CN111276378A - High-sensitivity K-Na-Cs-Sb reflective multi-alkali photoelectric cathode and preparation method and system thereof - Google Patents
High-sensitivity K-Na-Cs-Sb reflective multi-alkali photoelectric cathode and preparation method and system thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of photomultiplier tubes, particularly relates to a photocathode, and discloses a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode and a preparation method and a system thereof, wherein an alkali source component comprises three alkali sources, namely a K source, a Na source and a Cs source; the alkali source assembly is connected with the exhaust platform through a tail pipe to obtain ultrahigh vacuum degree; the side window type photomultiplier comprises a glass shell, a cathode and a plurality of dynodes, wherein the cathode and the dynodes are constructed into metal sheets with certain radian, and the inner surfaces of the cathode and the dynodes are plated with metal antimony layers; the side window type photomultiplier is connected to the alkali source assembly through a tail pipe; current is applied corresponding to the alkali source to make the alkali source self-heat, and alkali metal steam is released to react with the antimony layer to form a multi-alkali cathode structure. The introduction process of K, Na and Cs is monitored by monitoring the change of leakage current and photocurrent, so that the introduction amount of K, Na and Cs is accurately controlled, and the problem of low cathode sensitivity caused by excessive or insufficient introduction of K, Na and Cs is avoided.
Description
Technical Field
The invention belongs to the technical field of photocathodes, and particularly relates to a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode for a side window type photomultiplier and a preparation method thereof.
Background
A photocathode, particularly a photocathode used in a vacuum optoelectronic device such as a photomultiplier, is a device for capturing photons incident from the outside and exciting photoelectrons based on an external photoelectric effect. In vacuum photoelectric devices such as photomultiplier tubes, radiation signals with different wavelengths are converted into electric signals, which are realized by means of photocathodes. The common photocathode mainly comprises a double-alkali cathode and a multi-alkali cathode and is applied to the same type of whole tube.
The reflecting type multi-alkali photocathode is a photoelectric emission material which is commonly applied to a side window type photomultiplier and can convert photons into photoelectrons and finally output the photoelectrons in the form of electric signals or images. The side window type photomultiplier is a photoelectric detector widely applied to the fields of biological medicine, spectral analysis, environmental monitoring and the like, and the cathode sensitivity is a key index of the side window type photomultiplier. Usually, the multi-alkali photocathode adopts a K-Na-Cs-Sb multi-alkali cathode structure, wherein the more Na and K are close to 2:1, the more excellent the cathode structure is, the higher the sensitivity is, and the higher the corresponding photoelectric current is.
At present, the sensitivity of the reflective multi-alkali cathode is generally improved by controlling the preparation process in the prior art, for example, three stages of monitoring the photocurrent of the cathode preparation process and guiding K, Na and Cs are respectively required to maximize the photocurrent, so that the cathode Na: K is closer to 2:1, and the optimal cathode structure and the maximum sensitivity are obtained.
However, in the actual cathode manufacturing process, the photocurrent in the K-pulling process is usually small, and it is difficult to monitor the photocurrent. In addition, during the process of introducing Na, Na and K are added3Sb reacts relatively slowly so we see little or no significant change in photocurrent during Na incorporation. The Cs process, likewise, gives very little photocurrent. Therefore, in the experimental stage, the control of three stages of guiding K, Na and Cs is realized through monitoring the photocurrent and the reflectivity so as to control the evaporation of the film layer, but in the mass production process, the fact that the photocurrent is extremely small and the change is not obvious, particularly the photocurrent is extremely small in the process of guiding Cs and K, and the process of guiding Na is difficult to accurately monitor the activation process of the reflective multi-alkali cathode K, Na and Cs through the photocurrent in the batch production process due to the slow reaction is found, and even in the partial activation stage, the photocurrent monitoring can be completely disabled, so that the monitoring effect cannot be realized. This results in a cathode made using photo-monitoring, which is less sensitive or even non-sensitive.
Disclosure of Invention
The invention aims to provide a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photoelectric cathode, a preparation method and a system thereof.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation system of a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode comprises a side window type photomultiplier and an alkali source component, wherein:
the alkali source assembly comprises a cylindrical glass pipe sleeve, three alkali sources, namely a K source, an Na source and a Cs source, are arranged in the cylindrical glass pipe sleeve, the three alkalis are respectively connected with a pin electrode of the alkali source through a nickel wire to form a circuit loop, a certain current is applied to the corresponding alkali source through the pin electrode to enable the alkali source to generate heat, and a multi-alkali cathode structure is formed through released alkali metal steam;
the alkali source assembly is connected with the exhaust platform through a tail pipe so as to obtain ultrahigh vacuum degree;
the side window type photomultiplier comprises a glass shell and a core column, wherein the core column comprises an exhaust tail pipe and a valve electrode wire, a mesh electrode, a cathode, a plurality of dynodes, an anode and a baffle are arranged inside the side window type photomultiplier, the cathode and the dynodes are constructed into metal sheets with certain radian, and the inner surfaces of the cathode and the dynodes are plated with metal antimony layers; the mesh electrode, the cathode, the multiple dynodes, the anode and the baffle plate are fixed and supported in a cylindrical cavity of the glass shell through the first ceramic piece and the second ceramic piece;
the side window type photomultiplier is connected to the alkali source assembly through a tail pipe;
in the process of preparing the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode, certain currents are respectively conducted to a K source, a Na source and a Cs source to trigger the K source, the Na source and the Cs source to release corresponding alkali metal steam, the alkali metal steam enters the glass shell of the side window type photomultiplier through an exhaust tail pipe and reacts with a metal antimony layer on a cathode and a multiplier to form an antimony-alkali photocathode, and therefore the whole photomultiplier is activated;
in the process of alkali metal vapor reaction, the introduction process of K, Na and Cs in the process is monitored by monitoring the change of leakage current and photocurrent, and the introduction amount of K, Na and Cs is controlled.
The invention also provides a preparation method of the high-sensitivity K-Na-Cs-Sb reflection type multi-alkali photoelectric cathode realized according to the preparation system, which comprises the following steps:
step 1, vacuum baking, exhausting and wiring;
step 2, activating a cathode;
step 3, leakage current monitoring K activation stage;
step 4, monitoring Na activation stage by leakage current;
and 5, monitoring the Cs activation process by leakage current.
Wherein, the cathode activation process of the step 2 comprises the following steps:
and starting heating, raising the temperature to more than 200 ℃, monitoring the change of the leakage current along with the temperature, gradually raising the leakage current from 0.1nA to more than 10-20 nA along with the temperature rise, and judging that the temperature in the side window type photomultiplier reaches balance when the leakage current is stabilized to 30-40 nA.
Wherein, the leakage current monitoring K activation phase of the step 3 comprises:
4.8-7A of current is conducted to a K source, the K source generates heat to react and release K steam, and the K steam enters a side window type photomultiplier from an alkali source assembly and reacts with antimony on a cathode and a plurality of dynodes to form an antimony potassium compound; when the amplitude inflection point of the monitored leakage current occurs, cutting off the K source current, stopping introducing K, and completely reacting Sb with K to form K3A Sb structure;
wherein, the leakage current monitoring Na activation phase of the step 4 comprises:
after the K activation stage is finished, heating to over 220 ℃, and then supplying 4.8-6.5A of current to the Na source when the leakage current is stabilized at 30-40 nA; wherein, in the process of Na activation, a small amount of Na introduction modes which are repeated and gradually reduced are adopted, namely, a small amount of Na is introduced each time, and Na and K are reacted3After the Sb reaction is consumed, carrying out the next Na introduction operation, wherein the specific operations comprise:
the Na source is electrified with 4.8-6.5A current to release Na vapor and K3And (4) reacting Sb, rapidly increasing the electric leakage to 60-150 nA, continuously introducing Na for 5-7 min, turning off a power supply of the Na alkali source, and stopping introducing Na.
Keeping the baking at a high temperature of more than 220 ℃ for continuous baking, and reducing the current to initial 30-40nA when the reduction amplitude of the leakage current at one inflection point is more than 15 nA/min;
repeating the above method for many times to activate Na, and determining Na consumption by using leakage current; when the color of the cathode changes from green to blue, and the photocurrent is monitored to reach the maximum peak value in the stage, Na is stopped.
Wherein the leakage current monitoring Cs activation phase of step 5 includes:
after the Na activation stage is completed, cooling to a value below 220 ℃, enabling 4.8-6.5A of current to a Cs source, enabling leakage current to rise by 8-30 muA rapidly, enabling the photocurrent to be almost 0, continuously guiding Cs for 15-20 min, and then closing the Cs source; the leakage current begins to drop, the photocurrent rises, and when the leakage current is reduced by 50-60nA, the photoelectricity rises back to the maximum value;
and repeating the operations for 2-3 times, so that the photocurrent reaches the maximum peak value of the stage, and the Cs activation is completed.
The sensitivity of the K-Na-Cs-Sb reflective multi-alkali cathode used by the side window type photomultiplier determines the photoelectric detection performance of the side window type photomultiplier. In order to improve the sensitivity and the long-wave response capability of the reflective multi-alkali cathode, a traditional method generally adopts a method of monitoring the photocurrent produced by the cathode in real time, so that the maximum photocurrent of each process of K, Na and Cs produced by the cathode is obtained, and the maximum cathode sensitivity is obtained.
However, in the actual cathode manufacturing process, when K, Na and Cs are introduced, the photocurrent is very small or even no photocurrent, which results in failure of photocurrent monitoring polybase cathode manufacturing, and cannot realize precise control of K, Na and Cs, and an optimal cathode structure cannot be obtained, thus resulting in lower cathode sensitivity and poorer long-wave response. Particularly in the Na introduction process, the reaction of Na and K3Sb is slow, and the photocurrent hardly changes in the early process of Na introduction. At this time, the amount of Na introduced cannot be monitored by photocurrent, and excessive Na introduction is easily caused, resulting in extremely low cathode sensitivity and even no performance.
Therefore, the scheme of the invention provides a method for manufacturing a reflective multi-alkali cathode based on leakage current monitoring, which is based on monitoring leakage current of a multi-alkali cathode in an alkali metal activation process, combines photocurrent and cathode color, realizes accurate control of K, Na and Cs introduction amount in the cathode activation process, enables the cathode to form an optimal chemical structure, improves the sensitivity of the K-Na-Cs-Sb reflective multi-alkali cathode, and widens the long-wave response range of the K-Na-Cs-Sb reflective multi-alkali cathode.
Drawings
The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral.
FIG. 1 shows the device structure of K-Na-Cs-Sb reflective multi-alkali cathode.
FIG. 2 is a cross-sectional view of the side window photomultiplier tube taken along position A in FIG. 1.
Fig. 3 is a spectral response curve of a polybase cathode made using different monitoring means.
Detailed Description
In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.
In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.
Referring to fig. 1 and 2, an exemplary embodiment of the present invention provides a system for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode, which includes two parts, namely a side window type photomultiplier and an alkali source assembly.
The alkali source component comprises a cylindrical glass pipe sleeve 24, three alkali sources, namely a K source 231, an Na source 233 and a Cs source 232 are arranged in the cylindrical glass pipe sleeve 24, the three alkalis are respectively connected with a pin electrode 22 of the alkali source through nickel wires to form a circuit loop, a certain current is applied to the corresponding alkali source through the pin electrode 22 to enable the alkali source to generate heat, and a multi-alkali cathode structure is formed through released alkali metal steam.
The alkali source assembly is connected to the exhaust station through a tail pipe 21 to achieve ultra-high vacuum. Preferably, the vacuum degree inside the alkali source assembly reaches 5X 10-4Pa。
The side window type photomultiplier comprises a glass housing 12, a stem 11, the stem comprises a tail pipe 111 and a valve wire 112, a mesh electrode 14, a cathode (16), a plurality of dynodes 151-159, an anode 18 and a baffle 17 are arranged inside the side window type photomultiplier, wherein the cathode 16 and the dynodes 151-159 are constructed as a metal sheet with a certain radian, and the inner surface of the cathode is plated with a metal antimony layer. Preferably, the cathode 16 and the plurality of dynodes 151-159 are all metal nickel sheets with certain radian.
The mesh electrode 14, the cathode (16), the plurality of dynodes 151 to 159, the anode 18 and the baffle 17 are fixed and supported in the cylindrical cavity of the glass housing 12 by the first ceramic sheet 131 and the second ceramic sheet 132.
The side window photomultiplier is connected to the base supply assembly through a tail pipe 111.
In the process of preparing the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode, certain currents are respectively conducted to the K source 231, the Na source 233 and the Cs source 232 to trigger the K source 231, the Na source 233 and the Cs source 232 to release corresponding alkali metal vapor, the alkali metal vapor enters the glass shell of the side window type photomultiplier through the exhaust tail pipe and reacts with the metal antimony layers on the cathode 16 and the dynodes 151-159 to form an antimony-alkali photocathode, and therefore the whole photomultiplier is activated.
Particularly, in the alkali metal vapor reaction process, the introduction process of K, Na and Cs in the process is monitored by monitoring the change of leakage current and photocurrent, and the introduction amount of K, Na and Cs is controlled.
Referring to fig. 1, in the monitoring process of the change of the leakage current and the photocurrent, a positive voltage of 100V is applied with the cathode 16 of the side window type photomultiplier as a cathode and the first dynode 151 of the plurality of dynodes 151 to 159 as an anode; the leakage current and the photocurrent are collected through the micro-current meter, wherein when the lamp is turned off, the display value of the micro-current meter is a dark current value, when the lamp is turned on, the display value of the micro-current meter is a dark current value and a photocurrent value, and the difference value displayed by the micro-current meter before and after the lamp is turned on is used as the monitored photocurrent value.
The preparation process of the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode of the invention is described in more detail below with reference to FIGS. 1 and 2.
Vacuum baking exhaust
Starting the exhaust table, vacuumizing until the vacuum degree reaches 1 × 10-3And when Pa is needed, starting heating, raising the temperature to 260 ℃ at the rate of 5 ℃/min, keeping the temperature, baking for 2h, and naturally cooling to room temperature.
Wire connection
And connecting external power supply lines corresponding to the K source 231, the Na source 233 and the Cs source 232, wherein the power supply is a direct current power supply.
And then connected with a monitoring line for monitoring leakage current and photocurrent, wherein the anode of the power supply is connected with a first dynode 151, namely a first-stage dynode, and the cathode of the power supply is connected with a cathode 16 of the photomultiplier.
Cathode activation
And starting heating, raising the temperature to more than 200 ℃, monitoring the change of the leakage current along with the temperature, gradually raising the leakage current from 0.1nA to more than 10-20 nA along with the temperature rise, and judging that the temperature in the side window type photomultiplier reaches balance when the leakage current is stabilized to 30-40 nA.
Leakage current monitoring K activation phase
4.8-7A of current is conducted to a K source, the K source generates heat to react and release K steam, and the K steam enters a side window type photomultiplier from an alkali source assembly and reacts with antimony on a cathode and a plurality of dynodes to form an antimony potassium compound; when the amplitude inflection point of the monitored leakage current occurs, cutting off the K source current, stopping introducing K, and completely reacting Sb with K to form K3And (5) an Sb structure.
In the implementation process of the invention, when Sb is not completely reacted by K, K can be continuously absorbed by Sb to react to form an antimony potassium compound, and the electric leakage cannot obviously swell. When Sb is completely reacted by K, K is not absorbed any more, and the concentration of K vapor in the photomultiplier tube suddenly rises, so that the electric conduction between the cathode and the first multiplier is enhanced, and the leakage current also rises at a voltage of 100V.
Therefore, whether the antimony and the potassium completely react in the K activation stage and form stable K is judged by leakage current3And (5) Sb. Therefore, we determined that stable K is formed when monitoring the inflection point of the amplitude of the leakage current3Sb, the K source current is quickly cut off.
Leakage current monitoring Na activation phase
After the K activation stage is finished, heating to over 220 ℃, and then supplying 4.8-6.5A of current to the Na source when the leakage current is stabilized at 30-40 nA; wherein, in the process of Na activation, a small amount of Na introduction modes which are repeated and gradually reduced are adopted, namely, a small amount of Na is introduced each time, and Na and K are reacted3After the Sb reaction is consumed, carrying out the next Na introduction operation, wherein the specific operations comprise:
the Na source is electrified with 4.8-6.5A current to release Na vapor and K3And (4) reacting Sb, rapidly increasing the electric leakage to 60-150 nA, continuously introducing Na for 5-7 min, turning off a power supply of the Na alkali source, and stopping introducing Na.
Keeping the baking at a high temperature of more than 220 ℃ for continuous baking, and reducing the current to initial 30-40nA when the reduction amplitude of the leakage current at one inflection point is more than 15 nA/min;
repeating the above method for many times to activate Na, and determining Na consumption by using leakage current; when the color of the cathode changes from green to blue, and the photocurrent is monitored to reach the maximum peak value in the stage, Na is stopped.
In the embodiment of the invention, the Na feeding amount needs to be accurately controlled, and the Na introducing principle of 'small amount and multiple times, gradual reduction' is adopted, namely, a small amount of Na is introduced each time, and Na to be reacted is K times that of K3After the Sb reaction is consumed, Na is introduced. Determination of introduced Na and K3The Sb reaction is very important when the Na is consumed, and if the Na is introduced for the second time when the Na is not consumed, the Na is easily excessive, so that the cathode has low sensitivity or no performance.
In the Na activation process, Na enters the whole photomultiplier and can be adsorbed on the tube shell and the nickel sheet, after Na introduction is stopped, the Na which is adsorbed is slowly desorbed, the desorbed Na is reacted by K3Sb again to form dynamic balance, the Na vapor concentration of the cavity is relatively stable, and the leakage current is stable. When the Na of the whole tube is consumed, the Na vapor concentration in the cavity can be instantly and rapidly reduced, and the leakage current can be rapidly reduced. Therefore, the invention adopts electric leakage to monitor the Na reaction consumption degree in the Na guiding process, and realizes the accurate control of the Na activation process.
Leakage current monitoring Cs activation phase
After the Na activation stage is completed, cooling to a value below 220 ℃, enabling 4.8-6.5A of current to a Cs source, enabling leakage current to rise by 8-30 muA rapidly, enabling the photocurrent to be almost 0, continuously guiding Cs for 15-20 min, and then closing the Cs source; the leakage current begins to drop, the photocurrent rises, and when the leakage current is reduced by 50-60nA, the photoelectricity rises back to the maximum value;
and repeating the operations for 2-3 times, so that the photocurrent reaches the maximum peak value of the stage, and the Cs activation is completed.
Therefore, the K, Na and Cs activation process of the reflection type multi-alkali cathode is monitored by adopting electric leakage, so that the accurate control of K, Na and Cs is realized, the accurate control of Na is particularly realized, the cathode can obtain the optimal Na/K ratio, and the sensitivity and the long-wave response of the multi-alkali cathode are improved.
As shown in fig. 3, the test of the cathode manufactured by leakage current monitoring shows that the quantum efficiency of each wavelength is higher than that of the photocathode manufactured by monitoring only photocurrent and reflectivity in the conventional scheme, and the cut-off wavelength of the response is longer, so that the obtained sensitivity is obviously high.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.
Claims (11)
1. A preparation system of a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode is characterized by comprising a side window type photomultiplier and an alkali source component, wherein:
the alkali source assembly comprises a cylindrical glass pipe sleeve (24), three alkali sources, namely a K source (231), an Na source (233) and a Cs source (232), are arranged in the cylindrical glass pipe sleeve (24), the three alkalis are respectively connected with a pin electrode (22) of the alkali source through a nickel wire to form a circuit loop, a certain current is applied to the corresponding alkali source through the pin electrode (22) to enable the alkali source to heat, and a multi-alkali cathode structure is formed through released alkali metal steam;
the alkali source assembly is connected with the exhaust platform through a tail pipe (21) to obtain ultrahigh vacuum degree;
the side window type photomultiplier comprises a glass shell (12), a stem (11), wherein the stem comprises a tail pipe (111) and a valve electrode wire (112), a mesh electrode (14), a cathode (16) and a plurality of dynodes (151-159), an anode (18) and a baffle plate (17) are arranged inside the side window type photomultiplier, the cathode (16) and the plurality of dynodes (151-159) are constructed into a metal sheet with a certain radian, and the inner surface of the cathode (16) and the plurality of dynodes (151-159) is plated with a metal antimony layer; the mesh electrode (14), the cathode (16), the multiple dynodes (151-159), the anode (18) and the baffle plate (17) are fixed and supported in a cylindrical cavity of the glass shell (12) through a first ceramic piece (131) and a second ceramic piece (132);
the side window type photomultiplier is connected to the alkali source assembly through a tail pipe (111);
in the process of preparing the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode, certain currents are respectively conducted to a K source (231), a Na source (233) and a Cs source (232) to trigger the K source (231), the Na source (233) and the Cs source (232) to release corresponding alkali metal vapor, the alkali metal vapor enters the glass shell of the side window type photomultiplier through an exhaust tail pipe and reacts with metal antimony layers on a cathode (16) and dynodes (151-159) to form an antimony alkali photocathode, and therefore the whole photomultiplier is activated;
in the process of alkali metal vapor reaction, the introduction process of K, Na and Cs in the process is monitored by monitoring the change of leakage current and photocurrent, and the introduction amount of K, Na and Cs is controlled.
2. The system for preparing the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 1, wherein the cathode (16) and the plurality of dynodes (151-159) are all metal nickel sheets with certain radian.
3. The system for preparing the high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 1, wherein the degree of vacuum inside the alkali source assembly reaches 5 x 10-4Pa。
4. The system for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 1, wherein a positive voltage of 100V is applied to monitor the change of leakage current and photocurrent by using a cathode (16) of a side window type photomultiplier as a cathode and a first dynode (151) of a plurality of dynodes (151 to 159) as an anode; the leakage current and the photocurrent are collected through the micro-current meter, wherein when the lamp is turned off, the display value of the micro-current meter is a dark current value, when the lamp is turned on, the display value of the micro-current meter is a dark current value and a photocurrent value, and the difference value displayed by the micro-current meter before and after the lamp is turned on is used as the monitored photocurrent value.
5. A method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode implemented by the preparation system according to any one of the preceding claims 1 to 4, comprising the steps of:
step 1, vacuum baking, exhausting and wiring;
step 2, activating a cathode;
step 3, leakage current monitoring K activation stage;
step 4, monitoring Na activation stage by leakage current;
and 5, monitoring the Cs activation process by leakage current.
6. The method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 5, wherein the process of step 1 comprises:
carrying out vacuum baking and exhausting on the alkali source assembly: vacuumizing until the vacuum degree reaches 1 × 10-3When Pa is needed, starting heating, raising the temperature to 260 ℃ at the rate of 5 ℃/min, keeping the temperature, baking for 2h, and naturally cooling to room temperature;
conducting wire connection: external power supply lines corresponding to the K source (231), the Na source (233) and the Cs source (232) are connected, and the power supply is a direct-current power supply; then, a monitoring line for monitoring leakage current and photocurrent is connected, the positive pole of a power supply is connected with a first dynode (151), namely a first-stage dynode, and the negative pole is connected with a cathode (16) of the photomultiplier.
7. The method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 5, wherein the cathode activation process of step 2 comprises:
and starting heating, raising the temperature to more than 200 ℃, monitoring the change of the leakage current along with the temperature, gradually raising the leakage current from 0.1nA to more than 10-20 nA along with the temperature rise, and judging that the temperature in the side window type photomultiplier reaches balance when the leakage current is stabilized to 30-40 nA.
8. The method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 5, wherein the leakage current monitoring K activation stage of step 3 comprises:
4.8-7A of current is conducted to a K source, the K source generates heat to react and release K steam, and the K steam enters a side window type photomultiplier from an alkali source assembly and reacts with antimony on a cathode and a plurality of dynodes to form an antimony potassium compound; when the amplitude inflection point of the monitored leakage current occurs, cutting off the K source current, stopping introducing K, and completely reacting Sb with K to form K3And (5) an Sb structure.
9. The method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 5, wherein the leakage current monitoring Na activation stage of step 4 comprises:
after the K activation stage is completedHeating to above 220 ℃, and then supplying 4.8-6.5A of current to the Na source when the leakage current is stabilized at 30-40 nA; wherein, in the process of Na activation, a small amount of Na introduction modes which are repeated and gradually reduced are adopted, namely, a small amount of Na is introduced each time, and Na and K are reacted3After the Sb reaction is consumed, carrying out the next Na introduction operation, wherein the specific operations comprise:
the Na source is electrified with 4.8-6.5A current to release Na vapor and K3And (4) reacting Sb, rapidly increasing the electric leakage to 60-150 nA, continuously introducing Na for 5-7 min, turning off a power supply of the Na alkali source, and stopping introducing Na.
Keeping the baking at a high temperature of more than 220 ℃ for continuous baking, and reducing the current to initial 30-40nA when the reduction amplitude of the leakage current at one inflection point is more than 15 nA/min;
repeating the above method for many times to activate Na, and determining Na consumption by using leakage current; when the color of the cathode changes from green to blue, and the photocurrent is monitored to reach the maximum peak value in the stage, Na is stopped.
10. The method for preparing a high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode according to claim 5, wherein the leakage current monitoring Cs activation stage of step 5 comprises:
after the Na activation stage is completed, cooling to a value below 220 ℃, enabling 4.8-6.5A of current to a Cs source, enabling leakage current to rise by 8-30 muA rapidly, enabling the photocurrent to be almost 0, continuously guiding Cs for 15-20 min, and then closing the Cs source; the leakage current begins to drop, the photocurrent rises, and when the leakage current is reduced by 50-60nA, the photoelectricity rises back to the maximum value;
and repeating the operations for 2-3 times, so that the photocurrent reaches the maximum peak value of the stage, and the Cs activation is completed.
11. A high-sensitivity K-Na-Cs-Sb reflective multi-alkali photocathode prepared by the method of any one of claims 5-10.
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