Low-vacuum online graphitization system for determining 14C helium protection atmosphere by accelerator mass spectrometry

Abstract

The invention relates to a low-vacuum online graphitization system for 14C helium protection atmosphere determination by accelerator mass spectrometry, which belongs to the field of preparation of 14C graphite determination by AMS, and comprises a He source and purification assembly, a sample injection and combustion assembly, a gas flow rate adjusting and monitoring assembly, a CO2 chemical purification assembly, a CO2 physical purification trapping and graphitization assembly and a vacuum degree control assembly. The He source and purification assembly provides ultra-pure He gas as pipeline purge gas, carrier gas and graphitization shielding gas. The sample injection and combustion assembly efficiently and thoroughly converts solid organic carbon into CO2 gas. The gas flow rate adjusting and monitoring assembly adjusts and monitors the pipeline gas flow rate. And the CO2 chemical purification assembly is used for removing water vapor in the mixed gas. CO2 is further purified and graphitized by the CO2 physical purification and capture and graphitization assembly. The vacuum degree control assembly adjusts the flow rate of the purge gas and controls the internal pressure of the reduction unit. According to the invention, the carbon element in the solid sample can be efficiently converted into graphite with high quality.

Description

Technical Field

[0001] This invention relates to accelerator mass spectrometry (AMS) determination. In the field of graphite preparation, this invention relates in particular to an online graphitization system made of stainless steel based on a helium protective atmosphere and a low vacuum environment, which is used to efficiently and with high quality convert carbon elements in various solid samples into graphite. Background Technology

[0002] Its abundance in nature is approximately .natural Primarily originates from secondary neutrons in cosmic rays and from the upper atmosphere. Interatomic nuclear reactions, newly formed It will oxidize rapidly into And it is transported to the Earth's surface to participate in the global carbon cycle. It will spontaneously undergo radioactive decay reaction to transform into Its half-life is 5730±30 years.

[0003] Accelerator mass spectrometry (AMS) integrates accelerator technology, nuclear detection technology, and conventional mass spectrometry technology, enabling direct analysis of samples. , and Atoms are counted individually to calculate their concentration ratios, eliminating reliance on radioactive decay processes, requiring small sample volumes, and offering rapid measurement speeds. Furthermore, accelerator mass spectrometry effectively eliminates background interference from molecules and isotopes, exhibiting extremely high isotope abundance sensitivity (up to [missing information - likely a percentage]). ), is currently the measurement The most sensitive and accurate technique. Accelerator mass spectrometry typically requires preparing the sample into a graphite target using a catalytic reduction method. Analysis shows that this method requires first converting the original sample into a chemical form. This method achieves the separation of carbon from complex matrices, followed by purification, quantification, and catalytic reduction to prepare graphite within a high-vacuum graphitization system. The high-vacuum environment not only effectively reduces the risk of carbon contamination but also provides stable reaction conditions, facilitating the acquisition of graphite products with uniform composition and excellent performance. Currently, high-vacuum graphitization systems face the following challenges: 1. The high-vacuum environment places extremely high demands on the vacuum performance of the graphitization system, leading to high system costs and complex maintenance; 2. AMS... 1. Most of the high-vacuum graphitization systems built in laboratories are made of glass, which is easily broken; 2. Current high-vacuum graphitization systems cannot effectively prevent airborne particles from entering the system. Penetration into the interior of the graphitization system, causing Pollution. Summary of the Invention

[0004] The purpose of this invention is to solve the problem in the prior art where the high vacuum environment places extremely high demands on the vacuum performance of the graphitization system, leading to high system costs and complex maintenance. Simultaneously, it addresses the issue of excessive pressure differences between the inside and outside of the reaction system, and atmospheric... To address the risks of contamination seeping into the graphitization system and the fragility of the glass system, this invention provides an accelerator mass spectrometry method. Helium-protected atmosphere low-vacuum online graphitization system.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An accelerator mass spectrometry method A helium-protected atmosphere low-vacuum online graphitization system. This system constructs a helium-protected atmosphere and low-vacuum co-operating environment within a stainless steel sealed pipeline. It includes a helium source and purification assembly, a sample injection and combustion assembly, and a gas flow rate regulation and monitoring assembly connected in sequence. Chemical purification components Physical purification, collection, and graphitization components, as well as vacuum control components;

[0007] The helium source and purification components are used to provide ultrapure helium and serve as pipeline purging gas, carrier gas, and protective gas for graphitization reaction.

[0008] The sample introduction and combustion assembly is used to achieve automatic sample introduction and convert solid organic carbon into combustion. gas;

[0009] The gas flow rate regulation and monitoring component is used to regulate and monitor the gas flow rate in the pipeline;

[0010] The Chemical purification components are used to remove Water vapor in the gas mixture;

[0011] The Physical purification, trapping, and graphitization components are used for... Further purification and catalytic reduction to graphite;

[0012] The vacuum control component is used to adjust the gas flow rate during pipeline purging and control the helium pressure inside the reduction unit.

[0013] The The physical purification, collection, and graphitization components are connected to each other via two five-way valves. The chemical purification component and the vacuum control component are connected, and the entire pipeline is configured with four lines, each line having two reduction units, enabling the system to carry out eight graphitization reactions simultaneously.

[0014] The helium source and purification components include a helium cylinder, a U-shaped trap, and a liquid nitrogen tank. The U-shaped trap is submerged below the liquid nitrogen tank and is filled with 5A molecular sieves to freeze and adsorb impurity gases, especially trace amounts, from the helium. and These two gases can significantly interfere with subsequent reactions.

[0015] The sample introduction and combustion assembly includes a zero-background autosampler and a high-temperature oxidation furnace. The zero-background autosampler is equipped with a 40-position autosampler tray for sequentially feeding tin boat balls containing the sample and the combustion aid vanadium pentoxide into the high-temperature oxidation furnace. The high-temperature oxidation furnace can provide a maximum temperature of 1100°C and is equipped with a combustion tube. Inside the combustion tube, from top to bottom, are arranged an ash collection tube, reduced copper, chromium oxide, and silver-plated cobalt oxide, with each layer separated by quartz wool. The ash collection tube collects combustion residues (tin cups after high-temperature sintering and other residual ash), the reduced copper consumes the oxygen released from the high-temperature combustion and decomposition of the combustion aid vanadium pentoxide, and the chromium oxide further oxidizes incompletely burned carbon. Silver-plated cobalt oxide is used to remove halogen impurities such as chlorine. Therefore, this component can automatically introduce samples and efficiently and completely convert solid organic carbon into solid organic carbon through a high-temperature oxidation reaction. gas.

[0016] The gas flow rate regulation and monitoring component includes a gas flow rate control valve and a flow meter. The flow meter is used to monitor the gas flow rate in the pipeline. The gas flow rate control valve is used to adjust the gas flow rate according to the monitoring results to ensure that the gas in the pipeline flows through the reduction unit at a lower flow rate, which is beneficial. Complete capture.

[0017] The The chemical purification component is a magnesium perchlorate dehydration pipe, used to remove water through chemical absorption. Water vapor in the gas mixture.

[0018] The The physical purification, collection, and graphitization assembly includes nested reduction tubes, a vacuum gauge, a liquid nitrogen cup, and a tubular furnace. The nested reduction tubes consist of an inner reduction tube, an outer reduction tube, and a glass column. The inner reduction tube is filled with iron powder as a catalyst, and the outer reduction tube is filled with zinc powder as a reducing agent. The glass column isolates the inner reduction tube from the zinc powder. The liquid nitrogen cup is used to collect the liquid nitrogen during the purification stage. Frozen within nested reduction tubes; the tubular furnace is used to provide gradient heating to the nested reduction tubes during the graphitization stage, so that... It is gradually reduced to graphite.

[0019] The Physical purification, trapping, and graphitization components are used for Further purification and graphitization are performed by this component. During purification, the nested reduction tube is submerged below the liquid nitrogen cup surface. The mixed gas flows through the reduction tube. The system is frozen, and other gases are carried out of the graphitization system by the He carrier gas; when this component performs the graphitization function, it uses a tubular furnace to gradient-heat the nested reduction tubes. It gradually reverts to graphite.

[0020] The vacuum control component is a vacuum pump with adjustable vacuum level and flow rate. It can set the target pressure and pumping speed to control the gas flow rate in the pipeline and the internal pressure of the reduction unit.

[0021] The system is suitable for converting carbon in solid samples into graphite targets for use in accelerator mass spectrometry. Measurements can be performed, and the system can operate in a low vacuum and helium protective atmosphere, avoiding atmospheric... pollute.

[0022] A method for synthesizing graphite using a low-vacuum online graphitization system under a helium protective atmosphere includes the following steps:

[0023] S1. Sample preparation: Weigh the sample to be tested and the combustion accelerator vanadium pentoxide and seal them in a tin boat, press them into balls, and place them sequentially into the sample tray of the zero background autosampler;

[0024] S2. System preparation and purification: Immerse the U-shaped trap below the liquid nitrogen tank surface, introduce helium gas, and use the U-shaped trap to purify the helium gas, so that high-purity helium gas fills the entire pipeline;

[0025] S3. Condition setting and airtightness check: Heat the high-temperature oxidation furnace to the set temperature and check the airtightness of the reduction unit during the heating process;

[0026] S4. Generation and Collection: The nested reduction tube is immersed below the liquid nitrogen cup surface. The sample sphere is pushed into the high-temperature oxidation furnace for combustion and oxidation using a zero-background autosampler, generating... A mixed gas; under a helium carrier, the mixed gas sequentially passes through a magnesium perchlorate dehydration pipe to remove moisture, and then enters the reduction unit, wherein... The gas is frozen and captured, while the remaining gas is released.

[0027] S5. Repeated capture: completing a sample After collection, close the corresponding valves, remove the liquid nitrogen cup, and repeat step S4 until all reduction units are complete. Capture;

[0028] S6. Catalytic Reduction Graphitization: All nested reduction tubes are subjected to gradient heating using a tubular furnace, causing the trapped graphite to... In a helium atmosphere, it is first reduced to CO by the reducing agent Zn, and then further reduced to graphite under Fe catalysis.

[0029] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0030] 1. This invention utilizes a modular parallel reaction pipeline design connected by a five-way valve, enabling the system to simultaneously process up to eight samples. The trapping and graphitization reaction enabled high-throughput sample preparation.

[0031] 2. This invention employs a fully stainless steel sealed piping system, solving the problem of fragility and breakage inherent in traditional glass systems. It boasts high mechanical strength, long service life, and simple daily maintenance. Furthermore, based on a helium protective atmosphere, the system can operate stably under low vacuum conditions, significantly reducing reliance on ultra-high vacuum equipment and thus substantially lowering system construction costs and operational / maintenance complexity.

[0032] 3. This invention utilizes the extremely low gas permeability of stainless steel, combined with helium positive pressure protection and a controllable low vacuum environment, to construct a multi-layered gas isolation barrier, which can fundamentally and effectively prevent external atmosphere (especially those containing modern carbon) from entering the environment. This allows the material to penetrate deep into the reaction system, significantly reducing the risk of carbon contamination during sample preparation and ensuring an ultra-low system background, thus enabling high precision and high reliability. The dating provides a guarantee.

[0033] 4. The process of this invention can efficiently and with high quality convert carbon in various solid samples into graphite targets suitable for AMS measurement in a relatively mild low-vacuum / atmospheric-pressure helium environment, with a measurement limit of over 47,000 years. The test results of the standard samples are accurate and all within the generally accepted error range. Attached Figure Description

[0034] Figure 1 Accelerator mass spectrometry measurement for this invention A schematic diagram of a low-vacuum online graphitization system under a helium protective atmosphere. Detailed Implementation

[0035] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] See Figure 1 This embodiment describes an accelerator mass spectrometry measurement method. A helium-protected atmosphere low-vacuum online graphitization system. This system constructs a helium-protected atmosphere and low-vacuum co-operating environment within stainless steel sealed pipelines. Its components are connected in the following manner to form the overall gas path and reaction process:

[0038] In the helium source and purification assembly, helium cylinder 1 is connected sequentially to a U-shaped trap 2 and a liquid nitrogen tank 3 via pipelines to provide high-purity helium to the system. The U-shaped trap 2 is submerged below the liquid surface of the liquid nitrogen tank 3 and is filled with 5A molecular sieves to freeze and adsorb impurity gases, especially trace amounts, from the helium. and These two gases can significantly interfere with subsequent reactions.

[0039] In the sample introduction and combustion assembly, the zero-background autosampler 4 is connected to the inlet of the combustion tube 6 of the high-temperature oxidation furnace 5, which can automatically feed the sample tin boat ball into the combustion tube 6 for high-temperature oxidation. The zero-background autosampler 4 is equipped with a 40-position autosampler tray for sequentially feeding the tin boat ball containing the sample and the combustion aid vanadium pentoxide into the high-temperature oxidation furnace 5. The high-temperature oxidation furnace 5 can provide a maximum temperature of 1100 °C. The furnace is equipped with the combustion tube 6, which contains, from top to bottom, an ash tube, reduced copper, chromium oxide, and silver-plated cobalt oxide, with each layer separated by quartz wool. The ash tube is used to collect combustion residues (tin cups and other residual ash after high-temperature sintering), the reduced copper is used to consume the oxygen released by the high-temperature combustion and decomposition of the combustion aid vanadium pentoxide, and the chromium oxide can further oxidize the incompletely burned carbon. Silver-plated cobalt oxide is used to remove halogen impurities such as chlorine. Therefore, this component can automatically introduce samples and efficiently and completely convert solid organic carbon into solid organic carbon through a high-temperature oxidation reaction. gas.

[0040] The gas path leading from the outlet of high-temperature oxidation furnace 5 is sequentially connected to the gas flow rate regulation and monitoring component (including gas flow rate control valve 7 and flow meter 9) and... The chemical purification component (i.e., magnesium perchlorate dehydration tube 8) constitutes the post-combustion purification system for samples. The preliminary purification and flow regulation pathway for the mixed gas includes a magnesium perchlorate dehydration pipe 8 positioned between the gas flow rate control valve 7 and the flow meter 9. The outlet of the flow meter 9 is connected to the inlet of a three-way shut-off valve 10. The flow meter 9 monitors the gas flow rate within the pipeline, and the gas flow rate control valve 7 adjusts the gas flow rate based on the monitoring results to ensure that the gas flows through the reduction unit at a lower velocity, which is beneficial for gas purification. Complete capture. The magnesium perchlorate dewatering pipe 8 is used to remove [chloride] by chemical absorption. Water vapor in the gas mixture.

[0041] The five-way valve 11 serves as an airflow distribution hub, with its common port connected to the three-way shut-off valve 10, and the other four outlets connected to four independent parallel reaction pipelines. Each reaction pipeline is connected in series with two identical reduction units (for example, the first pipeline includes reduction unit 12 and reduction unit 14).

[0042] The core of each reduction unit is a nested reduction tube, equipped with control valves and a vacuum gauge. Taking the first reaction line as an example, one outlet of the five-way valve 11 is connected to the inlet of the three-way shut-off valve 12-1 of the reduction unit 12.

[0043] Within each reaction line, two reduction units are connected in series. Specifically, in the first line:

[0044] One outlet of the three-way shut-off valve 12-1 is connected to the inlet of the nested reduction tube for introducing gas into the tube, while the other outlet of the three-way shut-off valve 12-1 is connected to the inlet of the three-way shut-off valve 12-2. A vacuum gauge 12-3 is connected between the nested reduction tube and the three-way shut-off valve 12-2 to monitor the pressure within the reduction tube. The outlet of the three-way shut-off valve 12-2 is connected to the inlet of the three-way shut-off valve 14-1 of the reduction unit 14, thus achieving series connection with the downstream reduction unit.

[0045] Similarly, inside the reduction unit 14, one outlet of the three-way shut-off valve 14-1 is connected to its nested reduction tube, and the other outlet is connected to the three-way shut-off valve 14-2; the vacuum gauge 14-3 is connected between the reduction tube and the three-way shut-off valve 14-2; finally, the outlet of the three-way shut-off valve 14-2 is connected to a corresponding inlet of the five-way valve 16.

[0046] The connection method of the other three reaction pipelines is exactly the same as that of the first pipeline.

[0047] Downstream, the five-way valve 16 serves as a gas collection hub, with its four inlets connected to the ends of four reaction pipelines (i.e., the final outlet of the second reduction unit in each pipeline), and its common outlet connected to the inlet of the three-way shut-off valve 17.

[0048] The two outlets of the three-way shut-off valve 17 are connected to the vacuum pump 18 and the atmospheric exhaust port, respectively. By switching the three-way shut-off valve 17, the system can switch between vacuum mode (connected to the vacuum pump 18) and atmospheric exhaust mode (connected to the atmosphere).

[0049] The vacuum pump 18 can be switched to exhaust mode or evacuation mode, and in conjunction with the on / off states of each three-way shut-off valve, it can perform system purging, airtightness checks, and... Pressure and flow path control at different stages such as capture and graphitization.

[0050] Each nested reduction tube in the reduction unit can be immersed in a common liquid nitrogen cup 13 to achieve [the desired effect]. The low-temperature capture can be surrounded by a common tubular furnace 15 for gradient heating reaction.

[0051] Specifically, the nested reduction tube includes an inner reduction tube, an outer reduction tube, and a glass column. The inner reduction tube is filled with iron powder as a catalyst, and the outer reduction tube is filled with zinc powder as a reducing agent. The glass column is used to isolate the inner reduction tube from the zinc powder. The liquid nitrogen cup is used during the purification stage to... Frozen within nested reduction tubes; the tubular furnace is used to provide gradient heating to the nested reduction tubes during the graphitization stage, so that... It is gradually reduced to graphite. Specifically, this component performs... During purification, the nested reduction tube is submerged 1 / 3 of the liquid nitrogen cup below the liquid level. The mixed gas flows through the reduction tube. The system is frozen, and other gases are carried out of the graphitization system by the He carrier gas; when this component performs the graphitization function, it uses a tubular furnace to gradient-heat the nested reduction tubes. It gradually reverts to graphite.

[0052] Through the above connection method, the The physical purification, collection, and graphitization components are connected to each other via two five-way valves. The chemical purification component and the vacuum control component are connected, and the entire pipeline is configured with four lines, each line equipped with two reduction units, enabling the system to perform eight graphitization reactions simultaneously. This invention thus constructs a modular, parallel-processable low-vacuum online graphitization platform, effectively solving the problems of fragility, high cost, and atmospheric carbon contamination permeation in traditional high-vacuum glass systems.

[0053] Example 2

[0054] The carbon content of the samples was determined by EA-IRMS and .

[0055] A method for synthesizing graphite using a low-vacuum online graphitization system under a helium protective atmosphere includes the following steps:

[0056] 1. Weigh 1 mg of C sample and 10 mg of vanadium pentoxide (the combustion improver). The sample is placed in a tin boat and pressed into a sphere. The sample is then placed into the sample tray of the zero-background autosampler 4.

[0057] 2. The U-shaped trap 2 is submerged below the liquid nitrogen tank 3. The helium cylinder 1 is opened, and the three-way shut-off valve 17 switches the tangential vacuum pump 18. The high-purity helium flows through the high-temperature oxidation furnace 5, the magnesium perchlorate dehydration pipe 8, and the reduction unit 12 and reduction unit 14 on the same pipeline, and is then removed by the vacuum pump 18.

[0058] 3. Heat the high-temperature oxidation furnace 5 to 900 ℃. During this period, check the airtightness of the reduction unit. Set the target vacuum level of vacuum pump 18 to 1~10 mbar and the pumping speed to 30%. Switch the three-way shut-off valve 12-1 to the upward direction. After the reading of vacuum gauge 12-3 stabilizes to the target pressure, switch the three-way shut-off valve 12-2 to the upward direction. The same applies to reduction unit 14. Check the airtightness of the remaining reduction units by switching the pipeline through five-way valves 11 and 16. If the vacuum gauge reading does not change significantly within 5 minutes, it proves that the airtightness of the reduction unit is feasible.

[0059] 4. After the heating is completed, the nested reduction tube of the reduction unit 12 is submerged below the liquid surface of the liquid nitrogen cup 13. Close the three-way shut-off valve 17, switch the three-way shut-off valve 12-1 of the reduction unit 12 downward, and after the reading of the vacuum gauge 12-3 returns to atmospheric pressure, switch the three-way shut-off valve 12-2 downward as well. Then switch the three-way shut-off valve 17 to the atmospheric direction.

[0060] 5. The zero-background autosampler 4 pushes the sample sphere into the combustion tube 6 of the high-temperature oxidation furnace 5 for high-temperature combustion oxidation. High-purity helium gas will be used to generate... The mixed gas is continuously blown out of the high-temperature oxidation furnace 5. The gas flow rate control valve 7 adjusts the gas flow rate to 60 mL / min. The mixed gas passes through the magnesium perchlorate dehydration pipe 8 to remove moisture before reaching the reduction unit 12. It was frozen, and the remaining gases were released into the atmosphere along with the helium. The capture lasted for 5 minutes.

[0061] 6. After collection is complete, switch the three-way shut-off valve 17 to the direction of vacuum pump 18. Set the target vacuum level of vacuum pump 18 to 50 mbar and the pumping speed to 1%. Switch the three-way shut-off valve 12-1 of reduction unit 12 upwards. After the reading of vacuum gauge 12-3 stabilizes at around 500 mbar, switch the three-way shut-off valve 12-2 upwards and remove liquid nitrogen cup 13. The reading of vacuum gauge 12-3 will continue to rise to around 1100 mbar. The same applies to reduction unit 14, collecting the next sample and burning it. Other reduction units are accessed by switching pipelines via five-way valve 11 and five-way valve 16. Capture.

[0062] 7 or 8 restoration units After collection was completed, the nested reduction tubes of each reduction unit were heated using a tubular heater 15, first at 450 °C for 1 hour, and then at 550 °C for 1 hour. Under normal pressure and a helium atmosphere, the graphite is first reduced to CO by the reducing agent Zn, and then CO is further reduced to graphite by Fe catalysis. The chemical reactions that occur are as follows:

[0063]

[0064]

[0065] After the reaction was complete, each reduction unit was removed, and the graphite inside the inner reduction tube was taken out. After homogenizing the graphite, a small portion was used for EA-IRMS carbon content and... Measurements were taken, and the original sample was compared with the corresponding graphite. The value is used to assess the isotope segregation during the entire graphite preparation process.

[0066] Table 1 Test data of standard samples and blank samples

[0067]

[0068] use The accuracy of the evaluation method for standard samples OX II, IAEA-C7, and IAEA-C8, as well as the background sample anthracite, and the systematic background value were tested. The results of the test values ​​of standard samples OX II, IAEA-C7, and IAEA-C8 were all within the recognized error range, and the upper limit of the measured years could reach 47,000 years.

Claims

1. An accelerator mass spectrometry measurement 14 A low vacuum on-line graphitization system under helium protective atmosphere, characterized in that: The system constructs a helium protection atmosphere and a low vacuum environment in a stainless steel sealed pipeline, including a helium source and purification assembly, a sample injection and combustion assembly, a gas flow rate adjustment and monitoring assembly, a CO2 chemical purification assembly, a CO2 physical purification and graphitization assembly, and a vacuum degree control assembly connected in sequence; The helium source and purification assembly is used to provide ultra-pure helium and serve as pipeline purge gas, carrier gas and graphitization reaction protection gas; The sample injection and combustion assembly is used to realize automatic sample injection and convert solid organic carbon into CO2 gas; The gas flow rate adjustment and monitoring assembly is used to adjust and monitor the gas flow rate in the pipeline; The CO2 chemical purification assembly is a magnesium perchlorate water removal pipe used to remove water vapor in CO2 mixed gas by chemical absorption; The CO2 physical purification and graphitization assembly includes a nested reduction pipe, a vacuum gauge, a liquid nitrogen cup and a tubular heating furnace; the nested reduction pipe includes an inner reduction pipe, an outer reduction pipe and a glass pad column, the inner reduction pipe is filled with iron powder as a catalyst, the outer reduction pipe is filled with zinc powder as a reducing agent, and the glass pad column is used to isolate the inner reduction pipe and the zinc powder; the liquid nitrogen cup is used to freeze CO2 in the nested reduction pipe during the purification stage; and the tubular heating furnace is used to perform gradient heating on the nested reduction pipe during the graphitization stage, so that CO2 is gradually reduced to graphite. The sample injection and combustion assembly includes a zero-background automatic sampler and a high-temperature oxidation furnace; the zero-background automatic sampler is configured with a 40-position automatic sample injection disc for sequentially feeding tin boat balls containing samples and vanadium pentoxide, a combustion aid, into the high-temperature oxidation furnace; the high-temperature oxidation furnace is provided with an ash pipe, a reduced copper, a chromium oxide and a silver-coated cobalt oxide in the combustion tube from top to bottom, and each layer is isolated by quartz wool; the ash pipe is used to receive combustion residues, the reduced copper is used to consume oxygen released by the combustion aid decomposition, the chromium oxide is used to oxidize incompletely combusted carbon to CO2, and the silver-coated cobalt oxide is used to remove halogen impurities. The gas flow rate adjustment and monitoring assembly includes a gas flow rate control valve and a flow meter, the flow meter is used to monitor the gas flow rate in the pipeline, and the gas flow rate control valve is used to adjust the gas flow rate according to the monitoring result to ensure that CO2 is fully captured in the reduction unit.

2. An accelerator mass spectrometer assay as claimed in claim 1. 14 A low vacuum on-line graphitization system under helium protective atmosphere, characterized in that: The CO2 chemical purification assembly is a magnesium perchlorate water removal pipe used to remove water vapor in CO2 mixed gas by chemical absorption.

3. An accelerator mass spectrometer assay as claimed in claim 1. 14 A low vacuum on-line graphitization system under a helium protective atmosphere, characterized in that: The CO2 physical purification and graphitization assembly includes a nested reduction pipe, a vacuum gauge, a liquid nitrogen cup and a tubular heating furnace; the nested reduction pipe includes an inner reduction pipe, an outer reduction pipe and a glass pad column, the inner reduction pipe is filled with iron powder as a catalyst, the outer reduction pipe is filled with zinc powder as a reducing agent, and the glass pad column is used to isolate the inner reduction pipe and the zinc powder; the liquid nitrogen cup is used to freeze CO2 in the nested reduction pipe during the purification stage; and the tubular heating furnace is used to perform gradient heating on the nested reduction pipe during the graphitization stage, so that CO2 is gradually reduced to graphite.

4. An accelerator mass spectrometer assay as claimed in claim 1. 14 A low vacuum on-line graphitization system under a helium protective atmosphere, characterized in that: ​ 5. An accelerator mass spectrometer assay as claimed in claim 1. 14 A low vacuum on-line graphitization system under a helium protective atmosphere, characterized in that: ​ 6. An accelerator mass spectrometer assay as claimed in claim 1 14 A low vacuum on-line graphitization system under helium protective atmosphere, characterized in that: ​ 7. An accelerator mass spectrometer as claimed in claim 1 14 A low vacuum on-line graphitization system under helium protective atmosphere, characterized in that: The vacuum degree control component is a vacuum pump with adjustable vacuum degree and flow rate, which can set target pressure and pumping speed, thereby controlling the gas flow rate in the pipeline and the internal pressure of the reduction unit.

8. An accelerator mass spectrometer assay as claimed in claim 1 14 A low vacuum on-line graphitization system under helium protective atmosphere, characterized in that: The system is suitable for converting carbon in a solid sample into a graphite target for accelerator mass spectrometry 14 C determination and can be operated under low vacuum and a helium protective atmosphere, avoiding atmospheric 14 C contamination.

9. A method of synthesizing graphite using a low vacuum on-line graphitization system with a helium protective atmosphere, characterized by, The method comprises the following steps: S1. Sample preparation: the sample to be tested and the combustion improver vanadium pentoxide are weighed and packaged in a tin boat, pressed into a ball, and sequentially placed in the sample tray of a zero background automatic sampler; S2. System preparation and purification: immerse the U-shaped trap below the liquid level of the liquid nitrogen tank, introduce helium, purify the helium using the U-shaped trap, and fill the entire pipeline with high-purity helium; S3. Condition setting and airtightness check: heat the high-temperature oxidation furnace to the set temperature, and check the airtightness of the reduction unit during heating; S4. CO2 generation and capture: immerse the nested reduction pipe below the liquid level of the liquid nitrogen cup, push the sample ball into the high-temperature oxidation furnace for combustion oxidation through the zero background automatic sampler, and generate CO2 mixed gas; under the helium carrier, the mixed gas sequentially passes through the magnesium perchlorate water removal pipe to remove water, and then enters the reduction unit, wherein CO2 is frozen and captured, and the remaining gas is discharged; S5. Repeat capture: after completing the CO2 capture of one sample, close the corresponding valve, remove the liquid nitrogen cup, and repeat step S4 until all reduction units complete the CO2 capture; S6. Catalytic reduction graphitization: use a tubular heating furnace to perform gradient heating on all nested reduction pipes, so that the captured CO2 is first reduced to CO by the reducing agent Zn under a helium atmosphere, and then further reduced to graphite under the catalysis of Fe.

Images