Design method of high-integration PGNAA element detector for deep space exploration

Abstract

The invention discloses a design method of a high-integration PGNAA element detector for deep space exploration, aiming at the optimization design of a PGNAA device, each module assembly is designed and combined through a compact structure, a moderator structure of a conventional PGNAA element detector is removed, the function of a moderator is replaced by a detection sample, and the design of the high-integration PGNAA element detector for deep space exploration is realized. According to the invention, the quality factor Q is used as an optimization criterion, and the size of the neutron shielding body is optimized, so that the PGNAA element detector has the advantages of high integration, small size, good portability and the like, and can be mounted on a mechanical arm of the lunar vehicle to measure the type, content and distribution of lunar soil elements along with the movement of the lunar vehicle.

Description

Technical Field

[0001] The present invention belongs to the technical field of deep space detectors, and specifically relates to a design method for a highly integrated PGNAA element detector for deep space exploration. Background Art

[0002] Elemental analysis is a common method for deep space resource exploration. Through elemental detection, the content and distribution of resources on the moon can be determined, so that resource-rich areas can be selected for development and utilization. Currently, the main element detection instruments include gamma-ray spectrometers and X-ray spectrometers. Gamma-ray spectrometers achieve qualitative and quantitative analysis of the lunar surface and interior materials by measuring natural radioactive elements (U, Th, K) and gamma rays induced by cosmic rays. This is a passive analysis method. Due to the weak gamma signal on the moon, this method usually requires a lot of measurement time and has low elemental analysis accuracy.

[0003] Prompt Gamma Neutron Activation Analysis (PGNAA) is a non-destructive, online nuclear analysis method. It boasts high penetration, rapid analysis speed, high sensitivity, and the ability to analyze multiple elements simultaneously. It uses neutrons emitted from a neutron source to bombard the atomic nuclei of the substance being analyzed, triggering nuclear reactions (primarily inelastic scattering and radiative capture). The energy and intensity of the emitted prompt gamma rays are then measured to determine the elemental composition and content of the sample.

[0004] Deep space exploration usually has strict requirements on the overall mass and volume of the payload. However, traditional PGNAA devices usually take into account structural modules such as moderators, multipliers, and reflectors, which makes the PGNAA device large in size and mass and lacks portability. How to make the PGNAA device design simpler, smaller, and more reliable so that it can be directly installed on the lunar rover's robotic arm to achieve close-range element measurement will be of great significance to deep space resource exploration. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly integrated PGNAA element detector design method for deep space exploration to solve the problems raised by the above background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for designing a highly integrated PGNAA element detector for deep space exploration, comprising the following steps:

[0007] Step 1: Design the basic structure of the PGNAA element detector, including a gamma-ray detector, a neutron shield wrapped around the outer wall of the gamma-ray detector, and a neutron source embedded in the outer wall of the neutron shield in the form of a ring or point source;

[0008] Step 2: Select the component modules of the PGNAA element detector and build a PGNAA element detector model using Monte Carlo simulation software;

[0009] Step 3: Simulate and calculate the effective signal, signal-to-noise ratio, neutron flux and shielding rate in the PGNAA element detector model corresponding to neutron shields of different sizes, and calculate the quality factor Q, where:

[0010] Q = effective signal × signal-to-noise ratio × shielding rate,

[0011]

[0012] Step 4: Based on the quality factor Q calculated in step 3, draw the quality factor Q change curve of the PGNAA element detector corresponding to neutron shielding bodies of different sizes. According to the Q change curve, select the neutron shielding body size and material corresponding to the point with the optimal Q value, and select the gamma-ray detector and neutron source that match the neutron shielding body size. Determine the optimized PGNAA element detector model, and use Monte Carlo simulation software to simulate and calculate the change curve of the characteristic peak count of the target element in the sample with the sample content. When detecting elements, compare the element characteristic peak count with the change curve, and obtain the element content through the scale relationship, thereby completing the design of a highly integrated PGNAA element detector for deep space exploration.

[0013] At present, traditional PGNAA devices need to use components such as moderators to increase the thermal neutron flux at the sample, especially when using a higher energy DT source (14.1MeV). To slow down the energy to thermal neutrons, structures such as a neutron softening layer (preliminary neutron moderation) and a moderator (further neutron moderation) are usually required, which leads to a large device size and heavy weight. For deep space exploration, the large volume of soil (environment) to be tested in deep space exploration has a moderation effect on neutrons. The present invention has learned through simulation that when a neutron source with moderate energy is selected, no external moderator is required, and a good moderation effect can be achieved by relying solely on the moderation effect of the soil to be tested. Therefore, the present invention removes the external moderator and preliminarily reduces the overall weight of the device. In addition, the various components of the existing PGNAA device are usually independently and dispersedly arranged, which will take up a lot of space. The present invention integrates the various components, and the structural design is compact, which effectively improves the space utilization and flexibility of the device. Preferably, in step 2, the gamma-ray detector is selected from one of a BGO detector, a lanthanum bromide detector, and a sodium iodide detector, and the neutron source is selected from an isotope neutron source.

[0014] Compared with the DD source and DT source of neutron generators, the isotope neutron source has the advantages of stable neutron yield, no need for external power supply, small size and light weight. It is easier to meet the goal of miniaturized PGNAA devices and can still work normally in places where it is difficult to provide stable power supply, such as underwater and space. Compared with the DT source with an energy of 14.1MeV, the isotope neutron source has moderate energy and does not require the design of softening layer, moderator layer and other component modules to reduce the energy of neutrons. It can meet the moderation requirements only by relying on the moderation effect of the sample under test, thereby further reducing the overall weight of the device. The gamma-ray detector selects the BGO detector, lanthanum bromide detector, and sodium iodide detector with better performance at present. It is more beneficial for gamma-ray detection in deep space and other places with complex high environmental background conditions. It can effectively improve the statistics of the device and can better distinguish peaks with similar energy, thereby making the subsequent energy spectrum analysis more accurate and precise.

[0015] Preferably, the isotope neutron source is selected from one of a Cf-252 source and an Am-Be source.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Compared with the existing passive measurement methods for deep space element detection, the present invention uses the device's own neutron source to actively excite the gamma characteristic rays of elements in lunar soil samples, thereby realizing qualitative and quantitative analysis of elements, which can effectively shorten the measurement time and improve the statistical nature of the information.

[0018] 2. Regarding the optimal design of the PGNAA device, the present invention uses the quality factor Q as the optimization criterion. This evaluation standard simultaneously takes into account important parameters that affect the measurement performance of the device, such as the signal-to-noise ratio, effective signal, and shielding rate. It can effectively design the PGNAA device, thereby improving the device's sensitivity and measurement accuracy for sample analysis.

[0019] 3. The present invention has the advantages of high integration, small size, and good portability, so that it can be installed on the lunar rover's robotic arm and follow the movement of the lunar rover to realize the measurement of the type, content and distribution of lunar soil elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a design flow chart of a highly integrated PGNAA element detector for deep space exploration provided by an embodiment of the present invention;

[0021] Figure 2 This is a diagram of the connection structure of a gamma-ray detector, a neutron shield, and a neutron source provided by an embodiment of the present invention;

[0022] Figure 3 This is another connection structure diagram of the gamma-ray detector, neutron shield, and neutron source provided by an embodiment of the present invention;

[0023] Figure 4 is a graph showing a change in quality factor Q provided by an embodiment of the present invention;

[0024] Figure 5 This is a graph showing the variation of the characteristic peak count of the Ti element with the sample content provided by an embodiment of the present invention;

[0025] In the figure, 1-gamma ray detector, 2-neutron shield, 3-neutron source. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] See also Figure 1-Figure 5 The present invention provides a technical solution: a method for designing a highly integrated PGNAA element detector for deep space exploration, comprising the following steps:

[0028] Step 1: Design the basic structure of the PGNAA element detector. At present, the various components of the existing PGNAA device are usually independent and dispersed, which will take up a lot of space. The structural design of the present invention is compact, which effectively improves the space utilization and flexibility of the device. It specifically includes a gamma-ray detector, a neutron shielding body coated on the outer wall of the gamma-ray detector, and a neutron source embedded in the outer wall of the neutron shielding body in the form of a ring coating or a point source. The neutron moderator structure contained in the existing element detector is replaced by the sample to be tested, which effectively reduces the overall volume and mass of the device. The connection structure of the gamma-ray detector, neutron shielding body, and neutron source of the present invention is as follows: Figure 2 、 Figure 3 As shown;

[0029] Step 2: Select the component modules of the PGNAA element detector and build a PGNAA element detector model using Monte Carlo simulation software. In this embodiment, the PGNAA element detector model includes an americium-beryllium (Am-Be) neutron source, a bismuth germanate (BGO) ray detector, and a lithium carbonate neutron shield. The sample is soil containing multiple elements such as hydrogen (H), titanium (Ti), iron (Fe), silicon (Si), calcium (Ca), magnesium (Mg), manganese (Mn), sodium (Na), potassium (K), aluminum (Al), and oxygen (O);

[0030] Step 3: Simulate and calculate the effective signal, signal-to-noise ratio, neutron flux and shielding rate in the PGNAA element detector model corresponding to neutron shields of different sizes, and calculate the quality factor Q, where:

[0031] Q = effective signal × signal-to-noise ratio × shielding rate,

[0032]

[0033] Step 4: Based on the quality factor Q calculated in step 3, draw the quality factor Q change curve of the PGNAA element detector corresponding to the neutron shield of different sizes, such as Figure 4 As shown, according to the Q variation curve, the size of the neutron shielding body corresponding to the point with the optimal Q value is selected. When there is no restriction on weight or volume in actual demand, the geometric size corresponding to the maximum value of Q is usually selected as the design size of the neutron shielding body. However, if there is a restriction on weight or volume in actual demand, the size of the neutron shielding body with the quality factor Q closest to the maximum value of Q is selected as the design size, provided that the weight and volume requirements of the device are met. In this embodiment, the thickness of the neutron shielding body is 14 cm, and a gamma-ray detector and a neutron source that match the size of the neutron shielding body are selected to determine the optimized PGNAA element detector model. Monte Carlo simulation software is used to simulate and calculate the curve of the change of the characteristic peak count of the target element in the sample with the sample content. In this embodiment, taking Ti as an example, the characteristic peak count of the Ti element measured by the optimized device model shows a good linear correlation with the change of the sample content, as shown in FIG. Figure 5 As shown, when conducting deep space element detection, the content of the corresponding element can be obtained by comparing the gamma-ray characteristic peak counts of the corresponding element with the curve of the change of the element characteristic peak counts with the sample content, and finally, the design of a highly integrated PGNAA element detector for deep space detection is completed.

[0034] It should be noted that according to the basic theoretical formula: Where, P γ is the gamma-ray characteristic peak count, N is the number of target nuclide atoms, N A is Avogadro's constant, θ is the nuclide abundance, W is the mass of the target element; M is the molar mass of the target element (g / mol), σ is the neutron capture cross section, is the neutron injection rate, t is the irradiation time, γ is the branching ratio, and ε is the detection efficiency of the full energy peak. According to basic theory, when detecting a sample, the element mass content W should be equal to the characteristic gamma ray count P. γLinear correlation, that is, through the designed PGNAA element detector model, when using Monte Carlo simulation software to simulate and calculate the curve of the change of the characteristic peak count of the target element in the sample with the sample content, the characteristic peak count of the target element should be linearly correlated with the element content. When the linear relationship of the obtained change curve is poor, the internal standard method or the corresponding method should be used to correct the nonlinear effect. The method of correcting the nonlinear effect is a public existing technology and is clear to those skilled in the art, so it will not be elaborated here.

[0035] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. 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 highly integrated PGNAA element detector design method for deep space exploration, characterized in that: The following steps are involved: Step 1: Design the basic structure of the PGNAA element detector, including a gamma-ray detector, a neutron shield wrapped around the outer wall of the gamma-ray detector, and a neutron source embedded in the outer wall of the neutron shield in the form of a ring or point source; Step 2: Select the component modules of the PGNAA element detector and build a PGNAA element detector model using Monte Carlo simulation software; Step 3: Simulate and calculate the effective signal, signal-to-noise ratio, neutron flux and shielding rate in the PGNAA element detector model corresponding to neutron shields of different sizes, and calculate the quality factor Q, where: Q = effective signal × signal-to-noise ratio × shielding rate, Step 4: Based on the quality factor Q calculated in step 3, draw the quality factor Q change curve of the PGNAA element detector corresponding to neutron shielding bodies of different sizes and materials. According to the Q change curve, select the neutron shielding body size and material corresponding to the point with the optimal Q value, and select the gamma-ray detector and neutron source that match the neutron shielding body size, determine the optimized PGNAA element detector model, and use Monte Carlo simulation software to simulate and calculate the change curve of the characteristic peak count of the target element in the sample with the sample content. When detecting elements, the element characteristic peak count is compared with the change curve, and the element content is obtained through the scale relationship, thereby completing the design of a highly integrated PGNAA element detector for deep space exploration.

2. The method for designing a highly integrated PGNAA element detector for deep space exploration according to claim 1, characterized in that: In step 2, the gamma-ray detector is selected from one of a BGO detector, a lanthanum bromide detector, and a sodium iodide detector, and the neutron source is selected from an isotope neutron source.

3. The method for designing a highly integrated PGNAA element detector for deep space exploration according to claim 2, characterized in that: The isotope neutron source is selected from one of a Cf-252 source and an Am-Be source.

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