Inorganic scintillation crystal performance test system and method based on adjustable pinhole-shaped collimator

Abstract

The invention provides an inorganic scintillation crystal performance test system and method based on an adjustable pinhole-shaped collimator, and solves the problem that the existing inorganic scintillation crystal performance test system mostly stays at the research level of specific crystal and radioactive source conditions and does not have universality in the macroscopic application of radiation detection. The system comprises a base, a radioactive source, a radioactive source limiting unit, a collimation assembly, a collimation adjusting unit, a detector position adjusting unit and a rear-end testing unit. Through use of a system core structure, namely a collimation assembly composed of a plurality of pinhole-shaped collimators, radiation rays of a radioactive source are accurately emitted into a scintillation crystal at a determined angle, interference caused by scattering of the radiation rays and an environment background is reduced, and the detection accuracy is improved by combining a standard scintillation crystal and a standard radioactive source of the same kind. High-precision and sensitivity calibration of activity and energy consistency of the radioactive source is realized, flexible matching of various radioactive sources is further realized, and objective conditions of various radioactive isotopes in an application environment are restored as much as possible.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear radiation detection, and in particular relates to an inorganic scintillation crystal performance testing system and method based on an adjustable pinhole collimator. Background Art

[0002] Since the 1960s, the aerospace industry has developed rapidly. However, the diverse types of radiation and high radiation doses in the space environment have made the research and application of radiation discrimination and radiation resistance in radiation detection extremely urgent and critical. Scintillators can be used for radiation detection and discrimination due to their mechanism of generating photons when exposed to radiation. Inorganic scintillation crystals, in particular, have gradually attracted increasing attention and research due to their excellent scintillation properties such as high light output, high energy resolution, and rapid decay. Due to the energy differences and high doses of rays in various radiation detection applications, small-sized scintillation crystals have high detection accuracy but their efficiency cannot meet actual needs. Therefore, the demand for large-sized scintillation crystals is becoming increasingly strong. For large-sized scintillation crystals, the uniformity of scintillation properties such as light output in the crystal has a decisive impact on their detection performance. On this basis, the construction of a scintillation performance uniformity test system based on pulse height spectrum test systems, digital oscilloscopes, and other equipment to characterize these properties is of great significance.

[0003] Existing systems for testing the scintillation performance uniformity of large-scale scintillation crystals typically use a single pinhole collimator as its core structure. Under the condition that the radiation source maintains a certain distance from the sample to be tested, its radiation is emitted through a pinhole with a diameter and length determined by the collimator to reach the detector structure. Then, through a series of signal conversions, the output electronic signal is recorded by the back-end test data collection equipment and analyzed and processed to obtain the corresponding performance parameters.

[0004] Reference 1 “Sturm BW, Cherepy NJ, Drury OB, et al. Evaluation of large volume SrI 2 (Eu) scintillator detectors[C] / / IEEE Nuclear Science Symposuim &Medical Imaging Conference. IEEE, 2010: 1607-1611.” reports an experimental method based on a collimated gamma ray source. A pinhole collimator consisting of a slit formed by lead bricks is used to collimate the γ-ray source. 137 The Cs gamma rays were collimated and scanned to determine the uniformity of light collection at different locations on the crystal. The study found that the light collection uniformity of the packaged SrI2(Eu) crystal was significantly improved, with the energy resolution improved from 5.01% to 3.22%, providing an important basis for the optimized design of large scintillator detectors.

[0005] Literature 2 "Wu Y, Lindsey AC, Zhuravleva M, et al. Growth of inch-sizedKCa 0.8 Sr 0.2 I3: Eu 2+ scintillating crystals and high performance for gamma-ray detection[J]. CrystEngComm, 2016, 18(39): 7435-7440." reported an experimental method based on a collimated gamma-ray source. Similarly, a pinhole collimator consisting of a slit formed by lead bricks was used to collimate the gamma-ray source. 137 Cs γ-rays were collimated to systematically study KCa 0.8 Sr 0.2 I3:Eu 2+ The light collection and generation of the crystal are non-uniform. The study found that the tail end of the crystal is due to Eu 2+ The uneven distribution leads to degraded energy resolution, while the seed-end performance is better, providing key data for revealing the impact of doping distribution on performance.

[0006] Reference 3 “Large-size CsI:Na single crystals for future high energy physics experiment” reports an experimental method based on a collimated gamma-ray source, which uses a fully enclosed pinhole collimator with only the pinhole remaining. 137 Cs gamma rays were collimated to evaluate the axial uniformity of the CsI:Na crystal. The results showed that the energy resolution of the 51 mm × 51 mm × 152 mm crystal was stable at 6.5%, and the peak position was unaffected by the irradiation position, verifying its excellent performance consistency and laying the foundation for the application of large-scale crystals in high-energy physics experiments.

[0007] The above studies all used a self-built single pinhole collimator and precision collimation technology to achieve local scanning characterization of the internal performance of scintillation crystals, providing a key experimental means to reveal the inhomogeneity of scintillation crystals.

[0008] However, the current scintillation crystal performance uniformity characterization system, which uses a single pinhole collimator as the core structure of the test system, has many limitations. Due to the fixed parameters of the single pinhole collimator, such as the aperture and hole length, its own attenuation effect on radiation rays is also correspondingly fixed. At this time, in order to achieve the best balance between test efficiency and accuracy, the radioactive sources used in the test are mostly standard radioactive sources, and their activity is also fixed. Overall, it is difficult to match the complex composition of radioactive isotopes in the application environment. Under these conditions, scintillation crystals of different sizes will also have large differences in test results, and it is impossible to fully characterize their performance uniformity in various application environments. In short, the current scintillation crystal performance test system mostly remains at the research level of specific crystal and radioactive source conditions, and is not universal in the macro application of radiation detection.

[0009] In view of this, it is necessary to design an inorganic scintillation crystal performance testing system that is universal in macroscopic applications. Summary of the Invention

[0010] The purpose of the present invention is to solve the shortcomings of existing inorganic scintillation crystal performance testing systems, which mostly remain at the research level of specific crystal and radiation source conditions and lack universal applicability in macroscopic applications of radiation detection. Instead, a system and method for testing the performance of inorganic scintillation crystals based on an adjustable pinhole collimator is provided.

[0011] To achieve the above objectives, the technical solutions provided by the present invention are:

[0012] An inorganic scintillator crystal performance test system based on an adjustable pinhole collimator is characterized in that it includes a base, a radiation source, a radiation source limiting unit, a collimation assembly, a collimation adjustment unit, a detector position adjustment unit, and a back-end test unit;

[0013] Definition: One side of the base is the front end, and the other side opposite to it is the back end;

[0014] From the front end to the rear end, the base is fixed on and carries the detector position adjustment unit, the collimation adjustment unit and the radiation source limiting unit;

[0015] The radiation source limiting unit includes a support rod, a connecting rod, and a radiation source accommodating module; wherein the support rod is vertically mounted on the base, the connecting rod is vertically mounted on the support rod at one end, and the radiation source accommodating module is detachably mounted at the other end; the radiation source accommodating module is used to accommodate the radiation source, and a front surface thereof is provided with an opening, the center of the opening is located on the same horizontal line as the center of the radiation source, and the size of the opening is smaller than the size of the radiation source;

[0016] The collimation adjustment unit includes a support frame and an adjustment rod; wherein the support frame is fixed to the base; the adjustment rod is horizontally installed on the support frame from front to back, and its position is adjustable, but after installation, it will not rotate relative to the support frame to ensure stability during detection;

[0017] The collimation assembly includes a plurality of pinhole collimators (the present invention adopts a plurality of pinhole collimators, and the number of pinhole collimators can be selected according to the requirements of different application scenarios, thereby adjusting the total length of the collimation assembly); the plurality of pinhole collimators are coaxially installed on the adjustment rod and will not rotate relative to the adjustment rod, and the interval between adjacent pinhole collimators is less than 2 mm to ensure that the intensity scattering of radiation rays when passing through the area between adjacent pinhole collimators is minimized; each pinhole collimator is coaxially provided with a mounting hole. In addition, the pinhole collimator is evenly provided with 3-5 collimation holes of different apertures (the setting of different apertures is intended to meet different requirements for radiation attenuation in different application scenarios, so as to make the entire device more universal), and the center of each collimation hole is located on the same circle with the center of the pinhole collimator itself as the center. on the circumference of the center; the total length L of the collimation assembly in the horizontal direction and the two thicknesses in the vertical direction of the collimation hole can both meet the requirement that invalid radiation rays (i.e. unnecessary radiation rays, also known as attenuated rays) can be attenuated by more than 99%; the two thicknesses are respectively the distance p between the side of the collimation hole closest to the edge of the pinhole collimator and the edge of the pinhole collimator, and the distance h between the side of the collimation hole closest to the edge of the mounting hole and the edge of the mounting hole. Specifically, for example, for the collimation hole located above the mounting hole, its two thicknesses in the vertical direction are respectively the distance p between the upper edge of the collimation hole and the upper edge of the pinhole collimator, and the distance h between the lower edge of the collimation hole and the upper edge of the mounting hole; between each pinhole collimator, the distance between the center of the collimation hole and the center of the pinhole collimator itself is equal, and the collimation holes with the same aperture are located in the same orientation. Under the adjustment of the adjustment rod, the collimation hole on each pinhole collimator can be located on the same horizontal line with the center of the radiation source; in this way, the center of the collimation holes of each pinhole collimator located at the same orientation can also be located on the same horizontal line with the center of the radiation source.

[0018] The detector position adjustment unit includes a lifting assembly and a detector limiting assembly; wherein the detector limiting assembly is used to limit the position of the inorganic scintillation crystal detector, and its overall light-proof design is made of magnetic shielding material; the lifting assembly is used to stably support the detector limiting assembly and adjust the height of the detector limiting assembly so that the different height areas of the inorganic scintillation crystal detector are on the same horizontal line with the center of the radiation source;

[0019] The back-end test unit is connected to the inorganic scintillation crystal detector via an electrical signal transmission line (e.g., a BNC line) and is used to test the performance of the inorganic scintillation crystal detector. Different equipment is used depending on the test parameters. For example, a pulse height spectrum test device is used to measure light yield and energy resolution, and a digital oscilloscope is used to measure decay time.

[0020] Furthermore, the collimation assembly determines key parameters according to the following method:

[0021] ① According to the requirement that the attenuation flux of invalid radiation reaches more than 99%, the attenuation coefficient formula is:

[0022]

[0023] Where I is the total flux of the ray after passing through the collimator;

[0024] I0 is the total flux of the ray before it enters the collimator;

[0025] μ is the linear attenuation coefficient of the collimator component material under the action of radiation rays of specific energy;

[0026] x is the total length of the ray attenuated, that is, the total length L of the collimator assembly in the horizontal direction;

[0027] Based on this, the calculation formula for the attenuation percentage (D) of the attenuated ray flux is obtained:

[0028] D = 1-(I / I0)

[0029] Through calculation, the total length of the collimation assembly in the horizontal direction and the two thicknesses p and h of the maximum collimation hole in the pinhole collimator in the vertical direction are determined.

[0030] ② Determine the aperture and length of the collimating hole on the pinhole collimator

[0031] First, the limits of pore diameter and pore length are as follows:

[0032] The aperture is greater than or equal to 0.1 mm and less than or equal to one third of the vertical length of the irradiated cross section of the inorganic scintillation crystal detector to be tested;

[0033] The sum of the lengths of the collimating holes on all pinhole collimators is equal to the total length of the collimating assembly in the horizontal direction;

[0034] Secondly, in order to achieve precise control of the attenuated flux, the geometric solid angle formula is used to determine the specific collimation aperture and hole length used in each test:

[0035]

[0036] Among them, Atotal is the proportion of ray flux retained after passing through the collimator, that is, the proportion of effective radiation rays;

[0037] d is the aperture of the pinhole collimator;

[0038] L is the sum of the lengths of the collimating holes of the pinhole collimator, i.e. the total length;

[0039] Furthermore, the other end of the connecting rod is a snap-fit ​​structure, which enables free installation and removal of the radiation source accommodation module;

[0040] The upper surface of the radiation source accommodating module is provided with a placement hole (for smoothly placing the radiation source), and a matching cover is provided therewith;

[0041] The opening is a square hole, and the side length of the hole is smaller than the diameter of the radiation source, with a difference of 1-5 mm.

[0042] Furthermore, the support frame includes four first fixing rods and two second fixing rods;

[0043] The four first fixing rods are vertically mounted on the base and are symmetrically arranged in pairs (i.e., symmetrically distributed axially and radially on the horizontal plane) to form a cubic frame with a certain length, width and height;

[0044] The two second fixing rods are respectively installed between the two first fixing rods at the front end and the two first fixing rods at the rear end of the cubic frame, and the middle parts of the two second fixing rods are provided with square openings for inserting and removing the installation adjustment rods. In order to ensure that the two second fixing rods can be firmly installed in the cubic frame, a variety of existing technologies can be used for connection. The present application provides a method, specifically: each first fixing rod is provided with a through hole with an internal thread. After the second fixing rod is inserted into the two first fixing rods on the same side, the two ends of the second fixing rod can be fixed by using screws to maintain overall stability.

[0045] The adjusting rod is a square rod, which can fit in the gap of the square opening in the middle of the second fixed rod (the difference between the side length of the adjusting rod and the side length of the square opening does not exceed 5mm), ensuring that it can be smoothly plugged and unplugged before and after use; and the material selection of the adjusting rod must ensure that it has good load-bearing and sliding properties at the same time.

[0046] Furthermore, the pinhole collimator is a cylindrical radiation attenuator (depending on the type of radiation source being tested, a material with a strong attenuating effect on its radiation, such as lead, is used). A square mounting hole is coaxially located at its center, compatible with the adjustment rod, allowing for clearance between the rod and the square mounting hole (the difference between the side length of the square mounting hole and the side length of the adjustment rod does not exceed 5 mm). Four collimating holes of varying apertures are defined in the four directions, on both the positive and negative sides, with the center of the pinhole collimator as the origin (each hole has a different aperture, and the distance between the hole center and the center of the pinhole collimator is equal). The thickness of each pinhole collimator can be equal or different, adjusted according to actual needs and the degree of manufacturing difficulty.

[0047] Furthermore, the lifting assembly is a scissor-type lifting platform, the surface of which is paved with anti-slip material to ensure the horizontal stability of the detector limit assembly and the inorganic scintillation crystal detector, with an adjustment accuracy of no more than 5 μm;

[0048] The detector limiting assembly includes a limiting module and a limiting cover; wherein, the limiting module has a certain space inside to achieve a fixed limiting effect on the inorganic scintillation crystal detector, ensuring the stability and accuracy of the test process, and a through hole is provided on its side to facilitate the connection of the inorganic scintillation crystal detector with the back-end test unit; the limiting cover can be removed before and after use to facilitate the removal / placement of the inorganic scintillation crystal detector from the inside of the limiting module. After reinstallation, the gap between the limiting cover and the limiting module is further enhanced by using black light-shielding material to further enhance the light-shielding effect. The detector limiting assembly as a whole uses a material that can achieve both light-shielding and magnetic shielding effects. The black light-shielding material used in the above-mentioned gap ensures the shielding effect on light and magnetic fields and reduces the attenuation of incoming radiation. The difference between the diameter of the internal space of the limiting module and the maximum external diameter of the inorganic scintillation crystal detector does not exceed 5mm, the difference between the diameter of the upper opening and the diameter of the limiting cover does not exceed 5mm, and the difference between the diameter of the side through hole and the maximum diameter of the interface for connecting to the electrical signal transmission line does not exceed 5mm.

[0049] Furthermore, the collimator adjustment unit further includes a receiving assembly for receiving the pinhole collimator;

[0050] The storage component is located on the base below the adjustment rod, and has a semicircular groove with a diameter larger than the overall diameter of the pinhole collimator, and the difference is not less than 10 mm.

[0051] Furthermore, the radioactive source is 137 Cs or 60 High-energy gamma radiation sources primarily composed of radioactive elements or isotopes such as Co. While the default radiation source shape is circular in this disclosure, sources of different shapes and types can be used in practical applications depending on the specific situation. For this type of radiation source, a cylindrical lead sheet can be used as a pinhole collimator.

[0052] The inorganic scintillation crystal detector specifically comprises a scintillation crystal, a photomultiplier tube, and a housing. The scintillation crystal and photomultiplier tube are optically coupled via an optical transmission coupling agent to enhance the uniformity of light transmission. The outer shell of the housing is composed of a heat-resistant and impact-resistant material, which also shields external signals and light. Its dimensions closely match those of the scintillation crystal and photomultiplier tube, with a spacing of approximately 1mm, thereby securing the two. Scintillator crystals are primarily divided into standard scintillation crystals and test crystals. The former, with known performance parameters such as light yield and energy resolution, should be of the same type, size, and shape as the latter.

[0053] At the same time, the present invention also provides a testing method for the inorganic scintillation crystal performance testing system based on the adjustable pinhole collimator, which is special in that it includes the following steps:

[0054] Step 1: Install the radioactive source

[0055] Placing the radioactive source in the radioactive source containment module and mounting the radioactive source containment module on the other end of the connecting rod; that is, after selecting the radioactive source required for testing, opening the cover on the upper surface of the radioactive source containment module, placing the radioactive source into the module through the placement hole (ensuring that the center of the radioactive source is on the same horizontal line as the center of the opening), and then closing the cover. Thereafter, the radioactive source containment module is snapped into the snap structure of the connecting rod to complete the installation and fixation of the radioactive source;

[0056] Step 2: Install the Collimation Assembly

[0057] Install each pinhole collimator of the collimation assembly on the adjustment rod in sequence, and then install the adjustment rod horizontally on the support frame from front to back and fix it, ensuring that the collimation holes corresponding to each pinhole collimator have the same aperture and that the center of the collimation hole located above (i.e., the hole center) is in the same horizontal line as the center of the radiation source; during specific installation, one end of the adjustment rod can be installed on the second fixing rod at one end of the support frame, and then each pinhole collimator can be inserted into the adjustment rod, and then the other end of the adjustment rod can be installed in conjunction with the second fixing rod at the other end of the support frame, so that the center of the collimation hole located above the pinhole collimator is in the same horizontal line as the center of the radiation source;

[0058] Step 3: Install the inorganic scintillation crystal detector to be tested

[0059] Place the inorganic scintillation crystal detector to be tested in the detector limit assembly, and place the detector limit assembly stably on the upper surface of the lifting assembly. Adjust the height so that the initial height area of ​​the crystal in the inorganic scintillation crystal detector to be tested is aligned with the center of the radiation source and the center of the collimating hole above.

[0060] Step 4: Test the performance of the inorganic scintillation crystal detector to be tested

[0061] Connect the inorganic scintillation crystal detector to be tested to the back-end test unit, set the prerequisite parameters according to the type of test performance (for example, the prerequisite parameters for testing light yield and energy resolution are the operating voltage and main amplifier gain; the prerequisite parameter for testing decay time is the operating voltage. Generally speaking, the prerequisite parameters to be adjusted vary depending on the back-end test unit). After completing the settings, start the test and collect the test results.

[0062] After completing the initial height area test, adjust the lifting assembly to change the height area of ​​the inorganic scintillation crystal detector to be tested, and continue testing. After completing the current angle test, rotate the detector limit assembly as needed to perform the next set of tests. Repeat this process until all tests under the current collimation assembly parameter conditions are completed, that is, the scintillation crystal performance uniformity test is completed. Specifically:

[0063] Connect the back-end test unit and set the prerequisite parameters such as operating voltage and main amplifier gain. After completing the settings, start the test with one side of the detector limit assembly as the initial angle (0°) and collect the test results. After completing the initial height area test, adjust the lifting assembly to change the height area of ​​the crystal in the inorganic scintillation crystal detector to be tested according to a specific step size (the step size can be determined according to actual needs, for example: 5cm) and continue testing until it reaches the bottom area of ​​the crystal and completes the initial angle test. Then, rotate the detector limit assembly clockwise by 90° (this is a specific angle and the rotation angle can be determined according to actual needs) to perform the next set of tests. Repeat this process until it returns to the initial angle, completing all tests under the current collimation assembly parameter conditions (determining the aperture, hole length, total length in the horizontal direction, and thickness at two locations in the vertical direction).

[0064] If additional testing is required, the thickness of the collimator and the aperture of the upper collimating hole can be changed according to different requirements for radiation flux, and a secondary test can be performed. The overall process remains unchanged.

[0065] In practical applications, testing is usually performed using a standard radioactive source with known activity. However, the possibility of using a radioactive source with unknown activity cannot be ruled out. Therefore, the present invention also provides a method for calibrating a radioactive source using the above-mentioned inorganic scintillation crystal performance testing system based on an adjustable pinhole collimator (if crystal performance uniformity is the use of a standard radioactive source to test a crystal with unknown parameters, then calibration is based on this premise. After testing the standard scintillation crystal using a standard radioactive source and a radioactive source with an activity to be calibrated, the results are compared to achieve reverse calibration of the radioactive source to be calibrated). The special feature of the method is that it includes the following steps:

[0066] S1: Install the standard radiation source

[0067] Placing a standard radioactive source with a known activity A0 in the radioactive source containing module, and installing the radioactive source containing module on the other end of the connecting rod;

[0068] S2: Install the collimation assembly

[0069] Install each pinhole collimator of the collimation assembly on the adjustment rod in sequence, then install the adjustment rod horizontally on the support frame from front to back and secure it, ensuring that the collimation holes corresponding to each pinhole collimator have the same aperture and that the center of the upper collimation hole is on the same horizontal line as the center of the radiation source;

[0070] S3: Installing Inorganic Scintillation Crystal Detectors

[0071] Place the inorganic scintillation crystal detector containing the standard scintillation crystal in the detector limit assembly, and place the detector limit assembly stably on the upper surface of the lifting assembly. Adjust the height so that the initial height area of ​​the crystal in the inorganic scintillation crystal detector for testing is aligned with the center of the radiation source and the center of the collimating hole above.

[0072] S4: Testing of standard radioactive sources

[0073] Connect the inorganic scintillation crystal detector to the pulse height spectrum test equipment and ensure a light-proof environment; set the prerequisite parameters of the pulse height spectrum test equipment (including voltage, gain, build time, and test time). After completing the settings, start the test and collect the full-energy peak channel address Ch0 and count rate R0;

[0074] S5: Replacement and testing of radioactive sources to be calibrated

[0075] After completing S4, remove the voltage, turn off the pulse height spectrum test equipment, replace the standard radioactive source in the radioactive source containing module with the radioactive source to be calibrated, and then repeat the test process in S4 and collect the full energy peak channel address Ch1 and count rate R1. After completing the test, remove the voltage and turn off the pulse height spectrum test equipment;

[0076] S6: Radioactive source calibration (mainly calibrating activity and energy consistency)

[0077] Compare the differences in the full energy peak channel address and count rate results obtained in S4 and S5 to perform the following calibration calculations on the radioactive source to be calibrated:

[0078] ①Energy consistency: calculated by the following formula

[0079] Energy uniformity=(Ch1-Ch0) / Ch0

[0080] If the value is ≤1%, it is considered that the energy of the radioactive source to be calibrated is consistent with that of the standard radioactive source;

[0081] ② The activity A1 of the radioactive source to be calibrated is calculated using the following formula:

[0082] A1=A0×(R1 / R0)

[0083] At this point, the entire process of radioactive source calibration is completed.

[0084] Remember: When not in use, the back-end test unit must be turned off and the voltage divider at the tail end of the detector must be disconnected.

[0085] Principle of the present invention:

[0086] The present invention achieves dual-factor control of radiation flux and intensity by adjusting the total length L of the collimation assembly in the horizontal direction, the thickness of the collimation hole located at two points in the vertical direction, and the aperture of the collimation hole. In conjunction with the integrated front-end structure of the system and various test equipment at the back-end of the system, it can accurately and reliably restore the test results of the performance uniformity of inorganic scintillator crystals of different types and sizes in the real radiation environment of various application fields.

[0087] The total horizontal length of the system's collimation assembly, the two vertical thicknesses of the collimation hole located above, and the aperture of the collimator can all be flexibly adjusted according to actual application requirements. In conjunction with other components, precise axial-radial tests are performed on different crystals under different radiation conditions to obtain more realistic scintillation performance uniformity. This provides more accurate data support for evaluating its performance in actual applications, and realizes the construction of a comprehensive and reliable scintillation crystal uniformity characterization test system.

[0088] Advantages of the present invention:

[0089] This paper proposes a performance testing system for inorganic scintillator crystals based on an adjustable pinhole collimator structure, and also proposes a corresponding testing method based on this system. Compared with conventional technologies, the present invention has the following main benefits:

[0090] 1. This invention utilizes a collimation assembly comprised of multiple pinhole collimators, a core structure of the system, to precisely direct radiation from the radiation source into the scintillation crystal at a defined angle, minimizing interference from scattering and background radiation. By combining standard scintillation crystals with similar standard radiation sources, high-precision and sensitive calibration of the activity and energy consistency of the radiation source is achieved. This allows for flexible matching of various radiation sources and minimizes the objective conditions of the diverse radioactive isotopes in the application environment.

[0091] 2. By adjusting the total horizontal length (L) of the collimation assembly, the thickness of the upper collimation hole at two locations in the vertical direction, and the aperture of the collimation hole, the present invention can achieve complex control of radiation intensity and flux attenuation. Simultaneously, combined with the use of multiple types of pre-calibrated radiation sources, this provides testing conditions closer to real-world scenarios, enabling precise and rapid testing of the performance uniformity of scintillator crystals of different types, sizes, and shapes.

[0092] 3. Through flexible selection or adjustment of multiple components in the system, such as the radiation source, scintillation crystals, collimation assembly, and lifting assembly, the present invention expands its application scope and versatility based on existing one-dimensional or two-dimensional crystal uniformity characterization work. It can achieve precise characterization of the three-dimensional spatial performance distribution of the measured scintillation crystals. This has extremely important guiding significance for the application of selective cutting of large-scale scintillation crystals to obtain high-quality small-scale scintillation crystals.

[0093] In summary, the present invention, on the one hand, comprehensively deepens the application breadth and depth of scintillation crystal uniformity testing and characterization work, achieving a test effect in which components such as crystals, radiation sources, and collimators maintain dynamic balance when many conditions such as type, size, shape, and thickness change. On the other hand, it provides ideas for guiding the selective processing of high-quality small-sized crystals by, for example, characterizing the uniformity of the three-dimensional spatial performance of crystals, broadening the possible application paths of testing systems based on pinhole collimators, giving them stronger usage prospects and promotion potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 It is a schematic plan view of an inorganic scintillator crystal performance test system based on an adjustable pinhole collimator;

[0095] Figure 2 It is a schematic diagram of the three-dimensional structure of a single pinhole collimator;

[0096] Figure 3 is a schematic diagram of the emission path of the attenuated rays in the material area of ​​the collimator component;

[0097] Figure 4 is a schematic diagram of the emission path of the radiation rays in the aperture area of ​​the collimator assembly;

[0098] Figure 5 Schematic diagram of reference points for performing crystal axial inhomogeneity testing in the embodiments of the present invention;

[0099] Figure 6 Schematic diagram of reference points for performing radial inhomogeneity testing of crystals in the embodiments of the present invention;

[0100] Figure 7: This is the corresponding pulse height spectrum image of the same test point under two different collimator length and aperture settings in Example 1;

[0101] Figure 8 This is a photo of a high-quality cylindrical small-sized crystal with excellent performance uniformity obtained by cutting and processing the tested crystal based on the axial and radial performance uniformity test results in Example 1;

[0102] Figure 9 : This is the corresponding pulse height spectrum image of the same test point under two different collimator length and aperture settings in Example 2;

[0103] Figure 10 This is a photo of a high-quality cylindrical small-sized crystal with excellent performance uniformity obtained by cutting and processing the tested crystal based on the axial and radial performance uniformity test results in Example 2;

[0104] Figure 11 In Example 3, 137 Cs standard source and calibration 137 The corresponding pulse height spectrum image of the same test point (center) under Cs source radiation conditions. DETAILED DESCRIPTION

[0105] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments:

[0106] like Figure 1 As shown, a performance testing system for inorganic scintillator crystals based on an adjustable pinhole collimator includes a base, a high-energy gamma radiation source, a radiation source limiting unit, a collimation assembly, a collimation adjustment unit, a detector position adjustment unit, and a rear-end testing unit. Definition: One side of the base is the front end, and the other side opposite it is the rear end. From the front end to the rear end, the base is fixed to and supports the detector position adjustment unit, collimation adjustment unit, and radiation source limiting unit.

[0107] The radiation source limiting unit includes a support rod, a connecting rod and a radiation source accommodating module; wherein, the support rod is vertically installed on the base, the connecting rod is vertically installed on the support rod through one end thereof, and the other end is detachably mounted on the radiation source accommodating module through a snap-on structure; the radiation source accommodating module is used to accommodate the radiation source, and a square opening is provided on its front end surface, the center of the opening is located on the same horizontal line as the center of the radiation source, and the side length of the opening is smaller than the diameter of the radiation source; a placement hole is provided on the upper surface of the radiation source accommodating module, and a sealing cover is matched with it.

[0108] The collimation adjustment unit includes a support frame, an adjustment rod and a storage assembly for accommodating the pinhole collimator; the support frame includes four first fixing rods and two second fixing rods; the four first fixing rods are all vertically installed on the base, and are symmetrically arranged in pairs to form a cubic frame; the two second fixing rods are respectively installed between the two first fixing rods at the front end of the cubic frame and between the two first fixing rods at the rear end, and the middle part of the two second fixing rods is provided with a square opening for plugging and removing the adjustment rod; the adjustment rod is a square rod, which is horizontally installed on the support frame from front to back and can fit with the square opening gap in the middle of the second fixing rod. Its position is adjustable, but it will not rotate relative to the support frame after installation; the storage assembly is located on the base below the adjustment rod, and it has a semicircular groove with a diameter larger than the diameter of the pinhole collimator.

[0109] The collimation assembly includes a plurality of pinhole collimators; the plurality of pinhole collimators are coaxially installed on the adjustment rod and will not rotate relative to the adjustment rod, and the interval between adjacent pinhole collimators is less than 2mm; the pinhole collimator is a cylindrical radiation attenuation sheet (for example: the radiation source is 137 When Cs is set, the pinhole collimator is a cylindrical lead sheet. A square mounting hole adapted to the adjustment rod is coaxially provided at its center, which can be loosely fitted with the adjustment rod. The center of the pinhole collimator is used as the origin of the coordinate axis, and four collimating holes of varying apertures are provided on the collimator in the four directions on the positive and negative sides. The centers of the respective collimating holes are located on the same circle centered on the center of the pinhole collimator. The total length L of the collimating assembly in the horizontal direction and the thickness of the collimating holes at two locations in the vertical direction can both ensure that the attenuation flux of invalid radiation rays reaches more than 99%. The two thicknesses are, respectively, the distance p between the edge of the pinhole collimator and the side of the collimating hole closest to the edge of the mounting hole, and the distance h between the edge of the mounting hole and the side of the collimating hole closest to the edge of the mounting hole. The detector position adjustment unit includes a lifting assembly and a detector limiting assembly; among them, the detector limiting assembly is used to limit the position of the inorganic scintillation crystal detector, including a limiting module and a limiting cover. The overall design is light-proof and the material is magnetic shielding material (in this embodiment, black polytetrafluoroethylene and black electrical tape are used to achieve light-proof and magnetic shielding effects); the lifting assembly is used to stably support the detector limiting assembly and adjust the height of the detector limiting assembly so that the different height areas of the crystal in the inorganic scintillation crystal detector are on the same horizontal line with the center of the radiation source; the lifting assembly is a scissor-type lifting platform, the surface of which is paved with anti-slip material, and its adjustment accuracy does not exceed 5μm.

[0110] The back-end test unit is connected to the inorganic scintillation crystal detector and is used to test the performance of the inorganic scintillation crystal detector.

[0111] The key parameters of the collimation component in the above test system are determined according to the following method:

[0112] ① According to the requirement that the attenuation flux of invalid radiation reaches more than 99%, the attenuation coefficient formula is:

[0113]

[0114] Where I is the total flux of the ray after passing through the collimator;

[0115] I0 is the total flux of the ray before it enters the collimator;

[0116] μ is the linear attenuation coefficient of the collimator component material under the action of radiation rays of specific energy;

[0117] x is the total length of the ray attenuated, that is, the total length L of the collimator assembly in the horizontal direction;

[0118] Based on this, the calculation formula for the attenuation percentage (D) of the attenuated ray flux is obtained:

[0119] D= 1-(I / I0)

[0120] Through calculation, the total length of the collimation assembly in the horizontal direction and the two thicknesses p and h of the maximum collimation hole in the pinhole collimator in the vertical direction are determined.

[0121] ② Determine the aperture and length of the collimating hole on the pinhole collimator

[0122] First, the limits of pore diameter and pore length are as follows:

[0123] The aperture is greater than or equal to 0.1 mm and less than or equal to one third of the vertical length of the irradiated cross section of the inorganic scintillation crystal detector to be tested;

[0124] The sum of the lengths of the collimating holes on all pinhole collimators is equal to the total length of the collimating assembly in the horizontal direction;

[0125] Secondly, in order to achieve precise control of the attenuated flux, the geometric solid angle formula is used to determine the collimating hole diameter and hole length used in each test:

[0126]

[0127] Among them, A total is the proportion of ray flux retained after passing through the collimator, that is, the proportion of effective radiation rays;

[0128] d is the aperture of the pinhole collimator;

[0129] L is the sum of the lengths of the collimating holes of the pinhole collimator, i.e. the total length;

[0130] Here are some additional explanations for the two methods:

[0131] ① The total length L of the collimator assembly in the horizontal direction, and the thicknesses p and h of each collimator hole in the vertical direction mainly reflect the attenuation of "ineffective radiation rays", because the key point of the pinhole collimator is that only the total flux of radiation rays passing through the collimator hole needs to be considered after use. Take a complete collimator assembly composed of multiple pinhole collimators with the same hole length and thickness (t) as an example, Figure 2 As shown, at this time, only the incidence of the attenuated ray from the upper edge of the collimating hole 442 to the upper edge of the collimator and the lower edge of the collimating hole 442 to the upper edge of the central mounting hole is considered. The exit path of the attenuated ray in the corresponding collimator material area is as follows Figure 3 As shown (in fact, the attenuation of radiation rays in the collimator area outside the collimation hole can be regarded as the situation occurring on the p1-nt or h1-nt two-dimensional plane rotated 360°), from Figure 3 It is not difficult to see that there are three extreme cases of the path of the attenuated ray in the collimator, and their lengths are nt, p1, and l max , and according to the Pythagorean theorem we know that l max =((nt)^ 2 +(p1)^ 2 )^ 0.5 For attenuated rays, the shortest possible length is nt or p1. Therefore, based on the attenuation coefficient formula, the total horizontal length nt of the collimator assembly and the vertical thicknesses p and h of the collimator aperture must satisfy the following conditions: exp(-μ(nt)) < 1%, exp(-μ(p)) < 1%, and exp(-μ(h)) < 1%.

[0132] At this time, the total horizontal length of the collimation assembly involves the number of collimators and the hole length of a single collimator. The determination of the hole length value needs to be coordinated with the aperture (the combined regulation of the two can achieve the expected flux size, which is explained in detail in Section ②). After determining the hole length, the value range of n is calculated based on the total limit of exp(-μ(nt)) < 1% and the smallest positive integer is taken (if the apertures of the collimators are not equal, nt in the formula can be converted to L for calculation). Regarding the two thicknesses of the collimator in the vertical direction (the minimum distance p between the edge of each opening and the edge of the nearest collimator and the distance h between the edge of each opening and the edge of the nearest center mounting hole), it is first necessary to clarify that the collimator used in the present invention has multiple collimating holes. The sizes of different collimating holes are different, but the center of each collimating hole is located on a circle with the center of the collimator itself as the center. The collimator itself is circular. Therefore, the larger the radius of the collimating hole, the smaller the minimum distance p between its edge and the edge of the nearest collimator and the minimum distance h between the edge of the nearest center mounting hole. Under this condition, the pore diameter d is maximum (d max ) The p and h of the collimating hole are the smallest (p min / h min), in other words, if exp(-μ(p min ))<1% / exp(-μ(h min ))<1%, then the thickness of each collimating hole in the vertical direction also meets the flux attenuation requirement for the attenuated rays.

[0133] ② The aperture and length of the collimating hole on the pinhole collimator are determined mainly by considering the attenuation effect on the radiation entering the detector. This is the key point in the control link. At this time, the upper and lower limits of the flux attenuation effect need to be considered first.

[0134] Scintillator crystals have numerous applications in radiation detection, such as oil well logging, space payloads, and medical imaging. Here, we use scintillation crystal detectors used in high-energy physics experiments as an example. These typically pursue high spatial resolution and measurement accuracy, while minimizing background noise and ambient radiation. To achieve this, the collimator must provide high attenuation and precise control of the radiation. Currently, these applications require approximately 0.1-2% of the remaining flux after collimation, representing an attenuation ratio of 98-99.9%. It's important to note that aperture is the primary parameter determining the radiation flux, primarily limiting the incident angle θ at which the radiation is counted. Smaller apertures, with smaller θ, result in a higher signal-to-noise ratio for the radiation flux entering the back-end test unit, but this also results in greater flux loss and reduced detection efficiency. Aperture length, a secondary parameter that influences radiation flux in conjunction with aperture, also corresponds to the total horizontal length of the collimator assembly. A larger aperture length improves measurement accuracy (i.e., spatial resolution), but also results in greater flux loss.

[0135] In terms of aperture, taking into account the differences in size and shape of different tested crystals, its size should not exceed one-third of the length of the irradiated cross-section of the tested crystal to ensure the accuracy of the test point, and should not be less than 0.1mm. The reason is that if the aperture is too small, the area of ​​the detector irradiated will be extremely small and the detection sensitivity threshold will not be reached, resulting in the test being unable to proceed normally.

[0136] In terms of hole length, the structural design of the pinhole collimator determines that the hole length of the collimation assembly is almost equivalent to its total length L in the horizontal direction. Therefore, the sum of the hole lengths of the collimating holes in the same orientation on the pinhole collimator is equal to the total length of the collimation assembly in the horizontal direction.

[0137] To ensure that the test variables are controllable, the pinhole collimators used all maintain the same aperture on the top during testing;

[0138] After roughly clarifying some limitations of aperture and hole length, we consider their corresponding attenuation effect on ray flux to further clarify its regulating effect and limitation. At this time, we introduce the simplified geometric solid angle formula to link the three parameters of aperture, hole length and radiation flux together, and calculate the radiation ray flux A that completely passes through the collimator hole and exits the detector. total Perform calculations.

[0139] At this time: B=1-A total is the flux attenuation ratio of the radiation entering the detector relative to the flux before entering the collimating hole of the pinhole collimator. Considering that the collimation assembly used in the present invention is essentially a plurality of cylindrical pinhole collimators of the same thickness (or different thicknesses, similar to Part 1, the same thickness is used as the premise for preliminary discussion) placed on the same horizontal line, each collimator maintains a certain distance between them, such as Figure 4 As shown. At this time, it is necessary to consider the number of collimators n and the distance s between each collimator; the value of the distance s should be as small as possible (<2mm) to eliminate its influence on the radiation. Then t is used to represent the horizontal thickness of a single collimator or the length of the collimating hole, and L is the total horizontal thickness or total hole length of n collimators, L≈nt. At this time, the collimating holes of each collimator are as follows Figure 4 As shown, consider the incident angle of the radiation relative to the central axis of the collimator aperture to be θ. Regarding the upper and lower limits of B, it is first necessary to clarify that the main purpose of the pinhole collimator is to maximize the temporal and spatial resolution of the radiation source during the test, while reducing the interference of external magnetic fields and the large amount of scattering of radiation from the radiation source on the measured crystal performance. Therefore, regardless of its adjustment, its attenuation effect on the radiation flux is bound to be significant. Based on its application context, its upper and lower limits are more determined by the relative trade-off between improving test efficiency or further improving accuracy under existing high-precision conditions, which is mainly influenced by the values ​​of aperture and aperture length. If high precision is pursued, the aperture needs to be as small as possible and the aperture length as large as possible; if high efficiency is pursued, the opposite is true. This coincides with the geometric solid angle formula listed above. Considering that the radiation from a low-activity source, after attenuation by the collimator, is too small to meet the detection threshold (minimum limit) of the scintillation crystal detector, B is determined based on this. total The range is 98%~99.5%, which is close to the range of the above-mentioned high-energy physics experimental model.

[0140] This completes the description of the key parameters of the alignment assembly. Based on this, the following research work is carried out as shown in the following examples:

[0141] Example 1

[0142] Complete the installation of each component before testing:

[0143] For the scintillation crystal detector used in high-energy physics experiments, a LaBr3:Ce crystal with a doping concentration of 5%, a diameter and height of 38mm, was wrapped with a reflective layer of PTFE and then encapsulated in a special aluminum shell (diameter and height of 42mm) to prevent deliquesce and oxidation. It was then coupled to a photomultiplier tube using optical silicone oil and sealed in the detector housing, completing the overall assembly of the detector.

[0144] Use of radioactive sources 137 Cs standard source;

[0145] The lifting platform used has a surface size of 150mm×150mm and a lifting height range of 75-260mm;

[0146] The pinhole collimator used is made of pure lead and has four side openings. Figure 2 The same as shown. In this case, μ is 1.25 cm -1 , let A=0.99, then I / I0=e -μx =0.01, and we get x≈3.68cm. At this time, p min 、h min , L must be greater than this value - on this basis, the following parameters are determined: the complete diameter of a single collimator is 100 mm, the thickness is 10 mm, the diameter of the central mounting hole of the collimator is 50 mm, the diameters of the side circular openings 442, 443, 444, and 445 are 5 mm, 7 mm, 9 mm, and 11 mm respectively, the center distance of each hole from the core of the square opening 441 is 60 mm, and the horizontal distance from the nearest collimator edge is 40 mm.

[0147] In Example 1, the assembly and construction of the entire test system was completed according to the steps described in the technical solution, wherein the upper openings of the pinhole collimator 44 were selected as 443 and 445 respectively, and the total length of the collimation assembly in the horizontal direction was selected as 55mm and 40mm respectively (calculated that the attenuation effect of the two apertures and hole lengths on the flux was close to the upper and lower limits respectively), and two corresponding tests were carried out on this basis. Figure 5The marking points at different angles shown are used to test the non-uniformity of the relative light output and energy resolution in the scintillation crystal axis. Specifically, by adjusting the height of the lifting platform so that the center of the area where the crystal is 5 / 10 / 15 / 20 / 25 / 30mm away from the PMT incident surface is on the same horizontal line as the center of the opening above the collimator and the center of the circular radiation source, the output voltage of the high-voltage source is set to -700V, the gain of the main amplifier is set to 50, and the forming time is set to 1us. Finally, a computer is used to collect data images for 300s according to the pulse height spectrum test software. Tables 1 and 2 show the numerical comparison results of the relative light output and energy resolution of LaBr3:Ce used under the conditions of 443 opening and 55mm length and 445 opening and 40mm length, respectively. Figure 7 The corresponding pulse height spectrum images of the same point under two test conditions are shown.

[0148] In Example 1, in order to further characterize the local performance uniformity of the LaBr3:Ce crystal used in three-dimensional space, based on the existing axial uniformity results (Table 2), while keeping the same collimator parameters, the collimator was tested. Figure 6 The radial uniformity of the relative light output and energy resolution of the crystal was tested, and the results are shown in Table 3. The results show that the LaBr3:Ce crystal used is Figure 5 The uniformity and performance of the area 10-25mm from the PMT incident surface on the 90° and 180° axes are relatively the best. Based on this conclusion, the following are obtained by cutting from the corresponding areas: Figure 8 The dimensions shown are 6×6×6 mm 3 of cubic crystals.

[0149] Table 1

[0150]

[0151] Table 2

[0152]

[0153] Table 3

[0154]

[0155] Example 2

[0156] Complete the installation of each component before testing:

[0157] For the scintillation crystal detector used in high-energy physics experiments, a LaBr3:Ce,Sr crystal with a Ce doping concentration of 5% and an Sr doping concentration of 0.5%, a diameter of 38mm, and a height of 32mm was wrapped with a reflective layer of PTFE and then encapsulated in a special aluminum shell (diameter and height of 42mm) to prevent deliquescence and oxidation. It was then coupled to the PMT using optical silicone oil and sealed in the detector housing, completing the overall assembly of the detector.

[0158] The radiation source used is 662KeV 137 Cs standard source;

[0159] The lifting platform used has a surface size of 150mm×150mm and a lifting height range of 75-260mm;

[0160] The pinhole collimator used is made of pure lead and has four side openings. Figure 2 The same as shown. In this case, μ is 1.25 cm -1 , let A=0.99, then I / I0=e -μx =0.01, and we get x≈3.68cm. At this time, p min 、h min , L must be greater than this value - on this basis, the following parameters are determined: the complete diameter of a single collimator is 100 mm, the thickness is 10 mm, the diameter of the central mounting hole of the collimator is 50 mm, the diameters of the side circular openings 442, 443, 444, and 445 are 1 mm, 3 mm, 5 mm, and 7 mm respectively, the center distance of each hole from the core of the square opening 441 is 60 mm, and the horizontal distance from the nearest edge is 40 mm.

[0161] In Example 2, the overall test system was assembled and constructed according to the steps described in the technical solution, wherein the upper openings of the pinhole stopper 44 were selected as 443 and 445, and the total length of the collimation assembly in the horizontal direction was selected as 55mm and 40mm respectively (the attenuation effect of the two apertures and hole lengths on the flux was calculated to be close to the upper and lower limits, respectively). On this basis, two corresponding tests were performed. The relative light output and energy resolution axial non-uniformity tests of the crystal were carried out based on Figure 5Specifically, by adjusting the height of the lifting platform so that the center of the area where the crystal is 5 / 10 / 15 / 20 / 25 / 30mm away from the PMT incident surface is in the same horizontal line as the center of the opening above the collimator and the center of the circular radiation source, the output voltage of the high-voltage source is set to -700V, the gain of the main amplifier is set to 50, and the forming time is set to 1us. Finally, a computer is used to collect data images for 300s according to the pulse height spectrum test software. Tables 4 and 5 show the numerical comparison results of the relative light output and energy resolution of LaBr3:Ce,Sr used under the conditions of 443 opening and 55mm length and 445 opening and 40mm length, respectively. Figure 9 The corresponding pulse height spectrum images of the same point under two test conditions are shown.

[0162] Table 4

[0163]

[0164] Table 5

[0165]

[0166] Table 6

[0167]

[0168] In Example 2, in order to further characterize the local performance uniformity of the LaBr3:Ce crystal used in three-dimensional space, based on the existing axial uniformity results (Table 5), while keeping the same collimator parameters, the collimator was tested. Figure 6 The radial uniformity of the relative light output and energy resolution of the crystal was tested, and the results are shown in Table 6. The results show that the LaBr3:Ce crystal used is Figure 5 The uniformity of the area 20-30mm from the PMT incident surface on the 0° and 90° axes is relatively the best. Based on this conclusion, the following is obtained by cutting from the corresponding area: Figure 10 The dimensions shown are 6×6×6 mm 3 of cubic crystals.

[0169] Example 3

[0170] Complete the installation of each component before testing:

[0171] For the detector, a standard LaBr3:Ce crystal with a Ce doping concentration of 5% and a diameter and height of 38mm was wrapped with a reflective layer of PTFE and then encapsulated in a custom aluminum shell (42mm in diameter and height) to prevent deliquesce and oxidation. It was then coupled to the PMT using optical silicone oil and sealed in the detector housing, completing the overall assembly of the detector.

[0172] The radiation source used is 662KeV 137 Cs standard source and the 137 Cs source (energy: 662 KeV; activity: 1 μCi);

[0173] The lifting platform used has a surface size of 150mm×150mm and a lifting height range of 75-260m;

[0174] The pinhole collimator used is made of pure lead and has four side openings. Figure 2 The same as shown. In this case, μ is 1.25 cm -1 , let A=0.99, then I / I0=e -μx =0.01, and we get x≈3.68cm. At this time, p min 、h min , L must be greater than this value - on this basis, the following parameters are determined: the complete diameter of a single collimator is 100 mm, the thickness is 10 mm, the diameter of the central mounting hole of the collimator is 50 mm, the diameters of the side circular openings 442, 443, 444, and 445 are 1 mm, 3 mm, 5 mm, and 7 mm respectively, the center distance of each hole from the core of the square opening 441 is 60 mm, and the horizontal distance from the nearest edge is 40 mm.

[0175] In Example 3, the assembly and construction of the entire test system was completed according to the steps described in the technical solution, wherein the upper opening of the pinhole-shaped stopper 44 was selected as 444 and the total length of the collimator was selected as 38 mm. On this basis, two tests were performed: first, 137 The Cs standard source is loaded into the radiation source accommodation module 32, and the scissor lift platform 5 is adjusted so that the center of the standard LaBr3:Ce crystal is aligned with the 137 The centers of the Cs standard source and the collimator opening 444 are located on the same horizontal line. The high voltage source output voltage is set to -700V, the main amplifier gain is set to 50, and the forming time is set to 1us. Finally, a computer is used to collect a pulse height spectrum image for 300s according to the pulse height spectrum test software. After completing the above test, the pressure is released and the 137 Cs standard source is taken out and put into the calibration 137 Cs source, keep other conditions unchanged, re-pressurize and collect pulse height spectrum again. Figure 11 shown.

[0176] In Example 3, the energy consistency and activity of the radioactive source to be calibrated can be determined based on the channel address (channel value at the peak) of the full energy peak in the pulse height spectrum and the difference in count rate. Figure 9 The results show that the track addresses under the two test conditions are almost the same, proving that the calibration is required.137 Energy and Standards of Cs Sources 137 The Cs source is the same, both are 662KeV; the standard 137 The full energy peak count obtained by the Cs source test is 796.231, and the count rate is about 2.65, while the 137 The total energy peak count obtained from the Cs source test is 568.044, and the count rate is about 1.89, so it needs to be calibrated. 137 The activity of the Cs source is 1 (1.89 / 2.65) = 0.71μCi.

[0177] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present invention, and these modifications or replacements should all be included in the scope of protection of the present invention.

Claims

1. An inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator, characterized by: It includes a base, a radiation source, a radiation source limiting unit, a collimation assembly, a collimation adjustment unit, a detector position adjustment unit and a back-end test unit; Definition: One side of the base is the front end, and the other side opposite to it is the back end; From the front end to the rear end, the base is fixed on and carries the detector position adjustment unit, the collimation adjustment unit and the radiation source limiting unit; The radiation source limiting unit includes a support rod, a connecting rod, and a radiation source accommodating module; wherein the support rod is vertically mounted on the base, the connecting rod is vertically mounted on the support rod at one end, and the radiation source accommodating module is detachably mounted at the other end; the radiation source accommodating module is used to accommodate the radiation source, and an opening is provided on the front surface thereof, the center of the opening is located on the same horizontal line as the center of the radiation source, and the size of the opening is smaller than the size of the radiation source; The collimation adjustment unit includes a support frame and an adjustment rod; wherein the support frame is fixed to the base; the adjustment rod is horizontally installed on the support frame from front to back, and its position is adjustable, but it will not rotate relative to the support frame after installation; The collimation assembly includes a plurality of pinhole collimators; the plurality of pinhole collimators are coaxially installed on an adjustment rod at intervals and will not rotate relative to the adjustment rod, and the interval between adjacent pinhole collimators is less than 2 mm; each pinhole collimator is coaxially provided with a mounting hole, and in addition, 3-5 collimation holes of different apertures are evenly provided on the pinhole collimator, and the centers of the collimation holes are all located on the same circumference with the center of the pinhole collimator itself as the center; the total length L of the collimation assembly in the horizontal direction and the thickness of the collimation holes at two locations in the vertical direction can both meet the requirement of achieving more than 99% attenuation of invalid radiation rays; the two thicknesses are respectively the distance p between the side of the collimation hole closest to the edge of the pinhole collimator and the edge of the pinhole collimator, and the distance h between the side of the collimation hole closest to the edge of the mounting hole and the edge of the mounting hole; under the adjustment of the adjustment rod, the collimation holes on each pinhole collimator can be located on the same horizontal line as the center of the radiation source; The detector position adjustment unit includes a lifting assembly and a detector limiting assembly; wherein the detector limiting assembly is used to limit the position of the inorganic scintillation crystal detector, and its overall light-proof design is made of magnetic shielding material; the lifting assembly is used to stably support the detector limiting assembly and adjust the height of the detector limiting assembly so that the different height areas of the inorganic scintillation crystal detector are on the same horizontal line with the center of the radiation source; The back-end testing unit is connected to the inorganic scintillation crystal detector and is used to test the performance of the inorganic scintillation crystal detector.

2. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 1, characterized in that: The key parameters of the collimation assembly are determined according to the following method: ① Based on the requirement that the attenuation flux of invalid radiation reaches more than 99%, follow the attenuation coefficient formula to determine the total length of the collimation assembly in the horizontal direction, as well as the thicknesses p and h at two points in the vertical direction of the largest collimation hole on the pinhole collimator; ② Determine the aperture and length of the collimating hole on the pinhole collimator First, the aperture and hole length limits are clearly defined as follows: the aperture is greater than or equal to 0.1 mm and less than or equal to one-third of the vertical length of the irradiated cross section of the inorganic scintillation crystal detector to be tested; The sum of the lengths of the collimating holes on all pinhole collimators is equal to the total length of the collimating assembly in the horizontal direction; Secondly, in order to achieve precise control of the attenuated flux, the geometric solid angle formula is followed to specifically determine the aperture and length of the collimating hole.

3. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 1 or 2, characterized in that: The other end of the connecting rod is a snap-fit ​​structure, which can be used to install and remove the radiation source containing module; The upper surface of the radiation source accommodating module is provided with a placement hole, and a matching cover is provided therewith; The opening is a square hole, and the side length of the opening is smaller than the diameter of the radiation source.

4. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 3, characterized in that: The support frame includes four first fixing rods and two second fixing rods; The four first fixing rods are vertically mounted on the base and are symmetrically arranged in pairs to form a cubic frame; The two second fixing rods are respectively installed between the two first fixing rods at the front end and the two first fixing rods at the rear end of the cubic frame, and the middle part of the two second fixing rods is provided with a square opening for inserting and removing the adjustment rod; The adjusting rod is a square rod, which can be loosely matched with the square opening in the middle of the second fixing rod.

5. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 4, characterized in that: The pinhole collimator is a cylindrical radiation attenuation plate, and a square mounting hole adapted to the adjustment rod is coaxially arranged at its center, which can be loosely matched with the adjustment rod; and the center of the pinhole collimator itself is used as the origin as the coordinate axis, and four collimating holes of different apertures are opened in the four directions on the positive and negative sides.

6. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 5, characterized in that: The lifting assembly is a scissor lift platform, the platform surface of which is paved with anti-slip material and the adjustment accuracy does not exceed 5μm; The detector limiting assembly includes a limiting module and a limiting cover.

7. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 6, characterized in that: The collimator adjustment unit also includes a receiving assembly for receiving the pinhole collimator; The storage component is located on a base below the adjusting rod and has a semicircular groove with a diameter larger than the diameter of the pinhole collimator.

8. The inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to claim 7, characterized in that: The radiation source is a high-energy gamma radiation source.

9. A testing method using the inorganic scintillator crystal performance testing system based on an adjustable pinhole collimator according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: Install the radioactive source Placing the radioactive source in the radioactive source containing module, and installing the radioactive source containing module on the other end of the connecting rod; Step 2: Install the Collimation Assembly Install each pinhole collimator of the collimation assembly on the adjustment rod in sequence, then install the adjustment rod horizontally on the support frame from front to back and secure it, ensuring that the collimation holes corresponding to each pinhole collimator have the same aperture and that the center of the upper collimation hole is on the same horizontal line as the center of the radiation source; Step 3: Install the inorganic scintillation crystal detector to be tested Place the inorganic scintillation crystal detector to be tested in the detector limit assembly, and place the detector limit assembly stably on the upper surface of the lifting assembly. Adjust the height so that the initial height area of ​​the crystal in the inorganic scintillation crystal detector to be tested is aligned with the center of the radiation source and the center of the collimating hole above. Step 4: Test the performance of the inorganic scintillation crystal detector to be tested Connect the inorganic scintillation crystal detector to be tested to the back-end test unit, set the prerequisite parameters according to the type of test performance, and after completing the settings, start the test and collect the test results; After completing the initial height area test, adjust the lifting assembly to change the height area of ​​the crystal in the inorganic scintillation crystal detector to be tested, continue testing, and repeat this process. After completing the current angle test, rotate the detector limit assembly as needed to perform the next set of tests, and repeat this process until all tests under the current collimation assembly parameter conditions are completed.

10. A method for calibrating a radioactive source using the inorganic scintillation crystal performance testing system based on an adjustable pinhole collimator according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: Install the standard radiation source Placing a standard radioactive source with a known activity A0 in the radioactive source containing module, and installing the radioactive source containing module on the other end of the connecting rod; S2: Install the collimation assembly Install each pinhole collimator of the collimation assembly on the adjustment rod in sequence, then install the adjustment rod horizontally on the support frame from front to back and secure it, ensuring that the collimation holes corresponding to each pinhole collimator have the same aperture and that the center of the upper collimation hole is on the same horizontal line as the center of the radiation source; S3: Installing Inorganic Scintillation Crystal Detectors Place the inorganic scintillation crystal detector containing the standard scintillation crystal in the detector limit assembly, and place the detector limit assembly stably on the upper surface of the lifting assembly. Adjust the height so that the initial height area of ​​the crystal in the inorganic scintillation crystal detector for testing is aligned with the center of the radiation source and the center of the collimating hole above. S4: Testing of standard radioactive sources Connect the inorganic scintillation crystal detector to the pulse height spectrum test equipment and ensure a light-proof environment; set the prerequisite parameters of the pulse height spectrum test equipment, and after completing the settings, start the test and collect the full-energy peak channel address Ch0 and count rate R0; S5: Replacement and testing of radioactive sources to be calibrated After completing S4, remove the voltage, turn off the pulse height spectrum test equipment, replace the standard radioactive source in the radioactive source containing module with the radioactive source to be calibrated, and then repeat the test process in S4 and collect the full energy peak channel address Ch1 and count rate R1. After completing the test, remove the voltage and turn off the pulse height spectrum test equipment; S6: Radioactive Source Calibration Compare the differences in the full energy peak channel address and count rate results obtained in S4 and S5 to perform the following calibration calculations on the radioactive source to be calibrated: ①Energy consistency: calculated by the following formula Energy uniformity=(Ch1-Ch0) / Ch0 If the value is ≤1%, it is considered that the energy of the radioactive source to be calibrated is consistent with that of the standard radioactive source; ② The activity A1 of the radioactive source to be calibrated is calculated using the following formula: A1=A0×(R1 / R0) At this point, the entire process of radioactive source calibration is completed.

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