Method for analyzing cations in a carbonium mass spectrometer device based on c + ions 14 C

Abstract

The application discloses a kind of carbon positive ion mass spectrometer device based on C + Ion is carried out 14 C analysis method belongs to the technical field of nuclide analysis.The method comprises the following steps: eliminating C-H molecular ion interference by stripping target using specific gas through the way of sectional stripping and charge exchange, then forming C ‑ Ion by charge exchange target of non-metal gas, cooperating with pre-focusing, post-focusing and magnet analysis, to obtain high-intensity C ‑ Ion current intensity;C + Ion current intensity reaches 6-7 mA, C ‑ Ion current intensity after charge exchange reaches 260 μA; 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 C4H 10 . In the application, the C + Ion current intensity generated by ion source is several times higher than that of C 2+ , and the efficiency of generating C + by charge exchange using C 2+ and C ‑ is close, so the efficiency of C + analysis based on C 14 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 meeting the needs 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 for becoming... 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 The interference of N. Among them 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:

[0009] This invention provides a carbon positive ion mass spectrometry device based on C + Ions proceed 14 The method of C analysis, the method described:

[0010] 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.

[0011] 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:

[0012] In some of these embodiments, the C generated by the ion source + Ion current intensity >6 mA.

[0013] In some of these embodiments, the specific gas is any one or more of He, Ar, and N2.

[0014] In some embodiments, the nonmetallic gas is H2, CH4, C2H4, and C4H. 10 Any one or more of the following.

[0015] In some embodiments, the steps of the method include:

[0016] S1. A vacuum environment required for operation is obtained by evacuation;

[0017] S2, release the ion beam and provide the required extraction voltage to control C + The energy required for ion charge exchange;

[0018] 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+ ;

[0019] S4, adjusting the pre-focusing parameter according to the ion energy, so that the ion beam waist is located at the center of the charge exchange target, to reduce the consumption of the charge exchange gas;

[0020] S5, introducing light gas into the stripping target to perform C-H molecular ion stripping, and adjusting the gas flow of the light gas to ensure elimination of interference while obtaining a higher transmission efficiency;

[0021] S6, introducing a non-metallic charge exchange gas into the charge exchange target to perform charge exchange on the stripped beam;

[0022] S7, performing post-focusing on the C - ions after charge exchange, and performing magnetic field analysis by a magnet, and selecting ions by adjusting the magnetic field strength of the analysis magnet;

[0023] S8, adjusting the gas flow of the charge exchange gas, and measuring and recording the C - ion current I c- ;

[0024] S9, changing the extraction voltage, returning to S5, and repeating until the exit condition is met;

[0025] S10, calculating the charge exchange efficiency under different conditions, and obtaining the quantitative relationship between the charge exchange efficiency and the related parameters;

[0026] S11, performing C 14 analysis under the condition of the highest charge exchange efficiency, counting the C - ions by two sets of electrostatic analyzers and magnetic analyzers, and using a detector to count the C 14 ions, to obtain the C - / C 14 , C 13 / C 14 , and C 12 / C + values, and to give information such as the age of the sample.

[0027] In some embodiments, the ion beam in step S2 is a C + ion beam with a current of > 6 mA.

[0028] In some embodiments, the extraction voltage in steps S2 and S9 ranges from 25 to 80 kV.

[0029] In some embodiments, the related parameters in step S10 are energy and / or gas flow.

[0030] In some embodiments, the calculation method of the charge exchange efficiency is: .

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] 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 14 C-measurement provides a new measurement method;

[0033] 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;

[0034] 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.

[0035] 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

[0036] Figure 1 This invention discloses a C-based method according to one embodiment. 2+ / C + C after charging - Current intensity curve;

[0037] Figure 2 This invention discloses a C-based method according to one embodiment. + conduct 14 C. Measurement system block diagram. Detailed Implementation

[0038] 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.

[0039] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and specific examples and application scenarios.

[0040] 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.

[0041] Without considering the interference of CH molecular ions, for C 2+ / C + The 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.

[0042] 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:

[0043]

[0044] The solution to this differential equation can be written as:

[0045]

[0046] in, nc-H C-H molecular ion number density, n 0 is the initial molecular ion density, n target target molecular number density, L L is the length of the gas target, N L target thickness, is n target The integral on the charge exchanger path, in cm -2 As can be seen from the above formula, with the increase of the target thickness N L , the density of the molecular ion decreases exponentially, and only a sufficient target thickness can achieve the complete stripping of the C-H molecular ion, and the larger the dissociation cross section, the faster the change.

[0047] If a single target is used for C-H molecular ion stripping and C + ion charge exchange, a heavy gas target needs to be used, and multiple collisions will cause serious scattering loss, and the beam divergence angle will also increase. Even if the interference of the molecular ion can be eliminated in this process, due to 12 C / 13 C / 14 C trajectories are seriously divergent, resulting in very low system resolution, and high-precision analysis of C 14 is impossible. Especially at low energy, scattering is more serious, and resolution is difficult to improve. If a lighter charge exchange target is selected, it will help improve the resolution, but lighter gases such as H2 and He have very low charge exchange efficiency and are not suitable for negative ion generation.

[0048] Three interdependent factors: 1) To achieve efficient charge exchange, it is inevitable to choose a heavier non-metal gas molecular target; 2) To achieve molecular ion suppression, thick target stripping must be used; 3) In order to reduce the impact of scattering as much as possible during thick target stripping and charge exchange, without increasing the ion energy, a target with a smaller molecular weight must be selected, such as He. Therefore, based on the above three points, we propose the idea of segmented stripping and charge exchange, that is, using He gas to strip the molecular ion and then using a non-metal gas to charge exchange.

[0049] In some embodiments of the present application, a charge exchange system for carbon cation mass spectrometry is provided, which is composed as shown in Figure 2 Figure 1, comprising a pre-focusing module: used for preliminarily focusing the carbon cation generated by the ion source to adjust the beam waist position to the center of the charge exchange target; a stripping target (stripping gas): used to eliminate the interference of C-H molecular ions, the cavity can be filled with an appropriate amount of inert gas (such as He gas), and stripping is achieved through ion and gas collision; 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.

[0050] 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:

[0051] 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.

[0052] 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.

[0053] 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 .

[0054] 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.

[0055] 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.

[0056] Step 6: Non-metallic charge exchange gas is introduced into the charge exchange target to charge exchange the beam after stripping.

[0057] Step 7: The C - ions after charge exchange are focused by using a post-focusing module and enter a magnet analyzer, and the ions are selected by adjusting the magnetic field strength of the analyzer magnet.

[0058] Step 8: The flow rate of the charge exchange gas is adjusted, and the C - ion current is measured in a measurement module and recorded as .

[0059] Step 9: The extraction voltage is changed, and steps 5, 6, 7 and 8 are repeated, and the corresponding C - current is recorded.

[0060] Step 10: The charge exchange efficiency under different conditions is calculated, and the quantitative relationship between the charge exchange efficiency and parameters such as energy and gas flow rate is given. .

[0061] Step 11: C 14 analysis is performed under the condition of the highest charge exchange efficiency, and the obtained C - ions pass through two sets of electrostatic analyzers and magnetic analyzers, and the C 14 ions are counted by using a detector to obtain C - / C 14 , C 13 / C 14 and C 12 / C values, and information such as the age of the sample is given.

[0062] The parts not described in detail in the present application can refer to the prior art or be known to those skilled in the art, and the present embodiment is not limited thereto, and will not be described in detail here.

[0063] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the above specific embodiments, and the above specific embodiments are only illustrative and not limiting, and those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which all belong to the protection of the present application.

Claims

1. A method for C + ion mass spectrometry based on C 14 ions, characterized in that, The method: By means of sectional stripping and charge exchange, the target is stripped by using a specific gas to eliminate the interference of C-H molecular ions, and then the C - ions are formed by charge exchange of the target with a non-metallic gas, in combination with pre-focusing, post-focusing, magnetic analysis and electrostatic analysis, to obtain 14 C / 13 C and 14 C / 12 C values. The specific gas is any one or more of He, Ar, N2; The steps of the method include: S1, obtaining a working vacuum environment by pumping; S2, release the ion beam and provide the required extraction voltage to control C + Energy at the time of ion charge exchange; S3, set the gas inlet amount of the stripping target and the charge exchange target to 0, adjust the front and rear focusing parameters and the magnet magnetic field analysis parameters, so that C + Ions can achieve good focusing and transmission, and measure and record C + Flow intensity I c+ ; S4, adjusting 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 gas consumption of the charge exchange gas; S5, introducing the specific gas into the stripping target to perform C-H molecular ion stripping, and adjusting the gas flow of the specific gas to ensure elimination of interference while obtaining higher transmission efficiency; S6, introducing a non-metallic gas into the charge exchange target to perform charge exchange on the stripped beam; S7、to the charge exchange after C - After the ions are post-focused, they are analyzed by a magnetic field of an analyzing magnet, and the ions are selected by adjusting the magnetic field strength of the analyzing magnet. S8, adjust the flow rate of the charge exchange gas, measure and record C - Ion current I c- ; S9, changing the extraction voltage and returning to S5 until the exit condition is met; S10, the charge exchange efficiency under different conditions is obtained by calculation, and the quantitative relationship between the charge exchange efficiency and the related parameters is obtained; the calculation method of the charge exchange efficiency is: ; S11. Under the condition of the highest charge exchange efficiency 14 C analysis, the obtained C - ions pass through two sets of electrostatic and magnetic analyzers, and are detected by a detector 14 C - counted to obtain 14 C / 13 C and 14 C / 12 C values, giving the age information of the sample.

2. The method according to claim 1, wherein the carbonium ion mass spectrometry device is based on C + ions 14 C analysis, characterized by, C generated by the ion source + Ion current is greater than 6 mA.

3. The carbocation mass spectrometry device of claim 1, wherein the C + ions are analyzed based on C 14 in the method. The non-metallic gas is any one or more of H2, CH4, C2H4, and C4H 10 .

4. The carbocation mass spectrometer apparatus of claim 1, wherein the C + ions are analyzed based on C 14 In step S2 the ion beam is C with a current > 6 mA + Ion beam. ​ 5. The carbocation mass spectrometer apparatus of claim 1, wherein the C + ions are analyzed based on C 14 , wherein the C The extraction voltage range in steps S2 and S9 is 25-80 kV.

6. The carbocation mass spectrometer device of claim 1, wherein the C + ions are subjected to 14 C analysis. The relevant parameters in step S10 are energy and / or gas flow.

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