c)JCPDS-International Centre for Diffraction Data 2002, Advances in X-ray Analysis, Volume 45. 511