PARAMETERS REFINED BY FUNDAMENTAL USING PEAK RATIOS XRF PEAK
Transcript of PARAMETERS REFINED BY FUNDAMENTAL USING PEAK RATIOS XRF PEAK
XRF PEAK DECONVOLUTION
USING PEAK RATIOS
REFINED BY FUNDAMENTAL
PARAMETERS
Shinichi Terada
X-Bridge Technologies Co., Ltd.
Hiroki Yamashita and Yoshie Araki
X-tec. Co., Ltd.
This presentation was for an oral presentation at Denver
X-ray Conference 2011 held in Colorado Springs CO, USA
• Every quantification method calculates
concentrations based on XRF peak
intensity extracted from a spectrum
• Accuracy in peak intensity extraction is as
important as accuracy in quantification
calculation
All quantification calculations in XRF analysis such as
fundamental parameter method or calibration curve method
are based on XRF peak intensities of elements that are
extracted from spectra using sorts of peak deconvolution
methods.
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For extracting XRF peak intensity of each element,
peak deconvolution is very important.
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Energy (keV)
Accuracy of peak deconvolution is highly important because
errors in peak deconvolution results errors in composition
and/or thickness values.
Fixed intra-element peak intensity
ratio Gaussian fitting
• G(E, W) Gaussian function
• Ez,l Peak energy
• W(E) FWHM at energy E
• Pz Height of the main peak
(fitting parameter)
• Rz,l Intra-element peak height ratios
Model
Function
We highly recommend use of fixed intra-element peak ratio
Gaussian fitting for most of applications since it is stable for
small peaks near the detection limits.
How should we determine
intra-element peak intensity ratios?
• Dependent on..
– Composition / Thickness
• Absorption of XRF
• Secondary excitations (L & M L lines)
• Absorption of irradiating X-ray (L & M lines)
– Energy distribution of primary X-rays
• Very important for L lines
However, determinations of intra-element peak ratios are
not easy because they are dependent of composition of a
sample and excitation conditions.
In cases of K-lines, the ratios of generation of K-alfa and
K-beta are always constants. However, after generation
deep in the sample, some part of fluorescence X-rays are
absorbed by sample. K-alfa and K-beta have different
absorption probability. Therefore, ratios are dependent on
the composition.
In cases of L-lines, the situations are much more
complicated because of multiple L absorption edges. In the
extreme case, a characteristics X-ray that has the energy
between L-III and L-II does not excite L-beta but L-alfa.
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Energy (keV)
Profile
Cu-Kα
Zn-Kα
Cu-Kβ
Zn-Kβ
Are ratios determined for pure metal
good for alloys?
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Energy (keV)
Profile
Cu
Cu-Kα
Cu-Kβ
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Energy (keV)
Profile
Zn
Zn-Kα
Zn-Kβ
Cu
-K吸収端
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Energy (keV)
Profile
Zn
Cu
Cu-Ka
Cu-Kb
Zn-Ka
Zn-Kb
Cu-Zn Alloy Spectrum(Cu:38% Zn:62%)
Cu – K
Absorption
edgeZn-Kb fit is bad
because of heavy
absorption by Cu
atoms in the alloy
This is well known simple example of Cu-Zn alloy case. If we
try to make fixed intra-element ratio peak deconvolution
based on peak ratios obtained from Cu and Zn pure metal
samples, the fitting is not good. The error mainly appear as
bad fitting of Zn-Kb because only Zn-Kb among those four
peaks is above Cu-K absorption edge and strongly
absorbed by the sample.
Practical solutions in the past
• For trace analysis, a table is prepared for
each main matrix (e.g. steel, Al alloy, Cu
alloy, plastic, etc.)
• For composition analysis of the main
matrix, change in the ratios are ignored
Some XRF users and manufacturers used multiple sets of
intra-element peak ratio tables in order to solve the problem.
Others just have been ignored.
Refinement of ratios by FP
• After the initial calculation of XRF peak
intensity based on the default ratio table,
we can calculate approximate composition
• Once composition is known, theoretical
intensity of each line is calculated and
ratio table for the particular sample is
produced
Our new approach is refining the intra-element peak ratios
using fundamental parameter method. For the calculation,
we need the composition of the sample.
Iterative refinement of peak ratios
Peak Fitting using Rz,l,i
Spectrum => Pz,i
Quantification by FP
Pz,i => Cz,i
Cz,i ~ Cz,i-1?
END
Calculation Rz,l,i+1 by FP
i = i+1
Therefore, we do iterative refinement of peak ratios as well
as compositions.
After peak-ratio refinement
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Energy (keV)
Profile
Cu-Kα
Cu-Kβ
Zn-Kα
Zn-Kβ
Fittings for both
Zn-Kb and Cu-Kb
become better
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Energy (keV)
Profile
Cu
Cu-Kα
Cu-Kβ
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Energy (keV)
Profile
Zn
Zn-Kα
Zn-Kβ
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Energy (keV)
Profile
Zn
Cu
Cu-Ka
Zn-Ka
Zn-Kb
Cu-Kb
Cu-Zn Alloy Spectrum
(Cu:38% Zn:62%)
After doing the refinement, the fitting of the example
spectrum becomes much closer.
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Energy (keV)
Profile
Pd-Kα
Pd-Kβ
Ag-Kα
Ag-Kβ
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Inte
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Energy (keV)
Profile
Ag
Ag-Kα
Ag-Kβ
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Energy (keV)
Profile
Pd
Ag
Pd-Kb
Ag-Ka
Ag-Kb
Pd-Ka
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Energy (keV)
Profile
Pd-Kα
Pd-Kβ
Ag-Kα
Ag-Kβ
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Energy (keV)
Profile
Ag
Ag-Kα
Ag-Kβ
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Energy (keV)
Profile
Pd
Ag
Pd-Kb
Ag-Ka
Ag-Kb
Pd-Ka
Ag – Pd Alloy
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Based on Pure
metal Ratios
FP Refinement
Ag:25%,Pd75%
Pd
-K A
bs.
Ed
ge
This is similar example Ag-Pd alloy.
Au base alloy
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Energy (keV)
K9
K14
K24
K24 Au100%K14 Au58.5% Pd41.5%K9 Au37.5% Cu62% Ag0.5%
Normalized for Au-La
Au-Lα Au-Lβ
Au-Lγ
This is L-line example. Three different gold alloys that have
different composition have different intra-element peak
ratios as shown in these spectra.
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Profile
Pd-Kα
Pd-Kβ
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Energy (keV)
Profile
Au
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Energy (keV)
Profile
Pd
Au
Pd-Kα
Pd-Kβ
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Energy (keV)
Profile
Cu-Kα
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Energy (keV)
Profile
Au
Au Alloy
Peak ratio refinements
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Profile
Cu
Au
Cu-Kα
Au-LγAu-Ll
Au-LβAu-Lα
K18(Au-Pd)Au75% Pd25%
K18(Au-Cu)Au75% Cu25%
Au-LγAu-Ll
Au-LαAu-Lβ
The ratio refinement solves the issues in fittings.
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Eergy (keV)
Sn Alloy (Trace Impurity)
Sn Alloy SpectrumPb0.174%, Bi0.196%,As0.064%,
Cu2.99%,Ag0.55%,Sb1.06%, 14
Sn-Ka
Sn-Kb
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Eergy (keV)C
u-K
b
Pb-L
a,A
s-K
aB
i-L
a
Pb-L
b
Bi-
Lb
Cu-Ka
This is trace impurity example in Tin alloy.
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Profile
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Profile
Sn Alloy (Cont.)
Because of Errors in peak ratios of Pb and Bi, As intensity is calculated as 0
Cu
-Kβ
Pb
-Lα,As-Kα
Bi-Lα
Pb
-Lβ
Bi-Lβ
Cu
-Kβ
Pb
-Lα,As-Kα
Bi-Lα
Pb
-Lβ
Bi-Lβ
Based on Pure
metal ratios
Refined by FP
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Energy (keV)
Profile
Cu
Pb
As
Bi
Pb
-La
Bi-
La
Pb
-Lb
Bi-
Lb
Cu
-Kb
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Energy (keV)
Profile
Cu
Pb
As
Bi
Cu
-Kb
Pb
-La,A
s-K
a
Bi-
La
Pb
-Lb
Bi-
Lb
If we make fitting based on ratios obtained from pure
element, Cu, Pb and Bi are detected. However, if we refine
the ratios, As appears in the fitting result as shown.
This is serious known issue in trace impurity detections.
Conclusion
• Peak deconvolution software that uses
intra-element peak ratios refined by FP is
produced
• Improvements of the accuracy in peak
fittings for both main matrix analysis and
trace analysis were achieved
Note: International Patent Application has been
made for this invention. Applicants plans to
license the pending patent and one of the
authors is ready to provide consulting service to
those who want to implement the function into
their own software.
Please feel free to write to [email protected]