A processing method of a large-size sodium iodide scintillation crystal for nuclear radiation detection

Abstract

The present application relates to the field of sodium iodide crystal cutting, and particularly relates to a processing method of large-size sodium iodide scintillation crystal for nuclear radiation detection, comprising: determining an initial cutting point based on a required capacity length; before cutting processing is performed on the single initial cutting point, determining whether to adjust the position of the initial cutting point to obtain an execution cutting point based on a defect cracking index corresponding to the initial cutting point; based on a defect feature interference condition corresponding to a to-be-cut surface of the execution cutting point, determining whether to adjust a cutting speed setting mode from a self-adjusting speed cutting to a minimum speed cutting; and cutting is completed to obtain a target sub-crystal. The present application improves the cutting flexibility and cutting precision of the large-size sodium iodide crystal.

Description

Technical Field

[0001] This invention relates to the field of sodium iodide crystal cutting, and more particularly to a method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection. Background Technology

[0002] Sodium iodide scintillation crystals are widely used in nuclear detection due to their excellent energy resolution, high light output, and time response. With the increasing demands of nuclear detection, the need for large-size scintillation crystals (crystals with diameters greater than 200 mm) is growing. However, large-size sodium iodide crystals are prone to internal defects such as cracks, bubbles, and inclusions during growth, accompanied by complex residual stress fields. Traditional processing methods, which often set cutting points based on geometric dimensions, cannot account for the spatial distribution of internal defects and stress gradients, resulting in insufficient cutting precision. Often, cutting parameters are only adjusted when cutting into cracked areas; in some cases, the cutting path directly passes through areas of dense cracks or high stress gradients, causing the crystal to crack along cleavage planes, leading to low yields of large-size sodium iodide crystals. Therefore, improving the cutting precision of large-size sodium iodide crystals is a significant concern for those skilled in the art.

[0003] Chinese Patent Publication No. CN118553674B discloses an optimized method for wafer peeling and laser slicing, and its application. The method includes: first, establishing a wafer database containing different materials and thicknesses, storing the optimal laser parameters and cutting paths for each material; during processing, optimizing the cutting path based on the wafer material and thickness using a genetic algorithm or ant colony algorithm, and calling the matching laser parameters for slicing; monitoring the thickness, temperature, and modified layer state in real time during the process, and dynamically adjusting the laser parameters and path; predicting and optimizing the heating and cooling curves through machine learning to ensure peeling effect; finally, using a convolutional neural network to detect surface defects on the cleaned wafer, recording and analyzing the results. However, the above technical solution has the following problems: it cannot flexibly adjust the cutting strategy according to the actual cracking situation of the crystal, easily resulting in the cutting control method not meeting the cutting flexibility requirements of sodium iodide crystals, leading to poor cutting accuracy. Summary of the Invention

[0004] Therefore, the present invention provides a method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection, in order to overcome the problem in the prior art that the cutting strategy cannot be flexibly adjusted according to the actual cracking of the crystal, which easily leads to the cutting control method not meeting the cutting flexibility requirements of sodium iodide crystals and resulting in poor cutting accuracy of sodium iodide crystals.

[0005] To achieve the above objectives, the present invention provides a method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection, comprising: The crystal blank is impurity removed and then hot forged to obtain the target stage crystal. Determine the initial cutting points based on the required capacity length; Before cutting a single initial cutting point, determine whether to adjust the position of the initial cutting point to obtain the execution cutting point based on the defect cracking index corresponding to the initial cutting point. Based on the interference conditions of the defect features corresponding to the surface to be cut at the cutting point, determine whether to adjust the cutting speed setting mode from self-adjusting cutting to the lowest speed cutting. The target sub-crystal obtained from the cutting process is polished and packaged to obtain the target crystal product.

[0006] Furthermore, the required capacity length is determined based on the required length for preparation and the interval distance; If there are no crystal defects within the required capacity length from the initial end, then the required capacity length is the sum of the required preparation length and the loss distance, and the point at which the required capacity length is a distance from the initial end is recorded as the initial cutting point.

[0007] Furthermore, for initial cutting points where the defect cracking index is greater than the preset defect cracking index, the position of the initial cutting point is adjusted. The defect cracking index is determined based on the local density of defects and the proportion of defect volume in the reference neighborhood corresponding to the initial cutting point. The reference neighborhood is the cross-sectional region obtained by bidirectionally extending the crystal along the length direction of the target stage, with the cross-section corresponding to the initial cutting point as the center.

[0008] Furthermore, during the extension of the reference neighborhood, the extension distances in both directions are the same, and the extension distance is determined based on the stress concentration of the cross section corresponding to the initial cutting point. The extension distance is positively correlated with the stress concentration.

[0009] Furthermore, the initial cutting point is repositioned, including: Based on the reference neighborhood, several points are uniformly selected along the axial direction where the defect crack density is small and recorded as the analysis selection points. The analysis selection point with the largest crack concentration variation index is recorded as the execution cutting point. If the initial cutting point has a defect cracking index that is less than or equal to the preset defect cracking index, then the initial cutting point will be recorded as the cutting point to be cut.

[0010] Furthermore, when cutting based on the execution cutting point, the entry point and exit point of the execution cutting point are determined based on the edge fracturing index of the candidate cutting pair; The candidate cutting pair consists of two sub-regions in the edge region of the cross-section corresponding to the cutting point that meet the connection conditions. The sub-regions are obtained by uniformly dividing the edge region. The edge region is annular and is determined by the cross-section corresponding to the cutting point and the minimum feed distance. The connection condition is that the two sub-regions can be connected by a diameter passing through the center of the cross-section.

[0011] Furthermore, in response to the defect interference condition where the cutting speed adjustment degree is greater than the preset cutting speed adjustment degree, it is determined that the cutting speed setting mode should be adjusted from automatic speed adjustment cutting to the lowest speed cutting.

[0012] Furthermore, when the cutting speed setting method is self-adjusting cutting, for a single defect point, when the cutting direction of the cutting line approaches the cutting position of the defect point and reaches the preset adjustment distance corresponding to the defect point, the cutting speed is reduced based on the defect extension index. The adjustment range of the cutting speed is positively correlated with the fracture extension index.

[0013] Furthermore, for the condition that the defect proximity index is greater than the preset defect proximity index, it is determined to adjust the preset adjustment distance.

[0014] Furthermore, when adjusting the preset adjustment distance, the preset adjustment distance is increased according to the range of fusion defects; The preset adjustment distance is positively correlated with the volume of the fusion defect range.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention determines whether to adjust the position of the initial cutting point by using the defect cracking index. The defect cracking index is used to determine the proportion and smoothness of crystal defects such as cracks, inclusions and bubbles in the reference neighborhood corresponding to the initial cutting point, thereby determining whether it will affect the smoothness and fineness of the cutting surface. When the defect cracking index is greater than the preset defect cracking index, it is determined that cutting at the initial cutting point is more likely to cause crystal fragmentation, the defect distribution is scattered, and it is not suitable for smooth cutting. Therefore, the cutting position is adjusted, avoiding the situation where a single cutting point setting cannot adapt to the internal defect structure of the crystal, resulting in cutting failure. This makes the setting of the cutting point more in line with the actual conditions, and further improves the flexibility and adaptability of the cutting point setting.

[0016] Furthermore, this invention reflects the distribution of internal stress in the cross-section corresponding to the initial cutting point through stress concentration, and adjusts the extension distance according to the stress concentration to determine the reference neighborhood. This achieves flexible adjustment of the reference neighborhood, avoiding the poor cutting effect caused by the rigid selection of cutting points due to a fixed area setting method. This makes the selection of cutting points more flexible and further improves the yield of sodium iodide crystals.

[0017] Furthermore, this invention adjusts the initial cutting point using a defect concentration variation index to determine the execution cutting point. The defect concentration variation index is jointly determined by the defect cracking variation amount and the concentration trend index. The defect cracking variation amount is used to determine the degree of change in the number of crystal defects, while the concentration trend index is used to determine the gradual aggregation of defects such as cracks and bubbles. This allows for the selection of the optimal cutting cross-section within a reference neighborhood with a low defect cracking density, maximizing the saving of crystal material and further improving crystal utilization. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating how to determine whether to adjust the position of the initial cutting point based on the defect cracking index corresponding to the initial cutting point in an embodiment of the present invention. Figure 3 This is a flowchart illustrating how to determine whether to adjust the cutting speed setting from self-adjusting cutting to the lowest speed cutting based on defect feature interference conditions in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0020] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0021] It should be noted that in the description of this invention, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is merely for ease of description and does not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0022] Please see Figure 1The diagram shown is a schematic representation of a method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to an embodiment of the present invention. The method includes: The crystal blank is impurity removed and then hot forged to obtain the target stage crystal. Determine the initial cutting points based on the required capacity length; Before cutting a single initial cutting point, determine whether to adjust the position of the initial cutting point to obtain the execution cutting point based on the defect cracking index corresponding to the initial cutting point. Based on the interference conditions of the defect features corresponding to the surface to be cut at the cutting point, determine whether to adjust the cutting speed setting mode from self-adjusting cutting to the lowest speed cutting. The target sub-crystal obtained from the cutting process is polished and packaged to obtain the target crystal product.

[0023] In this embodiment of the invention, the target stage crystal is a cylindrical sodium iodide crystal after hot forging. The target stage crystal is scanned point-by-point using an ultrasonic scanning microscope, and the reflection signal at each point is recorded. Based on the strength of the reflection signal, it is converted into the grayscale value and color corresponding to the pixel in the target image. According to the principle that the reflection signal of crystal defects is stronger than that of other intact crystals, bright colors are determined to be crystal defects, and dark colors to be intact crystals. The location, shape, and depth distribution of the crystal defects are determined using multiple scanning modes, including horizontal scanning, vertical scanning, and perspective scanning, and 3D reconstruction is performed to obtain the location coordinates of the crystal defects. The defect region is defined as the smallest cuboid capable of containing a single crystal defect. Crystal defects include, but are not limited to, cracks, bubbles, and inclusions in the sodium iodide crystal.

[0024] In this embodiment of the invention, the temporary birefringence effect generated by sodium iodide crystal under stress is utilized. A stress birefringence meter is used to convert the stress distribution inside the target stage crystal into a polarized image with alternating bright and dark interference fringes. Image processing techniques are used to calculate the phase difference of each pixel in the polarized image, and the principal stress difference is obtained according to the stress-optics law. The boundary point with the smallest average principal stress difference is selected as the initial cutting point from the target stage crystal corresponding to the required capacity length. The boundary point is the point outside the defect region whose distance from the cross-section of the defect region surface is equal to the loss distance. The point is a circular point on the surface of the target stage crystal with a diameter equal to the diameter of the wire saw on the cutting line. The cross-section corresponding to each point is the cross-section of the target stage crystal at the center of the circular point. The cutting line is a diamond saw wire.

[0025] Please continue reading. Figure 1 As shown, the required capacity length is determined based on the required length for preparation and the interval distance; If there are no crystal defects within the required capacity length from the initial end, then the required capacity length is the sum of the required preparation length and the loss distance, and the point at which the required capacity length is a distance from the initial end is recorded as the initial cutting point.

[0026] In this embodiment of the invention, during a single crystal cut targeting a specific crystal stage, the initial cutting point corresponding to that cut is first obtained. The execution cutting point is then determined through position adjustment analysis. For the initial cutting point, any end along the length direction of the target crystal stage is selected and designated as the initial end. The interval distance is the distance between the initial cutting point and the current initial end. The required length is the length of the target crystal product required by the user, and the required capacity length is the sum of the required length and the interval distance. Cutting is stopped when the cut length of the target crystal stage is less than the required capacity length or when a target crystal product meeting the user's requirements cannot be cut.

[0027] The loss distance is used to determine the tolerance of the target sub-crystal loss during subsequent polishing. The larger the loss distance, the greater the tolerance of the finished target sub-crystal. The higher the user's requirements for the yield of large-size sodium iodide crystal processing, the larger the value of the loss distance.

[0028] This invention can simulate the cutting effects of different parameters to obtain the optimal values ​​for cutting large-size sodium iodide with the required precision. For example, by collecting cutting and grinding data of multiple sets of large-size sodium iodide crystal blanks with different sizes and defect distributions, different loss distances are set for cutting and subsequent grinding tests of the target sub-crystals. The pass rate and material utilization rate of the finished target sub-crystals are used as evaluation indicators, and the loss distance that simultaneously meets the user's requirements for pass rate and material utilization rate is selected as the preset value. Simulation results show that when the loss distance is 2.5mm, the pass rate of the finished product reaches 96%, the material utilization rate reaches 88%, and the overall performance is optimal. Therefore, the preset loss distance is 2.5mm.

[0029] Please see Figure 2 As shown, it is a flowchart of an embodiment of the present invention for determining whether to adjust the position of the initial cutting point based on the defect cracking index corresponding to the initial cutting point.

[0030] Specifically, for initial cutting points where the defect cracking index is greater than the preset defect cracking index, the position of the initial cutting point is adjusted. The defect cracking index is determined based on the local density of defects and the proportion of defect volume in the reference neighborhood corresponding to the initial cutting point. The reference neighborhood is the cross-sectional region obtained by bidirectionally extending the crystal along the length direction of the target stage, with the cross-section corresponding to the initial cutting point as the center.

[0031] In this embodiment of the invention, the defect cracking index is used to determine the density and smoothness of crystal defects within the reference neighborhood corresponding to the initial cutting point. A larger defect cracking index indicates a higher proportion of crystal defect volume and a more uneven distribution of crystal defects within the reference neighborhood, thus increasing the risk of cracking when cutting at that initial cutting point. In such cases, the initial cutting point should be adjusted to avoid cracking. The defect cracking index is determined based on the local defect density and defect volume proportion within the reference neighborhood corresponding to the initial cutting point, and is positively correlated with both. Preferably, the defect cracking index is the sum of the local defect density and defect volume proportion within the reference neighborhood corresponding to the initial cutting point.

[0032] Defect local density is used to determine the uniformity and aggregation of crystal defects in the spatial distribution within a reference neighborhood. A higher defect local density indicates closer proximity between adjacent defect regions, more clustered defect distribution, and a lower risk of multi-point fracture due to discrete defect distribution. Defect local density is determined based on the number of clustered defect groups and is positively correlated with this number. Preferably, the defect local density is the ratio of the number of clustered defect groups to the number of defect region groups within the reference neighborhood. A clustered defect group is a group of defect regions with a defect distance less than or equal to a preset defect distance. Each defect region group consists of two adjacent defect regions within the reference region, and the defect distance is the distance between the center points of the volumes of the two defect regions within the defect region group.

[0033] The larger the defect volume ratio, the higher the total volume ratio of crystal defects such as cracks, bubbles, and inclusions in the reference neighborhood, and the worse the continuity of the crystal bulk material in that region. Preferably, the defect volume ratio is the ratio of the total volume of the defect region in the reference neighborhood corresponding to the initial cutting point to the volume of the reference neighborhood. The volume of the reference neighborhood is the product of the cross-sectional area corresponding to the initial cutting point and the sum of the extension distances on both sides, where the sum of the extension distances on both sides of the cross-section corresponding to the initial cutting point is the sum of the extension distances on both sides of the cross-section corresponding to the initial cutting point.

[0034] In this embodiment of the invention, the larger the defect distance, the greater the distance between the two defect regions, the more discrete the distribution of crystal defects, the higher the difficulty of cutting, and the higher the user's requirements for the cutting accuracy of large-size sodium iodide, the lower the value of the preset defect distance. Preferably, by obtaining the defect distance in historical qualified working conditions, the average value of the defect distance after removing outliers is calculated to be 3.0 mm, which is recorded as the preset defect distance.

[0035] In this embodiment of the invention, multiple sets of crystal cross-sectional data with different local defect densities and defect volume ratios were collected. Initial cutting point position adjustment tests were conducted using different defect cracking indices. The cracking rate of the target sub-crystal after cutting and the surface roughness of the cut surface were used as evaluation indicators. A defect cracking index with a cracking rate below 5% and a surface roughness below 1.6 μm was selected as the preset value. Simulation results show that when the preset defect cracking index is 0.6, the cracking rate is 4.2%, the surface roughness is 1.5 μm, and the overall performance is optimal. Therefore, the preset defect cracking index is set to 0.6.

[0036] Specifically, during the extension of the reference neighborhood, the extension distances in both directions are the same, and the extension distance is determined based on the stress concentration of the cross section corresponding to the initial cutting point. The extension distance is positively correlated with the stress concentration.

[0037] In this embodiment of the invention, stress concentration is used to determine the degree of disorder in the stress distribution of the cross-section corresponding to the initial cutting point. The greater the stress concentration, the higher the risk of cracking in local areas within the cross-section. In this case, the extension distance of the reference neighborhood should be increased to obtain more selection space for the initial cutting point, thereby improving the cutting stability and yield of large-size sodium iodide scintillation crystals. The stress concentration is determined based on the principal stress difference of each pixel within the base distance on both sides of the cross-section corresponding to the initial cutting point. It is positively correlated with the maximum value of the principal stress difference and negatively correlated with the average value of the principal stress difference. Preferably, the stress concentration is the ratio of the maximum value of the principal stress difference of each pixel within the base distance on both sides of the cross-section corresponding to the initial cutting point to the average value.

[0038] The extension distance is the product of the base distance and the distance adjustment coefficient, which is the ratio of the stress concentration to the preset stress concentration.

[0039] In this embodiment of the invention, multiple sets of polarization images with different stress concentrations are acquired, and reference neighborhood extension tests are conducted with different base distances. The coverage rate of the main defects within the reference neighborhood and the increase in calculation time per extension are used as evaluation indicators. The optimal base distance is selected as one where the defect coverage rate is greater than 90% and the increase in calculation time is less than 15%. Simulation results show that when the base distance is 5.0 mm, the defect coverage rate is 92%, the calculation time increases by 12%, and the overall performance is optimal. Therefore, the base distance is set to 5.0 mm.

[0040] In this embodiment of the invention, the extension distance is adjusted by collecting data at different stress concentrations. The crack propagation inhibition rate and the residual stress reduction rate inside the daughter crystal are used as evaluation indicators. A threshold value of 85% for the crack propagation inhibition rate and 20% for the residual stress reduction rate is selected as the preset value. Simulation results show that when the preset stress concentration is 1.5, the crack propagation inhibition rate is 88% and the residual stress reduction rate is 21%, resulting in the best overall performance. Therefore, the preset stress concentration is set to 1.5.

[0041] Please continue reading. Figure 2 As shown, specifically, adjusting the position of the initial cutting point includes: Based on the reference neighborhood, several points are uniformly selected along the axial direction where the defect crack density is small and recorded as the analysis selection points. The analysis selection point with the largest crack concentration variation index is recorded as the execution cutting point. If the initial cutting point has a defect cracking index that is less than or equal to the preset defect cracking index, then the initial cutting point will be recorded as the cutting point to be cut.

[0042] In this embodiment of the invention, the defect crack density is used to determine the density of crystal defects within a reference neighborhood. A higher defect crack density indicates a denser distribution of crystal defects, resulting in a higher cutting risk at the initial cutting point. Therefore, the initial cutting point is adjusted towards a direction with lower defect crack density, thereby guiding the cutting point away from high-density defect areas and reducing the risk of chipping during cutting. The defect crack density is determined based on the number of crystal defects and the extended volume within the extension distance on both sides of the cross-section corresponding to the initial cutting point. It is positively correlated with the number of crystal defects and negatively correlated with the extended volume. Preferably, the defect crack density is the ratio of the number of crystal defects within the single-sided extension distance of the cross-section corresponding to the initial cutting point to the extended volume, with units of defects / mm. 2 The extended volume is the product of the extended distance and the cross-sectional area corresponding to the initial cutting point.

[0043] In this embodiment of the invention, the fracture concentration variation index is used to determine the degree of reduction in the number of crystal defects and the degree of fusion and aggregation among crystal defects when the initial cutting point is adjusted. A larger fracture concentration variation index corresponds to a greater reduction in the number of defects, a higher degree of aggregation among crystal defects, and a lower frequency of changes in the cutting speed. In this case, selecting this analysis point as the execution cutting point reduces the risk of the cutting line crossing a high-density defect region. The fracture concentration variation index is determined based on the change in defect cracking and the concentration trend index, and is positively correlated with both. Preferably, the fracture concentration variation index is the sum of the change in defect cracking and the concentration trend index. Among them, the change in defect cracking is the ratio of the difference between the number of crystal defects in the cross section corresponding to each analysis point and the number of crystal defects in the cross section corresponding to the initial cutting point to the number of crystal defects in the cross section corresponding to the initial cutting point; the central tendency index is the ratio of the number of overlapping defect points to the number of crystal defects in each analysis point. For a single defect point, if there are other crystal defects within its corresponding preset adjustment distance, the defect point is recorded as an overlapping defect point. For a single defect point, it is the smallest rectangle in the cross section corresponding to the analysis point that can enclose the single crystal defect.

[0044] In this embodiment of the invention, the larger the number of analysis selection points, the more accurate the selection of the cutting point and the higher the cutting precision. The more sensitive the user is to the cutting precision of large-size sodium iodide, the larger the value of the number of analysis selection points. Preferably, by obtaining the number of analysis selection points corresponding to historical qualified working conditions, the average number of selection points after removing outliers is calculated to be 6, which is recorded as the number of analysis selection points in this embodiment of the invention.

[0045] In this embodiment of the invention, multiple sets of crystal cross-sectional data with different defect cracking indices are collected, and cutting point adjustment tests are performed with different defect cracking indices. The surface roughness of the target sub-crystal after cutting is used as the evaluation index, and a threshold of surface roughness less than 1.6 μm is selected as the preset value. Simulation results show that when the preset defect cracking index is 0.6, the surface roughness is 1.5 μm. Further increasing or decreasing the defect cracking index will affect the surface roughness. Therefore, the preset defect cracking index is set to 0.6.

[0046] Specifically, when cutting based on the execution cutting point, the entry point and exit point of the execution cutting point are determined based on the edge fracturing index of the candidate cutting pair; The candidate cutting pair consists of two sub-regions in the edge region of the cross-section corresponding to the cutting point that meet the connection conditions. The sub-regions are obtained by uniformly dividing the edge region. The edge region is annular and is determined by the cross-section corresponding to the cutting point and the minimum feed distance. The connection condition is that the two sub-regions can be connected by a diameter passing through the center of the cross-section.

[0047] Wherein, the outer radius of the edge region is the radius of the smallest circle that can contain the cross-section corresponding to the cutting point, the inner radius is the difference between the outer radius and the minimum feed distance, and the center of the cross-section is the center of the smallest circle that can contain the cross-section corresponding to the cutting point.

[0048] The edge chipping index is the maximum stress value of a sub-region obtained by a multi-functional X-ray diffractometer. During cutting, the candidate cutting pair with the smallest average edge chipping index of the two sub-regions is selected for cutting. The diamond saw wire starts cutting from the entry point, and the feed direction during cutting is perpendicular to the crystal axis of the target stage and cuts out from the exit point, completing the cutting of the cross-section corresponding to the cutting point. The entry point is the sub-region with the smallest edge chipping index among the candidate cutting pairs.

[0049] In this embodiment of the invention, after the cutting line completes a cutting distance, it pauses for a period of time to allow the stress inside the target crystal to redistribute. During the cutting process, anhydrous organic coolant is continuously used to cool the cutting area. The larger the cutting distance, the greater the stress accumulation introduced by a single cut, the longer the pause, and the more fully the stress is released. The cutting distance and pause duration at the time of cutting are determined by obtaining the cutting distance and pause duration from historical qualified working conditions and calculating the average of the cutting distance and pause duration after removing outliers.

[0050] The minimum feed distance is the cutting distance for the first trial cut of the crystal at the target stage to verify the rationality of the cutting parameters. It is determined by obtaining the minimum feed distance in historical qualified working conditions and calculating the average value of the minimum feed distance after removing outliers.

[0051] In this embodiment of the invention, the larger the number of sub-regions, the more detailed the segmentation of the edge regions, the higher the calculation accuracy of the edge fracture index of each sub-region, the more accurate the analysis of the entry and exit points, and the lower the risk of crystal fracture. The higher the user's requirements for the cutting accuracy of large-size sodium iodide, the larger the number of sub-regions. Preferably, by obtaining the number of sub-regions corresponding to historical qualified working conditions, the average number of sub-regions after removing outliers is calculated to be 12, which is denoted as the number of sub-regions in this embodiment of the invention.

[0052] Please see Figure 3 As shown, it is a flowchart of an embodiment of the present invention for determining whether to adjust the cutting speed setting mode from self-adjusting cutting to the lowest speed cutting based on defect feature interference conditions.

[0053] Specifically, for defect interference conditions where the cutting speed adjustment degree is greater than the preset cutting speed adjustment degree, the cutting speed setting mode is adjusted from automatic speed adjustment cutting to the lowest speed cutting.

[0054] In this embodiment of the invention, the cutting speed adjustment degree is used to determine the degree of need to adjust the cutting speed. The larger the cutting speed adjustment degree, the more overlapping defect points there are within the adjustment range, and the higher the risk of large-area breakage during cutting. In this case, the cutting speed should be reduced to reduce impact and vibration, thereby adjusting the cutting speed setting mode from self-adjusting cutting to the lowest speed cutting to avoid crystal breakage caused by high-speed cutting. The cutting speed adjustment degree is determined based on the number of overlapping defect points within the adjustment range and is positively correlated with the number of overlapping defect points. Preferably, the cutting speed adjustment degree is the number of overlapping defect points within the adjustment range corresponding to the position of the diamond saw wire, and the adjustment range is the quotient of the distance between the center points of the areas of the two sub-regions in the selected cutting pair divided by the value of the number of crystal defects in the cross-section.

[0055] In this embodiment of the invention, multiple sets of wire saw cutting process data with different defect sizes and cutting speeds were collected. Different preset adjustment distances were set for self-adjusting speed tests. The chipping rate and cutting efficiency per unit time were used as evaluation indicators. A preset value was selected where the chipping rate was less than 3% and the cutting efficiency was more than 30% higher than the lowest cutting speed. Simulation results show that when the preset adjustment distance is 2.0 mm, the chipping rate is 2.5%, the cutting efficiency is improved by 35%, and the overall performance is optimal. Therefore, the preset adjustment distance is set to 2.0 mm.

[0056] In this embodiment of the invention, multiple sets of wire saw cutting process data with different crystal hardness and defect density were collected, and different minimum cutting speeds were set for cutting tests. The chipping rate and wire breakage rate were used as evaluation indicators, and the minimum speed with a chipping rate below 3% and a wire breakage rate below 1% was selected as the optimal value. Simulation results show that when the minimum cutting speed is 0.5 mm / s, the chipping rate is 2.8%, the wire breakage rate is 0.6%, and the overall performance is optimal. Therefore, the minimum cutting speed is 0.5 mm / s. In the minimum cutting, the diamond saw wire cuts at a speed of 0.5 mm / s until a defect feature interference condition occurs where the cutting speed adjustment degree is less than or equal to the preset cutting speed adjustment degree, at which point the self-adjusting speed cutting is resumed.

[0057] Please continue reading. Figure 3 As shown, specifically, when the cutting speed setting method is self-adjusting cutting, for a single defect point, when the cutting direction of the cutting line approaches the cutting position of the defect point and reaches the preset adjustment distance corresponding to the defect point, the cutting speed is reduced based on the defect extension index. The adjustment range of the cutting speed is positively correlated with the fracture extension index.

[0058] In this embodiment of the invention, the crack extension index is used to determine the extent to which a single crystal defect extends along the cutting direction. A larger crack extension index indicates a smaller angle between the overall distribution direction of the crystal defect and the cutting direction, a higher degree of parallelism, and a higher risk of cracking or chipping at that location in the target stage. The crack extension index is determined based on the minimum angle between the fitted surface of the defect location and the cross-section corresponding to the cutting point, and is positively correlated with the cosine of the minimum angle. Preferably, the crack extension index is the cosine of the minimum angle between the fitted surface of the defect location and the cross-section corresponding to the cutting point. The fitted surface of the defect location is obtained by performing planar fitting on the crystal defect. How to perform planar fitting is a matter well understood by those skilled in the art and will not be elaborated here.

[0059] The adjusted cutting speed is the difference between the original cutting speed and the speed adjustment amount. The speed adjustment amount is the product of the ratio of the fracture extension index to the preset fracture extension index and the basic adjustment amount. It is worth noting that the adjusted cutting speed has a minimum value, which is the cutting speed in the lowest speed cutting.

[0060] In this embodiment of the invention, different fracture extension indices were collected to test the adjustment of the cutting speed. The chipping rate of the cut surface was used as the evaluation index, and a fracture extension index with a chipping rate of less than 3% was selected as the preset value. Simulation results show that when the preset fracture extension index is 0.4, the chipping rate of the cut surface is 2.3%. Further increasing or decreasing the fracture extension index will affect the chipping rate of the cut surface. Therefore, the preset fracture extension index is set to 0.4.

[0061] Specifically, for the condition that the defect proximity index is greater than the preset defect proximity index, the preset adjustment distance is adjusted.

[0062] Specifically, when adjusting the preset adjustment distance, the preset adjustment distance is increased according to the range of fusion defects; The preset adjustment distance is positively correlated with the volume of the fusion defect range.

[0063] In this embodiment of the invention, the defect adjacency index is used to determine the density of crystal defects within a base distance at a single defect location. A larger defect adjacency index indicates more crystal defects near the defect location, increasing the risk of overlapping defects during cutting. In this case, the preset adjustment distance should be increased to expand the coverage of low-speed cutting, triggering the cutting speed adjustment earlier and preventing crystal breakage caused by the impact of high cutting speed. The defect adjacency index is determined based on the number of crystal defects within a base distance corresponding to a single defect location in the target stage crystal, and is positively correlated with the number of crystal defects within the base distance. Preferably, the defect adjacency index is the number of crystal defects within a base distance corresponding to a single defect location in the target stage crystal.

[0064] In this embodiment of the invention, the fusion defect range is used to determine the overall spatial coverage area formed by a single defect location and its adjacent defects within a basic distance. The larger the fusion defect range, the denser the distribution of crystal defects around the defect location, the higher the degree of overlap or adjacency of defect regions, and the higher the risk of the cutting line crossing multiple defects within this region. The fusion defect range is determined based on the target crystal defect volume corresponding to a single defect location and is positively correlated with the volume of the fusion defect range. Preferably, the fusion defect range is the smallest cuboid corresponding to a single defect location that can include the defect region of that defect location and the defect regions of all target crystal defects. The target crystal defects are the crystal defects within the basic distance corresponding to that defect location. The adjusted preset adjustment distance is the product of the unadjusted preset adjustment distance and the amplitude adjustment index. The amplitude adjustment index is the ratio obtained by the volume of the fusion defect range corresponding to the defect location to the average volume of the fusion defect ranges corresponding to each defect location.

[0065] In this embodiment of the invention, the historical working condition is a record of parameters during the crystal cutting process at the target stage within a certain period of time in the historical process. It records the parameter values ​​obtained in this method. For any working condition, if the cutting effect meets the cutting accuracy requirements of sodium iodide crystal, then the historical working condition is a historical qualified working condition. Whether the cutting effect corresponding to the historical working condition meets the cutting accuracy requirements of sodium iodide crystal can be determined based on, but not limited to, the dimensional tolerance of the target crystal product or the edge chipping rate of the cutting surface. How to determine whether the cutting accuracy requirements are met is a content that has been mastered by those skilled in the art and will not be elaborated here.

[0066] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection, characterized in that, include: The crystal blank is impurity removed and then hot forged to obtain the target stage crystal. Determine the initial cutting points based on the required capacity length; Before cutting a single initial cutting point, determine whether to adjust the position of the initial cutting point to obtain the execution cutting point based on the defect cracking index corresponding to the initial cutting point. Based on the interference conditions of the defect features corresponding to the surface to be cut at the cutting point, determine whether to adjust the cutting speed setting mode from self-adjusting cutting to the lowest speed cutting. The target sub-crystals obtained from the cutting process are polished and packaged to obtain the target crystal product.

2. The method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection according to claim 1, characterized in that, The required capacity length is determined based on the required length for preparation and the interval distance; If there are no crystal defects within the required capacity length from the initial end, then the required capacity length is the sum of the required preparation length and the loss distance, and the point at which the required capacity length is a distance from the initial end is recorded as the initial cutting point.

3. The method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection according to claim 2, characterized in that, For initial cutting points where the defect cracking index is greater than the preset defect cracking index, the position of the initial cutting point is adjusted. The defect cracking index is determined based on the local density of defects and the proportion of defect volume in the reference neighborhood corresponding to the initial cutting point. The reference neighborhood is the cross-sectional region obtained by bidirectionally extending the crystal along the length direction of the target stage, with the cross-section corresponding to the initial cutting point as the center.

4. The method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection according to claim 3, characterized in that, During the extension of the reference neighborhood, the extension distance in both directions is the same, and the extension distance is determined based on the stress concentration of the cross section corresponding to the initial cutting point. The extension distance is positively correlated with the stress concentration.

5. The method for processing large-size sodium iodide scintillation crystals for nuclear radiation detection according to claim 3, characterized in that, Adjusting the position of the initial cutting point includes: Based on the reference neighborhood, several points are uniformly selected along the axial direction where the defect crack density is small and recorded as the analysis selection points. The analysis selection point with the largest crack concentration variation index is recorded as the execution cutting point. If the initial cutting point has a defect cracking index that is less than or equal to the preset defect cracking index, then the initial cutting point will be recorded as the cutting point to be cut.

6. The method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to claim 5, characterized in that, When cutting based on the execution cutting point, the entry point and exit point of the execution cutting point are determined based on the edge fracturing index of the candidate cutting pair; The candidate cutting pair consists of two sub-regions in the edge region of the cross-section corresponding to the cutting point that meet the connection conditions. The sub-regions are obtained by uniformly dividing the edge region. The edge region is annular and is determined by the cross-section corresponding to the cutting point and the minimum feed distance. The connection condition is that the two sub-regions can be connected by a diameter passing through the center of the cross-section.

7. The method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to claim 6, characterized in that, To address the interference condition of a defect where the cutting speed adjustment is greater than the preset cutting speed adjustment, the cutting speed setting mode is adjusted from automatic speed adjustment to the lowest speed cutting.

8. The method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to claim 7, characterized in that, When the cutting speed setting is set to self-adjusting cutting, for a single defect point, when the cutting direction of the cutting line approaches the cutting position of the defect point and reaches the preset adjustment distance corresponding to the defect point, the cutting speed is reduced based on the defect extension index. The adjustment range of the cutting speed is positively correlated with the fracture extension index.

9. The method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to claim 8, characterized in that, If the defect proximity index is greater than the preset defect proximity index, the preset adjustment distance will be adjusted.

10. The method for fabricating a large-size sodium iodide scintillation crystal for nuclear radiation detection according to claim 9, characterized in that, When adjusting the preset adjustment distance, the preset adjustment distance is increased according to the range of fusion defects; The preset adjustment distance is positively correlated with the volume of the fusion defect range.

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