Photomultiplier transmission-type trialkali photocathode preparation system and preparation method

Abstract

The invention discloses a photomultiplier transmission-type trialkali photocathode preparation system and a photomultiplier transmission-type trialkali photocathode preparation method, and belongs to the technical field of photomultipliers, and alkali sources for preparing the photomultiplier transmission-type trialkali photocathode comprise a K source and an Rb / Cs mixed source. In the preparation process of the cathode, a layer of antireflection film is evaporated on a glass substrate, then four-step activation is carried out on K, Sb, K and Rb / Cs in sequence, and the proportion of Rb and Cs in the cathode can be accurately controlled by adjusting the proportion of Rb and Cs in an Rb / Cs mixed source, so that the prepared trialkali photoelectric cathode achieves the characteristic of low noise on the basis of not influencing high quantum efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of photomultiplier tubes, and in particular relates to a system and method for preparing a transmission-type three-alkali photocathode of a photomultiplier tube. Background Art

[0002] Transmission-type photomultiplier tubes based on K2CsSb photocathodes have been widely used in biotechnology, radiation measurement, high-energy physics and other fields due to their advantages such as high quantum efficiency, long life, short response time and low preparation cost. However, the noise of K2CsSb photomultiplier tubes can greatly interfere with weak signals, which makes the field of extremely weak light signal detection, such as neutrino detection, have extremely strict requirements on the noise performance of the photomultiplier tubes used. Photomultiplier tubes prepared by existing methods cannot meet the requirements. Summary of the invention

[0003] The purpose of the present invention is to provide a transmission type three-alkali photocathode and a preparation method thereof. In view of the fact that the electron affinity of Rb is higher than that of Cs, the prepared three-alkali cathode has the characteristics of high quantum efficiency and low noise.

[0004] The technical scheme for realizing the present invention is as follows: a photomultiplier tube transmission type three-alkali photocathode preparation system, comprising an alkali source component 1 and an end-window type photomultiplier tube 2, wherein the alkali source component 1 comprises an outer cylindrical glass tube sleeve 11 and an inner K source 12, an Rb / Cs mixed source 13, and a pin electrode 14, wherein a tail pipe 15 is arranged at one end of the cylindrical glass tube sleeve 11; a metal Sb ball 25 and a metal Mn / Be / Mg ball 26 are arranged at the end window 24 of the end-window type photomultiplier tube 2, and the metal Sb ball 25 and the metal Mn / Be / Mg ball 26 are arranged at the end window 24 of the end-window type photomultiplier tube 2. The Mg balls 26 are connected to the electrode wires 23 respectively. The end-window type photomultiplier tube 2 is connected to the alkali source assembly 1 through the exhaust tail pipe 22. The K source 12 and the Rb / Cs mixed source 13 are connected to the pin electrode 14 through the nickel wire to form a loop. When the cathode is activated, a certain current is applied to the K source 12 and the Rb / Cs mixed source 13 through the pin electrode 14, so that they generate heat themselves to release alkali metal vapor, which diffuses into the glass shell of the photomultiplier tube 2 through the exhaust tail pipe 22 and reacts with the metal Sb ball 25 therein to form an alkali antimony cathode.

[0005] The present invention also proposes a method for preparing a transmission-type three-alkali photocathode of a photomultiplier tube, using the above-mentioned preparation system, and the specific steps are as follows:

[0006] Step 1, degassing, vacuumizing and baking the alkali source assembly 1 and the photomultiplier tube 2 at room temperature;

[0007] Step 2, oxygen is introduced into the evacuated alkaline source assembly 1 and the photomultiplier tube 2 through the exhaust tail pipe 15, and the oxygen valve is closed until the vacuum degree reaches 40Pa; a 410nm monochromatic red light is incident on the photocathode from the end window center 24 of the photomultiplier tube 2, and the reflectivity monitoring curve is adjusted to 100%; at a temperature of 25°C, a current of 20A is introduced into the Mn metal ball 26, and glow oxidation is performed at the same time, and the reflectivity monitoring curve of the cathode surface is monitored. When it drops by about 3 percentage points, the evaporation is completed, so that the Mn sheet and oxygen fully react to form a uniform MnO anti-reflection film;

[0008] Step 3, turning on the K source for the first time, causing the reflectivity monitoring curve of the cathode surface to drop by about 5 percentage points;

[0009] Step 4, turning on the Sb source, causing the reflectivity monitoring curve of the cathode surface to drop by about 10 percentage points;

[0010] Step 5, turning on the K source for the second time, causing the reflectivity monitoring curve of the cathode surface to rise by about 30 percentage points;

[0011] Step 6, turn on the Rb / Cs mixed source, so that the reflectivity monitoring curve of the cathode surface rises by about 20 percentage points, completing the activation.

[0012] Compared with the prior art, the present invention has the following significant advantages: the present invention adopts a Rb / Cs mixed source as an alkali source for photocathode activation, which can accurately control the component ratio of elements in the K-Cs-Rb-Sb photocathode. Since the electron affinity of Rb is higher than that of Cs, the thermal electron emission of its photocathode surface is less than that of the traditional K2CsSb photocathode, so that the prepared transmission photomultiplier tube can achieve the effect of reducing noise while maintaining high quantum efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a device structure diagram of the K-Cs-Rb-Sb transmissive tri-alkali cathode.

[0014] Figure 2 The flowchart of the method for preparing a K-Cs-Rb-Sb transmission type tri-alkali cathode in one embodiment is shown.

[0015] Figure 3 This is a graph showing the reflectivity monitoring curve of K-Cs-Rb-Sb transmissive tri-alkali cathode activation in one embodiment. DETAILED DESCRIPTION

[0016] In order to make the technical content of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The embodiments disclosed herein 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 concepts and embodiments 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 used in any appropriate combination with other aspects disclosed by the present invention.

[0017] In one embodiment, in combination Figure 1 A transmission-type three-alkali photocathode preparation system for a photomultiplier tube comprises an alkali source component 1 and an end-window type photomultiplier tube 2. The alkali source component 1 comprises an external cylindrical glass tube sleeve 11 and an internal K source 12, an Rb / Cs mixed source 13, and a pin electrode 14. A tail pipe 15 is arranged at one end of the cylindrical glass tube sleeve 11. The end-window type photomultiplier tube 2 comprises a glass shell 21, an exhaust tail pipe 22, and a valveable electrode wire 23 group. A metal Sb ball 25 and a metal Mn / Be / Mg ball 26 are arranged at the end window 24 of the end-window type photomultiplier tube 2. The metal Sb ball 25 and the metal Mn / Be / Mg ball 26 are respectively connected to the electrode wire 23. The end-window type photomultiplier tube 2 is connected to the alkali source component 1 through the exhaust tail pipe 22.

[0018] The K source 12 and the Rb / Cs mixed source 13 are each connected to the pin electrode 14 through a nickel wire to form a loop. When the cathode is activated, a certain current is applied to the K source 12 and the Rb / Cs mixed source 13 through the pin electrode 14, causing them to generate heat to release alkali metal vapor, which diffuses into the glass shell of the photomultiplier tube 2 through the exhaust tail pipe 22 and reacts with the metal Sb ball 25 therein to form an alkali antimony cathode, thereby activating the entire photomultiplier tube.

[0019] In one embodiment, in combination Figure 2 , provides a method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube, the method comprising the following steps:

[0020] Step 1: Degas the alkali source assembly 1 and the photomultiplier tube 2 at room temperature of 25°C. First, start the mechanical pump of the exhaust station and open the pre-evacuation valve. When the vacuum degree is better than 60Pa, close the pre-evacuation valve and start the molecular pump to evacuate. When the vacuum degree is better than 2×10 -4 When the molecular pump reaches 0.04 Pa, the ion pump is turned off and the vacuum treatment is performed for another 2 minutes. The temperature is raised to 280°C at a rate of 6°C / min, and then kept at 280°C for 1 hour. The heating is stopped and the temperature is lowered to about 45°C. The baking is completed.

[0021] Step 2, introduce oxygen into the vacuum system through the exhaust tail pipe 15, and close the oxygen valve until the vacuum reaches 40Pa. Use 410nm monochromatic red light to enter the photocathode from the center of the end window 24, and adjust the reflectivity monitoring curve to 100%. At a temperature of 25°C, pass a current of 20A to the Mn metal ball 26, and perform glow oxidation at the same time, monitor the reflectivity monitoring curve of the cathode surface, and the evaporation is completed after it drops by about 3 percentage points, so that the Mn sheet and oxygen fully react to form a uniform MnO anti-reflection film;

[0022] Step 3, at a temperature of 200°C to 220°C, adjust the reflectivity value to 100%, turn on the K source for the first time, set the evaporation current of the K source to 1A, increase the evaporation current of K to 3A at a rate of 0.4A / min, and then increase the evaporation current of K to 6A at a rate of 0.2A / min, so that the reflectivity monitoring curve of the cathode surface drops by about 5 percentage points, turn off the K source, and wait for 20 minutes;

[0023] Step 4, under the condition of room temperature, adjust the reflectivity value to 100%, pass 0.5A evaporation current to the metal Sb ball, increase the Sb evaporation current at a rate of 0.1A / min until the reflectivity begins to decrease, continue to increase the current value to 3A at a rate of 0.05A / min, wait for the reflectivity monitoring curve of the cathode surface to drop by about 10 percentage points, then turn off the Sb source and wait for 10 minutes;

[0024] Step 5, at a temperature of 240°C to 250°C, adjust the reflectivity value to 100%, turn on the K source for the second time, set the evaporation current of the K source to 4A, increase the K evaporation current to 6.5A at a rate of 0.4A / 3min, so that the reflectivity monitoring curve of the cathode surface rises by about 30 percentage points. If the reflectivity continues to rise, increase the K evaporation current to 7A, then turn off the K source, and wait for 20min;

[0025] Step 6, at a temperature of 300°C to 310°C, adjust the reflectivity value to 100%, turn on the Rb / Cs mixed source, and the ratio of Rb and Cs in the mixed source is 3:1. Set the evaporation current of the mixed source to 1.5A, increase the evaporation current of the mixed source to 5A at a rate of 0.2A / min, and the reflectivity monitoring curve of the cathode surface starts to rise at about 4A. If it does not rise at 4A, increase the evaporation current to 6A at a rate of 0.25A / min until it rises by about 20 percentage points, turn off the Rb / Cs mixed source, and complete the activation.

[0026] By the above method, the ratio of the element composition of the prepared photocathode can be K:Cs:Rb:Sb=2:0.25:0.75:1. The electron affinity of Rb is higher than that of Cs. Therefore, the transmission photomultiplier tube based on the photocathode has the characteristic of reducing noise without affecting the high quantum efficiency, compared with the transmission K2CsSb photomultiplier tube. In the other two embodiments, the ratio of Rb and Cs in the mixed source is set to 1:1 and 2:1 respectively, which can also achieve the characteristic of noise reduction.

[0027] The noise generated by the photomultiplier tube is mainly caused by the thermal electron emission from the photocathode surface. Since the electron affinity of Rb is higher than that of Cs, on the basis of the traditional K2CsSb cathode activation process, the Rb source is doped into the Cs source to form a certain proportion of Rb / Cs mixed source. By adjusting the ratio of Rb and Cs and improving the activation process of the cathode, the thermal electron emission from the photocathode surface can be reduced, so that the prepared transmission photomultiplier tube can achieve the effect of reducing noise while maintaining high quantum efficiency.

Claims

1. A system for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube, characterized in that: The invention comprises an alkali source component 1 and an end-window type photomultiplier tube 2, wherein the alkali source component 1 comprises an outer cylindrical glass tube sleeve 11 and an inner K source 12, an Rb / Cs mixed source 13, and a pin electrode 14, and a tail tube 15 is arranged at one end of the cylindrical glass tube sleeve 11; a metal Sb ball 25 and a metal Mn / Be / Mg ball 26 are arranged at the end window 24 of the end-window type photomultiplier tube 2, and the metal Sb ball 25 and the metal Mn / Be / Mg ball 26 are respectively connected to the electrode wire 23 The end-window type photomultiplier tube 2 is connected to the alkali source assembly 1 through the exhaust tail pipe 22, and the K source 12 and the Rb / Cs mixed source 13 are connected to the pin electrode 14 through the nickel wire to form a loop. When the cathode is activated, a certain current is applied to the K source 12 and the Rb / Cs mixed source 13 through the pin electrode 14, so that they heat themselves and release alkali metal vapor, which diffuses into the glass shell of the photomultiplier tube 2 through the exhaust tail pipe 22 and reacts with the metal Sb ball 25 therein to form an alkali antimony cathode.

2. A method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube, characterized in that: The preparation system according to claim 1 is used, and the specific steps are: Step 1, degassing, vacuumizing and baking the alkali source assembly 1 and the photomultiplier tube 2 at room temperature; Step 2, oxygen is introduced into the evacuated alkaline source assembly 1 and the photomultiplier tube 2 through the exhaust tail pipe 15, and the oxygen valve is closed until the vacuum degree reaches 40Pa; a 410nm monochromatic red light is incident on the photocathode from the end window center 24 of the photomultiplier tube 2, and the reflectivity monitoring curve is adjusted to 100%; at a temperature of 25°C, a current of 20A is introduced into the Mn metal ball 26, and glow oxidation is performed at the same time, and the reflectivity monitoring curve of the cathode surface is monitored. When it drops by about 3 percentage points, the evaporation is completed, so that the Mn sheet and oxygen fully react to form a uniform MnO anti-reflection film; Step 3, turning on the K source for the first time, causing the reflectivity monitoring curve of the cathode surface to drop by about 5 percentage points; Step 4, turning on the Sb source, causing the reflectivity monitoring curve of the cathode surface to drop by about 10 percentage points; Step 5, turning on the K source for the second time, causing the reflectivity monitoring curve of the cathode surface to rise by about 30 percentage points; Step 6, turn on the Rb / Cs mixed source, so that the reflectivity monitoring curve of the cathode surface rises by about 20 percentage points, completing the activation.

3. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: At room temperature, the specific method of degassing, vacuuming and baking the alkali source assembly 1 and the photomultiplier tube 2 is as follows: Exhaust the alkali source component 1 and the photomultiplier tube 2. When the vacuum degree is better than 60Pa, start the molecular pump to evacuate. When the vacuum degree is better than 2×10 -4 When Pa, the molecular pump was turned off and the ion pump was started, and the vacuum treatment was performed for another 2 min; Baking and heating: Heat to 280°C at a rate of 6°C / min, then bake at 280°C for 1 hour, stop heating, cool to about 45°C, and the baking is complete.

4. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The specific process of step 3 is: At a temperature of 200℃~220℃, adjust the reflectivity value to 100%, turn on the K source for the first time, set the evaporation current of the K source to 1A, increase the evaporation current of K to 3A at a rate of 0.4A / min, and then increase the evaporation current of K to 6A at a rate of 0.2A / min, so that the reflectivity monitoring curve of the cathode surface drops by about 5 percentage points, turn off the K source, and wait for 20 minutes.

5. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The specific process of step 4 is: Under room temperature conditions, adjust the reflectivity value to 100%, pass an evaporation current of 0.5 A through the metal Sb ball, increase the Sb evaporation current at a rate of 0.1 A / min until the reflectivity begins to decrease, then continue to increase the current value to 3 A at a rate of 0.05 A / min, wait for the reflectivity monitoring curve of the cathode surface to drop by about 10 percentage points, then turn off the Sb source and wait for 10 minutes.

6. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The specific process of step 5 is: At a temperature of 240℃~250℃, adjust the reflectivity value to 100%, turn on the K source for the second time, set the evaporation current of the K source to 4A, increase the K evaporation current to 6.5A at a rate of 0.4A / 3min, so that the reflectivity monitoring curve of the cathode surface rises by about 30 percentage points. If the reflectivity continues to rise, increase the K evaporation current to 7A, then turn off the K source and wait for 20 minutes.

7. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The specific process of step 6 is: At a temperature of 300°C to 310°C, adjust the reflectivity value to 100% and turn on the Rb / Cs mixed source; set the evaporation current of the mixed source to 1.5A, increase the evaporation current of the mixed source to 5A at a rate of 0.2A / min, and the reflectivity monitoring curve of the cathode surface begins to rise at around 4A. If it does not rise at 4A, increase the evaporation current to 6A at a rate of 0.25A / min until it rises by about 20 percentage points, then turn off the Rb / Cs mixed source to complete the activation.

8. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The ratio of Rb to Cs in the mixed source is 3:

1.

9. The method for preparing a transmission-type tri-alkali photocathode of a photomultiplier tube according to claim 2, characterized in that: The element composition ratio of the photocathode is K:Cs:Rb:Sb=2:x:(1-x):1, 0.25≤x≤0.75.

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