A scintillation crystal strip of asymmetric surface configuration and a method of making the same

Abstract

This invention discloses a scintillation crystal strip with an asymmetric surface configuration and its preparation method, comprising the following steps: (1) cutting and grinding a scintillation crystal blank into a crystal strip, and optically polishing all its surfaces; (2) selecting one of the following asymmetric surface configurations: end-face scattering, single-sided perturbation, or orthogonal perturbation; (3) selectively covering the polished surfaces to be retained using a masking fixture according to the corresponding surface configuration, and performing a sanding process on the uncovered predetermined surfaces until the predetermined surfaces are processed to a sanded surface. This invention innovatively proposes to perform asymmetric surface treatment on the scintillation crystal strip to construct a spatial asymmetric surface configuration, creating an anisotropic photon scattering environment inside the crystal, reconstructing the random walk of photons into a transport with a directional trend, thereby improving the light collection efficiency of the scintillation crystal strip without strictly relying on a high-performance external reflective layer, and synergistically improving the light output and energy resolution.

Description

Technical Field

[0001] This invention relates to the field of nuclear radiation detection technology, and specifically to a scintillation crystal strip for an asymmetric surface configuration in a nuclear radiation detector and its preparation method. Background Technology

[0002] Scintillator detectors are a commonly used type of detector for nuclear radiation detection, possessing the advantage of high efficiency in detecting gamma rays. They are widely used in many fields such as high-energy physics, medical imaging, space research, and radiometric dosing. Energy resolution is a crucial performance indicator for scintillator detectors, especially for gamma-ray detection and identification equipment such as gamma spectrometers, where its quality directly determines the accuracy of nuclide identification and image quality. The energy resolution ΔE / E of a scintillator detector can be expressed by the following formula: Where, δ sc It is the intrinsic resolution of the crystal, which depends on the non-proportional response in the crystal's properties and the inhomogeneity in the scintillator; δ p The transmission resolution depends on the optical coupling quality between the crystal and the photoelectric converter, the uniformity of the response, and the uniformity of the photoelectron collection efficiency; δ st It is the statistical contribution of photoelectric conversion, and is related to the Poisson fluctuation of the number of collected photoelectrons; δ n This is a contribution from electronic noise, which can be ignored for high-gain optoelectronic devices. By analyzing the factors affecting the energy resolution of scintillator detectors, for a given crystal, δ... p and δ st This is a key factor affecting the energy resolution of the detector. To achieve optimal energy resolution, as much scintillation light as possible must be collected by the photomultiplier tube.

[0003] Bismuth germanate (BGO) and other crystals possess advantages such as high density and non-hygroscopicity, but their low actual light collection efficiency due to their high light output (intrinsic 8000-10000 ph / MeV) and high refractive index (n≈2.15) becomes a bottleneck limiting their energy resolution. Specifically, a large portion of the photons generated in the scintillator are retained in the scintillator due to total internal reflection (TIR) ​​at the crystal-air interface, resulting in self-absorption loss. This causes the number of photons that ultimately reach the photocathode to be much lower than the number generated, reducing the statistical fluctuation term and affecting the transmission resolution due to the non-uniformity of light collection.

[0004] Surface treatment is the core means to solve the light collection problem. Existing technologies mainly solve this problem through the following two symmetric schemes: (1) Global optical polishing, which forms a fully polished mirror surface and uses total internal reflection to confine photons within the crystal. However, for long strip crystals (such as BGO crystals), the path for photons to reach the readout end face is long, the probability is low, and self-absorption is severe, resulting in limited actual light output. (2) Global frosting, which solves the total internal reflection problem by backscattering light into the crystal. Although this method destroys the TIR condition, it causes photons to escape in all directions, requiring a high-performance external reflective layer for recovery. This not only increases the complexity and cost of the process, but also reduces the fill factor in dense arrays.

[0005] In summary, existing symmetric surface treatment schemes fail to actively intervene in the spatial probability distribution of photon transmission paths, representing a passive and crude light management strategy whose performance has approached theoretical limitations. Therefore, there is an urgent need in this field for a scintillation crystal strip with an asymmetric surface configuration capable of actively guiding photon flow, achieving directional photon enrichment, thereby fundamentally improving light output and optimizing energy resolution, and its fabrication method.

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a scintillation crystal strip with an asymmetric surface configuration and its preparation method. The invention innovatively proposes to perform asymmetric surface treatment on the scintillation crystal strip to construct a spatial asymmetric surface configuration, creating an anisotropic photon scattering environment inside the crystal, reconstructing the random walk of photons into transport with a directional trend, thereby improving the light collection efficiency of the scintillation crystal strip without strictly relying on a high-performance external reflective layer, and synergistically improving the light output and energy resolution.

[0008] To achieve the above and other related objectives, the present invention provides a method for preparing scintillation crystal strips with an asymmetric surface configuration, the method comprising the following steps:

[0009] (1) Cut and grind the scintillation crystal blank into crystal strips and optically polish all its surfaces;

[0010] (2) Select one of the following asymmetric surface configurations: end-face scattering, single-sided perturbation, or orthogonal perturbation;

[0011] (3) Selectively cover the polished surface to be retained using a masking fixture according to the selected asymmetric surface configuration, and perform a sanding process on the uncovered predetermined surface until the predetermined surface is processed to a sanded surface, thereby forming a scintillation crystal strip of asymmetric surface configuration;

[0012] in:

[0013] End-face scattering type: One end face of the crystal strip is frosted, while all other surfaces are optically polished;

[0014] Single-sided perturbation type: Only one side of the crystal strip is frosted, while the remaining surfaces remain optically polished;

[0015] Orthogonal perturbation type: The two adjacent and mutually perpendicular sides of the crystal strip are frosted, while the remaining surfaces are optically polished.

[0016] Optionally, the scintillation crystal is one of bismuth germanate crystal, lutetium silicate crystal, lutetium yttrium silicate crystal, lutetium gadolinium silicate crystal, and lutetium gadolinium yttrium silicate crystal;

[0017] Optionally, the scintillation crystal is a cerium-doped lutetium silicate crystal.

[0018] Optionally, the optical polishing in step (1) is chemical mechanical polishing, and the surface roughness Ra after optical polishing is ≤0.06μm.

[0019] Optionally, in step (1), the crystal strip is a cuboid with a square cross-section and dimensions of 4~6mm×4~6mm×30~45mm.

[0020] Optionally, the masking fixture is a polytetrafluoroethylene (PTFE) masking fixture.

[0021] Optionally, the sanding process in step (3) specifically involves: checking the parallelism of the glass grinding plate, mixing the grinding powder and water on the glass grinding plate workbench according to the ratio, and selecting the predetermined surface to be ground for grinding.

[0022] Optionally, the grinding powder is white corundum micro powder.

[0023] Optionally, the grinding process specifically involves: directional grinding of a predetermined surface of the exposed crystal strip under constant rotational speed (60-80 rpm) and pressure (50-80 g / cm²). For example, by controlling the grinding pressure, speed, and time, the crystal strip is pressed and pulled back and forth 5-10 times along the direction of its placement.

[0024] Optionally, the surface roughness of the predetermined surface after sanding treatment, i.e., the sanded surface, is 1.2μm≤Ra≤2.0μm.

[0025] To achieve optimal and repeatable photon scattering effects, the present invention uses white corundum micro powder as an abrasive to precisely grind the crystal surface on a glass substrate. This process combination can produce a uniform and controllable diffuse scattering surface morphology.

[0026] Optionally, the process also includes step (4): cleaning and drying the abrasive crystal strip.

[0027] Optionally, the cleaning process involves first rinsing with water, followed by ultrasonic cleaning.

[0028] The present invention also provides a scintillation crystal bar with an asymmetric surface configuration, wherein the scintillation crystal bar with an asymmetric surface configuration is prepared by the method described in any one of the above-mentioned methods.

[0029] The present invention also provides the application of the above-mentioned asymmetric surface configuration scintillation crystal strips in nuclear radiation detection.

[0030] As described above, the method for preparing scintillation crystal strips with asymmetric surface configurations according to the present invention has the following beneficial effects:

[0031] (1) Compared with the symmetric schemes of global optical polishing and global frosting, the present invention innovatively proposes to perform asymmetric surface treatment on scintillation crystal strips to construct a spatial asymmetric surface configuration, creating an anisotropic photon scattering environment inside the crystal, reconstructing the random walk of photons into transport with directional trends, thereby improving the light collection efficiency of scintillation crystal strips without strictly relying on high-performance external reflective layers, and synergistically improving light output and energy resolution.

[0032] (2) This invention improves upon existing grinding processes by using white corundum micro powder as an abrasive to precisely grind the crystal surface on a glass substrate. This process combination produces a uniform and controllable diffuse scattering surface morphology, achieving optimal and repeatable photon scattering effects. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the initial structure of the crystal strip. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] When describing the embodiments of the present invention in detail, for ease of explanation, the cross-sectional views showing the device structure will be partially enlarged without adhering to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention.

[0036] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one structure or feature shown in the accompanying drawings and other structures or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the accompanying drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The term “between” as used herein includes both endpoint values.

[0037] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0038] Example 1

[0039] A method for preparing scintillation crystal strips with an asymmetric surface configuration, the method being as follows:

[0040] (1) Cut and grind the BGO scintillation crystal blank into crystal strips, and use diamond suspension to perform fine optical polishing on all its surfaces;

[0041] (2) Select end face scattering type: Select one end face (F face) of the crystal strip for frosting treatment, and keep all other surfaces optically polished;

[0042] (3) A customized polytetrafluoroethylene (PTFE) masking fixture was used to tightly protect the optically polished surface that did not require treatment. White corundum micro powder was mixed with deionized water to form a suspension, which was then uniformly coated onto a flat glass grinding disc as the grinding medium. One end face (F face) of the exposed crystal strip was directionally ground under constant rotation speed (70 rpm) and pressure (60 g / cm²), and the roughness Ra of the obtained frosted surface was stable within the range of 1.6 μm ± 0.4 μm. The masking fixture was removed, and after rinsing with water, the crystal strip was ultrasonically cleaned and then placed in an oven for drying.

[0043] Gamma rays with a positron annihilation radiation characteristic energy of 511 keV are used as the excitation source, making them a dedicated detection target for PET imaging. Using this energy for evaluation provides the most direct reflection of the actual performance of the crystal strip of this invention in the target application.

[0044] The radiation source was sequentially aimed at three specific locations on the crystal strip: the top, middle, and bottom, for testing. At each test location, a sufficient number of energy spectra were collected, and the corresponding performance data for each location were recorded. The test results are shown in Table 1 below:

[0045]

[0046] Example 2

[0047] A method for preparing scintillation crystal strips with an asymmetric surface configuration, the method being as follows:

[0048] (1) Cut and grind the BGO scintillation crystal blank into crystal strips, and use diamond suspension to perform fine optical polishing on all its surfaces;

[0049] (2) Selecting the single-sided perturbation type: only one side (A side) of the crystal strip is frosted, while the remaining surfaces are optically polished;

[0050] (3) A customized polytetrafluoroethylene (PTFE) masking fixture was used to tightly protect the optically polished surface that did not require treatment. White corundum micro powder was mixed with deionized water to form a suspension, which was then uniformly coated onto a flat glass grinding disc as a grinding medium. One side (A side) of the exposed crystal strip was directionally ground under constant rotation speed (70 rpm) and pressure (60 g / cm²), and the roughness Ra of the resulting frosted surface was stable within the range of 1.6 μm ± 0.4 μm. The masking fixture was removed, and after rinsing with water, the crystal strip was ultrasonically cleaned and then placed in an oven for drying.

[0051] Gamma rays with a positron annihilation radiation characteristic energy of 511 keV are used as the excitation source, making them a dedicated detection target for PET imaging. Using this energy for evaluation provides the most direct reflection of the actual performance of the crystal strip of this invention in the target application.

[0052] The radiation source was sequentially aimed at three specific locations on the crystal strip: the top, middle, and bottom, for testing. At each test location, a sufficient number of energy spectrum readings were collected, and the corresponding performance data for each location were recorded. The test results are shown in Table 2 below:

[0053]

[0054] Example 3

[0055] A method for preparing scintillation crystal strips with an asymmetric surface configuration, the method being as follows:

[0056] (1) Cut and grind the BGO scintillation crystal blank into crystal strips, and use diamond suspension to perform fine optical polishing on all its surfaces;

[0057] (2) Select orthogonal perturbation type: The two adjacent and mutually perpendicular sides (A side and B side) of the crystal strip are frosted, and the remaining surfaces are optically polished.

[0058] (3) A customized polytetrafluoroethylene (PTFE) masking fixture was used to tightly protect the optically polished surface that did not require treatment. White corundum micro powder was mixed with deionized water to form a suspension, which was then uniformly coated onto a flat glass grinding disc as the grinding medium. Under constant rotation speed (70 rpm) and pressure (60 g / cm²), two adjacent and mutually perpendicular sides (surface A and surface B) of the exposed crystal strip were directionally ground, and the roughness Ra of the obtained frosted surface was stable within the range of 1.6 μm ± 0.4 μm. The masking fixture was removed, and after rinsing with water, the crystal strip was ultrasonically cleaned and then placed in an oven for drying.

[0059] Gamma rays with a positron annihilation radiation characteristic energy of 511 keV are used as the excitation source, making them a dedicated detection target for PET imaging. Using this energy for evaluation provides the most direct reflection of the actual performance of the crystal strip of this invention in the target application.

[0060] The radiation source was sequentially aimed at three specific locations on the crystal strip: the top, middle, and bottom, for testing. At each test location, a sufficient number of energy spectrum readings were collected, and the corresponding performance data for each location were recorded. The test results are shown in Table 3.

[0061]

[0062] Comparative Example 1

[0063] This comparative example employs a symmetrical scheme with global optical polishing. The test results are shown in Table 4 below:

[0064]

[0065] Comparative Example 2

[0066] This comparative example uses a symmetrical scheme with global frosting treatment. The test results are shown in Table 5 below:

[0067]

[0068] As can be seen from the test data of Examples 1-3 and Comparative Examples 1-2, the asymmetric surface configuration of the present invention has better energy resolution and light output performance than the symmetric configuration (i.e., global polishing, global frosting).

[0069] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method of making a scintillation crystal strip of asymmetric surface configuration, characterized by: Includes the following steps: (1) Cut and grind the scintillation crystal blank into crystal strips and optically polish all its surfaces; (2) Select an orthogonal perturbation asymmetric surface configuration, and perform frosting on two adjacent and mutually perpendicular sides of the crystal strip, while keeping the remaining surfaces optically polished; (3) Selectively cover the polished surface to be retained using a masking fixture according to the selected asymmetric surface configuration, and perform sanding treatment on the uncovered predetermined surface until the predetermined surface is processed to a sanded surface, thereby forming a scintillation crystal strip of asymmetric surface configuration. The roughness of the sanded surface is 1.2μm≤Ra≤2.0μm. The specific sanding process in step (3) is as follows: check the parallelism of the glass grinding plate, mix the white corundum micro powder and water on the glass grinding plate workbench according to the ratio, select the predetermined surface to be ground and grind it. The grinding is specifically as follows: under a constant rotation speed of 60~80 rpm and a pressure of 50-80 g / cm², perform directional grinding on the predetermined surface of the exposed crystal strip.

2. A method of making a scintillation crystal bar of asymmetric surface configuration as defined in claim 1, wherein: The scintillation crystal is one of the following: bismuth germanate crystal, lutetium silicate crystal, lutetium yttrium silicate crystal, lutetium gadolinium silicate crystal, lutetium gadolinium yttrium silicate crystal, and cerium-doped lutetium silicate crystal.

3. The method for preparing a scintillation crystal strip with an asymmetric surface configuration as described in claim 1, characterized in that: The surface roughness Ra after optical polishing in step (1) is ≤0.06μm.

4. The method for preparing a scintillation crystal strip with an asymmetric surface configuration as described in claim 1, characterized in that: In step (1), the crystal strip is a cuboid with a square cross-section.

5. The method for preparing a scintillation crystal strip with an asymmetric surface configuration as described in claim 1, characterized in that: It also includes step (4): cleaning and drying the crystal strips after the sanding process.

6. A scintillation crystal strip with an asymmetric surface configuration prepared by any one of claims 1 to 5.

7. The application of the scintillation crystal strip with the asymmetric surface configuration according to claim 6 in nuclear radiation detection.

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