- Email: [email protected]
Quantitative X-ray fluorescence analysis at the ESRF ID18F microprobe
Nuclear Instruments and Methods in Physics Research B 199 (2003) 396–401 www.elsevier.com/locate/nimb
Quantitative X-ray fluorescence analysis at the ESRF ID18F microprobe B. Vekemans a,*, L. Vincze a, A. Somogyi a, M. Drakopoulos b, L. Kempenaers a, A. Simionovici b, F. Adams a a
MiTAC, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium b ID22 ESRF, BP 220-F-38043, Grenoble Cedex, France
Abstract The new ID18F end-station at the European synchrotron radiation facility (ESRF) in Grenoble (France) is dedicated to sensitive and accurate quantitative micro-X-ray fluorescence (XRF) analysis at the ppm level with accuracy better than 10% for elements with atomic numbers above 18. For accurate quantitative analysis, given a high level of instrumental stability, major steps are the extraction and conversion of experimental X-ray line intensities into elemental concentrations. For this purpose a two-step quantification approach was adopted. In the first step, the collected XRF spectra are deconvoluted on the basis of a non-linear least-squares fitting algorithm (AXIL). The extracted characteristic line intensities are then used as input for a detailed Monte Carlo (MC) simulation code dedicated to XRF spectroscopy taking into account specific experimental conditions (excitation/detection) as well as sample characteristics (absorption and enhancement effects, sample topology, heterogeneity etc.). The iterative use of the MC code gives a Ôno-compromiseÕ solution for the quantification problem. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 07.85.)m; 07.85.Qe; 02.70.Lq Keywords: Microanalysis; Synchrotron X-ray fluorescence analysis; Quantification; Monte Carlo simulation
1. Introduction A new user end-station ID18F is constructed at the European synchrotron radiation facility (ESRF) in order to improve the capabilities of micro-SRXRF as a method for quantitative nondestructive elemental analysis of microheterogeneous materials [1]. The characteristics of the third
*
Corresponding author. Tel.: +32-3-820-2363; fax: +32-3820-2376. E-mail address: [email protected] (B. Vekemans).
generation synchrotron source of X-rays should realize an average accuracy of quantification in the range 3–5% for micrometer-sized objects at concentrations at or below the ppm level, limited by the accuracy of the physical constants governing the X-ray interaction process. During the beam line design and construction special attention has been paid to the stability of the set-up and to the precise monitoring of the microscopic X-ray beam impinging on the sample in terms of intensity and to a lesser extent degree of linear polarization. Due to the relatively low resolving power of the employed Si(Li) detector, the process of evaluating
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 1 3 9 6 - 4
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
XRF spectra (i.e. accurately determining the net X-ray intensities) is prone to many errors and requires dedicated software. Our laboratory developed for this purpose a software package called AXIL (analysis of X-rays by iterative least squares) [2,3] which is based on the non-linear least-squares fitting of a mathematical model of the XRF spectrum to the experimental data. The resulting net X-ray intensities are then converted to concentrations usually by means of a fundamental parameter procedure (FPM) [4]. Another approach is based on Monte Carlo (MC) simulations for dealing with the energy and spatial distribution of the X-ray microbeam, the interaction between the exciting photons and the sample taking into account the geometrical arrangement of the set-up [5–8]. In this work, this quantification scheme is verified and applied to investigate the short- and long-term stability of the ID18F microprobe by evaluation of repetitive XRF measurements on standard reference materials.
2. XRF spectrum evaluation Using the spectrum evaluation module of the AXIL program the analyst has to build a mathematical model ymodel ðiÞ (i.e. the spectrum region to be fitted, the selection of a suitable background compensation method and the selection of a number of X-ray line groups, e.g. Ca–K, Ba–LII , Ta–LIII ), ymodel ðiÞ ¼ yback ðiÞ þ
X j
Aj
Nj X
Rjk yj ði; Ejk Þ:
ð1Þ
k¼1
The characteristic line group j consists of Nj lines (index k) at energy Ejk and has the total group intensity Aj . The intensity of the kth line within the group equals Rjk Aj where Rjk is the relative line ratio of that line in the group. The individual lines are modeled as Gaussian functions yj ði; Ejk Þ centered around Ejk . In a next step, the parameters of the constructed model are then optimized by means of a non-linear least-squares strategy in order to describe the experimental spectrum yðiÞ. This is done by using a modified Marquardt algorithm to minimize the
397
weighted sum of differences v2 between the experimental data yðiÞ and the user defined model function [3]. For micro-XRF data, next to resolving peak overlap, the correct background compensation in the neighbourhood of intense matrix lines is found to be valuable [9].
3. XRF Monte Carlo simulation The MC technique is applied to simulate the relevant photon–matter interactions which occur when the analyzing microbeam illuminates the sample. The types of interactions taken into consideration are the (i) photoelectric effect, (ii) Rayleigh (elastic) scattering, (iii) Compton (inelastic) scattering, (iv) photoelectron bremsstrahlung. A detailed description of the code can be found elsewhere [5–7]. Taking into account the solid angle and the detector response of the modeled detector, the complete spectral response can be calculated including the scattered background as well as the fluorescence lines.
4. Quantification by means of XRF Monte Carlo simulation The quantification is done by extraction of Xray line intensities of the experimental spectrum and the MC simulation spectrum for a given sample composition. The simulated composition is then adjusted until the MC simulation X-ray line intensities agree with the experimental X-ray line intensities (see Fig. 1), ðkþ1Þ
Cj
ðkÞ
¼ Cj ðkÞ Cj
ðkÞ Ij;sim
Ij;exp ; Pn ðkÞ Il;exp ðkÞ l¼1 Cl
ð2Þ
Il;sim
where is the calculated concentration of element j after k iterations; Ij;exp is the experimental ðkÞ and Ij;sim is the net intensity of element j. The adjustment of an element concentration is stopped when its relative intensity deviation ðjðIj;exp ðkÞ Ij;sim Þ=Ij;exp jÞ is below 0.5%, or if the simulated intensity deviates from the experimental intensity within the statistical uncertainty.
398
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
Fig. 1. The quantification scheme based on MC simulation uses the AXIL module to convert the experimental and simulated spectra into X-ray line intensities which are then used as input for a detailed MC simulation code dedicated to XRF spectroscopy.
Fig. 2. NIST SRM 613 (trace element in glass) experimental spectrum ( ) with the corresponding background derived with the AXIL spectrum evaluation module (- - -). The MC simulated spectrum (—) is adjusted by scaling its Sr peak to the experimental Sr peak.
Fig. 3. Repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) standard (see Fig. 2) at the end of a synchrotron run (time <0 h) and the next synchrotron run (time >0 h). Variation of (a) Sr line intensity and its normalization by (b) synchrotron current (SRCUR), (c) ionization chamber (ION), (d) mini-ionization chamber (MINI ION), (e) Compton scatter peak (Compt) and (f) 1/2 h interval statistical variation (error bars equal to the measured standard deviations) after normalization with mini-ionization chamber (MINI ION).
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
5. Experimental The ID18F spectrometer is situated in the last experimental hutch of the ID18 beamline at the ESRF. The primary beam is tunable in the 6–28 keV range by means of undulators and made monochromatic by means of a fixed exit double crystal Si(1 1 1) monochromator. The beam is then further confined to sizes down to typically 5 5 lm using compound refractive lenses (CRLs). The characteristic X-rays are detected with a Si(Li) detector of Gresham in combination with the CANBERRA 2026 spectroscopy amplifier/9635 ADC. A detailed description of the beamline can be found elsewhere [1]. The intensities of the incoming and the focused beam are monitored respectively by an ionization chamber and a miniature ionization chamber. The latter consists of a 50 lm diameter pinhole and was specially de-
399
veloped at the ESRF to measure the focused beam intensity just before its impact on the sample [10]. In order to investigate the stability of the set-up repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) standard were performed at the end of a synchrotron run (140 50 s) and continued in the next run (300 50 s). For this purpose a 63element CRL was applied to achieve a 1:8ðVÞ 14ðHÞ lm beam at 21 keV.
6. Results and discussion ID18F delivers a microbeam with a degree of polarization which is better than 99.5% [1]. By this, the experimental data feature an excellent peakto-background ratio. In case of complex spectra however (e.g. Fig. 2) a dedicated spectrum
Fig. 4. Individual quantitative results of the measurements of the same spot on the NIST SRM 613 when the quantification scheme shown in Fig. 1 is used. Mean values (m) and standard deviations (s) for the total series of spectra are indicated. If applicable, certified values are indicated by the dashed line together with the relative deviations from the calculated concentration values.
400
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
evaluation routine is still needed to resolve peak overlap and to compensate for the background. The repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) show variation of the elemental line intensities during the synchrotron runs. Fig. 3 indicates that next to the scatter, the response of the mini-ionization chamber which monitors the beam intensity just before the beam hits the sample can be applied to normalize individual spectra during and between synchrotron runs. Considering 1/2 h intervals, the intensities then vary according to the counting statistics and do not differ statistically in time. The MC quantification scheme described above was applied on the NIST SRM 613 spectra from the repetitive measurements giving quantification results shown in Fig. 4. Considerable care and effort is made by NIST into the manufacturing of this standard to ensure homogeneity. The certificate reports the addition of nominal trace con-
centrations of 50 ppm and a target level of precision and accuracy for certification of 5% or better. The matrix is 72% SiO2 , 12% CaO, 14% Na2 O and 2% Al2 O3 . To start the quantification procedure shown in Fig. 1, the concentrations of the trace elements were set to 50 ppm, except for Sr that was selected as an internal reference element (fixed to its certified concentration, i.e. 78.4 ppm, during the actual quantifications). With the use of the internal reference line, no external standard was necessary for the quantification. Fig. 4 shows relative concentration deviations of 8–10% are achieved between certified and calculated concentrations in case of medium or large line peaks. Large deviations are due to the poor statistical quality of the small line peaks. The maximum number of iterations per spectrum was set to 15 by taking the average composition of the last five iterations. The average number of iterations was 12 corresponding to approximately 11 min on a PC Celeron 500 MHz.
Fig. 5. Statistical 1/2 h interval variation of the individual quantitative data shown in Fig. 4. The error bars are equal to the measured standard deviation on the derived concentrations within 1/2 h intervals.
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
The 1/2 h interval quantitative results of the individual quantification data are shown in Fig. 5 and confirm again that the concentrations do not differ statistically in time.
401
time. Applying the quantification scheme to this series of short measurements an accuracy of 8– 10% is achieved for medium or large line peaks in an acceptable time of approximately 11 min on a PC Celeron 500 MHz.
7. Conclusions References A two-step quantification scheme based on a non-linear least-squares fitting algorithm (AXIL) and a detailed MC simulation code for XRF spectroscopy is applied to investigate the stability of the ESRF ID18F beamline. In spite of the excellent background reduction as the result of the high degree of linear polarization, a reliable spectrum evaluation method is needed to resolve peak overlap and to compensate for the remaining background in the spectra. The derived elemental intensities must be normalized by means of the scatter information of the acquired spectrum or the response of the mini-ionization chamber, specially developed at the ESRF for this purpose. The repetitive short point measurements on the homogeneous NIST SRM 613 standard reveal that the concentrations do not differ statistically in
[1] A. Somogyi, M. Drakopoulos, L. Vincze, B. Vekemans, C. Camerani, K. Janssens, A. Snigirev, F. Adams, X-Ray Spectrom. 30 (2001) 242. [2] B. Vekemans, K. Janssens, L. Vincze, F. Adams, P. Van Espen, Spectrochim. Acta 50B (2) (1995) 149. [3] P. Van Espen, K. Janssens, J. Nobels, Chemom. Int. Lab. Syst. 1 (1986) 109. [4] F. He, P. Van Espen, Anal. Chem. 63 (1991) 2237. [5] L. Vincze, K. Janssens, F. Adams, M.L. Rivers, K.W. Jones, Spectrochim. Acta B 50 (1995) 127. [6] L. Vincze, K. Janssens, F. Adams, Spectrochim. Acta B 48 (1993) 553. [7] L. Vincze, K. Janssens, B. Vekemans, F. Adams, J. Anal. At. Spectrom. 14 (3) (1999) 529. [8] L. Vincze, K. Janssens, B. Vekemans, F. Adams, Spectrochim. Acta B (1999) 1711. [9] K. Janssens, B. Vekemans, F. Adams, P. Van Espen, P. Mutsaers, Nucl. Instr. and Meth. B 109/110 (1996) 179. [10] M. Kocsis, J. Surr, ESRF in-house development.
Quantitative X-ray fluorescence analysis at the ESRF ID18F microprobe B. Vekemans a,*, L. Vincze a, A. Somogyi a, M. Drakopoulos b, L. Kempenaers a, A. Simionovici b, F. Adams a a
MiTAC, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium b ID22 ESRF, BP 220-F-38043, Grenoble Cedex, France
Abstract The new ID18F end-station at the European synchrotron radiation facility (ESRF) in Grenoble (France) is dedicated to sensitive and accurate quantitative micro-X-ray fluorescence (XRF) analysis at the ppm level with accuracy better than 10% for elements with atomic numbers above 18. For accurate quantitative analysis, given a high level of instrumental stability, major steps are the extraction and conversion of experimental X-ray line intensities into elemental concentrations. For this purpose a two-step quantification approach was adopted. In the first step, the collected XRF spectra are deconvoluted on the basis of a non-linear least-squares fitting algorithm (AXIL). The extracted characteristic line intensities are then used as input for a detailed Monte Carlo (MC) simulation code dedicated to XRF spectroscopy taking into account specific experimental conditions (excitation/detection) as well as sample characteristics (absorption and enhancement effects, sample topology, heterogeneity etc.). The iterative use of the MC code gives a Ôno-compromiseÕ solution for the quantification problem. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 07.85.)m; 07.85.Qe; 02.70.Lq Keywords: Microanalysis; Synchrotron X-ray fluorescence analysis; Quantification; Monte Carlo simulation
1. Introduction A new user end-station ID18F is constructed at the European synchrotron radiation facility (ESRF) in order to improve the capabilities of micro-SRXRF as a method for quantitative nondestructive elemental analysis of microheterogeneous materials [1]. The characteristics of the third
*
Corresponding author. Tel.: +32-3-820-2363; fax: +32-3820-2376. E-mail address: [email protected] (B. Vekemans).
generation synchrotron source of X-rays should realize an average accuracy of quantification in the range 3–5% for micrometer-sized objects at concentrations at or below the ppm level, limited by the accuracy of the physical constants governing the X-ray interaction process. During the beam line design and construction special attention has been paid to the stability of the set-up and to the precise monitoring of the microscopic X-ray beam impinging on the sample in terms of intensity and to a lesser extent degree of linear polarization. Due to the relatively low resolving power of the employed Si(Li) detector, the process of evaluating
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 2 ) 0 1 3 9 6 - 4
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
XRF spectra (i.e. accurately determining the net X-ray intensities) is prone to many errors and requires dedicated software. Our laboratory developed for this purpose a software package called AXIL (analysis of X-rays by iterative least squares) [2,3] which is based on the non-linear least-squares fitting of a mathematical model of the XRF spectrum to the experimental data. The resulting net X-ray intensities are then converted to concentrations usually by means of a fundamental parameter procedure (FPM) [4]. Another approach is based on Monte Carlo (MC) simulations for dealing with the energy and spatial distribution of the X-ray microbeam, the interaction between the exciting photons and the sample taking into account the geometrical arrangement of the set-up [5–8]. In this work, this quantification scheme is verified and applied to investigate the short- and long-term stability of the ID18F microprobe by evaluation of repetitive XRF measurements on standard reference materials.
2. XRF spectrum evaluation Using the spectrum evaluation module of the AXIL program the analyst has to build a mathematical model ymodel ðiÞ (i.e. the spectrum region to be fitted, the selection of a suitable background compensation method and the selection of a number of X-ray line groups, e.g. Ca–K, Ba–LII , Ta–LIII ), ymodel ðiÞ ¼ yback ðiÞ þ
X j
Aj
Nj X
Rjk yj ði; Ejk Þ:
ð1Þ
k¼1
The characteristic line group j consists of Nj lines (index k) at energy Ejk and has the total group intensity Aj . The intensity of the kth line within the group equals Rjk Aj where Rjk is the relative line ratio of that line in the group. The individual lines are modeled as Gaussian functions yj ði; Ejk Þ centered around Ejk . In a next step, the parameters of the constructed model are then optimized by means of a non-linear least-squares strategy in order to describe the experimental spectrum yðiÞ. This is done by using a modified Marquardt algorithm to minimize the
397
weighted sum of differences v2 between the experimental data yðiÞ and the user defined model function [3]. For micro-XRF data, next to resolving peak overlap, the correct background compensation in the neighbourhood of intense matrix lines is found to be valuable [9].
3. XRF Monte Carlo simulation The MC technique is applied to simulate the relevant photon–matter interactions which occur when the analyzing microbeam illuminates the sample. The types of interactions taken into consideration are the (i) photoelectric effect, (ii) Rayleigh (elastic) scattering, (iii) Compton (inelastic) scattering, (iv) photoelectron bremsstrahlung. A detailed description of the code can be found elsewhere [5–7]. Taking into account the solid angle and the detector response of the modeled detector, the complete spectral response can be calculated including the scattered background as well as the fluorescence lines.
4. Quantification by means of XRF Monte Carlo simulation The quantification is done by extraction of Xray line intensities of the experimental spectrum and the MC simulation spectrum for a given sample composition. The simulated composition is then adjusted until the MC simulation X-ray line intensities agree with the experimental X-ray line intensities (see Fig. 1), ðkþ1Þ
Cj
ðkÞ
¼ Cj ðkÞ Cj
ðkÞ Ij;sim
Ij;exp ; Pn ðkÞ Il;exp ðkÞ l¼1 Cl
ð2Þ
Il;sim
where is the calculated concentration of element j after k iterations; Ij;exp is the experimental ðkÞ and Ij;sim is the net intensity of element j. The adjustment of an element concentration is stopped when its relative intensity deviation ðjðIj;exp ðkÞ Ij;sim Þ=Ij;exp jÞ is below 0.5%, or if the simulated intensity deviates from the experimental intensity within the statistical uncertainty.
398
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
Fig. 1. The quantification scheme based on MC simulation uses the AXIL module to convert the experimental and simulated spectra into X-ray line intensities which are then used as input for a detailed MC simulation code dedicated to XRF spectroscopy.
Fig. 2. NIST SRM 613 (trace element in glass) experimental spectrum ( ) with the corresponding background derived with the AXIL spectrum evaluation module (- - -). The MC simulated spectrum (—) is adjusted by scaling its Sr peak to the experimental Sr peak.
Fig. 3. Repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) standard (see Fig. 2) at the end of a synchrotron run (time <0 h) and the next synchrotron run (time >0 h). Variation of (a) Sr line intensity and its normalization by (b) synchrotron current (SRCUR), (c) ionization chamber (ION), (d) mini-ionization chamber (MINI ION), (e) Compton scatter peak (Compt) and (f) 1/2 h interval statistical variation (error bars equal to the measured standard deviations) after normalization with mini-ionization chamber (MINI ION).
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
5. Experimental The ID18F spectrometer is situated in the last experimental hutch of the ID18 beamline at the ESRF. The primary beam is tunable in the 6–28 keV range by means of undulators and made monochromatic by means of a fixed exit double crystal Si(1 1 1) monochromator. The beam is then further confined to sizes down to typically 5 5 lm using compound refractive lenses (CRLs). The characteristic X-rays are detected with a Si(Li) detector of Gresham in combination with the CANBERRA 2026 spectroscopy amplifier/9635 ADC. A detailed description of the beamline can be found elsewhere [1]. The intensities of the incoming and the focused beam are monitored respectively by an ionization chamber and a miniature ionization chamber. The latter consists of a 50 lm diameter pinhole and was specially de-
399
veloped at the ESRF to measure the focused beam intensity just before its impact on the sample [10]. In order to investigate the stability of the set-up repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) standard were performed at the end of a synchrotron run (140 50 s) and continued in the next run (300 50 s). For this purpose a 63element CRL was applied to achieve a 1:8ðVÞ 14ðHÞ lm beam at 21 keV.
6. Results and discussion ID18F delivers a microbeam with a degree of polarization which is better than 99.5% [1]. By this, the experimental data feature an excellent peakto-background ratio. In case of complex spectra however (e.g. Fig. 2) a dedicated spectrum
Fig. 4. Individual quantitative results of the measurements of the same spot on the NIST SRM 613 when the quantification scheme shown in Fig. 1 is used. Mean values (m) and standard deviations (s) for the total series of spectra are indicated. If applicable, certified values are indicated by the dashed line together with the relative deviations from the calculated concentration values.
400
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
evaluation routine is still needed to resolve peak overlap and to compensate for the background. The repetitive measurements of the same point on the homogeneous NIST SRM 613 (trace elements in glass) show variation of the elemental line intensities during the synchrotron runs. Fig. 3 indicates that next to the scatter, the response of the mini-ionization chamber which monitors the beam intensity just before the beam hits the sample can be applied to normalize individual spectra during and between synchrotron runs. Considering 1/2 h intervals, the intensities then vary according to the counting statistics and do not differ statistically in time. The MC quantification scheme described above was applied on the NIST SRM 613 spectra from the repetitive measurements giving quantification results shown in Fig. 4. Considerable care and effort is made by NIST into the manufacturing of this standard to ensure homogeneity. The certificate reports the addition of nominal trace con-
centrations of 50 ppm and a target level of precision and accuracy for certification of 5% or better. The matrix is 72% SiO2 , 12% CaO, 14% Na2 O and 2% Al2 O3 . To start the quantification procedure shown in Fig. 1, the concentrations of the trace elements were set to 50 ppm, except for Sr that was selected as an internal reference element (fixed to its certified concentration, i.e. 78.4 ppm, during the actual quantifications). With the use of the internal reference line, no external standard was necessary for the quantification. Fig. 4 shows relative concentration deviations of 8–10% are achieved between certified and calculated concentrations in case of medium or large line peaks. Large deviations are due to the poor statistical quality of the small line peaks. The maximum number of iterations per spectrum was set to 15 by taking the average composition of the last five iterations. The average number of iterations was 12 corresponding to approximately 11 min on a PC Celeron 500 MHz.
Fig. 5. Statistical 1/2 h interval variation of the individual quantitative data shown in Fig. 4. The error bars are equal to the measured standard deviation on the derived concentrations within 1/2 h intervals.
B. Vekemans et al. / Nucl. Instr. and Meth. in Phys. Res. B 199 (2003) 396–401
The 1/2 h interval quantitative results of the individual quantification data are shown in Fig. 5 and confirm again that the concentrations do not differ statistically in time.
401
time. Applying the quantification scheme to this series of short measurements an accuracy of 8– 10% is achieved for medium or large line peaks in an acceptable time of approximately 11 min on a PC Celeron 500 MHz.
7. Conclusions References A two-step quantification scheme based on a non-linear least-squares fitting algorithm (AXIL) and a detailed MC simulation code for XRF spectroscopy is applied to investigate the stability of the ESRF ID18F beamline. In spite of the excellent background reduction as the result of the high degree of linear polarization, a reliable spectrum evaluation method is needed to resolve peak overlap and to compensate for the remaining background in the spectra. The derived elemental intensities must be normalized by means of the scatter information of the acquired spectrum or the response of the mini-ionization chamber, specially developed at the ESRF for this purpose. The repetitive short point measurements on the homogeneous NIST SRM 613 standard reveal that the concentrations do not differ statistically in
[1] A. Somogyi, M. Drakopoulos, L. Vincze, B. Vekemans, C. Camerani, K. Janssens, A. Snigirev, F. Adams, X-Ray Spectrom. 30 (2001) 242. [2] B. Vekemans, K. Janssens, L. Vincze, F. Adams, P. Van Espen, Spectrochim. Acta 50B (2) (1995) 149. [3] P. Van Espen, K. Janssens, J. Nobels, Chemom. Int. Lab. Syst. 1 (1986) 109. [4] F. He, P. Van Espen, Anal. Chem. 63 (1991) 2237. [5] L. Vincze, K. Janssens, F. Adams, M.L. Rivers, K.W. Jones, Spectrochim. Acta B 50 (1995) 127. [6] L. Vincze, K. Janssens, F. Adams, Spectrochim. Acta B 48 (1993) 553. [7] L. Vincze, K. Janssens, B. Vekemans, F. Adams, J. Anal. At. Spectrom. 14 (3) (1999) 529. [8] L. Vincze, K. Janssens, B. Vekemans, F. Adams, Spectrochim. Acta B (1999) 1711. [9] K. Janssens, B. Vekemans, F. Adams, P. Van Espen, P. Mutsaers, Nucl. Instr. and Meth. B 109/110 (1996) 179. [10] M. Kocsis, J. Surr, ESRF in-house development.