Detector in-orbit calibration polarization X-ray source and test system thereof

Abstract

The invention discloses a detector in-orbit calibration polarization X-ray source and a test system thereof. The detector in-orbit calibration polarization X-ray source is characterized in that the detector in-orbit calibration polarization X-ray source comprises a radioactive source used for generating X-rays and emitting the X-rays to a film; the film is used for exciting the incident X-ray to generate the X-ray with set energy, and the X-ray is incident to the diffraction crystal; the radioactive source box is used for installing a radioactive source and a film; the diffraction crystal is used for performing Bragg diffraction on incident X-rays to generate polarized X-rays and enabling the polarized X-rays to enter the collimator; the crystal box is used for installing a diffraction crystal; the collimator is used for collimating the incident X-ray and limiting the emergent direction of the polarized X-ray; and the vibration source structure assembly is used for installing the radioactive source box, the crystal box and the collimator. According to the invention, polarized X-rays with different energies within 2-8keV can be generated, the beam divergence angle is less than or equal to 1 degree, and the bandwidth is lt; and the voltage is 200 eV. The method can be used for monitoring the polarization performance and stability of the gas pixel detector.

Description

Technical Field

[0001] The invention belongs to the technical field of polarized X-rays, and in particular relates to a polarized X-ray source and a test system thereof for on-orbit calibration of a gas pixel detector. Background Art

[0002] X-ray polarimetry is a cutting-edge and hot topic in high-energy astronomy. However, due to the lack of advanced technology, the polarimetry of X-ray astrophysical sources has been basically limited to the detection of a single bright source, the Crab Nebula, so far. This field has been dormant for nearly four decades. With the breakthrough of soft X-ray polarimetry technology based on the photoelectric effect, polarimetry has once again become a hot topic in X-ray astronomy. Gas pixel detectors (GPDs) are based on the photoelectric effect and have the characteristics of long life, high accuracy, strong reliability and low systematic error. They have the ability to simultaneously image, polarize, time-varying and measure energy spectra of 2-8keV X-rays. They can perform accurate X-ray polarimetry on a variety of cosmic sources, from neutron stars to black hole binaries, as well as extended sources such as supernova remnants, pulsars and massive jets.

[0003] GPD is mainly composed of drift layer, gas electron multiplication layer and anode pixel readout ASIC chip. The main gas in GPD is dimethyl ether, and the effective area is 15mm×15mm. After X-ray photons are incident on the detector, the photons interact with the working gas to produce photoelectrons. The photoelectrons propagate in the gas and ionize to produce positive and negative ion pairs. The generated secondary ions enter the gas electron multiplication layer under the action of the drift electric field and are amplified. Finally, they are collected and read out by the pixel ASIC chip. According to the image read out by the pixel ASIC chip, the algorithm can be used to reconstruct the track of the photoelectron to obtain the polarization information of the photon. During on-orbit operation, GPD is mainly used to receive rays from other celestial bodies in space, but the performance of GPD may change due to internal gas adsorption, slow gas leakage, gas aging and other reasons. Generally, the mission cycle of spacecraft is four years or longer. The complexity of GPD requires precise monitoring of its performance and stability during the mission cycle, especially the polarization response.

[0004] Operating and calibrating the GPD on-orbit will bring serious challenges. So far, only the Crab Nebula is known to emit polarized X-rays, but it cannot be used as a polarization calibration source because its flux varies over time and the effect on its polarization is unclear. In order to achieve high-sensitivity polarization detection, a filter wheel that meets the operating mode required during the observation needs to be installed above the GPD on the spacecraft, and the filter wheel is installed on the on-orbit polarization calibration source. By rotating the filter wheel, long-term observation of space X-ray objects can be achieved. After a period of time (such as 2 months), two days are used to receive the polarized X-rays emitted by the on-orbit polarization calibration source, and the GPD is calibrated and compared with the ground calibration results to determine the changes in the modulation factor, energy resolution and response stability of the GPD. Then, the received X-ray data of other celestial bodies in space are processed accordingly to eliminate systematic errors. This information will help to enhance the understanding of the performance of the GPD and evaluate the reliability of scientific results.

[0005] At present, the realization of 2-8keV polarization calibration source mainly adopts the scheme of X-ray tube plus crystal diffraction. According to the Bragg diffraction principle, through theoretical calculation, the appropriate X-ray tube and crystal are selected. The diffraction angle of the crystal is 45°. The completely non-polarized X-rays generated by the X-ray tube are incident on the crystal. After diffraction, polarized X-rays with a polarization degree close to 1 are generated. However, because the installation of X-ray tubes is very complicated, spacecraft has strict requirements on mass, volume and power, and it is also difficult to operate X-ray tubes during on-orbit operation, it is difficult to complete the production of polarized X-rays by X-ray tube plus crystal diffraction on the spacecraft filter wheel bracket. The spacecraft requires the on-orbit polarization source to generate one or two polarized X-rays with different energies in the range of 2-8keV. In order to ensure that the stray light of the on-orbit polarization X-rays is as small as possible, the bandwidth FWHM is required to be less than 200eV. In the observation mode, the beam of the on-orbit polarization source cannot generate counts on the GPD, so the divergence angle of the outgoing beam of the on-orbit polarization source must be small enough, requiring ≤1°. Summary of the invention

[0006] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a polarized X-ray source and a test system for on-orbit calibration of GPD, so as to monitor the polarization performance and stability of the GPD during on-orbit operation and solve the problem that an X-ray tube cannot be installed on a spacecraft.

[0007] The technical solution of the present invention is:

[0008] A polarized X-ray source for GPD on-orbit calibration, comprising:

[0009] A radiation source for generating X-rays incident on the diffraction crystal;

[0010] Thin film, used to stimulate X-rays of set energy;

[0011] Radioactive source box, used to install radioactive source and film;

[0012] A diffraction crystal, used for performing Bragg diffraction on incident X-rays to generate polarized X-rays and injecting them into a collimator;

[0013] Crystal box: used to install diffraction crystal;

[0014] A collimator is used to collimate the polarized X-rays generated by Bragg diffraction and limit the emission direction of the polarized X-rays;

[0015] Polarization source structural assembly, the main mechanical structure of the polarization X-ray calibration source, is used to install the radiation source box, crystal box and collimator.

[0016] The above-mentioned GPD calibrates the polarized X-ray source on-orbit. The X-rays emitted by the radiation source + film are incident on the diffraction crystal at a certain diffraction angle, and are mirror-reflected on the surface of the crystal and the parallel crystal planes inside. The reflected X-rays interfere with each other to produce diffraction fringes, that is, X-ray Bragg diffraction occurs, and polarized X-rays are produced. After being collimated by a collimator, the influence of stray light can be eliminated.

[0017] The on-orbit polarized X-ray source is installed in the filter wheel above the GPD in the spacecraft. By rotating the filter wheel, long-term observation of space X-ray celestial bodies can be achieved. The GPD is aligned with the on-orbit polarized X-ray source at intervals (such as 2 months). It takes two days to receive the polarized X-rays emitted by the on-orbit polarized source, calibrate the GPD, and compare it with the ground calibration results to determine the changes in the modulation factor, energy resolution and response stability of the GPD. Then, the received X-ray data of other celestial bodies in space are processed accordingly to eliminate system errors. The spacecraft requires that the energy range of the polarized X-rays generated by the on-orbit polarized source is 2-8keV, the bandwidth FWHM <200eV, and the polarization degree is close to 1. Considering that in the observation mode, when the on-orbit polarized source on the rotating wheel leaves the GPD incident position, the beam of the on-orbit polarized source cannot generate counts in the GPD, so the divergence angle of the outgoing beam of the on-orbit polarized source must be small enough, currently required to be ≤1°.

[0018] In order to meet the requirements of spacecraft for on-orbit polarization sources, it is necessary to test the performance of the developed on-orbit polarization source, including the energy, bandwidth, count rate and divergence angle of the polarized X-ray. A test system for on-orbit calibration of polarized X-ray sources is proposed, including:

[0019] An on-orbit calibration polarization source device, including a radiation source, a film, a radiation source box, a diffraction crystal, a crystal box, a collimator and a polarization source structural assembly, generates polarized X-rays;

[0020] A polarization source device adjustment bracket, with a mounting slide and a z-axis direction ruler, used for the installation and vertical adjustment of the polarization source device;

[0021] A detector, a SDD detector, is used to receive polarized X-rays generated by a polarization source device and measure an energy spectrum;

[0022] Detector adjustment bracket with mounting slide and x-axis scale for detector installation and left-right position adjustment;

[0023] A fixed bracket with scales in the x- and y-axis directions and mounting slides, used for fixing the polarization source device adjustment bracket and the detector adjustment bracket and adjusting the horizontal position;

[0024] High-purity He gas cylinder, which is used to pass high-purity He gas into the polarization source device to eliminate the influence of Ar characteristic lines in the air;

[0025] The shielding cover is used to shield the radiation generated by the polarization source device and reduce the impact of nuclear radiation caused during the test.

[0026] The GPD on-orbit calibration polarized X-ray source and test system development process includes the following steps:

[0027] 1) Selection of radiation source: The energy detection range of GPD is 2-8keV, so we use a radiation source that emits K α 5.90keV and K β 6.49keV photon 55 The Fe nuclide acts as a radiation source, producing X-rays that are incident on the diffraction crystal;

[0028] 2) Film selection: Certain polarized X-rays of specific energy require 55 K emitted by Fe nuclides α 5.90keV photons pass through a specific film to stimulate the corresponding characteristic X-rays, which are then produced by Bragg diffraction of the corresponding crystal. 55 The nuclide is excited through the Ti film to generate Ti K α 4.511keV and Ti K β The characteristic line of 4.931keV is excited by a thin film containing chlorine to produce ClK α 2.62keV and Cl K β 2.81keV characteristic line, so if you only need to generate 5.9keV polarized X-rays, you don't need a film. If you need to generate polarized X-rays with energy <5.9keV, you need to select a specific film and place it in front of the radiation source exit window. By simulating the relationship between film thickness and characteristic X-ray fluorescence yield, the film thickness is determined according to the maximum value of the characteristic X-ray fluorescence yield;

[0029] 3) Selection of diffraction crystals: Determine the corresponding Bragg diffraction crystal and its crystal plane index according to the required polarized X-ray energy, and determine the diffraction angle. Determine the diameter of the radiation source and the film according to the effective area and diffraction angle of the GPD. When designing the diffraction crystal, it is necessary to select a suitable size based on the diameter of the radiation source and the diffraction angle, and also reserve edge dimensions for installation and fixation. The diffraction crystal must be cleaned before installation to remove most of the particle contamination and other contamination during the surface smoothing process. The cleaning methods for different crystals are different. For ease of installation, a crystal box is designed according to the size of the diffraction crystal. The non-incident surface of the crystal is padded with a buffer gasket of a certain thickness and installed in the crystal box. The flatness of the crystal must be ensured during the installation of the crystal;

[0030] 4) Determination of the mechanical installation accuracy of the polarization source device structure: According to the Bragg diffraction principle, during the design of the on-track polarization source device, the position and angle relationship between the radiation source, diffraction crystal, and collimator will directly affect the polarization degree and beam intensity of the outgoing X-rays. The factors that determine the accuracy of the position and angle are mainly the following three aspects: lattice defects of the crystal, installation accuracy of the mechanical design, and design of the collimator.

[0031] Crystals used in practice often have defects, which can be described by the mosaic diffusion angle of the crystal. The mosaic angle is related to crystal defects. The fewer crystal defects, the smaller the mosaic angle, and the better the monochromaticity of polarized X-rays generated by Bragg diffraction. Therefore, it is necessary to select crystals with better crystal quality and smaller mosaic angle. The mosaic angle of the selected diffraction crystal needs to be tested before use.

[0032] The installation accuracy of mechanical design needs to be guaranteed 55 The angle accuracy between the normal of the Fe radiation source surface and the diffraction crystal surface, as well as the angle accuracy between the diffraction crystal surface and the X-ray emission axis (the direction of the collimator maximum transmittance axis), the former directly affects the Bragg diffraction angle, and the latter affects the effective area. That is, the installation accuracy of the radiation source emission surface, the crystal diffraction surface and the collimator emission surface is controlled. In the process of mechanical design and processing of polarization source structure components, crystal boxes, and radiation source boxes, the accuracy of the diffraction angle is guaranteed to be ±0.05°, and the component plane design and processing have appropriate tolerances to meet the design accuracy requirements. All components are cleaned and anti-corrosion after processing, and the surface is scratch-proof and damage-proof. After processing, gloves must be worn for handling to prevent sweat corrosion. In addition, ultrasonic cleaning with anhydrous ethanol and deionized water and nitrogen drying are required before installation. During the installation process, screws are used for installation and fixation, and precision plates and dial indicators are used for flatness correction to ensure and improve installation accuracy.

[0033] The design requirements for the collimator are the maximum grazing incidence angle, transmittance, detection energy range and inner wall roughness of the collimator. Bragg diffraction itself has a strong directional selectivity, and collimators need to be installed at both the incident and exit positions of the Bragg diffraction to limit the Bragg diffraction angle. If the quality of the selected crystal is relatively high, only a collimator needs to be installed at the polarized X-ray exit position to select X-rays parallel to the exit axis. The collimator is required to collimate 2-8keV X-rays, eliminate stray X-rays, and meet the requirement that the X-ray beam divergence angle is ≤1°.

[0034] 5) Collimator selection: X-rays emitted by the radiation source are considered to be parallel polarized X-rays after Bragg diffraction of the crystal. Lead glass capillaries are selected as collimators for 2-8keV X-rays. Capillary collimators are thin sheets of high-lead glass, which contain millions of micron-sized collimation channels. Based on the principle of angle sensitivity, they use the high lead content and high roughness of the inner wall of the collimation channel to absorb stray X-rays, and use the high-precision pointing of the collimation channel to collimate 2-50keV X-rays. The structural diagram is shown below. Figure 8 As shown, the channel is perpendicular to the collimator surface and the channel inclination angle is 0°. The angular sensitivity of the collimator depends on the regularity and accuracy of the channel arrangement. The reflection of X-rays on the inner wall of the channel is avoided by increasing the roughness of the inner wall, while the possible transmission of X-rays between channels is avoided by increasing the lead content of the lead glass.

[0035] Select the appropriate collimator size according to the effective area of ​​the radiation source, the crystal size and the diffraction angle. Determine the maximum grazing incidence angle of the collimator according to the requirements of the polarized X-ray beam divergence angle. The maximum grazing incidence angle should be ≤ the beam divergence angle, and the size is determined by the size of the capillary collimator.

[0036] α=arctan(D / L)

[0037] Where D is the channel aperture of the capillary collimator, L is the channel length of the capillary collimator, and also the thickness of the collimator, L / D is the aspect ratio of the collimator, and α is the maximum grazing incidence angle of the collimator. Fig. 9 Schematic diagram of capillary collimator size and maximum grazing incidence angle. When a large aspect ratio is selected, better collimation effect can be obtained.

[0038] In order to improve the transmittance of polarized X-rays, the opening area ratio of the capillary collimator should be as large as possible.

[0039]

[0040] Wherein, η is the opening area ratio, D is the channel aperture of the capillary collimator, and d is the wall thickness of the collimator channel. The larger D / (D+d) is, the greater the transmittance of the capillary collimator is.

[0041] The maximum energy value of the polarized X-rays generated by the present invention is 6.49keV, which belongs to the range of soft X-rays. Soft X-rays have weak penetrating power and can basically be absorbed by one or two channel walls, avoiding the cross-light effect. In order to avoid the possible transmission of X-rays between channels, the lead content of the lead glass is determined according to the energy value of the polarized X-rays generated and the thickness of the channel wall. Because the transmittance of solids to X-rays is

[0042] T=e -μt

[0043] In the formula, T is the transmittance, μ is the absorption coefficient, which indicates the degree of absorption of X-rays by the material per unit length, and t is the sample thickness. Factors that affect transmittance include the density and composition of the solid material, the energy of the X-rays, and the thickness of the sample.

[0044] To eliminate the reflection of X-rays on the inner wall of the channel, the inner wall of the channel of the capillary collimator must have a certain roughness. Generally speaking, for 2-8keV X-rays, the roughness of the inner wall of the collimator channel is generally 10nm-60nm.

[0045] The size of the collimator should reserve the edge size for installation and fixation. The collimator should be cleaned before installation to improve the collimation effect of the microchannel plate. During the installation process, a certain thickness of gasket is placed on the edge of the incident surface of the microchannel plate crystal for buffering, and its flatness should be ensured during the installation of the collimator.

[0046] 6) Ar gas in the air can produce Ar characteristic lines, with energies of Ar, K α 2.96keV and Ar K β 3.19keV, which interferes with the test process. Therefore, it is necessary to design vents in the polarization source device structure during the test. The actual on-orbit process is a vacuum state and there is no need to design vents.

[0047] 7) In order to reduce the impact of nuclear radiation during the test, Fe 55 The radiation source needs to be placed in the radiation source box first, and the box for installing the radiation source should be designed. A buffer pad should be placed on the non-emitting surface of the radiation source. For polarized X-ray source devices that require a film, the film should be placed in front of the radiation source's emission window. The film needs to be cleaned before installation. Protective measures should be taken during the installation process to prevent nuclear radiation.

[0048] 8) Installation of polarization source structure components: According to the dimensions, diffraction angle and installation accuracy determined in the above steps, the polarization source structure is designed and manufactured. The accuracy of the diffraction angle of the component structure is ±0.05°. The plane design and processing of the component require appropriate tolerances to meet the design accuracy requirements. Before installation, in order to prevent the dust generated on the surface of the polarization source structure during the processing from affecting the polarized X-rays, the polarization source structure components, air pipe adapters and screws need to be ultrasonically cleaned. The crystal box, collimator and radiation source box are installed in the polarization source mechanical structure in turn. Protective measures must be taken during the installation process to prevent nuclear radiation.

[0049] 9) Install the polarization source device adjustment bracket and the detector adjustment bracket on the fixed bracket, and install the polarization source device on the polarization source device adjustment bracket.

[0050] 10) Connect the high-purity He gas pipe to the air hole of the polarization source device through the adapter, install the gas pipe quick connector, and connect the high-purity He gas ventilation pipe to check the air tightness of the ventilation pipe. By adjusting the He flow rate, observe whether the Ar characteristic line in the energy spectrum disappears completely, and determine the high-purity He gas flow rate when the Ar characteristic line in the energy spectrum disappears completely. The high-purity He gas should not be too large, otherwise it will damage the radioactive source and the beryllium window of the detector.

[0051] 11) Install the detector on a bracket that can adjust the front and rear positions of the SDD detector. Align the outgoing polarized X-rays with the SDD detector by adjusting the positions of the detector and the polarization source device. Place the entire polarization source device in a shielding device, turn on the high-purity He gas, and ventilate for several minutes to remove the Ar gas in the polarization source device. Then turn on the SDD detector and perform an energy spectrum test on the polarized X-rays generated by the polarization source device.

[0052] 12) Perform data analysis on the energy spectrum tested by the detector to obtain the peak position, broadening and counting rate of the polarized X-rays. Compare the test results with the design requirements to determine whether the energy and broadening of the generated polarized X-rays meet the design requirements.

[0053] Compared with the prior art, the present invention has the following positive effects:

[0054] 1) Adoption 55 Fe radiation source + crystal diffraction + collimator to obtain a polarized X-ray source, which solves the problem of not being able to install an X-ray tube on a spacecraft;

[0055] 2) Introducing high-purity He gas into the component can eliminate the influence of the Ar characteristic line in the air;

[0056] 3) Obtain polarized X-rays with detailed information including peak position, half-peak width, counting rate and diffraction angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a schematic diagram of the principle of generating polarized X-rays based on Bragg diffraction in the present invention.

[0058] Figure 2 This is a schematic diagram of the principle of calibrating a polarized X-ray source based on GPD on-orbit and a diagram of its relative position to the GPD when on-orbit.

[0059] Figure 3 is the PVC film thickness and Cl K in the present invention α 2.62keV fluorescence yield relationship diagram.

[0060] Figure 4 This is a diagram of the device of the on-orbit calibration polarization X-ray source test system based on GPD of the present invention.

[0061] Figure 5 The present invention is a flow chart of the steps for developing an on-orbit calibration polarized X-ray source and a test system thereof based on GPD.

[0062] Figure 6 The experimental results of the polarized X-ray source without film developed based on GPD and tested by SDD detector;

[0063] (a) is the energy spectrum, and (b) is the Gaussian fitting result of the full energy peak.

[0064] Figure 7 The experimental results of the polarized X-ray source with thin film developed based on GPD and tested by SDD detector;

[0065] (a) is the energy spectrum, and (b) is the Gaussian fitting result of the full energy peak.

[0066] Figure 8 Schematic diagram of the structure of the lead glass capillary collimator.

[0067] Fig. 9 Schematic diagram of the size and maximum grazing incidence angle of the capillary collimator. DETAILED DESCRIPTION

[0068] In the following specific implementation examples, the present invention will be further described in detail in conjunction with the accompanying drawings. By describing the implementation examples in sufficient detail, it is possible for those skilled in the art to practice the present invention. Without departing from the spirit and scope of the present invention, logical, implementation and other changes may be made to the implementation. Therefore, the following detailed description should not be understood as limiting, and the scope of the present invention is limited only by the claims.

[0069] The working principle of the on-orbit polarization source is based on the Bragg diffraction of the crystal. The schematic diagram is as follows: Figure 1Bragg diffraction is defined as the superposition of coherent Thomson scattering on a periodic medium (such as the lattice of a crystal). Bragg diffraction is valid for energies <10 keV and only when Bragg's law is satisfied:

[0070]

[0071] Where θ is the grazing incidence angle measured relative to the crystal surface; E is the photon energy; d is the distance between adjacent crystal planes; n is the diffraction order; h is Planck's constant; and c is the speed of light. λ That is, the integrated reflection efficiency is defined as

[0072]

[0073] Where P λ (θ) is the diffraction intensity of parallel monochromatic X-rays of unit intensity at a diffraction angle of θ. Unpolarized incident radiation that satisfies the Bragg diffraction formula can be decomposed into two orthogonal polarization components: the π component is polarized parallel to the plane of incidence (defined as the plane of the incident radiation direction and the normal to the diffraction plane), while the σ component is perpendicular to the plane. The former will be absorbed by the crystal, while the latter will be diffracted. Definition After diffraction, the non-polarized light becomes partially polarized light, the polarization direction is perpendicular to the incident plane, and the degree of polarization is

[0074]

[0075] When the diffraction angle θ = 45°, k = 0, a fully polarized X-ray with a polarization degree of 1 can be obtained. The Bragg diffraction process has a narrow energy band (for a perfect crystal, <1eV), and its efficiency decreases rapidly with the change of photon wavelength or incident angle. Therefore, the first task in designing an on-orbit polarization calibration source is to select an X-ray source and crystal plane with appropriate energy, so that the diffraction angle is as close to 45° as possible to achieve a higher polarization degree.

[0076] Embodiment 1:

[0077] This embodiment provides an on-orbit calibration polarization source based on GPD. The polarization source includes a radiation source, a radiation source box, a diffraction crystal, a crystal box, a collimator, a vent, an air pipe adapter, and a polarization source assembly structure. Please refer to Figure 2 The GPD is 50-80 mm away from the exit of the on-track polarization source. The energy of the polarized X-ray is selected to be 5.9 keV. The design parameters are determined according to the Bragg diffraction principle.

[0078] X-ray Source Crystal Diffraction angle / ° Outgoing energy Degree of Polarization <![CDATA[ 55 Fe nuclide]]> (220)LiF 47.56° 5.9keV 88.22％

[0079] The polarization source device in the embodiment 1 generates polarized X-rays with an energy of 5.9 keV, a bandwidth of <200 eV, and a polarization degree of 88.22%;

[0080] The radiation source in Example 1 is provided by the Russian company Khlopin. 55 Fe radiation source, according to the effective area of ​​GPD is 15mm×15mm, according to 15×2 0.5 =21.21, choose the size of Ф22mm×5mm 55 Fe radioactive source, the radioactive source meets the requirements of ISO / 98 / C64343 and can emit K α 5.90keV and K β 6.49keV photons, generating X-rays incident on the Bragg diffraction crystal, the device in Example 1 does not use a thin film;

[0081] In the embodiment 1, according to the Bragg diffraction principle, the diffraction crystal is selected as a (220)-face lithium fluoride (LiF) crystal provided by Beijing Shouliang Technology Co., Ltd., with a purity of 4 9s, a thickness of 2 mm, and a plane spacing of The test results of the X-ray double crystal rocking curve of LiF crystal are as follows:

[0082] Location Half peak width θ 0° 20″ 32°50′57″ 180° 24″ 32°41′57″

[0083] The maximum mosaic angle of the crystal is 24″, and the crystal quality is good, meeting the requirements of the polarization source device. The cleaning method of the LiF crystal is: use anhydrous ethanol to clean for 10 minutes and blow dry with nitrogen. During the storage and installation of the LiF crystal, pay attention to moisture-proof, avoid direct contact and use metal tweezers to pick it up.

[0084] In the embodiment 1, the collimator adopts the lead glass capillary collimator provided by Northern Night Vision, the collimator size is 30mm×30mm, the capillary collimator channel length L is 5mm, the collimation channel diameter D is 83μm, the channel inclination angle is 0°, the wall thickness d is 7μm, the maximum grazing incidence angle α is 0.952°, the opening area ratio η is 71.5%, and the inner wall roughness is ≥13nm. When the lead content of the collimator is calculated to be 37% by the Monte Carlo method, the intensity of 5.9keV X-rays is reduced to 9.83% through the two channel walls. The selected collimator satisfies the polarized X-ray beam divergence angle ≤1° and the transmittance ≥70%, which can eliminate the reflection of 2-8keV X-rays on the inner wall of the collimator channel and the transmission that may occur between the channels.

[0085] The cleaning method of the lead glass capillary collimator is as follows: before cleaning, the dust and impurities on the surface of the collimator should be cleaned to avoid affecting the cleaning effect, and then acetone and deionized water are used for ultrasonic cleaning for 10 minutes respectively to remove particles, contaminants and dust on the surface and in the holes of the microchannel plate.

[0086] The polarization source device structure in the embodiment 1 is made of aluminum alloy material, the main component of which is aluminum, and the aluminum component accounts for more than 95%. Because the mosaic angle of the diffraction crystal LiF is small, the divergence angle of the collimator is 0.952°, so 55 The installation accuracy of the Fe radiation source surface, the diffraction crystal surface and the collimator surface must be controlled within ±0.315°, so that the diffraction angle range is 46.608°≤θ≤48.512°, and the diffraction energy range is 5.811keV≤E≤5.990keV. If the peak position of the polarized X-ray emitted by the developed polarization source device is within this range, it can be proved that the design and installation of the polarization source device meet the requirements.

[0087] The model of the air pipe adapter in the embodiment 1 is PL6-G02.

[0088] The polarization source device structure, crystal box, radiation source box, air pipe adapter and screws in the first embodiment are cleaned before installation by ultrasonic cleaning, pure water cleaning for 10 minutes, anhydrous ethanol cleaning for 15 minutes and pure water cleaning for 10 minutes.

[0089] The steps for installing the polarization source device structure in the first embodiment are as follows:

[0090] 1) Crystal installation: After cleaning the crystal, place a 0.5mm cushion pad on the non-incident surface of the LiF crystal, and then place it in the crystal box to complete the installation. During the installation process, do not touch the surface of the LiF crystal with your hands, as the moisture on your hands will damage the crystal surface and cause permanent damage; it needs to be done in a clean environment to prevent water vapor in the air from contacting the crystal surface; do not touch the crystal with hard objects such as metal tweezers, and do not place the crystal directly on a hard table. During the installation of the crystal, the flatness of the crystal must be ensured.

[0091] 2) Radiation source installation: In Fe 55 A 0.5mm thick cushion pad is placed on the non-emitting surface of the radioactive source, and then placed in the radioactive source box to complete the installation. During the installation process, the flatness of the radioactive source and the radioactive source box must be ensured, and protective measures must be taken. Special tweezers are required to pick up the radioactive source, and the operator must take protective measures, wear protective clothing, protective gloves and glasses to prevent nuclear radiation.

[0092] 3) Installation of the air pipe adapter: Screw the threaded end of the PL6-G02 adapter into the vent hole of the polarization source device.

[0093] 4) Installation of the collimator: Place a 0.5 mm thick gasket on the edge of the incident surface of the lead glass microchannel plate for buffering, and cover the output surface with a 4 μm thick polypropylene film (96% transparency at 2.6 keV) to protect the small holes from dust infiltration, and then place it in the polarization source device for installation. Ensure its flatness during the installation of the collimator.

[0094] 5) Installation of the polarization source device: Install the crystal box and the radiation source box into the polarization source device structure in sequence to complete the final assembly of the polarization source device. During the installation process, protective measures must be taken to prevent nuclear radiation.

[0095] Embodiment 2:

[0096] This embodiment provides an on-orbit calibration polarization source based on GPD, and the design parameters are

[0097] X-ray Source Crystal Diffraction angle / ° Outgoing energy Degree of Polarization <![CDATA[ 55 Fe nuclide + PVC membrane]]> (002) HOPG 44.82° 2.62keV 99.86％

[0098] The polarization source device in the embodiment 2 generates polarized X-rays with an energy of 2.62keV, a bandwidth of <200eV, and a polarization degree of 99.86%;

[0099] The radiation source used in Example 2 is the same as that in Example 1, provided by Khlopin Company of Russia. 55 Fe radioactive source, size is Ф22mm×5mm, the radioactive source meets ISO / 98 / C64343 requirements, and can emit K α 5.90keV and K β 6.49keV photons, passing through the PVC membrane, produce Cl K α 2.62keV and Cl K β The characteristic line of 2.81keV is used to calculate the PVC film thickness and Cl K using Geant 4. α The relationship between the 2.62keV fluorescence yield, such as Figure 3 As shown. It is concluded that when the PVC film thickness is 16μm, the Cl Kα2.62keV fluorescence yield is the largest. In principle, the thinner the PVC film, the better. However, because the thinnest PVC material currently available is 100μm, a 100μm thick PVC is selected to cover the 55 On the exit window of the Fe radioactive source.

[0100] In the embodiment 2, according to the Bragg diffraction principle, the diffraction crystal selected is a HOPG crystal with a (0002) surface provided by Jiangsu Xianfeng Nanomaterial Technology Co., Ltd., with a purity of >99.99% and a size of 30×30×2.0 mm. 3 , face spacing The test results of the X-ray twin rocking curve of HOPG crystal are as follows:

[0101] Location Half peak width θ 0° 9′24″ 13°28′3″ 180° 10′12″ 13°18′51″

[0102] The maximum mosaic angle is 0.17°, which meets the requirements of the polarization source device. The cleaning process of the HOPG crystal is as follows:

[0103] (1) Soak Si in pure water and perform ultrasonic cleaning for at least 5 minutes to remove most of the particle contamination and other contamination during the surface planarization process;

[0104] (2) Then, the Si is immersed in acetone and ethanol in turn, and ultrasonically cleaned for no less than 5 minutes, mainly to remove organic contamination. After washing, it is rinsed with pure water for no less than 1 minute and dried.

[0105] The collimation parameters in the embodiment 2 are the same as those of the collimator in the embodiment 1, the collimator size is 30 mm×30 mm, the collimation channel length L is 5 mm, the collimation channel diameter D is 83 μm, the channel wall thickness d is 7 μm, the maximum grazing incidence angle α is 0.952°, the opening area ratio η is 71.5%, and the inner wall roughness is ≥13 nm. When the lead content of the collimator is 37%, the intensity of 2.62 keV X-rays is reduced to 0.13% through one channel wall.

[0106] In the embodiment 2, the polarization source device structure is also made of aluminum alloy. Because the mosaic angle of the diffraction crystal HOPG crystal is 0.17°, the maximum grazing incidence angle of the collimator is 0.952°, 55 The installation accuracy of Fe radiation source + PVC film, diffraction crystal surface and collimator surface are all controlled within ±0.0.261°, so the diffraction angle range is 43.868°≤θ≤45.772°, and the diffraction energy range is 2.579keV≤E≤2.667keV. If the peak position of the polarized X-ray emitted by the developed polarization source device is within this range, it can be proved that the design and installation of the polarization source device meet the requirements.

[0107] The air pipe adapter in the second embodiment is the same as that in the first embodiment, and the polarization source device structure, crystal box, radiation source box, air pipe adapter and screws are cleaned before installation in the same manner as that in the first embodiment.

[0108] The steps for installing the polarization source device structure in the second embodiment are as follows:

[0109] 1) Crystal installation: After cleaning the crystal, place a 0.5mm buffer pad on the non-incident surface of the HOPG crystal, and then place it in the crystal box to complete the installation. During the installation process, do not touch the surface of the HOPG crystal with your hands. It needs to be done in a clean environment to prevent water vapor in the air from contacting the crystal surface. Do not touch the crystal with hard objects such as metal tweezers, and do not place the crystal directly on a hard table. During the installation of the crystal, the flatness of the crystal must be ensured.

[0110] 2) The installation of the radiation source, the air pipe adapter, the collimator and the polarization source device are the same as in Example 1.

[0111] Embodiment 3:

[0112] This embodiment provides a test system for calibrating a polarization source device on-orbit based on GPD, including a polarization source device structure, a polarization source device adjustment bracket, a fixing bracket, a detector, a detector adjustment bracket, a high-purity He gas cylinder and a ventilation pipe, and a shielding device. Figure 4 .

[0113] The high-purity He gas used in Example 3 is provided by Bazhou Anxing Gas Co., Ltd., with a purity of ≥99.999%, a filling pressure of 15.0±0.5MPa, and an implementation standard of GB / T4844.3-1995. The high-purity He gas flow rate is 350mL / min, and the Ar peak in the energy spectrum completely disappears at 350ml / min.

[0114] The ventilation tube in the third embodiment is a flexible tube with an outer diameter of 6 mm and an inner diameter of 4 mm.

[0115] The material used for the fixing bracket, the polarization source adjustment bracket and the detector adjustment bracket in the third embodiment is the same as that of the polarization source device, which is an aluminum alloy containing more than 95% aluminum.

[0116] The fixed bracket in the third embodiment is provided with scales in the x-axis and y-axis directions and mounting slides, which are used for fixing the polarization source device adjustment bracket and the detector adjustment bracket and adjusting the horizontal position.

[0117] The polarization source device adjustment bracket in the third embodiment is provided with a mounting slide and a z-axis direction ruler, and is used for the installation and vertical adjustment of the polarization source device.

[0118] The detector adjustment bracket in the third embodiment is provided with a mounting slide and an x-axis direction scale for mounting the detector and adjusting the left and right positions.

[0119] The detector in the embodiment 3 adopts the SDD detector provided by Amptek Corporation of the United States, the model is AmptekX-123, the detector thickness is 500 μm, the area is 25 mm 2 , used to measure the energy spectrum of polarized X-rays generated by the polarization source device, and calculate the peak position, broadening and counting rate of polarized X-rays.

[0120] The shielding device in the third embodiment is a shielding device formed by stacking 50 mm thick lead bricks. The height of the shielding device is higher than the maximum height of the test system of the polarization source device, and can effectively shield the radiation generated by the test system of the polarization source device.

[0121] Figure 5 This is a flow chart for the development of an on-orbit calibration polarized X-ray source device and its test system based on GPD in the present invention.

[0122] Experimental Results

[0123] The energy spectrum of Example 1 obtained by SDD detector testing is as follows: Figure 6 As shown in (a), Gaussian fitting is performed on the full energy peak, and the fitting formula used is:

[0124]

[0125] Where y is the count, y0 is the offset, A is the area, and x is the c is the peak position, and w is the full width corresponding to when x is equal to the standard deviation ±σ. The fitting results are shown in Figure 6 (b) shows that sigma is the standard deviation, FWHM is the half-peak width, and Height is x=x c The peak position is 5.91785keV, the half-peak width is 133.84eV, the energy range is 2-8keV, the bandwidth is <200eV, and the counting rate is 10.46s -1 To increase the counting rate of polarized X-rays, the activity of the radiation source can be increased, and the peak position is 5.811keV-5.990keV, which meets the design requirements.

[0126] The energy spectrum of Example 2 obtained by SDD detector testing is as follows Figure 7 As shown in (a), Gaussian fitting is performed on the full energy peak, and the results are as follows Figure 7 As shown in (b), the peak position is 2.62963keV, the half-peak width is 103.87eV, the energy range is 2-8keV, the bandwidth is <200eV, and the counting rate is 0.85s -1 The polarized X-rays with peaks at 2.579keV-2.667 meet the design requirements.

[0127] The above is only one specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A detector on-orbit calibration polarized X-ray source, characterized in that: include A radiation source for generating X-rays and directing them onto the film; The film is used to excite the incident X-rays to generate X-rays of set energy and then incident on the diffraction crystal; Radioactive source box, used to install radioactive source and film; A diffraction crystal, used for performing Bragg diffraction on incident X-rays to generate polarized X-rays and injecting them into a collimator; Crystal box, used to mount the diffraction crystal; A collimator is used to collimate the incident X-rays and limit the emission direction of the polarized X-rays; Polarization source structural assembly, used to install radiation source box, crystal box and collimator.

2. The detector on-orbit calibration polarized X-ray source according to claim 1, characterized in that: Whether a thin film is needed and the type of thin film are determined according to the set energy level, and the thickness of the thin film is determined according to the maximum value of the X-ray fluorescence yield of the set energy.

3. The detector on-orbit calibration polarized X-ray source according to claim 1, characterized in that: According to the set energy size, the corresponding Bragg diffraction crystal type, crystal plane index and diffraction angle are determined.

4. The detector on-orbit calibration polarized X-ray source according to claim 1, characterized in that: The diameters of the radiation source and the film are determined according to the effective area and the diffraction angle of the gas pixel detector; and the size of the diffraction crystal is determined according to the diameter and the diffraction angle of the radiation source.

5. The detector on-orbit calibration polarized X-ray source according to claim 1, characterized in that: The set energy range is 2-8keV; the radiation source is K α 5.90keV and K β 6.49keV photon 55 Fe nuclide.

6. The detector on-orbit calibration polarized X-ray source according to claim 5, characterized in that: The collimator is a lead glass capillary, which contains millions of collimation channels of micron size; the lead content of the lead glass capillary collimator is 37%, the length L of the collimation channel is 5 mm, the diameter D of the collimation channel is 83 μm, the wall thickness d of the collimation channel is 7 μm, the inner wall roughness of the collimation channel is ≥13 nm, the maximum grazing incidence angle α of the lead glass capillary is 0.952°, and the opening area ratio η of the lead glass capillary is 71.5%.

7. The detector on-orbit calibration polarized X-ray source according to any one of claims 1 to 6, characterized in that: A buffer gasket is provided between the non-emitting surface of the radiation source and the radiation source box, and a buffer gasket is provided between the non-diffraction surface of the diffraction crystal and the crystal box.

8. A detector on-orbit calibration polarized X-ray source test system, characterized in that: Including polarization source device, detector, and high-purity He gas cylinder; The polarization source device comprises a radiation source, a film, a radiation source box, a diffraction crystal, a crystal box, a collimator and a polarization source structural component; the radiation source is used to generate X-rays and inject them into the film; the film is used to excite the incident X-rays to generate X-rays of set energy and inject them into the diffraction crystal; the radiation source box is used to install the radiation source and the film; the diffraction crystal is used to perform Bragg diffraction on the incident X-rays to generate polarized X-rays and inject them into the collimator; the crystal box is used to install the diffraction crystal; the collimator is used to collimate the incident X-rays and limit the emission direction of the polarized X-rays; the polarization source structural component is used to install the radiation source box, the crystal box and the collimator; The detector is used to receive the polarized X-rays generated by the polarization source device and measure the energy spectrum; The high-purity He gas cylinder is used to introduce high-purity He gas into the polarization source device to eliminate the influence caused by the Ar characteristic line in the air.

9. The test system according to claim 8, characterized in that: It also includes a shielding cover, a polarization source device adjustment bracket, a detector adjustment bracket and a fixed bracket; the shielding cover is used to shield the radiation generated by the polarization source device to reduce the impact of nuclear radiation caused during the test; the polarization source device adjustment bracket is used to install and adjust the polarization source device; the detector adjustment bracket is used to install and adjust the detector; the fixed bracket is used to fix and adjust the polarization source device adjustment bracket and the detector adjustment bracket.

10. The test system according to claim 8, characterized in that: It also includes a data processing unit for performing data analysis on the energy spectrum tested by the detector, calculating the peak position, broadening and counting rate of polarized X-rays, and comparing the test results with design requirements.

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