High-sensitivity high-temperature photomultiplier photocathode with long service life and preparation method thereof

Abstract

The invention belongs to the technical field of photomultipliers, particularly relates to a photocathode, and discloses a high-sensitivity high-temperature photomultiplier photocathode with long service life and a preparation method thereof. According to the method for preparing the high-temperature photoelectric cathode in a sandwich mode, firstly, a K3Sb bottom layer is evaporated, then Na activation is carried out, and finally, a K3Sb surface layer is evaporated, so that alkali metal Na is buried in the K3Sb layer, a sandwich structure is formed, metal antimony and alkali metal K and Na are fully reacted, the chemical proportion of the cathode is optimized, the sensitivity of the cathode is improved by more than one time, and the sensitivity of the cathode reaches more than 50 microamperes / lm. Alkali metal adsorbed by the antimony beads is removed by electrifying, and an annular heating device is designed to locally heat the tube wall of the high-temperature tube and a fixed ceramic chip in the high-temperature tube so as to remove alkali metal adsorbed on the surface of the high-temperature tube, so that the damage of the alkali metal to the photoelectric cathode at high temperature is avoided, the preparation of the cathode with the service life of more than 400 hours is realized, and the service life is prolonged by more than 3 times.

Description

Technical Field

[0001] The present invention relates to the technical field of photomultiplier tubes, in particular to high-temperature photomultiplier tubes, and in particular to a high-sensitivity high-temperature photomultiplier tube photocathode with a long service life and a preparation method thereof. Background Art

[0002] High-temperature photomultiplier tube (hereinafter referred to as high-temperature tube) is a special high-temperature resistant electric vacuum photoelectric detection device that works in a high-temperature environment above 175°C. It is mainly used in key areas such as oilfield logging and geological exploration. The high-temperature photocathode (hereinafter referred to as high-temperature cathode) is the core photoelectric detection element of the high-temperature tube, usually a semiconductor metal film composed of three elements: Na, K, and Sb. The cathode sensitivity and life of the high-temperature cathode are the two core performance indicators. The cathode sensitivity of the high-temperature photocathode determines the photoelectric detection capability of the high-temperature tube, and the life of the high-temperature cathode determines the service life of the high-temperature tube.

[0003] The conventional method for making a high-temperature cathode is to first evaporate a layer of metal antimony film on a light window substrate, and then use alkali metal K and Na gas in turn to activate the antimony film from the outside to the inside to form a high-temperature photocathode. However, the traditional outside-to-inside activation method cannot fully mix and react metal antimony and alkali metals, and the stoichiometric ratio of the three elements Na, K, and Sb in the formed high-temperature cathode is also difficult to achieve the optimal structure. Therefore, the high-temperature cathode prepared by this method has low sensitivity.

[0004] In terms of life, when the high-temperature cathode works in a high-temperature environment above 175°C, the antimony beads adsorbed with alkali metals K and Na in the high-temperature tube are exposed to the high temperature and release alkali metal K and Na gases to react with the high-temperature cathode, destroying the stoichiometric ratio of the elements in the cathode crystal structure, which leads to a significant decrease in cathode sensitivity and ultimately leads to its life decay and cathode failure. Alkali metals adsorbed on the high-temperature tube wall and ceramic fixing plate are another major factor that causes the cathode life decay to be fast at high temperatures. Summary of the invention

[0005] In view of the defects of the prior art, according to the first aspect of the present invention, a method for preparing a high-sensitivity high-temperature photomultiplier tube photocathode with a long service life is provided, and the high-temperature photomultiplier tube photocathode is prepared by a "sandwich" process, firstly vapor-depositing a K3Sb bottom layer, then activating it with Na, and finally vapor-depositing a K3Sb surface layer, thereby burying the alkali metal Na in the K3Sb layer to form a "sandwich" structure, so that the metal antimony and the alkali metal K and Na react fully, thereby optimizing the chemical ratio of the cathode and improving the sensitivity of the cathode.

[0006] According to the second aspect of the purpose of the present invention, after the antimony alkali evaporation activation of the cathode is completed, a critical current slightly lower than its evaporation current is applied to the antimony evaporation source, so that the antimony evaporation source generates heat due to its own resistive thermal effect, thereby evaporating the unstable alkali metals adsorbed by its antimony beads and being discharged by the exhaust system, thereby preventing the antimony beads in the high-temperature tube from releasing alkali metals K and Na to damage the photocathode, thereby extending the service life of the photocathode of the high-temperature photomultiplier tube with the cathode lifted.

[0007] According to the third aspect of the purpose of the present invention, in order to further reduce the alkali metal residues on the wall of the high-temperature tube and the internal ceramic fixing plate, a consistent annular heating device is proposed. After the cathode preparation is completed, the glass tube wall of the high-temperature tube is locally heated by the heating device, so that the alkali metals adsorbed on the inner wall of the tube shell and the ceramic fixing plate are desorbed and discharged from the tube by heat, thereby improving the cathode life.

[0008] The method for preparing the high-temperature photomultiplier tube photocathode of the present invention can significantly improve the service life of the high-temperature photomultiplier tube photocathode, and achieve the preparation of a high-temperature cathode with a service life of more than 400 hours, which is more than 3 times longer than the existing design.

[0009] It should be understood that all combinations of the aforementioned concepts and the additional concepts described in more detail below can be considered as part of the inventive subject matter of the present disclosure as long as such concepts are not mutually inconsistent. In addition, all combinations of the claimed subject matter are considered as part of the inventive subject matter of the present disclosure.

[0010] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or nearly identical component shown in each figure may be represented by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings.

[0012] Figure 1 1 is a front view of a high temperature photomultiplier tube according to an example of the present invention.

[0013] Figure 2 1 is a top view of a high temperature photomultiplier tube according to an example of the present invention.

[0014] Figure 3 It is a comparison between the conventional preparation method of the photocathode of a high temperature photomultiplier tube and the preparation method exemplified in the present invention.

[0015] Figure 4 It is a schematic diagram of the "sandwich" structure of the high-temperature cathode preparation according to the present invention.

[0016] Figure 5 It is a front view schematic diagram of a ring-shaped heating device according to an example of the present invention.

[0017] Figure 6 Schematic top view of a ring-shaped heating device according to an example of the present invention.

[0018] Figure 7 It is a schematic diagram of the working principle of the annular heating device of the present invention.

[0019] Figure 8 This is a comparison of the spectral response curves of high-temperature cathodes prepared by different processes.

[0020] Fig. 9 It is a comparison of the life test process curves of high-temperature cathodes prepared by different processes. DETAILED DESCRIPTION

[0021] In order to better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0022] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed by the present invention are not limited to any implementation. In addition, some aspects disclosed by the present invention can be used alone or in any appropriate combination with other aspects disclosed by the present invention.

[0023] Combination Figure 3 As shown, according to the method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to an embodiment of the present invention, in view of the problem that the traditional method cannot fully mix and react the metal antimony and the alkali metal to form an optimal structure, we propose a preparation process using a "sandwich" structure, by first vapor-depositing a layer of K3Sb bottom layer on the glass light window, and then vapor-depositing a Na layer on the surface of the K3Sb, and then vapor-depositing a layer of K3Sb surface layer after the Na layer is evaporated, to form a "sandwich" structure, and finally high-temperature baking is performed to fully react Na and K3Sb to form Na2KSb, so that the metal antimony and the alkali metals K and Na fully react, thereby optimizing the chemical ratio of the cathode and improving the sensitivity of the cathode.

[0024] In a further embodiment, in order to increase the life of the cathode, after the antimony alkali evaporation activation of the cathode is completed, a critical current value slightly lower than its evaporation current of 0.05A~0.1A is applied to the antimony beads, so that the antimony beads are heated due to their own resistive thermal effect, thereby evaporating the unstable alkali metals adsorbed on the antimony beads, avoiding the release of alkali metals K and Na from the antimony beads when working at high temperatures and reacting with the photocathode to damage the cathode, thereby extending the high-temperature service life of the cathode.

[0025] In a further embodiment, in order to further reduce the alkali metal residues on the inner wall of the high-temperature tube shell and the ceramic fixing plate, this patent also designs an annular sleeve heating device. After the high-temperature tube completes cathode activation, the glass tube wall of the high-temperature tube is locally heated to 350°C through the annular sleeve heating device, so that the alkali metal adsorbed on the inner wall of the tube shell is desorbed and discharged into the tube by heat, thereby further reducing the alkali metal residues and improving the life of the high-temperature cathode.

[0026] Combination Figure 3 The example shown, the proposed method for preparing the high-sensitivity high-temperature photomultiplier tube photocathode comprises the following steps:

[0027] First, a K3Sb bottom layer is evaporated on the glass window, and then a Na layer is evaporated on the surface of the K3Sb. After the Na layer is evaporated, a K3Sb surface layer is evaporated to form a "sandwich" structure.

[0028] Finally, after high-temperature baking, Na and K3Sb are fully reacted to form a Na2KSb high-temperature photocathode.

[0029] In the preparation process, the K3Sb bottom layer and the K3Sb surface layer are prepared by simultaneous evaporation deposition of alkali metal potassium and metal antimony, the evaporation temperature is 200°C to 210°C, the potassium evaporation current is 5.0 to 6A, and the antimony evaporation current is 1.0 to 1.4A.

[0030] For Na layer evaporation, the evaporation temperature is 220° C. to 240° C., the Na evaporation current is 5.0A to 5.5A, and the Na evaporation amount is set to: when the photocurrent reaches a maximum value and drops to 50% of the maximum value, stop evaporating Na.

[0031] As a preferred embodiment, after cathode activation is completed, a critical current slightly lower than its evaporation current is applied to the antimony beads to cause the antimony beads to generate heat themselves, thereby removing unstable alkali metals adsorbed on their surfaces.

[0032] As a preferred embodiment, the process of removing alkali metals using antimony beads includes:

[0033] At 200°C, a current of 0.6A to 0.8A was applied to the antimony beads for 1 hour, and then the current was reduced to 0.5A, and the alkali metal removal was continued for more than 6 hours.

[0034] As a preferred embodiment, after the cathode activation is completed, the annular sleeve heating device heats only the glass tube wall of the high-temperature tube, so that the alkali metal adsorbed on the inner wall of the tube shell is desorbed and discharged into the tube, reducing the damage of free alkali metal to the cathode at high temperature.

[0035] As a preferred embodiment, the operation of removing alkali metals by adsorption on the inner wall of the shell and tube includes:

[0036] Start the annular sleeve heating device for preheating, wait until the temperature inside the heater reaches 350℃~400℃, then put the heater of the annular sleeve heating device on the tube wall of the photomultiplier tube and heat for 3~5 minutes. Use the heater to locally heat the tube wall of the photomultiplier tube to remove the alkali metal adsorbed on the tube wall and the fixed ceramic.

[0037] Combined with Figure 1-Figure 9 As shown, we will explain exemplary implementations of various aspects of the present invention in more detail.

[0038] It should be understood that in the embodiments of the present invention, for a photomultiplier tube, the preparation of the high-temperature photocathode is usually completed inside the high-temperature photomultiplier tube. Figure 1 and Figure 2 It is a schematic diagram of the structure of a high-temperature photomultiplier tube. For those skilled in the art, the photomultiplier tube mainly consists of a tube shell 1, a focusing electrode 2, a high-temperature cathode (not shown), multiple multiplier electrodes (not shown), a ceramic fixing plate (not shown), an anode (not shown), a core column 7, an insulating lead wire 8, etc. Only the components related to the preparation of the high-temperature photocathode related to the present invention are marked in the figure.

[0039] The top of the tube shell is the incident light window 11 of the high temperature tube, the photocathode grows on the inner surface of the incident light window 11, and the side of the tube shell is the tube wall 12. The tube shell 1 and the stem 7 are sealed by high temperature welding to form a vacuum chamber of the high temperature tube. The stem 7 includes 16 evenly distributed pins 71, a stem disk 72, and a tail tube 73. The high temperature cathode, focusing electrode 2, multiplier electrode, anode, and insulated lead 8 are all connected to the corresponding pins 71 of the stem 7 through nickel wires, so as to realize the voltage loading of the corresponding connected components through each pin 71 of the stem.

[0040] When preparing the photocathode, the high temperature photomultiplier tube is connected to the vacuum exhaust stage through the core column tail pipe 73 to obtain a vacuum higher than 1×10 -3 Pa high vacuum environment.

[0041] Acquisition of K and Na alkali metals

[0042] like Figure 1 As shown, both the K source 4 and the Na source 5 are tubular alkali sources, the outer shell of which is a nickel-chromium alloy tube, and potassium chromate or sodium chromate, zirconium powder, and aluminum powder are contained in the tube.

[0043] As an optional method, the K source 4 and the Na source 5 are welded to the core pin 71 of the high-temperature tube through a nickel wire to form a closed circuit with an external power supply.

[0044] When preparing the photocathode, current is loaded to the alkali source through the core pin. The nickel-chromium alloy shell of the alkali source heats up to form a high temperature under the action of resistive thermal effect, causing the internal potassium chromate or sodium chromate, zirconium powder, and aluminum powder to undergo a replacement reaction, releasing metal K or Na vapor, and performing metal K and Na evaporation.

[0045] Antimony evaporation method

[0046] like Figure 2 As shown, the antimony evaporation sources 211 and 212 are made of Φ0.18 mm nickel wire covered with antimony beads, one end of which is connected to the insulating lead 8 and the other end is connected to the focusing electrode 2, and is further connected to the corresponding pin 71 of the core column 7 through the nickel guide wire.

[0047] Similarly, by loading a certain current on the nickel wire, the nickel wire of the antimony evaporation source is heated by the resistance thermal effect to evaporate the antimony. In order to improve the uniformity of the cathode film layer, two antimony evaporation sources 211 and 212 are assembled in parallel to form a symmetrical structure to improve the uniformity of the coating film layer.

[0048] Preparation of "sandwich" structure of high temperature cathode

[0049] like Figure 3 and Figure 4 As shown in the figure, the "sandwich" preparation method of the high-temperature photocathode mainly includes four preparation processes: baking and degassing, K3Sb bottom layer evaporation, Na activation, and K3Sb surface layer evaporation. Then, high-temperature baking is used to fully react Na with K3Sb to form Na2KSb, and metal antimony and alkali metal K and Na are fully reacted. After the cathode preparation is completed, the alkali metal is removed and sealed.

[0050] like Figure 4 As shown, the cathode film layer is prepared by first evaporating a K3Sb bottom layer on the light window by simultaneously evaporating Sb and K, and then evaporating a Na layer on the surface of the K3Sb bottom layer. After the Na layer is evaporated, a K3Sb surface layer is evaporated to form a "sandwich" structure. Finally, it is baked at high temperature to allow Na and K3Sb to fully react to form Na2KSb5.

[0051] The specific implementation process is as follows:

[0052] (1) Baking and degassing

[0053] A high temperature oven is used to provide the high temperature activation environment required by the high temperature cathode, and high temperature baking and degassing is performed at 320℃~400℃ for 3h~5h to fully remove the gas in the high temperature tube shell and tube core. In this example, the degassing vacuum degree shall not be less than 1×10-3 Pa.

[0054] (2) K3Sb bottom layer preparation

[0055] At 200-210° C., metal antimony and alkali metal K are evaporated simultaneously, so that the metal antimony and alkali metal K are fully mixed and chemically reacted during the evaporation process to form K3Sb, which is deposited on the inner surface of the light window.

[0056] As an optional embodiment, the antimony evaporation current is generally 0.7-1 A, and the K evaporation current is 5.7-6.5 A. When the cathode photocurrent reaches the maximum value, the evaporation of metal antimony and alkali metal K is stopped, and the K3Sb bottom layer is prepared.

[0057] (3) Na layer deposition

[0058] The Na evaporation was continued at 220° C. to 240° C., and the Na evaporation current was 5.0 A to 5.5 A. When the photocurrent rose to a maximum, the maximum photocurrent was recorded, and the Na evaporation was continued until the photocurrent dropped to 50% of the maximum value, and the Na evaporation was completed.

[0059] (4) K3Sb surface deposition

[0060] The temperature is lowered to 200°C to 210°C, and the metal antimony and alkali metal K are simultaneously evaporated using the same process as the preparation of the K3Sb bottom layer. When the cathode photocurrent reaches the maximum value, the evaporation of metal antimony and alkali metal K is stopped, and the preparation of the K3Sb bottom layer is completed.

[0061] (5) High temperature baking

[0062] The temperature was raised to 220°C to 240°C and the mixture was kept warm and baked for 10 to 15 minutes until the photocurrent reached a maximum value, thereby forming a Na-K-Sb high-temperature photocathode.

[0063] (6) Alkali metal removal

[0064] (6-1) Antimony beads alkali metal removal

[0065] After cathode activation is completed, a critical current slightly lower than the evaporation current is applied to the antimony beads to cause the antimony beads to generate heat themselves to remove the unstable alkali metals adsorbed on their surfaces.

[0066] As an example, a current of 0.6A to 0.8A is applied to the antimony evaporation source at 200°C for 1 hour, and then the current is reduced to 0.5A, and the alkali metal removal is continued for more than 6 hours.

[0067] (6-2) Removal of alkali metals by adsorption on the tube wall

[0068] Figure 5 and Figure 6The front view and top view of the annular heating device are respectively, and the annular heating device comprises a bracket 111, a nut 112, a cross bar 113, a heater 114, and a sliding bolt 115. The heater is connected to the slot of the cross bar through the sliding bolt, and the heater can be adjusted left and right by moving the sliding bolt. The cross bar is sleeved on the bracket, and the cross bar can be adjusted up and down by rotating the nut, thereby realizing the height adjustment of the heater.

[0069] like Figure 7 As shown, by adjusting the height and horizontal position of the heater, the heater sleeve is placed on the side wall of the high-temperature tube, and the heating wire inside the heater is powered by the electrode 1141 on the heater, thereby achieving local heating of the high-temperature tube wall to remove the alkali metal adsorbed on the tube wall and the ceramic inside the tube.

[0070] As an optional embodiment, it is necessary to first start the annular sleeve heating device for preheating, heating to 350°C ~ 400°C, and then put the annular sleeve heating device on the side wall of the photomultiplier tube for heating, and keep heating for 3 to 5 minutes. The annular sleeve heating device is used to locally heat the tube wall of the photomultiplier tube, which removes alkali metals while avoiding damage to the photocathode due to high temperature.

[0071] It should be understood that too long a heating time will also cause the gain of the multiplication system to decrease, so the heating time needs to be strictly controlled. After the alkali metal is removed, the photomultiplier tube is sealed and, after post-processing, the cathode sensitivity and life are evaluated.

[0072] Test Evaluation

[0073] Cathode sensitivity test

[0074] Figure 8 The spectral response curves of the high-temperature photocathode prepared by the conventional process and the method of the aforementioned embodiment of the present invention are compared. Compared with the photocathode prepared by the conventional process, the photocathode prepared by the "sandwich" preparation method of the embodiment of the present invention has a higher sensitivity, and the cathode sensitivity can reach more than 50μA / lm, which is more than 1 times higher.

[0075] Lifespan Assessment

[0076] Fig. 9 The life test was conducted at 175°C to test the life of the high-temperature cathode manufactured by the conventional method and the method of the above embodiment of the present invention. Referring to the common practice in the industry, the time when the cathode sensitivity drops to half of the initial value was taken as the photocathode life. The life of the high-temperature tube prepared by conventional technology is about 95h. The life of the tube manufactured by this patent can reach more than 400h, which is more than 3 times longer.

[0077] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life, characterized in that: The preparation process using a "sandwich" structure includes the following steps: First, a K3Sb bottom layer is evaporated on the glass window, and then a Na layer is evaporated on the surface of the K3Sb. After the Na layer is evaporated, a K3Sb surface layer is evaporated to form a "sandwich" structure. Finally, after high-temperature baking, Na and K3Sb are fully reacted to form a Na2KSb high-temperature photocathode.

2. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 1, characterized in that: In the preparation process, the K3Sb bottom layer and the K3Sb surface layer are prepared by simultaneous evaporation deposition of alkali metal potassium and metal antimony, the evaporation temperature is 200°C to 210°C, the potassium evaporation current is 5.0 to 6.0A, and the antimony evaporation current is 1.0 to 1.4A.

3. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 1, characterized in that: In the preparation process, for the Na layer evaporation, the evaporation temperature is 220° C. to 240° C., the Na evaporation current is 5.0A to 5.5A, and the Na evaporation amount is set to: when the photocurrent reaches the maximum value and drops to 50% of the maximum value, stop evaporating Na.

4. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 1, characterized in that: After cathode activation is completed, a critical current slightly lower than the evaporation current is applied to the antimony beads to cause the antimony beads to generate heat themselves to remove the unstable alkali metals adsorbed on their surfaces.

5. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 4, characterized in that: Treatment using antimony beads to remove alkali metals includes: At 200°C, a current of 0.6A to 0.8A was applied to the antimony beads for 1 hour, and then the current was reduced to 0.5A, and the alkali metal removal was continued for more than 6 hours.

6. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 1, characterized in that: After the cathode is activated, the annular sleeve heating device heats only the glass tube wall of the high-temperature tube, so that the alkali metal adsorbed on the inner wall of the tube shell is desorbed and discharged into the tube, reducing the damage of free alkali metal to the cathode at high temperature.

7. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 6, characterized in that: The operation of removing alkali metals by adsorption on the inner wall of the shell and tube includes: Start the annular sleeve heating device for preheating, wait until the temperature inside the heater reaches 350℃~400℃, then put the heater of the annular sleeve heating device on the tube wall of the photomultiplier tube and heat for 3~5 minutes. Use the heater to locally heat the tube wall of the photomultiplier tube to remove the alkali metal adsorbed on the tube wall and the fixed ceramic.

8. The method for preparing a high-sensitivity, high-temperature photomultiplier tube photocathode with a long service life according to claim 6 or 7, characterized in that: The annular sleeve heating device is designed to include a bracket (111), a nut (112), a cross bar (113), a heater (114) and a sliding bolt (115); The heater (114) is an electric heater, which is connected to the slot of the cross bar (113) via a sliding bolt (115). The position of the heater (114) can be adjusted left and right by moving the sliding bolt (115); the cross bar (113) is sleeved on the bracket (111), and the position of the cross bar (113) can be adjusted up and down by rotating the nut, thereby realizing the adjustment of the height of the heater in the horizontal and vertical directions; By adjusting the height and horizontal position of the heater (114), the heater (114) is sleeved on the side wall of the high-temperature tube, and the heating wire inside the heater is powered through the electrode (1141) on the heater, thereby locally heating the tube wall of the high-temperature tube to remove the alkali metal adsorbed on the tube wall and the ceramic inside the tube.

9. A high-sensitivity, high-temperature photomultiplier tube Na2KSb photocathode prepared by the method of any one of claims 1 to 8.

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