An X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements

Abstract

The present invention provides an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements, wherein a high voltage generator emits electrons toward a target in an X-ray tube, the target emits primary X-rays in response to the electron incidence, a semi-ring bent crystal diffractor separates X-rays in a preset energy range, and focuses and directs them to a sample in a sample chamber, the sample responds to the X-ray incidence in a preset energy range and emits fluorescent X-rays, a full ring bent crystal diffractor in a radioactive element detection assembly separates characteristic X-rays of radioactive elements, and focuses and directs them to a detector, and different radioactive element detection assemblies are used to detect and receive characteristic X-rays of different radioactive elements. The present invention can improve the diffraction effect and focusing of the light source, realize the screening of monochromatic X-rays, greatly reduce the detection limit of radioactive elements, improve the measurement accuracy, and at the same time overcome the overlapping interference problem of multiple radioactive element spectral peaks at different mass concentrations from the monochromaticity of the hardware.

Description

Technical Field

[0001] The invention relates to the technical field of post-processing analysis, and in particular to an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements. Background Art

[0002] In recent years, my country's post-processing analysis technology has followed the development trend of foreign technology. According to the characteristics of radioactive samples and analysis needs, a graphite crystal pre-diffraction-X-ray fluorescence analysis system has been developed. The analysis method of radioactive elements uranium (U), neptunium (Np), and plutonium (Pu) in the post-processing process has been established, and applied to the intermediate pilot plant for the post-processing of power reactor spent fuel (referred to as the "pilot plant"). Based on the ordinary energy dispersive X-ray fluorescence analyzer, this instrument inserts a graphite diffractor between the sample and the detector, eliminating the influence of the sample's own radioactivity on the detector while reducing the scattering background, solving the problem of high sample radioactivity.

[0003] However, the structure of the existing core component graphite crystal diffractor is to fix the cylindrical graphite crystal as a whole on the inner wall of the metal shell, that is, the entire graphite crystal structure is cylindrical. For example, the Chinese utility model patent with announcement number CN209606354U discloses "a shuttle-shaped shielded graphite crystal derivative", which reduces the direct damage of high-intensity rays to the detector by directly depositing cylindrical graphite crystals on the inner wall of the metal shell and installing a shuttle-shaped shielding body from one end. The Chinese utility model patent with announcement number CN208103943U discloses "a new type of graphite crystal derivative", which also designs a cylindrical graphite crystal with a built-in shielding core. Both of the above-mentioned cylindrical graphite crystal structures have defects. The cylindrical structure can only show curvature in one direction, that is, it has only one radius of curvature. When irradiated by a point light source, the light source will be converged onto a radial straight line, and the wavelength of diffraction at each point is different. It can neither be focused to one point nor guarantee monochromaticity. The selectivity for rays of specific wavelengths is poor, the background scattering is high, and the collection efficiency of X-ray photons is reduced, which directly affects the detection limit and measurement accuracy of U, Np and Pu elements.

[0004] In addition, in the pilot plant application, there are many measurement points for trace U, Np and Pu, and the analysis concentration span is large. When the mass concentration of Np is at the same order of magnitude as U and Pu or greater than the mass concentration of U and Pu, Np will interfere with the determination of U and Pu to a certain extent; at the same time, the concentration ratio of U to Pu is greater than 100:1, and the concentration of Pu cannot be accurately measured. The overlapping interference problem of the three spectral peaks of U, Np and Pu has never been solved. Although the above-mentioned cylindrical graphite crystal diffractor can realize the bandpass selection of the area to be measured, it cannot solve the problem of overlapping interference of multi-element spectral lines. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an X-ray fluorescence analysis system for the simultaneous measurement of trace radioactive elements in view of the above-mentioned deficiencies in the prior art, which can improve the diffraction effect and focusing of the light source on the basis of the traditional graphite crystal pre-diffraction technology, realize the screening of monochromatic X-rays, reduce the detection limit of U, Np and Pu, improve the measurement accuracy, and overcome the overlapping interference problem of the three spectral peaks of U, Np and Pu at different mass concentrations.

[0006] The technical solution adopted to solve the technical problem of the present invention is:

[0007] The present invention provides an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements, comprising: a high voltage generator, an X-ray tube, a semi-ring bent crystal diffractor, a sample chamber, and a plurality of radioactive element detection components.

[0008] The high voltage generator is arranged at one side of the X-ray tube and is used to emit electrons toward the target material in the X-ray tube so that the target material emits primary X-rays in response to the electron incidence.

[0009] The semi-ring bent crystal diffractor is disposed between the X-ray tube and the sample chamber, and is used to separate X-rays of a preset energy range from the primary X-rays, and focus and direct them to the sample in the sample chamber.

[0010] The sample chamber is used to place a radioactive sample, and the radioactive sample emits fluorescent X-rays in response to the incidence of X-rays in the preset energy range.

[0011] The radioactive element detection assembly includes a full ring bent crystal diffractor and a radioactive element detector. The full ring bent crystal diffractor is arranged between the sample chamber and the radioactive element detector, and is used to separate the characteristic X-rays of the radioactive elements from the fluorescent X-rays, and guide them to the detector after focusing.

[0012] Different radioactive element detection assemblies are used to detect and receive characteristic X-rays of different radioactive elements.

[0013] Optionally, a line connecting an exit point of the primary X-ray on the target material and an incident point of the primary X-ray on the radioactive sample is set as the first axis segment,

[0014] The diffraction surface of the semi-ring bent crystal diffractor is a concave surface, which is formed by rotating a first circular arc with a curvature radius R1 around the first axis segment by 180°.

[0015] The exit point of the primary X-ray on the target, the incident point of the primary X-ray on the radioactive sample and the first arc are on a circle with a curvature radius of R1;

[0016] Let the line connecting the emission point of the fluorescent X-ray on the radioactive sample and the focal point of the fluorescent X-ray of the radioactive element be the second axis segment,

[0017] The diffraction surface of the full-ring bent crystal diffractor is a concave surface, which is formed by rotating a second circular arc with a curvature radius R2 around the second axis segment by 360°.

[0018] The emission point of the fluorescent X-ray on the radioactive sample, the focusing point of the fluorescent X-ray of the radioactive element and the second arc are on a circle with a curvature radius of R2.

[0019] Optionally, the radioactive elements include uranium, neptunium and plutonium, and the radioactive element detection components are correspondingly provided with three groups, namely, uranium detection components, neptunium detection components and plutonium detection components;

[0020] The preset energy range is 12-20 keV.

[0021] Optionally, the first arc has a curvature radius R1 of 320-380 mm and a length D1 of 50-60 mm.

[0022] The curvature radius of the second arc is R2, which is 400-450 mm, and the length D2 is 50-60 mm.

[0023] The length L1 of the first axis segment and the length L2 of the second axis segment are both calculated using formula (1):

[0024] L=2Rsin(2θ) (1)

[0025] The length r1 of the perpendicular line from the midpoint of the first arc to the first axis segment and the length r2 of the perpendicular line from the midpoint of the second arc to the second axis segment are both calculated using formula (2):

[0026] r=2Rsin 2 (θ) (2)

[0027] Wherein, L is the length of the corresponding axis segment, r is the length of the perpendicular line from the midpoint of the corresponding arc to the corresponding axis segment, R is the radius of curvature of the corresponding arc, and θ is the diffraction angle of the corresponding bent crystal diffractor;

[0028] The diffraction angle θ of the corresponding bent crystal diffractor is calculated using formula (3):

[0029] nλ=2dsinθ (3)

[0030] Wherein, d is the interplanar spacing of the bent crystals in the corresponding bent crystal diffractor; θ is the diffraction angle of the corresponding bent crystal diffractor; λ is the wavelength of the diffracted rays; and n is the reflection order.

[0031] Optionally, the semi-ring bent crystal diffractor is made of a lithium fluoride plate, the lithium fluoride plate has a concave surface, and the concave surface forms a diffraction surface of the semi-ring bent crystal diffractor, or,

[0032] The semi-ring bent crystal diffractor comprises a carrier having a concave surface, graphite crystals are deposited on the concave surface, and the surface of the graphite crystals forms the diffraction surface of the semi-ring bent crystal diffractor.

[0033] Optionally, the full ring bent crystal diffractor is made of lithium fluoride and has a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full ring bent crystal diffractor, or,

[0034] The full-ring bent crystal diffractor includes two half-ring bent crystal diffractors, and the half-ring bent crystal diffractor includes a carrier, the carrier has a concave surface, and graphite crystals are deposited on the concave surface. The two half-ring bent crystal diffractors are symmetrically spliced ​​to form the full-ring bent crystal diffractor, and the two concave surfaces deposited with graphite crystals enclose a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full-ring bent crystal diffractor.

[0035] Optionally, the full-ring bent crystal diffractor further includes a shielding core, which is a shuttle-shaped structure, located in the shuttle-shaped hole and arranged coaxially with the shuttle-shaped hole, and is used to block direct light from entering the detector.

[0036] Optionally, the power of the X-ray tube is 300-400W, and the target material is an Ag target or a W target.

[0037] Optionally, the sample is placed in a sample bottle, the sample bottle is placed in the center of a sealed sample chamber, and the sample chamber is placed in the center of a box chamber.

[0038] The sample chamber is provided with a first transmission window for incident fluorescent X-rays, and is also provided with a second transmission window for emission of characteristic X-rays of radioactive elements. A closed optical path channel is provided between the second transmission window and the detector, and the optical path channel passes through the chamber and is connected to the helium source.

[0039] Optionally, a control system is also included, which is electrically connected to multiple radioactive element detection components and is used to receive signals output by the radioactive element detection components and process them to obtain the dose of the radioactive element.

[0040] The X-ray fluorescence analysis system of the present invention comprises a plurality of groups of bent crystal diffractors, wherein a group of semi-annular bent crystal diffractors is placed between the X-ray tube and the sample to achieve monochromatic selection of the characteristic line of the target material of the X-ray tube, improve the energy density of the characteristic line of the target material, and increase the excitation effect on the radioactive elements in the sample; in addition, a plurality of groups of annular bent crystal diffractors are placed between the sample and the detector unit, and each group of annular bent crystal diffractors corresponds to a detector, which respectively receives characteristic X-rays of different radioactive elements. Experiments show that this structure can improve the diffraction effect and focusing of the light source on the basis of the traditional graphite crystal pre-diffraction technology, and the detector signal will only retain the pure peak to be measured of the corresponding radioactive element, thereby achieving the screening of monochromatic X-rays, reducing the detection limit of U, Np and Pu, improving the measurement accuracy, and overcoming the overlapping interference problem of the three spectrum peaks of U, Np and Pu at different mass concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements provided in Example 1 of the present invention.

[0042] Figure 2 Schematic diagram of a bent crystal diffractor according to an embodiment of the present invention;

[0043] Figure 3 Schematic diagram of the structure of a graphite bent crystal diffractor according to an embodiment of the present invention;

[0044] Figure 4 for Figure 3 BB cross-section diagram. DETAILED DESCRIPTION

[0045] The following will be combined with the accompanying drawings in the present invention to clearly and completely describe the technical solutions in the invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention.

[0046] In the description of the present invention, it should be noted that the directions or positional relationships indicated by “upper” and the like are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience and simplification of the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0047] In the description of the present invention, the terms “first” and “second” are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0048] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connect", "set", "install", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] The present invention provides an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements, comprising: a high voltage generator, an X-ray tube, a semi-ring bent crystal diffractor, a sample chamber, and a plurality of radioactive element detection components.

[0050] The high voltage generator is arranged at one side of the X-ray tube and is used to emit electrons toward the target material in the X-ray tube so that the target material emits primary X-rays in response to the electron incidence.

[0051] The semi-ring bent crystal diffractor is disposed between the X-ray tube and the sample chamber, and is used to separate X-rays of a preset energy range from the primary X-rays, and focus and direct them to the sample in the sample chamber.

[0052] The sample chamber is used to place a radioactive sample, and the radioactive sample emits fluorescent X-rays in response to the incidence of X-rays in the preset energy range.

[0053] The radioactive element detection assembly includes a full ring bent crystal diffractor and a radioactive element detector. The full ring bent crystal diffractor is arranged between the sample chamber and the radioactive element detector, and is used to separate the characteristic X-rays of the radioactive elements from the fluorescent X-rays, and guide them to the detector after focusing.

[0054] Different radioactive element detection assemblies are used to detect and receive characteristic X-rays of different radioactive elements.

[0055] Embodiment 1:

[0056] like Figure 1 As shown, this embodiment provides an X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements, including: a high voltage generator, an X-ray tube 1, a semi-ring bent crystal diffractor 2, a sample chamber 4, and a plurality of radioactive element detection components.

[0057] The high voltage generator is arranged at one side of the X-ray tube 1, and is used to emit electrons toward the target material in the X-ray tube 1, so that the target material emits primary X-rays in response to the electron incidence.

[0058] The semi-ring bent crystal diffractor 2 is disposed between the X-ray tube 1 and the sample chamber 4, and is used to separate the X-rays in a preset energy range from the primary X-rays, and focus and direct them to the sample in the sample chamber.

[0059] The sample chamber 4 is used to place a radioactive sample, and the radioactive sample emits fluorescent X-rays in response to the incident X-rays in the preset energy range.

[0060] The radioactive element detection assembly includes a full ring bent crystal diffractor and a radioactive element detector. The full ring bent crystal diffractor is arranged between the sample chamber 4 and the radioactive element detector, and is used to separate the characteristic X-rays of the radioactive elements from the fluorescent X-rays, and guide them to the detector after focusing.

[0061] Different radioactive element detection assemblies are used to detect and receive characteristic X-rays of different radioactive elements.

[0062] In this embodiment, the radioactive elements include uranium, neptunium and plutonium, and the radioactive element detection components are provided with three groups, namely uranium detection components, neptunium detection components and plutonium detection components;

[0063] The preset energy range is 12-20 keV. The characteristic X-ray energies of uranium, neptunium and plutonium are included in the above preset energy range. Through the diffraction of the semi-ring bent crystal diffractor 2, the monochromatic selection of the characteristic line of the X-ray tube target is realized, the energy density of the characteristic line of the target is improved, and the excitation effect on the U, Np and Pu elements is increased.

[0064] Among them, the uranium detection component includes a uranium full-ring bent crystal diffractor 10 and a uranium detector 13. The uranium full-ring bent crystal diffractor 10 is used to diffract the characteristic X-rays of U, that is, to separate the characteristic X-rays of the uranium element with an energy of 13.26 keV from the fluorescent X-rays, and focus and guide them to the uranium detector 13.

[0065] The neptunium detection assembly includes a neptunium full-ring bent crystal diffractor 11 and a neptunium detector 14. The neptunium full-ring bent crystal diffractor 11 is used to diffract the characteristic X-rays of Np, that is, to separate the characteristic X-rays of the neptunium element with an energy of 13.945 keV from the fluorescent X-rays, and focus and guide them to the neptunium detector 14.

[0066] The plutonium detection assembly includes a plutonium full-ring bent crystal diffractor 12 and a plutonium detector 15 . The plutonium full-ring bent crystal diffractor 12 is used to diffract the characteristic X-rays of Pu, separate the characteristic X-rays of the plutonium element with an energy of 14.279 keV from the fluorescent X-rays, and focus and guide them to the plutonium detector 15 .

[0067] According to the characteristic X-ray energies of U (Lα1: 13.26keV), Np (Lα1: 13.945keV) and Pu (Lα1: 14.279keV) elements, three sets of full-ring bent crystal diffractors allow X-rays with an energy range of 12 to 20keV to reach the detector position, eliminating the influence of sample radioactivity and reducing the scattering background, thereby improving the detection limit of the analytical method.

[0068] The uranium detector 13, the neptunium detector 14 and the plutonium detector 15 are used to detect, process and convert the characteristic X-ray fluorescence of U, Np and Pu emitted by the sample. It is composed of three high-performance silicon drift detectors (FAST-SDD), and the angle between the three detectors is 60° to 180°. The three detectors fundamentally overcome the overlapping interference problem of the three spectra from the hardware monochromaticity. The detector signal will only retain the pure peak to be measured, and the detection limit of U, Np and Pu elements will be greatly reduced.

[0069] Specifically, the uranium detector 13 is used to detect the characteristic X-rays of U, the neptunium detector 14 is used to detect the characteristic X-rays of Np, and the plutonium detector 15 is used to detect the characteristic X-rays of Pu. Figure 1 The angle between the three detectors shown is 90°. Depending on the actual arrangement position, the angle between the three detectors can be 60° to 180°. The three detectors fundamentally overcome the overlapping interference problem of the three spectra from the perspective of hardware monochromaticity. The detector signal will only retain the pure peak to be measured, and the detection limit of U, Np, and Pu elements will be greatly reduced.

[0070] Three groups of radioactive element detection components receive characteristic X-rays of U, Np and Pu respectively, which can eliminate the influence of sample radioactivity, reduce the scattering background, and thus improve the detection limit of the analytical method.

[0071] The X-ray fluorescence analysis system of this embodiment includes four groups of bent crystal diffractors, one group of semi-annular bent crystal diffractors is placed between the X-ray tube 1 and the sample to achieve monochromatic selection of the characteristic line of the target material of the X-ray tube, improve the energy density of the characteristic line of the target material, and increase the excitation effect on the radioactive elements in the sample; the other three groups of annular bent crystal diffractors are placed between the sample and the detector unit, and each group of annular bent crystal diffractors corresponds to a detector, which receives the characteristic X-rays of U, Np and Pu respectively. Experiments show that this structure can improve the diffraction effect and focusing of the light source on the basis of traditional graphite crystal pre-diffraction technology. The detector signal will only retain the pure peak to be measured of the corresponding radioactive element, realize the screening of monochromatic X-rays, greatly reduce the detection limit of U, Np and Pu, improve the measurement accuracy, and overcome the overlapping interference problem of the three spectral peaks of U, Np and Pu at different mass concentrations.

[0072] In this embodiment, the line connecting the exit point of the primary X-ray on the target and the incident point of the primary X-ray on the radioactive sample is set as the first axis segment.

[0073] The diffraction surface of the semi-ring bent crystal diffractor is a concave surface, which is formed by rotating a first circular arc with a curvature radius R1 around the first axis segment by 180°.

[0074] The exit point of the primary X-ray on the target, the incident point of the primary X-ray on the radioactive sample and the first arc are on a circle with a curvature radius of R1;

[0075] Let the line connecting the emission point of the fluorescent X-ray on the radioactive sample and the focal point of the fluorescent X-ray of the radioactive element be the second axis segment,

[0076] The diffraction surface of the full-ring bent crystal diffractor is a concave surface, which is formed by rotating a second circular arc with a curvature radius R2 around the second axis segment by 360°.

[0077] The emission point of the fluorescent X-ray on the radioactive sample, the focusing point of the fluorescent X-ray of the radioactive element and the second arc are on a circle with a curvature radius of R2.

[0078] That is, the full ring curved crystal diffractor is a hyperbolic crystal with two radii of curvature, that is, a curved surface obtained by rotating a circular arc segment with a radius of curvature R around the line connecting the light source and the focus, and the rotation radius is r. The polychromatic X-rays emitted by the light source are irradiated onto the hyperbolic crystal at a certain incident angle. The crystal constant 2d is fixed, and the X-rays that conform to the Bragg equation 2dsinθ=nλ can be diffracted on the crystal. The hyperbolic crystal can diffract the polychromatic rays emitted by the point light source and converge them into a point, increasing the energy density of the target point and ensuring monochromaticity.

[0079] The semi-ring bent crystal diffractor is half of the full ring bent crystal diffractor, and also has a hyperbolic structure, without a shielding core in the middle, which increases the receiving area of ​​the ray and retains some direct X-rays. The semi-ring bent crystal diffractor realizes the monochromatic selection of the characteristic line of the X-ray tube target, improves the energy density of the characteristic line of the target, and increases the excitation effect on the U, Np and Pu elements.

[0080] Specifically, the half-ring bent crystal diffractor 2 is placed between the X-ray tube 1 and the sample chamber 4, and can diffract the target characteristic line of the X-ray tube 1. Since the polychromatic primary X-rays emitted by the X-ray tube 1 are irradiated onto the hyperbolic crystal at a certain incident angle, the X-rays that conform to the Bragg equation can be diffracted on the crystal, and the bremsstrahlung part of the primary X-rays does not conform to the diffraction conditions of the half-ring bent crystal diffractor 2, so no background is generated in the fluorescence signal of the sample. In this way, the energy density of the W characteristic line can be increased by 10 4 Above, the focal spot size is controlled within 50um×50um.

[0081] The rear section adopts a full-ring bent crystal diffractor with a hyperbolic structure. This bent crystal diffractor takes into account the radiation shielding and selective pass characteristics of the ordinary cylindrical graphite pre-diffraction system, and has the excellent monochromaticity of the hyperbolic structure, which increases the diffraction effect and focusing of the light source, diffracts the polychromatic rays emitted by the point light source and converges them to a specific point, increases the energy density of the target point, and ensures monochromaticity, greatly reducing the detection limits of U, Np and Pu elements and improving the measurement accuracy.

[0082] In this embodiment, the curvature radius R1 of the first arc is 320-380 mm, and the length D1 is 50-60 mm.

[0083] The curvature radius of the second arc is R2, which is 400-450 mm, and the length D2 is 50-60 mm.

[0084] The length L1 of the first axis segment and the length L2 of the second axis segment are both calculated using formula (1):

[0085] L=2Rsin(2θ) (1)

[0086] The length r1 of the perpendicular line from the midpoint of the first arc to the first axis segment and the length r2 of the perpendicular line from the midpoint of the second arc to the second axis segment are both calculated using formula (2):

[0087] r=2Rsin 2 (θ) (2)

[0088] Wherein, L is the length of the corresponding axis segment, r is the length of the perpendicular line from the midpoint of the corresponding arc to the corresponding axis segment, R is the radius of curvature of the corresponding arc, and θ is the diffraction angle of the corresponding bent crystal diffractor;

[0089] The diffraction angle θ of the corresponding bent crystal diffractor is calculated using formula (3):

[0090] nλ=2dsinθ (3)

[0091] Wherein, d is the interplanar spacing of the bent crystals in the corresponding bent crystal diffractor; θ is the diffraction angle of the corresponding bent crystal diffractor; λ is the wavelength of the diffracted rays; and n is the reflection order.

[0092] That is, the three full-ring bent crystal diffractors are three hyperbolic bent crystals with different Bragg angles and focal line distances, and the difference in their structures depends on the characteristic X-ray energy and wavelength of the elements U, Np, and Pu to be measured.

[0093] Specifically, the working principle of the bent crystal diffractor is based on the Bragg diffraction equation (3) and the Rowland circle geometry.

[0094] According to the Bragg diffraction conditions, at a fixed incident angle, only X-rays with a wavelength that conforms to the Bragg diffraction equation will be diffracted when they are irradiated on the bent crystal diffractor, while X-rays with other wavelengths will be scattered.

[0095] The following takes the uranium full-ring bent crystal diffractor 10 as an example to calculate various parameters of the bent crystal diffractor.

[0096] The uranium full ring bent crystal diffractor 10 is mainly designed for the wavelength of the La line of U, which allows the wavelength of 0.0911nm (U La) to be reflected to the detector through the diffractor. The wavelength calculation is shown as follows:

[0097] U:La energy E is 13.61keV, wavelength

[0098]

[0099] It is known that the d of graphite crystal is 0.3352nm, 2d is 0.6704nm, and the diffraction order is n=1. Then the diffraction angle is

[0100]

[0101] like Figure 2 As shown, the rays emitted by the light source S located on the Rowland circle are all irradiated on the graphite crystal 19 at a diffraction angle θ, and finally converge at a symmetrical exit point S', and meet the Bragg diffraction condition. According to the arrangement of the instrument components and the optical path structure, assuming that the Rowland circle radius is R = 420mm, taking the point P where the light source irradiates the graphite crystal as an example, the distance SS' from the X-ray source to the detector is:

[0102]

[0103] The graphite crystal rotates along the line SS' connecting the light source and the convergence point, that is, the convergence from S to S' is completed. The radius of the rotation axis is:

[0104]

[0105] Therefore, the radius in the meridian direction is R = 420 mm, the radius in the sagittal direction is r = 15.5 mm, and the single piece of graphite crystal is along Figure 2 The line connecting the points S and S' shown is rotated 180°, and the two graphite crystals 19 are attached together to finally form a 360° ring structure.

[0106] In this embodiment, a crystal support plate with a hyperbolic structure is firstly processed by a diamond cutting machine, and then a highly oriented pyrolytic graphite crystal 19 is deposited on the hyperbolic crystal support plate. Figure 3As shown, the meridian radius is 420 mm, the sagittal radius is 15.5 mm, and the length h of the graphite bent crystal diffractor is determined to be 55 mm according to the actual arrangement of the instrument components. A pyrolytic graphite layer (HOPG) with a thickness of 200 μm and a mosaic degree of 0.8° is deposited on the inner side of the carrier 21. Figure 4 for Figure 3 From the BB cross-section diagram, it can be seen that the upper and lower crystal support plates are spliced ​​into one, and finally the processing of the entire graphite bent crystal diffractor is completed.

[0107] As shown in Table 1, the wavelength, diffraction angle, focal distance and sagittal radius of the three elements U (Lα1: 13.26keV), Np (Lα1: 13.945keV) and Pu (Lα1: 14.279keV) are listed according to Formula 1-1, where the focal distance is the distance between the sample and the detector.

[0108] Table 1

[0109]

[0110] The parameter calculation of the semi-ring bent crystal diffractor 2 also refers to the above process. The preset energy range of 12 to 20 keV is substituted into formula (4) to calculate the λ range, and then the calculated λ range is substituted into formula (5) to calculate the θ range. Then, the curvature radius R1 of the first arc and the length L1 of the first axial segment of the semi-ring bent crystal diffractor 2 are calculated according to formulas (1) and (2) respectively.

[0111] Through experiments, the X-ray fluorescence analyzer designed and processed by the bent crystal diffractor with a hyperbolic structure in the present invention has a detection limit of 0.038 mg / L and a quantitative limit of 0.125 mg / L for U element at 60 kV / 5 mA, and a relative standard deviation (RSD) of 2.68%.

[0112] In this embodiment, the semi-ring bent crystal diffractor includes a carrier having a concave surface, graphite crystals are deposited on the concave surface, and the surface of the graphite crystals forms the diffraction surface of the semi-ring bent crystal diffractor.

[0113] In other embodiments, the semi-ring bent crystal diffractor may be made of a lithium fluoride plate having a concave surface, and the concave surface forms a diffraction surface of the semi-ring bent crystal diffractor.

[0114] In this embodiment, Figure 3As shown, the full-ring bent crystal diffractor includes two half-ring bent crystal diffractors, and the half-ring bent crystal diffractor includes a carrier 21, and the carrier 21 has a concave surface, and graphite crystals 19 are deposited on the concave surface. The two half-ring bent crystal diffractors are symmetrically spliced ​​to form the full-ring bent crystal diffractor, and the two concave surfaces deposited with graphite crystals 19 enclose a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full-ring bent crystal diffractor.

[0115] The material of graphite crystal is highly oriented pyrolytic graphite (HOPG). After high-temperature treatment, the performance of pyrolytic graphite is close to that of single crystal graphite, and it can reflect X-rays efficiently.

[0116] The carrier 21 uses a copper substrate and needs to be calculated and processed into a specific hyperbolic structure. Considering the process requirements of graphite coating deposition, two half-ring bent crystal diffractors are spliced ​​into a full-ring bent crystal diffractor structure.

[0117] Specifically, the full ring bent crystal diffractor further includes a shielding core 20, and a bracket 22 is used to fix and support the shielding core 20. The shielding core 20 is a shuttle-shaped structure, made of tungsten alloy, located in the shuttle-shaped hole, and arranged coaxially with the shuttle-shaped hole, and is used to block direct light from entering the detector, reduce the damage of the ray to the detector, and reduce the scattered background, and improve the detection limit of the analysis method. And it avoids the fluorescence radiation from being directly transmitted from the sample to the detector without diffraction.

[0118] In other embodiments, the full-ring bent crystal diffractor is made of lithium fluoride and has a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full-ring bent crystal diffractor.

[0119] In this embodiment, the X-ray tube adopts a high-power small-volume light tube with a power of 300-400W. The light tube is easy to disassemble and replace, and the target material is an Ag target or a W target.

[0120] The X-ray tube 1, the high voltage generator and the cooling device constitute an X-ray generating unit, which is used to emit primary X-rays. In this embodiment, a tungsten (W) target X-ray tube is selected according to the characteristic X-ray energy of the U, Np and Pu elements to be measured. The W target has a good excitation effect on the Lα energy level of the U, Np and Pu elements. The maximum tube voltage of the X-ray tube is 75KV, the maximum tube current is 15mA, and the power is 350W.

[0121] In this embodiment, the sample to be tested is placed in a sample bottle 3 , the sample bottle 3 is placed at the center of a sealed sample chamber 4 , and the sample chamber 4 is placed at the center of a box chamber 5 .

[0122] The sample bottle 3 is made of lightweight polyethylene to reduce absorption of X-rays; when the sample to be tested in the sample bottle 3 contaminates the sample chamber 4, the sample chamber 4 can be disassembled and replaced.

[0123] The sample chamber 4 is provided with a first transmission window 7 for the incidence of fluorescent X-rays, and is also provided with a second transmission window (exit window 6, exit window 8 and exit window 9 respectively) for the emission of characteristic X-rays of radioactive elements. The first transmission window and the second transmission window are channels for the primary X-ray incidence and characteristic X-ray emission measurement chambers, and are both made of polyetheretherketone (PEEK) material with low X-ray absorption, and are sealed with carbon sealing gaskets and fixed by pressure covers. The windows are replaceable.

[0124] The first transmission window 7 is a primary incident window for X-rays, and the exit windows 6, 8 and 9 are secondary exit windows for X-rays.

[0125] Specifically, the thickness of the primary incident window is 1mm; the thickness of the secondary exit window is 0.5mm. The transmission window is made of polyetheretherketone (PEEK), which has low absorption of X-rays and has good corrosion resistance, radiation resistance, and aging resistance. The transmission window should avoid using carbon fiber material. In addition to the main element carbon (C), carbon fiber also contains a small amount of bromine (Br) element. Due to the presence of Br element, it will cause the appearance of 1300-1350 impurity peaks on the left side of the La characteristic peak of U, which will cause the sensitivity and detection limit of the U element to deteriorate. The transmission window is sealed with a carbon sealing gasket with a thickness of 2mm. The window is fixed by a pressure cover and the window is replaceable.

[0126] The X-ray tube 1, the radioactive element detector, the half-ring bent crystal diffractor, the full-ring bent crystal diffractor and other components are placed on the bottom plate or outside of the chamber 5. The chamber 5 can be made of stainless steel or carbon steel, which is mainly used to shield the radioactivity of the sample. In this embodiment, the chamber 5 uses 321 stainless steel as the shell, and the outside of the shell is shielded by carbon steel of a certain thickness.

[0127] A sealed optical path is provided between the second transmission window and the detector, and the optical path passes through the chamber and is connected to the helium source through the first gas inlet 16, the second gas inlet 17 and the third gas inlet 18 respectively.

[0128] Filling the optical path structure of the system with helium can reduce the attenuation of the fluorescence signal by air in the optical path system, increase the signal intensity, enhance the detection sensitivity, and further reduce the detection limit of U, Np and Pu elements.

[0129] Since the X-ray fluorescence analysis system uses four sets of bent crystal diffractors, the overall optical path structure is relatively long, and the air in the optical path has a strong attenuation effect on the fluorescence signal. Therefore, helium is filled in the closed optical path. The density of helium is relatively small, and the attenuation of X-rays is only 14% of that of air under the same atmospheric pressure, which greatly reduces the attenuation of X-rays.

[0130] The sample chamber 4 is designed in combination with the box chamber 5, which can ensure the overall sealing of the sample chamber 4 and the box chamber 5. When the sample to be tested contaminates the sample chamber 4, the sample chamber 4 can be disassembled and replaced.

[0131] In this embodiment, a control system is also included. The control system is electrically connected to the multiple radioactive element detection components and is used to receive the signals output by the radioactive element detection components and process the signals to obtain the dose of the radioactive element.

[0132] In addition, the X-ray tube 1 is also connected to a cooling device to cool the X-ray tube 1 .

[0133] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements, characterized in that: include: High voltage generator, X-ray tube, semi-ring bent crystal diffractometer, sample chamber, multiple radioactive element detection components, The high voltage generator is arranged at one side of the X-ray tube and is used to emit electrons toward the target material in the X-ray tube so that the target material emits primary X-rays in response to the electron incidence. The semi-ring bent crystal diffractor is disposed between the X-ray tube and the sample chamber, and is used to separate X-rays of a preset energy range from the primary X-rays, and focus and direct them to the sample in the sample chamber. The sample chamber is used to place a radioactive sample, and the radioactive sample emits fluorescent X-rays in response to the incidence of X-rays in the preset energy range. The radioactive element detection assembly includes a full ring bent crystal diffractor and a radioactive element detector. The full ring bent crystal diffractor is arranged between the sample chamber and the radioactive element detector, and is used to separate the characteristic X-rays of the radioactive elements from the fluorescent X-rays, and guide them to the detector after focusing. Different radioactive element detection components are used to detect and receive characteristic X-rays of different radioactive elements; The full ring bent crystal diffractor has a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full ring bent crystal diffractor, or, The full-ring bent crystal diffractor includes two half-ring bent crystal diffractors, and the half-ring bent crystal diffractor includes a carrier, the carrier has a concave surface, and graphite crystals are deposited on the concave surface. The two half-ring bent crystal diffractors are symmetrically spliced ​​to form the full-ring bent crystal diffractor, and the two concave surfaces deposited with graphite crystals enclose a shuttle-shaped through hole, and the hole wall of the shuttle-shaped through hole forms the diffraction surface of the full-ring bent crystal diffractor.

2. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to claim 1, characterized in that: Let the line connecting the exit point of the primary X-ray on the target and the incident point of the primary X-ray on the radioactive sample be the first axis segment, The diffraction surface of the semi-ring bent crystal diffractor is a concave surface, which is formed by rotating a first circular arc with a curvature radius R1 around the first axis segment by 180°. The exit point of the primary X-ray on the target, the incident point of the primary X-ray on the radioactive sample and the first arc are on a circle with a curvature radius of R1; Let the line connecting the emission point of the fluorescent X-ray on the radioactive sample and the focal point of the fluorescent X-ray of the radioactive element be the second axis segment, The diffraction surface of the full-ring bent crystal diffractor is a concave surface, which is formed by rotating a second circular arc with a curvature radius R2 around the second axis segment by 360°. The emission point of the fluorescent X-ray on the radioactive sample, the focusing point of the fluorescent X-ray of the radioactive element and the second arc are on a circle with a curvature radius of R2.

3. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to claim 2, characterized in that: The radioactive elements include uranium, neptunium and plutonium, and the radioactive element detection components are provided with three groups, namely uranium detection components, neptunium detection components and plutonium detection components; The preset energy range is 12-20 keV.

4. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to claim 3, characterized in that: The first arc has a curvature radius R1 of 320-380 mm and a length D1 of 50-60 mm. The curvature radius of the second arc is R2, which is 400-450 mm, and the length D2 is 50-60 mm. The length L1 of the first axis segment and the length L2 of the second axis segment are both calculated using formula (1): L=2Rsin(2θ) (1) The length r1 of the perpendicular line from the midpoint of the first arc to the first axis segment and the length r2 of the perpendicular line from the midpoint of the second arc to the second axis segment are both calculated using formula (2): r=2Rsin 2 (i) (2) Wherein, L is the length of the corresponding axis segment, r is the length of the perpendicular line from the midpoint of the corresponding arc to the corresponding axis segment, R is the radius of curvature of the corresponding arc, and θ is the diffraction angle of the corresponding bent crystal diffractor; The diffraction angle θ of the corresponding bent crystal diffractor is calculated using formula (3): nλ=2dsinθ (3) Wherein, d is the interplanar spacing of the bent crystals in the corresponding bent crystal diffractor; θ is the diffraction angle of the corresponding bent crystal diffractor; λ is the wavelength of the diffracted rays; and n is the reflection order.

5. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to any one of claims 1 to 4, characterized in that: The semi-ring bent crystal diffractor is made of a lithium fluoride plate, the lithium fluoride plate has a concave surface, and the concave surface forms a diffraction surface of the semi-ring bent crystal diffractor, or, The semi-ring bent crystal diffractor comprises a carrier having a concave surface, graphite crystals are deposited on the concave surface, and the surface of the graphite crystals forms the diffraction surface of the semi-ring bent crystal diffractor.

6. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to any one of claims 1 to 4, characterized in that: The full ring bent crystal diffractor is made of lithium fluoride.

7. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to claim 6, characterized in that: The full-ring bent crystal diffractor also includes a shielding core, which is a shuttle-shaped structure, located in the shuttle-shaped through hole and coaxially arranged with the shuttle-shaped through hole, and is used to block direct light from entering the detector.

8. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to any one of claims 1 to 4, characterized in that: The power of the X-ray tube is 300-400W, and the target material is an Ag target or a W target.

9. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to any one of claims 1 to 4, characterized in that: The sample is placed in a sample bottle, the sample bottle is placed in the center of a sealed sample chamber, and the sample chamber is placed in the center of a box chamber. The sample chamber is provided with a first transmission window for incident fluorescent X-rays, and is also provided with a second transmission window for emission of characteristic X-rays of radioactive elements. A closed optical path channel is provided between the second transmission window and the detector, and the optical path channel passes through the chamber and is connected to the helium source.

10. The X-ray fluorescence analysis system for simultaneous measurement of trace radioactive elements according to any one of claims 1 to 4, characterized in that: It also includes a control system, which is electrically connected to the multiple radioactive element detection components and is used to receive signals output by the radioactive element detection components and process them to obtain the dose of the radioactive element.

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