JP2006071496A - Sample shape correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate fluorescent X-ray analysis method while eliminating a complicated process when considering correction of a predetermined sample specified for the thickness of the sample.
A sample shape correction method for correcting the shape of a sample to be analyzed by a fluorescent X-ray analysis method, wherein a background intensity BG1 of a high energy region AR-H in which no peak appears in a fluorescent X-ray spectrum of the sample. The thickness of the sample is corrected based on BG2.
[Selection] Figure 1

Description

  The present invention relates to a sample shape correction method for correcting the shape of a sample to be quantitatively analyzed by a fluorescent X-ray analysis method, and more particularly to a sample shape correction method for correcting the thickness of a sample.

  X-ray fluorescence analysis is an analysis method used for quantifying elements by analyzing fluorescent X-rays obtained as a result of irradiating a sample with X-rays.

  FIG. 5 is a configuration diagram of a fluorescent X-ray analyzer. In FIG. 5, reference numeral 101 denotes an X-ray tube. The sample 103 is irradiated with primary X-rays 102 from the X-ray tube 101, and fluorescent X-rays 104 generated by excitation from the sample 103 are converted into energy dispersive X-rays. The detector (EDS detector) 105 detects the sample and analyzes the sample.

  In general, the quantitative analysis is based on the premise that the area of the sample is sufficiently larger than the X-ray irradiation region and that the thickness of the sample does not affect the X-ray intensity detected by the detector. Therefore, in the fluorescent X-ray analysis apparatus shown in FIG. 5, correct quantitative analysis accuracy cannot be obtained unless the sample 103 is in an ideal shape (a shape in which primary X-rays are sufficient and have no irregularities). When such a condition is not satisfied, it is necessary to align the sample shape so that the same condition is always obtained.

  That is, when the area of the sample 103 is small and the X-ray does not sufficiently hit or when the sample is thin and the X-ray is transmitted, the analysis value is calculated to be lower than the true value. In order to eliminate this influence, pre-processing such as solidification by surface pressing and surface polishing is often performed.

Therefore, a method of correcting the shape so that measurement can be performed without pre-processing the sample has been considered. Patent Document 1 below relates to absorption of a coexisting component with respect to the main component, assuming that the sample to be analyzed is composed of a main component for obtaining a calibration curve based on an intensity ratio of fluorescent X-rays and scattered X-rays and a coexisting component The correction factor is calculated by theoretical calculation assuming the composition of the sample to be analyzed, and a calibration curve using the correction factor is applied to the intensity ratio measured and calculated from the sample to be analyzed. The required technology is disclosed.
Japanese Patent Laid-Open No. 10-824949

  By the way, in the method according to Patent Document 1, a calibration curve is obtained in advance, the intensity of fluorescent X-rays and the intensity of scattered X-rays are measured, and the ratio of both intensities is calculated. The process of calculating | requiring the content rate of the main component of a sample is calculated | required by theoretical calculation supposing this composition, and using each of these factors.

  In consideration of correction of a predetermined sample specified for the thickness of the sample, a highly accurate analysis method is desired while eliminating a complicated process.

  The present invention has been made in view of the above circumstances, and enables a highly accurate fluorescent X-ray analysis method while eliminating the need for complicated steps when considering the correction specified for the thickness of a predetermined sample. An object is to provide a sample shape correction method.

  The fluorescent X-ray analysis method according to the present invention is a sample shape correction method for correcting the shape of a sample to be analyzed by the fluorescent X-ray analysis method, in order to solve the above-mentioned problem, The thickness of the sample is corrected based on the background intensity in the high energy region where no peak appears in the X-ray spectrum.

  The background BG1 and the background BG2 in the high energy area hardly change for any sample of polymer material, especially plastic samples. Therefore, when analyzing a sample of the polymer material, even if the thickness is insufficient, the thickness can be corrected based on the sample shape correcting method of the present invention.

  Since the sample shape correction method according to the present invention corrects the thickness of the sample based on the background intensity of the high energy region where no peak appears in the fluorescent X-ray spectrum of the sample, the correction specified to the sample thickness of the predetermined sample In consideration of the above, it is possible to provide a highly accurate X-ray fluorescence analysis method while eliminating a complicated process.

  Hereinafter, the best mode for carrying out the present invention will be described. The present embodiment is a sample shape correction method applicable to a fluorescent X-ray analysis method in the case where a plastic which is a specific example of a polymer material is used as an analysis target sample and elements constituting the plastic are quantified.

  Plastic is a kind of polymer material, and is a material having a relatively low density and no base. In the fluorescent X-ray analysis method, it is desired that the sample has a sufficient thickness so that the thickness of the sample does not affect the X-ray intensity detected by the detector. However, in a situation where only a plastic sample with a sufficient thickness cannot be prepared, it is desirable to enable quantitative analysis without destroying the sample.

  Therefore, in the case of a plastic sample, according to the present invention, the thickness of the sample is corrected based on the background intensity in the high energy region where no peak appears in the fluorescent X-ray spectrum of the plastic. Hereinafter, the principle that enables correction in the thickness direction of a plastic sample will be described.

  FIG. 1 is an X-ray fluorescence spectrum diagram showing a spectrum 1 of a plastic sample with sufficient thickness and a spectrum 2 of a plastic sample with insufficient thickness. The horizontal axis corresponds to energy (keV), and the vertical axis corresponds to the element concentration. The density is a value obtained by further dividing the count value C at time S (seconds) by the current value mA. Peaks of spectrum 1 and spectrum 2 indicate each element. In the spectrum 1, the concentration of each element is related to the area of the peak.

  In the case of spectrum 2, the peak is smaller than that of spectrum 1 for all elements. When the thickness of the sample is not sufficient, the peak area is reduced. That is, when the sample is thin, the concentration of each element is calculated to be low.

  In FIG. 1, no peaks appear in the spectrum 1 and the spectrum 2 in the area where the energy is 30 keV or higher, that is, in the high energy area, and only the background BG1 and the background BG2 are seen. The background is an energy region where few peaks are seen. The background BG1 and the background BG2 of this high energy area, especially the area AR-H of 33.5 keV to 35.5 keV, hardly change for any sample of plastic.

  FIG. 2 is a diagram in which the areas SP1 and SP2 of the background BG1 and the background BG2 of the area AR-H of 33.5 keV to 35.5 keV are extracted and compared. In the present embodiment, the areas SP1 and SP2 of the background BG1 and the background BG2 of the area AR-H can be regarded as changing only depending on the thickness of the plastic sample.

  FIG. 3 is a characteristic diagram showing a change in the area ratio of the background BG in the area AR-H with respect to a change in the thickness of the plastic sample in the high energy area. The area ratio y of BG changes linearly up to the thickness d3. Here, the area ratio y means a relative value BG / BG0 with respect to the background reference area BG0 of the reference thickness d0.

  In the present embodiment, the thickness of the plastic sample is corrected based on the area ratio of the background BG by utilizing the fact that the area ratio of the sample and the BG is linear in the region up to the thickness d3 (area ratio y3). To do. For example, if the samples of spectrum 1 and spectrum 2 in FIG. 1 have thicknesses d1 and d2, respectively, spectrum 2 can be converted to a spectrum corresponding to thickness d1 by multiplying spectrum 2 by a coefficient y1 / y2. .

  Specifically, for one intensity I2 of the Pb peak in the spectrum 2 corresponding to the thickness d2 in FIG. 1, the above-described coefficient y1 / y2 is applied to this I2 to obtain the Pb peak of the spectrum 1 corresponding to the thickness d1. It can be converted into one intensity I1. Therefore, when the calibration curve of the intensity I1 and the concentration is obtained for the thickness d1, the intensity I2 at the other thickness d2 is also calculated using the intensity (y1 / y2) · I2 converted so as to correspond to the thickness d1. The concentration can be obtained from the calibration curve. As described above, according to the present embodiment, the concentration of a component such as Pb can be measured using a calibration curve regardless of the thickness of the sample.

  FIG. 4 is a configuration diagram of a fluorescent X-ray analyzer that applies the sample shape correction method of the present invention to correct the thickness of a plastic sample and performs quantitative analysis of the plastic sample. The configuration in which the primary X-ray 102 from the X-ray tube 101 is irradiated onto the sample 103 and the fluorescent X-ray 104 generated by being excited from the sample 103 is detected by the EDS detector 105 is as described above.

  The EDS detector 105 detects the fluorescent X-rays 104 with, for example, a Si semiconductor detector 110. The Si semiconductor detector 110 converts the detected X-ray intensity into a current and outputs the current, and the signal processing unit 111 uses the area of the background BG as described above to output the spectrum from the Si semiconductor detector 110 to a predetermined spectrum. It converts into the thing equivalent to the sample of thickness d1. As a result, the concentration of the predetermined component can be obtained using the calibration curve provided for the sample having the thickness d1.

  As described above, even if the sample 103 is a plastic with insufficient thickness, the computer system 112 corrects the thickness based on the above-described sample shape correction method, and performs a quantitative analysis of the plastic sample through a complicated process. Although it is unnecessary, it can be performed with high accuracy.

It is a fluorescent X-ray spectrum figure of two plastic samples from which thickness differs mutually. It is an enlarged view of the background of a high energy area. It is a characteristic view which shows the change of the area ratio of background BG with respect to the change of the thickness of the plastic sample in a high energy area. 1 is a configuration diagram of a fluorescent X-ray analyzer that applies a sample shape correcting method of the present invention to correct a thickness of a plastic sample and quantitatively analyze the plastic sample. It is a block diagram of a general fluorescent X-ray analyzer.

Explanation of symbols

101 X-ray tube, 102 Primary X-ray, 103 Sample, 104 Fluorescent X-ray, 105 EDS detector, 110 Signal processor, 112 Computer system

Claims (2)

A sample shape correction method for correcting the shape of a sample to be analyzed by a fluorescent X-ray analysis method,
A sample shape correction method, wherein the thickness of the sample is corrected based on the background intensity of a high energy region where no peak appears in the fluorescent X-ray spectrum of the sample.   2. The sample shape correcting method according to claim 1, wherein the thickness of the polymer material sample is corrected.

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