Short Pulse X-ray Source Polarimeter and Polarimetry Method

Abstract

The present invention relates to the field of plasma physics nuclear detection technology, and in particular provides a short-pulse X-ray source polarization measuring instrument and a polarization measuring method. The measuring method includes: the incident X-ray falls on a scatterer through a collimation component to generate scattered photons, and the scattered photon signals are detected by a semiconductor pixel detector; the measured value E1 of the energy of the scattered photons is obtained by using the semiconductor pixel detector, and the energy E0 of the X-ray photons is calculated based on the measured value E1; the pixel position of the scattered photons is obtained by using the semiconductor pixel detector; based on the pixel position of the scattered photons, the polarization direction and polarization degree of the X-ray are obtained by data fitting. The purpose is to solve the problem that the existing polarization measuring instrument cannot quickly measure the polarization degree and realize the measurement of the energy of the incident X-ray without knowing the polarization direction of the X-ray, and realize the single-shot measurement function of the polarization degree and energy spectrum of the short-pulse X-ray source.

Description

Technical Field

[0001] The present invention relates to the technical field of plasma physics nuclear detection, and in particular, to a short-pulse X-ray source polarization measuring instrument and a polarization measuring method. Background Art

[0002] The ultrashort pulse X-ray source generated by laser or accelerator driving is widely used in basic physics research, non-destructive testing, biomedical imaging, ultrafast microscopic process scientific research and other fields due to its short pulse width, micro focus, wide energy spectrum and other characteristics;

[0003] Polarization is a basic property of the X-ray source. For example, in the X-ray source based on synchrotron radiation mechanism and Thomson scattering mechanism, the X-ray is generated by the transverse oscillation of electrons in the characteristic direction and has a very high degree of polarization; in the X-ray source based on bremsstrahlung mechanism or Kα radiation, the degree of polarization of the X-ray is often low; by measuring the polarization characteristics of the X-ray source, the motion of electrons and the mechanism of X-ray radiation generation can be studied; on the other hand, since polarization affects the characteristics of the interaction between X-ray and matter, for example, in the Compton scattering physical process of the interaction between X-ray and matter, the Compton scattering cross-section along the polarization direction of the X-ray is low. Based on this principle, using a high-degree-of-polarization X-ray source in X-ray fluorescence CT can effectively reduce the Compton scattering background and improve the signal-to-noise ratio of the fluorescence signal. Therefore, in the research of X-ray source generation and application, the measurement of its polarization characteristics has important significance and value.

[0004] Currently, the existing methods for measuring the polarization of short-pulse X-ray sources in the prior art are as follows:

[0005] 1. A polarization measuring instrument based on Bragg diffraction and two orthogonally arranged X-ray detectors. This method uses two orthogonally arranged crystal diffracted rays. When the X-ray is incident on the crystal surface at a 45° angle, only the X-ray with the polarization direction parallel to the crystal surface will undergo Bragg diffraction. By measuring the intensities of the two crystal diffracted rays, the polarization degree of the X-ray can be measured; however, when the above method is actually used, the polarization direction of the X-ray needs to be known. Otherwise, the detector needs to be rotated and measured multiple times at different angles to find the polarization direction before the polarization degree can be measured, which cannot meet the single-shot measurement function of the short-pulse X-ray source;

[0006] 2. A polarization measuring instrument based on Compton scattering and two orthogonally arranged X-ray detectors. This method scatters X-rays using a scatterer and places detectors in two mutually perpendicular scattering directions to measure the intensity of the scattered rays. When measuring the polarization degree of X-rays using the above method, the polarization direction of the X-rays also needs to be known. Otherwise, the detector needs to be rotated and measured multiple times at different angles to find the polarization direction before the polarization degree can be measured, which also cannot meet the single-shot measurement function of short-pulse X-ray sources.

[0007] 3. A polarization measuring instrument based on Compton scattering and an imaging plate (IP) that surrounds the scatterer once as an X-ray detector. This method can measure the intensity of scattered rays in any scattering direction when the scattering angle is close to 90° through the IP plate that surrounds the scatterer once. At this time, the polarization direction of the X-rays does not need to be known. By measuring the intensity of scattered rays in each scattering direction, the polarization direction of the X-rays can be measured, and then the polarization degree of the X-rays can be measured. However, when using the above method, since the signal reading of the IP requires scanning with a scanner, the scanning process often takes dozens of minutes, resulting in extremely low measurement efficiency. On the other hand, the IP does not have the ability to measure single-photon energy, resulting in the inability of this method to simultaneously measure the energy of incident X-rays.

[0008] In summary, the existing methods for measuring the polarization degree of X-rays cannot quickly measure the polarization degree and realize the measurement of the energy of incident X-rays in the case of unknown X-ray polarization direction. Summary of the Invention

[0009] The purpose of the present invention is to provide a polarization measuring instrument and a polarization measuring method for short-pulse X-ray sources, so as to solve the problem that the existing polarization measuring instruments in the background technology cannot quickly measure the polarization degree and realize the measurement of the energy of incident X-rays in the case of unknown X-ray polarization direction, and realize the single-shot measurement function of the polarization degree and energy spectrum of short-pulse X-ray sources.

[0010] The technical solution of the first aspect of the present invention provides a polarization measuring instrument for short-pulse X-ray sources, including a first shielding box, and a second shielding box communicated with the first shielding box is provided on one side of the first shielding box. This polarization measuring instrument further includes:

[0011] A collimation component, including a first collimation member and a second collimation member installed on both sides of the first shielding box. Collimation holes are provided at the centers of the first collimation member and the second collimation member, and the collimation holes are used to limit the position, lateral width, and propagation direction of the X-rays entering.

[0012] A cylindrical dipole magnet is provided inside the first shielding box. Both ends of the cylindrical dipole magnet are respectively in contact with the first collimator and the second collimator. The cylindrical dipole magnet is coaxially arranged with the collimation hole and the outer diameter of the cylindrical dipole magnet matches the inner diameter of the first shielding box;

[0013] A cylindrical absorber is sleeved inside the cylindrical dipole magnet. The cylindrical absorber is coaxially arranged with the collimation hole and is used to absorb electrons and ions;

[0014] A semiconductor pixel detector is installed on one side of the second shielding box far from the collimation assembly and is coaxially arranged with the collimation hole;

[0015] A scatterer is installed on the side of the semiconductor pixel detector close to the collimation assembly and is coaxially arranged with the collimation hole;

[0016] A filter is installed between the collimation assembly and the second shielding box.

[0017] Furthermore, the cylindrical dipole magnet includes:

[0018] A housing and a plurality of permanent magnets installed inside the housing.

[0019] Furthermore, the cylindrical absorber includes:

[0020] A through hole configured to match the diameter of the collimation hole.

[0021] Furthermore, the diameter of the through hole is 1 mm to 2 mm.

[0022] Furthermore, the cylindrical absorber is made of polytetrafluoroethylene.

[0023] Furthermore, the pixel plane of the semiconductor pixel detector is configured to be perpendicular to the axis of the collimation assembly.

[0024] The technical solution of the second aspect of the present invention provides a short-pulse X-ray polarization measurement method, including the following steps:

[0025] The incident X-ray passes through the collimation assembly and falls on the scatterer to generate scattered photons, and the scattered photon signal is detected by the semiconductor pixel detector;

[0026] Use the semiconductor pixel detector to obtain the measured value E1 of the energy of the scattered photons, and calculate the energy E0 of the X-ray photons based on the measured value E1;

[0027] Use the semiconductor pixel detector to obtain the pixel position of the scattered photons;

[0028] Based on the pixel position of the scattered photons, then obtain the polarization direction and polarization degree of the X-ray through data fitting.

[0029] Further, detecting the scattered photon signal by the semiconductor pixel detector specifically includes:

[0030] Calculating the distance between the scattered photon signal and the center of the semiconductor pixel detector, removing the direct central signal, retaining the scattered photon signal, and counting the total number of scattered photons.

[0031] Further, obtaining the scattered photon pixel position by using the semiconductor pixel detector includes:

[0032] Presetting a direction x on the pixel plane of the semiconductor pixel detector, and calculating the angle ξ between the scattered photon and the direction x.

[0033] Further, based on the scattered photon pixel position, the expression relationship for obtaining the polarization direction and degree of polarization of the X-ray through data fitting is:

[0034] f(ξ) = K * (1 + μ cos(2(ξ - ξ0) + π));

[0035] Wherein, K is the total number of scattered photons, μ represents the degree of polarization of the incident X-ray, and ξ0 is the angle between the polarization direction of the incident X-ray and the preset x direction.

[0036] The beneficial effects of the present invention include:

[0037] 1. Compared with the prior art, the short-pulse X-ray source polarization measuring instrument and polarization measuring method provided by the present invention, by setting a semiconductor pixel detector and a scatterer, using the semiconductor pixel detector to detect the spatial distribution and energy of the scattered X-ray photons, and realizing the measurement of the X-ray polarization degree according to the spatial distribution of the scattered photons. The overall measurement process does not require prior knowledge of the X-ray polarization direction and does not require rotating the detector, and can realize the measurement of the X-ray polarization direction. At the same time, the energy of the incident X-ray can also be measured; on the other hand, the real-time and fast readout of the scattered signal is realized by setting the semiconductor pixel detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments of the present invention. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0039] Figure 1 It is a schematic diagram of the overall structure of the polarization measuring instrument provided by the embodiment of the present invention;

[0040] Figure 2 It is a sectional view of the polarization measuring instrument provided by the embodiment of the present invention;

[0041] Figure 3 It is a flowchart of the polarization measurement method provided by an embodiment of the present invention;

[0042] Figure 4 It is a schematic structural diagram of the collimation component provided by an embodiment of the present invention;

[0043] Figure 5 It is a signal distribution diagram of scattered photons provided by an embodiment of the present invention;

[0044] Icons: 100 - First shielding box, 110 - First collimator, 111 - Connection plate, 112 - Columnar body, 120 - Second collimator, 130 - Collimation hole, 140 - Cylindrical dipole magnet, 150 - Cylindrical absorber, 200 - Second shielding box, 210 - Semiconductor pixel detector, 220 - Scatterer, 230 - Filter. Specific embodiments

[0045] Next, the technical solutions in the embodiments of the present invention will be described with reference to the accompanying drawings in the embodiments of the present invention.

[0046] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0047] Please refer to Figure 1 and Figure 2 As shown, the technical solution of the first aspect of the present invention provides a short-pulse X-ray source polarization measuring instrument, including a first shielding box 100. A second shielding box 200 communicating with the first shielding box 100 is provided on one side of the first shielding box 100. The polarization measuring instrument further includes:

[0048] A collimation component, including a first collimator 110 and a second collimator 120 installed on both sides of the first shielding box 100. Collimation holes 130 are provided at the centers of the first collimator 110 and the second collimator 120. The collimation holes 130 on the first collimator 110 and the second collimator 120 are coaxially arranged and have matching shapes and sizes; the collimation holes 130 are used to limit the position, lateral width, and propagation direction of the X-ray entering;

[0049] Among them, as Figure 4As shown, both the first collimator 110 and the second collimator 120 are composed of a connecting plate 111 and a columnar body 112. The size of the columnar body 112 matches that of the following cylindrical dipole magnet 140. There is a sealed connection between the left and right sides of the first shielding box 100 and the columnar body 112. The first shielding box 100 and the second shielding box 200 can be made of one or more metal materials such as lead, aluminum, and tungsten, specifically depending on achieving the shielding effects of radiation shielding and electromagnetic shielding. The purpose is to prevent interference from ions that enter without passing through the collimation hole 130.

[0050] The cylindrical dipole magnet 140 is arranged inside the first shielding box 100. The two ends of the cylindrical dipole magnet 140 are respectively in contact with the first collimator 110 and the second collimator 120. The cylindrical dipole magnet 140 is coaxially arranged with the collimation hole 130 and the outer diameter of the cylindrical dipole magnet 140 matches the inner diameter of the first shielding box 100. The cylindrical dipole magnet 140 is used to generate a magnetic field to deflect electrons and ions, and then the following cylindrical absorber 150 absorbs the electrons and ions that enter the collimation hole 130.

[0051] The cylindrical absorber 150 is sleeved inside the cylindrical dipole magnet 140. The cylindrical absorber 150 is coaxially arranged with the collimation hole 130 and is used to absorb electrons and ions. The inner diameter of the cylindrical absorber 150 is configured to be the same as the diameter of the collimation hole 130, the outer diameter of the cylindrical absorber 150 is configured to be the same as the inner diameter of the cylindrical dipole magnet 140, and the length of the cylindrical absorber 150 is configured to be the same as the length of the cylindrical dipole magnet 140.

[0052] The semiconductor pixel detector 210 is installed on the side of the second shielding box 200 away from the collimation assembly and is coaxially arranged with the collimation hole 130.

[0053] The scatterer 220 is installed on the side of the semiconductor pixel detector 210 close to the collimation assembly and is coaxially arranged with the collimation hole 130. The scatterer 220 uses an existing Compton scatterer.

[0054] The filter 230 is installed between the collimation assembly and the second shielding box 200 and is configured to match the shape of the collimation hole 130. The filter 230 is used to absorb low-energy X-rays and reflect visible light, ensuring that only high-energy X-rays can pass through the filter 230 and enter the scatterer 220. The size of the filter 230 is such that it can completely block the collimation hole 130, and its size is not limited here. In actual applications, an appropriate metal coating of the filter 230 can be selected as needed. In this embodiment, the metal coating of the filter 230 is preferably an aluminum sheet, and its thickness depends on actual requirements.

[0055] For example, the cylindrical dipole magnet 140 includes: a housing and a plurality of permanent magnets installed in the housing. The cylindrical secondary magnet can be configured to be composed of a plurality of permanent magnets with different polarization directions, and the number thereof is determined according to the actual magnetic field strength requirement, which is not limited herein;

[0056] For example, the cylindrical absorber 150 includes:

[0057] A through hole configured to match the diameter of the collimation hole 130. The diameter of the through hole is 1 mm to 2 mm. The cylindrical absorber 150 is made of polytetrafluoroethylene. The cylindrical absorber 150 is used to decelerate and absorb charged particles. By using a low-density material such as polytetrafluoroethylene, the bremsstrahlung stray X-ray yield generated when the charged particles are absorbed can be minimized, so as to achieve the purpose of reducing the background noise of the detector.

[0058] For example, the pixel plane of the semiconductor pixel detector 210 is configured to be perpendicular to the axis of the collimation assembly, so that the pixel plane of the semiconductor pixel detector 210 is perpendicular to the photon incident direction, in order to achieve the technical effect of having the ability to measure scattered photons in any scattering direction;

[0059] Please refer to Figure 3 As shown, the technical solution of the second aspect of the present invention provides a short-pulse X-ray polarization measurement method, including the following steps:

[0060] Step S1: The incident X-ray passes through the collimation assembly and falls on the scatterer 220 to generate scattered photons, and the scattered photon signals are detected by the semiconductor pixel detector 210;

[0061] Among them, please refer to Figure 5 As shown, detecting the scattered photon signals by the semiconductor pixel detector 210 specifically includes:

[0062] Calculating the distance between the scattered photon signal and the center of the semiconductor pixel detector 210, removing the central direct signal, retaining the scattered photon signal and counting the total number of scattered photons; Figure 5 The left part in shows that the central circular response region is the response of the X-ray passing through the scatterer 220 and directly hitting the semiconductor pixel detector 210, and the discrete points around are the signals of the scattered photons; Figure 5 The right part in is a schematic diagram after removing the central response region;

[0063] Step S2: Using the semiconductor pixel detector 210 to obtain a measured value E1 of the scattered photon energy, and calculating the energy E0 of the X-ray photon based on the measured value E1;

[0064] Among them, since the scatterer 220 is in close contact with the sensitive plane of the semiconductor pixel detector 210, the scattering angle of the scattered photons detected by the semiconductor pixel detector 210 is approximately 90°. According to the Compton scattering principle, the energy E0 of the incident X-ray photons can be calculated from the measured value E1 of the energy of the scattered photons by the semiconductor pixel detector 210. The calculation formula is as follows:

[0065] E0 = E1 / (1 - E1 / (m e c 2 ));

[0066] where m e c 2 is the rest energy of an electron, approximately 511 keV;

[0067] Step S3: Use the semiconductor pixel detector 210 to obtain the pixel position of the scattered photons;

[0068] Among them, step S3 specifically includes: preset a direction x on the pixel plane of the semiconductor pixel detector 210, and calculate the angle ξ between the scattered photons and the direction x;

[0069] Step S4: Based on the pixel position of the scattered photons, then obtain the polarization direction and polarization degree of the X-ray through data fitting;

[0070] Among them, the expression relationship for obtaining the polarization direction and polarization degree of the X-ray through data fitting based on the pixel position of the scattered photons is:

[0071] f(ξ) = K * (1 + μ cos(2(ξ - ξ0) + π));

[0072] where K is the total number of scattered photons, μ represents the polarization degree of the incident X-ray, and ξ0 is the angle between the polarization direction of the incident X-ray and the preset x direction.

[0073] In summary, the short-pulse X-ray source polarization measuring instrument and polarization measuring method disclosed in this embodiment, by setting the semiconductor pixel detector 210 and the scatterer 220, use the semiconductor pixel detector 210 to detect the spatial distribution and energy of the scattered X-ray photons, and realize the measurement of the X-ray polarization degree according to the spatial distribution of the scattered photons. The overall measurement process does not require prior knowledge of the X-ray polarization direction and does not require rotating the detector, and can realize the measurement of the X-ray polarization direction. At the same time, it can also measure the polarization degree and energy spectrum of the incident X-ray source; on the other hand, by setting the semiconductor pixel detector 210, real-time and fast readout of the scattered signal is achieved.

[0074] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. Short-pulse X-ray source polarization measuring instrument, characterized in that It includes a first shielding box, and a second shielding box communicating with the first shielding box is provided on one side of the first shielding box. The polarization measuring instrument further includes: A collimation assembly, including a first collimator and a second collimator installed on both sides of the first shielding box. Collimation holes are provided at the centers of the first collimator and the second collimator, and the collimation holes are used to limit the position, lateral width, and propagation direction of the X-ray entering; A cylindrical dipole magnet, provided in the first shielding box. The two ends of the cylindrical dipole magnet are respectively attached to the first collimator and the second collimator. The cylindrical dipole magnet is coaxially arranged with the collimation hole and the outer diameter of the cylindrical dipole magnet matches the inner diameter of the first shielding box; A cylindrical absorber, sleeved inside the cylindrical dipole magnet. The cylindrical absorber is coaxially arranged with the collimation hole and is used to absorb electrons and ions; A semiconductor pixel detector, installed on one side of the second shielding box away from the collimation assembly and coaxially arranged with the collimation hole; A scatterer, installed on the side of the semiconductor pixel detector close to the collimation assembly and coaxially arranged with the collimation hole; A filter, installed between the collimation assembly and the second shielding box; The working steps of the short-pulse X-ray source polarization measuring instrument are as follows: The incident X-ray falls on the scatterer through the collimation assembly to generate scattered photons, and the scattered photon signal is detected by the semiconductor pixel detector; Using the semiconductor pixel detector to obtain the measured value E1 of the scattered photon energy, and calculating the energy E0 of the X-ray photon based on the measured value E1; Using the semiconductor pixel detector to obtain the pixel position of the scattered photon; Based on the pixel position of the scattered photon, then obtaining the polarization direction and polarization degree of the X-ray through data fitting.

2. The short-pulse X-ray source polarization measuring instrument according to claim 1, characterized in that The cylindrical dipole magnet includes: A housing and a plurality of permanent magnets installed in the housing.

3. The short-pulse X-ray source polarization measuring instrument according to claim 1, characterized in that The cylindrical absorber includes: A through hole, configured to match the diameter of the collimation hole.

4. The short-pulse X-ray source polarization measuring instrument according to claim 3, characterized in that The diameter of the through hole is 1 mm to 2 mm.

5. The short-pulse X-ray source polarization measuring instrument according to claim 1, characterized in that The cylindrical absorber is made of polytetrafluoroethylene.

6. The short-pulse X-ray source polarization measuring instrument according to any one of claims 1 to 5, characterized in that The pixel plane of the semiconductor pixel detector is configured to be perpendicular to the axis of the collimation assembly.

7. The short-pulse X-ray source polarization measuring instrument according to claim 6, characterized in that Specifically, detecting the scattered photon signal by the semiconductor pixel detector includes: Calculating the distance between the scattered photon signal and the center of the semiconductor pixel detector, removing the center direct signal, retaining the scattered photon signal and counting the total number of scattered photons.

8. The short-pulse X-ray source polarization measuring instrument according to claim 7, characterized in that Using the semiconductor pixel detector to obtain the pixel position of the scattered photon includes: Presetting a direction x on the pixel plane of the semiconductor pixel detector and calculating the angle ξ between the scattered photon and the direction x.

9. The short-pulse X-ray source polarization measuring instrument according to claim 8, characterized in that Based on the pixel position of the scattered photon, the expression relationship for obtaining the polarization direction and polarization degree of the X-ray through data fitting is: f(ξ)=K*(1 + μcos(2(ξ - ξ0)+π)); Wherein, K is the total number of scattered photons, μ represents the polarization degree of the incident X-ray, and ξ0 is the angle between the polarization direction of the incident X-ray and the preset x direction.

Images