A device and method for inverting lunar rock types through annihilation radiation

Abstract

The present invention discloses a device and method for inverting lunar rock types through annihilation radiation, belonging to the technical field of lunar geological structure detection. The method uses a proton accelerator to obtain high-current proton bombardment of typical lunar rock composition samples, and simultaneously uses a detector to measure the induced gamma energy spectrum information generated by the samples. The proton stream bombards the samples to be tested, obtains 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, and calculates the ratio of the two. Different lunar rock types are accurately distinguished based on different ratios. The present invention achieves accurate distinction of lunar rock types by successfully stimulating the annihilation radiation of typical rocks using 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 its geological structure, has become increasingly in-depth, creating a particularly pressing need for high-precision remote sensing measurements of the Moon. Orbital gamma-ray spectroscopy is an important tool for studying the surface elemental composition, lithology, geological evolution, and radiation environment of celestial bodies.

[0003] Currently, researchers at home and abroad primarily perform lithologic inversion based on the characteristic gamma-ray spectra of rock-forming elements combined with information from radioactive elements. For example, a Th content greater than a certain value (generally 5 ppm) is considered a KREEP rock, while an Fe content greater than 6% or an FeO content greater than 8% is considered a basalt. However, experiments have shown that the FeO content in some KREEP rocks is even greater than 10% (lunar rock samples 15386, 15404, and 72275). This shows that relying solely on the characteristic gamma-ray peaks of one or a few indicator elements to calibrate the working curve is susceptible to the influence of abnormal values ​​of certain nuclides.

[0004] Furthermore, Gasnault et al. used Lunar Prospector fast neutron data to calibrate a lithology identification curve based on differences in the total fast neutron load characteristics of rock samples. However, this method is significantly affected by variations in the Fe content of lunar samples. Ge Liangquan et al. from Chengdu University of Technology used the effective atomic mass of the lunar surface medium at the sampling point as a reference when constructing a positive correlation model between the effective atomic number and the annihilation radiation fluence rate, and used the slope of the fitted curve to determine the calibration results.

[0005] The above methods are all "relative calibration" of the working curve, that is, they are unable 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 rocks through annihilation radiation, the method comprising: using a proton accelerator to obtain high-current protons to bombard typical lunar rock composition samples, and simultaneously using a detector to measure the induced gamma energy spectrum information generated by the samples.

[0008] Positron annihilation gamma radiation ("annihilation radiation") is a key feature of the gamma-ray spectrum emitted by the lunar surface. Annihilation radiation emitted from the lunar surface carries a wealth of geological information about the surface. Variations in its flux directly reflect characteristics of the lunar surface medium, such as elemental composition, density, and regolith maturity. The annihilation radiation fluence rates produced by different lunar rocks are specific. Inferring lunar rock types from these annihilation radiation fluences can more accurately characterize the geological characteristics of key lunar regions, providing valuable insights for lunar resource development, forward base site selection, and the construction of lunar scientific research stations.

[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 inverting typical lithology by directly collecting annihilation radiation characteristic peaks, and the results can be directly observed and evaluated.

[0010] As a preferred technical solution, the specific method includes the following steps:

[0011] (1) Detector scale;

[0012] (2) Experimental measurement: The sample to be tested is placed on the experimental bench, with the center of the end face of the sample to be tested aligned with the center of the proton accelerator, and the center of the end face of the detector is perpendicular to the beam direction of the proton accelerator and maintains the same horizontal plane; the proton accelerator generates an initial beam, and after collimation, a proton flow of different energy and beam intensity is obtained through the energy degrader to bombard the sample to be tested, and 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.

[0013] As a further preferred technical solution, in step (1), the detector calibration method is:

[0014] 1) Use Cs-137 and Co-60 gamma radiation sources for energy calibration. The calibration results are as follows:

[0015] (1)

[0016] Where E is energy, keV, ch is the channel address of the energy spectrum;

[0017] 2) Using Cs-137 (activity: 1.6*103 Bq) for efficiency calibration, the detector deposition efficiency is: 4%@661keV;

[0018] (3) The energy resolution of the instrument was calibrated using a Cs-137 source. The energy resolution of the detector was approximately 10.8% @ 661 keV.

[0019] 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.

[0020] A second object of the present invention is to provide a device for inverting lunar rock types through annihilation radiation, comprising a proton accelerator, a detector, a multi-channel energy 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.

[0021] As a preferred technical solution, the experimental platform is provided with a conveyor belt, the sample to be tested is placed on the conveyor belt, and the conveyor belt is controlled by a stepper motor. This can realize automatic sample replacement, thereby reducing the impact of radioactivity of the sample after irradiation and activation on the experimenter.

[0022] As a preferred technical solution, the proton accelerator is shielded by multiple layers of lead plates, and the hardware part of the multi-channel energy spectrometer is placed in a lead box.

[0023] Compared with the existing technology, the advantages of the present invention are: the present invention successfully stimulates the annihilation radiation of typical rocks, thereby using a direct ground calibration method to accurately distinguish the types of lunar rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the device design of the present invention;

[0025] Figure 2 annihilation radiation characteristic peak count rate at different beam intensities;

[0026] Figure 3 This is a diagram of the lithology identification principle (flow chart) in the present invention;

[0027] Figure 4 Count rates and P value results of annihilation radiation produced by different rocks. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings. Example

[0029] In this embodiment,

[0030] 1.1 The instruments and equipment used include:

[0031] (1) Proton accelerator (either cyclotron or linear), whose performance can meet the following requirements: beam energy ≥ 100 MeV, beam intensity ≥ 20 nA / s;

[0032] (2) Scintillation detector (Beijing Nuclear Instrument Factory CH158-06, size φ75mm*75mm);

[0033] (3) Multi-channel energy 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; maximum data throughput of a single channel ≥ 500 kcps; linear gain adjustment range 0.5-32, integral nonlinearity ≤ 0.05%; differential nonlinearity ≤ 1%);

[0034] The design principle diagram of the experimental device including the above instruments is shown in the figure. Figure 1 As shown:

[0035] Proton Accelerator 1 ( Figure 1 The figure shows the initial beam generated by the beam terminal (part of the proton accelerator). After collimation, it passes through an energy degrader to obtain proton fluxes of different energies and intensities, which bombard the "lunar rock" sample 4. Simultaneously, a scintillation detector 3 (using a cesium iodide probe) at the front end of a multi-channel energy spectrometer 2 detects the sample 4. The sample 4 is placed on a conveyor belt 5 on the experimental platform. The conveyor belt 5 is controlled by a stepper motor to achieve 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 multiple layers of lead plates 6. The hardware of the multi-channel energy spectrometer 2 is placed in a lead box.

[0036] 1.2 Experimental materials used:

[0037] Simulated lunar surface rocks, including KREEP rock, high-titanium basalt, low-titanium basalt, high-aluminum basalt, anorthosite, and dunite (calibration sample), were packaged in φ70mm*70mm polyethylene sample boxes. The sample numbers and chemical compositions of these experimental materials are shown in Table 2. These composition data are derived from public data returned from previous lunar exploration sampling missions and are prepared based on the element content of the main beam (for details, 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 example were prepared according to the aforementioned composition ratios.

[0038] 1.3 Experimental principles and specific experimental methods:

[0039] Experiments were conducted using Proton Accelerator 1. The proton beam intensity, after conversion to the fluence rate (taking into account the radiation resistance of the detector), was determined to have a linearly decreasing relationship with energy, as shown in Table 1 below. A high-energy proton cascade shower experiment was conducted to obtain parameters such as the contribution of annihilation radiation from different "lunar rocks" to the count rate in the 0.511 MeV energy window and the 0-10 MeV energy spectrum response.

[0040]

[0041] The specific experimental methods are:

[0042] A method for inverting lunar rock types using annihilation radiation comprises the following steps:

[0043] 1.1 Detector scale:

[0044] (1) Energy calibration is performed using Cs-137 and Co-60 gamma radiation sources. The calibration results are as follows:

[0045] (1)

[0046] Where, E is the energy, keV, ch is the channel address of the energy spectrum;

[0047] (2) Using Cs-137 (activity: 1.6×10 3 Bq) for efficiency calibration, the detector deposition efficiency is: 4%@661keV;

[0048] (3) The energy resolution of the instrument was calibrated using a Cs-137 source. The detector energy resolution was approximately 10.8% @ 661 keV.

[0049] 1.2 Sample testing:

[0050] The sample 4 to be tested was placed on the conveyor belt 5 of the experimental bench, with the center of the end face of the sample 4 aligned with the center of the proton accelerator 1. The center of the end face of the scintillation detector 3 was 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 was 60 cm, and the distance from the end face of the scintillation detector 3 to the side of the sample 4 was 10 cm. To reduce the impact of the experimental environment background and the risk of detector count rate overload, a 10 cm thick lead shielding layer was constructed.

[0051] Proton accelerator 1 generates proton beams of different energies and beam intensities to bombard the samples to be tested. The count rate of annihilation radiation in the 511keV energy window and the count rate in the 969-1133keV characteristic peak region of the different samples to be tested are obtained, and the ratio of the two is calculated. Based on different ratios, different lunar rock types can be accurately distinguished.

[0052] 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 fluence rate;

[0053] The count rates (cps) of annihilation radiation (511keV) produced by different types of rocks are specific. The count rates of the 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.

[0054]

[0055] 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 inverting lunar rock types through annihilation radiation, characterized in that: The method comprises: using a proton accelerator to obtain high-current protons to bombard a typical lunar rock composition sample, and simultaneously using a detector to measure induced gamma energy spectrum information generated by the sample; The specific method includes the following steps: (1) Detector calibration: the detector calibration method is: 1) Use Cs-137 and Co-60 gamma radiation sources for energy calibration. The calibration results are as follows: ； 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 is approximately 10.8% @ 661 keV. (2) Experimental measurement: The sample to be tested is placed on the experimental bench, with the center of the end face of the sample to be tested aligned with the center of the proton accelerator, and the center of the end face of the detector is perpendicular to the beam direction of the proton accelerator and maintains the same horizontal plane; the proton accelerator generates an initial beam, and after collimation, a proton flow of different energy and beam intensity is obtained through the degrader to bombard the sample to be tested, and 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 the different ratios and the count rate in the 511keV energy window, different types of lunar rocks can be accurately distinguished.

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