Uranium mine logging instrument based on ultra-short pulse neutrons and working method thereof

Abstract

The application discloses a kind of uranium mine logging instrument based on ultrashort pulse neutron and working method thereof, it is related to uranium mine exploration well logging field;Logging instrument includes control communication nipple arranged in sequence along its axial direction, ultrashort pulse neutron generator for emitting fast neutron pulse with pulse width less than 1 microsecond to formation, shielding body, dual thermal neutron detection assembly for detecting thermal neutron and superhot neutron on spatially consistent measurement point, gamma detector for detecting non-elastic scattering gamma ray and capture gamma ray emitted by formation element, and fast neutron detector and multichannel synchronization and high-speed acquisition circuit for detecting and outputting source intensity monitoring signal of fast neutron pulse in real time;The logging instrument of the application emits ultrashort fast neutron pulse and detects neutron yield in real time, combines to obtain neutron time spectrum and multi-dimensional information of gamma energy spectrum with accurate time stamp, carries out high-precision, anti-interference inversion to formation uranium content, and efficiently and accurately obtains formation information.

Description

Technical Field

[0001] This invention relates to the field of uranium exploration logging technology, and more specifically, to a uranium logging instrument based on ultrashort pulse neutrons and its working method. Background Technology

[0002] Uranium resource exploration and evaluation rely on efficient logging technology. Among existing technologies, gamma-ray logging is widely used, but it indirectly calculates uranium content by measuring gamma rays emitted from uranium-series decay products, which is limited by the assumption of "uranium-radium balance." In nature, due to geological changes or fluid migration, uranium and radium often differentiate, leading to a disruption of the balance. This causes significant deviations in gamma-ray logging results, failing to accurately reflect uranium grade and limiting the accuracy of resource assessment. To overcome this fundamental deficiency, transient fission neutron (PFN) uranium logging technology has emerged. This technology uses a neutron generator to emit pulsed neutrons, directly bombarding uranium-235 nuclides in the formation and detecting the transient hyperthermal neutrons produced by their fission to determine uranium content. Because the signal directly originates from the fission reaction of uranium-235, PFN uranium logging technology can directly determine uranium content, fundamentally eliminating the impact of uranium-radium balance disruption and effectively solving the problems of traditional gamma-ray logging.

[0003] However, while existing PFN uranium logging tools have achieved their technological advantages, they still face several pressing technical challenges that limit their measurement accuracy and widespread application:

[0004] 1) Source intensity fluctuations introduce measurement errors: The core of PFN uranium logging technology lies in inverting uranium content through fission neutron count rate; however, the neutron yield of downhole neutron generators is extremely sensitive to operating conditions such as temperature and pressure, and its output intensity will fluctuate accordingly. This instability of source intensity is directly transmitted to the detection and counting of hyperthermal neutrons. Even if the formation uranium content remains unchanged, the count rate will change, thus introducing systematic errors that are difficult to accurately compensate for, affecting the reliability of quantitative results.

[0005] 2) Limited information dimension leads to correction difficulties: Existing PFN uranium logging tools mainly rely on neutron signals and lack synchronous detection of other physical parameters of the formation. When faced with complex lithology, such as rock layers rich in neutron-absorbing elements, highly mineralized formation water, or complex geological conditions such as porosity changes, the interaction between neutrons and the formation becomes complex. It is difficult to effectively identify and correct these environmental interferences based on a single neutron information, resulting in multiple interpretations and uncertainties in the uranium content interpretation results.

[0006] 3) Insufficient time resolution leads to low signal-to-noise ratio: To distinguish between neutrons and gamma rays, PFN uranium logging technology uses pulsed neutron sources. However, the neutron pulse width of existing instruments is usually wide, reaching the order of tens of microseconds. The excessively wide pulse results in a long neutron emission duration. During and after the pulse, the neutrons from the neutron source and the transient neutron signals generated by uranium-235 fission overlap severely in the time domain. This overlap makes it extremely difficult to effectively separate the weak fission signal from the strong background noise, ultimately resulting in a low measurement signal-to-noise ratio and limited detection sensitivity and depth.

[0007] In summary, existing PFN uranium logging tools still have significant shortcomings in terms of measurement stability, environmental adaptability, and detection sensitivity. Therefore, there is an urgent need in this field for a new type of logging instrument that can overcome these deficiencies to achieve more stable, accurate, and reliable direct determination of uranium content. Summary of the Invention

[0008] 1. The technical problem that the invention aims to solve

[0009] The purpose of this invention is to improve the technical problems of poor measurement stability, environmental adaptability, and detection sensitivity in existing PFN uranium ore logging tools due to factors such as source strength fluctuations and insufficient time resolution caused by single information dimensions. The invention proposes using an ultrashort pulse neutron generator to generate fast neutron pulses, combined with a fast neutron detector to correct source strength fluctuations, and simultaneously acquiring neutron time decay spectra and time-gated gamma spectra under ultrashort pulse excitation. By utilizing multi-dimensional information for comprehensive inversion calculation of uranium content, the invention effectively improves the measurement stability, environmental adaptability, and detection sensitivity of the logging tool, and enhances the reliability of the measurement results.

[0010] 2. Technical Solution

[0011] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0012] In a first aspect, the present invention provides a uranium ore logging tool based on ultrashort pulse neutrons, comprising a control and communication subsection, an ultrashort pulse neutron generator, a shield, a dual thermal neutron detection assembly and a gamma detector arranged sequentially along the axis of the logging tool, as well as a control and communication subsection, several fast neutron detectors, and a multi-channel synchronization and high-speed acquisition circuit.

[0013] The ultrashort pulse neutron generator is electrically connected to the control and communication stub and is used to transmit fast neutron pulses with a pulse width of less than 1 microsecond to the formation.

[0014] The fast neutron detector is arranged around the periphery of the ultrashort pulse neutron generator to detect and output the source strength monitoring signal of each fast neutron pulse in real time; optionally, the fast neutron detector is selected from diamond detector, silicon carbide detector, and plastic scintillator coupled photodiode.

[0015] The shielding body is located between the ultrashort pulse neutron generator and the dual thermal neutron detection assembly, and is used to shield direct radiation from the neutron source;

[0016] The dual thermal neutron detection component is used to detect thermal neutrons and ultrathermal neutrons, the gamma detector is used to detect gamma rays, and the multi-channel synchronization and high-speed acquisition circuit is used to acquire the detection signals of each detector, and after synchronously acquiring and associating the neutron time spectrum and gamma energy spectrum based on the timestamp, the data is uploaded to the logging computer so that the logging computer can use a pre-trained inversion algorithm model to invert the formation uranium content after receiving the uploaded data.

[0017] Furthermore, the dual thermal neutron detection assembly includes a thermal neutron detector and an ultrathermal neutron detector, used to simultaneously detect thermal neutrons formed by ground slowing and transient ultrathermal neutrons generated by uranium-235 fission at spatially consistent measurement points.

[0018] The dual thermal neutron detection assembly includes a first scintillation crystal, a second scintillation crystal, a first photoelectric converter, and a first housing. Both the first and second scintillation crystals are sensitive to thermal neutrons. A first shielding and slowing layer is disposed on the outer wall of the first scintillation crystal. The first scintillation crystal and the first shielding and slowing layer constitute the ultrathermal neutron detector. The second scintillation crystal constitutes the thermal neutron detector. The ultrathermal neutron detector and the thermal neutron detector are disposed face-to-face and form a closely adjacent structure of the dual thermal neutron detection assembly.

[0019] The first photoelectric converter is coupled to the end face of the second scintillation crystal away from the superthermal neutron detector, and the first scintillation crystal, the second scintillation crystal and the first photoelectric converter form a detection part with a common optical path along the same axis; the first housing is fixed to the outside of the detection part, and the detection part is supported as an integral component.

[0020] Optionally, the first scintillation crystal is selected from... 6 Li glass, Ce:LiCAF, 6 LiF / ZnS(Ag), CLYC, CLLB, LiI(Eu), zirconia crystal, or EJ-299 plastic scintillator; the second scintillator crystal is selected from... 6 Li glass, Ce:LiCAF, 6LiF / ZnS(Ag), CLYC, CLLB, LiI(Eu), zirconia crystal or EJ-299 plastic scintillator.

[0021] Furthermore, the dual thermal neutron detection assembly includes a thermal neutron detector, an ultrathermal neutron detector, and a second housing, wherein the thermal neutron detector and the ultrathermal neutron detector are disposed within the second housing;

[0022] The thermal neutron detector has a through hole in the middle, and the detection unit of the ultrathermal neutron detector is embedded in the through hole to form the nested structure of the dual thermal neutron detection assembly.

[0023] Furthermore, the thermal neutron detector is configured as a first microstructure gas detector, which includes an annular chamber structure with an axial through hole, the annular chamber structure being filled with ³He gas; a cathode drift electrode and an anode readout electrode are respectively provided at both ends of the annular chamber structure along its axial direction, and the cathode drift electrode and the anode readout electrode are respectively connected to the internal chamber of the annular chamber structure;

[0024] The superthermal neutron detector includes a third scintillation crystal, a second photoelectric converter, and a second shielding moderation layer. The third scintillation crystal is a crystal sensitive to thermal neutrons. The second shielding moderation layer covers all the outer surfaces of the third scintillation crystal, forming a detection unit embedded in the axial through-hole of the first microstructure gas detector. The second photoelectric converter is coupled to the end face of the outer wall of the detection unit perpendicular to the axial direction of the first microstructure gas detector.

[0025] Furthermore, the superthermal neutron detector can also be designed as another structure: the superthermal neutron detector is fixed in the axial through hole of the first microstructure gas detector, including a second microstructure gas detector and a third shielding and slowing layer. The third shielding and slowing layer is covered and disposed on all the outer wall surfaces of the second microstructure gas detector, and the structure and size of the second microstructure gas detector covered with the third shielding and slowing layer are adapted to the axial through hole.

[0026] Optionally, the first, second, and third shielding and moderating layers include a neutron shielding layer and a moderating layer disposed inside the neutron shielding layer; the moderating layer is a polyethylene moderating layer or a paraffin moderating layer, and the neutron shielding layer is a cadmium layer.

[0027] Furthermore, the gamma detector also includes a third housing;

[0028] The dual-probe assembly includes a third housing, within which are a near-source probe and a far-source probe for detecting inelastic scattered gamma rays and capturing gamma rays emitted by geological elements. The near-source probe and the far-source probe are fixedly spaced within the third housing and are both configured as radiation-resistant scintillation crystals connected to a third photoelectric converter. A central cavity is formed between the near-source probe and the far-source probe, and along with the inner wall of the third housing. The multi-channel synchronous and high-speed acquisition circuit is integrated within this central cavity. A shielding layer covers the inner wall of the third housing, serving to shield against electromagnetic interference and reduce neutron radiation damage.

[0029] Optionally, the gamma detector further includes a fixed bracket disposed inside the housing, the fixed bracket supporting and fixedly connected to the near-source probe and the far-source probe respectively, for defining the relative position between the near-source probe and the far-source probe; optionally, the radiation-resistant scintillation crystal is selected from CeBr3 crystal, LaBr3(Ce) crystal, CsI(Tl) crystal, Cs3Cu2I5(Tl) crystal, GSO:Ce crystal, LYSO:Ce crystal, BGO crystal, PWO crystal, BaF2 crystal, CeF3 crystal, G-(Gd,La)2Si2O7:Ce³ + Crystals, Rb2AgBr3:Cu crystals, Cs3Cu2I5(Li / Tl) crystals, LuAG:Ce ceramic crystals, GYAGG ceramic crystals, GAGG crystals; optionally, the shielding layer is selected from aluminum shielding layers, copper shielding layers, lead shielding layers, tungsten shielding layers, and tungsten alloy shielding layers.

[0030] Furthermore, the multi-channel synchronization and high-speed acquisition circuit includes several signal processing channels electrically connected to the ultrashort pulse neutron generator, fast neutron detector, dual thermal neutron detection assembly and gamma detector, as well as an analog-to-digital converter and an FPGA processor. The FPGA processor is configured with pulse counting and time spectrum analysis functions based on the master clock.

[0031] The input terminal of the analog-to-digital converter is connected to the output terminal of each of the signal processing channels to convert the input signal into a digital signal; the output terminal of the analog-to-digital converter is connected to the FPGA processor, and the output terminal of the FPGA processor is communicatively connected to the logging computer for data communication and data transmission.

[0032] In a second aspect, the present invention provides a method for operating the uranium ore logging tool based on ultrashort pulse neutrons provided in the first aspect of the present invention, comprising the following steps:

[0033] Step 1) Lower the logging instrument to the target formation and establish communication between the logging instrument and the logging computer on the ground through the control communication sub. The logging computer issues instructions to set the pulse frequency and width of the ultrashort pulse neutron generator and the measurement parameters of each detector.

[0034] Step 2) Control the ultrashort pulse neutron generator to emit a fast neutron pulse toward the formation via the control communication sub-section, and simultaneously use the fast neutron detector to detect the neutron yield of the fast neutron pulse in real time, recording the fast neutron count N used for normalization of the neutron count. fast ;

[0035] Step 3) Divide the data into several time gates based on the timestamp and time sequence, and collect signals in stages; the time gates include: an inelastic scattering window, through which the inelastic scattering gamma spectrum is collected by the gamma detector; a thermal neutron measurement window, through which the thermal neutron count and ultrathermal neutron count are collected simultaneously by the dual thermal neutron detection component; and a captured gamma window, through which the captured gamma spectrum is collected by the gamma detector; each time gate collects data in parallel according to the corresponding time window.

[0036] Step 4) Using the multi-channel synchronization and high-speed acquisition circuit, the acquired inelastic scattering gamma spectrum, thermal neutron count and hyperthermal neutron count, gamma spectrum and master clock are synchronized to generate neutron time decay spectrum and time-gated gamma spectrum; wherein, the neutron time decay spectrum is characterized by the count ratio calculated based on the hyperthermal neutron count and thermal neutron count.

[0037] Step 5) Based on the pre-trained inversion algorithm model, and using the fast neutron count N... fast The parameters of the neutron time decay spectrum and the characteristic element information extracted from the time-gated gamma spectrum are comprehensively inverted to output the uranium content and geological parameters of the target layer; wherein, the inversion algorithm model is selected from a multiple linear regression model or a machine learning model, the characteristic element information includes the hydrogen / silicon element count ratio and the chlorine / hydrogen element count ratio, and the geological parameters include porosity and lithology.

[0038] Furthermore, when the dual thermal neutron detector components are in a close-proximity structure, the calculation process for the count ratio is as follows:

[0039] In the same thermal neutron field, the first scintillation crystal and the second scintillation crystal are calibrated, the ratio of thermal neutron detection efficiency between the crystals is calculated, and then the ratio of the first scintillation crystal's efficiency for ultrathermal neutron detection and the second scintillation crystal's efficiency for thermal neutron detection is determined.

[0040] Based on the spatial structure read out by the common optical path of the detection unit and the multi-channel synchronous and high-speed acquisition circuit, pulse signals of thermal neutrons, hyperthermal neutrons, and gamma rays are acquired.

[0041] Based on the pulse waveform discrimination algorithm, the collected pulse signals of thermal neutrons, hyperthermal neutrons and gamma rays are identified in real time. The pulse signals of thermal neutrons and hyperthermal neutrons are recorded, and the pulse signals of gamma rays are removed to obtain the time spectrum of thermal neutrons and the time spectrum of hyperthermal neutrons. The counts of thermal neutrons and hyperthermal neutrons are counted respectively.

[0042] Based on the ratio of the detection efficiency of the first scintillation crystal for ultrathermal neutrons to that of the second scintillation crystal for thermal neutrons, and the statistical ultrathermal neutron count and thermal neutron count, the count ratio of ultrathermal neutrons to thermal neutrons is output; wherein, the ratio between the detection efficiency of the first scintillation crystal for ultrathermal neutrons and that of the second scintillation crystal for thermal neutrons is equal to the ratio of the thermal neutron detection efficiency between the crystals.

[0043] Furthermore, when the dual thermal neutron detector assembly has a nested structure, the calculation process for the count ratio is as follows:

[0044] In the same thermal neutron field, the thermal neutron detector and the ultrathermal neutron detector without a second or third shielding moderation layer are calibrated, and the ratio of their thermal neutron detection efficiencies is calculated to determine the ratio of the thermal neutron detector's thermal neutron detection efficiency to the ultrathermal neutron detector's ultrathermal neutron detection efficiency.

[0045] Based on the different signal processing channels of the multi-channel synchronization and high-speed acquisition circuit, thermal neutron signals and hyperthermal neutron signals are processed respectively, and thermal neutron time spectra and hyperthermal neutron time spectra are acquired.

[0046] Based on the collected thermal neutron time spectrum and ultrathermal neutron time spectrum, the thermal neutron count and ultrathermal neutron count are counted respectively.

[0047] Based on the ratio of the thermal neutron detector's thermal neutron detection efficiency to the ultrathermal neutron detector's ultrathermal neutron detection efficiency, and the statistical counts of thermal and ultrathermal neutrons, the count ratio of ultrathermal neutrons to thermal neutrons is output; wherein, the ratio between the thermal neutron detector's thermal neutron detection efficiency and the ultrathermal neutron detector's ultrathermal neutron detection efficiency is equal to the ratio of the thermal neutron detection efficiency of the thermal neutron detector and the ultrathermal neutron detector without a second or third shielding moderation layer.

[0048] 3. Beneficial effects

[0049] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0050] (1) The uranium mine logging instrument based on ultrashort pulse neutrons provided by the present invention sets up a fast neutron detector to directly monitor the neutron source strength in real time, accurately track the neutron yield fluctuation of each fast neutron pulse, and perform normalization correction accordingly. This eliminates the systematic error caused by the instability of neutron yield from the root, so that all subsequent measurement data are based on a more reliable foundation, thereby obtaining quantitative results with improved reliability.

[0051] (2) The uranium logging tool based on ultrashort pulse neutrons provided by the present invention uses an ultrashort pulse neutron generator to emit fast neutron pulses of 14MeV with a pulse width of less than 1 microsecond. Combined with multi-channel synchronization and high-speed acquisition circuit, it can achieve nanosecond-level time resolution capability, thereby enabling clear and accurate separation of neutron signals and gamma signals from different sources on the time axis, significantly improving the detection sensitivity and depth of the logging tool.

[0052] (3) The dual thermal neutron detection component of the uranium ore logging tool based on ultrashort pulse neutrons provided by the present invention adopts a close-fitting structure or a nested structure. On the one hand, through ingenious mechanical and functional integration, it realizes the measurement of thermal neutron detection and ultrathermal neutron detection functional components under strict source distance conditions, fundamentally eliminating the error caused by the spatial separation of thermal neutron detector and ultrathermal neutron detector, so that the final thermal neutron count can truly reflect the neutron flux at the position of ultrathermal neutron detector, and obtain more accurate and reliable thermal neutron detection data. On the other hand, the detection unit with common optical path readout proposed by the close-fitting structure only needs one readout electronic channel when used in conjunction with the electronic method of pulse waveform discrimination. The detection component proposed by the nested structure can reduce the number of electronic channels to a minimum of 2. That is, it simplifies the existing complex multi-channel electronic channels into one channel, greatly improving the integration of the logging tool structure.

[0053] (4) The gamma detector used in the uranium logging tool based on ultrashort pulse neutrons provided by the present invention is a dual-source-spacing integrated gamma detector. By integrating the multi-channel synchronization and high-speed acquisition circuit into the central cavity formed by the third shell, near-source-spacing probe and far-source-spacing probe, a spatial multiplexing architecture is formed, which effectively solves the problems of volume redundancy and source-spacing inaccuracy of discrete detectors. On the one hand, the integrated structure can avoid the relative position deviation between probes caused by mechanical vibration or temperature changes, and obtain more accurate and reliable characteristic gamma ray detection data by ensuring the long-term stability of measurement geometry. On the other hand, by efficiently integrating the detection function and signal readout function in the limited space of the shell, the overall volume and weight of the gamma detector are reduced, and the integration of the logging tool is further improved from the perspective of single detector integration, so as to improve the applicability of the logging tool.

[0054] (5) The uranium logging tool based on ultrashort pulse neutrons provided by this invention adopts a modular design to highly integrate multiple functional detectors into one unit, and can acquire multi-dimensional data by sequentially running them into the well. Specifically, during data acquisition, several time gates are divided according to the time sequence based on the timestamp, and multi-dimensional data are used in stages, including inelastic scattering gamma spectrum, thermal neutron count and ultrathermal neutron count, and gamma spectrum. On the one hand, through the fine time gate design, the contribution of background noise and interference signals is greatly suppressed, thereby obtaining an extremely high signal-to-noise ratio. The fusion of multi-dimensional information makes the extracted formation information purer and more realistic. On the other hand, by using more accurate multi-dimensional information such as thermal neutrons and gamma rays, time and energy for joint inversion and cross-validation, the identification difficulties caused by formation complexity and environmental interference are effectively overcome, and the accuracy and confidence of fluid identification and quantitative interpretation are significantly improved, ultimately obtaining more accurate detection results with higher logging efficiency. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the overall structure of the logging instrument disclosed in an embodiment of the present invention;

[0056] Figure 2 This is a schematic diagram of a dual thermal neutron detector assembly with a closely spaced structure disclosed in an embodiment of the present invention;

[0057] Figure 3 This is a schematic diagram of a nested dual thermal neutron detector assembly disclosed in an embodiment of the present invention;

[0058] Figure 4 This is a schematic diagram of the installation of the gamma detector and high-speed acquisition circuit disclosed in an embodiment of the present invention;

[0059] Figure 5 This is a schematic diagram of data acquisition and time gate disclosed in an embodiment of the present invention.

[0060] The specific meanings of each mark in the diagram are as follows:

[0061] 101-Control and communication subsection; 102-Ultra-short pulse neutron generator; 103-Fast neutron detector; 104-Shielding enclosure; 105-Thermal neutron detector; 106-Ultra-thermal neutron detector; 107-Near-source distance probe; 108-Far-source distance probe; 109-Multi-channel synchronization and high-speed acquisition circuit;

[0062] 111-First scintillation crystal; 112-Second scintillation crystal; 113-Neutron shielding layer; 114-Moderizing layer; 115-First photoelectric converter; 116-First housing;

[0063] 121-Cathode drift electrode; 122-Anode readout electrode; 123-Axial through hole; 124-Third scintillation crystal; 125-Second photoelectric converter; 126-Second housing;

[0064] 131-Central cavity; 132-Shielding layer; 133-Third housing; 134-Third photoelectric converter. Detailed Implementation

[0065] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings.

[0066] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0067] The following description, in conjunction with the specific embodiments shown in the accompanying drawings, further describes the uranium ore logging instrument based on ultrashort pulse neutrons and its working method disclosed in this invention.

[0068] Combination Figure 1 As shown in the embodiment, the uranium ore logging tool based on ultrashort pulse neutrons disclosed includes an ultrashort pulse neutron generator 102, a shield 104, a dual thermal neutron detection assembly and a gamma detector arranged sequentially along its axis, as well as a control and communication subsection 101, several fast neutron detectors 103 and a multi-channel synchronization and high-speed acquisition circuit 109; the fast neutron detectors 103 are typically set to 2 to 6;

[0069] The ultrashort pulse neutron generator 102 is electrically connected to the control and communication sub-junction 101, and is used to emit fast neutron pulses with a pulse width of less than 1 microsecond into the formation. The repetition frequency of the ultrashort pulse neutron generator 102 is adjustable, and the emitted fast neutron pulses are preferably in the nanosecond range and 14 MeV. The control and communication sub-junction 101 is electrically connected to a well logging computer on the ground, and is used to communicate with the well logging computer, distribute power, and send control commands. A plurality of fast neutron detectors 103 are arranged around the ultrashort pulse neutron generator 102, and are used to detect and output the source strength monitoring signal of each fast neutron pulse in real time. In specific implementation, the fast neutron count N is obtained by detecting the neutron yield of each fast neutron pulse. fast This count is then used for subsequent normalization processing to correct source strength fluctuations. Optionally, at least two fast neutron detectors 103 are arranged around the ultrashort pulse neutron generator 102, and they are evenly distributed along the periphery of the ultrashort pulse neutron generator 102. The fast neutron detectors 103 are selected from diamond detectors, silicon carbide detectors, and plastic scintillators with photodiodes. In this embodiment, four fast neutron detectors 103 are arranged. Figure 1 For ease of demonstration, only two of the symmetrically arranged arrays are shown, both of which use diamond detectors because diamond detectors have excellent radiation resistance, a time response of less than 1 ns, and high detection efficiency for 14 MeV neutrons.

[0070] The shield 104 is located between the ultrashort pulse neutron generator 102 and the dual thermal neutron detection assembly, and is used to shield direct neutrons and gamma rays from the neutron source, protecting the gamma detector from transient radiation interference. In this embodiment, the shield 104 is a tungsten shield, which is configured as a plate structure with a shape adapted to the internal radial cross-section of the logging tool.

[0071] The dual thermal neutron detection assembly includes a thermal neutron detector 105 and an ultrathermal neutron detector 106, used to simultaneously detect thermal neutrons generated by formation slowing and transient ultrathermal neutrons generated by uranium-235 fission at spatially consistent measurement points. Traditional uranium logging tools typically separate the thermal neutron detector 105 and ultrathermal neutron detector 106 axially, such as gas detectors using ³He tubes. Due to wellbore size limitations (usually less than 60mm in diameter), the spacing between the ultrathermal neutron detector 106 and the thermal neutron detector 105 is usually large. Because the distribution of formation thermal neutrons along the well axis changes dynamically over time, the separate design of the ultrathermal neutron detector 106 and the thermal neutron detector 105 causes the thermal neutron count to fail to accurately reflect the neutron flux at the location of the ultrathermal neutron detector 106, introducing spatial inconsistency errors. Therefore, in the dual thermal neutron detection assembly selected by the logging tool of the present invention, the thermal neutron detector 105 and the ultrathermal neutron detector 106 are integrated in the same position, thereby ensuring spatial consistency when installed in the logging tool. The design of the two detectors in the same position eliminates the spatial inconsistency error introduced by the axial separation setting of traditional logging tools, so that the final thermal neutron count can truly reflect the neutron flux at the position of the ultrathermal neutron detector 106, and improve the detection accuracy.

[0072] The gamma detector includes a near-source probe 107 and a far-source probe 108, used to detect inelastic scattered gamma rays and captured gamma rays emitted by elements in the formation. The near-source probe 107 and the far-source probe 108 are composed of two high-resolution radiation-resistant scintillation crystals coupled to photomultiplier tubes or silicon photomultipliers. Their high-resolution characteristics are used to accurately identify the characteristic gamma rays of different elements, such as C, O, Si, Ca, H, and Cl. Optionally, the radiation-resistant scintillation crystal is selected from CeBr3 crystal, LaBr3(Ce) crystal, CsI(Tl) crystal, Cs3Cu2I5(Tl) crystal, GSO:Ce crystal, LYSO:Ce crystal, BGO crystal, PWO crystal, BaF2 crystal, CeF3 crystal, and G-(Gd,La)2Si2O7:Ce³. +The crystals used include Rb2AgBr3:Cu crystal, Cs3Cu2I5(Li / Tl) crystal, LuAG:Ce ceramic crystal, GYAGG ceramic crystal, and GAGG crystal. In this embodiment, the radiation-resistant scintillation crystal is selected from LaBr3(Ce) crystal because of its excellent energy resolution and short decay time (approximately 16 ns), making it suitable for high count rate and high time resolution measurements. Considering the economic cost of the logging tool, the radiation-resistant scintillation crystal can be selected from CeBr3 crystal.

[0073] The multi-channel synchronization and high-speed acquisition circuit 109 is electrically connected to the control communication subsection 101, the ultrashort pulse neutron generator 102, the fast neutron detector 103, the dual thermal neutron detection assembly, and the gamma detector, respectively. It is used to control the emission of neutron pulses, receive the detection signals of the dual thermal neutron detection assembly and the gamma detector, and synchronously acquire and correlate the neutron time spectrum and the gamma energy spectrum based on the timestamp. In this embodiment, the multi-channel synchronization and high-speed acquisition circuit 109 includes several signal processing channels electrically connected to the ultrashort pulse neutron generator 102, the fast neutron detector 103, the dual thermal neutron detection assembly, and the gamma detector, as well as an analog-to-digital converter and an FPGA processor. The FPGA processor internally configures a pulse counting module and a time spectrum analysis module based on the master clock. The input terminal of the analog-to-digital converter is connected to the output terminal of each of the signal processing channels to convert the input signal into a digital signal. The output terminal of the analog-to-digital converter is connected to the FPGA processor, and the output terminal of the FPGA processor is communicatively connected to the control communication sub-junction 101 so that the control communication sub-junction 101 processes the data associated with the acquisition by the multi-channel synchronization and high-speed acquisition circuit 109 before uploading it to the surface logging computer, or directly uploads it to the logging computer for data processing. The logging computer is loaded with a pre-trained inversion algorithm model to accurately invert the uranium content of the formation based on the uploaded data. Optionally, other geological parameters, such as porosity and lithology, are also output during model inversion.

[0074] The above-described embodiments disclose a uranium ore logging tool based on ultrashort pulse neutrons, wherein the dual thermal neutron detection components integrated at the same location include adjacent structures and nested structures, combined with... Figure 2 and Figure 3 They are described below.

[0075] Figure 2The diagram shows a dual thermal neutron detection assembly with a close-proximity structure, including a first scintillation crystal 111, a second scintillation crystal 112, a first photoelectric converter 115, and a first housing 116. Both the first scintillation crystal 111 and the second scintillation crystal 112 are thermal neutron-sensitive crystals. The outer wall of the first scintillation crystal 111 is covered with a first shielding and slowing layer. The first scintillation crystal 111 and the first shielding and slowing layer constitute an ultrathermal neutron detector 106. The second scintillation crystal 112 constitutes a thermal neutron detector 105. The thermal neutron detector 105 and the ultrathermal neutron detector 106 constitute the dual thermal neutron detection assembly with a close-proximity structure.

[0076] During design and installation, the superthermal neutron detector 106 and the thermal neutron detector 105 are fitted face-to-face. The first photoelectric converter 115 is coupled to the end face of the thermal neutron detector 105 away from the superthermal neutron detector 106. The first scintillation crystal 111, the second scintillation crystal 112, and the first photoelectric converter 115 form a detection unit with a common optical path along the same axis. The first housing 116 is fixed to the outside of the detection unit, supporting the detection unit as an integral component.

[0077] In the specific assembly of the dual thermal neutron detection component, all outer surfaces of the first scintillation crystal 111 are first covered with the first shielding and slowing layer; one outer surface of the second scintillation crystal 112 is selected from below the first scintillation crystal 111 and is attached to the bottom surface of the first scintillation crystal 111 covered with the first shielding and slowing layer, and the first photoelectric converter 115 is disposed on the end surface of the second scintillation crystal 112 away from the bottom surface; the vertical direction is defined as the up-down direction, and the first scintillation crystal 111, the second scintillation crystal 112 and the first photoelectric converter 115 are arranged sequentially in the top-down direction. Optionally, in order to achieve the purpose of the first scintillation crystal 111, the second scintillation crystal 112 and the first photoelectric converter 115 forming a common optical path for readout along the same axis, the first scintillation crystal 111 and the second scintillation crystal 112 are both configured as an axisymmetric structure in the vertical direction, and the center of the first photoelectric converter 115 is disposed on the axis.

[0078] The surfaces of the ultrathermal neutron detector 106 and the thermal neutron detector 105 that are in contact with each other are defined as the first surface and the second surface. In specific implementations, to facilitate the bonding and installation of the dual scintillation crystal surfaces, the first surface and the second surface are set to have the same shape and size. In this embodiment, as shown... Figure 2 As shown, the first scintillation crystal 111 and the second scintillation crystal 112 are configured with the same regular hexahedral structure, such as a cuboid or a cube, to ensure the formation of a coaxial common optical path readout structure, and the first scintillation crystal 111 is selected 6Li glass, the second scintillation crystal 112 selected 6 LiF / ZnS(Ag); In practical applications, the actual size of the scintillation crystal can be flexibly selected according to the size of the dual thermal neutron detector assembly.

[0079] By attaching the hyperthermal neutron detector 106 and the thermal neutron detector 105 face-to-face and connecting them to the first photoelectric converter 115 to form a detection unit, the thermal neutron detector 105 and the hyperthermal neutron detector 106 are structurally integrated in the same position. This not only results in a compact structure and small size, making it easier to assemble into a small-sized logging tool for use in small-sized wellbores, but also eliminates the axial position error when they are separately set on the logging tool, enabling more accurate acquisition of thermal neutron counts and hyperthermal neutron counts at the detection location. Furthermore, by setting the first scintillation crystal 111, the second scintillation crystal 112, and the first photoelectric converter 115 as a coaxial common optical path readout structure, the consistency of the dual scintillation crystals from the first photoelectric converter 115 to the multi-channel synchronous and high-speed acquisition circuit 109 is ensured, preventing the introduction of additional errors that could cause inaccurate counting.

[0080] Figure 2 In the dual thermal neutron detection assembly shown, one function of the first housing 116 is to connect the first scintillation crystal 111, the second scintillation crystal 112 and the first photoelectric converter 115 into a single structure; another function is to shield electromagnetic interference, etc. Therefore, the first housing 116 is set as a closed housing made of metal material, such as stainless steel, to enclose the detection unit.

[0081] Optionally, the enclosed housing is designed to include a housing one and a housing two; the housing one is configured as a cavity structure with one end open; the housing two is connected to the housing one and includes at least an end cap that closes the opening; a chamber for accommodating the detector is formed between the housing one and the housing two, and the detector is detachably fixed in the cavity. In a specific implementation, the housing one or the housing two has a mounting hole communicating with the interior of the cavity, so that the power line and signal line of the first photoelectric converter 115 can pass through to realize power supply and signal output of the ultrathermal neutron detector 106 and the thermal neutron detector 105.

[0082] A specific example of an optional structure for the first housing 116 is as follows: both housing one and housing two are configured as hollow structures with one end open. A first support and a second support are respectively provided inside housing one and housing two. A wire hole for power lines and signal lines to pass through is provided on the bottom surface of housing two opposite to the opening. The outer wall of the first scintillation crystal 111 is covered with a first shielding and slowing layer and then secured within the first support. The second scintillation crystal 112 is secured within the second support. The first photoelectric converter 115 is located on the end face of the second scintillation crystal 112 away from the opening of housing two. During assembly, housing one and housing two are connected vertically with their openings facing each other. The open end of housing one is fitted onto the outer wall of the open end of housing two until the bottom surface of the first scintillation crystal 111 is in contact with the top surface of the second scintillation crystal 112. The first scintillation crystal 111 and the second scintillation crystal 112 are fixed in the housing one and housing two, respectively, and their positions correspond, coinciding along their vertical axes.

[0083] Figure 3 The diagram shows a nested dual thermal neutron detector assembly, which also includes a second housing 126. The thermal neutron detector 105 and the ultrathermal neutron detector 106 are nested within the second housing 126 to form the nested dual thermal neutron detector assembly. The thermal neutron detector 105 has a through hole in the middle, and the detection unit of the ultrathermal neutron detector 106 is embedded in the through hole.

[0084] Optionally, the nested dual thermal neutron detector assembly can be configured in two ways: a nested structure formed by a superthermal neutron detector 106 constructed with a scintillation crystal and a microstructured gas detector, or a nested structure formed by two microstructured gas detectors.

[0085] Figure 3 The diagram illustrates a nested structure formed by a superthermal neutron detector 106 constructed from a scintillation crystal and a microstructured gas detector. The superthermal neutron detector 105 serves as the first microstructured gas detector, which includes an annular chamber structure with an axial through-hole 123. The annular chamber structure is filled with He gas. The microstructured electrodes of the first microstructured gas detector can be fabricated using printed circuit board (PCB) or silicon wafer technology, and the chamber is sealed by a ceramic or metal frame. The diameter of the axial through-hole 123 is 5-15 mm to accommodate superthermal neutron detectors 106 of different sizes. A cathode drift electrode 121 and an anode readout electrode 122 are respectively provided at both ends of the annular chamber structure along its axial direction. The cathode drift electrode 121 and the anode readout electrode 122 are respectively connected to the internal chamber of the annular chamber structure. The field cage inside the annular chamber needs to be appropriately configured according to the shape of the chamber to create a uniform and strong electric field inside the chamber, facilitating particle detection.

[0086] The superthermal neutron detector 106 includes a third scintillation crystal 124, a second photoelectric converter 125, and a second shielding and slowing layer. The third scintillation crystal 124 is a crystal sensitive to thermal neutrons. The second shielding and slowing layer covers all the outer surfaces of the third scintillation crystal 124, forming a detection unit embedded in the axial through-hole of the first microstructure gas detector. During assembly of the superthermal neutron detector 106, the second photoelectric converter 125 is coupled to the end face of the outer wall of the detection unit perpendicular to the axial direction of the first microstructure gas detector. Figure 3 The nested structure shown has the third scintillation crystal 124 configured as a regular hexahedron, i.e., a cuboid. Optionally, the diameter of the circumcircle of the cuboid is adapted to the diameter of the axial through-hole 123. Defining the direction of the first microstructure gas detector's axial upward cathode drift electrode 121 as upward and the direction of the anode readout electrode 122 as downward, the second photoelectric converter 125 is coupled and disposed on the bottom surface of the cuboid. Optionally, the third scintillation crystal 124 is selected... 6 Li glass, the second photoelectric converter 125 selects SiPM.

[0087] As an optional implementation, the first scintillation crystal 111 and the third scintillation crystal 124 may also be selected from Ce:LiCAF, 6 LiF / ZnS(Ag), CLYC, CLLB, LiI(Eu), zirconia crystal, or EJ-299 plastic scintillator, wherein the second scintillator crystal 112 may also be selected from... 6 The photoelectric converters 115 and 125 may also be selected from PTM, and can be made of Li glass, Ce:LiCAF, CLYC, CLLB, LiI(Eu), zirconia crystal or EJ-299 plastic scintillator.

[0088] To define the field of view of the dual thermal neutron detector assembly and reduce background interference, the second housing 126 is enclosed and fitted around the outside of the thermal neutron detector 105. The second housing 126 can be designed as a stainless steel housing structure with a top cover. The thermal neutron detector 105 and the ultrathermal neutron detector 106 are fixed together and then fixedly installed within the structure of the second housing 126. Optionally, the second housing 126 can be designed with the same structure as the first housing 116, that is, forming a chamber between the first and second housings to accommodate the two detectors. The thermal neutron detector 105 and the ultrathermal neutron detector 106 are fixed on the first and second housings, respectively. In actual use, the first or second housing is fitted together. When the first or second housing is fitted into the set position, the detection unit of the ultrathermal neutron detector 106 is precisely embedded in the axial through hole 123 of the thermal neutron detector 105. In this embodiment, the thermal neutron detector 105 and the ultrathermal neutron detector 106 do not directly contact each other, but the second housing 126 serves as a support structure for the two detectors to be fixed relative to each other.

[0089] The installation structure of the nested structure formed by two microstructured gas detectors is as follows: the superthermal neutron detector 106 is fixed within the axial through-hole 123 of the first microstructured gas detector, and includes a second microstructured gas detector and a third shielding and slowing layer. The third shielding and slowing layer covers all the outer wall surfaces of the second microstructured gas detector, and the structure and dimensions of the second microstructured gas detector covered with the third shielding and slowing layer are adapted to the axial through-hole 123; the two microstructured gas detectors are installed within the second housing 126 using a method similar to... Figure 3 The nested structure shown is installed and fixed in the same way. Optionally, in this embodiment, the second microstructure gas detector is set as a cylindrical structure. The outer diameter of the cylindrical structure after being covered with the second shielding and moderating layer is adapted to the inner diameter of the axial through hole 123, ensuring that the superthermal neutron detector 106 can be fixed in the axial through hole 123.

[0090] Define the direction of the upward-pointing cathode drift electrode 121 of the first microstructure gas detector as upward and the direction of the anode readout electrode 122 as downward. Then, the second microstructure gas detector includes a cylindrical cavity structure, a second cathode drift electrode that closes the upper end face of the cylindrical cavity structure, and a second anode readout electrode that closes the lower end face of the cylindrical cavity structure. The cylindrical cavity structure is filled with He gas.

[0091] As an optional implementation, the first, second, and third shielding and slowing layers in the above embodiments have the same structure, each including a neutron shielding layer 113 and a slowing layer 114 disposed inside the neutron shielding layer 113; for example, Figure 2The moderating layer 114 covers all areas of the outer wall surface of the first scintillation crystal 111. Figure 3 A moderated layer 114 covers all the outer surfaces of the third scintillation crystal 124, and a neutron shielding layer 113 covers the outer surface of the moderated layer 114. The moderated layer 114 is a polyethylene moderated layer or a paraffin moderated layer, used to moderate hyperthermal neutrons into thermal neutrons. Specifically, the neutron shielding layer 113 covers all the outer surfaces of the moderated layer 114. In this embodiment, all neutron shielding layers 113 are cadmium layers with a thickness of 0.2~0.8mm, and the plating is achieved by electroplating. All moderated layers 114 have a thickness of 1~10mm and are paraffin moderated layers. Essentially, the thickness of the neutron shielding layer 113 needs to be sufficient to block all thermal neutrons, and the thickness of the moderated layer 114 needs to be sufficient to moderate all hyperthermal neutrons into thermal neutrons.

[0092] In the above two nested dual thermal neutron detector assembly implementation schemes, the outer thermal neutron detector is configured as an annular cavity structure with an axial through-hole 123, and the ultrathermal neutron detector 106 is nested within the axial through-hole 123. Without increasing the radial dimension of the instrument, the axial co-position functional integration of the thermal neutron detector 105 and the ultrathermal neutron detector 106 is achieved. The nested structure fundamentally solves the inherent problem of inconsistent space in traditional separate dual neutron detectors, which not only has a small size but also greatly improves the accuracy of thermal neutron counting and ultrathermal neutron counting at the same position.

[0093] Traditional gamma logging tools require axial separation of two detectors with different source distances during installation, resulting in technical problems such as system complexity, volume redundancy, and source distance inaccuracy under vibration. This application, however... Figure 4 As shown, a dual-probe system with mechanically rigid gamma detectors is used. The dual-probe integrated multi-channel synchronization and high-speed acquisition circuit 109 forms a spatial multiplexing architecture and is packaged in an integrated manner. This solves the problems of volume redundancy and source distance inaccuracy of discrete detectors, effectively reduces redundant cables in the system, and improves the reliability of the detection structure.

[0094] Specifically, such as Figure 4As shown, the gamma detector also includes a third housing 133; the dual-probe assembly includes a near-source probe 107 and a far-source probe 108, which are fixedly disposed at intervals inside the third housing 133 and are both configured as radiation-resistant scintillation crystals connected to a third photoelectric converter 134; a central cavity 131 is formed between the near-source probe 107 and the far-source probe 108 and the inner wall of the third housing 133, and the multi-channel synchronization and high-speed acquisition circuit 109 is integrated within the central cavity 131; a shielding layer 132 is covered on the inner wall of the third housing 133, which is used to shield electromagnetic interference and reduce neutron radiation damage. Optionally, the radiation-resistant scintillation crystal is selected from CsI(Tl) crystal, Cs3Cu2I5(Tl) crystal, GSO:Ce crystal, LYSO:Ce crystal, BGO crystal, PWO crystal, BaF2 crystal, CeF3 crystal, and G-(Gd,La)2Si2O7:Ce³. + Crystals such as Rb2AgBr3:Cu crystal, Cs3Cu2I5(Li / Tl) crystal, LuAG:Ce ceramic crystal, GYAGG ceramic crystal, and GAGG crystal are used. In this embodiment, CsI(Tl) crystal is selected. The third photoelectric converter 134 can be a photomultiplier tube, which is coupled to the radiation-resistant scintillation crystal.

[0095] By forming a spatial multiplexing architecture for the dual-probe assembly and the multi-channel synchronization and high-speed acquisition circuit 109 within the third housing 133, the overall size of the gamma detector is significantly reduced, improving its adaptability. Furthermore, by integrating the dual-probe assembly and the multi-channel synchronization and high-speed acquisition circuit 109 into a single structure within the third housing 133, the near-source distance probe 107 and the far-source distance probe 108 are relatively fixed, preventing microscopic shifts or axial movement in the relative position between the neutron source and the detector caused by vibration and impact during downhole operations, thus effectively improving the detector's measurement accuracy. Consequently, when the gamma detector is installed in the logging tool, the spacing between the near-source distance probe 107 and the far-source distance probe 108 along the logging tool's axial direction within the third housing 133 must meet the minimum source distance difference. In this embodiment, the control communication sub-section 101 and the multi-channel synchronization and high-speed acquisition circuit 109 are integrated on the same circuit board and placed together within the central cavity 131.

[0096] Optionally, the shielding layer 132 used to shield electromagnetic interference and reduce neutron radiation damage is a metal shielding layer. The metal shielding layer not only shields electromagnetic noise and reduces neutron radiation damage, but also provides physical protection for the dual-probe assembly and multi-channel synchronous and high-speed acquisition circuit 109 inside the third housing 133, enhancing the detector's mechanical strength and overall structural stability, and extending the equipment's service life. Optionally, the shielding layer 132 is selected from aluminum shielding layers and copper shielding layers; in this embodiment, an aluminum shielding layer is selected.

[0097] During the assembly of the gamma detector, to avoid source distance misalignment and ensure stable source distance between the near-source distance probe 107 and the far-source distance probe 108, two methods can be used. First, the near-source distance probe 107 and the far-source distance probe 108 can be directly fixed to the inner walls of the third housing 133. Second, they can be indirectly fixed to the third housing 133 using other methods, such as using a fixing bracket to fix the two probes to determine their relative positions. When using a fixing bracket to fix the near-source distance probe 107 and the far-source distance probe 108 inside the third housing 133, a rigid titanium alloy bracket is used, and the source distance error is controlled within the industry's allowable range. Mechanical rigidity ensures that the source distance between the near-source distance probe 107 and the far-source distance probe 108 remains constant, guaranteeing accurate measurement results.

[0098] As an optional implementation, provided that the minimum source distance difference requirement is met between the near-source distance probe 107 and the far-source distance probe 108, the fixed bracket can be configured as a fixed bracket with a movable adjustment part to adapt to different sizes of third housing 133 to form central cavities 131 of different sizes, thereby meeting the requirements of installing multi-channel synchronous and high-speed acquisition circuits 109 of various sizes on logging tools of different sizes. The movable adjustment part can be adjusted in the following way: for example, the structure of the fixed bracket connecting the near-source distance probe 107 is defined as the first end of the fixed bracket, and the structure connecting the far-source distance probe 108 is defined as the second end of the fixed bracket, then the movable adjustment part is used to adjust the distance between the first end and the second end; optionally, the movable adjustment part can be a lead screw and slider mechanism.

[0099] The multi-channel synchronization and high-speed acquisition circuit 109 includes several signal processing channels electrically connected to the ultrashort pulse neutron generator 102, fast neutron detector 103, dual thermal neutron detection assembly, and gamma detector, as well as an analog-to-digital converter and an FPGA processor. The FPGA processor is configured with pulse counting and time spectrum analysis functions based on the master clock. During communication, the input terminal of the analog-to-digital converter is connected to the output terminal of each of the signal processing channels to convert the input signal into a digital signal. The output terminal of the analog-to-digital converter is connected to the FPGA processor, and the output terminal of the FPGA processor is communicatively connected to the control communication sub-section 101 so that the control communication sub-section 101 processes the data and transmits it to the logging computer. The number of signal processing channels is determined based on the design of each detector. For example, when the dual thermal neutron detector assembly is designed as an adjacent structure, at least one signal processing channel is needed to simultaneously obtain thermal neutron signals and ultrathermal neutron signals. When the dual thermal neutron detector assembly is designed as a nested structure, at least two signal processing channels are needed to simultaneously obtain thermal neutron signals and ultrathermal neutron signals, respectively. Gamma detectors require at least two signal processing channels, and any fast neutron detector requires at least one signal processing channel.

[0100] Another embodiment of the present invention proposes a working method for the above-mentioned uranium ore logging tool based on ultrashort pulse neutrons, which specifically includes the following steps:

[0101] Step 1) Lower the logging instrument to the target formation and establish communication between the logging instrument and the logging computer on the ground through the control communication sub 101. The logging computer issues instructions to set the pulse frequency and width of the ultrashort pulse neutron generator 102 and the measurement parameters of each detector.

[0102] Step 2) Control the ultrashort pulse neutron generator 102 to emit a fast neutron pulse toward the formation via the control communication subsection 101, and simultaneously use the fast neutron detector 103 to detect the neutron yield of the fast neutron pulse in real time, and record the fast neutron count N used for normalization of the neutron count. fast ;

[0103] Step 3) Divide the data into several time gates based on the timestamp and collect signals in stages; the time gates include: an inelastic scattering window, through which the inelastic scattering gamma spectrum is collected by the gamma detector; a thermal neutron measurement window, through which the thermal neutron count and ultrathermal neutron count are simultaneously collected by the dual thermal neutron detection assembly; and a captured gamma window, through which the captured gamma spectrum is collected by the gamma detector; specifically, during data collection, each time gate collects data in parallel according to its corresponding time window, such as... Figure 5 As shown.

[0104] Specifically, such as Figure 5As shown, the inelastic scattering window is the early stage from 0 to t1, with t1 ranging from 1 to 5 microseconds; the thermal neutron measurement window is the middle stage from t1 to t2, with t2 ranging from 10 to 20 microseconds; and the captured gamma window is the late stage from t2 to t3, with t3 ranging from 50 to 100 microseconds. That is, the opening time of the inelastic scattering window is synchronized with or slightly delayed by the time the ultrashort pulse neutron generator 102 emits the fast neutron pulse, and its duration covers the main process of the inelastic scattering reaction; the opening time of the ultrathermal neutron measurement window is later than that of the inelastic scattering window to avoid the neutron source background; and the opening time of the captured gamma window is later than after the neutron pulse has completely disappeared.

[0105] Step 4) The multi-channel synchronization and high-speed acquisition circuit 109 is used to synchronize the acquired inelastic scattering gamma spectrum, thermal neutron count and hyperthermal neutron count, gamma spectrum and master clock to generate neutron time decay spectrum and time-gated gamma spectrum; wherein, the neutron time decay spectrum is characterized by the count ratio calculated based on the hyperthermal neutron count and thermal neutron count.

[0106] Step 5) Based on the pre-trained inversion algorithm model, and using the fast neutron count N... fast The parameters of the neutron time decay spectrum and the characteristic element information extracted from the time-gated gamma spectrum are comprehensively inverted to output the uranium content and geological parameters of the target layer. The inversion algorithm model is selected from a multiple linear regression model or a machine learning model, and is pre-trained using historical detection data and uranium content and geological parameter data of the formation as training data. The characteristic element information includes the hydrogen / silicon element count ratio and the chlorine / hydrogen element count ratio, and the geological parameters include porosity and lithology.

[0107] When the dual thermal neutron detector components are in a close-proximity configuration, the calculation process for the count ratio is as follows:

[0108] In the same thermal neutron field, the first scintillation crystal 111 and the second scintillation crystal 112 are calibrated, and the ratio of their thermal neutron detection efficiencies is calculated. This determines the ratio φ1 / φ2 of the thermal neutron detection efficiency of the first scintillation crystal 111 to that of the second scintillation crystal 112, where φ1 represents the thermal neutron detection efficiency of the first scintillation crystal 111 and φ2 represents the thermal neutron detection efficiency of the second scintillation crystal 112. Given that the first shielding and moderation layer provides good thermal neutron shielding and moderation for both thermal and ultrathermal neutrons, the efficiency with which thermal neutrons incident on the first scintillation crystal 111 are detected should be equal to its thermal neutron detection efficiency in the thermal neutron field. Furthermore, the first scintillation crystal 111 and the second scintillation crystal 112 can be calibrated synchronously or asynchronously.

[0109] Based on the spatial structure read out by the common optical path of the detection unit and the multi-channel synchronous and high-speed acquisition circuit 109, pulse signals of thermal neutrons, hyperthermal neutrons, and gamma rays are acquired.

[0110] The pulse waveform discrimination algorithm is used to identify the collected pulse signals of thermal neutrons, hyperthermal neutrons, and gamma rays in real time. The pulse signals of thermal neutrons and hyperthermal neutrons are recorded, and the pulse signals of gamma rays are removed to obtain the time spectra of thermal neutrons and hyperthermal neutrons. The counts of thermal neutrons N2 and hyperthermal neutrons N1 are counted respectively. The pulse waveform discrimination algorithm can effectively distinguish the interference of gamma ray signals during neutron detection by identifying the hyperthermal neutron pulse signals and thermal neutron pulse signals. The pulse waveform discrimination algorithm is preset in the FPGA processor.

[0111] Based on the ratio φ1 / φ2 of the detection efficiency of the first scintillation crystal 111 for ultrathermal neutrons and the detection efficiency of the second scintillation crystal 112 for thermal neutrons, and the statistical ultrathermal neutron count N1 and thermal neutron count N2, the count ratio R of ultrathermal neutrons to thermal neutrons is output, R=n1 / n2=(N1 / φ1) / (N2 / φ2), where n1 represents the ultrathermal neutron flux at the detection location and n2 represents the thermal neutron flux at the detection location; wherein, the ratio between the detection efficiency of the first scintillation crystal 111 for ultrathermal neutrons and the detection efficiency of the second scintillation crystal for thermal neutrons is equal to the ratio of the thermal neutron detection efficiencies between the crystals.

[0112] When the dual thermal neutron detector assembly is a nested structure, the calculation process for the count ratio is as follows:

[0113] In the same thermal neutron field, the thermal neutron detector 105 and the ultrathermal neutron detector 106 without a second or third shielding moderation layer are calibrated, and the ratio R1 of their thermal neutron detection efficiencies is calculated. This leads to the determination of the ratio R2 between the thermal neutron detector 105's thermal neutron detection efficiency and the ultrathermal neutron detector 106's ultrathermal neutron detection efficiency. Since the calibration condition is in the same thermal neutron field, their thermal neutron fluxes are equal, and the ratio of their detected thermal neutron fluxes is equivalent to the ratio of their thermal neutron detection efficiencies. Therefore, under the condition that the second shielding moderation layer provides good thermal neutron shielding and ultrathermal neutron moderation, the efficiency with which the thermal neutrons incident on the third scintillation crystal 124 are detected should theoretically be equal to its thermal neutron detection efficiency in the thermal neutron field, i.e., theoretically R1 = R2.

[0114] Based on the different signal processing channels of the multi-channel synchronization and high-speed acquisition circuit 109, thermal neutron signals and hyperthermal neutron signals are processed respectively, and thermal neutron time spectra and hyperthermal neutron time spectra are acquired.

[0115] Based on the collected thermal neutron time spectrum and ultrathermal neutron time spectrum, the thermal neutron count N2 and ultrathermal neutron count N1 are counted respectively. Among them, when the first microstructure gas detector of the thermal neutron detector 105 performs thermal neutron detection, thermal neutrons in the stratum can freely enter the ³He gas region of the first microstructure gas detector, generate ionized particles through the ³He(n,p)T reaction, and be collected by the anode readout electrode 122. The thermal neutron count N2 is obtained after data acquisition and processing.

[0116] Based on the ratio R2 of the thermal neutron detection efficiency of the thermal neutron detector 105 to the ultrathermal neutron detection efficiency of the ultrathermal neutron detector 106, and the statistical thermal neutron count N2 and ultrathermal neutron count N1, the count ratio R of ultrathermal neutrons to thermal neutrons is output; wherein, the ratio between the thermal neutron detection efficiency of the thermal neutron detector 105 and the ultrathermal neutron detector 106 is equal to the ratio of the thermal neutron detection efficiency of the thermal neutron detector 105 to that of the ultrathermal neutron detector 106 without a second or third shielding moderation layer.

[0117] In summary, the uranium logging tool and its working method based on ultrashort pulse neutrons disclosed in this invention not only ensure the ultra-high accuracy and reliability of logging data through source correction, time resolution technology, and detector structure design, but also achieve superior operational efficiency through information fusion and structural integration, proposing a new development direction for the field of pulse neutron logging.

[0118] The present invention and its embodiments have been described above illustratively. This description is not restrictive and is merely one embodiment of the present invention, and is not actually limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A uranium ore logging tool based on ultrashort pulse neutrons, characterized in that, It includes an ultrashort pulse neutron generator, a shield, a dual thermal neutron detection assembly and a gamma detector arranged sequentially along the axis of the logging tool, as well as a control and communication sub, several fast neutron detectors, and a multi-channel synchronization and high-speed acquisition circuit. The ultrashort pulse neutron generator is electrically connected to the control and communication stub and is used to transmit fast neutron pulses with a pulse width of less than 1 microsecond to the formation. The fast neutron detector is arranged around the periphery of the ultrashort pulse neutron generator to detect and output the source strength monitoring signal of each fast neutron pulse in real time. The shielding body is located between the ultrashort pulse neutron generator and the dual thermal neutron detection assembly, and is used to shield direct radiation from the neutron source; The dual thermal neutron detection component is used to detect thermal neutrons and ultrathermal neutrons, the gamma detector is used to detect gamma rays, and the multi-channel synchronization and high-speed acquisition circuit is used to acquire the detection signals of each detector, and upload the data to the logging computer after synchronously acquiring and associating the neutron time spectrum and gamma energy spectrum based on the timestamp. After receiving the uploaded data, the logging computer uses a pre-trained inversion algorithm model to invert the formation uranium content. The dual thermal neutron detection assembly includes a thermal neutron detector and an ultrathermal neutron detector, which are used to simultaneously detect thermal neutrons formed by ground slowing and transient ultrathermal neutrons generated by uranium-235 fission at spatially consistent measurement points. The dual thermal neutron detection assembly includes a first scintillation crystal, a second scintillation crystal, a first photoelectric converter, and a first housing. Both the first and second scintillation crystals are sensitive to thermal neutrons. A first shielding and slowing layer is disposed on the outer wall of the first scintillation crystal. The first scintillation crystal and the first shielding and slowing layer constitute the ultrathermal neutron detector. The second scintillation crystal constitutes the thermal neutron detector. The ultrathermal neutron detector and the thermal neutron detector are disposed face-to-face and form a closely adjacent structure of the dual thermal neutron detection assembly. The first photoelectric converter is coupled to the end face of the second scintillation crystal away from the superthermal neutron detector, and the first scintillation crystal, the second scintillation crystal and the first photoelectric converter form a detection part with a common optical path along the same axis; the first housing is fixed to the outside of the detection part, and the detection part is supported as an integral component.

2. The uranium ore logging tool based on ultrashort pulse neutrons according to claim 1, characterized in that, The dual thermal neutron detection assembly includes a thermal neutron detector, an ultrathermal neutron detector, and a second housing, wherein the thermal neutron detector and the ultrathermal neutron detector are disposed within the second housing; The thermal neutron detector has a through hole in the middle, and the detection unit of the ultrathermal neutron detector is embedded in the through hole to form the nested structure of the dual thermal neutron detection assembly.

3. The uranium ore logging instrument based on ultrashort pulse neutrons according to claim 2, characterized in that, The thermal neutron detector is configured as a first microstructure gas detector, which includes an annular chamber structure with an axial through hole, and the annular chamber structure is filled with ³He gas; a cathode drift electrode and an anode readout electrode are respectively provided at both ends of the annular chamber structure along its axial direction, and the cathode drift electrode and the anode readout electrode are respectively connected to the internal chamber of the annular chamber structure; The superthermal neutron detector includes a third scintillation crystal, a second photoelectric converter, and a second shielding moderation layer. The third scintillation crystal is a crystal sensitive to thermal neutrons. The second shielding moderation layer covers all the outer surfaces of the third scintillation crystal, forming a detection unit embedded in the axial through-hole of the first microstructure gas detector. The second photoelectric converter is coupled to the end face of the outer wall of the detection unit perpendicular to the axial direction of the first microstructure gas detector.

4. The uranium ore logging tool based on ultrashort pulse neutrons according to claim 3, characterized in that, The superthermal neutron detector is fixed in the axial through hole of the first microstructure gas detector and includes a second microstructure gas detector and a third shielding and slowing layer. The third shielding and slowing layer is disposed on all the outer wall surfaces of the second microstructure gas detector, and the structure and size of the second microstructure gas detector covered with the third shielding and slowing layer are adapted to the axial through hole.

5. The uranium ore logging tool based on ultrashort pulse neutrons according to claim 1, characterized in that, The gamma detector includes a third housing, a near-source probe and a far-source probe disposed within the third housing, for detecting inelastic scattered gamma rays and captured gamma rays emitted by elements in the formation. The near-source probe and the far-source probe are fixedly disposed at intervals inside the third housing, and both are configured as radiation-resistant scintillation crystals connected to the third photoelectric converter; a central cavity is formed between the near-source probe and the far-source probe, and on the inner wall of the third housing, and the multi-channel synchronous and high-speed acquisition circuit is integrated within the central cavity; a shielding layer is covered on the inner wall of the third housing, which is used to shield electromagnetic interference and reduce neutron radiation damage.

6. The uranium ore logging tool based on ultrashort pulse neutrons according to claim 1, characterized in that, The multi-channel synchronization and high-speed acquisition circuit includes several signal processing channels electrically connected to the ultrashort pulse neutron generator, fast neutron detector, dual thermal neutron detection assembly and gamma detector, as well as an analog-to-digital converter and an FPGA processor. The FPGA processor is configured with a pulse counting module and a time spectrum analysis module based on the master clock. The input terminal of the analog-to-digital converter is connected to the output terminal of each of the signal processing channels, and is used to convert the input signal into a digital signal; the output terminal of the analog-to-digital converter is connected to the FPGA processor, and the output terminal of the FPGA processor is communicatively connected to the control communication section, so that the control communication section can process the data and transmit it to the logging computer.

7. A method for operating a uranium ore logging instrument based on ultrashort pulse neutrons as described in claim 1 or 4, characterized in that, Includes the following steps: Step 1) Lower the logging instrument to the target formation and establish communication between the logging instrument and the logging computer on the ground through the control communication sub. The logging computer issues instructions to set the pulse frequency and width of the ultrashort pulse neutron generator and the measurement parameters of each detector. Step 2) Control the ultrashort pulse neutron generator to emit a fast neutron pulse toward the formation via the control communication sub-section, and simultaneously use the fast neutron detector to detect the neutron yield of the fast neutron pulse in real time, recording the fast neutron count N used for normalization of the neutron count. fast ; Step 3) Divide the time series into several time gates based on timestamps and collect signals in stages; Several of the time gates include: an inelastic scattering window, through which the inelastic scattering gamma spectrum is acquired by the gamma detector; a thermal neutron measurement window, through which the thermal neutron count and ultrathermal neutron count are simultaneously acquired by the dual thermal neutron detection assembly; and a captured gamma window, through which the captured gamma spectrum is acquired by the gamma detector. Step 4) Using the multi-channel synchronization and high-speed acquisition circuit, the acquired inelastic scattering gamma spectrum, thermal neutron count and hyperthermal neutron count, gamma spectrum and master clock are synchronized to generate neutron time decay spectrum and time-gated gamma spectrum; wherein, the neutron time decay spectrum is characterized by the count ratio calculated based on the hyperthermal neutron count and thermal neutron count. Step 5) Based on the pre-trained inversion algorithm model, and using the fast neutron count N... fast The parameters of the neutron time decay spectrum and the characteristic element information extracted from the time-gated gamma spectrum are comprehensively inverted to output the uranium content and geological parameters of the target layer; wherein, the inversion algorithm model is selected from a multiple linear regression model or a machine learning model, the characteristic element information includes the hydrogen / silicon element count ratio and the chlorine / hydrogen element count ratio, and the geological parameters include porosity and lithology.

8. The working method of the uranium ore logging tool based on ultrashort pulse neutrons according to claim 7, characterized in that, When the dual thermal neutron detector components are in a close-proximity configuration, the calculation process for the count ratio is as follows: In the same thermal neutron field, the first scintillation crystal and the second scintillation crystal are calibrated, the ratio of thermal neutron detection efficiency between the crystals is calculated, and then the ratio of the first scintillation crystal's efficiency for ultrathermal neutron detection and the second scintillation crystal's efficiency for thermal neutron detection is determined. Based on the spatial structure read out by the common optical path of the detector and the multi-channel synchronous and high-speed acquisition circuit, pulse signals of thermal neutrons, hyperthermal neutrons and gamma rays are acquired. Based on the pulse waveform discrimination algorithm, the collected pulse signals of thermal neutrons, hyperthermal neutrons and gamma rays are identified in real time. The pulse signals of thermal neutrons and hyperthermal neutrons are recorded, and the pulse signals of gamma rays are removed to obtain the time spectrum of thermal neutrons and the time spectrum of hyperthermal neutrons. The counts of thermal neutrons and hyperthermal neutrons are counted respectively. Based on the ratio of the detection efficiency of the first scintillation crystal for ultrathermal neutrons to the detection efficiency of the second scintillation crystal for thermal neutrons, and the statistical ultrathermal neutron count and thermal neutron count, the count ratio of ultrathermal neutrons to thermal neutrons is output; wherein, the ratio between the detection efficiency of the first scintillation crystal for ultrathermal neutrons and the detection efficiency of the second scintillation crystal for thermal neutrons is equal to the ratio of the thermal neutron detection efficiency between the crystals. When the dual thermal neutron detector assembly is a nested structure, the calculation process for the count ratio is as follows: In the same thermal neutron field, the thermal neutron detector and the ultrathermal neutron detector without a second or third shielding moderation layer are calibrated, and the ratio of their thermal neutron detection efficiencies is calculated to determine the ratio of the thermal neutron detector's thermal neutron detection efficiency to the ultrathermal neutron detector's ultrathermal neutron detection efficiency. Based on the different signal processing channels of the multi-channel synchronization and high-speed acquisition circuit, thermal neutron signals and hyperthermal neutron signals are processed respectively, and thermal neutron time spectra and hyperthermal neutron time spectra are acquired. Based on the collected thermal neutron time spectrum and ultrathermal neutron time spectrum, the thermal neutron count and ultrathermal neutron count are counted respectively. Based on the ratio of the thermal neutron detector's thermal neutron detection efficiency to the ultrathermal neutron detector's ultrathermal neutron detection efficiency, and the statistical counts of thermal and ultrathermal neutrons, the count ratio of ultrathermal neutrons to thermal neutrons is output; wherein, the ratio between the thermal neutron detector's thermal neutron detection efficiency and the ultrathermal neutron detector's ultrathermal neutron detection efficiency is equal to the ratio of the thermal neutron detection efficiency of the thermal neutron detector and the ultrathermal neutron detector without a second or third shielding moderation layer.

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