JP2006038822A - Fluorescent x-ray analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact fluorescent X-ray analyzer capable of analyzing a trace element of not more than 1 ppm, in an analysis of heavy-metal elements in a sample being measured. <P>SOLUTION: In the fluorescent X-ray analyzer, the energy of a measuring element band is absorbed by a primary filter which is made up of a light element, such as Si or the like, and energy of an excitation energy band is transmitted, thereby enhancing the strength of excitation X-rays. In addition, a secondary target which is selected for respective measuring elements and constituted of Te, Mo, Co or the like, is arranged around the primary filter, and fluorescent X-rays generated at the secondary target are used as excitation rays. Furthermore, a background component generated from the sample is absorbed by a secondary filter, and the energy of a measuring range is transmitted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention particularly relates to a primary filter, a secondary target and a secondary filter of a fluorescent X-ray analyzer.

  In X-ray fluorescence analysis, a primary filter or a secondary target may be used to reduce the background of the analytical element energy range. However, they are used alone, and the radiation beam bundle from the X-ray tube is not used effectively, and a part of X-rays transmitted through the filter, scattered rays generated from the secondary target, and fluorescent X-rays. Diverges and does not effectively irradiate the measurement sample. Therefore, the X-ray intensity cannot be sufficiently obtained, the analysis accuracy is not improved, and the measurement has to be performed for a long time.

  JP-A-5-240808 (page 2-3, FIG. 1) JP-A-2001-305079 (page 2-3, FIG. 1) JP-A-2004-61223 (page 2-3, page 1) 1) Japanese Patent Application Laid-Open No. 2004-150990 (page 4, FIG. 2)

  By the way, in recent years, harmful substances contained in soil, waste and food, especially rice, have become a problem. As a countermeasure, in Europe, the proposed directive “Restriction on the Use of Specific Hazardous Substances in Electrical and Electronic Equipment (RoHS)” was adopted, and when this directive was issued, cadmium (Cd), lead (Pb), Use of specific hazardous substances such as bromine (Br) flame retardants is severely restricted. Also in Japan, the Soil Contamination Countermeasures Law has been implemented since January 2003, and investigation of toxic heavy metals such as factory ruins is indispensable. In addition, the Ministry of Agriculture, Forestry and Fisheries has decided to regulate the Cd content in rice to 0.4 ppm in the “Food Sanitation Law” of 2004. Under such circumstances, there is a need for an apparatus that can easily measure trace elements of various harmful heavy metals.

  In order to meet these requirements, for example, elemental analysis can be performed by an X-ray analyzer using a large-capacity X-ray tube or a detector of a liquid nitrogen-cooled large-area detection element. However, if such an X-ray tube or detector is used, utilities such as high power, cooling water, and liquid nitrogen are required. Therefore, it causes a cost increase. The equipment becomes larger, requires a large installation area and a large space, and frequently requires maintenance time. In these respects, the cost increases.

  The present invention has been made to solve the above-mentioned conventional problems, and its object is to organically combine a primary filter and a secondary target, and to combine the secondary filters to measure the element energy range. It is intended to provide a relatively inexpensive fluorescent X-ray analyzer that reduces the background of the light and increases the primary X-ray excitation intensity and enables analysis of trace elements in the measurement sample.

Principle of invention

  First, the principle of the present invention will be described with reference to FIGS. FIGS. 1B and 1C are detailed views of the X-ray monochromatic mechanism 7. 2A shows a spectrum of continuous X-rays from an X-ray tube (tungsten (W) target), and FIG. 2B shows a spectrum of primary X-rays 3 when the X-ray monochromator 7 is inserted. Show the distribution.

  X-rays emitted from the X-ray tube 4 (FIG. 2A) are monochromated by the X-ray monochromator 7 and the monochromatic X-ray 3 (FIG. 2B) is irradiated to the measurement sample 1. The generated fluorescent X-ray 5 passes through the secondary filter 12, is detected by the semiconductor detector 6, and is subjected to elemental analysis based on the detected signal height and the number thereof.

  The primary filter 8 shown in FIG. 1B uses silicon (Si) as a filter and has a shape in which the upper part of a cone is cut off. The primary filter 8 is installed at the center of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4 and absorbs energy near the measurement element. This serves to reduce the background near the measurement element. On the other hand, it plays a role of irradiating the sample 1 by transmitting a high energy component above the absorption edge of the measurement element serving as an excitation source. The use of Si does not generate an impure line in the measurement region, and the generated fluorescent X-ray Si-Kα ray is absorbed by the secondary filter 11 and does not reach the detector 6, and the total X-ray dose of the semiconductor detector is calculated. It can be suppressed. This improves the peak-to-background (P / B) ratio and leads to improved energy resolution.

  The secondary target 9 shown in FIG. 1B is arranged around the primary filter 8 and is manufactured in a shape hollowed out from a cone. Of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4, the X-rays at both ends are irradiated to the conical secondary target 9 and the sample 1 is irradiated with the fluorescent X-rays generated from the X-ray tube 4. Is responsible for. Thereby, since the X-rays that have not been used for the excitation of the measurement sample so far can be effectively used as the diverging beam, the intensity of the fluorescent X-rays 5 can be increased. Therefore, trace element analysis is also possible.

When analyzing the toxic heavy metal element cadmium (Cd), the thickness of the primary filter 8 depends on the X-ray tube target and the tube voltage used, but a thickness of 10 to 20 mm is suitable for the Si filter. Among the X-rays of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4, the X-ray passing through the center portion absorbs an energy component of 25 keV or less by the Si primary filter 8. Thereby, the background of the energy region below 25 keV is reduced. At the same time, an energy component of 25 keV or more is transmitted by the primary filter 8 and used as an excitation source. Of the X-rays of the radial beam bundle (solid angle Ω), X-rays at both ends are irradiated onto the secondary target 9 and the generated fluorescent X-rays 3 are irradiated onto the sample 1. As the material of the secondary target 9, a heavy element of tellurium (Te) having an atomic number of 52 or an oxide thereof is used, and the fluorescent X-ray Te-Kα ray (27.468 keV) or the like is used as an excitation ray.
Therefore, by simultaneously irradiating the sample 1 with the monochromatic beam transmitted through the primary filter 8 and the fluorescent X-rays generated from the secondary target 9, the fluorescent X-ray intensity of the measurement sample element Cd is increased, and P / B ratio can be improved, and trace element analysis becomes possible.

When analyzing elements such as arsenic (As), selenium (Se), bromine (Br), lead (Pb), mercury (Hg), etc., which are toxic heavy metals, the thickness of the primary filter 8 depends on the X-ray tube target used and Although it depends on the tube voltage, a thickness of 1 to 3 mm is suitable for the Si filter. Among the X-rays of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4, the X-ray passing through the center part absorbs an energy component of 17 keV or less by the Si primary filter 8. Thereby, the background of the energy region below 17 keV is reduced. At the same time, an energy component of 17 keV or more is transmitted by the primary filter 8 and used as an excitation source. Of the X-rays of the radial beam bundle (solid angle Ω), X-rays at both ends are irradiated onto the secondary target 9 and the generated fluorescent X-rays 3 are irradiated onto the sample 1. As the material of the secondary target 9, a heavy element of zircon (Zr) having an atomic number of 40 to silver (Ag) having an atomic number of 47 or an oxide thereof, for example, fluorescent X-ray Mo-Kα ray (17. 441 keV) is used as the excitation line.
Therefore, by simultaneously irradiating the sample 1 with the monochromatic beam transmitted through the primary filter 8 and the fluorescent X-rays generated from the secondary target 9, the measurement sample elements As, Se, Br, Pb, Hg, etc. The fluorescent X-ray intensity can be increased and the P / B ratio can be improved, and trace element analysis becomes possible.

When analyzing the harmful heavy metal element chromium (Cr), the thickness of the primary filter 8 depends on the X-ray tube target and the tube voltage used, but a thickness of 0.1 to 0.3 mm is suitable for the Si filter. Yes. In this case, a plate-like filter is used. Among the X-rays of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4, the X-ray passing through the center portion absorbs an energy component of 6 keV or less by the Si primary filter 8. This reduces the background of the energy region below 6 keV. At the same time, an energy component of 6 keV or more is transmitted by the primary filter 8 and used as an excitation source. Of the X-rays of the radial beam bundle (solid angle Ω), X-rays at both ends are irradiated to the secondary target, and the generated fluorescent X-rays 3 are irradiated to the sample 1. As the material of the secondary target 9, a heavy element of iron (Fe) having an atomic number of 26 to copper (Cu) having an atomic number of 29 or an oxide thereof, for example, fluorescent X-ray Co-Kα ray (6. 924 keV) is used as the excitation line.
Therefore, by simultaneously irradiating the sample 1 with the monochromatic beam transmitted through the primary filter 8 and the fluorescent X-rays generated from the secondary target 9, the fluorescent X-ray intensity of the measurement sample element Cr is increased, and P / B ratio can be improved, and trace element analysis becomes possible.

  In FIG. 1 (c), the secondary target (2) 11 and the primary filter (2) 10 are installed at the outlet of the secondary target 9, and the X-rays transmitted through the primary filter 8 and the secondary target 9 The secondary target (2) 11 is irradiated with high-energy component scattered radiation, and the sample 1 is irradiated with the generated fluorescent X-rays. Thereby, the excitation line by the secondary target (2) 11 is superimposed on the excitation line of FIG. 1B, and the intensity of the fluorescent X-ray 5 can be increased. Further, the primary filter (2) 10 has a role of transmitting the excitation line and absorbing the background component in the analysis line region. Therefore, the P / B ratio can be improved and trace element analysis can be performed.

In the preceding paragraph, when analyzing the toxic heavy metal element cadmium (Cd), the thickness of the primary filters 8 and 10 depends on the type of X-ray tube target used and the tube voltage. And a thickness of 3-5 mm is suitable. Among the X-rays of the radial beam bundle (solid angle Ω) generated from the X-ray tube 4, the X-ray passing through the center part absorbs energy components of 25 keV or less by the Si primary filters 8 and 10. Thereby, the background of the energy region below 25 keV is reduced. At the same time, energy components of 25 keV or more are transmitted by the primary filters 8 and 10 and used as an excitation source. Of the X-rays of the radial beam bundle (solid angle Ω), the X-rays at both ends are irradiated to the secondary target 9 and the generated fluorescent X-rays 3 are irradiated to the sample 1. Further, the secondary target (2) 11 on the outlet side has a thickness of 0.01 to 0.3 mm, and the secondary targets 9 and 11 are made of heavy elements of tellurium (Te) of atomic number 52 or more or their oxidation as the material of the secondary targets 9 and 11. A fluorescent X-ray Te-Kα ray (27.468 keV) or the like is used as an excitation ray.
Therefore, by simultaneously irradiating the monochromatic beam transmitted through the primary filters 8 and 10 and the fluorescent X-rays generated from the secondary targets 9 and 11, the fluorescent X-ray intensity of the measurement sample element Cd is increased, and P / B ratio can be improved, and trace element analysis becomes possible.

The invention's effect

  As described above, since the X-rays in the energy band of the measurement element range are almost absorbed by the primary filters 8 and 10, the background is reduced, while the ratio of the X-ray intensity in the energy band as an excitation component is reduced. The use of secondary targets 9 and 11 is significantly higher. Therefore, trace element analysis becomes possible.

As the material of the primary filter of the present invention, it is preferable to use an element having an atomic number of 6 or more and 28 or less, more preferably a single crystal of magnesium (Mg), aluminum (Al), Si or an oxide thereof. used (MgO, SiO _2, etc.) or a nitride _{(Si 3} N 4, AlN, etc.).

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In this embodiment, heavy metals (for example, Cr, Pb, As, Se, Cd, Br, Hg) harmful to the human body contained in soil and electronic materials are analyzed, and whether the content is below a predetermined reference value. An example of an apparatus that performs a pass / fail judgment on whether or not is described.

  In FIG. 1, this apparatus is provided with a measurement sample 1, an X-ray tube 4 that irradiates the measurement sample 1 with primary X-rays 3, an X-ray monochromator 7, and fluorescent X-rays generated from the measurement sample 1. 5 is provided. An X-ray monochromator 7 is provided in the primary X-ray optical path, and a primary filter 8 and a secondary target 9 are placed therein. A secondary filter is placed in front of the detector. The X-ray at the center of the inner radial beam bundle (Ω) of the primary X-ray 3 is absorbed and / or transmitted through the primary filter 8 and irradiated onto the measurement sample 1. The primary filter 8 reduces or removes the component that becomes the background of the analysis line. On the other hand, the X-rays contributing to the excitation of the primary X-rays are partially absorbed by the primary filter, but most of them are transmitted and irradiated to the measurement sample 1. Further, X-rays at both ends of the radial beam bundle (Ω) are applied to the conical secondary target 10 to excite the target element to generate fluorescent X-rays, which are applied to the measurement sample 1.

The X-ray monochromatization mechanism 7 is provided at a position where the fluorescent X-ray 5 directed from the sample 1 toward the detector 6 is not absorbed. Therefore, the primary filter 8 absorbs and transmits only the primary X-ray 3 and does not absorb the fluorescent X-ray 5.
In order to improve analysis accuracy, a secondary filter 12 may be provided in the optical path of the fluorescent X-ray 5. When analyzing Cd in plastic, the sum peak caused by the X-ray spectrum from Br or Pb contained in the plastic just overlaps with the Cd-Kα ray, and increases the background. In order to improve the analysis accuracy, it is necessary to remove these peaks. The secondary filter 12 reduces or eliminates the background caused by the thumb peak generated in the measurement sample 1.

  When toxic heavy metal elements are measured with this apparatus, tungsten (W), rhenium (Re) are used as targets of the X-ray tube used in the X-ray source from the viewpoint of background reduction, particularly removal of interference lines. ), Tantalum (Ta), gold (Au), platinum (Pt), molybdenum (Mo), palladium (Pd), and lanthanum (La) are generally preferred.

As the detector, for example, a silicon drift detector (SDD) or a mercury iodide detector (HgI ₂ ) that has excellent energy resolution and performs electronic cooling by a Peltier element regardless of liquid nitrogen cooling is adopted. Is preferred.

As shown in FIG. 2 (a), the primary filter 8 uses Si, but a simple substance such as carbon (C), Mg, Al, MgO, Al ₂ O ₃ , Si ₃ N ₄ , or AlN. Further, oxides, nitrides, and combinations of two or more of them alone or compounds may be used. As for the shape, a conical shape, a disk shape, a quadrangular pyramid shape, or the like may be used.

  The secondary target 10 is selected for each analytical element. In general, a target material having a constituent element having an energy slightly higher than the absorption edge energy of the analytical element is selected. It may be a single metal or an oxide thereof. Table 1 shows the secondary target material for each measurement element group.

Prepare a plurality of monochromatization mechanisms with different thicknesses and materials of the primary filter and secondary target, respectively, according to the measurement element group, program in advance, and perform measurement while automatically replacing the monochromatization mechanism It is composed.

The invention's effect

As described above, according to the present invention, the excitation X-ray intensity can be increased using the secondary target while reducing the background by the primary filter. Further, by using a light element as a primary filter material and using a secondary filter, the spectrum of elements constituting conventionally used heavy metal filters such as Mo, Zr, Ag, and Cu does not appear or is attenuated. Therefore, the influence of disturbing lines due to these spectra is almost zero. As described above, the X-ray intensity can be increased and the background can be reduced. In addition, by using a secondary filter, it is possible to suppress spectrum overlap such as a thumb peak appearing in the analysis range. As a result, the lower limit of detection of harmful heavy metal elements can be reduced to 0.5 ppm or less, and the analysis time can be greatly shortened.
Compared with the case of using a high-power X-ray tube, it is only necessary to use a low-power X-ray tube, so that the cost can be reduced. In addition, since continuous X-rays with high output can be used as an excitation component, a plurality of elements other than harmful heavy metal elements can be excited efficiently.

  1 is a schematic diagram showing a fluorescent X-ray apparatus according to an embodiment of the present invention. FIGS. 1B and 1C are detailed internal views of the X-ray excitation optical system.   It is a graph which shows the relationship of the energy area | region made monochromatic by the distribution map of the continuous X-ray from an X-ray tube, and a primary filter and a secondary target.

Table 1

  It is a graph which shows the secondary target material for every measurement element area | region.

Explanation of symbols

1: Measurement sample 2: Sample holder 3: Primary X-ray 4: X-ray tube 5: Fluorescent X-ray 6: Detector 7: X-ray monochromator 8: Primary filter 9: Secondary target 10: Primary Filter (2)
11: Secondary target (2)
12: Secondary filter 13: Continuous X-ray irradiation distribution from the X-ray tube 14: Continuous X-ray irradiation distribution transmitted through the primary filter 15: Fluorescent X-ray from the secondary target

Claims (5)

By irradiating the measurement sample with primary X-rays from the X-ray source via the X-ray monochromatization mechanism, and detecting the fluorescent X-rays generated from the measurement sample receiving the primary X-rays with a detector, In a fluorescent X-ray analyzer that performs elemental analysis of a measurement sample,
The X-ray monochromatization mechanism consists of a primary filter and a secondary target. Of the radiation beam from the X-ray tube, the beam near the center is monochromatic by the primary filter, and the energy components at both ends are secondary targets. A fluorescent X-ray analysis apparatus characterized in that the measurement sample is simultaneously irradiated with these monochromatized beams and used as an X-ray excitation source. In claim 1,
A secondary target 2 and a primary filter 2 are newly provided at the outlet of the secondary target, and background components generated from the secondary target are absorbed by the primary filter 2 to be monochromatic, and generated from the secondary target 2. A fluorescent X-ray analyzer characterized in that the sample is irradiated with the fluorescent X-rays and the fluorescent X-rays generated from the secondary target to increase the ratio of peak to background intensity. In claims 1 and 2,
The X-ray fluorescence analyzer according to claim 1, wherein the primary filter is made of silicon, aluminum, magnesium, oxides, nitrides or alloys thereof. In claims 1 and 2,
A fluorescent X-ray analyzer characterized in that a secondary filter is provided between the measurement sample and the detector, the sum peak of the interference peak is removed, and the analysis accuracy of the measurement element spectrum is improved. An X-ray fluorescence analyzer characterized in that the secondary filter is one of 20-200 μm thick thin films of germanium, palladium, rhodium, selenium, and aluminum when analyzing environmental sample harmful heavy metals.

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