Method for determining xenon isotope based on electron cyclotron resonance mass spectrometer

Abstract

The invention provides a method for measuring xenon isotope based on an electron cyclotron resonance mass spectrometer, which comprises the following steps: S1, introducing a xenon sample to be measured into the electron cyclotron resonance mass spectrometer, controlling the gas flow, and ensuring the vacuum degree of the electron cyclotron resonance mass spectrometer; s2, debugging the electron cyclotron resonance mass spectrometer to enable the signal of the electron cyclotron resonance mass spectrometer to be stable; and S3, setting parameters of the electron cyclotron resonance mass spectrometer, and analyzing the xenon sample to be detected to obtain response values and mass spectrograms of corresponding elements. According to the method for measuring the xenon isotope by using the electron cyclotron resonance mass spectrometer, ionization and simultaneous measurement of the xenon isotope composition can be realized under low concentration, and the method has the advantages of low detection limit, high sensitivity, high accuracy, rapid detection and the like, provides more visual and high-reliability data for nuclear industry field check, and is suitable for popularization and application. And reliable data support is provided for determining nuclear activity properties.

Description

Technical Field

[0001] The present invention relates to the technical field of isotope analysis, and in particular to a method for measuring xenon isotopes based on an electron cyclotron resonance mass spectrometer. Background Art

[0002] ICP-MS and ICP-AES based on inductively coupled plasma (ICP) have the advantages of simultaneous detection of multiple elements, fast analysis speed, good selectivity, and wide linear range, and are widely used in metal impurity analysis. For mass spectrometers, the higher the ionization degree of the ion source, the better the ionization rate, and the higher the measurement sensitivity. As the ion source of ICP-MS, the ionization rate of ICP in practical applications is about 1%, the beam intensity is low, and there are many polyatomic ions, which seriously interfere with the measurement sensitivity of ICP-MS.

[0003] Radioactive xenon (Xe) is 235 U and 239 The fission product of the chain reaction of Pu and other fissile nuclides. The radioactive xenon in the global atmosphere mainly comes from the daily operation of nuclear explosions, nuclear power reactors and isotope production reactors. The Comprehensive Nuclear-Test-Ban Treaty proposes that suspicious nuclear explosions can be detected by monitoring the activity changes of radioactive xenon isotopes in the global atmosphere. At the same time, it is also an important radioactive nuclide to determine whether the reactor is operating safely. Experimental fission products 131 Xe / 129 Xe, 132 Xe / 129 Xe, 134 Xe / 129 Xe combined with reactor-related data can be used to derive useful information about the fuel being processed. The reprocessing plant uses the PUREX chemical process to extract plutonium from spent fuel. In the two operating steps of mechanical cutting and nitric acid dissolution, about 95% of the rare gases are directly discharged into the atmosphere through the flue to mix with the air without being chemically affected. The isotopic abundance information of the xenon gas produced by fission is extracted from the flue gas, and combined with the reactor theoretical calculation, the information of the nuclear fuel being processed can be derived. In the 1960s, E.A. Villarino and others from the Idaho National Laboratory in the United States proposed the concept of using the abundance ratio of Kr and Xe stable isotopes in the ambient atmosphere as a means of monitoring reprocessing nuclear activities.

[0004] At present, the radioactive method (such as high-purity germanium gamma spectrometer, proportional counter) is mainly used at home and abroad to measure the concentration of enriched gas. 127 Xe, 131m Xe, 133m Xe, 133 Xe, 135The activity or content of Xe has the advantage of fast analysis speed, but the disadvantage is poor precision (about 2% to 5%). There are a few methods that use magnetic mass spectrometers (such as Helix SFT, Helix MC Plus, MAT253, MC-ICP-MS) to measure xenon isotope ratios. Xe has 9 stable isotopes, so in order to measure the abundance composition of all Xe isotopes, the detector of the above-mentioned mass spectrometer is generally composed of multiple electron multipliers and Faraday cups or at least two injections are used to complete the measurement of all isotopes. In addition, since the first ionization potential of Xe is 12.13eV, it is an element with a low ionization degree, and the ion source directly determines the technical indicators such as the sensitivity of the mass spectrometer to a large extent, it is very necessary to select an ion source with strong ionization ability. At present, there is no research on the measurement of Xe isotope ratios and its application using a quadrupole mass spectrometer based on an ECR ion source.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The object of the present invention is to provide a method for determining xenon isotopes based on an electron cyclotron resonance mass spectrometer, which can realize ionization at low concentration (ppb level) and simultaneous determination of the composition of xenon isotopes, and its detection results have excellent technical indicators such as accuracy, precision, sensitivity and detection limit.

[0007] A first aspect of the present invention provides a method for determining xenon isotopes based on an electron cyclotron resonance mass spectrometer, comprising the following steps:

[0008] S1. Pass the xenon gas sample to be tested into the electron cyclotron resonance mass spectrometer, control the gas flow rate, and ensure the vacuum degree of the electron cyclotron resonance mass spectrometer;

[0009] S2. Debugging the electron cyclotron resonance mass spectrometer to stabilize the signal of the electron cyclotron resonance mass spectrometer;

[0010] S3. Setting the parameters of the electron cyclotron resonance mass spectrometer, analyzing the xenon gas sample to be tested, and obtaining the response value and mass spectrum of the corresponding element.

[0011] Preferably, in step S1, the gas flow rate is controlled to be (0.4-0.6) ml / min, more preferably 0.5 ml / min.

[0012] Preferably, in step S1, the vacuum degree of the electron cyclotron resonance mass spectrometer is ensured to be (4-6)×10 -3 Pa, more preferably 5×10 -3 Pa.

[0013] Preferably, in step S1, the xenon gas sample to be measured includes: any one of: working standard xenon gas, xenon tail gas emitted from nuclear facilities, or xenon gas before and after purification. The method of the present invention can measure both working standard Xe gas and Xe tail gas emitted from nuclear facilities, and can also calibrate the isotope ratio of Xe gas before and after purification.

[0014] Preferably, in step S1, the concentration of the xenon sample to be tested is at the ppb level.

[0015] Preferably, in step S2, the debugging includes: detector baseline calibration, quadrupole tuning, resolution tuning and mass axis calibration.

[0016] Preferably, in step S3, the electron cyclotron resonance mass spectrometer parameters include: mass number, dwell time, number of channels, interval and number of main scans.

[0017] The second aspect of the present invention provides a system for using the above-mentioned method for determining xenon isotopes based on an electron cyclotron resonance mass spectrometer, comprising: an electron cyclotron resonance mass spectrometer and a gas sampling device connected thereto.

[0018] Preferably, the gas sampling device comprises a xenon gas storage device and a gas flow controller which are connected in sequence, and the gas flow controller is connected to the electron cyclotron resonance mass spectrometer.

[0019] Preferably, the electron cyclotron resonance mass spectrometer is provided with an ECR ion source module, a quadrupole mass analyzer module and an ion detector module.

[0020] The electron cyclotron resonance (ECR) ion source is a kind of ion source that uses the electric field in high-frequency electromagnetic waves (microwaves) to heat electrons, so that the electrons have high enough energy. These electrons collide with atoms in the gas, "knock off" the outer electrons of the gas atoms to produce singly charged ions. Compared with traditional ion sources, the biggest advantage of the ECR ion source is its strong ion beam current and high ionization rate (90%). Based on the above advantages of the ECR ion source, the ECR ion source was used to replace the traditional ICP ion source in ICP-MS, and an electron cyclotron resonance mass spectrometer (ECR-MS) was developed. The specific principle can be found in patent CN202018004196.8.

[0021] Beneficial effects:

[0022] The method of detecting xenon isotope abundance using ECR-MS in the present invention can realize ionization and simultaneous measurement of xenon isotope composition at low concentration (1ppm), and has the advantages of low detection limit, high sensitivity, high accuracy, rapid detection, etc., providing more intuitive and reliable data for on-site inspections in the nuclear industry, and providing reliable data support for determining the nature of nuclear activities. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The present invention provides an electron cyclotron resonance mass spectrometer and a schematic structural diagram of a gas sampling device connected thereto.

[0025] Figure 2 This is the xenon isotope measurement mass spectrum provided by the present invention.

[0026] Explanation of the accompanying drawings: 1. Xenon gas storage device; 2. Gas flow controller; 3. Electron cyclotron resonance mass spectrometer; 4. ECR ion source module; 5. Quadrupole mass analyzer module; 6. Ion detector module; 7. First sample injection line; 8. Second sample injection line. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example

[0031] This embodiment provides a method for determining xenon isotopes based on an electron cyclotron resonance mass spectrometer, comprising the following steps:

[0032] Connect the standard Xe gas cylinder to the inlet line of the mass spectrometer through a gas pressure reducing valve; if it is actual sampling, you can choose to collect the gas sample to be tested in a gas sampling bag or a stainless steel sample bottle, and connect the gas bag / gas cylinder to the inlet line of the mass spectrometer through a KF16 clamp.

[0033] The gas flow controller 2 on the sample inlet line was controlled by software to have a gas flow rate of 0.5 ml / min, ensuring that the vacuum degree of the electron cyclotron resonance mass spectrometer was within 5 × 10 -3 Pa, the mass spectrometer signal is stabilized through the following adjustments.

[0034] (1) Detector baseline correction

[0035] Through the mass spectrometer control software, open the cross correction interface, select full pass, and click the start correction button to start the cross correction step, that is, start the simulated background baseline subtraction. When the simulated background baseline subtraction is completed, click stop to complete the baseline correction.

[0036] (2) Quadrupole tuning

[0037] Through the mass spectrometer control software, open the quadrupole frequency modulation interface, set the starting frequency of the Q1 quadrupole and Q2 quadrupole to 1.9 MHz respectively, and then click the start frequency modulation button in turn. The software will debug the frequency according to the set step size until the minimum RF current under the given RF voltage is found, which means the frequency modulation is successful.

[0038] (3) Resolution tuning

[0039] After the quadrupole driving frequency is successfully tuned, the K and B values ​​of the corresponding mass segments are adjusted according to the actual changes in the mass spectrum peak shape to make the resolution of all isotope mass spectrum peak shapes reach the standard resolution, that is, about 0.75amu.

[0040] (4) Mass axis correction

[0041] Through the mass spectrometer control software, open the mass axis calibration interface and select the corresponding calibration isotope, such as 129 Xe, click Scan, and when the mass spectrum of the corresponding element appears after the scan is completed, click Fit to observe the deviation after fitting, and click Save to save the mass axis fitting function of the corresponding value. If the deviation is too large, manually modify the corresponding isotope voltage and refit.

[0042] After completing the above debugging, perform sample analysis and create a new method: select the appropriate mass number, set parameters such as dwell time, number of channels, interval, main scan times, and finally obtain the response value (ion count) and mass spectrum of the corresponding element.

[0043] like Figure 1As shown, this embodiment also provides a system using the above-mentioned method for determining xenon isotopes based on electron cyclotron resonance mass spectrometer, including: an electron cyclotron resonance mass spectrometer 3 (ECR-MS) and a gas sampling device connected thereto.

[0044] Specifically, the electron cyclotron resonance mass spectrometer 3 is provided with an ECR ion source module 4, a quadrupole mass analyzer module 5 and an ion detector module 6 (electron multiplier); the gas injection device includes a xenon gas storage device 1 and a gas flow controller 2 connected by a first injection line 7, and the gas flow controller 2 is connected to the electron cyclotron resonance mass spectrometer 3 through a second injection line 8.

[0045] ECR-MS uses an ECR ion source, which can provide a single-charged high-current ion beam, such as 60mA, and uses a magnetron to generate microwaves with a frequency of 2.45GHz. The ECR ion source inputs energy through microwaves, and the microwave energy enters the discharge chamber through the input window via waveguide or antenna coupling. Under the action of the high-intensity magnetic field generated by the permanent magnetic system on the upper surface of the window, the outer electrons of the gas molecules in the discharge chamber perform cyclotron motion. When the cyclotron angular frequency is equal to the angular frequency of the external microwave, it is in a resonant state. The moving electrons can continuously and effectively receive energy from the microwaves to increase the electron temperature and ionize the gas. After the ions are "screened" by the quadrupole mass analyzer, ions with a specific mass-to-charge ratio can be detected by the detector. By scanning the mass-to-charge ratio of a specific or each ion in the entire mass-to-charge ratio range, the ion signal intensity of the corresponding mass-to-charge ratio and a partial or complete mass spectrum can be obtained.

[0046] The following tests were also conducted during the experiment:

[0047] (1) Background noise test

[0048] After the basic parameters of the ECR-MS mass spectrometer are debugged, the pure Ar gas cylinder is connected to the ECR-MS sampling device pipeline. The gas flow rate is controlled to 0.5 ml / min by the mass flow controller. At this time, the vacuum degree of the ECR-MS is 5×10 -3 After the instrument signal is stable, a sequence is established to measure the ion counts at mass numbers 5amu and 220amu, with a dwell time of 20ms, 3 channels, an interval of 0.01, and 3 main scans. 20 data are measured respectively, and the average value is taken to calculate the background noise. The test data are shown in Table 1.

[0049] Table 1

[0050]

[0051] It can be seen from the data in Table 1 above that the background noise is less than 0.5 cps (5 amu, 220 amu).

[0052] (2) Testing and calculation of detection limit

[0053] After the basic parameters of the ECR-MS mass spectrometer are debugged, 0ppm, 1ppm and 10ppm Xe standard gases are prepared, of which 0ppm is replaced by high-purity Ar gas. The gas flow rate is controlled to 0.5ml / min by the gas flow controller 2 software. At this time, the vacuum degree of the ECR-MS is 5×10 -3 Pa. After the instrument signal is stable, a sequence is established to measure the ion counts at each isotope of the corresponding element, with a dwell time of 20ms, 3 channels, an interval of 0.01, 3 main scans, and 10 data points measured respectively. The detection limit calculation formula is as follows:

[0054]

[0055] Where: DL——Detection limit

[0056] SD——Blank standard deviation

[0057] A——isotope abundance

[0058] K——Slope of the fitting curve

[0059] Take the average value of 10 groups and get the test data in Table 2.

[0060] Table 2

[0061]

[0062]

[0063] Based on the above data, it can be calculated that for Xe gas injection, the detection limit of ECR-MS is Xe<2ppb.

[0064] (3) Sensitivity test

[0065] After the basic parameters of the ECR-MS mass spectrometer are debugged, 1ppm Xe standard gas is connected to the ECR-MS sampling device pipeline. The gas flow rate is controlled to 0.5ml / min by the gas flow controller 2 software. At this time, the vacuum degree of the ECR-MS is 5×10 -3 Pa. After the instrument signal is stable, a sequence is established to measure the ion counts at each isotope of the corresponding element, with a dwell time of 20 ms, 3 channels, an interval of 0.02, and 3 main scans.

[0066] Ten groups of data were tested, and the average of the response values ​​was calculated. After deducting the background noise, the sensitivity of each isotope was obtained, as shown in Table 3.

[0067] Table 3

[0068] <![CDATA[ 129 Car]]> <![CDATA[ 131 Car]]> <![CDATA[ 132 Car]]> <![CDATA[ 134 Car]]> <![CDATA[ 136 Car]]> Background noise 4085 3186 3769 1379 1125 Response value 256923 193266 234304 82028 63596 Sensitivity 252838 190080 230535 80649 62471

[0069] Can get 129 The sensitivity of Xe is 0.3Mcps / 1ppm.

[0070] (4) Absolute isotope abundance test

[0071] After the basic parameters of the ECR-MS mass spectrometer are debugged, 1ppm Xe standard gas is connected to the ECR-MS sampling device pipeline. The gas flow rate is controlled to 0.5ml / min by the gas flow controller 2 software. At this time, the vacuum degree of the ECR-MS is 5×10 -3 After the instrument signal is stable, a new method sequence is created with a dwell time of 50 ms, 3 channels, an interval of 0.02, and the number of main scans set to 3 times. The ion counts of each isotope of Xe are measured, 10 data are measured, and the abundance of each isotope is calculated. The accuracy of the absolute measurement results of ECR-MS isotopes is verified by comparing them with the isotope abundance reference value of natural Xe. The absolute abundance measurement results are shown in Table 4 and Figure 2 .

[0072] Table 4

[0073]

[0074] From Table 4 and Figure 2 The results show that the relative standard deviation of the measured values ​​of the 9 stable isotope abundances of Xe is ≤1.73%, indicating that the measurement method is stable and reliable. The error analysis of the measured values ​​of the abundance of Xe and the reference value is performed to characterize the accuracy of the isotope abundance measurement results of Xe based on ECR-MS. It can be seen from the data in Table 4 that the relative error between the measured values ​​of the abundance of each isotope and the reference value is within ±2.42%.

[0075] (5) Isotope abundance ratio test

[0076] After the basic parameters of the ECR-MS mass spectrometer are debugged, 1ppm Xe standard gas is connected to the ECR-MS sampling device pipeline. The gas flow rate is controlled to 0.5ml / min by the gas flow controller 2 software. At this time, the vacuum degree of the ECR-MS is 5×10 -3 After the instrument signal is stable, create a new method sequence with a dwell time of 50ms, 3 channels, an interval of 0.02, and the number of main scans as 3. 129 Xe is the reference isotope, and other isotopes of Xe are analyzed. 129 Abundance ratio of Xe, click Isotope Ratio, add 124 Xe / 129 Xe, 126 Xe / 129 Xe, 128 Xe / 129 Xe, 130 Xe / 129 Xe, 131 Xe / 129 Xe, 132 Xe / 129 Xe, 134 Xe / 129 Xe, 136 Xe / 129 Xe measures 10 data points respectively, and the isotope ratio is calculated or derived by the software.

[0077] Isotope abundance ratio is of great significance for studying nuclear fuel burnup, nuclear activities, etc. The isotope abundance ratio data of Xe are shown in Table 5.

[0078] Table 5

[0079]

[0080] From the above data, we can see that the measurement precision of Xe isotope ratio is good, the maximum relative standard deviation of the measurement result is 1.85%, and the relative error with the reference value of Xe isotope ratio is within ±3.05%.

[0081] In summary, the method for measuring xenon isotopes based on an electron cyclotron resonance mass spectrometer of the present invention can not only measure the working standard Xe gas, but also measure the Xe tail gas discharged from nuclear facilities, and can calibrate the isotope ratio of Xe gas before and after purification; in addition, the present invention also has the following advantages:

[0082] (1) Trace detection: The method of the present invention can ionize and measure xenon isotope ratios at low concentrations (1 ppm);

[0083] (2) Low detection limit: The detection limit of the Xe isotope ratio determined by the method of the present invention reaches the ppb level, less than 2 ppb;

[0084] (3) High sensitivity: The sensitivity of 129Xe is 0.3Mcps / 1ppm;

[0085] (4) The absolute abundance measurement results are highly precise and the relative error is small: the method of the present invention measures the Xe isotope abundance with a relative standard deviation of ≤1.73% and a relative error of ±2.42%;

[0086] (5) The isotope abundance ratio measurement results are highly precise and have a small relative error: The method of the present invention measures the Xe isotope abundance ratio with a relative standard deviation of ≤1.85% and a relative error of ±3.05%.

[0087] (6) Ability to simultaneously measure the isotopic composition of Xe: Compared with the magnetic mass spectrometer with a multi-collector detection system, it can simultaneously measure nine stable isotopes of Xe;

[0088] (7) Simple and quick operation: The detection method described in the present invention has a simple gas sampling device, simple operation steps, and data processing can be completed by software.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry, characterized in that: The steps include: S1. Pass the xenon gas sample to be tested into the electron cyclotron resonance mass spectrometer, control the gas flow rate, and ensure the vacuum degree of the electron cyclotron resonance mass spectrometer; S2. Debugging the electron cyclotron resonance mass spectrometer to stabilize the signal of the electron cyclotron resonance mass spectrometer; S3. Setting the parameters of the electron cyclotron resonance mass spectrometer, analyzing the xenon gas sample to be tested, and obtaining the response value and mass spectrum of the corresponding element.

2. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S1, the gas flow rate is controlled to be (0.4-0.6) ml / min.

3. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S1, the vacuum degree of the electron cyclotron resonance mass spectrometer is ensured to be (4-6)×10 -3 Pa.

4. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S1, the xenon gas sample to be tested includes: any one of: working standard xenon gas, xenon tail gas discharged from nuclear facilities, or xenon gas before and after purification.

5. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S1, the concentration of the xenon sample to be tested is at the ppb level.

6. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S2, the debugging includes: detector baseline calibration, quadrupole tuning, resolution tuning and mass axis calibration.

7. The method for determining xenon isotopes based on electron cyclotron resonance mass spectrometry according to claim 1, characterized in that: In step S3, the parameters of the electron cyclotron resonance mass spectrometer include: mass number, dwell time, number of channels, interval and main scan times.

8. A system using the method for determining xenon isotopes based on an electron cyclotron resonance mass spectrometer as described in any one of claims 1 to 7, characterized in that: include: An electron cyclotron resonance mass spectrometer and a gas sampling device connected thereto.

9. The system according to claim 8, characterized in that The gas sampling device comprises a xenon gas storage device and a gas flow controller which are connected in sequence, and the gas flow controller is connected to the electron cyclotron resonance mass spectrometer.

10. The system according to claim 8, characterized in that The electron cyclotron resonance mass spectrometer is provided with an ECR ion source module, a quadrupole mass analyzer module and an ion detector module.

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