CN106855473A - A kind of method for preparing the fluid sample of carbon 14 in live graphite - Google Patents

Abstract

The invention discloses a method for preparing a carbon-14 liquid sample in radioactive graphite. The method comprises: providing a sealed reaction vessel with a tritium-containing water vapor adsorption device in the reaction vessel, so that the inner space of the reaction vessel is Divided into a first space and a second space; the first space is provided with a radioactive graphite sample, and the second space is provided with a carbon dioxide absorbing liquid; the sealed reaction vessel is filled with combustion-supporting gas to make the The air pressure in the reaction vessel reaches 1MPa-4MPa; the radioactive graphite sample is burned in the combustion-supporting gas to form tritium-containing water vapor and carbon dioxide gas in the first space; keep for a period of time to make the tritium-containing water vapor and carbon dioxide gas diffuse to the second space through the adsorption device, the tritium-containing water vapor is absorbed by the adsorption device, and the carbon dioxide gas is absorbed by the absorption liquid; the sealed reaction vessel is exhausted gas.

Description

A method for preparing a carbon-14 liquid sample in radioactive graphite

technical field

The invention relates to the technical field of nuclear industry, in particular to a method for preparing a carbon-14 liquid sample in radioactive graphite.

Background technique

A large amount of graphite materials are used in the nuclear industry, and graphite becomes radioactive after being irradiated by neutrons. In order to deal with radioactive graphite, it is necessary to establish an analytical method for the radioactivity contained in graphite, especially to accurately determine the content of carbon-14 in it. The difficulty in the analysis of carbon-14 is to prepare the carbon-14 in the solid graphite material into a liquid sample, which is convenient for subsequent analysis of carbon-14 with sophisticated radioactive analysis instruments.

At present, the "combustion-absorption method" is widely used to prepare liquid samples of carbon-14. That is, the graphite containing carbon-14 is ignited in air or oxygen and other combustion gases to convert the carbon into carbon dioxide, and then absorb the carbon dioxide with the absorbing liquid. Because radioactive graphite also contains another radionuclide - tritium. Tritium-containing water vapor will be formed during the combustion process and will also be absorbed by the absorbing liquid. Therefore, it will seriously interfere with the subsequent carbon-14 radioactivity measurement. Therefore, before absorbing the liquid, there must be a process of removing the water vapor containing tritium in the water. For example, Qiu Yongmei et al. reported the preparation method and experimental device of carbon-14 in the article Development of Experimental System for ¹⁴ C Analysis and Sample Preparation in Reactor Decommissioned Graphite (Atomic Energy Science and Technology, 2010, Vol.44(suppl.): 119-123) . The method for preparing carbon-14 samples can be summarized as follows: graphite is heated and burned in an oxygen atmosphere, the gas passes through a condensation tube and a silica gel drier to remove tritium-containing water, and a carbon-14 liquid sample is prepared through the absorption liquid in the collector. However, the method and device have the following disadvantages: (1) complex equipment, many parts, large volume, and poor integration; (2) it is difficult to achieve standardization, and most of them are temporary experimental devices, which are not conducive to large-scale production and popularization; (3) Difficult to control: too small a gas flow rate is not conducive to the complete combustion of graphite, and too high a gas flow rate is not conducive to the complete absorption of carbon dioxide gas by the absorption liquid; (4) There are many radioactive wastes: the entire pipeline will be contaminated by carbon-14 and tritium (5) There is danger in the equipment: graphite powder has a large specific surface area, and it is easy to explode when mixed with oxygen.

In order to partially solve the shortcomings of the above methods, especially for the consideration of operational safety, there is also a technology of using a high-pressure sample combustion device (oxygen bomb) to prepare carbon-14 samples. A significant difference between this type of technique and the previously described sample preparation methods is the introduction of a special sample combustion device (oxygen bomb). Specifically, the method is as follows: burning graphite and oxygen in a closed high-pressure sample combustion device to generate carbon dioxide and tritiated water vapor; then opening the valve of the combustion device to guide the combustion to generate carbon dioxide and tritiated water vapor In the device for removing water vapor and absorbing carbon dioxide provided by Qiu Yongmei et al. However, this method and device still have the following disadvantages: (1) In addition to the sample combustion device, additional devices for removing tritium-containing water vapor and absorbing carbon dioxide are required: the equipment is complex, poorly integrated, and most of them require temporary construction to remove water and absorb carbon dioxide device, which is not conducive to the popularization and use of the device. If there is no supporting device, the interference of tritium cannot be removed, and it is difficult to be used for the accurate analysis of C-14; (2) the gas release operation of the sample combustion device must be manually controlled, and the work intensity is high: the gas release operation of the sample combustion device needs to be performed according to Internal residual pressure is used to mediate a deflation valve to keep the deflation rate slow and steady. At present, this operation can only be completed by manually controlling the spiral air release valve, and the staff needs to continue to mediate for several hours, and the work intensity is very high; (3) The manual air release operation causes the absorption to be unstable, and the experimental error is large: the sample combustion device releases The gas also needs to pass slowly into the tritium water adsorption material and sodium hydroxide solution, and the passing speed has a direct impact on the absorption effect of tritium water and carbon dioxide. In particular, when the passing speed is too fast, the absorption rate will decrease, which will affect the measured carbon-14 content. However, by manually controlling the spiral deflation valve to adjust the deflation rate, the deflation rate fluctuates greatly, the absorption is unstable, the experimental error is large, and the repeatability of the results is poor.

Therefore, providing a simple and effective method for preparing liquid samples of carbon-14 in radioactive graphite has become a technical problem to be solved at present.

Contents of the invention

The invention provides a simple and effective method for preparing a carbon-14 liquid sample in radioactive graphite.

A method for preparing a carbon-14 liquid sample in radioactive graphite, the method comprising: providing a sealed reaction vessel with a tritium-containing water vapor adsorption device in the reaction vessel, thereby dividing the inner space of the reaction vessel into a first space and a second space; radioactive graphite samples are arranged in the first space, and carbon dioxide absorbing liquid is arranged in the second space; gas-supporting gas is filled into the sealed reaction vessel to make the reaction vessel The air pressure reaches 1-4MPa; the radioactive graphite sample is burned in the combustion-supporting gas to form tritium-containing water vapor and carbon dioxide gas in the first space; keep for a period of time to make the tritium-containing water vapor and carbon dioxide gas Diffusion from the adsorption device to the second space, the tritium-containing water vapor is absorbed by the adsorption device, and the carbon dioxide gas is absorbed by the absorption liquid; and exhausting the sealed reaction container.

The above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the sealed reaction vessel includes: a pressure-bearing steel cylinder, a top end cap, a sealing cap, two electrodes and a ignition wire; The end cap is inserted into the top opening of the pressure-bearing steel cylinder, and the sealing cap fixes the top end cap on the pressure-bearing steel cylinder; the two electrodes are arranged on the top end cap at intervals, and from The outside extends to the inside of the pressure-bearing steel cylinder, and one end of the two electrodes extending to the inside of the pressure-bearing steel cylinder is electrically connected through the ignition wire; the method for making the radioactive graphite sample burn in the combustion gas is to provide the The ignition wire is energized.

The above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the adsorption device includes a first gas-permeable partition, a second gas-permeable partition spaced apart from the first gas-permeable partition, and a second gas-permeable partition arranged on the The water vapor adsorption material and a rubber sealing ring between the first air-permeable partition and the second air-permeable partition.

As in the above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the inner wall of the pressure-bearing steel cylinder is cylindrical, the adsorption device is cylindrical or truncated-conical, and its side is bonded to the inner wall of the pressure-bearing steel cylinder , and rely on rubber sealing ring to achieve side wall sealing.

As in the above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the water vapor adsorption material is water-absorbing silica gel.

As in the above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein a step or a protrusion is formed on the inner wall of the pressure-bearing steel cylinder, so that the adsorption device is clamped on the step or protrusion.

The method for preparing a carbon-14 liquid sample in radioactive graphite as described above, wherein, the two electrodes and the ignition wire are arranged in the first space; the inflation and exhaust valve is arranged on the pressure-bearing steel cylinder and directly connected The second space is connected; the method of filling the sealed reaction vessel with supporting gas is to fill pure oxygen through the filling and exhaust valve.

As in the above method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the absorbing liquid is sodium hydroxide solution.

The method for preparing a carbon-14 liquid sample in radioactive graphite as described above, wherein a magnetic rotor is placed in the absorption liquid; the tritium-containing water vapor and carbon dioxide gas pass through the adsorption device to the second space The step of diffusing further includes: placing the reaction vessel on a magnetic stirring device, and driving the magnetic rotor through magnetic force to stir the absorbing liquid.

As in the above-mentioned method for preparing a carbon-14 liquid sample in radioactive graphite, wherein the time for stirring the absorption liquid is 5-10 minutes.

Compared with the prior art, the method of the present invention allows the carbon dioxide in the reacted gas to diffuse to the surface of the lye to absorb, avoiding the difficulty of manually controlling the deflation process guided by the catheter, not only reducing the work intensity, but also greatly improving the efficiency of sample preparation. Efficiency, but also reduce human experimental errors and uncertainties, and improve the reliability of the sample preparation process.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is a schematic structural diagram of an experimental device for preparing a liquid sample of carbon-14 in radioactive graphite provided by an embodiment of the present invention.

Fig. 2 is a flowchart of a method for preparing a liquid sample of carbon-14 in radioactive graphite provided by an embodiment of the present invention.

Explanation of reference numbers

experimental device 10 Pressure cylinder 101 top end cap 102 sealing cap 103 electrode 104 Ignition wire 105 Sample crucible 106 Fill and exhaust valve 107 beaker 108 absorb lye 109 Adsorption device 110 The first breathable partition 111 water vapor adsorption material 112 The second air-permeable partition 113 rubber sealing ring 114 first space 115 second space 116 Magnetic rotor 117

detailed description

The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Please refer to Fig. 1 , the experimental device 10 for preparing the liquid sample of carbon-14 in radioactive graphite provided by the embodiment of the present invention comprises: a pressure-bearing steel cylinder 101, a top end cap 102, a sealing cap 103, two electrodes 104, a point Fire wire 105 , a sample crucible 106 , a filling and exhausting valve 107 , a beaker 108 , a carbon dioxide absorbing lye 109 and a tritium-containing water vapor adsorption device 110 .

The shape and size of the pressurized steel cylinder 101 are not limited, and can be set as required. It can be understood that the pressure-bearing steel cylinder 101 can also be a container made of other metal materials that can withstand high pressure. In this embodiment, the pressure-bearing steel cylinder 101 is cylindrical, its sides and bottom are sealed, and its top is open and has threads that match the sealing cap 103 .

The top end cap 102 is used to form a sealed reaction chamber with the pressurized steel cylinder 101 that can withstand high pressure. In use, the top end cap 102 is inserted into the top opening of the pressure-bearing steel cylinder 101 .

The sealing cap 103 is used to fix the top end cap 102 on the pressure steel cylinder 101 . The structure of the sealing cover 103 can be set as required. In this embodiment, the sealing cap 103 has a screw thread matched with the top of the pressure-bearing steel cylinder 101 , and the sealing cap 103 and the top end cap 102 are integrally structured. When in use, the sealing cap 103 is fixedly connected with the pressure-bearing steel cylinder 101 by screwing, thereby pressing the top end cap 102 to ensure a good seal.

The two electrodes 104 are spaced apart on the top end cap 102 and extend from the outside to the inside of the pressure cylinder 101 . The exposed ends of the two electrodes 104 are used to connect to an external power source, and the ends extending to the inside of the pressure-bearing steel cylinder 101 are used to apply a voltage to achieve ignition. The ignition method is not limited, and may be arc discharge or the like. It can be understood that the location of the two electrodes 104 is not limited to the top end cap 102 , and can also be arranged on the pressure-bearing steel cylinder 101 , as long as they extend from the outside to the inside of the pressure-bearing steel cylinder 101 . In this embodiment, one end of the two electrodes 104 extending to the inside of the pressure cylinder 101 is electrically connected through an ignition wire 105 . When the external power supply is powered on, a circuit is formed by the two electrodes 104 and the ignition wire 105, and the ignition wire 105 will instantly ignite and fuse itself. The ignition wire 105 will ignite the graphite sample to be tested in the sample crucible 106 to make the sample burn and gasify. It can be understood that the electrode 104 and the ignition wire 105 are optional structures, and the present invention can also achieve ignition through other ignition devices or ignition methods, such as heating the entire reaction vessel.

The sample crucible 106 is set in the pressure-bearing steel cylinder 101 and is used to carry the graphite sample to be tested. The sample crucible 106 can be set on a fixing device inside the pressure cylinder 101 . In this embodiment, the sample crucible 106 is fixed on an electrode 104, and the electrode 104 is arranged on the top end cover 102, so that the sample crucible 106 can be opened while the top end cover 102 is opened. Take it out from the pressure-bearing steel cylinder 101 so as to contain the sample. It can be understood that the sample crucible 106 is not limited to a crucible, as long as it is a sample carrying device that can withstand high temperature.

The charging and exhausting valve 107 is used to fill the pressure-bearing steel cylinder 101 with combustion-supporting gas such as oxygen before combustion, and discharge the waste gas in the pressure-bearing steel cylinder 101 after the combustion and absorption are completed. The inflation and exhaust valve 107 may be arranged on the pressure-bearing steel cylinder 101 or on the top end cap 102 . Preferably, the filling and exhausting valve 107 is arranged on the pressure-bearing steel cylinder 101 and located at the back of the sample crucible 106 , so as to prevent the sample inside the sample crucible 106 from being blown away by air flow during the filling process. The filling and exhausting ports of the existing devices are usually arranged on the top end cover 102, facing the sample crucible loaded with samples. When the device is filled with oxygen, the incoming gas flow may blow the sample away. In this embodiment, the inflation and exhaust valve 107 is arranged on the side wall of the pressure-bearing steel cylinder 101 close to the bottom.

The adsorption-containing device 110 is arranged in the pressure steel cylinder 101 to divide the inner space of the pressure cylinder 101 into a first space 115 and a second space 116 . The sample crucible 106 is disposed in the first space 115 . The adsorption device 110 has a plurality of through holes, and the first space 115 and a second space 116 communicate only through the adsorption device 110 . The tritium-containing water vapor and carbon dioxide gas produced by the reaction in the first space 115 can diffuse to the second space 116 through the adsorption device 110, and the tritium-containing water vapor can be absorbed by the water in the adsorption device 110. Vapor absorbent material absorbs. The adsorption device 110 includes a first air-permeable partition 111, a second air-permeable partition 113 spaced apart from the first air-permeable partition 111, a second air-permeable partition arranged between the first air-permeable partition 111 and the second air-permeable partition. 113 between the water vapor adsorption material 112 and a rubber sealing ring 114 . Preferably, the edge of the second air-permeable partition 113 is fixed on the rubber sealing ring 114 to form a container for placing the water vapor adsorption material 112 . In this embodiment, the adsorption device 110 is in the shape of a cylinder or a truncated cone, and its side is attached to the inner wall of the pressure-bearing steel cylinder 101 , and the side wall is sealed by the rubber sealing ring 114 . A step or a protrusion (not shown) may be formed on the inner wall of the pressure-bearing steel cylinder 101, so that the adsorption device 110 can be clamped on the step or protrusion. The water vapor adsorption material 112 may be water-absorbing silica gel or the like. There are a lot of gaps when the water-absorbing silica gel and other materials are piled up, and together with the first gas-permeable partition 111 and the second gas-permeable partition 113, the gas can freely circulate between the first space 115 and a second space 116 channel.

The beaker 108 is arranged in the second space 116 inside the pressure-bearing steel cylinder 101 and is used for containing the absorption lye 109 . The absorption lye 109 is used to absorb carbon dioxide. It can be understood that the beaker 108 can also be other containers for absorbing the lye 109 . In this embodiment, the beaker 108 is arranged at the bottom of the pressure cylinder 101 . The absorption lye 109 is an aqueous sodium hydroxide solution.

Further, the beaker 108 may also include a magnetic rotor 117 . The magnetic rotor 117 is used to stir the absorption lye 109, thereby accelerating the absorption of carbon dioxide by the absorption lye 109. It can be understood that the magnetic rotor 117 is an optional structure.

It can be understood that the beaker 108, the sample crucible 106 and the carbon dioxide absorbing lye 109 are generally not produced and sold together with other components, and are only put into the experimental device 10 when preparing a liquid sample of carbon-14 in radioactive graphite, so , the beaker 108 , the sample crucible 106 and the carbon dioxide absorbing lye 109 may not be understood as a part of the experimental device 10 .

Please refer to FIG. 2 , the embodiment of the present invention further provides a method for preparing a liquid sample of carbon-14 in radioactive graphite. The method includes the following steps:

S11, providing a sealed reaction vessel, the reaction vessel has a tritium-containing water vapor adsorption device 110, thereby dividing the internal space of the reaction vessel into a first space 115 and a second space 116; the first space 115 A sample of radioactive graphite is arranged inside, and a carbon dioxide absorbing lye 109 is arranged inside the second space 116;

S12, filling the sealed reaction vessel with a gas-supporting gas such as oxygen, so that the air pressure in the reaction vessel reaches 1-4 MPa;

S13, burning the radioactive graphite sample in a combustion-supporting gas to form tritium-containing water vapor and carbon dioxide gas in the first space 115;

S14, maintain for a period of time, make the tritium-containing water vapor and carbon dioxide gas diffuse to the second space 116 through the adsorption device 110, the tritium-containing water vapor is absorbed by the adsorption device 110, and the carbon dioxide gas absorbed by the absorption lye 109; and

S15, exhausting the sealed reaction container.

It can be understood that, in the step S14, as the absorption of lye 109 absorbs carbon dioxide, the carbon dioxide in the first space 115 and the second space 116 will diffuse spontaneously, and after a certain period of time, the absorption of lye 109 in the pressure steel cylinder 101 will All carbon dioxide is completely absorbed. In the prior art, the reacted gas is discharged from the pressurized reaction vessel, and then the tritium-containing water vapor is guided through a conduit to be absorbed into the lye by the adsorption device and carbon dioxide gas. This method needs to manually adjust the flow rate to keep the flow rate small enough to avoid affecting the effect of detritium adsorption and carbon dioxide absorption. Moreover, as the air pressure in the reaction vessel gradually drops, continuous manual adjustment is required to ensure a stable flow rate. In the step S14, the absorption lye 109 may be further stirred, so as to accelerate the absorption of carbon dioxide by the absorption lye 109 .

It can be understood that the experimental device 10 and method of the present invention can not only prepare liquid samples of carbon-14 in radioactive graphite, but also can be used for any reaction to generate more than two different gases, and some gases need to be removed, and some gases need to be removed. Experiments that need to be collected.

The following are specific examples of the method for preparing a liquid sample of carbon-14 in radioactive graphite according to the present invention.

Example 1

In the present embodiment, the method for preparing a liquid sample of carbon-14 in radioactive graphite by using experimental device 10 is as follows:

(1) Open the sealing cover 103 of the experimental device 10, and take out the top end cover 102;

(2) Place the sample crucible 106 on the inner support below the top end cover 102, load the quality 0.05-0.2g radioactive graphite sample to be measured in the sample crucible 106, and connect the ignition wire 105;

(3) Put the beaker 108 equipped with a fixed volume of 5.0-20.0ml sodium hydroxide to absorb the lye 109 into the bottom of the pressure cylinder 101;

(4) according to needs, in the tritium water vapor adsorption device 110, pack an appropriate amount of silica gel water vapor adsorption material 112, put into this pressure-bearing steel cylinder 101 inside after sealing, guarantee that the inner wall of this pressure-bearing steel cylinder 101 is sealed by this adsorption device 110 around;

(5) Put back the top end cap 102, make the electrode 104, ignition wire 105, sample crucible 106, and the sample to be burned be packed in this pressure-bearing steel cylinder 101;

(6) seal the screw seal cover 103;

(7) Charge an appropriate amount of high-pressure oxygen from the filling and exhausting valve 107, so that the internal pressure of the pressurized steel cylinder 101 reaches 1MPa-4MPa;

(8) The whole experimental device 10 is placed in cold water, and leak detection ensures that the experimental device 10 is sealed;

(9) Connect the electrode 104 to an external power supply, and ignite the ignition wire 105 and the graphite sample to be burned by igniting the external power supply;

(10) After the sample combustion is completed and cooled, the experimental device 10 is placed on a magnetic stirring device, and the magnetic rotor 117 in the beaker 108 is driven by magnetic force to stir the absorption lye 109 for 5-10 minutes to promote the absorption of the lye 109 to the Absorption of carbon dioxide in gases;

(11) After the carbon dioxide is absorbed completely, the gas in the pressurized steel cylinder 101 is discharged through the filling and exhausting valve 107, without considering the discharge speed, and the deflation process can be quickly completed;

(12) Open the sealing cover 103, take out the beaker 108, and the sodium hydroxide in the beaker 108 absorbs the lye 109 as a follow-up analysis sample.

In order to detect the absorption of lye 109 in the experimental device 10 and the preparation method of the present invention to the absorption of carbon dioxide in the gas, in the present embodiment, in the process of discharging the gas in the pressurized steel cylinder 101 through the inflation and exhaust valve 107, Through the conduit, the exhausted gas is first slowly passed into the second sodium hydroxide absorption lye in another beaker, which is the second sodium hydroxide absorption lye to further absorb the carbon dioxide remaining in the gas. As a result, it was found that the carbon dioxide absorbed in the second sodium hydroxide absorption lye was almost zero. It can be seen that the absorption lye 109 in the experimental device 10 and the preparation method of the present invention can completely absorb the carbon dioxide in the pressurized steel cylinder 101 .

The invention has the following advantages: the device of the invention integrates functions such as tritium-containing water vapor absorption, carbon dioxide absorption, and sample combustion inside the pressure-bearing steel cylinder, and is easy to operate; the method of the invention makes the carbon dioxide in the reacted gas diffuse to reach the absorption base The surface of the liquid avoids the difficulty of manually controlling the deflation process guided by the catheter, which not only reduces the work intensity, greatly improves the efficiency of sample preparation, but also reduces artificial experimental errors and uncertainties, and improves the reliability of the sample preparation process .

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (10)

1. A method for preparing a carbon-14 liquid sample in radioactive graphite, the method comprising: A sealed reaction vessel is provided, and a tritium-containing water vapor adsorption device is provided in the reaction vessel, so that the internal space of the reaction vessel is divided into a first space and a second space; radioactive graphite samples are arranged in the first space, and the A carbon dioxide absorbing liquid is arranged in the second space; Fill the sealed reaction vessel with combustion-supporting gas, so that the air pressure in the reaction vessel reaches 1MPa-4MPa; Combusting the radioactive graphite sample in a combustion-supporting gas, forming tritium-containing water vapor and carbon dioxide gas in the first space; Keeping for a period of time, the tritium-containing water vapor and carbon dioxide gas diffuse to the second space through the adsorption device, the tritium-containing water vapor is absorbed by the adsorption device, and the carbon dioxide gas is absorbed by the absorption liquid absorb; The sealed reaction vessel was vented. 2. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 1, is characterized in that, described sealed reaction vessel comprises: pressure-bearing steel cylinder, top end cap, sealing cap, two electrodes and ignition wire The top end cap is inserted into the top opening of the pressure-bearing steel cylinder, and the sealing cap fixes the top end cap on the pressure-bearing steel cylinder; the two electrodes are arranged at intervals on the top end cap , and extend from the outside to the inside of the pressure-bearing steel cylinder, the two electrodes extend to the inside of the pressure-bearing steel cylinder, and are electrically connected through the ignition wire; the method for burning the radioactive graphite sample in the combustion gas is as follows: Apply power to the ignition wire. 3. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 2, is characterized in that, described adsorption device comprises the first air-permeable dividing plate, the second air-permeable dividing plate that is arranged at intervals with this first air-permeable dividing plate The board, the water vapor adsorption material and the rubber sealing ring arranged between the first air-permeable partition and the second air-permeable partition. 4. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 3, is characterized in that, the inner wall of described pressure-bearing steel cylinder is cylindrical, and described adsorption device is cylindrical or truncated cone, and its side and described The inner wall of the above-mentioned pressure-bearing steel cylinder is fitted, and the side wall is sealed by the rubber sealing ring. 5. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 3, is characterized in that, described water vapor adsorption material is water-absorbing silica gel. 6. The method for preparing a carbon-14 liquid sample in radioactive graphite as claimed in claim 2, wherein a step or a protrusion is formed on the inner wall of the pressure-bearing steel cylinder, so that the adsorption device is fixed on the inner wall of the pressurized steel cylinder. Steps or bumps. 7. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 2, is characterized in that, described two electrodes and ignition wire are arranged in described first space; The pressure-bearing steel cylinder is directly connected with the second space; the method of filling the sealed reaction vessel with combustion-supporting gas is to fill with pure oxygen through the filling and exhaust valve. 8. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 1, is characterized in that, described absorption liquid is sodium hydroxide solution. 9. the method for preparing carbon-14 liquid sample in radioactive graphite as claimed in claim 1 is characterized in that, a magnetic rotor is placed in the described absorbing liquid; The described tritium-containing water vapor and carbon dioxide gas are passed through the The step of diffusing the adsorption device into the second space further includes: placing the reaction vessel on a magnetic stirring device, and driving the magnetic rotor through magnetic force to stir the absorption liquid. 10. The method for preparing a carbon-14 liquid sample in radioactive graphite as claimed in claim 9, characterized in that the time for stirring the absorbing liquid is 5-10 minutes.