Device and method for inverting lunar rock type through annihilation radiation

Abstract

The invention discloses a device and method for inverting lunar rock types through annihilation radiation, and belongs to the technical field of lunar geologic structure detection.The method comprises the steps that a proton accelerator is used for obtaining high-current proton bombardment typical lunar rock component samples, meanwhile, a detector is used for measuring induced gamma-ray energy spectrum information generated by the samples, proton flow bombardment is conducted on the samples to be detected, and the samples to be detected are obtained; the method comprises the following steps: acquiring the counting rate of annihilation radiation of different samples to be detected in a 511keV energy window and the counting rate of the annihilation radiation in a 969-1133 keV characteristic peak region, calculating the ratio of the two counting rates, and accurately distinguishing different types of lunar rocks according to different ratios; according to the invention, through successful excitation of typical rock annihilation radiation, accurate distinguishing of lunar rock types is realized by adopting a direct ground calibration method.

Description

Technical Field

[0001] The present invention relates to the technical field of lunar geological structure detection, and in particular to a device and method for inverting lunar rock types through annihilation radiation. Background Art

[0002] With the continuous development of aerospace technology, human exploration of the moon, especially the exploration of its geological structure, has become more and more in-depth, and the demand for high-precision remote sensing measurements of the moon is particularly prominent. Orbital gamma ray spectrometry is an important means of studying the surface element composition, rock type, geological evolution law, and radiation environment of space bodies.

[0003] At present, domestic and foreign scholars mainly perform lithology inversion based on "characteristic gamma spectra of rock-forming elements combined with characteristic information of radioactive elements". For example, when the Th content is greater than a certain value (generally 5ppm), it is considered to be KREEP rock, and when the Fe content is greater than 6% or the FeO content is greater than 8%, it is judged to be basalt. However, experiments show that the FeO content in some KREEP rocks is even greater than 10% (moon rock samples No. 15386, No. 15404, and No. 72275). It can be seen that the calibration of the working curve is only based on the characteristic peaks of gamma rays of one or several indicator elements, and the judgment results are easily affected by the abnormal values ​​of certain nuclides.

[0004] In addition, Gasnault et al. used the fast neutron detection data of the Lunar Prospector to calibrate the lithology identification working curve by the difference in the total fast neutron characteristics of rock samples, but this method is greatly affected by the change in the content of Fe in lunar samples. In the process of constructing a positive correlation model between the effective atomic number of the lunar surface medium and the annihilation radiation injection rate, Ge Liangquan et al. of Chengdu University of Technology used the "effective atomic mass of the medium at the lunar surface sampling point" as a reference and judged the calibration result by the slope of the fitting curve.

[0005] The above methods are all "relative calibration" of the working curve, that is, they have not been able to detect the characteristic peaks of gamma rays of typical rocks through ground experiments, and the inversion process can only provide indirect proof. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for inverting lunar rock types through annihilation radiation to solve the above-mentioned problem.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a method for inverting the type of lunar rock by annihilation radiation, the method comprising: using a proton accelerator to obtain a sample of typical lunar rock composition bombarded by high-current protons, and simultaneously using a detector to measure the induced gamma energy spectrum information generated by the sample.

[0008] Positron annihilation gamma radiation (abbreviated as "annihilation radiation") is one of the important characteristics of the gamma-ray spectrum emitted by the lunar surface. The annihilation radiation emitted from the lunar surface carries a large amount of geological information on the surface of celestial bodies, and its flux changes can directly reflect the elemental composition, density, maturity of lunar soil and other characteristics of the lunar surface medium. The annihilation radiation flux rate generated by different rocks on the lunar surface is specific. By inverting the types of lunar surface rocks through the annihilation radiation flux rate characteristics, the geological characteristics of key areas on the moon can be more accurately reflected, providing an important reference for lunar resource development, forward base site selection and lunar scientific research station construction.

[0009] Compared with the relative calibration based on the principle of "effective atomic mass = 2 times effective atomic number" in the prior art, the present invention uses a method of directly collecting annihilation radiation characteristic peaks to invert typical lithology, and the results can be directly observed and evaluated.

[0010] As a preferred technical solution, the specific method includes the following steps: (1) Detector calibration; (2) Experimental measurement: The sample to be tested is placed on the experimental bench, with the end face center of the sample to be tested aligned with the center of the proton accelerator, and the end face center of the detector is perpendicular to the beam direction of the proton accelerator and maintained in the same horizontal plane; the proton accelerator generates an initial beam, which is then collimated and then passed through an energy degrader to obtain proton fluxes of different energies and beam intensities to bombard the sample to be tested. The annihilation radiation count rate in the 511keV energy window and the count rate in the 969-1133keV characteristic peak area of ​​different samples to be tested are obtained, and the ratio of the two is calculated. According to different ratios, different types of lunar rocks can be accurately distinguished.

[0011] As a further preferred technical solution, in step (1), the detector calibration method is: 1) Use Cs-137 and Co-60 gamma radiation sources for energy calibration. The calibration results are as follows: (1) Where, E is energy, keV, ch is the channel address of the energy spectrum; 2) Using Cs-137 (activity: 1.6*103 Bq) for efficiency calibration, the detector deposition efficiency is: 4%@661keV; (3) The energy resolution of the instrument was calibrated using a Cs-137 source. The detector energy resolution was approximately 10.8%@661keV.

[0012] The principle of the present invention is that the interaction between protons and matter produces electromagnetic cascades, hadron cascades, neutron-gamma and other reactions, and the induced gamma radiation, especially the annihilation radiation, produced by them has obvious differences.

[0013] A second object of the present invention is to provide a device for inverting the types of lunar rocks through annihilation radiation, comprising a proton accelerator, a detector, a multi-channel spectrometer and an experimental bench, on which a sample to be tested is placed, wherein the centers of the proton accelerator and the detector are aligned with the center of the end face of the sample to be tested.

[0014] As a preferred technical solution, a conveyor belt is provided on the experimental stand, the sample to be tested is placed on the conveyor belt, and the conveyor belt is controlled by a stepper motor, so that automatic sample change can be achieved, thereby reducing the impact of the radioactivity of the sample after irradiation and activation on the experimenter.

[0015] As a preferred technical solution, the proton accelerator is shielded by multiple layers of lead plates, and the hardware part of the multi-channel spectrometer is placed in a lead box.

[0016] Compared with the prior art, the advantages of the present invention are: the present invention realizes accurate distinction of lunar rock types by using a direct ground calibration method through successful stimulation of typical rock annihilation radiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the device design of the present invention; Figure 2 Count rate of annihilation radiation characteristic peak at different beam intensities; Figure 3 This is a diagram of the principle (flow chart) of lithology identification in the present invention; Figure 4 The count rates and P value results of annihilation radiation produced by different rocks. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings. Example

[0019] In this embodiment, 1.1 The instruments and equipment used include: (1) Proton accelerator (either cyclotron or linear), as long as its performance meets the following requirements: beam energy ≥ 100 MeV, beam intensity ≥ 20 nA / s; (2) Scintillation detector (CH158-06 from Beijing Nuclear Instrument Factory, specification φ75mm*75mm); (3) Multi-channel spectrometer (its performance only needs to meet the following requirements: energy spectrum measurement range 0-10 MeV; number of channels ≥ 8192; pulse pair resolution time ≤ 200 ns; single channel maximum data throughput ≥ 500 kcps; linear gain multiple adjustment range 0.5-32, integral nonlinearity ≤ 0.05%; differential nonlinearity ≤ 1%); The design schematic diagram of the experimental device including the above instruments is shown in Figure 1 As shown: Proton Accelerator 1 ( Figure 1 What is shown in the figure is the initial beam generated by the beam terminal as a part of the proton accelerator. After being collimated, the proton flow of different energies and fluxes is obtained through the degrader to bombard the "moon rock" sample 4. At the same time, the scintillation detector 3 (using cesium iodide probe) at the front end of the multi-channel energy spectrometer 2 detects the sample 4; the sample 4 is placed on the conveyor belt 5 of the experimental bench, and the conveyor belt 5 is controlled by a stepper motor to realize automatic sample replacement, thereby reducing the impact of the radioactivity of the sample 4 after irradiation and activation on the experimenter. The scintillation detector 3 and the proton accelerator 1 are shielded by multi-layer lead plates 6, and the hardware part of the multi-channel energy spectrometer 2 is placed in a lead box; 1.2 Experimental materials used: The simulated lunar surface rocks, including: KREEP rock, high-titanium basalt, low-titanium basalt, high-aluminum basalt, anorthite and peridotite (calibration sample), are packaged in a φ70mm*70mm polyethylene sample box. The sample numbers and chemical compositions of these experimental materials are shown in Table 2. The data of these compositions are derived from the public data returned by the lunar exploration sampling, and are made according to the main beam element content (see: Heiken, GH, Vaniman, DT, and French, BM (1991). Lunar Sourcebook: A User's Guide to the Moon. Cambridge University Press.). The samples in this embodiment are configured according to the composition ratio.

[0020] 1.3 Experimental principles and specific experimental methods: Experiments were carried out using proton accelerator 1. The proton beam intensity was converted to a linear decreasing relationship between the beam intensity and the energy after injection rate conversion (taking into account the radiation resistance of the detector), as shown in Table 1 below. High-energy proton cascade shower experiments were carried out to obtain parameters such as the contribution of annihilation radiation of different "moon rocks" to the count rate in the 0.511MeV energy window, and the 0-10MeV energy spectrum response.

[0021]

[0022] The specific experimental method is: A method for inverting lunar rock types through annihilation radiation comprises the following steps: 1.1 Detector scale: (1) Use Cs-137 and Co-60 gamma radiation sources for energy calibration. The calibration results are as follows: (1) In the formula, E is the energy, keV, ch is the channel address of the energy spectrum; (2) Using Cs-137 (activity: 1.6×10 3 Bq) for efficiency calibration, the detector deposition efficiency is: 4%@661keV; (3) Use Cs-137 source to calibrate the energy resolution of the instrument. The detector energy resolution is about 10.8%@661keV. 1.2 Sample testing: The sample 4 to be tested is placed on the conveyor belt 5 of the experimental bench, with the end face center of the sample 4 to be tested aligned with the center of the proton accelerator 1, and the end face center of the scintillation detector 3 is perpendicular to the beam direction of the proton accelerator 1 and maintained at the same horizontal plane. At the same time, the distance from the proton accelerator 1 to the end face of the sample 4 is 60 cm, and the distance from the end face of the scintillation detector 3 to the side of the sample 4 is 10 cm. In order to reduce the background impact of the experimental environment and the risk of detector count rate overload, a lead shielding layer with a thickness of 10 cm is built; Proton accelerator 1 generates proton fluxes of different energies and beam intensities to bombard the samples to be tested, obtains the annihilation radiation count rate in the 511keV energy window and the 969-1133keV characteristic peak area count rate of different samples to be tested, and calculates the ratio of the two, and accurately distinguishes different types of lunar rocks according to different ratios; The relationship between the annihilation radiation intensity and the proton fluence rate is as follows: Figure 2 As shown, from Figure 2 It can be seen that the present invention can achieve successful excitation of typical rock annihilation radiation, and the annihilation radiation intensity is positively correlated with the proton injection rate; The count rates (cps) of annihilation radiation (511keV) produced by different types of rocks are specific. The count rates of 1022keV characteristics (969-1133keV characteristic peak area) of different rocks are combined, and the ratio P value of the two is calculated. The results are shown in Table 3. The principle of distinguishing lunar rock types based on P value and count rate is as follows Figure 3 As shown, the results are Figure 4 shown.

[0023]

[0024] 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 protection scope of the present invention.

Claims

1. A method for inverting lunar rock types through annihilation radiation, characterized in that: The method comprises: using a proton accelerator to obtain high-current protons to bombard typical lunar rock composition samples, and simultaneously using a detector to measure induced gamma energy spectrum information generated by the samples.

2. The method according to claim 1, characterized in that The specific method includes the following steps: (1) Detector calibration; (2) Experimental measurement: The sample to be tested is placed on the experimental bench, with the end face center of the sample to be tested aligned with the center of the proton accelerator, and the end face center of the detector is perpendicular to the beam direction of the proton accelerator and maintained in the same horizontal plane; the proton accelerator generates an initial beam, which is then collimated and then passed through an energy degrader to obtain proton fluxes of different energies and beam intensities to bombard the sample to be tested. The annihilation radiation count rate in the 511keV energy window and the count rate in the 969-1133keV characteristic peak area of ​​different samples to be tested are obtained, and the ratio of the two is calculated. According to different ratios, different types of lunar rocks can be accurately distinguished.

3. The method according to claim 2, characterized in that In step (1), the detector calibration method is: 1) Use Cs-137 and Co-60 gamma radiation sources for energy calibration. The calibration results are as follows: （1） Where, E is energy, keV, ch is the channel address of the energy spectrum; 2) Using Cs-137 (activity: 1.6*103 Bq) for efficiency calibration, the detector deposition efficiency is: 4%@661keV; (3) The energy resolution of the instrument was calibrated using a Cs-137 source. The detector energy resolution was approximately 10.8%@661keV.

4. A device for inverting lunar rock types through annihilation radiation, characterized in that: The invention comprises a proton accelerator, a detector, a multi-channel energy spectrometer and an experimental stand, on which a sample to be tested is placed, wherein the centers of the proton accelerator and the detector are both aligned with the center of the end surface of the sample to be tested.

5. The device according to claim 4, characterized in that A conveyor belt is arranged on the experimental bench, the sample to be tested is placed on the conveyor belt, and the conveyor belt is controlled by a stepping motor.

6. The device according to claim 4, characterized in that The proton accelerator is shielded by multiple layers of lead plates, and the hardware part of the multi-channel spectrometer is placed in a lead box.

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