Long-life micro-channel plate type photomultiplier

Abstract

The invention discloses a long-life micro-channel plate type photomultiplier, and solves the problems that a micro-channel plate type photomultiplier is short in service life, and an existing long-life micro-channel plate type photomultiplier is high in preparation threshold and high in cost. According to the invention, an atomic layer deposition coating technology is adopted, a metal oxide film layer is coated on a traditional lead-containing glass microchannel plate, and a positive ion blocking electrode is arranged between a photoelectric cathode and a lead-containing microchannel plate assembly, so that in the process of moving towards the photoelectric cathode, the metal oxide film layer is coated on the metal oxide film layer; the positive ions are pressed back to the lead-containing micro-channel plate assembly under the action of an electric field in the direction from the positive ion blocking electrode to the lead-containing micro-channel plate assembly, and do not move to the photoelectric cathode, so that the photoelectric cathode is prevented from being damaged, and the service life of the micro-channel plate type photomultiplier can be prolonged.

Description

Technical Field

[0001] This invention pertains to photomultiplier tubes, specifically a long-life microchannel plate-type photomultiplier tube. Background Technology

[0002] A photomultiplier tube is a photodetector that can convert extremely weak light signals into electrical signals and amplify them. Microchannel plate photomultiplier tubes (MCP-PMTs) are a type of photomultiplier tube that use microchannel plates (MCPs) as electron multiplication components. They are characterized by small size, fast time response, and high time resolution, and are often used for measuring ultrafast time histories from sub-nanosecond to nanosecond.

[0003] Next-generation electron-positron colliders, exemplified by the Super Taumon device, require high-time-resolution MCP-PMTs as core photodetectors to distinguish final-state particles across a wide momentum range. Large electron-positron colliders typically operate for decades, necessitating long lifetimes for the MCP-PMTs. The lifetime of an MCP-PMT is characterized by the amount of accumulated output charge at the anode; the greater the ability to accumulate output charge, the better the lifetime performance.

[0004] The lifetime of MCP-PMT is limited by the positive ion feedback effect of MCP: during photoelectron multiplication, positive ions (such as H⁺, CO⁺) generated in the MCP channel bombard the photocathode under the influence of an electric field, such as... Figure 1 As shown, the cathode quantum efficiency decreases with increasing anode cumulative output charge. The conventional MCP-PMT anode cumulative output reaches 500 mC / cm². 2 At that time, the cathode quantum efficiency decreased by more than 50%.

[0005] To address these issues, international research has focused on suppressing positive ion generation and migration, including using atomic layer deposition (ALD) to coat lead-free glass microchannels, introducing anti-ion feedback films on the MCP input surface, and optimizing cathode processes. International research has shown that growing conductive and secondary electron emission layers on the inner walls of lead-free glass microchannels using ALD can increase the lifetime of MCP-PMTs to 10 C / cm. 2 That's all. However, the difficulty of this technology lies in the fabrication of lead-free glass microchannels, which is more complex than the fabrication of traditional lead-containing glass microchannel plates. Furthermore, the optimal process parameters for atomic layer deposition (ALD) film deposition need to be determined through extensive experimentation, resulting in high fabrication costs. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of short lifespan of microchannel plate photomultiplier tubes and high manufacturing threshold and cost of existing long-life microchannel plate photomultiplier tubes, and to provide a long-life microchannel plate photomultiplier tube.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A long-life microchannel plate photomultiplier tube is characterized by comprising an incident window, a photocathode, a positive ion blocking electrode, a lead-containing microchannel plate assembly, and an anode, which are sequentially arranged in the optical path of the light in the wavelength band to be measured. It also includes a sealing structure, in which the entrance window, photocathode, positive ion blocking electrode, lead-containing microchannel plate assembly, and anode are sealed. The photocathode, positive ion blocking electrode, lead-containing microchannel plate assembly, and sealing structure are respectively connected to a pressure-dividing assembly. The pressure-dividing assembly provides pressure to the photocathode, positive ion blocking electrode, lead-containing microchannel plate assembly, and sealing structure, while simultaneously satisfying the following: The potential of the positive ion blocking electrode is higher than that of the photocathode and the lead-containing microchannel plate assembly, and the potential of the lead-containing microchannel plate assembly is higher than that of the photocathode. The inner wall of the microchannel in the lead-containing microchannel plate assembly is coated with a metal oxide film.

[0008] Furthermore, the sealing structure is a ceramic-metal sealing structure, including a ceramic shell and multiple metal connectors, the multiple metal connectors extending to the outside of the ceramic shell and respectively connected to the pressure dividing assembly; The multiple metal connectors are located at one end inside the ceramic tube shell and are respectively connected to the photocathode, the positive ion blocking electrode (3), and the lead-containing microchannel plate assembly.

[0009] Furthermore, the metal oxide film is one of aluminum oxide film, magnesium oxide film, and zinc oxide film; The thickness of the metal oxide film is 6 nm to 10 nm.

[0010] Furthermore, the positive ion blocking electrode is a metal structure with a grid, wherein the duty cycle of the grid in the metal structure is 70% to 90%, and the shape of the grid is a regular square or a regular hexagon.

[0011] Furthermore, the lead-containing microchannel plate assembly is a single lead-containing microchannel plate, a double-layer cascaded lead-containing microchannel plate, or a triple-layer cascaded lead-containing microchannel plate.

[0012] Furthermore, the distance between the photocathode and the positive ion blocking electrode is 0.8 mm to 1.2 mm; The spacing between the positive ion blocking electrode and the lead-containing microchannel plate assembly is 1.6 mm to 2.4 mm.

[0013] Furthermore, the incident window is made of one of the following materials: magnesium fluoride crystal, quartz glass, or borosilicate glass.

[0014] Furthermore, the photocathode is made of one of the following: ultraviolet solar-blind material, visible light material, or infrared-responsive material.

[0015] The beneficial effects of this invention are: (1) The present invention provides a long-life microchannel plate photomultiplier tube. Since the potential of the positive ion blocking electrode is higher than that of the lead-containing microchannel plate assembly, the positive ions generated by the lead-containing microchannel plate assembly are subjected to the electric field force from the positive ion blocking electrode to the lead-containing microchannel plate assembly during the process of moving towards the photocathode. This causes the positive ions to be suppressed back to the lead-containing microchannel plate assembly and not to move onto the photocathode, thus avoiding damage to the photocathode.

[0016] (2) The present invention provides a long-life microchannel plate photomultiplier tube, which uses atomic layer deposition coating technology to deposit a metal oxide film layer in the microchannel of a traditional lead-containing microchannel plate assembly, thereby reducing the number of residual gas molecules adsorbed on the surface of the microchannel, thereby reducing the generation of positive ions and damage to the photocathode, and improving the service life of the microchannel plate photomultiplier tube. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of positive ion bombardment of the photocathode in an existing microchannel plate photomultiplier tube, where e - ⊕ represents electrons, and ⊕ represents positive ions; Figure 2 This is a schematic diagram of the structure of an embodiment of a long-life microchannel plate photomultiplier tube according to the present invention; Figure 3 This is a schematic diagram of a microchannel in a lead-containing microchannel plate assembly, as shown in an embodiment of a long-life microchannel plate photomultiplier tube of the present invention. Figure 4 This is a schematic diagram of the potential structure of the photocathode, positive ion blocking electrode, and lead-containing microchannel plate assembly in an embodiment of a long-life microchannel plate photomultiplier tube of the present invention. Figure 5 This is a simulation result of the electron motion trajectory in an embodiment of a long-life microchannel plate photomultiplier tube according to the present invention; Figure 6 This is a diagram showing the trajectory of positive ions in an embodiment of a long-life microchannel plate photomultiplier tube according to the present invention. Figure 7 The results show the measured lifetime of the long-life microchannel plate photomultiplier tube (MCP-PMT) and the conventional MCP-PMT in this invention; where the horizontal axis represents the cumulative output charge of the anode and the vertical axis represents the output charge of a single pulse.

[0018] The attached figures are labeled as follows: 1-Incident window; 2-Photocathode; 3-Positive ion blocking electrode; 4-Lead-containing microchannel plate assembly; 401-Microchannel wall; 402-Microchannel; 403-Metal oxide film layer; 5-Anode; 6-Sealing structure; 7-Pressure divider assembly. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This embodiment provides a long-life microchannel plate photomultiplier tube, such as... Figure 2 As shown, the assembly includes an incident window 1, a photocathode 2, a positive ion blocking electrode 3, a lead-containing microchannel plate assembly 4, and an anode 5, sequentially arranged in the optical path of the light in the wavelength band to be measured. Light of the wavelength band to be measured passes through the incident window 1 and is incident on the photocathode 2, where photoelectrons are generated. Depending on the wavelength band to be measured, the incident window 1 can be made of magnesium fluoride crystal, quartz glass, or borosilicate glass. The photocathode 2 is a semiconductor compound attached to the inside of the incident window 1, and its function is to convert incident light into photoelectrons. Depending on the wavelength band to be measured, the photocathode 2 can be made of ultraviolet solar-blind material, visible light-responsive material, or infrared-responsive material.

[0021] In this embodiment, the lead-containing microchannel plate assembly 4 functions to amplify the photoelectrons emitted by the photocathode 2, thereby forming a detectable electron flow signal. The lead-containing microchannel plate assembly 4 can be a single lead-containing microchannel plate, a cascaded pair of lead-containing microchannel plates, or a cascaded triple lead-containing microchannel plate, selected according to the desired amplification level. Figure 1 As shown, when a conventional MCP-PMT (microchannel plate photomultiplier tube) is working, electrons e - Emitted from photocathode 2, incident on... Figure 3 In the microchannel 402 shown, electrons are accelerated and multiplied, bombarding the residual gas molecules adsorbed on the surface of the microchannel wall 401, causing them to desorb and ionize to generate positive ions ⊕. Under the action of the electric field, the positive ions ⊕ move in the opposite direction to the electrons. If the positive ions ⊕ bombard the surface of the photocathode 2, the performance of the photocathode 2 will deteriorate, thereby reducing the lifespan of the conventional MCP-PMT (microchannel plate photomultiplier tube). Figure 1 In the middle, e - ⊕ represents electrons, and ⊕ represents positive ions.

[0022] The present invention deposits a metal oxide film layer 403 on the inner wall of the microchannel of a conventional lead-containing microchannel plate assembly 4, which can reduce the number of residual gas molecules adsorbed on the surface of the microchannel, thereby reducing the generation of positive ions and damage to the photocathode, and improving the lifespan of the MCP-PMT. Figure 3 This is a schematic diagram of a single channel of the microchannel plate used in this embodiment. A metal oxide film 403 with a thickness on the nanometer scale is deposited on the microchannel wall 401 of the conventional microchannel plate using atomic layer deposition technology. The metal oxide film 403 is one of aluminum oxide film, magnesium oxide film, and zinc oxide film, and the thickness of the metal oxide film 403 is between 6nm and 10nm.

[0023] In this embodiment, an aluminum oxide film with a thickness of 6 nm is deposited on the inner wall of the microchannel of the lead-containing microchannel plate assembly 4.

[0024] A positive ion blocking electrode 3 is placed between the photocathode 2 and the lead-containing microchannel plate assembly 4. A negative high voltage is applied to the photocathode 2, and the potential of the positive ion blocking electrode is higher than that of the photocathode 2 and also higher than that of the lead-containing microchannel plate assembly 4. The distance between the positive ion blocking electrode 3 and the photocathode 2 and the lead-containing microchannel plate assembly 4 is set so that electrons emitted by the photocathode 2 accelerate between the photocathode 2 and the positive ion blocking electrode 3, while electrons decelerate between the positive ion blocking electrode 3 and the lead-containing microchannel plate assembly 4.

[0025] like Figure 4 In this embodiment, the potential settings for the photocathode 2, the positive ion blocking electrode 3, and the lead-containing microchannel plate assembly 4 are as follows: The photocathode 2 is 1 mm apart from the positive ion blocking electrode 3, and the lead-containing microchannel plate assembly 4 is 2 mm apart from the positive ion blocking electrode 3. The potential of the photocathode 2 is -2200V, the potential of the positive ion blocking electrode 3 is -1900V, and the potential of the lead-containing microchannel plate assembly 4 is -2000V. When electrons move from the photocathode 2 to the positive ion blocking electrode 3, their kinetic energy increases by 300 eV; when electrons move from the positive ion blocking electrode 3 to the lead-containing microchannel plate assembly 4, their kinetic energy decreases by 100 eV. Ultimately, when electrons move from the photocathode 2 to the lead-containing microchannel plate assembly 4, their kinetic energy increases by 200 eV, allowing for normal subsequent electron multiplication output.

[0026] like Figure 5 The figure shows a simulation of the electron trajectory as electrons move from the photocathode 2, through the positive ion blocking electrode 3, to the lead-containing microchannel plate assembly 4. Based on... Figure 5 It is known that setting the positive ion blocking electrode 3 and setting it to a higher potential than that of the photocathode 2 and the lead-containing microchannel plate assembly 4 will not affect the normal operation of the MCP-PMT.

[0027] The positive ion blocking electrode 3 is a metal structure with a grid, the duty cycle of which is 70% to 90%, and the grid shape is a regular square or regular hexagon. Although the present invention uses an oxide film layer to reduce the number of residual gas molecules adsorbed on the microchannel surface, a small number of positive ions are still generated during the operation of the MCP-PMT and move towards the cathode, causing the lifetime of the MCP-PMT to decrease slowly.

[0028] Figure 6 In this embodiment, the trajectory of positive ions is determined by the addition of a positive ion blocking electrode 3. Since the potential of the positive ion blocking electrode 3 is higher than that of the lead-containing microchannel plate assembly 4, the positive ions generated by the lead-containing microchannel plate assembly 4 are forced back onto the lead-containing microchannel plate assembly 4 by an electric field force from the positive ion blocking electrode 3 to the lead-containing microchannel plate assembly 4 during their movement towards the photocathode 2, thus preventing damage to the photocathode 2.

[0029] The anode 5 is made of metal and is used to receive electrons multiplied by the lead-containing microchannel plate assembly 4, and output them to the back-end digitizer or oscilloscope. The anode 5 can be a single anode or multiple anodes. The sealing structure 6 is a ceramic-metal sealing structure, specifically a ceramic tube shell and multiple metal connectors. The multiple metal connectors extend to the outside of the ceramic tube shell at intervals and are connected to the voltage divider assembly 7. The ends of the multiple metal connectors located inside the ceramic tube shell are respectively connected to the photocathode 2, the positive ion blocking electrode 3, and the lead-containing microchannel plate assembly 4. The sealing structure 6 is used to form a sealed vacuum environment for the entrance window 1, the photocathode 2, the positive ion blocking electrode 3, the lead-containing microchannel plate assembly 4, and the anode 5, so as to realize the acceleration and multiplication of electrons in the vacuum.

[0030] The function of the voltage divider assembly 7 is to provide a voltage divider circuit for the photocathode 2, positive ion blocking electrode 3, microchannel plate assembly 4, and sealing structure 6. It consists of a high-voltage connector, a circuit board, and resistors and capacitors soldered onto it.

[0031] The lifetime of the aforementioned long-life microchannel plate photomultiplier tube (MCP-PMT) was tested, and the test results are as follows: Figure 7 As shown, Figure 7 The lifetime test results of a conventional MCP-PMT are also presented. The horizontal axis represents the cumulative output charge at the anode, and the vertical axis represents the output charge of a single pulse. Figure 7 It can be seen that for a conventional MCP-PMT, when the accumulated output charge at the anode reaches 1 C / cm 2 At that time, the light response signal output drops to 20% of the initial value. For the microchannel plate photomultiplier tube (MCP-PMT) of this invention, the anode cumulative output reaches 8.3 C / cm. 2At that time, the light response signal output only dropped to 87% of the initial value. It is evident that this invention can significantly improve the lifespan of microchannel plate photomultiplier tubes.

[0032] The above description is merely a specific embodiment of the present invention and a comparison of the effects of the specific embodiments with relevant comparative examples. However, the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A long-life microchannel plate photomultiplier tube, characterized in that: It includes an incident window (1), a photocathode (2), a positive ion blocking electrode (3), a lead-containing microchannel plate assembly (4), and an anode (5) arranged sequentially on the optical path of the light in the wavelength band to be measured. It also includes a sealing structure (6), in which the entrance window (1), photocathode (2), positive ion blocking electrode (3), lead-containing microchannel plate assembly (4), and anode (5) are sealed within the sealing structure (6). The photocathode (2), positive ion blocking electrode (3), lead-containing microchannel plate assembly (4), and sealing structure (6) are respectively connected to a pressure dividing assembly (7). The pressure dividing assembly (7) is used to provide pressure to the photocathode (2), positive ion blocking electrode (3), lead-containing microchannel plate assembly (4), and sealing structure (6), while satisfying the following: The potential of the positive ion blocking electrode (3) is higher than that of the photocathode (2) and the lead-containing microchannel plate assembly (4), and the potential of the lead-containing microchannel plate assembly (4) is higher than that of the photocathode (2). The inner wall of the microchannel of the lead-containing microchannel plate assembly (4) is coated with a metal oxide film layer (403).

2. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that: The sealing structure (6) is a ceramic-metal sealing structure, including a ceramic tube shell and multiple metal connectors. The multiple metal connectors extend to the outside of the ceramic tube shell and are respectively connected to the pressure dividing assembly (7). One end of each of the metal connectors located inside the ceramic tube is connected to a photocathode (2), a positive ion blocking electrode (3), and a lead-containing microchannel plate assembly (4).

3. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that: The metal oxide film is one of aluminum oxide film, magnesium oxide film, and zinc oxide film; The thickness of the metal oxide film is 6 nm to 10 nm.

4. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that: The positive ion blocking electrode (3) is a metal structure with a grid, wherein the duty cycle of the grid in the metal structure is 70% to 90%, and the shape of the grid is a regular quadrilateral or a regular hexagon.

5. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that: The lead-containing microchannel plate assembly (4) is a single lead-containing microchannel plate, a double-layer cascaded lead-containing microchannel plate, or a triple-layer cascaded lead-containing microchannel plate.

6. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that: The distance between the photocathode (2) and the positive ion blocking electrode (3) is 0.8 mm to 1.2 mm; The spacing between the positive ion blocking electrode (3) and the lead-containing microchannel plate assembly (4) is 1.6 mm to 2.4 mm.

7. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that, The incident window (1) is made of one of the following materials: magnesium fluoride crystal, quartz glass, or borosilicate glass.

8. The long-life microchannel plate photomultiplier tube according to claim 1, characterized in that, The photocathode (2) is made of one of the following: ultraviolet solar blind material, visible light material, or infrared band responsive material.

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