A K / Ar statutory year system and method without mass correlation

Abstract

The present application provides a K / Ar dating system and method without mass correlation, the system comprising: a controllable excitation X-ray tube for emitting X-rays to the sample to be tested; an X-ray spectrometer for measuring the X-ray spectrum; a control and data acquisition device for controlling the radiation intensity of the X-ray tube, the energy of X-ray photons, and acquiring and storing the test data of the X-ray spectrometer; the angle between the emission direction of the X-ray beam and the central axis direction of the X-ray spectrometer is 90 degrees, and in the same plane, the plane is parallel to the normal of the plane where the sample to be tested receives X-ray irradiation. The advantages of the present application are: it can realize the simultaneous measurement of the K and Ar contents of the dating sample; the resource requirements are small, the measurement accuracy is high, and the implementation process is simple and fast, which is particularly suitable for dating samples of extraterrestrial bodies in vacuum environments such as the moon and asteroids.

Description

Technical Field

[0001] The present application belongs to the technical field of rock dating, and specifically relates to a K / Ar dating system and method that does not require mass correlation. Background Art

[0002] Rock dating is one of the key data for studying the origin of the universe or geological changes. Since the K element is present in high concentrations in rocks, it is relatively easy to detect and is not very selective for samples, so the K / Ar dating method is widely used in geological research. Especially in the in-situ dating technology of extraterrestrial planets, the K / Ar method is basically the only feasible dating method. The U.S. "Curiosity" Mars rover used the K / Ar method to achieve the first in-situ dating of extraterrestrial bodies in the history of human deep space exploration.

[0003] The K / Ar method usually uses X-ray fluorescence analysis to determine the content of K element. However, due to the extremely low content of Ar in rocks, conventional X-ray fluorescence analysis methods cannot obtain Ar content measurements. The measurement of Ar content in the laboratory usually relies on large magnetic analysis mass spectrometers or high-precision quadrupole mass spectrometers. Therefore, the K / Ar dating method in the laboratory has large measurement equipment, complex implementation process, and requires precise knowledge of the mass of the analyzed sample to accurately obtain the K / Ar content ratio in the sample. There are many measurement error factors introduced during the implementation and analysis process, which reduces the dating accuracy. Summary of the invention

[0004] The purpose of the present application is to overcome the defects of the existing K / Ar statutory year, such as the large measurement device, complicated implementation process, and the need to accurately know the mass of the analysis sample in order to normalize the K / Ar content ratio in the sample.

[0005] In order to achieve the above objectives, the present application proposes a K / Ar legal year system without mass correlation, the system comprising:

[0006] An X-ray tube with controllable excitation, used to emit X-rays to the sample to be tested;

[0007] X-ray spectrometer, used to measure X-ray energy spectrum;

[0008] Control and data acquisition equipment, used to control the X-ray tube radiation intensity, X-ray photon energy, and to acquire and store the test data of the X-ray spectrometer;

[0009] The angle between the direction of the X-ray beam emission and the central axis of the X-ray spectrometer is 90 degrees, and in the same plane, the normal of the plane and the plane where the sample to be tested receives X-ray irradiation are parallel to each other;

[0010] The size of the plane where the sample to be tested receives X-ray irradiation is larger than the X-ray irradiation size after beam limiting.

[0011] As an improvement of the above system, the controllably excited X-ray tube includes a cold cathode X-ray tube or a hot cathode X-ray tube; the electron current of the X-ray is continuously adjustable within the range of 1-1000μA; the high voltage of the X-ray tube is continuously adjustable within the range of 0.5-50kV; the anode target of the X-ray tube is a tungsten target or a target of other materials; the X-ray tube is a transmission target or a reflection target; a beam limiting hole is added to the ray output end of the X-ray tube, and the size of the beam limiting hole makes the diameter of the ray beam irradiating the sample less than 5mm.

[0012] As an improvement of the above system, the X-ray spectrometer adopts a silicon drift detector or a silicon detector, with an energy resolution better than 200eV, a measurement X-ray energy range of not less than 1-20keV, and a data counting rate ≥10 4 counts / s, the output channels shall be no less than 1024, and the effective area shall be ≥10mm 2 .

[0013] As an improvement of the above system, the sample to be tested is in powder or block form; if it is a powder sample, it needs to be wrapped with a plastic film or compressed into a shape; the surface of the sample to be tested that receives X-ray irradiation is a plane.

[0014] As an improvement of the above system, if the test is performed in a non-vacuum environment, the system further includes a high vacuum test chamber, and the X-ray tube, the X-ray energy spectrometer and the sample to be tested are placed in the high vacuum test chamber.

[0015] The present application also provides a K / Ar legal dating method without mass correlation, which is implemented based on the above system and includes:

[0016] Step S1: grinding and polishing the surface of the sample to be tested;

[0017] Step S2: The X-ray beam emission direction is maintained at a 90-degree angle to the central axis direction of the X-ray spectrometer, and the plane of the sample to be tested is placed perpendicular to the X-ray beam irradiation direction; the size of the X-ray beam limiting hole, the energy of the X-ray, the X-ray intensity, and the tilt angle of the sample are adjusted to obtain the maximum dynamic range of the K and Ar characteristic peaks; the state of the system is maintained when the maximum dynamic range of the K and Ar characteristic peaks is maintained;

[0018] Step S3: discretely change the high voltage of the X-ray tube from 5kV to 50kV, and discretely change the electron current of the X-ray tube at each high voltage, ranging from 1μA to 100μA; under each high voltage and electron current condition, test the X-ray fluorescence spectrum of the sample to be tested, and obtain the K characteristic energy peak count rate C k and the background count rate C at the characteristic energy peak of Ar Ar , and the ratio C k / CAr ;

[0019] The sample to be tested is rotated counterclockwise for multiple times, with each rotation angle being less than 5 degrees, and the test process of step S3 is repeated at each angle position;

[0020] Compare the ratio C obtained by the above process k / C Ar range, find out the test condition of its maximum value, set the layout of the system to the geometric layout of the maximum ratio, and keep the values ​​of the high voltage of the X-ray tube, the electron current, the angle of the sample to be tested and the size of the beam limiting hole unchanged;

[0021] Start the X-ray spectrometer and continuously collect or intermittently accumulate K characteristic energy peak counts in 10 7 above;

[0022] Arrangement S4: using the finite energy channel fluorescence spectrum analysis method near the characteristic energy peaks of Ar and K to estimate the areas under the characteristic energy peaks of Ar and K respectively;

[0023] The target fitting region is selected to cover the rising edge of the characteristic energy peak from 1 keV before the characteristic energy peak of Ar to the characteristic energy peak of K; the Gaussian function is selected as the model of each characteristic energy peak covered in the target fitting region; a low-order polynomial of order 3 to 10 is selected as the background fluorescence spectrum model; the sum of the model of the characteristic energy peak and the background fluorescence spectrum model is used as the final data model; the least squares method is used to fit the model parameters; the areas under the peaks of the characteristic energy peaks of K and Ar, and the proportional coefficients of the areas under the peaks of the characteristic energy peaks of Ar and K are calculated;

[0024] A geological standard sample of known age is measured to obtain a proportionality coefficient k between the known age of the standard sample and the ratio of the areas under the measured Ar and K characteristic energy peaks. The age of the sample to be tested is obtained by using the coefficient k and the ratio of the areas under the Ar and K characteristic energy peaks of the sample to be tested.

[0025] As an improvement to the above method, if the test is conducted in a non-vacuum environment, after grinding and polishing the sample to be tested, place the sample to be tested under a hot air blower for more than 10 minutes, and the air gun temperature is greater than 200 degrees Celsius.

[0026] As an improvement to the above method, if the test is conducted in a non-vacuum environment, after the layout of the system is set to the geometric layout with the maximum ratio, the X-ray tube, X-ray spectrometer and the sample to be tested are placed in a vacuum environment with a vacuum degree better than 10 -4 Pa, and maintain it for more than 24 hours before conducting subsequent tests.

[0027] As an improvement to the above method, when the sample to be tested is rotated counterclockwise for multiple times for testing, the cumulative counterclockwise rotation angle is less than 50 degrees.

[0028] As an improvement to the above method, if other Ar isotopes exist in the sample to be tested, the proportion of Ar isotopes is measured using a mass spectrometer.

[0029] Compared with the prior art, the advantages of this application are:

[0030] The application uses a set of miniaturized X-ray fluorescence analysis devices with special configurations, which can achieve simultaneous measurement of K and Ar content in dating samples, and can perform repeated measurements on the same micro-area or different areas of the sample multiple times, avoiding the influence of uneven K and Ar content in the sample on the dating accuracy. For samples without Ar isotope interference or in-situ analysis of extraterrestrial bodies, direct dating can be performed without other instruments for Ar isotope measurement. Compared with traditional K and Ar separate dating technology, the present invention has less resource requirements, high measurement accuracy, and a simple and fast implementation process, and is particularly suitable for in-situ dating of extraterrestrial bodies in vacuum environments such as the moon and asteroids. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Shown is a schematic diagram of the K / Ar legal year system that does not require mass correlation;

[0032] Figure 2 Shown are the characteristic peaks of K and Ar of the sample under atmospheric environment;

[0033] Figure 3 Shown is the characteristic peak diagram of K and Ar under vacuum environment;

[0034] Figure 4 The figure shows the comparison between the measured energy spectrum and the fitted energy spectrum after fitting (including the Ar net value peak and background curve);

[0035] Figure 5 Shown is a flow chart for optimizing the high voltage and electron current parameters of an X-ray tube under vacuum (same layout angle and speed-limiting hole). DETAILED DESCRIPTION

[0036] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0037] The purpose of the present invention is to overcome the defects of the prior art, and a K / Ar dating system and method without mass correlation is proposed. By using a set of miniaturized X-ray fluorescence analysis devices with special configuration, the simultaneous measurement of K and Ar contents of dating samples can be achieved, and repeated measurements can be performed on the same micro-area or different areas of the sample to avoid the influence of uneven K and Ar element contents of the sample on the dating accuracy. For samples without Ar isotope interference or in-situ analysis of extraterrestrial bodies, direct dating can be performed without the need for other instruments to carry out Ar isotope measurement. Compared with traditional K and Ar separate dating technology, the present invention has less resource requirements, high measurement accuracy, and a simple and fast implementation process. It is particularly suitable for in-situ dating of extraterrestrial bodies in vacuum environments such as the moon and asteroids. No need for mass correlation means that in the entire sample dating analysis process, the ratio of the area under the K and Ar peaks is used throughout the process, and K / Ar dating can be performed without measuring the mass of the sample to be tested.

[0038] The K / Ar legal dating system without mass correlation provided in the present application comprises: a controllable excited X-ray tube, an X-ray spectrometer, a sample to be analyzed, a control and data acquisition device, and a high vacuum experimental chamber; the X-ray tube, the X-ray spectrometer, and the sample to be analyzed are placed in the vacuum chamber; the control and data acquisition device is placed outside the vacuum system. Among them:

[0039] The controllably excited X-ray tube includes a cold cathode X-ray tube or a hot cathode X-ray tube; the electron current of the X-ray is continuously adjustable within the range of 1-1000μA; the high voltage of the X-ray tube is continuously adjustable within the range of 0.5-50kV; the anode target of the X-ray tube is a tungsten target or a target of other materials; the X-ray tube is a transmission target or a reflection target; a beam limiting hole is added to the ray output end of the X-ray tube, and the size of the beam limiting hole makes the diameter of the ray beam irradiating the sample less than 5mm.

[0040] The X-ray spectrometer uses a silicon drift detector or a silicon detector, which can measure single X-ray photons with an energy resolution better than 200eV, a measurement range of X-ray energy not less than 1-20keV, and a data counting rate ≥10 4 counts / s, the output energy channel number is not less than 1024, the effective area of ​​the X-ray spectrometer detector is ≥10mm 2 .

[0041] The control and data acquisition equipment is used to control the radiation intensity of the X-ray tube, the energy of X-ray photons, and to acquire and store X-ray spectrometer data.

[0042] The sample to be analyzed is in powder or block form. Powder samples need to be wrapped in plastic film or compressed. The absorption of Ar and K characteristic rays by the film thickness can be ignored. Whether it is a powder sample or a block sample, the X-ray irradiation surface is a plane, and there is no shape requirement for the non-irradiated surface.

[0043] The high vacuum chamber provides a high vacuum environment for testing and analysis. The main purpose is to eliminate the measurement interference caused by Ar in the atmospheric environment. If the test is conducted in a vacuum environment such as the moon or an asteroid, a vacuum chamber is not required.

[0044] The layout of the K / Ar statutory year system without mass correlation is as follows Figure 1 shown.

[0045] The angle between the X-ray beam emission direction and the normal direction of the X-ray spectrometer detector is maintained at 90 degrees at the initial position; the X-ray beam emission center position and the detector center position are on the same horizontal plane; the size of the sample to be tested is larger than the X-ray irradiation size after beam limiting, the X-ray beam center direction and the detector center axis direction are in the same horizontal plane, and the plane is parallel to the normal of the plane where the sample to be tested receives X-ray irradiation.

[0046] The dating process using the K / Ar dating system that does not require mass correlation includes four steps: sample pretreatment, test system layout optimization, vacuum system testing, and data processing.

[0047] Step 1: The sample pretreatment process is to first grind the surface of the sample to be tested with sandpaper, then polish the grinded sample, and then place the sample under a hot air blower for more than 10 minutes, and the air gun temperature is set to be greater than 200 degrees Celsius. The above process is to remove the adsorbed Ar that may exist on the sample surface. This process is suitable for dating tests in laboratory environments. If the test is conducted in a vacuum environment such as the moon or asteroid, this step is not required.

[0048] Step 2: Test system layout optimization can be performed in an atmospheric environment. The layout optimization process includes:

[0049] The initial position of the angle between the X-ray beam emission direction and the normal direction of the X-ray spectrometer detector remains unchanged at 90 degrees. The sample plane to be tested is placed perpendicular to the irradiation direction of the beam. Figure 1 As shown. Under this initial geometric layout, by adjusting the size of the X-ray beam limiting hole, the energy of the X-ray, the X-ray intensity, and the tilt angle of the sample, the maximum dynamic range of the K and Ar characteristic peaks is obtained. The maximum dynamic range of the K and Ar characteristic peaks is the optimal layout of the test system. The vacuum test is carried out under the optimal layout.

[0050] Step 3: Test under vacuum system:

[0051] Step 301: Figure 5 As shown, the X-ray tube high voltage is set to 5kV, and the electron current of the X-ray tube is discretely changed under high voltage, ranging from 1μA to 100μA. For each electron current, a sample X-ray fluorescence spectrum is tested, as shown in FIG. Figure 3As shown. The K characteristic peak count rate C is evaluated at this voltage and current. k , and the background count rate C at the Ar characteristic energy Ar , we get C under this high voltage and electron current k / C Ar . Background count rate C at Ar characteristic energy Ar Take the average of the counting rate at the rising and falling points of the Ar characteristic peak, see Figure 2 Mark in the middle;

[0052] Step 302: Discretely change the high voltage of the X-ray tube from 5 kV to 50 kV, and discretely change the electron current of the X-ray tube at each high voltage, ranging from 1 μA to 100 μA, test a sample X-ray fluorescence spectrum at each high voltage and each electron current, and obtain the C of each X-ray fluorescence spectrum. k / C Ar Dynamic range;

[0053] Step 303: The above process is only for one sample angle and one beam limiting hole C k / C Ar The dynamic range measurement operation process also requires rotating the sample counterclockwise, with each rotation angle being less than 5 degrees, and repeating steps 301 and 302 at each angle position. The cumulative counterclockwise rotation angle of the sample is about 50 degrees.

[0054] Step 304: Compare the C obtained by the above experimental process k / C Ar The experimental conditions for the maximum ratio are found, including the high voltage of the X-ray tube, the electron current, the sample angle, the size of the beam limiting hole, etc. The layout of the experimental device is restored to the geometric layout of the maximum ratio and fixed, and then the vacuum is evacuated to make the vacuum degree of the system better than 10 -4 Pa and maintained for more than 24 hours to further reduce the small amount of Ar that may be adsorbed on the sample surface during the layout optimization process.

[0055] Step 305: When the vacuum degree and vacuum maintenance time reach the set limit, set the high voltage and electron current of the X-ray tube to be consistent with the parameter values ​​optimized under atmospheric conditions, start the X-ray spectrometer, and continuously collect or intermittently accumulate the peak count of K in 10 7 Above, such as Figure 2 shown.

[0056] Step 4: Data Processing:

[0057] The data processing adopts the finite energy channel fluorescence spectrum analysis method near the characteristic energy of Ar and K to estimate the area under the peak of the characteristic energy Gaussian peak of Ar and K respectively. The selected target fitting region covers the area from 1 keV before the characteristic energy peak of Ar to the rising edge of the characteristic peak of K. The Gaussian function is selected as the model of each characteristic energy peak covered in the target fitting region, and the low-order polynomial of order 3 to 10 is selected as the background fluorescence spectrum model. The sum of the two is used as the final data model. The least squares method is used to find the best model parameter match for the data by minimizing the sum of squares of the errors. Through the actual physical meaning of each parameter, the peak position and half-width of the characteristic energy peak of Ar are determined, and the parameter ranges such as the peak position, peak height, half-width and various coefficients of the polynomial of the characteristic peak appearing in the target fitting region are defined and the initial values ​​of these parameters are given. The area under the peak of the characteristic energy peaks of K and Ar, and the proportional coefficients of the area under the peaks of Ar and K are calculated respectively. Finally, the final fitting result is obtained as shown in the figure. Figure 4 As shown in the figure, the actual data curve is highly consistent with the fitting curve, and the goodness of fit reaches 0.99.

[0058] By measuring a geological standard sample of known age, we can obtain the proportionality coefficient k between the known age of the standard sample and the measured area ratio under the Ar and K peaks. By using this coefficient k and the area ratio under the Ar and K peaks of the sample to be analyzed, we can get the age of the analyzed sample. If the analyzed sample does not have the interference of Ar isotopes, this coefficient can be used to directly determine the age of the analyzed sample. If other Ar isotopes exist in the analyzed sample, the proportion of Ar isotopes can be measured by other mass spectrometers. In this case, it can also be achieved without the need for sample mass correlation to directly determine the age. 40 Ar / 40 K, to achieve accurate dating of samples.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. A K / Ar legal dating method without mass correlation is implemented based on a K / Ar legal dating system without mass correlation, the system comprising: An X-ray tube with controllable excitation, used to emit X-rays to the sample to be tested; X-ray spectrometer, used to measure X-ray energy spectrum; Control and data acquisition equipment, used to control the X-ray tube radiation intensity, X-ray photon energy, and to acquire and store the test data of the X-ray spectrometer; The angle between the direction of the X-ray beam emission and the central axis of the X-ray spectrometer is 90 degrees, and in the same plane, the normal of the plane and the plane where the sample to be tested receives X-ray irradiation are parallel to each other; The size of the plane of the sample to be tested that receives X-ray irradiation is larger than the size of the X-ray irradiation after beam limiting; The method comprises: Step S1: grinding and polishing the surface of the sample to be tested; Step S2: The X-ray beam emission direction is maintained at a 90-degree angle to the central axis direction of the X-ray spectrometer, and the plane of the sample to be tested is placed perpendicular to the X-ray beam irradiation direction; the size of the X-ray beam limiting hole, the energy of the X-ray, the X-ray intensity, and the tilt angle of the sample are adjusted to obtain the maximum dynamic range of the K and Ar characteristic peaks; the state of the system is maintained when the maximum dynamic range of the K and Ar characteristic peaks is maintained; Step S3: discretely change the high voltage of the X-ray tube from 5kV to 50kV, and discretely change the electron current of the X-ray tube at each high voltage, ranging from 1μA to 100μA; under each high voltage and electron current condition, test the X-ray fluorescence spectrum of the sample to be tested, and obtain the K characteristic energy peak count rate C k and the background count rate C at the characteristic energy peak of Ar Ar , and the ratio C k / C Ar ; The sample to be tested is rotated counterclockwise for multiple times, with each rotation angle being less than 5 degrees, and the test process of step S3 is repeated at each angle position; Compare the ratio C obtained by the above process k / C Ar range, find out the test condition of its maximum value, set the layout of the system to the geometric layout of the maximum ratio, and keep the values ​​of the high voltage of the X-ray tube, the electron current, the angle of the sample to be tested and the size of the beam limiting hole unchanged; Start the X-ray spectrometer and continuously collect or intermittently accumulate K characteristic energy peak counts in 10 7 above; Step S4: using a finite energy channel fluorescence spectrum analysis method near the characteristic energy peaks of Ar and K to estimate the areas under the characteristic energy peaks of Ar and K respectively; The target fitting region is selected to cover the rising edge of the characteristic energy peak from 1 keV before the characteristic energy peak of Ar to the characteristic energy peak of K; the Gaussian function is selected as the model of each characteristic energy peak covered in the target fitting region; a low-order polynomial of order 3 to 10 is selected as the background fluorescence spectrum model; the sum of the model of the characteristic energy peak and the background fluorescence spectrum model is used as the final data model; the least squares method is used to fit the model parameters; the areas under the peaks of the characteristic energy peaks of K and Ar, and the proportional coefficients of the areas under the peaks of the characteristic energy peaks of Ar and K are calculated; A geological standard sample of known age is measured to obtain a proportionality coefficient k between the known age of the standard sample and the ratio of the areas under the measured Ar and K characteristic energy peaks. The age of the sample to be tested is obtained by using the coefficient k and the ratio of the areas under the Ar and K characteristic energy peaks of the sample to be tested.

2. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: The controllably excited X-ray tube comprises a cold cathode X-ray tube or a hot cathode X-ray tube; the electron current of the X-ray is continuously adjustable within the range of 1-1000 μA; the high voltage of the X-ray tube is continuously adjustable within the range of 0.5-50 kV; the anode target of the X-ray tube is a tungsten target or a target of other materials; the X-ray tube is a transmission target or a reflection target; a beam limiting hole is added to the ray output end of the X-ray tube, and the size of the beam limiting hole makes the diameter of the ray beam irradiating the sample less than 5 mm.

3. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: The X-ray spectrometer uses a silicon drift detector or a silicon detector, with an energy resolution better than 200 eV, an X-ray energy range of no less than 1-20 keV, and a data counting rate ≥ 10 4 counts / s, the output channels shall be no less than 1024, and the effective area shall be ≥10mm 2 .

4. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: The sample to be tested is in powder or block form; if it is a powder sample, it needs to be wrapped with a plastic film or compressed into a shape; the surface of the sample to be tested that receives X-ray irradiation is a plane.

5. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: If the test is performed in a non-vacuum environment, the system further comprises a high vacuum test chamber, in which the X-ray tube, the X-ray energy spectrometer and the sample to be tested are placed.

6. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: If the test is carried out in a non-vacuum environment, after grinding and polishing the sample to be tested, place the sample to be tested under a hot air blower for more than 10 minutes, and the air gun temperature should be greater than 200 degrees Celsius.

7. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: If the test is conducted in a non-vacuum environment, after setting the system layout to the maximum ratio geometric layout, place the X-ray tube, X-ray spectrometer and the sample to be tested in a vacuum environment with a vacuum degree better than 10 -4 Pa, and maintain it for more than 24 hours before conducting subsequent tests.

8. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: When the sample to be tested is rotated counterclockwise multiple times for testing, the cumulative counterclockwise rotation angle is less than 50 degrees.

9. The K / Ar legal dating method without mass correlation according to claim 1, characterized in that: If other Ar isotopes exist in the sample to be tested, the proportion of Ar isotopes is measured using a mass spectrometer.

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