A weighted correction method for XRF imaging of curved surface micro-regions

Abstract

The present invention discloses a weighted correction method for curved micro-region XRF imaging. The method is as follows: 1) Scan the sample to obtain the spectral diagram of the sample and the fluorescence intensity I, and record the deviation angle θ of the X-ray incident on the sample in the horizontal plane and the deviation angle #imgabs0# in the vertical plane during scanning; 2) Estimate the mass attenuation coefficient of the sample for the incident X-ray and the mass attenuation coefficient of the sample for the outgoing fluorescence as the same value μ, and use the angular weighting function #imgabs1# to correct the fluorescence intensity I to obtain the fluorescence intensity I1 when the X-ray is vertically incident; 3) Obtain the change amount y of the distance from the X-ray lens to the object surface, and use the distance weighting function f(y) to correct the fluorescence intensity I1 to obtain the fluorescence intensity I2 when the X-ray is vertically incident on the sample and the incident distance remains unchanged; 4) Correct the spectral data based on the fluorescence intensity I2, correct the corresponding pixel values in the imaging diagram, and obtain the corrected fluorescence scanning image.

Description

Technical Field

[0001] The present invention belongs to the technical field of object detection, and relates to a scanning method, in particular to a weighted correction method for curved surface micro-region XRF imaging. Background Art

[0002] At present, most micro-region X-ray fluorescence spectrometers can only move freely in a two-dimensional plane. Therefore, when scanning a curved surface or an object with an uneven surface, the X-ray focus cannot be always maintained on the object surface, and the distance between the X-ray lens and the sample surface and the X-ray incident angle will change, making it impossible to accurately obtain the element distribution information on the object surface.

[0003] The only micro-region X-ray fluorescence spectrometer that can change the working distance uses a three-dimensional displacement stage instead of a two-dimensional motion system. This method can only keep the distance between the spectrometer and the object surface unchanged and cannot control the influence of the incident angle change on the detector count.

[0004] When using the existing micro-region X-ray fluorescence spectrometer to scan a curved surface object, it is impossible to control the working distance and working angle of the spectrometer to be unchanged at each scanning point, which will greatly affect the accuracy of the detector count. Therefore, a quantitative correction method is needed to enable the detector to obtain accurate counts in these situations. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a weighted correction method for curved surface micro-region XRF imaging to ensure the accuracy of micro-region XRF for large-area scanning of curved surface objects. Through the method of theoretical weighted correction, the influence of distance change and deviation of X-ray incident angle on the detection count is eliminated, and the detection accuracy is improved on the premise of ensuring safety.

[0006] The technical solution of the present invention is as follows:

[0007] A weighted correction method for curved surface micro-region XRF imaging, the steps of which include:

[0008] 1) Scanning the sample to obtain the spectral data of the sample, and recording the deviation angle θ of the X-ray incident on the sample in the horizontal plane and the deviation angle

[0009] 2) Estimating the mass attenuation coefficient of the sample for the incident X-ray and the mass attenuation coefficient of the sample for the outgoing fluorescence to be the same value μ, and using to correct the fluorescence intensity I in the spectral data to obtain the fluorescence intensity when the X-ray is vertically incident where

[0010] ρ is the density of the sample, and x is the depth of the X-ray incident into the sample;

[0011] 3) Record the change amount y of the distance from the X-ray lens to the sample surface, and use to correct the fluorescence intensity I1, and obtain the corrected fluorescence intensity I2 = I1 × f(y), where s is the distance from the sample surface to the detector when the incident distance is unchanged, and I2 represents the fluorescence intensity value when the X-ray is vertically incident on the sample and the incident distance is unchanged;

[0012] 4) Correct the spectral data based on the fluorescence intensity I2, and correct the corresponding pixel values in the fluorescence scanning image according to the corrected spectral data to obtain the corrected fluorescence scanning image.

[0013] Furthermore, use a micro-area X-ray fluorescence spectrometer to scan the sample.

[0014] A weighted correction system for curved surface micro-area XRF imaging, characterized in that it includes a scanning device and a data processing unit, wherein,

[0015] The scanning device is used to scan the sample, obtain the spectral data of the sample, and record the deviation angle θ of the X-ray incident on the sample in the horizontal plane and the deviation angle in the vertical plane during scanning

[0016] and the changing distance y from the sample surface to the X-ray lens to the sample surface, and send them to the data processing unit; The data processing unit is used to estimate the mass attenuation coefficient of the sample for the incident X-ray and the mass attenuation coefficient of the sample for the outgoing fluorescence as the same value μ, and use where ρ is the density of the sample, x is the depth of the X-ray incident into the sample; and record the change amount y of the distance from the X-ray lens to the sample surface, and use to correct the fluorescence intensity I1, and obtain the corrected fluorescence intensity I2 = I1 × f(y), where s is the distance from the sample surface to the detector when the incident distance is unchanged, and I2 represents the fluorescence intensity value when the X-ray is vertically incident on the sample and the incident distance is unchanged; then correct the spectral data based on the fluorescence intensity I2, and correct the corresponding pixel values in the fluorescence scanning image according to the corrected spectral data to obtain the corrected fluorescence scanning image.

[0017] The advantages of the present invention are as follows:

[0018] Using the present invention can, on the premise of ensuring the safety of the equipment and the scanned object, reduce the deviation caused by the deviation of the X-ray incident angle and the distance change in the scanned area where the curvature of some objects is too large through a weighted correction function, with higher imaging accuracy and a larger scanning range. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the scanning curved surface of the μXRF imaging system.

[0020] Figure 2 It is a schematic diagram of the X-ray fluorescence process.

[0021] Figure 3 It is a schematic diagram of angular deviation and a simplified schematic diagram.

[0022] Figure 4 It is a schematic diagram of distance change.

[0023] Figure 5 It is a flowchart of the method of the present invention. Detailed Description of the Invention

[0024] The present invention will be further described in detail below with reference to the drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0025] The micro-area X-ray fluorescence spectrometer mainly consists of three parts: an X-ray source, a polycapillary X-ray lens, and an X-ray detector. As shown in Figure 1 , the X-rays emitted by the X-ray source are converged on the surface of the object by the polycapillary X-ray lens, and the X-ray fluorescence spectrum emitted by the surface of the object is obtained using the X-ray detector. Considering the attenuation of X-rays in air, the two main factors affecting the detector count: the X-ray incident angle and the incident distance (i.e., the distance from the polycapillary X-ray lens to the sample surface), the weighting function can be derived through relevant formulas, and the detection accuracy can be improved by weighting.

[0026] Using the derivation formula of the primary fluorescence intensity, the weighting function with respect to the deviation angle is derived

[0027] Consider a smooth and uniform sample s. Assume that the sample contains a fluorescent element i with a relative concentration of c i , the density of the sample s is ρ, the incident angle is α, the exit angle is β, and the spectral distribution of the X-rays output by the light source is I λ , the X-ray intensity is expressed as the count per second under a unit cross-section, and the fluorescence intensity received by the detector is proportional to the following factors:

[0028] After attenuation through the incident path, the incident light intensity a reaching the dx volume is:

[0029]

[0030] where μ s,λis the mass attenuation coefficient of the sample for incident light with wavelength λ, x is the depth at which the X-ray penetrates into the sample, dλ represents a small wavelength range used to describe the influence of wavelength variation within a certain range on the fluorescence intensity, and multiplying it by the spectral distribution gives the light intensity.

[0031] The fraction of the X-rays output by the light source absorbed by the element in the volume dx is:

[0032]

[0033] where μ i,λ is the mass attenuation coefficient of element i for incident light with wavelength λ.

[0034] The fraction of the intensity of the outgoing X-ray fluorescence after attenuation by the sample is:

[0035]

[0036] where μ s,λi is the mass attenuation coefficient of the sample for fluorescence.

[0037] Since the incident light is assumed to be per unit area, the outgoing light should also be converted to per unit area, and the adjustment factor is:

[0038]

[0039] The fluorescence intensity I detected by the detector is proportional to the above factors related to the angle:

[0040] The mass attenuation coefficient refers to the degree of attenuation of X-rays by a substance per unit mass. For the sake of analysis, during the derivation process, the mass attenuation coefficient μ s,λ of the sample for incident X-rays and the mass attenuation coefficient μ s,λi of the sample for outgoing fluorescence are both roughly estimated as the same value μ, then

[0041]

[0042] As Figure 3 shown, in the simplified schematic diagram, the blue line represents the X-ray incident vertically, the orange line represents the X-ray when the incident angle changes. When incident vertically, the incident angle is 90°, the exit angle is 60°. Let the deviation angle of the ray on the horizontal plane be θ, and the deviation angle on the vertical plane be After the incident angle changes, the measured intensity is I, the intensity after weighted correction is I1, and the angle weighting function is Then

[0043] Using the derivation formula of the fluorescence intensity, the angle weighting function can be obtained as:

[0044]

[0045] Among them,

[0046] The relationship between the X-ray intensity and the distance follows the inverse square law. The X-rays radiated from the ray source propagate in a straight line in space at a certain radiation angle. As the propagation distance increases, on the spherical surfaces with different radii centered on the focal point, the X-ray intensity is inversely proportional to the square of the distance.

[0047] I′ = I0 / d 2

[0048] Among them, I0 is the X-ray intensity at the focal point, d is the radius of the spherical surface centered on the focal point, and I′ is the X-ray intensity at a distance d from the focal point.

[0049]

[0050] Among them, s is the distance from the object surface to the detector when the distance is unchanged, and y is the changed distance. Then the corrected final fluorescence intensity I2 = I1 × f(y).

[0051] The distance weighting function is:

[0052]

[0053] Figure 5 is the specific flow chart of weighted correction. First, use the device to scan the sample to obtain the spectral data information of the sample, and record the changed values of the angle and distance during scanning. Then, use the angle weighting function and the distance weighting function f(y) to weight the fluorescence intensity I in the measured spectral data to obtain the fluorescence intensity value I2 when the X-ray is vertically incident and the distance from the X-ray lens to the object surface is unchanged. According to the spectral data of each scanning point, the relative content of the distribution of each element in the corresponding scanning position area can be calculated. The content of the element determines the brightness and darkness of the corresponding color in the element distribution map, that is, the image pixel value, and also reflects the intensity of the X-ray fluorescence signal, that is, the size of the detector count. The correction of the curved surface micro-area XRF imaging is to correct the detector count at each position. By weighting and correcting the fluorescence intensity, the spectral data can be corrected, and then the corresponding pixel values in the fluorescence scanning image can be corrected to improve the accuracy of the fluorescence scanning image.

[0054] Although specific embodiments of the present invention are disclosed for illustrative purposes, the purpose is to help understand the content of the present invention and implement it accordingly. Those skilled in the art can understand that: without departing from the spirit and scope of the present invention and the appended claims, various substitutions, changes, and modifications are possible. Therefore, the present invention should not be limited to the content disclosed in the best embodiments, and the scope of protection required by the present invention is defined by the scope of the claims.

Claims

1. A weighted correction method for curved surface micro-region XRF imaging, the steps of which include: 1) Scan the sample to obtain the spectral data of the sample, and record the deviation angle θ of the X-ray incident on the sample in the horizontal plane and the deviation angle in the vertical plane during scanning 2) Estimate the mass attenuation coefficient of the sample for the incident X-ray and the mass attenuation coefficient of the sample for the emitted fluorescence as the same value μ, and use to correct the fluorescence intensity I in the spectral data to obtain the fluorescence intensity when the X-ray is incident vertically where ρ is the density of the sample, and x is the depth at which the X-ray penetrates into the sample; 3) Record the change amount y of the distance from the X-ray lens to the sample surface, and use to correct the fluorescence intensity I1 to obtain the corrected fluorescence intensity I2 = I1 × f(y), where s is the distance from the sample surface to the detector when the incident distance remains unchanged, and I2 represents the fluorescence intensity value when the X-ray is incident perpendicularly on the sample and the incident distance remains unchanged; 4) Correct the spectral data based on the fluorescence intensity I2, and correct the corresponding pixel values in the fluorescence scanning image according to the corrected spectral data to obtain a corrected fluorescence scanning image.

2. The method according to claim 1, characterized in that, Use a micro-region X-ray fluorescence spectrometer to scan the sample.

3. A weighted correction system for curved surface micro-region XRF imaging, characterized in that, It includes a scanning device and a data processing unit, wherein, The scanning device is used to scan a sample, obtain spectral data of the sample, and record the deviation angle θ of the X-ray incident on the sample in the horizontal plane and the deviation angle in the vertical plane during scanning, as well as the changed distance y from the sample surface to the X-ray lens, and send them to the data processing unit; The data processing unit is configured to estimate the mass attenuation coefficient of the sample for the incident X-ray and the mass attenuation coefficient of the sample for the emitted fluorescence as the same value μ, and use to correct the fluorescence intensity I in the spectral data to obtain the fluorescence intensity when the X-ray is incident vertically. where ρ is the density of the sample, x is the depth at which the X-ray enters the sample; and to obtain the change amount y of the distance from the X-ray lens to the sample surface, and use to correct the fluorescence intensity I1 to obtain the corrected fluorescence intensity I2 = I1×f(y), where s is the distance from the sample surface to the detector when the incident distance is constant, and I2 represents the fluorescence intensity value when the X-ray is incident vertically on the sample and the incident distance is constant; then correct the spectral data based on the fluorescence intensity I2, and correct the corresponding pixel values in the fluorescence scan image according to the corrected spectral data to obtain the corrected fluorescence scan image.

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