SU1441282A1 - Method of radiometric measurement of concentration of an element in a substance - Google Patents

Abstract

The invention relates to physical methods for analyzing the composition of a substance, in particular to X-ray fluorescence, and can be used in determining the concentration of elements in liquid, powder and solid samples. The aim of the invention is to improve the accuracy of determination. The method of X-ray radiometric determination of the concentration of an element in a substance containing only interfering elements 1, the photopeak of the characteristic x-ray emission of which is energetically resolved from the photopeak of the analytical line of the characteristic radiation of the element being detected and the peak of the scattered radiation, consists in irradiating all; or x-rays from the source, recording the characteristic x-rays of the element being detected, irradiation targets from a material whose atomic number is much less than the atomic number of the element being detected, and the element to be determined, added in an amount that ensures that the counting rates of the characteristic radiation of the element being determined and the scattered radiation are equal, the secondary radiation from the target of the analyte of the analyte with a given surface density and registering the sum of the parts q and q of the intensities of the characteristic and scattered radiations, respectively, after the passage of these radiations mi of the absorber, with part q and q determined on the basis of the results of measurements of the reference samples, with the same concentration of the element being determined and differently interfering, and calculating the concentration of the element being determined from the ratio of the registered counting rates from the sample and from the target after the passage of the absorber., 3 Il., 2 tab. (L to 00 1C

Description

The invention relates to physical methods for analyzing the composition of a substance, in particular, to the X-ray fluorescence method5 and can be used in determining the concentration of elements in liquid, powder and solid samples.

The aim of the invention is to improve the accuracy of determination by more fully compensating for the effect of changes in the composition of the filler, especially at high concentrations of the element being determined in the analyzed substance.

FIG. t shows the spectrum of the secondary radiation of the source selenium-75 from the reflector 5 containing tungsten (I is the counting rate of pulses due to radiation with energy E); Fig. 2 shows the dependence of the analytical parameter H on the trioxide-tungsten concentration in the analyzed substance; Fig. 3 shows the dependence of the analytical parameters in the prototype method and in the proposed method on the concentration of tungsten in the analyzed substance.

Improvement of accuracy in the proposed method is achieved by using radiation of a target made of a material with atomic number much smaller than the atomic number of the element to which the determinate element is added in an amount that ensures equal counts of characteristic radiation and scattered radiation. Transmission of an absorber from an analyte of a given surface density by this radiation allows one to more fully take into account the effect of the matrix effect on the analysis results.

The radiation spectrum of the target contains the detected element and scattered radiation J characterized by approximately the same counting rate, and therefore, by varying the discrimination levels and the width of the spectrometer window, select the spectral region of the current flow registration, which provides the optimum ratio between the fields of the characteristic radiation element and the target source radiation scattered by the source. Such a choice is a necessary and sufficient condition for a more complete account of the matrix effect.

The sample thickness of the analyte and the target is taken, exceeding

o

j 0 5

about

five

0

the saturation layer for scattered radiation, and the absorber surface density corresponding to a six to eight-fold attenuation of the total flux.

The spectral region to which the spectrometer is tuned when registering the radiation count rate of the target is chosen experimentally in the development of specific analysis techniques. For example, by changing the position and width of the spectral region when registering radiation transmitted through an absorber, conditions are found that ensure that the analytical parameters are equal to the samples with the same content of the element being determined, but with different material composition of the filler, etc.

The method is carried out as follows.

1. Trial of the analyte

in an amount sufficient to provide an all-encompassing layer for the scattered primary radiation, and consequently, for the characteristic x-ray radiation of the element being detected, is pressed into the measuring sleeve.

The absorber is made in a similar way, but unlike the sample, a certain amount of the analyte is taken depending on its surface density.

2. The test is set in the path of the primary radiation of the radiation source and the intensity is recorded

, „„ Characteristic radiation

"R

a definable element in the channel ana

the lytic line of the spectrometer in the form of pulses collected during the exposure time.

3. Instead of a sample, a thickness target is set that is thick for scattered primary radiation, and an analyte absorber is placed between it and the analyte of a given analyte of a given surface density so that the detector detects the radiation of the target passing through this absorber ().

The spectral region in which the radiation of the target is recorded is chosen experimentally by measuring the emission spectra of a target that has passed through reference absorbers with the same concentration of the element being determined and different concentrations

interfering element

The error of determination in the range of 8–25% is 2.5–2 rel.%, while analyzing the same samples by the prototype method, the total maximum error was 5 rel.%. The choice of the position and width of the spectral region in which the radiation of the target is recorded determines

31441282

as well as the intensity of the characteristic radiation of a detectable element from the same reference samples. The spectral region of the radiation registration of the reflector is located so that it partially captures the photopeak of the characteristic radiation of the element being detected and the partially scattered radiation which I suppose q in the total recorded radiation is the characteristic radiation of the element being detected and which fraction is q. scattered. The significance of the choice of the spectral region is seen from a comparison of the results given in the table for non-optimal (from the point of view of compensation of the effect of molybdenum concentration) areas of 54-94 keV and 78-20 118 keV and optimal - 66-106 keV. When choosing a spectral region of 54–94 keV, samples containing molybdenum give underestimated concentrations of the element being detected, compared to

™ ..7 with molybdenum free samples.

while for the spectral region of 78–118 keV, the same samples give an overestimated value of the concentration of the element being determined.

Yu. Measurements of samples with a tungsten concentration of 25-40 wt.% Are carried out at an exposure time of 60 s; The target contains 8 wt.% tungsten. The optimal spectral region is 60-95 keV,

35 The measurement results are presented in table. 2 and in FIG. 3, where the shaded area demonstrates the measurement error caused by the presence in the sample of 4 wt.% Molybdenum (O - sample,

40 of which molybdenum is absent - samples with a concentration of 4% molybdenum). Thus, using a scavenger from the analyte for translucency of the radiation from a stasis, the counting rates are calculated

. (or the number of pulses) in this

area and take the ratio Y (analytical parameter) for each

benchmark and compare the results.

By changing the position and width of the energy interval, one finds its position and the width at which the values are equal for all standards.

4. Calculate the magnitude of the ratio of the car - -g of the measured numbers of pulses and on the calibration dependent element in the analyzed substance. Example. The proposed method and the prototype method analyzed samples of a mixture of tungsten and molybdenum prepared on the basis of cement, and the determined element is tungsten, interfering with molybdenum.

Measurements were performed using a RPS4-01 spectrometer with a scintilla radiation detector. The selen-75 radioisotope was used, and the target was an artificial cement-based mixture with a concentration of WO ,, equal to 6% by weight. The surface density of the scavenger was 1.2 g / cm, the exposure time was 20 s.

The results of measurements of samples with a content of tungsten trioxide to 25% are given in table. one.

FIG. 1 shows the energy content of a target consisting of

the radiation spectrum coming from the target, where I is the counting rate, and the optimal spectral region, at which the matrix effect is most fully taken into account, and FIG. 2 - dependence of the analytical parameter 1 - I ar ° the concentration of the element being determined in the sample, where O is the sample in which molybdenum is absent, and (O is the sample containing; respectively, 7.5% and 15% by weight molybdenum.

From the obtained experimental data it is clear that the total is maximal

: from a light material and a detectable element in an amount that ensures the equality of the count rates of its characteristic radiation and scattered radiation, makes it possible to reduce by several times the measurement error of the concentration of the detected element due to an uncontrolled change in the concentration of the interfering element.

Claims (1)

Invention Formula The method of X-ray radiometric determination of the concentration of an element in The error of determination in the range of 8–25% is 2.5–2 rel.%, while analyzing the same samples by the prototype method, the total maximum error was 5 rel.%. The choice of the position and width of the spectral region in which the radiation of the target is recorded determines  what dopu q in the total recorded radiation is the characteristic radiation of the element being detected and what fraction q. scattered. The importance of the choice of the spectral region can be seen from the comparison of the results given in the table for the non-optimal (from the point of view of compensation of the effect of molybdenum concentration) areas of 54-94 keV and 78-118 keV and the optimum - 66-106 keV. When choosing a spectral region of 54-94 keV, samples containing molybdenum give an underestimated concentration of the element being detected, compared to : from a light material and a detectable element in an amount that ensures the equality of the count rates of its characteristic radiation and scattered radiation, makes it possible to reduce by several times the measurement error of the concentration of the detected element due to an uncontrolled change in the concentration of the interfering element. Invention Formula The method of X-ray radiometric determination of the concentration of an element in q and q are determined on the basis of the results of measurements of reference samples with the same concentration, the element being measured and the different concentrations of interfering elements, characterized in that, in order to increase the determination accuracy, a target made of a material with an substance containing interfering elements is used. the photopeaks of the characteristic x-ray radiation of which are energetically resolved with the photo-peak of the analytical line of the characteristic x-ray radiation of the element being detected and the peak of the scattered radiation, schiys irradiating saturated sample analyte d ciency atomic number, many substances gamma- or X-iz menpshm atomic number determined emo- radiation source register ha th element, which is added oprakteristicheskogo ray of thinned emy element in an amount radiation of a detectable element, exposing the equality of velocities of the target, containing 45 counts of the characteristic x-ray element, radiography of the secondary radiation determined by the emitted radiation of the target absorber from the anomaly and scattered radiation, and about the lysable substance of a given surface concentration element of the nost density and registration sum-sug by the value of the ratio of speed we are parts of q, and q intensities20 of the characteristic radiation detectable element from the analyzed sample to the total count rate of the radiation of the target that passed through the absorber. Table 1 characteristic x-ray radiation of a detectable element and scattered radiation after passing an absorber J q and q are determined on the basis of the results of measurements of reference samples with the same concentration, determined by the element and different concentrations of interfering elements, characterized in that, in order to increase the accuracy of determination, a target made of a material with an effective atomic number is used. of the element to which it is added. 20 60 too 180 Рig.1 q, rel. in U 10 15 20 25 30 9 Ig. 2 C / KfCOff- / 3jO  momi / n 1 I i / 7 before / b / 0 c / rocoS г53260C, / o Fig.z C / KfCOff- / 3jOO momi / n 1 I i / 7 before / b / 0 c / rocoS