RO104795B1 - Calibration method of spectrometers with x rays fluorescence - Google Patents

Abstract

The method consists of the theoretical correction (coefficient K) of the main effect, that of radiation absorption X, developing in Taylor series the expression of intensity line of the measured element, depending on the coefficients mass absorption of the sample for maximum of excitation and for the line of the element of measured around the values corresponding to the composition chosen as a reference. Using concentrations corrected K, Ci is determined on the basis of standards calibration coefficients Ao (noise), Ai; Kj, Bk from form equations: k-c-a + aj. + yaj. + y b.i.i. firi k minimizing the mean square error, using the intensity of the line of the measured element 7 ,, the intensity j what overlaps over 7, and intensities Ik what secondly excites the measured element.

Description

The invention relates to a method of calibrating the X-ray fluorescence spectrometers, used to determine the percentage mass concentration, of the chemical elements in a material.

Calibration methods are known, whereby the concentration coefficients are determined empirically, based on a large number of standards.

The disadvantage of these methods is the large number of standards required, the lower precision, they are difficult to handle and, in many cases, the appropriate standards are difficult to obtain.

Another simplistic method is to use sets of standards for a narrow composition beach, with linear calibration and does not allow the measurement of compositions outside the beach. This greatly limits the usability of the method.

The methods with theoretical corrections are less accessible to the users, due to the constants to be determined and due to the need for special standards.

The aim of the invention is to simplify the calibration of X-ray fluorescence spectrometers, valid in a wide range of compositions, valid and with a small number of standards, with the possibility to take into account also chemical elements, which are not measured by the apparatus.

The problem solved by the invention consists in the theoretical correction according to the principal effect, the one of absorption of the X radiation, and correction according to the secondary excitation and the superposition of lines is made using standards.

The method according to the invention eliminates the disadvantages presented above, in that a suitable reference composition is chosen, with a mass absorption coefficient μ ₀₁ for the maximum excitation and μ ₀₂ for the line of the measuring element, at emergency for each standard. the correction of the intensity of the emergent X-radiation Ti by their Tay10 series development according to the mass absorption coefficients for the maximum excitation μ _; , and for the emergent radiation μ ₂ around the values μ _0Ι and μ ₀₂ , and with these corrected intensities (I _io ) the calibration coefficients are determined by the method of the smallest squares minimizing the mean square error, using also the intensities of the elements that cause secondary excitations and overlapping lines.

An example is given below of a calibration for chromium, from steel samples, in relation to Fig. 1 and 2, which represents:

- fig.l, the path of the X radiation in the sample;

- Fig. 2, the intensities measured according to the concentrations and the corrected concentrations.

According to the invention, taking into account, at excitation, only the wavelength corresponding to the excitation maximum.

f \

1. = const sinet v J = consti

F, ⁺ · sinet by Taylor series development sina (p _l -µ _0] ) + μ ₂ -µ ₀₂ ^sin Ηΰ, ⁺ Η ₀ 2 sin ² α (Δμβ ² + (Δμ2) ² (sin α · μ0Ι + μ _ΰ2 ) ² = 1. I where I = const -I - ιο ιο is _t where

I; - the intensity of the X-ray fluorescence (chromium line) emerging from the sample;

I _jg - corrected fluorescence X-ray intensity;

I _e - the intensity of the X radiation of the excitation maximum upon entering the sample;

α - X-ray output angle (fig.l)

The concentration is determined, depending on the intensity corrected, in the absence of effects other than absorption:

C constl. = corist -l.K ' ¹ l

The correct concentration KC = const.f is represented in the graph in fig.2 by the + sign, and the real one by points.

The fact that it is taken into consideration, at excitation, only the maximum does not bother, because at correction only Δµ, and Δμ ₂ and Po P2 appear ·

Using these values, the calibration is made taking into account the noise (A _o ), the line of the measured element (To be) the line overlaps (Axes) and the secondary excitations (B //,). The correct concentration is: 15

K-CA in the considered example ^ U _Cr —A ₀ + A _Cr l _Cr + B _c f _Cr + B _Nj I _Nl I _Cr + + bMZM (ZcA-B _w I _{v /} l _Cr

The absorption effect of the elements not measured by the apparatus, here the carbon, is taken into account within the mass absorption coefficients. Thus, calibrations can be made for material types, for which suitable standards are not available, for example, calibration for C120 steel with 2% carbon and 12% chromium, using carbon stainless steel standards below 0.1%.

Table 1 shows the Cr concentrations in the standards, the corrected and the measured ones, and in Table 2, the composition of the standards and the reference concentrations.

TABLE 1

Ό 0.194 0,185 0,240 00 ^ t tut Μ η Μ0 + H τ-1 cn cn tut • θ ' ο a cn cn CM C- ο Ο cn cn cn cn η t> CM tut τ-Η τ-Η 00 * η > n cn Ο \ a\ τ-Η Ο \ a l> "η MO MO ο Ό ο cn A V-4 CM CM r-H τ-1 "Ή τ ^- 4 CM CM 00 σ \ <3 \ <3 \ 00 cn cn cm " τ-! t-4 + H τ-Η MO a 00 r MO xt TF tut cn *-1 τ ^- 4 1 r-i a n Γ CM CM Ά ιη into the cn r-Q i-4 CM t> t-4 μο CM CM cn Μ0 MO r> 1 rh ΜΟ τΤ tut • cn © \ κ r t τ-Η rh + H r a > n τ-1 CM oo ι> a rT τ- ( t-4 T's CM a co m CM CM MO οο " oo " A-- 4 V-M τ-1 cn CM a CM 00 00 A\ . θ ' θ ' a CM CM. CM τΗ A A ° L CM_ • n tut tut cn CM CM CM M » Ο C / 5 υ a Ο 03 > 03 40 Ο <υ μ < et a υ Q-H ό ύ υ Ο-ί β c ¢ 3 U ο a a ζ υ U υ

TABLE 2

Mo cT 0,228 0.22 0.149 0.039 1 0.237 1 0.236 .1 1 1.75 1.07 2.92 0.55 1 £ 0.5 rh cr © 0.11 0.02 0.023 CC <c vo 4.70 5.40 4.25 4.24 3.21 0.35 22.4 1.07 0.39 1.05 WITH 0.4 1 0.218 0.136 0.074 CC θ ' 0,015 0.26 0.083 0.18 0.112 0.38 1 0.143 0.20 0.22 us t — 1 tH 13.87 a DC cT 8.30 13.07 VO co σΓ r-i 24.93 21.6 24:48 23.6 26.4 0.148 1 0.40 1 2.97 4.42 Co. 1 1 1 1 1 1 1 ί 1 1 1 10.2 1 1 Ί. Mn N- ( 1.68 0.75 1.82 0.358 rH d ^- θ ' 0.73 0.60 1 0.73 and 0.90 oo CT 0.53 rh θ ' 0.171 1 0.521 0.98 Cr oc 24.21 20,83 18.22 17.17 VO DC rh 16.22 15.21 14.71 13.92 12.40 5.99 5.17 3.03 0.338 0.194 > "a θ ' 0,219 0.158 i. 0.032 1 1 0,185 I 0.183 1 1 0.39 0.94 1.21 0.98 1 P > C  θ ' 1 0.32 0.43 1 VO CT rh 1.72 r cn rh 1.52 1.58 1.91 1 1 1 0.16 0.088 co 1 0.041 0.0082 0.0036 .0051 1 0.0054 1 0.0053 1 1 1 0.024 1 0.027 σν a a θ ' 1 0.016 0.021 0.017 0.0082 ¹ 0.012 ¹ 0.011 1 1 1 -1 0.030 1 0.017 0.044 co 0.5 6'0 6 * 0 0.82 CT CC θ ' r-1 c- © 0.56 0.54 0.55 t 0.36 0.28 0.56 0.20 1.21 · rh a CC A 0.478 U 1 0.147 0.139 0.092 0.047 VT) A © 0,061 1 0.04 0.067 | - l 0.043 0.038 0.39 0.71 oo CC θ ' 0.158 0.44 Conc. of ref. samples rh cn TT IC VO a 00 σ \ 10 rh rh CT H DC H tut H H

The determination of the unknown composition is made by the method of successive approximations, determining in steps, correct K, depending on the composition of the sample.

Calibration and composition determination are done on the computer.

The method of the invention has the following advantages:

- allows calibration for a wide range of compositions;

- it is applicable with a small number of standards or with standards of a different type than the measured samples;

- can take into account the unmeasured elements;

- it can also be applied graphically, in the absence of computers;

- it is simple, easy to handle and with high precision.

Claims (1)

Claim X-ray fluorescence spectrometer etching method, characterized in that a suitable reference composition is chosen, with a mass absorption coefficient μ _0Ι for the maximum of 5 excitation and μ ₀₂ for the line of the measuring element, during emergencies, for each standard, the correction of the emergent X-ray intensity (/, ·) by Taylor series development as a function of the coefficients of 1θ mass absorption for the excitation maximum U "and for the emergent radiation μ ₂ around the values μ _0Ι and μ ₀₂ , and with these corrected intensities (/, ·") the coefficients of etionation are determined by me15 the sum of the smallest squares minimizing the error medium, also using the intensities of the elements that cause secondary excitations and line overlap.