Method for performing < 14 > C analysis based on C < + > ions in carbocation mass spectrometry device

Abstract

The invention discloses a method for performing < 14 > C analysis based on C < + > ions in a carbocation mass spectrometry device, and belongs to the technical field of nuclide analysis. The method comprises the following steps: eliminating C-H molecular ion interference by using a specific gas stripping target in a segmented stripping and charge exchange mode, forming C-ions through a non-metal gas charge exchange target, and obtaining high-strength C-ion current intensity by matching pre-focusing, post-focusing and magnet analysis; the current intensity of C < + > ions reaches 6-7 mA, and the current intensity of C <-> ions after charge exchange reaches 260 microamperes; the specific gas is any one or more of He gas, Ar gas and N2 gas, and the non-metal gas is any one or more of H2, CH4, C2H4 and C4H10. The flow intensity of C < + > generated by the ion source is several times higher than that of C < 2 + >, and the efficiency of generating C <-> through charge exchange by using C < + > and C < 2 + > ions is close, so that the efficiency of 14C analysis based on C < + > can be several times higher than that of using C < 2 + >.

Description

Technical Field

[0001] This invention belongs to the field of radionuclide analysis technology, specifically relating to a carbon-positive ion mass spectrometer based on C + Ions proceed 14 C-analysis method. Background Technology

[0002] 14 Nuclear analysis, as an important scientific and technological tool, plays an irreplaceable role in many fields such as earth science, environmental science, archaeology, biomedicine, and marine science. Accelerator mass spectrometry (AMS) is a modern nuclear analysis technique that emerged in the 1970s, mainly used to measure the isotopic abundance of long-lived radionuclides. However, AMS devices suffer from problems such as cumbersome graphitization sample preparation, large size, and high cost, resulting in low measurement efficiency and hindering large-scale application in fields with large sample volumes.

[0003] With the continuous development of technology, 14 The application areas of C-analysis technology are constantly expanding, and the increasing demand for detection is driving the development of existing technologies. 14 The contradiction between insufficient supply of dedicated C-ion mass spectrometers and the growing shortage of such instruments is becoming increasingly prominent. Carbon-positive ion mass spectrometry (C-PIMS), as an advanced method for nuclide analysis, boasts advantages such as high analysis speed, compact structure, and ease of automation, and holds promise as a promising approach. 14 A powerful alternative to the C-AMS system in terms of specialization, miniaturization, and automation.

[0004] Research on C-PIMS, both domestically and internationally, is still in its early exploratory stages, and improving system measurement efficiency is one of the key issues. This applies to both accelerator mass spectrometry and carbocation mass spectrometry. 14 Two problems exist in C analysis: 1) interference from CH molecular ions; 2) 14 Interference from N. 14 Nitrogen cannot form stable anions; therefore, the process of forming carbon anions can eliminate... 14 Interference from N. Current carbocation mass spectrometry mainly uses C. 2+ Ions proceed 14 C-analysis revealed the following interfering ions: 12 CH2 2+ The ECR ion source has high ionization efficiency and can generate high-density plasma internally, which can effectively suppress CH molecular ions and induce C. 2+ The ion stream itself contains only a very small amount of... 12 CH2 2+Molecular ions, simply producing C 2+ It can eliminate most interference. 12 CH2 2+ The ions are metastable with a lifetime of approximately 2 μs and are easily stripped. Using C... 2+ During charge exchange, a thicker target is required to achieve high charge exchange efficiency, and the charge exchange process is crucial for... 12 CH2 2+ For ions, this is a stripping process, and the stripping cross-section is much larger than the electron-capturing cross-section formed by negative ions. Therefore, in the charge exchange process, using a charge exchange target of appropriate thickness, and through sufficient collisions, can completely eliminate the interference of molecular ions while also generating enough carbon. - Ions. Therefore, C 2+ It can be applied to carbon-positive ion mass spectrometry. 14 C's analysis, but C 2+ The current intensity is weak, resulting in low system measurement efficiency.

[0005] During the discharge process of the ECR ion source, with the same C consumption, C + The ion current is much higher than that of C. 2+ The ion current is strong, and the utilization rate of C can be further improved if He is mixed with CO2 in a certain proportion. Based on C... + conduct 14 C analysis revealed interference from monovalent CH molecular ions, such as... 12 CH2 + and 13 CH + It is stable and exists, while 14 N can form C through charge exchange. - Ion elimination. Can C+ be used in carbocation mass spectrometry? + Ions proceed 14 The key to C analysis lies in how to eliminate the interference of CH molecular ions and obtain sufficiently high C values. - Ion yield. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems in the aforementioned related technologies.

[0007] Therefore, the purpose of this invention is to provide a carbon positron mass spectrometer based on C + Ions proceed 14 The method of C analysis, C generated by the ion source + Current ratio C 2+ Several times higher, when using C + Ions proceed 14During C analysis, interference from CH molecular ions can be eliminated, and efficient charge exchange can be achieved, thus making the measurement efficiency comparable to that using C. 2+ Increased several times.

[0008] To solve the above-mentioned technical problems, the present invention is implemented as follows: This invention provides a carbon positive ion mass spectrometry device based on C + Ions proceed 14 The method of C analysis, the method described: By employing segmented stripping and charge exchange, interference from CH molecular ions is eliminated using a specific gas stripping target, and then C is formed using a non-metallic gas charge exchange target. - Ions, combined with pre-focusing, post-focusing, magnet analysis, and electrostatic analysis, yield... 14 C / 13 C and 14 C / 12 The value of C.

[0009] Furthermore, in the carbocation mass spectrometry apparatus according to the present invention, based on C + Ions proceed 14 The C analysis method may also have the following additional technical features: In some of these embodiments, the C generated by the ion source + Ion current intensity >6 mA.

[0010] In some of these embodiments, the specific gas is any one or more of He, Ar, and N2.

[0011] In some embodiments, the nonmetallic gas is H2, CH4, C2H4, and C4H. 10 Any one or more of the following.

[0012] In some embodiments, the steps of the method include: S1. A vacuum environment required for operation is obtained by evacuation; S2, release the ion beam and provide the required extraction voltage to control C + The energy required for ion charge exchange; S3. Set the air intake of the stripping target and charge exchange target to 0, and adjust the focusing parameters before and after the process, as well as the magnetic field analysis parameters of the magnet, to make C + Ions can achieve good focusing and transport, and C can be measured and recorded. + Current Intensity I c+ ; S4. Adjust the pre-focusing parameters according to the ion energy so that the ion beam waist is located at the center of the charge exchange target, thereby reducing the consumption of charge exchange gas. S5. Light gas is introduced into the stripping target to perform CH molecular ion stripping. The flow rate of the light gas is adjusted to achieve high transmission efficiency while ensuring the elimination of interference. S6. A non-metallic charge exchange gas is introduced into the charge exchange target to perform charge exchange on the stripped beam. S7, regarding C after charge exchange - Ions are post-focused and then analyzed by a magnetic field. The ions are selected by adjusting the magnetic field strength of the analytical magnet. S8. Adjust the flow rate of the charge-exchange gas, and measure and record C. - Ion current intensity I c- ; S9. Change the output voltage and return to S5 until the exit condition is met. S10. The charge exchange efficiency under different conditions is obtained through calculation, and the quantitative relationship between the charge exchange efficiency and related parameters is obtained. S11. Performed under conditions of highest charge exchange efficiency. 14 C analysis, the obtained C - Ions pass through two sets of electrostatic analyzers and magnetic analyzers, and are then analyzed using detectors. 14 C - Counting, obtaining 14 C / 13 C and 14 C / 12 The C-value provides information such as the age of the sample.

[0013] In some embodiments, the ion beam in step S2 is a C2 ion beam with a current intensity >6 mA. + Ion beam.

[0014] In some of these implementations, the lead-out voltage range in steps S2 and S9 is 25~80 kV.

[0015] In some of these implementations, the relevant parameters in step S10 are energy and / or gas flow rate.

[0016] In some of these implementations, the charge exchange efficiency is calculated as follows: .

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: In this embodiment of the invention, the provided carbon-positive ion mass spectrometry device is based on C + Ions proceed 14 The C analysis method employs segmented stripping and charge exchange to eliminate CH molecular ions and 14 N interference, achieving C-based [structure / implementation] in a carbocation mass spectrometer. + of 14C-measurement provides a new measurement method; In this embodiment of the invention, the provided carbon-positive ion mass spectrometry device is based on C + Ions proceed 14 The C-analysis method enables the use of carbon cation mass spectrometry devices. 14 C++ analysis efficiency is improved by an order of magnitude, using C++ + C obtained through charge exchange - The current ratio uses C 2+ Several times higher, with measurement efficiency an order of magnitude higher; In this embodiment of the invention, the provided carbon-positive ion mass spectrometry device is based on C + Ions proceed 14 The C-analysis method, which combines light target stripping with thick target charge exchange, can efficiently reduce energy loss and eliminate molecular ion interference, while reducing the beam divergence angle, thereby significantly improving measurement accuracy.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] Figure 1 This invention discloses a C-based method according to one embodiment. 2+ / C + C after charging - Current intensity curve; Figure 2 This invention discloses a C-based method according to one embodiment. + conduct 14 C. Measurement system block diagram. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and specific examples and application scenarios.

[0022] Typical ECR ion sources produce C 2+ The current intensity is approximately 0.6~1.0 mA, while C + The current intensity can reach up to 6~7 mA, and in addition, C + The ion charge exchange cross section is greater than C 2+ Ions, if C can be converted +Ions applied 14 If C is analyzed, the utilization rate of C will increase by about an order of magnitude, further improving the system's measurement efficiency.

[0023] Without considering the interference of CH molecular ions, for C 2+ / C + Charge exchange efficiency was studied, and it was found to be higher than 6% when using nonmetallic gases for charge exchange. With an ion source extraction voltage of 45 kV, using C... 2+ Ions undergo charge exchange, and after the exchange is complete, C is obtained. - The current intensity was only 19 μA, while using C + During charge exchange, C - The current intensity can reach 260 μA, compared to C 2+ Approximately one order of magnitude higher, please refer to [link / reference]. Figure 1 As shown. Based on the above experimental data and phenomena, the following will delve into the following discussion... Ions as the basis for development 14 The potential possibilities and advantages of C measurement work.

[0024] Assuming the energy is in the range of tens to hundreds of keV, the dissociation cross section of the CH molecular ion If the fundamental value is constant, then the change in molecular ion number density per unit path can be expressed as:

[0025] The solution to this differential equation can be written as:

[0026] in, n c-H The number density of CH molecular ions. n 0 represents the initial molecular ion density. n target For target molecule number density, L The length of the gas target, N L For target thickness, is n target The integral along the charge exchanger path, in cm. -2 As can be seen from the above formula, with the target thickness... N L As the density of the molecular ions increases, the density of the molecular ions decreases exponentially. Only a sufficient target thickness is needed to achieve complete stripping of CH molecular ions, and the larger the dissociation cross section, the faster the change.

[0027] For example, using a single target for CH molecular ion stripping and C +Ion charge exchange requires a heavy gas target, and multiple collisions lead to severe scattering losses and increased beam divergence. Even if interference from molecular ions can be eliminated during this process, due to… 12 C / 13 C / 14 The trajectory of C deviates significantly, resulting in very low system resolution, making it impossible to perform [further analysis]. 14 High-precision analysis of carbon is crucial, especially at low energies where scattering is more severe, making it difficult to improve resolution. Using a lighter charge-exchange target could help improve resolution, but lighter gases such as H₂ and He have very low charge-exchange efficiency and are not suitable for generating negative ions.

[0028] Three interdependent factors exist: 1) To achieve efficient charge exchange, selecting a heavier non-metallic gas molecular target is unavoidable; 2) To suppress molecular ions, thick target stripping is necessary; 3) To minimize the impact of scattering during thick target stripping and charge exchange, a target with a smaller molecular weight, such as He, must be selected without increasing the ion energy. Therefore, based on these three considerations, we propose a segmented stripping and charge exchange approach: using He gas for molecular ion stripping followed by charge exchange with a non-metallic gas.

[0029] In some embodiments of the present invention, a charge exchange system for carbon cation mass spectrometry is provided, comprising the following configuration: Figure 2 As shown, it includes: a pre-focusing module: used to initially focus the carbocations generated by the ion source to adjust the beam waist position to be centered on the charge exchange target; a stripping target (stripping gas): used to eliminate interference from CH molecular ions, the cavity can be filled with an appropriate amount of inert gas (such as He gas), and stripping is achieved through collisions between ions and gas; and a charge exchange target (charge exchange gas): used to form C - Ions, the cavity is equipped with non-metallic charge exchange gases (such as ethylene (C2H4) and isobutane (C4H4)). 10 (etc.); Post-focusing module: used for focusing C after charge exchange. - Ions are refocused to ensure ion beam quality and transmission efficiency; Magnet analysis module: used for analyzing the C after charge exchange. - Ion selection; Measurement module: measuring C - The ion current is strong, and the charge exchange efficiency is calculated. Following the measurement module are sequentially arranged an electrostatic analyzer, a magnet analysis module (analyzer), and another electrostatic analyzer, which is then used with a detector to... 14 C - Counting, obtaining 14 C / 13 C and 14 C / 12 The C-value provides information such as the age of the sample.

[0030] In some embodiments of the present invention, a C-based carbon cation mass spectrometer is provided. + Ions proceed 14 The C-analysis method includes the following steps: Step 1: Start the vacuum system. Through the coordinated operation of multiple vacuum pumps and vacuum valves, the gas in the system is gradually extracted to form a high vacuum environment.

[0031] Step 2: Adjust parameters such as ion source power and working gas pressure to generate 6~7 mA C. + The ion beam is used to select an appropriate extraction voltage value (extraction voltage adjustable from 25 to 80 kV) according to the measurement requirements in order to control the energy during the charge exchange of carbocations.

[0032] Step 3: Set the air intake of the stripping target and charge exchange target to 0. By adjusting the focusing module parameters and analyzing the magnetic field of the magnet, make C... + Ions can achieve good focusing and transport, and C is performed in the measurement module. + Current intensity measurement, denoted as .

[0033] Step 4: Adjust the parameters of the prefocusing module according to the different ion energies so that the ion beam waist is located at the center of the charge exchange target, thereby reducing the consumption of charge exchange gas.

[0034] Step 5: Introduce a lighter gas, such as He, into the stripping target to perform CH molecular ion stripping. Adjust the He gas flow rate to achieve high transmission efficiency while eliminating interference.

[0035] Step 6: Introduce a non-metallic charge exchange gas into the charge exchange target to perform charge exchange on the stripped beam.

[0036] Step 7: Use the post-focusing module to focus on the C after charge exchange. - Ions are focused and sent to a magnet for analysis. The ions are then selected by adjusting the magnetic field strength of the magnet.

[0037] Step 8: Adjust the charge exchange gas flow rate, and measure C in the measurement module. - The ion current intensity is measured and recorded as . .

[0038] Step 9: Change the lead-in voltage, repeat steps 5, 6, 7, and 8, and record the corresponding C. - Current intensity.

[0039] Step 10: Calculate the charge exchange efficiency under different conditions and provide a quantitative relationship between charge exchange efficiency and parameters such as energy and gas flow rate. Charge Exchange Efficiency .

[0040] Step 11: Perform under conditions of highest charge exchange efficiency 14 C analysis, the obtained C - Ions pass through two sets of electrostatic analyzers and magnetic analyzers, and are then analyzed using detectors. 14 C - Counting, obtaining 14 C / 13 C and 14 C / 12 The C-value provides information such as the age of the sample.

[0041] Any part of this invention not described in detail can be referred to in the prior art or in the art known to those skilled in the art. This embodiment does not limit such part and will not describe it in detail here.

[0042] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A carbon positive ion mass spectrometer based on C + Ions proceed 14 The C-analysis method is characterized by... The method described: By employing segmented stripping and charge exchange, interference from CH molecular ions is eliminated using a specific gas stripping target, and then C is formed using a non-metallic gas charge exchange target. - Ions, combined with pre-focusing, post-focusing, magnet analysis, and electrostatic analysis, yield... 14 C / 13 C and 14 C / 12 The value of C.

2. The carbon positive ion mass spectrometer based on C according to claim 1 + Ions proceed 14 The C-analysis method is characterized by... C generated by the ion source + The ion current is stronger than 6 mA.

3. The carbon positive ion mass spectrometer based on C according to claim 1 + Ions proceed 14 The C-analysis method is characterized by... The specific gas is any one or more of He, Ar, and N2.

4. The carbon positive ion mass spectrometer based on C according to claim 1 + Ions proceed 14 The C-analysis method is characterized by... The non-metallic gases are H2, CH4, C2H4, and C4H. 10 Any one or more of the following.

5. The carbon positive ion mass spectrometer based on C according to claim 1 + Ions proceed 14 The C-analysis method is characterized by... The steps of the method include: S1. A vacuum environment required for operation is obtained by evacuation; S2, release the ion beam and provide the required extraction voltage to control C + The energy required for ion charge exchange; S3. Set the air intake of the stripping target and charge exchange target to 0, and adjust the focusing parameters before and after the process, as well as the magnetic field analysis parameters of the magnet, to make C + Ions can achieve good focusing and transport, and C can be measured and recorded. + Current Intensity I c+ ; S4. Adjust the pre-focusing parameters according to the ion energy so that the ion beam waist is located at the center of the charge exchange target, thereby reducing the consumption of charge exchange gas. S5. Light gas is introduced into the stripping target to perform CH molecular ion stripping. The flow rate of the light gas is adjusted to achieve high transmission efficiency while ensuring the elimination of interference. S6. A non-metallic charge exchange gas is introduced into the charge exchange target to perform charge exchange on the stripped beam. S7, regarding C after charge exchange - Ions are post-focused and then analyzed by a magnetic field. The ions are selected by adjusting the magnetic field strength of the analytical magnet. S8. Adjust the flow rate of the charge-exchange gas, and measure and record C. - Ion current intensity I c- ; S9. Change the output voltage and return to S5 until the exit condition is met. S10. The charge exchange efficiency under different conditions is obtained through calculation, and the quantitative relationship between the charge exchange efficiency and related parameters is obtained. S11. Performed under conditions of highest charge exchange efficiency. 14 C analysis, the obtained C - Ions pass through two sets of electrostatic analyzers and magnetic analyzers, and are then analyzed using detectors. 14 C - Counting, obtaining 14 C / 13 C and 14 C / 12 The C-value provides information about the age of the sample.

6. The carbon positive ion mass spectrometer based on C according to claim 5 + Ions proceed 14 The C-analysis method is characterized by... In step S2, the ion beam is a C2 ion beam with a current intensity >6 mA. + Ion beam.

7. The carbon positive ion mass spectrometer based on C according to claim 5 + Ions proceed 14 The C-analysis method is characterized by... The voltage range for steps S2 and S9 is 25~80 kV.

8. The carbon positive ion mass spectrometer based on C according to claim 5 + Ions proceed 14 The C-analysis method is characterized by... The relevant parameters in step S10 are energy and / or gas flow rate.

9. The carbon positive ion mass spectrometer based on C according to claim 5 + Ions proceed 14 The C-analysis method is characterized by... The charge exchange efficiency is calculated as follows: .

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