Composite entrance window for alpha / beta scintillation detector and method of manufacture, detector

Abstract

The application discloses a composite incident window for an alpha / beta scintillation detector and a preparation method and a detector, and belongs to the technical field of nuclear radiation detection. The composite incident window comprises a black polyimide layer and an aluminum reflection layer arranged on at least one surface of the black polyimide layer. The black polyimide layer is used for absorbing ambient light to achieve a light shielding function and provide mechanical support, and the thickness thereof is adjustable in the range of 1 micrometer to 50 micrometers to adapt to the detection requirements of different energy alpha / beta particles. The aluminum reflection layer is used for reflecting the fluorescence generated by a scintillator to improve the light collection efficiency, and the thickness thereof is 60 nm to 100 nm. The application solves the contradiction between the ray transmittance, light reflection efficiency and mechanical strength of a traditional incident window by decoupling the functions of light shielding absorption of the black polyimide and reflection of the aluminum layer, and has excellent light shielding property, high reflectivity, good mechanical strength and long-term stability.

Description

Technical Field

[0001] This invention belongs to the field of nuclear radiation detection technology, specifically relating to a composite incident window for α / β scintillation detectors and its preparation method, as well as the detector itself. Background Technology

[0002] Scintillation detectors are core instruments for monitoring alpha and beta radioactive contamination. Their working principle is as follows: alpha or beta particles penetrate the entrance window, lose energy within the scintillator, and generate fluorescence. This fluorescence is received by photoelectric conversion devices such as photomultiplier tubes and converted into electrical signals. The performance of the entrance window directly determines the detector's detection efficiency, stability, and lifespan. To detect the weakly penetrating alpha particles and low-energy beta particles, the entrance window must be thin enough to ensure effective X-ray transmission. Simultaneously, to prevent ambient light from entering the detector and causing noise, the entrance window needs good light-blocking properties; to efficiently collect the fluorescence emitted by the scintillator, the side of the entrance window facing the inside of the detector must have high reflectivity. Furthermore, in practical use, the entrance window must withstand a certain amount of mechanical stress to prevent damage.

[0003] Currently, commercially available α / β scintillation detectors mainly employ the following incident window schemes: Aluminum foil windows: with a thickness of several micrometers to more than ten micrometers, have high light reflectivity and good light blocking properties, but poor mechanical strength. Thin windows are very easy to break, and increasing the thickness will significantly reduce the radiation transmittance.

[0004] Aluminized polyester film windows: An aluminum layer of approximately 30nm is deposited on the surface of a polyester film. The polyester substrate provides support, while the aluminum layer serves both reflective and light-blocking purposes. This is currently the most common solution. However, the aluminum layer is too thin, resulting in a reflectivity typically below 70%, and the aluminum layer is prone to oxidation and cracking after long-term use, leading to performance degradation. The mechanical strength of the polyester film itself is also limited.

[0005] Metal beryllium windows: They have excellent X-ray transmission performance, but low surface reflectivity, often requiring an additional reflective coating. They are also expensive to produce and have high processing toxicity.

[0006] Polyimide film windows: They have excellent temperature resistance, radiation resistance and mechanical properties, but ordinary (transparent or amber) polyimide has extremely low reflectivity to visible light, so an additional reflective layer is required for use in scintillation detectors.

[0007] The existing solutions presented by the above-mentioned approaches inherently contradict each other in terms of particle transmittance, light reflection efficiency, and mechanical strength: increasing the thickness of the reflective layer to improve reflectivity or increasing the thickness of the substrate to improve strength both sacrifice X-ray transmittance; pursuing high transmittance by using ultra-thin windows raises concerns about mechanical strength. Furthermore, the light-shielding function of traditional solutions is highly dependent on the thickness and integrity of the reflective layer; once the aluminum layer degrades, the light-shielding performance decreases accordingly. For the detection of low-energy β particles, ultra-thin windows with even lower areal density are required, posing an even greater challenge to mechanical strength. In special applications such as aerosol monitoring, the incident window also needs to possess good airtightness and corrosion resistance, which existing solutions cannot fully meet.

[0008] Therefore, developing a novel entrance window that can balance high X-ray transmittance, high light shielding, high reflectivity, good mechanical strength, and long-term stability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, this invention provides a composite incident window for an α / β scintillation detector, its fabrication method, and the detector itself. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a composite incident window for an α / β scintillation detector, employing a double-layer composite structure, comprising: Black polyimide layer and aluminum reflective layer; The black polyimide layer serves as the substrate of the composite incident window; the thickness of the black polyimide layer is 1-50 μm; the thickness of the black polyimide layer is selected according to the energy of the target detection particles. The aluminum reflective layer is disposed on at least one surface of the black polyimide layer; the thickness of the aluminum reflective layer is 60-100 nm.

[0010] Secondly, the present invention provides a method for preparing a composite incident window for an α / β scintillation detector, comprising: A black polyimide-based film of a predetermined thickness is selected as the black polyimide layer; In a vacuum environment, an aluminum reflective layer is deposited on at least one surface of the black polyimide layer to obtain a composite film; The composite film is annealed in a vacuum or inert gas environment to obtain the annealed composite film. According to the preset requirements, the annealed composite film is cut into the required shape and size to obtain the composite incident window.

[0011] Thirdly, the present invention provides a detector, comprising: A scintillator, a photoelectric converter, and a composite incident window as described in the first aspect; the composite incident window is disposed in the incident light path of the scintillator.

[0012] The beneficial effects of this invention are: The solution provided by this invention breaks the triangular contradiction between X-ray transmittance, light reflectance, and mechanical strength. While maintaining high X-ray transmittance, it achieves excellent mechanical properties thanks to the high strength of the black polyimide layer. This allows for tear and puncture resistance far exceeding that of traditional aluminum foil / aluminized polyester windows while maintaining an extremely thin thickness. High reflectance is achieved through an independently optimized aluminum reflective layer. Ambient light shielding is absorbed by the black polyimide layer and will not fail due to the potential aging of the surface aluminum reflective layer, exhibiting good long-term light-shielding stability. This invention can adapt to different thicknesses of black polyimide layers to flexibly meet the detection needs from low-energy to high-energy particles. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a composite incident window for an α / β scintillation detector provided in an embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the steps of a method for fabricating a composite incident window for an α / β scintillation detector according to an embodiment of the present invention. Figure 3 A schematic diagram of the principle of a detector provided in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the working process of a detector provided in an embodiment of the present invention. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0015] In existing entrance windows, the conflict between ray transmittance, light reflection efficiency, and mechanical strength is difficult to reconcile. Specifically: If high X-ray transmittance is desired, the window must be extremely thin (several micrometers or even submicrometers), but at this point the mechanical strength is severely insufficient, making it extremely easy to puncture or tear. If the light reflectivity is increased by increasing the thickness of the aluminum layer, the radiation transmittance decreases sharply. Increasing the thickness of the substrate to enhance mechanical strength will also sacrifice radiation transmittance. If a pure metal window (such as aluminum foil) is used in pursuit of high light reflectivity, although the reflectivity is high, the radiation transmittance and mechanical strength cannot be simultaneously achieved.

[0016] In this "ebb and flow" coupling relationship, existing single material systems cannot simultaneously achieve the optimization of all three performance indicators.

[0017] Existing solutions rely on single or double-layer thin-film structures for their light-shielding, light-reflecting, and mechanical support functions, resulting in highly coupled functions. Some solutions employ multi-layer physical structures to distribute functions (e.g., assigning light-shielding to the light-shielding film, light-collecting to the aluminum-coated film on the inner wall of the housing, and sealing to the black silicone ring). However, this approach disperses different functions across different components, increasing system complexity and assembly difficulty, and fails to achieve functional decoupling within the window itself.

[0018] The thickness of the incident window in existing commercial α / β detectors is basically fixed (e.g., the surface density of aluminized polyester windows is typically 1.2 mg / cm³). 2 (corresponding to a thickness of approximately 2–6 μm), there is a lack of standardized thickness selection schemes for α / β particles with different energies. For ³H (endpoint energy 18.6 keV), ¹ 4 For low-energy β emitters such as C (endpoint energy 156keV), the current thickness is still too thick, resulting in low detection efficiency; while for high-energy β or α particles, although the current thickness can meet the transmittance requirements, the problem of insufficient mechanical strength still exists.

[0019] For specialized applications such as aerosol detectors, the entrance window must also meet additional requirements such as airtightness and corrosion resistance. Existing polyester film windows lack sufficient mechanical strength and have limited airtightness. The light-blocking performance of the aluminum coating on the front window of a PIPS detector decreases after degradation, and the protective coating may age more rapidly in corrosive aerosol environments. Current technology has not yet provided a comprehensive entrance window solution that combines high mechanical strength, excellent airtightness, reliable light blocking, and good α / β ray transmittance.

[0020] In view of the shortcomings of the prior art, the technical problem to be solved by the embodiments of the present invention can be summarized as follows: A composite incident window is provided that achieves a better balance among the three performance indicators of X-ray transmittance, light reflection efficiency, and mechanical strength: How to ensure that the window is thin enough (to maintain high α / β ray transmittance), while simultaneously possessing high light reflection efficiency (to effectively collect scintillation light) and sufficient mechanical strength (to resist puncture, tearing and wear during daily use), thus breaking the inherent contradiction of the trade-off between the three indicators in existing solutions.

[0021] Achieving structural functional decoupling between window light-blocking and light-reflection functions: By combining materials and designing structures, the highly coupled light-blocking, light-reflecting, and mechanical support functions of traditional solutions are separated and optimized, allowing each function to be undertaken by different constituent layers of the composite window or by different material properties, thereby improving the flexibility and overall performance of the system design.

[0022] We offer a series of thickness options to suit the detection needs of alpha / beta particles at different energies: Develop a composite window scheme with a window thickness that can be flexibly adjusted within a wide range (from submicron to tens of micron), enabling the detector to select an appropriate window thickness based on the energy characteristics of the target particles (high-energy β, conventional β, low-energy β, α, etc.), thereby achieving an optimal match between detection efficiency and mechanical strength.

[0023] Improve the long-term operational stability and environmental adaptability of the window: By selecting substrate materials with high mechanical strength, excellent radiation resistance, good chemical stability, and low gas permeability, the problems of easy breakage of existing thin windows and decreased conductivity / shielding performance caused by aluminum layer degradation are solved. By optimizing the coating structure and thickness, the adhesion and durability of the aluminum layer in long-term use are ensured, reducing the frequency of detector maintenance and operation and maintenance costs.

[0024] Expanding the engineering feasibility of applications in special scenarios such as aerosol detectors and inert gas detectors: Based on solving the aforementioned general technical problems, further consideration is given to the additional requirements of special applications such as aerosol detectors for the airtightness and corrosion resistance of the incident window, so that the composite window solution can be extended to a wider range of radiation detection equipment types.

[0025] To achieve the decoupling and synergy of light shielding, reflection, and support functions, embodiments of the present invention provide a composite incident window for an α / β scintillation detector, a method for its fabrication, and a detector.

[0026] Below, we will first introduce a composite incident window for an α / β scintillation detector provided by an embodiment of the present invention.

[0027] like Figure 1 As shown in the embodiment of the present invention, a composite incident window for an α / β scintillation detector adopts a double-layer composite structure and may include: Black polyimide layer and aluminum reflective layer; The black polyimide layer serves as the substrate for the composite incident window; the thickness of the black polyimide layer ranges from 1 to 50 μm; the thickness of the black polyimide layer is selected based on the energy of the target detection particles. An aluminum reflective layer is disposed on at least one surface of a black polyimide layer; the thickness of the aluminum reflective layer is 60-100 nm.

[0028] Polyimide (PI) is a high-performance engineering plastic. In this embodiment of the invention, black polyimide (a thin film made black by adding colorants such as carbon black) was chosen as the base material for the following reasons: Black polyimide has extremely low transmittance in the visible light band; the transmittance of the black polyimide layer in the visible light band is less than 1.0 × 10⁻⁶. -4It can effectively block external ambient light from entering the detector through volume absorption, without relying on aluminum layer thickness or additional light-blocking layer. Polyimide itself has excellent mechanical properties, with tensile strength >145MPa and elongation at break >35%, and it still has high tear resistance and puncture resistance in film form. Polyimide has an extremely wide temperature range (-269°C to 400°C) and can maintain stability in extreme temperature environments; Polyimide has good radiation resistance and chemical inertness, and is not easily degraded when exposed to nuclear radiation environments or corrosive aerosols for a long time; Polyimide has a low effective atomic number (about 6.5), resulting in less scattering and energy absorption of α / β particles, which helps maintain high X-ray transmittance.

[0029] For substrates composed of ultrathin black polyimide layers of 1–3 μm, to further improve mechanical strength, a layer of metal or polymer micromesh (such as stainless steel mesh or PET mesh) can be laminated to one or both sides of the black polyimide layer to form a support structure. Although this support mesh will slightly reduce X-ray transmittance, it can significantly enhance tear resistance, making it particularly suitable for low-energy beta detection.

[0030] Understandably, although black polyimide aluminized film is already quite common in the market (e.g., for use in light-shielding packaging, electromagnetic shielding, etc.), using it as the entrance window for an α / β scintillation detector is not a conventional choice for those skilled in the art, for the following reasons: First, there is the existence of technological bias: In the field of α / β scintillation detectors, the dominant entrance window solution has long been aluminized polyester film (used by major manufacturers such as Ludlum and Berthold). Polyester film is widely accepted in the industry due to its low cost and mature processing. Those skilled in the art are accustomed to the design formula that "the aluminum layer is responsible for both light shielding and reflection," and lack technical inspiration to change the substrate material from polyester to black PI while simultaneously transferring the light shielding function to the substrate. Although black PI aluminized film has been used in other fields, introducing it into the entrance window of α / β detectors requires overcoming industry inertia and path dependence; it is not an obvious and simple replacement.

[0031] Second, the concept of functional decoupling is unprecedented in existing technologies: in existing α / β detector entrance windows (including aluminized polyester windows, aluminum foil windows, etc.), both the light-blocking and reflection functions are highly coupled to the aluminum layer. The functional decoupling design proposed in this invention, which separates the volumetric absorption and light-blocking of the black PI substrate from the independent reflection of the aluminum layer, is unprecedented in the field of entrance windows. Even though black aluminized PI film is a known material, using it in a decoupled rather than integrated manner to solve the specific technical contradictions of detector entrance windows requires a departure from conventional thinking in this field.

[0032] Third, the targeted selection of material properties: Black PI was chosen as the substrate not because of its performance after aluminum plating, but because of its volumetric absorption and light-blocking properties due to its black color, as well as the comprehensive properties of PI material itself, such as high mechanical strength, low atomic number (low attenuation of α / β rays), radiation resistance, and low permeability. These properties are highly matched with the requirements of the detector's entrance window and are the result of multi-objective optimization, rather than being directly derived from the known properties of the material itself.

[0033] Fourth, there are practical barriers to technology transfer: directly applying general-purpose black PI aluminized film to α / β scintillation detectors requires solving a series of engineering problems, such as maintaining mechanical strength after significant thickness reduction (from the conventional 25-50μm to 1-7.5μm), controlling aluminum layer adhesion, suppressing pinhole defects, and verifying radiation resistance performance. It cannot be achieved simply by cutting and installing; it requires systematic material selection and process optimization.

[0034] The inventiveness of this invention lies not in the novelty of the black PI aluminum-coated film material itself, but in its unique structure of functional decoupling applied to the specific technical field of the entrance window of an α / β scintillation detector, and in solving the long-standing triadic contradiction of light blocking, reflection, and intensity in this field, achieving unexpected technical effects.

[0035] Alternatively, in addition to polyimide, other polymers with high mechanical strength, low atomic number, the ability to be made black, and good film-forming properties can also be used as a substrate, for example: Black polyetheretherketone (PEEK) film: PEEK has extremely high mechanical strength and temperature resistance, but it is more difficult to produce as a film than PI and is more expensive. Black polyethylene terephthalate (PET) film: PET is cheaper, but its mechanical strength and temperature resistance are significantly inferior to PI, and its long-term stability is poor. Black polyethylene naphthalate (PEN) film: properties are between those of PI and PET.

[0036] All the aforementioned alternative substrates can achieve the functional decoupling approach of this invention, but their overall performance under extreme environments (high temperature, strong radiation, corrosive atmosphere) is inferior to that of black PI. They can be selectively replaced based on the cost and performance requirements of specific application scenarios. Users can choose the appropriate alternative based on the cost and performance requirements of specific application scenarios.

[0037] Aluminum is one of the metals with the highest reflectivity in the visible light band (reflectivity >90%), and it also has advantages such as low density, moderate cost, and good adhesion to polyimide. The reasons for choosing aluminum as the reflective layer material in this invention are as follows: High reflectivity ensures that the scintillating light generated by the scintillator is efficiently reflected back to the photoelectric conversion device, thereby improving light collection efficiency; An aluminum reflective layer is applied to one or both sides of the black polyimide layer, which improves light shielding. The aluminum layer is also conductive, which can dissipate static electricity buildup on the detector surface and avoid charge interference. The aluminum layer can be uniformly deposited on the polyimide surface using physical vapor deposition (PVD) technology. The thickness can be precisely controlled at the nanometer level without affecting the overall film's flexibility and X-ray transmittance.

[0038] The aluminum reflective layer has a reflectivity of more than 90% in the visible light band.

[0039] An aluminum reflective layer is disposed on one or both sides of the black polyimide layer.

[0040] Alternatively, in addition to aluminum, other highly reflective metals can also be used as the reflective layer, for example: Silver (Ag): Its visible light reflectance can reach over 95%, which is higher than that of aluminum. However, silver is easily oxidized and darkens, and its long-term stability is poor, requiring an additional protective layer. Gold (Au): It has excellent chemical stability, but its reflectivity in the visible light band is lower than that of aluminum (about 70-80%), and it is expensive. Multilayer dielectric films (such as TiO2 / SiO2) can achieve extremely high reflectivity, but the preparation process is complex and the thickness is large, which may affect the X-ray transmittance.

[0041] For certain specialized detectors, embodiments of the present invention can place the aluminum reflective layer only in the edge region of the incident window or form a grid pattern, leaving the black polyimide layer exposed in the central region. This central region has the highest X-ray transmittance, while the edge reflective layer can still collect some scintillation light. This approach can be used when X-ray transmittance is extremely important, but light collection efficiency will be reduced.

[0042] Understandably, for short-term missions requiring extremely high light collection efficiency and environmental friendliness, silver reflective layers are a viable alternative; for long-term stable or space applications, gold reflective layers are superior but require accepting reduced reflectivity. Aluminum is the best choice balancing performance, cost, and stability.

[0043] The composite incident window provided in this embodiment of the invention can be adapted to different detection requirements by adjusting the parameters given in Table 1.

[0044] Table 1. Parameters related to the composite incident window

[0045] The composite incident window provided in this invention achieves decoupling and synergy of light shielding, reflection, and support functions through material and structural innovation. It can ensure high α / β ray transmittance while also possessing high light shielding, high light collection efficiency, and excellent mechanical reliability.

[0046] The black polyimide layer, serving as the supporting structure, is black due to the presence of colorants such as carbon black. It exhibits extremely strong volume absorption of visible light and very low transmittance, thus independently fulfilling its light-shielding function without relying on the thickness of the reflective layer. Simultaneously, polyimide materials possess high tensile strength (>145 MPa) and elongation at break (>35%), providing excellent mechanical strength and tear resistance even when very thin. The black polyimide layer can be selected from 1 μm to 50 μm to meet the detection requirements of different energy α / β particles: for example, 1-3 μm for low-energy β, 7.5-12.5 μm for conventional α / β, and 25-50 μm for high-energy β or harsh operating conditions.

[0047] An aluminum reflective layer is formed on at least one surface of a black polyimide layer via physical vapor deposition (such as magnetron sputtering or evaporation), with a thickness of 60 nm to 100 nm. Within this thickness range, the aluminum layer achieves a visible light reflectance of over 90%, specifically designed to efficiently reflect the fluorescence generated by the scintillator back to the photoelectric conversion device, thereby improving light collection efficiency. Since the light-shielding function is already handled by the substrate, the aluminum layer thickness can be independently optimized to achieve the best reflective effect without the need for additional thickness for light shielding, thus avoiding additional attenuation of X-ray transmission.

[0048] The core inventive point of this invention lies in its functional decoupling design: the light-shielding, reflection, and support functions, which are traditionally coupled to an aluminum layer or a single material, are distributed to different components within the composite structure. The black PI substrate, composed of a black polyimide layer, utilizes its black color to achieve volumetric light absorption and provides mechanical support; the aluminum layer is specifically responsible for high reflectivity. These three components are independent of each other and can be optimized separately.

[0049] The core innovation of the composite incident window provided in this invention lies in distributing the three highly coupled functions of light blocking, reflection and mechanical support in the traditional scheme to different structural layers, as shown in Table 2, thereby achieving functional decoupling and breaking the contradiction of "one gaining while the other loses" between various performance indicators.

[0050] Table 2 Functional allocation of different structural layers

[0051] Through the above functional decoupling design, the composite incident window provided in this embodiment of the invention achieves the following: The light-shielding performance no longer depends on the thickness of the aluminum layer, so the aluminum layer does not need to be too thick (to avoid affecting the radiation transmittance), and there is no need to worry about cracks in the aluminum layer causing light-shielding failure. Reflective properties are independent of light-shielding properties; the aluminum layer can be optimized for high reflectivity and long-term adhesion without simultaneously meeting light-shielding requirements. Mechanical strength is provided by a high-strength polyimide substrate, which provides far greater tear resistance than aluminum foil or aluminized polyester film of the same thickness, even at an ultra-thin thickness of 1μm.

[0052] This invention breaks the triangular contradiction between X-ray transmittance, light reflectance, and mechanical strength. While maintaining high X-ray transmittance, it achieves excellent mechanical properties thanks to the high strength of the black polyimide layer. It provides tear and puncture resistance far exceeding that of traditional aluminum foil / aluminized polyester windows while maintaining an extremely thin thickness. High reflectance is achieved through an independently optimized aluminum reflective layer. Ambient light shielding is absorbed by the black polyimide layer and will not fail due to the potential aging of the surface aluminum reflective layer, exhibiting good long-term light-shielding stability. This invention allows for the selection of black polyimide layers of different thicknesses to flexibly adapt to detection requirements ranging from low-energy to high-energy particles.

[0053] Preferably, in embodiments of the present invention, a transparent protective coating (such as SiO2, MgF2, or optical adhesive) can be added to the outside of the aluminum reflective layer (towards the scintillator) to prevent oxidation and scratches of the aluminum layer and improve durability. This protective layer needs to be transparent to visible light, and its thickness should be controlled at the nanometer level to avoid significantly increasing radiation attenuation.

[0054] In embodiments of the present invention, black polyimide layers and aluminum reflective layers can be alternately stacked (e.g., aluminum reflective layer / black polyimide layer / aluminum reflective layer / black polyimide layer) to form a multilayer structure. This multilayer structure can further reduce pinhole defects and improve light shielding and airtightness, but the total thickness increases and the radiation transmittance decreases. It is suitable for applications with extremely high requirements for mechanical strength and shielding, but low requirements for radiation energy.

[0055] Secondly, corresponding to the above-described composite incident window embodiments, this invention also provides a method for preparing a composite incident window for an α / β scintillation detector, such as... Figure 2 As shown, it may include: S1, Select a black polyimide base film of a preset thickness as the black polyimide layer.

[0056] Use commercially available or custom-made black polyimide film, and select the thickness (e.g., 1μm, 7.5μm, 12.5μm, 25μm, or 50μm) according to the target particle energy. The surface of the film should be clean, free of oil and wrinkles.

[0057] S2, In a vacuum environment, an aluminum reflective layer is deposited on at least one surface of the black polyimide layer to obtain a composite film, which may include: A black polyimide layer is placed in a vacuum coating chamber, and an aluminum reflective layer is deposited on one or both sides of the black polyimide layer by magnetron sputtering, resistance heating, or electron beam evaporation. The thickness of the aluminum reflective layer is 60-100 nm.

[0058] During the deposition of the aluminum reflective layer, the vacuum level is set to The deposition rate can be controlled between 0.5-2 nm / s, and the thickness of the aluminum reflective layer can be monitored online using a quartz crystal film thickness gauge.

[0059] S3. Anneal the composite film in a vacuum or inert gas environment to obtain the annealed composite film.

[0060] After aluminum plating, annealing is performed under vacuum or inert gas protection at a temperature of 150-200℃ for 30-60 minutes to eliminate internal stress in the film and enhance the adhesion between the aluminum reflective layer and the black polyimide layer.

[0061] S4. According to the preset requirements, the annealed composite film is cut into the required shape and size to obtain the composite incident window.

[0062] For example, in this embodiment of the invention, a black polyimide film (DuPont Kapton® 30 EN) with a thickness of 7.5 μm can be selected, and an 80 nm aluminum layer can be deposited on one side of its surface using magnetron sputtering at a vacuum level of 1.0 × 10⁻⁶. - The deposition rate was 1.0 nm / s at 3 Pa, followed by vacuum annealing at 180 °C for 45 minutes. The resulting composite incident window had a transmittance of <1.0 × 10⁻⁶ Pa in the visible light band. -4 The aluminum layer has a reflectivity of 92% and a tensile strength of 360 MPa, making it suitable for conventional α / β detection.

[0063] The embodiments of the present invention have the following advantages: Synergistic enhancement of high X-ray transmittance and high mechanical strength: Utilizing the excellent mechanical properties of the black polyimide layer substrate (tensile strength >145MPa), it provides tear and puncture resistance far exceeding that of traditional aluminum foil / aluminized polyester windows while maintaining an extremely thin thickness of 1μm; at the same time, the low atomic number ensures high transmittance of α / β particles. The tensile strength of the black polyimide layer is >145MPa, and the elongation at break is >35%, which is far higher than that of aluminum foil (approximately 45–70MPa) and polyester film; even at an extremely thin thickness of 1μm, its tear resistance far exceeds that of traditional materials such as aluminized polyester of the same thickness, making it less prone to damage in harsh environments such as field surveys; the low effective atomic number (approximately 6.5) ensures high transmittance of α / β rays, and the low-energy β detection efficiency can be further improved by selecting a thinner PI (1–3μm).

[0064] Decoupling of light-shielding and reflection functions: Ambient light shielding is achieved through volumetric absorption of the black polyimide (PI) layer substrate, resulting in excellent light-shielding performance regardless of aluminum layer thickness; flicker light reflection is independently handled by the aluminum reflective layer. These two functions do not interfere with each other and can be optimized separately, solving the problem of mutual constraints between "light shielding-reflection-thickness" in traditional solutions. The reflectivity of the aluminum reflective layer is >90%, far exceeding that of traditional aluminized polyester windows (<70%), significantly improving light collection efficiency. In the dual-layer composite structure, the black polyimide layer and the aluminum reflective layer serve as backups for each other. Even if the aluminum reflective layer is slightly damaged, the black polyimide (PI) layer can still maintain its basic light-shielding function, exhibiting higher reliability.

[0065] A range of thicknesses is available to meet diverse energy detection needs: By selecting black polyimide layers of varying thicknesses (1–50 μm), it is possible to flexibly adapt to energy levels ranging from low-energy β(³H, ¹) to high-energy β(³H, ¹) detectors. 4 C) From alpha particles to high-energy β ( 90 Sr / 90 To meet the detection needs of Y and ³²P, a series of products have been developed.

[0066] Long-term working stability and environmental adaptability: Polyimide has wide temperature range stability (-269°C). With properties such as resistance to temperatures up to 400°C, radiation, and chemical corrosion, it can be used for extended periods in harsh conditions such as nuclear facilities, space environments, and corrosive aerosols. The aluminum layer adheres better to the black polyimide layer than the polyester substrate, reducing the risk of cracking and peeling, while maintaining conductivity and reflectivity. The improved durability of the entrance window significantly reduces equipment downtime and replacement costs due to breakage of the thin window, extending its service life.

[0067] Reduce system complexity and maintenance costs: The integrated composite window integrates three functions—light shielding, reflection, and mechanical support—into a single-layer window, simplifying the detector structure compared to multi-layer, distributed functional solutions; with improved window durability, replacement frequency and maintenance costs are significantly reduced.

[0068] Extends to specialized applications such as aerosol detectors: Due to the excellent airtightness of the black PI substrate (helium porosity as low as 10), - ³cm³·m - ²·atm - ¹·d - ¹) and chemical inertness, the composite incident window provided in the embodiments of the present invention has excellent light shielding, reflection, radiation transmission and sealing performance, and can be directly used in equipment such as radioactive aerosol monitors that have additional requirements for airtightness and corrosion resistance.

[0069] Understandably, the embodiments of the present invention redistribute the highly coupled light-shielding function, light-reflection function, and mechanical support function in the conventional solution, thereby achieving decoupling of functions within the layer: The black polyimide layer, serving as the substrate of the composite incident window, primarily functions as a light-shielding layer (volume absorption of visible light) and provides mechanical support (high strength and tear resistance). The aluminum reflective layer mainly handles the reflection of scintillation light (high reflectivity) and static electricity discharge. Through the synergistic design of absorption by the black substrate and reflection by the metal layer, the conventional design of light shielding relying solely on the thickness of the aluminum layer or reflection relying solely on the thickness of the metal layer is broken, allowing each function to be optimized independently without mutual constraints.

[0070] In existing technologies, the light-blocking of incident windows either relies on the opacity of the metal foil itself (such as aluminum foil windows), a very thin metal coating (such as aluminized polyester windows), or additional mechanical light-blocking components (such as black silicone rings or light-blocking films). This invention, for the first time, uses a black PI substrate as the main material of the composite incident window, utilizing the strong absorption characteristics of its inherent black pigment (such as carbon black) for visible light to achieve volumetric absorption-type light blocking that is independent of the metal layer thickness. This design allows the aluminum reflective layer to focus on improving reflectivity without having to consider light blocking, thus controlling the thickness of the aluminum reflective layer to a relatively thin range of 60-100 nm, ensuring high reflectivity (>90%) while avoiding additional attenuation of α / β particles.

[0071] The incident window thickness of existing commercial α / β detectors is basically fixed, which cannot be flexibly adapted to low-energy β(³H, ¹) detectors. 4 From C) to alpha particles and then to high-energy β ( 90 Sr / 90 The invention utilizes a wide energy range of γ and π²P. By selecting black PI substrates of varying thicknesses (1 μm-50 μm), a series of thickness designs are achieved, allowing the same composite window structure to cover the detection needs of different energy rays while maintaining a reasonable balance between mechanical strength and optical performance.

[0072] Based on different application scenarios and requirements for conductivity, antistatic properties, reflectivity, and cost, this invention proposes two optional configurations: single-sided aluminum plating and double-sided aluminum plating. Single-sided aluminum plating is suitable for portable devices where cost and light shielding are priorities; double-sided aluminum plating is suitable for applications requiring antistatic properties, double-sided reflection, or higher mechanical stability, such as space exploration and industrial monitoring.

[0073] Thirdly, embodiments of the present invention also provide a detector, such as... Figure 3 As shown, it may include: A scintillator, a photoelectric converter, and a composite incident window as described in the first aspect; the composite incident window is disposed in the incident light path of the scintillator.

[0074] The working process of the detector, such as Figure 4 As shown, it may include: Alpha / β ray penetration: Alpha or β particles in the measured environment pass through the composite incident window. Due to the low effective atomic number of the black polyimide layer (approximately 6.5) and the fact that the total thickness of the window can be optimized according to detection requirements (1-50 μm), the rays reach the scintillator with high transmittance.

[0075] Ambient light shielding: When visible light from the external environment is incident on the outer surface of the composite incident window, the black polyimide layer almost completely blocks the ambient light through volume absorption (transmittance <1.0×10⁻⁶). -4 The aluminum reflective layer further reflects residual transmitted light, ensuring that no ambient light enters the scintillator.

[0076] Scintillation light generation: α / β particles that penetrate the incident window deposit energy in the scintillator, exciting the scintillator (plastic scintillator or ZnS(Ag) coating) to produce fluorescence.

[0077] Scintillation light reflection and collection: Scintillation light propagates in all directions. Light incident on the direction of the composite entrance window is efficiently reflected (reflectivity > 90%) back into the detector after encountering the aluminum reflective layer, where it is superimposed on the light directly incident on the photoelectric conversion device, and finally transmitted to the photoelectric conversion device through the light guide or optical coupling layer.

[0078] Signal conversion and output: The photoelectric conversion device (PMT, SiPM or photodiode) converts the received scintillation light into electrical pulse signals. After amplification, shaping and analysis by the signal processing circuit, the output is the count rate or dose rate data that is proportional to the activity of the incident α / β particles.

[0079] In this embodiment of the invention, a composite incident window is installed at the front end of the detector's probe housing, with the aluminum reflective layer facing inward. A scintillator (such as a plastic scintillator or a scintillator coated with ZnS(Ag)) is attached to the rear of the aluminum reflective layer, and a photoelectric converter is located behind the scintillator.

[0080] When the detector is operating, α / β particles emitted from the surface being measured pass through the composite incident window. Due to the low atomic number and thinness (as low as 1 μm) of the black polyimide layer, particle energy loss is minimal, resulting in high transmittance. Upon entering the scintillator, the particles are excited and emit fluorescence, which is dispersed in all directions. A portion of this fluorescence directed towards the composite incident window is efficiently reflected back into the detector by the aluminum reflective layer, where it superimposes with the fluorescence directly incident on the photoelectric conversion device. This superposition is ultimately received by the photoelectric conversion device and converted into an electrical signal. Ambient light is almost completely absorbed by the black polyimide layer before reaching the aluminum reflective layer, preventing it from entering the scintillator and generating interference signals.

[0081] According to the embodiments of the present invention, black polyimide layers of different thicknesses can be selected based on the energy characteristics of the target detection particles to achieve the optimal matching of detection efficiency and mechanical strength as shown in Table 3.

[0082] Table 3. Optimal matching design of detection efficiency and mechanical strength

[0083] The advantages of the embodiments of the present invention compared with the prior art are shown in Table 4.

[0084] Table 4. Advantages of the present invention compared with existing technologies

[0085] This invention further applies a composite entrance window to a detector, utilizing the low permeability and chemical corrosion resistance of the black polyimide layer to simultaneously fulfill multiple functions such as light shielding, reflection, airtightness, and X-ray transmission, thus replacing existing entrance windows. It is understood that the core inventive point of this invention does not lie in any particular material itself, but rather in the specific technical field of applying a black polyimide layer and an aluminum reflective layer through a specific structural combination and functional allocation to the entrance window in an α / β scintillation detector, thereby resolving the long-standing contradiction between light shielding, reflection, and intensity.

[0086] It should be noted that, in the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A composite incident window for an α / β scintillation detector, employing a double-layer composite structure, characterized in that, The dual-layer composite structure includes a black polyimide layer and an aluminum reflective layer; The black polyimide layer serves as the substrate of the composite incident window; the thickness of the black polyimide layer is 1-50 μm; the thickness of the black polyimide layer is selected according to the energy of the target detection particles. The aluminum reflective layer is disposed on at least one surface of the black polyimide layer; the thickness of the aluminum reflective layer is 60-100 nm.

2. The composite incident window for an α / β scintillation detector according to claim 1, characterized in that, The black polyimide layer has a transmittance of less than 1.0 × 10⁻⁶ in the visible light band. -4 .

3. A composite incident window for an α / β scintillation detector according to claim 1, characterized in that, The aluminum reflective layer has a reflectivity of more than 90% in the visible light band.

4. A method for fabricating a composite incident window for an α / β scintillation detector, characterized in that, include: A black polyimide-based film of a predetermined thickness is selected as the black polyimide layer; In a vacuum environment, an aluminum reflective layer is deposited on at least one surface of the black polyimide layer to obtain a composite film; The composite film is annealed in a vacuum or inert gas environment to obtain the annealed composite film. According to the preset requirements, the annealed composite film is cut into the required shape and size to obtain the composite incident window.

5. The method for fabricating a composite incident window for an α / β scintillation detector according to claim 4, characterized in that, The process of depositing an aluminum reflective layer on at least one surface of the black polyimide layer in a vacuum environment to obtain a composite film includes: A black polyimide layer is placed in a vacuum coating chamber, and an aluminum reflective layer is deposited on one or both sides of the black polyimide layer by magnetron sputtering, resistance heating, or electron beam evaporation; the thickness of the aluminum reflective layer is 60-100 nm.

6. The method for fabricating a composite incident window for an α / β scintillation detector according to claim 4, characterized in that, During the deposition of the aluminum reflective layer, the vacuum level is set to .

7. The method for fabricating a composite incident window for an α / β scintillation detector according to claim 4, characterized in that, The annealing temperature is 150-200℃, and the annealing time is 30-60 minutes.

8. A detector, characterized in that, include: A scintillator, a photoelectric converter, and a composite incident window as described in any one of claims 1-3; the composite incident window is disposed on the incident light path of the scintillator.

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