Method for measuring oxygen isotope of hematite based on secondary ion mass spectrometry

Abstract

The invention discloses a method for measuring oxygen isotope of hematite based on secondary ion mass spectrometry, which comprises the following steps: bombarding a hematite standard sample with known oxygen isotope by using a secondary ion mass spectrometer through a cesium ion source by using a beam spot with the diameter of 15-25 mu m, and carrying out 50 groups of measurement, calculating the standard deviation between the standard sample groups and the average value between the standard sample groups; when two times of the standard deviation between the standard sample groups is smaller than a preset threshold value, instrument mass fractionation IMF is determined based on the hematite standard sample delta 18O value of the known oxygen isotope and the average value between the standard sample groups; and after the same depth measurement is carried out on the unknown hematite sample, the delta < 18 > O value of the unknown hematite sample is calculated through the instrument mass fractionation IMF and the average value between unknown sample groups. Through comparative analysis of fractionation characteristics and instrument stability, the oxygen isotope of the to-be-measured sample can be accurately measured. The method is rapid, efficient and high in reliability, and the determination precision of the oxygen isotope of the hematite is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of chemical detection, and more specifically, relates to a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry. Background Art

[0002] Hematite is a common iron oxide mineral and the primary source of iron ore. It occupies a crucial position in global iron ore resources and has a significant impact on economic development. Hematite also holds extensive research interest in earth and environmental sciences. In particular, the study of this mineral's oxygen isotopes has important applications in paleoclimate temperature reconstruction, planetary science, and environmental science. Therefore, in-depth research on hematite's oxygen isotopes is not only of great scientific significance but also holds significant economic value.

[0003] At present, the main technologies for accurate analysis of oxygen isotopes in hematite include laser fluorination and secondary ion mass spectrometry (SIMS). Laser fluorination heats the sample with a laser and reacts with bromine pentafluoride to produce oxygen, and then uses a mass spectrometer to measure the oxygen isotope ratio. Although this method has high precision, the sample preparation process is complicated, which limits its wide application. In contrast, secondary ion mass spectrometry (SIMS) is a micro-area analysis technology with high spatial resolution. It can perform oxygen isotope analysis at the micron scale and is particularly suitable for studying the isotope distribution inside minerals. In addition, SIMS also has the characteristics of extremely small sampling volume. The sample remains basically intact after analysis and can be used for subsequent research.

[0004] The working principle of SIMS technology is to use a primary ion beam (such as cesium ions, with an intensity of about 1-2nA and a beam spot of about 10μm) to bombard the surface of a solid sample and sputter out secondary ions. These secondary ions are separated by a mass analyzer under the action of an accelerating voltage (usually 10kV) and eventually reach the receiver. The receiver system obtains the absolute intensity or ratio of the signal by measuring the ion flow intensity of a specific mass (usually the measurement time is about 1 minute). In oxygen isotope analysis, two Faraday cup receivers measure simultaneously. 16 O and 18 O ion current intensity, the ratio R= 18 O / 16 O, and δ 18 The form of O is expressed as (δ 18 O = (R / 0.0020052-1) × 1000). For oxygen isotope analysis of oxygen-containing minerals, the typical precision of SIMS is about 0.2‰-0.3‰ (1SD).

[0005] However, as early as 15 years ago, Huberty et al. discovered that SIMS analysis of hematite oxygen isotopes suffers from a crystal orientation effect, resulting in poor analytical precision (SD > 1‰), which severely limits the application of hematite oxygen isotope analysis in geochemical studies. The crystal orientation effect refers to the phenomenon that differences in atomic arrangement and chemical bond orientation on different crystal planes of a mineral crystal lead to changes in ion yield and isotopic fractionation in secondary ion mass spectrometry (SIMS) analysis.

[0006] Currently, there are methods for using electron backscatter diffraction to correct for the effects of hematite crystal orientation on SIMS oxygen isotope analysis. Another approach is to reduce the secondary ion emission voltage (from 10 kV to 5 kV) to mitigate the effects of crystal orientation. However, this method requires instrument recalibration, is difficult to operate, and results in an increased beam spot size and reduced spatial resolution.

[0007] Therefore, developing a method that can improve the accuracy of hematite oxygen isotope analysis without sacrificing spatial resolution, while reducing technical difficulty and enhancing operability has become an urgent need in current research. Summary of the Invention

[0008] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry, the purpose of which is to reduce the significant differences in isotope ratios of hematite oxygen isotopes in different surface areas, thereby avoiding affecting the reliability of the test.

[0009] To achieve the above object, according to one aspect of the present invention, a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry is provided, the method comprising:

[0010] Using a secondary ion mass spectrometer, a cesium ion source was used to bombard hematite standard samples with known oxygen isotopes using a beam spot diameter of 15-25 μm. Fifty groups of measurements were performed, each consisting of 40 2-second cycles. The standard deviation and mean value between the standard sample groups were calculated.

[0011] When the standard deviation between the two standard sample groups is less than the preset threshold, the hematite standard sample δ 18 The O value and the average value between the standard sample groups determine the instrument mass fractionation IMF;

[0012] After measuring the same depth of the unknown hematite sample, the δ 18 O value.

[0013] Preferably, the method comprises:

[0014] Before the beam spot bombards the hematite standard sample with known oxygen isotope, the stability test of the instrument is performed. The stability test uses at least 3 glass standard samples. If the glass standard sample δ 18 A distribution range of less than 1‰ indicates that the instrument has passed the stability test.

[0015] Preferably, during measurement, two or more crystal faces of the hematite particle sample need to be tested alternately.

[0016] Preferably, the calculation method of the instrumental mass fractionation IMF comprises:

[0017] Calculate the arithmetic mean of each group of 40 2-second cycle data to obtain the arithmetic mean within the standard sample group and calculate the standard deviation within the standard sample group;

[0018] Calculating the inter-group mean and inter-group standard deviation of standard samples of the same group of multiple particles based on the intra-group arithmetic mean and the intra-group standard deviation of the standard samples;

[0019] If the standard deviation between the standard sample groups is less than the preset threshold, the current group is taken, and the average value of the standard sample groups corresponding to the current group and the delta of the standard sample are used. 18 O value calculation IMF.

[0020] Preferably, the method further comprises:

[0021] When measuring an unknown hematite sample, the same ion beam sputtering time window as that of the hematite standard sample with known oxygen isotopes must be maintained.

[0022] Preferably, the method further comprises:

[0023] The glass standard sample, the hematite standard sample with known oxygen isotope and the unknown hematite sample are fixed on a glass sheet by double-sided tape, and a test target is formed after vacuum curing of epoxy resin, and the surface of the test target is flat.

[0024] Preferably, the δ 18 The O value is -1.12±0.14‰.

[0025] Preferably, when using a secondary ion mass spectrometer for measurement, the measurement time for each group is 2-3 minutes, and the interval between two adjacent groups of measurements is ≤5 minutes.

[0026] Preferably, based on a hematite standard sample of known oxygen isotope δ 18 The method for determining the instrumental mass fractionation IMF by comparing the O value with the average value between the standard sample groups includes:

[0027] Instrumental mass fraction IMF = δ of the hematite standard sample based on known oxygen isotopes 18 The average value of the standard sample group was subtracted from the O value.

[0028] Preferably, after measuring the same depth of the unknown hematite sample, the δ 18 O-value methods include:

[0029] δ of unknown hematite samples 18 O value = instrument mass fraction IMF + the average value among the unknown sample groups.

[0030] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0031] This paper provides a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry. By comparing fractionation characteristics and instrument stability, it can accurately determine the oxygen isotopes of the sample being tested. This method is rapid, efficient, and highly reliable, significantly improving the precision of hematite oxygen isotope measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0033] Figure 1 This is a flow chart of a method for measuring oxygen isotopes in hematite based on secondary ion mass spectrometry provided in the first embodiment;

[0034] Figure 2 a is a graph showing the relationship between the oxygen isotope values ​​of the hematite standard sample measured using SIMS and the measured depth in Example 1;

[0035] Figure 2 b is a graph showing the relationship between the precision of the oxygen isotope measurement values ​​of the hematite standard sample obtained by SIMS in Example 1 and the measurement depth;

[0036] Figure 2 c is a graph showing the relationship between the oxygen isotope values ​​of the hematite sample tested using SIMS and the measured depth in Example 1;

[0037] Figure 3 a is a side view of the sample target provided in Example 1;

[0038] Figure 3 b is a distribution diagram of the glass standard sample, the hematite standard sample and the sample to be tested on the sample target surface in the first embodiment. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0040] Existing techniques can reduce the potential for significant differences in isotope ratios between different surface regions of hematite oxygen isotopes. To mitigate this, researchers have proposed various approaches. For example, Huberty suggests combining SIMS with electron backscatter diffraction (EBSD) to assess the influence of crystal orientation, and attempts to minimize the crystal orientation effect by reducing the incident intensity of primary ions. However, these methods still suffer from significant reproducibility issues in practical applications, resulting in significant intra- and inter-granular variations in SIMS-based hematite oxygen isotope test results.

[0041] Since the measurement of hematite oxygen isotopes is affected by the crystal orientation effect, it is necessary to study the distribution law of its internal oxygen isotopes in order to establish a correction method and improve the precision of the test results.

[0042] Example 1

[0043] This embodiment provides a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry, the method comprising the following steps: Figure 1 As shown:

[0044] S101: Using secondary ion mass spectrometry, bombard a hematite standard sample of known oxygen isotope composition with a cesium ion source using a 15-25 μm diameter beam spot. Perform 50 sets of measurements, each consisting of 40 2-second cycles. Calculate the standard deviation and mean between-set standard.

[0045] The stability test of the SIMS was performed before the beam spot was bombarded with a hematite standard sample of known oxygen isotopes.

[0046] Use glass standard samples with known oxygen isotope values ​​to test the stability of the secondary ion mass spectrometer. At least three glass standard samples are used. If the glass standard samples δ 18The O distribution range is less than 1‰, which means the instrument has passed the stability test. For example, collect 10 sets of oxygen isotope values ​​of glass standard sample Nist610, and record them as δ 18 O Measured-Nist610-1 , δ 18 O Measured -Nist610-2,…,δ 18 O Measured-Nist610-10 ).

[0047] When using secondary ion mass spectrometry, the measurement time for each group is 2-3 minutes, and the interval between two adjacent groups of measurements is ≤5 minutes.

[0048] Calculate the glass standard deviation SD of the above 10 sets of data 玻璃 , recorded as SD Nist610 , if SD is satisfied Nist610 <0.5‰, proceed to the next step; otherwise, debug the secondary ion mass spectrometer and repeat the first step until the conditions are met.

[0049] Collect oxygen isotopes of hematite standard samples 18 O and 16 O instrument signal and calculate its oxygen isotope ratio data using the Vienna Standard Mean Ocean Water (VSMOW); 18 O / 16 O=0.0020052) for normalization, the formula is as follows: 18 O VSMOW =(( 18 O / 16 O)Measured value / 0.0020052-1)×1000. For example:

[0050] 2000 measurements were performed on 10 particles of a hematite standard sample (SH9264) with known oxygen isotope values.

[0051] The first measured ratio of the first particle is recorded as D -SH9264-p1-C1 ,

[0052] The kth measurement ratio of the first particle is recorded as D -SH9264-p1-Ck , where k = 1, 2,…, 2000.

[0053] The first measurement ratio of the jth particle is recorded as D -SH9264-pj-C1 , where j = 1, 2, ..., 10

[0054] The kth measurement ratio of the jth particle is recorded as D -SH9264-pj-Ck , where j = 1, 2,…, 10, k = 1, 2,…, 2000.

[0055] The measurement results of each particle are divided into a group of 40 consecutive measurements.

[0056] Group 1: 1st to 40th measurements.

[0057] Group 2: 41st to 80th measurements.

[0058] Group i: kth to k+39th measurements.

[0059] Where i = 1, 2, ..., 50; k = (i-1) * 40 + 1, the values ​​are (1, 41, 81, ..., 1961)

[0060] The last group: measurements 1961 to 2000.

[0061] Calculate the arithmetic mean of each group of 40 2-second cycle data to obtain the arithmetic mean within the standard sample group and calculate the standard deviation within the standard sample group;

[0062] Calculating the inter-group mean and inter-group standard deviation of standard samples of the same group of multiple particles based on the intra-group arithmetic mean and the intra-group standard deviation of the standard samples;

[0063] If the standard deviation between the standard sample groups is less than the preset threshold, the current group is taken, and the average value of the standard sample groups corresponding to the current group and the delta of the standard sample are used. 18 O value calculation IMF.

[0064] Calculate the arithmetic mean and standard deviation of the hematite standard sample within the standard sample group:

[0065] The arithmetic mean and standard deviation of the standard sample group i of the jth particle in the SH9264 sample are expressed as A -SH9264-pj-gi and SD -SH9264-pj-gi ,

[0066]

[0067] Where j = 1, 2,…, 10; i = 1, 2,…, 50; k = (i-1)*40+1, and the resulting values ​​are (1, 41, 81,…, 1961) respectively.

[0068]

[0069] Among them, j=1,2,…,10; i=1,2,…,50; k=(i-1)*40+1, and the resulting values ​​are (1,41,81,…,1961) respectively.

[0070] Then calculate the average value and standard deviation of all hematite standard sample particles in the same group, that is, the same measurement depth.

[0071] The average value of the standard samples in group i is:

[0072] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50;

[0073] The standard deviation between standard samples in group i is:

[0074] Where j = 1, 2,…, 10; i = 1, 2,…, 50.

[0075] S102: When the standard deviation between the two standard sample groups is less than the preset threshold, the hematite standard sample δ 18 The O value was compared with the average value among the standard sample groups to determine the instrument quality fractionation IMF.

[0076] In this embodiment, the first preset threshold is set to 0.5‰. If 2SD -SH9264-gi If the value of i is less than or equal to 0.5‰, the current value of i is taken and the process proceeds to S103; otherwise, the process continues until the condition is met. The range of i is 1-50, and the first i that meets the condition is used as the reference, and the subsequent values ​​are discarded.

[0077] According to the known value of δ 18 O SH9264 =-1.12‰, calculate the instrumental mass fractionation IMF:

[0078] IMF=δ 18 O SH9264 -AA SH9264-gi .

[0079] S1043: After measuring the same depth of the unknown hematite sample, calculate the δ of the unknown hematite sample by using the instrument mass fractionation IMF and the average value between the unknown sample groups. 18 O value standard sample.

[0080] When measuring an unknown hematite sample, the same ion beam sputtering time window as that of the hematite standard sample with known oxygen isotopes must be maintained.

[0081] Calculate the inter-group mean and inter-group standard deviation of all unknown oxygen isotope values ​​of hematite samples (UH01) in the same group of unknown samples at the same depth as the measurement of the hematite standard sample particles.

[0082] The average value of unknown samples among groups i is:

[0083] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50;

[0084] The oxygen isotope value δ of the unknown hematite sample was obtained by combining the instrument mass fractionation of the detection instrument and the average value between the unknown sample groups. 18 O UH01 , δ 18 O UH01 =IMF+AA UH01-gi .

[0085] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the method of using a glass standard sample with a known oxygen isotope value to perform a stability test on a detection instrument includes:

[0086] Using the detection instrument to collect instrument signals of no less than three glass standard samples, and obtain the oxygen isotope value of each glass standard sample;

[0087] Calculating the distribution range of oxygen isotope values ​​of all the glass standard samples;

[0088] If the distribution range is less than 1‰, it means that the detection instrument has passed the stability test.

[0089] In this embodiment 1, 10 glass standard samples are selected.

[0090] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the method of performing multiple sets of measurements on the crystal faces of each hematite standard sample particle with a known oxygen isotope value by the detection instrument includes:

[0091] During measurement, two or more crystal faces of the hematite particle sample need to be tested alternately.

[0092] In the first embodiment of the present invention, multiple measurements are performed on different crystal planes of a hematite standard sample with known oxygen isotope values. By calculating the variation range of the hematite measurement values ​​in different test time periods, the measurement value with a variation range less than or equal to the variation range of the instrument is taken as the best measurement result. The corresponding sampling time and sampling range are determined as the optimal test time and sampling range of the hematite sample, thereby improving the measurement precision.

[0093] The optimal test time and sampling range is to obtain a stable interval of the later measurement value through long-term measurement. The stable measurement value is manifested by a smaller SD. When the instrument is stable, the sampling range at the same time point is the same. In this embodiment, the standard deviation between the standard sample groups is set to meet 2SD. -SH9264-gi Less than 0.5‰.

[0094] like Figure 2 a is a graph showing the relationship between the test ratio of three different hematite standard sample SH9264 particles and the measurement depth. Figure 2b is a graph showing the relationship between the precision of the test ratios of three different hematite standard sample SH9264 particles (represented here by 2 times the standard deviation, i.e., 2SD) and the measurement depth.

[0095] For hematite samples with uniform oxygen isotope values, for example, the precision of the oxygen isotope value of the hematite standard sample SH9264 with three known oxygen isotope values ​​is 2SD = 0.14‰. Although the differences in the oxygen isotope values ​​tested by SIMS on multiple particle surfaces are large, for example, using a 40-cycle test with a test time of 3 minutes, the precision is 2SD = 1.57‰. Figure 2 As shown in Figure (a), the oxygen isotope ratios of three different hematite standard sample SH9264 particles gradually converge with increasing test depth and test time. This significantly improves measurement precision. When the test cycle is increased to 1520 (54 minutes), the precision increases to 2SD = 0.48‰. At 2000 cycles (76 minutes), the precision increases to 2SD = 0.34‰.

[0096] like Figure 2 As shown in a, the horizontal axis is the number of cycles measured, a total of 2000 cycles, and each cycle is 2 seconds. The vertical axis is the change in the hematite oxygen isotope ratio, which is represented by 2 times the standard deviation between groups, that is, 2SD. It can be seen that with the increase of time (that is, the number of cycles), the change in the hematite oxygen isotope ratio becomes smaller. For example, the 2SD from the first cycle to the fortieth cycle is 1.57‰, which is Figure 2 The 2SD of the first point in b, from the 1481st cycle to the 1520th cycle, is 0.48‰. Figure 2 The 38th point of b. The 2SD from the 1961st cycle to the 2000th cycle is 0.34‰, which is Figure 2 The last point of b.

[0097] like Figure 2 As shown in a, the relationship between the measured oxygen isotope values ​​of the hematite standard sample obtained by SIMS and the measured depth. Figure 2 As shown in c, the relationship between the oxygen isotope measurement values ​​of the hematite sample obtained by SIMS and the measurement depth. Since SIMS is a relative measurement method, it was found that at the same measurement depth, the test values ​​of different hematite samples have consistent instrument quality fractionation. The consistency of instrument quality fractionation is determined from Figure 2 a and Figure 2The difference between the ordinates of the two curves in Figure c is consistent. By calibrating hematite standard particles with known oxygen isotope values ​​against hematite samples with unknown oxygen isotope values, accurate oxygen isotope values ​​for the hematite samples can be obtained, enabling high-precision measurements. This discovery provides a scientific basis for addressing measurement bias caused by hematite crystal orientation effects and lays the foundation for calibration methods.

[0098] like Figure 2 As shown in b, the horizontal axis is the number of cycles of measurement, a total of 2000 cycles, each cycle is 2 seconds. The vertical axis is the measured value of the hematite oxygen isotope ratio, expressed as δ 18 The calculation method is: using Vienna Standard Mean Ocean Water (VSMOW; 18 O / 16 O=0.0020052) for normalization, the formula is as follows: 18 O VSMOW =(( 18 O / 16 O)Measured value / 0.0020052-1)×1000. Figure 2 a and Figure 2 c are two different hematite samples. Figure 2 a is the curve of the measurement values ​​of 3 SH9264 changing with time; Figure 2 Figure c shows the time-varying curve of the three UH01 measurements. The difference between the three SH9264 measurements and the average of the three UH01 measurements remains constant over time. This indicates that the instrumental fractionation characteristics of the two samples are identical, meaning that the instrumental mass fractionation of hematite is identical at the same test time, depth, and cycles.

[0099] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the method for obtaining the standard deviation between each group of standard samples of each hematite standard sample particle with a known oxygen isotope value includes:

[0100] The inter-group average of the standard samples for all particles at the same measurement depth is calculated from the intra-group arithmetic mean and the intra-group standard deviation of the hematite standard sample particles with known oxygen isotope values ​​within the group;

[0101] The standard deviation SD between standard sample groups was calculated from the mean value between the standard sample groups. 已知 ;

[0102] If the standard deviation SD between the standard sample groups 已知 Meet 2SD 已知 < the first preset threshold, indicating that the sampling range of the hematite standard sample particles with known oxygen isotope values ​​has passed the test.

[0103] In this embodiment 1, the arithmetic mean value and the standard deviation of the hematite standard sample within the standard sample group are calculated:

[0104] The arithmetic mean and standard deviation of the i-th group of the j-th particle in the hematite standard sample SH9264 are expressed as A -SH9264-pj-gi and SD -SH9264-pj-gi ,

[0105]

[0106] Where j = 1, 2,…, 10; i = 1, 2,…, 50; k = (i-1)*40+1, and the resulting values ​​are (1, 41, 81,…, 1961) respectively.

[0107]

[0108] Among them, j=1,2,…,10; i=1,2,…,50; k=(i-1)*40+1, and the resulting values ​​are (1,41,81,…,1961) respectively.

[0109] Then calculate the first average value of all hematite standard sample particles in the same group, that is, the same measurement depth, and the standard deviation between the standard sample groups.

[0110] The average value of the standard samples in group i is:

[0111] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50;

[0112] The standard deviation between standard samples in group i is:

[0113] Where j = 1, 2,…, 10; i = 1, 2,…, 50.

[0114] The first preset threshold is set to 0.5‰. If 2SD -SH9264-gi If the condition is <=0.5‰, the current value of i is used and the next step is entered; otherwise, the calculation continues until the condition is met. The range of i is 1-50.

[0115] In the first embodiment, the value of i is 38, the inter-group mean value of the standard samples of the i=38th group is -61.92‰, and the inter-group standard deviation of the standard samples of the i=38th group is 0.48‰.

[0116] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the calculation method of the instrument mass fractionation of the detection instrument is:

[0117] The average value among the standard samples that meet the sampling range test is subtracted from the known oxygen isotope value of the hematite standard sample.

[0118] Instrumental mass fraction IMF = δ of the hematite standard sample based on known oxygen isotopes 18 The average value of the standard sample group was subtracted from the O value.

[0119] In this embodiment 1, the known value δ of the hematite standard sample 18 O SH9264 =-1.12‰, instrumental mass fractionation IMF: IMF = δ 18 O SH9264 -AA SH9264-gi In this example, the value of IMF is 60.80‰

[0120] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the method for obtaining the oxygen isotope value of the hematite sample by combining the instrument mass fractionation of the detection instrument includes:

[0121] The inter-group mean of the unknown samples of all particles at the same measurement depth was calculated from the arithmetic mean and standard deviation of the unknown samples within the group for each hematite sample with unknown oxygen isotope value.

[0122] In this Example 1, the arithmetic mean and standard deviation of the unknown sample group of the hematite sample (UH01) with unknown oxygen isotope value are calculated:

[0123] The arithmetic mean and standard deviation of the unknown sample group i of the jth particle in the hematite sample UH01 with unknown oxygen isotope value are expressed as A -UH01-pj-gi and SD -UH01-pj-gi ,

[0124]

[0125] Where j = 1, 2,…, 10; i = 1, 2,…, 50; k = (i-1)*40+1, and the resulting values ​​are (1, 41, 81,…, 1961) respectively.

[0126] When i = 38, the arithmetic mean of the unknown sample group of j = 1 UH01 particles is -61.25‰; when i = 38, the arithmetic mean of the unknown sample group of j = 2 UH01 particles is -62.71‰; when i = 38, the arithmetic mean of the unknown sample group of j = 3 UH01 particles is -62.98‰, and the standard deviation of the unknown sample group is calculated;

[0127]

[0128] Among them, j=1,2,…,10; i=1,2,…,50; k=(i-1)*40+1, and the resulting values ​​are (1,41,81,…,1961) respectively.

[0129] Then calculate the average value of all hematite standard sample particles in the same group, that is, the unknown sample group at the same measurement depth.

[0130] The average value of unknown samples among groups i is:

[0131] Where j = 1, 2,…, 10; i = 1, 2,…, 50.

[0132] In this Example 1, the average value among the unknown sample groups of the hematite sample UH01 is -62.31‰.

[0133] In conjunction with this embodiment, there is also a preferred implementation scheme. Specifically, the calculation method of the oxygen isotope value of the hematite sample is:

[0134] The instrument mass fraction of the detection instrument plus the average value between the unknown sample groups.

[0135] δ of unknown hematite samples 18 O value = instrument mass fraction IMF + the average value among the unknown sample groups.

[0136] In this Example 1, the oxygen isotope value δ of the hematite sample with unknown oxygen isotope value is 18 O UH01 , δ 18 O UH01 =IMF+AA UH01-gi .

[0137] In this example, the oxygen isotope value of the hematite sample with unknown oxygen isotope value is -1.52‰.

[0138] In combination with this embodiment, there is also a preferred implementation scheme, specifically, at least one glass standard with a known oxygen isotope value, at least one hematite standard sample with a known oxygen isotope value, and at least one hematite sample with an unknown oxygen isotope value have a flat test target surface during testing.

[0139] like Figure 3 a and Figure 3 As shown in b, there are multiple hematite standard samples SH9264, multiple samples to be tested UH01 and multiple glass standard samples Nist610 on the sample target surface.

[0140] In combination with this embodiment, there is also a preferred implementation scheme. Specifically, double-sided tape is stuck on a glass sheet, and the glass standard sample with known oxygen isotope value, the hematite standard sample with known oxygen isotope value, and the hematite sample with unknown oxygen isotope value are stuck on the double-sided tape.

[0141] In the first embodiment, a target is first prepared, which includes a glass standard sample, a hematite standard sample and a hematite sample to be tested.

[0142] Since the stability of the instrument requires a standard sample with known oxygen isotope results to monitor, the glass standard sample NIST610 developed by the National Institute of Standards and Technology of the United States was selected. This standard sample has a uniform oxygen isotope value δ 18 O Nist610 =10.91±0.20‰.

[0143] Due to the matrix effect of the ion probe, a sample with similar composition to the sample to be tested is needed as a standard sample. Therefore, a hematite sample that has been tested for oxygen isotopes using a traditional method is selected as a standard sample. The oxygen isotope value of the hematite SH9264 sample selected in this Example 1 is δ 18 O SH9264 =-1.12±0.14‰. Here, SH9264 is used as the standard sample to obtain the test time range and sampling interval of hematite, and the instrument mass fractionation of the instrument is calculated to establish the method. A hematite UH01 sample with a similar source to the standard sample is selected as the test sample for testing. The oxygen isotope of this hematite sample has been measured by traditional methods as follows: δ 18 O UH01 =-1.12±0.14‰. A hematite sample UH01 with known oxygen isotope value was used as the test sample to verify this method.

[0144] The specific process of making the target is as follows: stick a 10cm*5cm double-sided tape on a 10cm*10cm glass sheet, and stick 10-12 particles of a glass standard sample Nist610 with a particle size of 100-250 microns, 10-12 particles of a hematite standard sample SH9264 with a known oxygen isotope with a particle size of 100-250 microns, and 10-12 particles of an unknown hematite sample UH01 with a particle size of 100-250 microns into a 1 cm diameter circle on the double-sided tape. Mix the epoxy resin with the coagulant; place a polyethylene hollow column with a smooth surface and an inner diameter of 1 inch vertically on the double-sided tape, and place the above-mentioned glass and hematite particles in the middle of the polyethylene hollow column; slowly inject the vacuumed mixture of the epoxy resin and the coagulant along the inner surface of the polyethylene hollow column, vacuum again and let it stand to solidify the mixture, then remove the polyethylene hollow column and tear off the double-sided tape to obtain a solidified hematite standard sample slice that can be taken out of the polyethylene hollow column. Use fine sandpaper and polishing disc to grind and polish the hematite target in turn, so that the glass standard sample Nist610 and the hematite standard sample SH9264, and the sample to be tested UH01 are exposed on one side of the target surface, and the entire surface is bright and smooth. The prepared target is as follows Figure 1 shown. Figure 3 a is the overall image, which is a disc. Figure 3 b is the surface morphology. Figure 3 b is Figure 3 a Distribution diagram of the sample target surface at 50 times magnification.

[0145] In this embodiment 1, the hematite was tested using secondary ion mass spectrometry (SIMS).

[0146] First, clean the surface of the sample target with clean water, place the sample target in a beaker filled with alcohol, use an ultrasonic instrument to ultrasonically clean the sample for three minutes, and then place the sample target in a drying oven to dry for one hour.

[0147] A Q150TE gold plating machine from Quorum is used to plate a continuous gold film on the exposed surface of the cleaned wafer sample target. To ensure good conductivity of the sample, the coating thickness is between 20nm and 50nm. For example, it can be 20nm or only 45nm.

[0148] The signal required for testing hematite oxygen isotopes is measured using a secondary ion mass spectrometer. Using a cesium ion source, the focused ion beam is irradiated onto the glass or hematite sample on the sample target. A beam spot with a diameter of about 20 μm is used to excite the sample to produce secondary ions. Subsequently, the secondary ions released by the sample 16 O and 18O passes through the electric field and magnetic field in turn and finally reaches the ion signal detection system. Collecting oxygen isotopes of hematite standard samples 18 O and 16 O instrument signal and calculate its oxygen isotope ratio data using the Vienna Standard Mean Ocean Water (VSMOW); 18 O / 16 O=0.0020052) for normalization, the formula is as follows: 18 O VSMOW =(( 18 O / 16 = (O) measured value / 0.0020052-1) × 1000. During the detection process, two Faraday cups were used to simultaneously receive the secondary ion signal. Each test cycle consisted of at least 2000 cycles, with each cycle lasting 2 seconds.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry, characterized in that the method include: Using a secondary ion mass spectrometer, a cesium ion source was used to bombard hematite standard samples with known oxygen isotopes using a beam spot diameter of 15-25 μm. Fifty groups of measurements were performed, each consisting of 40 2-second cycles. The standard deviation and mean value between the standard sample groups were calculated. When the standard deviation between the two standard sample groups is less than the preset threshold, the hematite standard sample δ 18 The O value and the average value between the standard sample groups determine the instrument mass fractionation IMF; After measuring the same depth of the unknown hematite sample, the δ 18 O value.

2. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: The method comprises: Before the beam spot bombards the hematite standard sample with known oxygen isotope, the stability test of the instrument is performed. The stability test uses at least 3 glass standard samples. If the glass standard sample δ 18 A distribution range of less than 1‰ indicates that the instrument has passed the stability test.

3. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: During measurement, two or more crystal faces of the hematite particle sample need to be tested alternately.

4. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: The calculation method of the instrumental mass fractionation IMF includes: Calculate the arithmetic mean of each group of 40 2-second cycle data to obtain the arithmetic mean within the standard sample group and calculate the standard deviation within the standard sample group; Calculating the inter-group mean and inter-group standard deviation of standard samples of the same group of multiple particles based on the intra-group arithmetic mean and the intra-group standard deviation of the standard samples; If the standard deviation between the standard sample groups is less than the preset threshold, the current group is taken, and the average value of the standard sample groups corresponding to the current group and the delta of the standard sample are used. 18 O value calculation IMF.

5. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: The method further comprises: When measuring an unknown hematite sample, the same ion beam sputtering time window as that of the hematite standard sample with known oxygen isotopes must be maintained.

6. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 2, characterized in that: The method further comprises: The glass standard sample, the hematite standard sample with known oxygen isotope and the unknown hematite sample are fixed on a glass sheet by double-sided tape, and a test target is formed after vacuum curing of epoxy resin, and the surface of the test target is flat.

7. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: The δ 18 The O value is -1.12±0.14‰.

8. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 1, characterized in that: When using secondary ion mass spectrometry for measurement, the measurement time for each group is 2 to 3 minutes, and the interval between two adjacent groups of measurements is ≤5 minutes.

9. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to any one of claims 1 to 8, characterized in that: The hematite standard sample δ based on known oxygen isotopes 18 The method for determining the instrumental mass fractionation IMF by comparing the O value with the average value between the standard sample groups includes: Instrumental mass fraction IMF = δ of the hematite standard sample based on known oxygen isotopes 18 The average value of the standard sample group was subtracted from the O value.

10. The method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry according to claim 9, characterized in that: After measuring the unknown hematite sample at the same depth, the δ 18 O-value methods include: δ of unknown hematite samples 18 O value = instrument mass fraction IMF + the average value among the unknown sample groups.

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