X-ray fluorescence spectrometer

Abstract

Provided is an x-ray fluorescence spectrometer. When a partition wall (10) has been closed, a sample chamber (1) and an irradiation chamber (2) are substituted with nitrogen, and a spectral chamber (3) is evacuated. A sample (4) is placed in the sample chamber (1) after the substitution is complete, and in response to an instruction from an operator, measurement is performed in a wait mode in which the sample (4) is irradiated with primary x-rays (6) and measurement begins after a prescribed amount of time has passed or a non-wait mode in which the sample (4) is irradiated with the primary x-rays (6) and measurement begins immediately. The prescribed amount of time of the wait mode is the amount of time, found in advance, until the ratio of the measurement intensity to a final arrival measurement intensity for x-ray fluorescence (8) of a prescribed wavelength becomes equal to or greater than a prescribed numerical value or is the amount of time until the ratio of the change in a preliminary measurement intensity to the preliminary measurement intensity for x-ray fluorescence (8) of a prescribed wavelength during preliminary measurement immediately after the sample (4) is irradiated with the primary x-rays (6) becomes equal to or less than a prescribed numerical value.

Description

X-ray fluorescence analyzer Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-146534, filed August 28, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an X-ray fluorescence analyzer for analyzing a sample in a nitrogen atmosphere.

[0003] A conventional X-ray fluorescence analyzer includes a sample chamber that houses a sample, an irradiation chamber that houses an X-ray source that irradiates the sample with primary X-rays and is in communication with the sample chamber, a spectroscopy chamber that houses a detection means that disperses secondary X-rays, such as fluorescent X-rays, generated from the sample and measures their intensity, and a partition wall that is disposed between the irradiation chamber and the spectroscopy chamber and that can be opened and closed to allow the secondary X-rays to pass (see Patent Document 1).When analyzing a liquid or powder sample with this analyzer, the partition wall is closed to separate the irradiation chamber from the spectroscopy chamber, and the sample chamber and the irradiation chamber are replaced with an inert gas and the spectroscopy chamber is evacuated to a vacuum so as to prevent the sample from scattering or volatilizing and to minimize X-ray attenuation.

[0004] This device does not require the purging of the spectroscopic chamber with an inert gas, so the purging can be completed in a short time and the amount of inert gas consumed is small. Furthermore, since only the secondary X-rays pass through the partition, the attenuation of the X-rays is sufficiently small. Therefore, secondary X-rays of sufficient intensity can be obtained and there is no risk of the partition being deteriorated or damaged by the irradiation of the primary X-rays.

[0005] Patent No. 3962075

[0006] The inert gas used is helium or nitrogen. Figure 8 shows the relationship between the energy and relative transmittance of fluorescent X-rays in the measurement atmosphere using each gas. The relative transmittance is the ratio of the reference intensity measured for each fluorescent X-ray, measured using a solid sample, with the partition open to connect the irradiation chamber and the spectroscopic chamber, and the sample chamber, irradiation chamber, and spectroscopic chamber all evacuated to a vacuum, to the reference intensity measured using the partition closed to separate the irradiation chamber and spectroscopic chamber, with the sample chamber and irradiation chamber purged with an inert gas, and only the spectroscopic chamber evacuated to a vacuum. In Figure 8, "helium / vacuum" refers to the measurement atmosphere using helium as the inert gas, and "nitrogen / vacuum" refers to the measurement atmosphere using nitrogen as the inert gas. Also, in Figure 8, "Kα" and "Lα" are expressed as "Ka" and "La."

[0007] Nitrogen has a higher density than helium, and when nitrogen is used as an inert gas, the relative transmittance of fluorescent X-rays of 4 keV or less decreases, so it is desirable to use helium as the inert gas, which attenuates X-rays less, and helium gas is usually used. However, since helium is expensive and not easily available, it is desirable to be able to use nitrogen when performing analysis using analytical lines with energies higher than P-Kα.

[0008] An example of the analysis of liquid samples using conventional equipment is the analysis of sulfur concentration in fuel oil, which requires high accuracy. The specimen is a sample cell covered with a polymer sample film and filled with fuel oil, which is a liquid sample. However, when analyzing the same fuel oil multiple times, it was found that the accuracy was lower in a nitrogen atmosphere than in a helium atmosphere, even when the sample was adjusted to avoid reproducibility issues.

[0009] The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an X-ray fluorescence analyzer that can perform sufficiently accurate analysis of samples in a nitrogen atmosphere and that also allows for analysis that places emphasis on the number of samples analyzed per unit time.

[0010] To achieve the above object, an X-ray fluorescence analyzer according to the present invention includes a sample chamber for accommodating a sample, an irradiation chamber that accommodates an X-ray source that irradiates the sample with primary X-rays and communicates with the sample chamber, a spectroscopy chamber that accommodates detection means that disperses secondary X-rays generated from the sample and measures their intensity, and a partition that is disposed between the irradiation chamber and the spectroscopy chamber and can be opened and closed to allow the secondary X-rays to pass through. The X-ray fluorescence analyzer also includes control means for controlling the operation of the X-ray fluorescence analyzer, such that when the partition is closed to separate the irradiation chamber from the spectroscopy chamber, the sample chamber and the irradiation chamber are replaced with nitrogen and the spectroscopy chamber is evacuated, and when the partition is open to communicate with the irradiation chamber and the spectroscopy chamber, the sample chamber, the irradiation chamber, and the spectroscopy chamber are evacuated.

[0011] Furthermore, when the control means replaces the atmosphere in the sample chamber and the irradiation chamber with nitrogen, the control means stores the sample in the sample chamber after the replacement is complete, and, depending on the operator's instructions, either a standby mode in which the sample is irradiated with primary X-rays and measurement by the detection means begins a predetermined time later, or a non-standby mode in which the sample is irradiated with primary X-rays and measurement by the detection means begins immediately.

[0012] Here, the predetermined time in the standby mode is the predetermined time until the ratio of the measured intensity to the final measured intensity for fluorescent X-rays of a predetermined wavelength becomes equal to or greater than a predetermined value, or the time until the ratio of the change in the preliminary measured intensity to the preliminary measured intensity for fluorescent X-rays of a predetermined wavelength becomes equal to or less than a predetermined value in preliminary measurement by the detection means immediately after the sample is irradiated with primary X-rays.

[0013] The present inventors have thoroughly investigated the above-mentioned problem and have concluded that the cause is that the inert gas in the sample chamber and irradiation chamber is heated by the irradiation of the sample with primary X-rays, causing density instability. This is due to the fact that nitrogen has a lower thermal conductivity than helium, i.e., it conducts heat more slowly. This led to the development of the present invention. Specifically, according to the present invention, by executing the standby mode, which starts measurement after a predetermined time has elapsed, the nitrogen density in the sample chamber and irradiation chamber is stabilized, enabling sufficiently accurate analysis of samples in a nitrogen atmosphere, particularly in the analysis of light elements with low fluorescent X-ray energy (long wavelength), which are susceptible to changes in nitrogen density. On the other hand, in the analysis of heavy elements with high fluorescent X-ray energy (short wavelength), which are less affected by changes in nitrogen density, the non-standby mode, which starts measurement immediately after the sample is irradiated with primary X-rays, allows for analysis that emphasizes the number of samples analyzed per unit time. In this application, light elements refer to elements with atomic number 21 (Sc) or less, and heavy elements refer to elements with atomic number 22 (Ti) or more.

[0014] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims is included in the present invention.

[0015] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation purposes and should not be used to define the scope of the present invention. The scope of the present invention is defined by the appended claims. In the accompanying drawings, the same part numbers in multiple drawings indicate the same parts. This is a schematic diagram of an X-ray fluorescence analyzer according to one embodiment of the present invention. It is an enlarged cross-sectional view of the vicinity of the partition wall in FIG. 1. It is a view taken in the direction of arrow III in FIG. 2. It is a cross-sectional view taken along line IV-IV in FIG. 3 with the partition wall open. It is a cross-sectional view taken along line IV-IV in FIG. 3 with the partition wall closed. It is a diagram showing the change in P-Kα measured intensity versus measurement time in the X-ray fluorescence analyzer of this embodiment, and a Boltzmann curve approximating this change. It is a diagram showing the Boltzmann curve obtained by converting the vertical axis of FIG. 5. It is a diagram showing the intensity change rate curve versus measurement time obtained by plotting the rate of change in measured intensity versus measured intensity for the Boltzmann curve of FIG. 6. It is a diagram showing the relationship between the energy of fluorescent X-rays and the relative transmittance ratio in each measurement atmosphere of helium or nitrogen.

[0016] An X-ray fluorescence analyzer according to one embodiment of the present invention will now be described. As shown in Fig. 1, this apparatus comprises a sample chamber 1 in which a sample 4 placed in a sample holder 5 is held by a holding mechanism (not shown), an irradiation chamber 2 that communicates with the sample chamber 1 and contains an X-ray source 7 such as an X-ray tube that irradiates primary X-rays 6 onto the sample 4 from below, a spectroscopy chamber 3 that contains a detection means 9 that disperses secondary X-rays 8 such as fluorescent X-rays emitted from the sample 4 and measures their intensity, and a partition wall 1 that is disposed between the irradiation chamber 2 and the spectroscopy chamber 3 and can be opened or closed to allow the secondary X-rays 8 to pass through. The irradiation of the primary X-rays 6 onto the sample 4 and its stopping are controlled by opening or closing a shutter (not shown) that blocks the primary X-rays 6 continuously emitted from the X-ray source 7, in order to stabilize the output of the primary X-rays 6.

[0017] The detection means 9 includes a divergence slit 41 that collimates the secondary X-rays 8, a spectroscopic element 42 that disperses the secondary X-rays collimated by the divergence slit 41, two receiving slits 43 and 45 that collimate the secondary X-rays dispersed by the spectroscopic element 42, a scintillation counter 44 that serves as a first detector that detects the secondary X-rays collimated by the first receiving slit 43, and a gas flow proportional counter 46 that serves as a second detector that detects the secondary X-rays collimated by the second receiving slit 45. Although only one divergence slit 41 and one spectroscopic element 42 are shown in the figure, a plurality of divergence slits 41 and one spectroscopic element 42 are selected and used, as are the receiving slits 43 and 45 and the detectors 44 and 46. However, the second receiving slit 45 and the gas flow proportional counter 46 are integrated. The spectroscopic element 42, the receiving slits, and the detectors 43-44 and 45-46 are linked by a linking means such as a goniometer (not shown) to maintain a constant angular relationship. That is, this apparatus is a bottom-illuminated, wavelength-dispersive, scanning X-ray fluorescence analyzer.

[0018] This device also includes a field-limiting slit replacement mechanism 20 that has and replaces a plurality of field-limiting slits that limit the field of view of the detection means 9. As shown in Figure 2, which is an enlarged cross-sectional view of the vicinity of the partition wall 10 in Figure 1, a shaft (rail) 24 extending in a direction perpendicular to the plane of the page is provided on the upper side of the horizontal wall portion 32 between the sample chamber 1 and the spectroscopic chamber 3. Meanwhile, a bearing 23 that slidably engages with the shaft 24 is provided on the lower side of the horizontal portion of the slit plate 21 of the field-limiting slit replacement mechanism 20. The field-limiting slit replacement mechanism 20 appropriately moves the slit plate 21 in a direction perpendicular to the plane of the page using these shafts 24, bearings 23, a motor (not shown), and the like. In order to appropriately limit the field of view of the divergence slit 41, i.e., the field of view of the detection means 9 (FIG. 1), a plurality of field-limiting slits (holes) 22A to 22C of different diameters are provided in the portion of the slit plate 21 facing the sample 4, aligned in the direction of movement of the slit plate 21, as shown in FIG. 3, which is a view seen in the direction of arrow III in FIG. 2, and by appropriately moving the slit plate 21, a desired field-limiting slit 22 is positioned in the optical path of the secondary X-rays 8 (FIG. 2).

[0019] In this apparatus, the partition 10 is attached to the back side of the slit plate 21 at a portion facing the sample 4 ( FIG. 2 ), and as shown in FIG. 4A , which is a cross-sectional view taken along the line IV-IV in FIG. 3 , comprises a partition film 11 made of, for example, a circular polyimide film having a thickness of 1.2 μm; a reinforcing member 12 made of, for example, a stainless steel honeycomb structure (with numerous voids) having a thickness of approximately 3 to 5 mm and having approximately the same diameter as the partition film 11 and attached for reinforcement; a ring-shaped partition body 13 made of, for example, brass that holds them together; and an O-ring 14 fitted to the underside of the partition body 13 so as to protrude from the bottom surface of the partition body 13. Two holes are provided on the top left and right of the partition body 13, and the lower ends of pins 25 that slidably pass through the slit plate 21 are press-fitted into each hole. A ring 26 is fitted to the upper end of the pin 25, and a compression spring 27 is inserted between the ring 26 and the slit plate 21 so that the pin 25 passes through.

[0020] For liquid or powder samples when the partition wall 10 is used, there is usually no point in limiting the field of view to a small area, and it is desirable not to reduce the overall intensity of the secondary X-rays 8 ( FIG. 1 ) captured by the detection means 9. Therefore, as shown in FIG. 3 , the slit plate 21 has an open hole in the portion corresponding to the partition wall film 11, with a slit 22D having the same diameter as the largest field-limiting slit 22C. This slit 22D is also positioned on the same line as the multiple field-limiting slits 22A to 22C. As shown in FIG. 2 , a base 28, which is a ring-shaped metal plate with a smooth surface, is provided on the irradiation chamber 2 side of the wall 31 between the irradiation chamber 2 and the spectroscopic chamber 3 so that the O-ring 28 can be in airtight contact with it.

[0021] With the above-described configuration, when the sample chamber 1, irradiation chamber 2, and spectroscopic chamber 3 are at the same pressure, the partition 10 is pulled up by the extension force of the compression spring 27 so that its upper surface contacts the back side of the slit plate 21, as shown in Fig. 4A, and the O-ring 14 is separated from the base 28, allowing the slit plate 21 to move freely as described above. In other words, when analyzing a solid sample, an appropriate field-limiting slit is selected from the field-limiting slits 22A to 22C (Fig. 3) using the field-limiting slit exchange mechanism 20 shown in Fig. 1, and the irradiation chamber 2 and spectroscopic chamber 3 are connected via the through-hole 31a in the wall 31, and all chambers 1, 2, and 3 are evacuated, allowing analysis to be performed with high sensitivity without attenuating the secondary X-rays 8 due to the partition 10.

[0022] On the other hand, when analyzing a liquid sample or a powder sample, the partition 10 is moved by the field-limiting slit replacement mechanism 20 to a position covering the through-hole 31a, and the sample chamber 1 and the irradiation chamber 2 are replaced with nitrogen, while the spectroscopic chamber 3 is evacuated. More specifically, all chambers 1, 2, and 3 are first evacuated with the partition 10 open, and then the partition 10 is moved to a position covering the through-hole 31a. While continuing to evacuate the spectroscopic chamber 3, nitrogen is introduced into the sample chamber 1 and the irradiation chamber 2. Then, as shown in FIG. 4B , the force due to the pressure difference between the irradiation chamber 2 and the spectroscopic chamber 3 overcomes the extension force of the compression spring 27, and the partition 10 is pressed down so that the O-ring 14 is pressed against the base 28. 1 can be maintained in a nitrogen atmosphere at approximately atmospheric pressure, and the spectroscopic chamber 3 can be maintained in a vacuum atmosphere, and secondary X-rays 8 generated from the sample 4 pass through slit 22D in Fig. 4B, the gaps in partition membrane 11 and reinforcing member 12, the ring in partition body 13, the ring in base 28, and through-hole 31a in wall portion 31, and are detected by detection means 9 in Fig. 1. That is, in this device, partition 10 can be freely opened and closed, and the field-limiting slit replacement mechanism 20 also serves as the opening and closing mechanism.

[0023] The fluorescent X-ray analyzer of this embodiment is equipped with a control means 47 such as a computer that controls the operation of the fluorescent X-ray analyzer, and when the partition wall 10 is closed and the irradiation chamber 2 and the spectroscopic chamber 3 are separated by the control means 47, the sample chamber 1 and the irradiation chamber 2 are replaced with nitrogen and the spectroscopic chamber 3 is evacuated, and when the partition wall 10 is open and the irradiation chamber 2 and the spectroscopic chamber 3 are connected, the sample chamber 1, the irradiation chamber 2 and the spectroscopic chamber 3 are evacuated.

[0024] Furthermore, in this apparatus, when the sample chamber 1 and the irradiation chamber 2 are purged with nitrogen, the control means 47 places the sample 4 in the sample chamber 1 after the purge is complete, and in response to an operator's instruction from an input means (not shown), such as a keyboard or touch panel, the control means 47 executes either a standby mode in which the sample 4 is irradiated with primary X-rays 6 and measurement by the detection means 9 begins a predetermined time later, or a no-standby mode in which the sample 4 is irradiated with primary X-rays 6 and measurement by the detection means 9 begins immediately. The standby mode is instructed when the operator desires sufficiently accurate analysis of samples in a nitrogen atmosphere, particularly in the analysis of light elements with low fluorescent X-ray energy (long wavelength). On the other hand, the no-standby mode is instructed when the operator desires analysis that prioritizes the number of samples analyzed per unit time in the analysis of heavy elements with high fluorescent X-ray energy (short wavelength).

[0025] Here, the predetermined time in the standby mode can be set in two ways as follows: In the first setting, first, in a nitrogen atmosphere, for the fluorescent X-rays (analytical rays) to be measured by the X-ray fluorescence analyzer of this embodiment, that is, the lowest-energy fluorescent X-ray, for example, P-Kα, is measured using an arbitrary sample 4 containing P (phosphorus), and primary X-rays 6 are irradiated. Immediately, measurement by the detection means 9 is initiated and repeated, for example, every 10 seconds, to obtain the change in the P-Kα measured intensity (intensity (kcps)) versus measurement time (time (sec)), as shown by the group of black square points in Figure 5 . This is then approximated by a Boltzmann curve, yielding the curve shown by the solid line in Figure 5 .

[0026] If the vertical axis of FIG. 5 is converted to an Intensity (%) axis, where 100% is the measured intensity 500 seconds after the Boltzmann curve becomes sufficiently horizontal and the measured intensity is determined to have reached the final measured intensity, the Boltzmann curve shown in FIG. 6 is obtained. In FIG. 6, the measurement time at which the measured intensity reaches 99.85% of the final measured intensity (rounded to two decimal places to 99.9%, or 0.1% less than the final measured intensity) can be read as 147 seconds. In other words, in this example, the predetermined time set by the first setting is the predetermined time of 147 seconds required for the ratio of the measured intensity to the final measured intensity for fluorescent X-ray P-Kα of a predetermined wavelength to reach or exceed the predetermined value of 99.9%, and this time is applied to all samples 4.

[0027] In the second setting, the predetermined time in the standby mode is determined for each sample 4, for example, every 10 seconds, during preliminary measurement by the detection unit 9 immediately after irradiation with the primary X-rays 6. To this end, first, to ensure that the predetermined time in the standby mode does not depend on the magnitude of the measured intensity, the intensity change rate curve versus measurement time (time (sec)) in FIG. 7 is examined, which is obtained by plotting the ratio of change in measured intensity (Intensity change rate (%)) to measured intensity for the Boltzmann curve in FIG. 6 . According to FIG. 7 , the intensity change rate (the ratio of change in preliminary measurement intensity to preliminary measurement intensity) 147 seconds after the start of preliminary measurement is read as 0.007%. That is, in this example, the predetermined time in the second setting is the time until the ratio of change in preliminary measurement intensity to preliminary measurement intensity for fluorescent X-rays P-Kα of a predetermined wavelength in preliminary measurement by the detection unit 9 immediately after irradiation with the primary X-rays 6 on the sample 4 falls below the predetermined value of 0.007%. This predetermined time is determined for each sample 4, and the actual measurement is started after this predetermined time has elapsed.

[0028] Using the standby mode of the X-ray fluorescence analyzer of this embodiment, a sample cell filled with 4 ml of fuel oil and covered with a 3.6 μm thick polyester film was used to analyze the concentration of trace amounts (10 ppm) of sulfur in fuel oil. When the results were verified according to ASTM D2622, the maximum difference in the analysis results was 0.3 ppm, which fully satisfied the specified limit of 0.9 ppm or less.

[0029] As described above, this apparatus stabilizes the nitrogen density in the sample chamber 1 and the irradiation chamber 2 by executing the standby mode, which starts measurement after the predetermined time has elapsed. This allows for sufficiently accurate analysis of the sample 4 in a nitrogen atmosphere, particularly in the analysis of light elements, such as P (phosphorus), that are susceptible to changes in nitrogen density and have low fluorescent X-ray energy (long wavelength). On the other hand, in the analysis of heavy elements, such as heavy elements that have high fluorescent X-ray energy (short wavelength), changes in nitrogen density have little effect. Therefore, by executing the no-standby mode, in which measurement begins immediately after the primary X-rays 6 are irradiated onto the sample 4, analysis can be performed with an emphasis on the number of samples analyzed per unit time. Similarly to the analysis of light elements, the standby mode can also be executed to emphasize accuracy and perform sufficiently accurate analysis. Note that when analyzing both heavy and light elements by scanning from highest to lowest fluorescent X-ray energy in a single scan, if the measurement of the fluorescent X-rays of the heavy elements takes longer than the predetermined time required in the standby mode, sufficiently accurate analysis of the light elements can be achieved by executing the no-standby mode, even if measurement by the detection means begins immediately after the primary X-rays are irradiated onto the sample.

[0030] It should be noted that the present invention is not limited to this embodiment, and can also be applied to a top-illuminated type device, a wavelength dispersive type device in which the detecting means is fixed, and an energy dispersive type device.

[0031] Although the preferred embodiment has been described above with reference to the drawings, those skilled in the art will readily understand various changes and modifications within the scope of the present invention, which are within the scope of the present invention as defined by the appended claims.

[0032] REFERENCE SIGNS LIST 1 Sample chamber 2 Irradiation chamber 3 Spectroscopic chamber 4 Sample 6 Primary X-rays 7 X-ray source 8 Secondary X-rays 9 Detecting means 10 Partition wall 47 Control means

Claims

1. An X-ray fluorescence analyzer comprising: a sample chamber for accommodating a sample; an irradiation chamber that communicates with the sample chamber and accommodates an X-ray source that irradiates the sample with primary X-rays; a spectroscopy chamber that accommodates detection means that disperses secondary X-rays generated from the sample to measure their intensity; and a partition that is disposed between the irradiation chamber and the spectroscopy chamber and can be opened and closed to allow the secondary X-rays to pass, the X-ray fluorescence analyzer further comprising a control means for controlling the operation of the X-ray fluorescence analyzer, wherein the control means replaces the atmosphere in the sample chamber and irradiation chamber with nitrogen and evacuates the spectroscopy chamber when the partition is closed to separate the irradiation chamber from the spectroscopy chamber; and evacuates the sample chamber, irradiation chamber, and spectroscopy chamber when the partition is open to allow the irradiation chamber and the spectroscopy chamber to communicate with each other; When the sample chamber and the irradiation chamber are purged with nitrogen, a sample is placed in the sample chamber after the purging is complete, and, in response to an instruction from an operator, a standby mode is executed in which the sample is irradiated with primary X-rays and measurement by the detection means begins a predetermined time later, or a non-standby mode is executed in which the sample is irradiated with primary X-rays and measurement by the detection means begins immediately, and the predetermined time in the standby mode is a predetermined time until the ratio of the measured intensity to the final measured intensity for fluorescent X-rays of a predetermined wavelength becomes equal to or exceeds a predetermined numerical value, or the time until the ratio of the amount of change in preliminary measured intensity to the preliminary measured intensity for fluorescent X-rays of a predetermined wavelength in a preliminary measurement by the detection means immediately after the sample is irradiated with primary X-rays becomes equal to or less than a predetermined numerical value.

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