One-dimensional time-coded laser neutron source imaging device and source size measurement method

Abstract

The application discloses a one-dimensional time coding laser neutron source imaging device and a source size measurement method, and the device comprises a laser neutron source, a time sequence signal encoder and a photoelectric detector; the laser neutron source is used for emitting neutrons; the time sequence signal encoder comprises a neutron visible light converter, an optical fiber array and an optical fiber combiner; the neutron visible light converter is used for converting the neutrons penetrating through a target object into visible light; the optical fiber array comprises a plurality of optical fibers fixed at ends, and the plurality of optical fibers are of different lengths, so that the light signals of different spatial coordinates converted by the neutron visible light converter are converted to different time coordinates; and the optical fiber combiner is used for combining the light signals converted to the different time coordinates to form a one-dimensional time sequence signal and output the one-dimensional time sequence signal to the photoelectric detector. The application aims to realize compact and radiation anti-interference neutron imaging, improve the anti-interference performance of laser neutron source imaging, and reduce the cost of laser neutron source imaging and nondestructive testing.

Description

Technical Field

[0001] This invention belongs to the field of neutron radiographic nondestructive testing technology, specifically relating to a one-dimensional time-coded laser neutron source imaging device and a source size measurement method. Background Technology

[0002] Neutron radiography, as a non-destructive testing technique, has wide applications in multiple disciplines. Traditional neutron sources include nuclear reactor neutron sources, radioisotope neutron sources, accelerator neutron sources, and neutron tube neutron sources, whose imaging flux rates are typically below 10. 8 / (cm 2 The next-generation spallation neutron source has pulsed high fluence rates (up to 10⁻⁶ s⁻¹). 17 / (cm 2With the characteristics of short pulse widths (on the order of tens to hundreds of picoseconds) and short pulse widths (on the order of hundreds of nanoseconds), and with the advancement of chirped pulse laser amplification technology, ultrashort and ultra-intense laser-driven neutron sources have become an emerging solution. These laser-driven neutron sources, due to their short pulse widths (on the order of tens to hundreds of picoseconds) and micro-focus characteristics, possess high flux rates and excellent temporal resolution, and are expected to supplement the shortcomings of traditional sources. Existing neutron radiography systems typically employ a recording scheme of "laser neutron source - object under test - scintillator - optical system - area array camera." That is, the neutron beam first passes through the object under test to form a spatial intensity distribution. The neutron beam carrying object information then irradiates the scintillator, converting the neutron signal into a visible light signal. Finally, the visible light signal is relayed by the optical system (usually composed of fiber arrays or imaging lenses) to the recording surface of the area array camera. By capturing the intensity distribution information of the visible light, information such as the material, thickness, and morphology of the object under test can be deduced. However, in the application scenarios of laser-driven neutron sources, traditional imaging methods suffer from the following technical bottlenecks: First, there is strong electromagnetic interference at the experimental site. Irradiating a target sphere with an extremely powerful laser generates intense electromagnetic pulses and radiation interference. These high-energy electromagnetic pulses can severely interfere with or even cause the camera to "crash," resulting in data loss and equipment damage. Although electromagnetic shielding can be applied to the camera, because the camera uses an imaging lens or a short fiber optic array for light reception, it remains close to the target chamber, and electromagnetic interference remains severe. Secondly, the optical path layout of traditional imaging methods is limited. Traditional imaging systems often rely on straight optical paths or deflection by a single mirror to guide light, and shielding is usually added to the deflected area. This optical path layout is difficult to arrange flexibly in a limited space. The limited internal space of a large laser target chamber, coupled with the presence of numerous diagnostic devices externally, makes the installation location of neutron imaging equipment extremely narrow, making traditional direct-light or simple reflection schemes difficult to implement. Finally, traditional imaging schemes are often extremely expensive. Considering the limited neutron yield of laser neutron sources and the limited luminous efficiency of scintillators, in order to obtain a sufficient signal-to-noise ratio, traditional optical systems need to use large-aperture, high-performance lenses with very low F-numbers to increase light collection or use arrays of optical fibers composed of a large number of optical fibers for optical signal transmission. For area array cameras, high-sensitivity cameras or image intensifiers with high quantum efficiency are often used, which greatly increases the cost of the system. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a one-dimensional time-coded laser neutron source imaging device and a source size measurement method to address the above-mentioned problems in the prior art. The present invention aims to achieve compact, radiation-resistant neutron imaging, improve the anti-interference performance of laser neutron source imaging, and reduce the cost of laser neutron source imaging and non-destructive testing.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A one-dimensional time-coded laser neutron source imaging device includes a laser neutron source, a time-series signal encoder, and a photodetector. The laser neutron source is used to emit neutrons towards a target object. The time-series signal encoder includes a neutron-visible light converter, an optical fiber array, and an optical fiber combiner. The neutron-visible light converter is used to convert neutrons transmitted through the target object into visible light. The optical fiber array includes multiple optical fibers with their collection ends fixed in an array shape. The multiple optical fibers are of unequal length to convert optical signals converted by the neutron-visible light converter at different spatial coordinates to different time coordinates. The optical fiber combiner is used to combine the optical signals converted to different time coordinates to form a one-dimensional time-series signal, which is then converted into an electrical signal output by a single-pixel photodetector.

[0005] Optionally, the different time coordinates are t0, t0+Δt, ..., t0+(n-1)Δt, where t0 is the time coordinate of the first optical fiber, Δt is the time required for the optical signal to propagate in an optical fiber of length L0, n is the number of optical fibers in the fiber array, L0 is the length difference between the optical fibers in the fiber array, and the lengths of the optical fibers in the fiber array are L... g ,L g +L0,…,L g +(n-1)L0,L g This is the length of the first optical fiber.

[0006] Optionally, the laser neutron source, the neutron visible light converter, and the collecting ends of each optical fiber in the fiber array are arranged inside the shielded target chamber. Each optical fiber passes through the optical fiber guiding window on the outer wall of the shielded target chamber and is connected to the optical fiber combiner. The optical fiber combiner and the photodetector are arranged outside the shielded target chamber.

[0007] Optionally, the neutron visible light converter is a scintillator, which is a single scintillator or multiple scintillators located at the light input end of each optical fiber in the optical fiber array.

[0008] Optionally, the constant parameter M between the decay time constant τ of the scintillator and the length difference L0 of the optical fibers in the fiber array satisfies a preset range [M]. min M max To ensure that optical signals received by the fiber optic combiner at different time coordinates do not alias, where M min and M max These are the preset minimum and maximum values ​​of the constant parameter M, respectively. The functional expression of the constant parameter M is: ; Where n0 is the refractive index of the optical fiber for the scintillator's emission band, c is the speed of light in vacuum, and τ is the decay time constant of the scintillator.

[0009] Optionally, the collecting ends of each optical fiber in the optical fiber array are evenly arranged on the same straight line.

[0010] Optionally, the neutron-visible light converter is in direct contact with the collecting end of each fiber in the fiber array; or a distance L is provided between the neutron-visible light converter and the collecting end of each fiber in the fiber array, and a fiber collimator is provided at the collecting end of each fiber in the fiber array, thereby improving the spatial resolution of neutron imaging in the one-dimensional time-coded laser neutron source imaging device. for ,in denoted as the numerical aperture of the optical fiber.

[0011] Optionally, the output of the photodetector is connected to an oscilloscope or a computing terminal for non-destructive testing.

[0012] Furthermore, the present invention also provides a source dimension measurement method, comprising the following steps: S101, the knife edge is used as the target object of the one-dimensional time-coded laser neutron source imaging device and placed between the laser neutron source and the neutron visible light converter of the one-dimensional time-coded laser neutron source imaging device. S102, neutrons are emitted towards the target object through a laser neutron source, and the one-dimensional time-series signal output by the photodetector when neutrons are emitted towards the target object through the laser neutron source is obtained as the imaging result of the knife edge; S103, an edge expansion function is generated by fitting the transition region from dark to light in the imaging result of the knife edge; S104, Differentiate the edge spread function to extract the full width at half maximum (FWHM) of the edge spread function; S105, the size of the laser neutron source is obtained by dividing the full width at half maximum (FWHM) of the edge spread function by the magnification of the one-dimensional time-coded laser neutron source imaging device; the magnification of the one-dimensional time-coded laser neutron source imaging device is the ratio of the distance between the blade edge and the neutron visible light converter to the distance between the blade edge and the laser neutron source.

[0013] Compared with existing technologies, the present invention mainly achieves the following beneficial effects: The device of the present invention includes a laser neutron source, a time-series signal encoder, and a photodetector. The laser neutron source is used to emit neutrons. The time-series signal encoder includes a neutron-visible light converter, an optical fiber array, and an optical fiber combiner. The neutron-visible light converter is used to convert neutrons that have passed through a target object into visible light. The optical fiber array includes multiple optical fibers fixed at both ends. The multiple optical fibers are of unequal length to convert the light signals converted by the neutron-visible light converter to different time coordinates. The optical fiber combiner is used to combine the light signals converted to different time coordinates to form a one-dimensional time-series signal and output it to the photodetector. The present invention can realize compact, radiation-resistant neutron imaging, improve the anti-interference performance of laser neutron source imaging, and reduce the cost of laser neutron source imaging and non-destructive testing. The present invention is particularly suitable for high-precision and high-reliability application scenarios such as non-destructive structural integrity verification of various equipment. It can realize a compact, radiation-resistant neutron imaging solution, and is particularly suitable for large scientific device application scenarios in space-constrained and complex electromagnetic environments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a one-dimensional time-coded laser neutron source imaging device in an embodiment of the present invention.

[0015] Figure 2 The following are various arrangements of the time series signal encoder in the embodiments of the present invention, wherein (a) the neutron visible light converter 21 adopts multiple scintillators and is arranged with gaps between them and the end face of the optical fiber input side, (b) the neutron visible light converter 21 adopts multiple scintillators and is arranged with gaps between them and the end face of the optical fiber input side, (c) the neutron visible light converter 21 adopts a single scintillator and is arranged in close contact with the end face of the optical fiber input side, and (d) the neutron visible light converter 21 adopts a single scintillator and is arranged in close contact with the end face of the optical fiber input side.

[0016] Figure 3 This is a schematic diagram of the spatial resolution of neutron imaging in a one-dimensional time-coded laser neutron source imaging device according to an embodiment of the present invention.

[0017] Figure 4 The figures are neutron-excited fluorescence curves in the embodiments of the present invention, wherein (a) is the theoretical neutron-excited fluorescence curve and (b) is the measured neutron-excited fluorescence curve.

[0018] Figure 5 The waveform of the Gaussian pulsed neutron source with a full width at half maximum (FWHM) of 100 picoseconds is shown in this embodiment of the invention.

[0019] Figure 6 For the purposes of this embodiment of the invention Figure 4The results of the theoretical neutron-excited fluorescence curve convolution experiment are shown in (a), where (a) is the neutron-excited fluorescence curve after convolution, and (b) is a magnified view of the neutron-excited fluorescence curve before and after convolution at the rising edge of the curve.

[0020] Figure 7 This is a schematic diagram of the laser neutron source imaging principle of a wedge-shaped target object in an embodiment of the present invention.

[0021] Figure 8 This is a diagram showing the optical signal intensity output by the fiber optic combiner 23 in this embodiment of the invention.

[0022] Figure 9 This is a peak intensity information diagram of different channels of the wedge-shaped target object in an embodiment of the present invention.

[0023] Figure 10 The convolution kernel of the photodetector 3 and the detected electrical signal are shown in the embodiment of the present invention, where (a) is the convolution kernel of the photodetector 3 and (b) is the electrical signal after passing through the photodetector 3.

[0024] Figure 11 The images show the convolution kernel and the electrical signal after passing through a photodetector after being acquired by an oscilloscope 4 with a bandwidth of 1 GHz in this embodiment of the invention, where (a) is the convolution kernel and (b) is the electrical signal acquired by the oscilloscope 4.

[0025] Figure 12 This is a comparison chart of the neutron attenuation coefficient derived from the oscilloscope signal and the original attenuation coefficient of the wedge-shaped target object in an embodiment of the present invention.

[0026] Figure 13 This is a schematic diagram illustrating the principle of laser neutron source size measurement using the knife-edge method in this embodiment of the invention.

[0027] Figure 14 This is a schematic diagram of the fiber array structure used for measuring the size of a laser neutron source in an embodiment of the present invention.

[0028] Figure 15 These are the recorded points in the imaging results when fitting the edge expansion function in this embodiment of the invention.

[0029] Figure 16 This is a schematic diagram of the edge diffusion function obtained by fitting and the original curve in an embodiment of the present invention.

[0030] Legend: 1. Laser neutron source; 2. Time series signal encoder; 21. Neutron-visible light converter; 22. Fiber array; 23. Fiber combiner; 3. Photodetector; 4. Oscilloscope. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0032] like Figure 1 As shown, the one-dimensional time-coded laser neutron source imaging device in this embodiment includes a laser neutron source 1, a time-series signal encoder 2, and a photodetector 3. The laser neutron source 1 is used to emit neutrons towards the target object. The time-series signal encoder 2 includes a neutron-visible light converter 21, an optical fiber array 22, and an optical fiber combiner 23. The neutron-visible light converter 21 is used to convert the neutrons that have passed through the target object into visible light. The optical fiber array 22 includes multiple optical fibers with their collection ends fixed in an array shape. The multiple optical fibers are of unequal length to convert the light signals with different spatial coordinates after conversion by the neutron-visible light converter 21 to different time coordinates. The optical fiber combiner 23 is used to combine the light signals converted to different time coordinates to form a one-dimensional time-series signal, which is then converted into an electrical signal output by the single-pixel photodetector 3.

[0033] The time-series signal encoder 2 is used to convert optical signals encoded at different spatial coordinates to optical signals encoded at different time coordinates, and to encode the converted optical signals at different time coordinates into a one-dimensional time-series signal. As an optional implementation, in this embodiment, the different time coordinates are t0, t0+Δt, ..., t0+(n-1)Δt, where t0 is the time coordinate of the first optical fiber, Δt is the time required for the optical signal to transmit in an optical fiber of length L0, n is the number of optical fibers in the fiber array 22, L0 is the length difference between the optical fibers in the fiber array 22, and the lengths of the optical fibers in the fiber array 22 are L... g ,L g +L0,…,L g +(n-1)L0,L g Let L be the length of the first optical fiber. After the neutron passes through the neutron-visible light converter 21, the neutron is converted into a visible light signal, which enters the fiber array 22 for visible light time encoding. The fiber array 22 consists of a series of optical fibers of unequal length, with a length difference of L0 between the fibers. The system has N fiber collecting ends, which are placed at spatial coordinates (x1, y1, z1), (x2, y2, z2), ..., (x... n ,y n ,z n The corresponding fiber lengths are L. g , L g +L0, ...,L g+(n-1)L0, and then these optical fibers of different lengths are coupled into the optical fiber combiner 23. After passing through the time sequence signal encoder 2, different spatial coordinates (x1,y1,z1), (x2,y2,z2), ..., (x n ,y n ,z n The neutron beam signal is encoded and converted to different time coordinates, namely t0, t0+Δt, ...t0+(n-1)Δt, where Δt is the time required for the optical signal to propagate in an optical fiber of length L0. ; Where n0 is the refractive index of the optical fiber for the scintillator emission band, and c is the speed of light in a vacuum.

[0034] In this embodiment, the laser neutron source 1, the neutron-visible light converter, and the collecting ends of each optical fiber in the fiber array 22 are arranged inside the shielded target chamber. Each optical fiber passes through an optical fiber guiding window on the outer wall of the shielded target chamber and is connected to an optical fiber combiner 23. The optical fiber combiner 23 and the photodetector 3 are arranged outside the shielded target chamber. When using the shielded target chamber for shielding, this embodiment only requires a very small optical fiber guiding window on the shielded target chamber, which can further avoid electromagnetic radiation interference.

[0035] In this embodiment, the neutron-visible light converter 21 is a scintillator, which is a single scintillator located at the light-incident end of each fiber in the fiber array 22, such as... Figure 2 As shown in (b) and (d) above, or the scintillators are multiple scintillators located at the input ends of each fiber in the fiber array 22, such as... Figure 2 As shown in (a) and (c), for some large target objects, the price of a whole scintillator is extremely high, and the cost of using a small scintillator coupled to the optical fiber input end is much lower.

[0036] For the time-series signal encoder 2, in order to ensure that the optical signals collected from different fiber collecting ends do not overlap at the fiber combiner 23, the attenuation time constant τ of the scintillator and the length difference L0 between the fibers must satisfy a certain relationship. Specifically, in this embodiment, the constant parameter M between the attenuation time constant τ of the scintillator and the length difference L0 between the fibers in the fiber array 22 satisfies a preset range [M]. min M max To ensure that optical signals received by the fiber combiner 23 at different time coordinates do not alias, where M min and M max Let M be the preset minimum and maximum values ​​of the constant parameter M, respectively. The function expression for the constant parameter M is: ; Where n0 is the refractive index of the optical fiber for the scintillator's emission band, c is the speed of light in vacuum, and τ is the decay time constant of the scintillator. The constant parameter M is an empirical constant that needs to be set according to the actual situation; generally, it should be set to 10 > M > 2, i.e., M min and M max The values ​​are 2 and 10 respectively. This is to ensure that the optical signals from different fiber optic collection channels are sufficiently separated in time to avoid crosstalk. A larger constant parameter M ensures greater independence of the optical signals from different fiber optic collection channels, but an excessively large M will make the fiber optic collection system too bulky. Taking the typical fast-response scintillator EJ-232 for neutron detection as an example, when the scintillator thickness is 1 mm, existing literature measures the scintillator's emission rise time to be less than 30 picoseconds, while the photoexcitation fluorescence decay constant is 0.6 nanoseconds. Experimental measurements show that the decay time constant when the scintillator is excited by short-pulse neutrons (pulse width approximately 100-200 picoseconds) is approximately 1.2 nanoseconds, with the shortest reaching 1.055 nanoseconds. The theoretical neutron-excited fluorescence curve was simulated, as shown below. Figure 4 As shown in (a) of the simulation, the rise time parameter was set to 30 picoseconds, while the decay time constant τ was set to 1 nanosecond. Figure 4 Figure (b) shows the measured neutron-excited fluorescence curve. It can be seen that the simulated theoretical neutron-excited fluorescence curve is comparable to the measured one, but the theoretical curve has a longer tail, while the measured curve returns to background intensity after approximately 700 picoseconds. Since laser neutron sources often have pulse widths on the order of hundreds of picoseconds, the pulse width of the neutron source will broaden the instantaneous neutron-excited fluorescence curve through convolution. Considering a neutron source with a half-width of 100 picoseconds, its temporal behavior is as follows... Figure 5 As shown, its full width at half maximum (FWHM) is 100 picoseconds. FWHM describes the width of the pulse duration; the smaller the value, the shorter and more concentrated the pulse. Figure 6 To Figure 4 The results of the theoretical neutron-excited fluorescence curve convolution experiment are shown in (a), where (a) is the neutron-excited fluorescence curve after convolution, and (b) is a magnified view of the neutron-excited fluorescence curve before and after convolution at the rising edge of the curve. Curve c is... Figure 4 The instantaneous neutron-excited fluorescence curve obtained in (a) is shown, and curve d represents the neutron-excited fluorescence curve before and after convolution. (Comparison) Figure 6 As can be seen in (a) and (b), the neutron-excited fluorescence curve is broadened due to the picosecond pulse width of the neutron source. Considering that the optical fiber is a broadband silica multimode fiber with a typical core refractive index of approximately 1.46, when L0 = 1 meter, a time difference of approximately 4.9 nanoseconds will be introduced at the collection ends of different channels. At this point, according to the aforementioned formula... The constant parameter M can be calculated to be 4.9.

[0037] As an optional implementation, the neutron-visible light converter 21 is in direct contact with the collecting ends of each fiber in the fiber array 22, such as... Figure 2 As shown in (c) and (d) in the diagram; when the optical fiber is close to the scintillator, the spatial resolution δ of neutron imaging is equal to the fiber core diameter d. For typical quartz multimode fiber, the core diameter is generally on the order of hundreds of micrometers. Although reducing the fiber core diameter can improve the spatial resolution to tens of micrometers or even shorter, it will also significantly reduce the number of photons. For applications of laser neutron sources, the fiber core diameter should be on the order of hundreds of micrometers, such as a 500-micrometer fiber core diameter. As another optional implementation, a distance L can be provided between the neutron-visible light converter 21 and the collecting end of each fiber in the fiber array 22, and an optical fiber collimator can be provided at the collecting end of each fiber in the fiber array 22, such as... Figure 2 As shown in (a) and (b), fiber optic collimators, depending on their model, can collect visible light signals within a region with a diameter ranging from millimeters to centimeters, increasing the number of photons. This is extremely important for low-neutron-yield laser neutron source applications. However, this comes at the cost of spatial resolution. For a typical fiber optic collimator, such as an aspherical fiber optic collimator from a domestic manufacturer, the typical outer shell diameter is 11 mm, and the input spot diameter is 2.4 mm. For an air-gap double-cemented collimator, the typical outer shell diameter is 24 mm, and the input spot diameter is approximately 8.6 mm. This means that the corresponding spatial resolutions δ are 2.4 mm and 8.6 mm, respectively. It is particularly noteworthy that the reference... Figure 1 and Figure 3 The neutron source imaging experiment results show that the resolution is on the order of millimeters to centimeters. Compared with existing methods, this embodiment does not significantly reduce the imaging resolution.

[0038] When a distance L is provided between the neutron-visible light converter 21 and the collecting ends of each fiber in the fiber array 22, the spatial resolution of neutron imaging is... The range of optical signals collected by the optical fiber is related to the region of the optical signal collected, and at a distance L, the range of optical signals collected by the optical fiber is also related to the numerical aperture NA of the optical fiber, such as... Figure 3 As shown, the spatial resolution of neutron imaging in a one-dimensional time-coded laser neutron source imaging device. for ,in The numerical aperture of the optical fiber is denoted as . As an optional implementation, the collecting end of each optical fiber in the neutron-visible light converter 21 and the optical fiber array 22 is fitted with a protective sleeve to protect the light-gathering performance of each optical fiber in the optical fiber array 22.

[0039] As an optional implementation method, such as Figure 1As shown, the output of the photodetector 3 in this embodiment is connected to an oscilloscope 4. It can also be connected to a host computer or other electrical signal processing terminal used for non-destructive testing. The time-series encoded optical signal is coupled to the photodetector 3 via an optical fiber combiner 23. The photodetector 3 converts these time-encoded optical signals into electrical signals, which are then collected by the oscilloscope 4. By reading the peak intensity information at different times, the neutron beam intensity information at different spatial locations can be obtained. Considering the impact of the bandwidth of photodetector 3 and oscilloscope 4 on the measurement, both bandwidths will broaden the sequential optical pulse signal output by fiber combiner 23 through convolution. For photodetector 3, if a DXM50 photodetector is used, the bandwidth can reach 50GHz, and its typical impulse response function has a full width at half maximum (FWHM) of approximately 11 picoseconds. This has a negligible impact on the optical pulse signal output by fiber combiner 23. If a DET025A photodetector is used, the bandwidth is 2GHz, and its typical impulse response function has a full WHM of approximately 400 picoseconds. That is, photodetector 3 will broaden the sequential optical pulse signal output by fiber combiner 23 through convolution with a Gaussian function with a full WHM of 400 picoseconds. For oscilloscope 4, considering a typical 1GHz oscilloscope, the typical impulse response function has a full WHM of less than 1 nanosecond. Oscilloscope 4 will broaden the sequential optical pulse signal output by fiber combiner 23 through convolution with a Gaussian function with a full WHM of approximately 1 nanosecond.

[0040] The collecting ends of each fiber in the fiber array 22 can be arranged into the desired array shape as needed. For example, as an optional implementation, the collecting ends of each fiber in the fiber array 22 are uniformly arranged on the same straight line. In this embodiment, it is assumed that the number of fiber collecting end channels is 9, the length difference between the fibers is 1 meter, and the object under test is considered to be a wedge-shaped object with non-uniform thickness, and the neutron transmission intensity decreases linearly with spatial position, such as... Figure 7 As shown, assuming the nine fiber optic collection channels are uniformly arranged, the collected optical signal should exhibit linear attenuation. The neutron attenuation coefficients for the spatial positions of the nine fiber optic collection channels are simulated as (0.9, 0.8, 0.7, ..., 0.2, 0.1). The simulated optical signal intensity output by the fiber combiner 23 is as follows: Figure 8 As shown, the peak intensity information of different channels is as follows: Figure 9 As shown, by reading the peak intensity information of the light pulse at different times, the intensity information of the neutron beam at different spatial locations can be deduced.

[0041] In this embodiment, the sequence pulses output by the fiber combiner 23, simulated under the aforementioned experimental setup, pass through a 2GHz bandwidth photodetector 3. The convolution kernel of this pulses, along with the electrical signal after passing through the photodetector 3, is as follows: Figure 10As shown, (a) is the convolution kernel of photodetector 3, and (b) is the electrical signal after passing through photodetector 3. Figure 11 In this embodiment of the invention, the convolution kernel acquired by an oscilloscope 4 with a bandwidth of 1 GHz and the electrical signal after passing through a photodetector are shown, where (a) is the convolution kernel and (b) is the electrical signal acquired by the oscilloscope 4. Based on the electrical signals recorded by the oscilloscope 4, the peak values ​​of each pulse signal are extracted and normalized proportionally. The neutron attenuation coefficient derived from the oscilloscope signal and the original attenuation coefficient can then be plotted. Figure 12 ,from Figure 12 It can be seen that the two match perfectly, and the system can reflect the linear attenuation coefficient of a wedge-shaped object with non-uniform thickness.

[0042] In summary, to effectively address the key issues in traditional laser neutron source imaging, this embodiment employs fiber array 22 with fibers of varying lengths to directly acquire the light signals generated by the scintillator. A single-pixel photodetector 3 is used at the rear end for signal collection, replacing the traditional lens-camera imaging method. This eliminates the need for expensive high-magnification lenses, allowing efficient transmission of scintillating light to a remote detector. As a non-metallic light-guiding medium, optical fiber is naturally immune to electromagnetic interference. This embodiment extends the fiber transmission to a shielded area far from the target chamber, placing the photodetector 3 and other detection units such as the oscilloscope outside of strong electromagnetic radiation, fundamentally avoiding the impact of strong electromagnetic pulses generated by laser target illumination on the imaging device. This embodiment uses a multi-channel fiber + single-pixel photodetector 3 + oscilloscope 4 acquisition method, unlike the traditional area array recording method. By using the non-uniform length fiber array 22 to encode the spatial position signal onto a time signal, only a single-pixel photodetector 3 is needed to detect neutron signals in two-dimensional space. This embodiment proposes a multi-channel fiber optic imaging method, especially suitable for large objects. It eliminates the need for large scintillators; signal acquisition can be achieved simply by placing the fiber optic collection ends of different channels at different locations. For weak signal measurements, the proposed method only requires a single high-sensitivity single-pixel photodetector 3 to replace the traditional high-sensitivity area array camera, significantly reducing costs.

[0043] The one-dimensional time-coded laser neutron source imaging device in this embodiment can be used to achieve non-destructive testing of target objects. The testing process is as follows: the target object is placed between the laser neutron source 1 and the neutron-visible light converter 21; neutrons are emitted from the laser neutron source 1 towards the target object, and the one-dimensional time-series signal output by the photodetector 3 when neutrons are emitted from the laser neutron source 1 towards the target object is acquired as the imaging result of the target object. The imaging result of the target object expresses the neutron transmission intensity at each spatial location on the target object, which can be used to determine whether internal defects exist at each spatial location on the target object. Based on the imaging result of the target object, the required defect judgment method can be adopted as needed. For example, as an optional implementation, the presence of defects at a spatial location can be determined by whether the deviation between the neutron transmission intensity at each spatial location on the target object and its corresponding neutron transmission intensity calibration value exceeds a preset threshold. As another optional implementation, the presence of defects at a spatial location can be determined by whether the statistical values ​​such as the deviation, root mean square, variance, and standard deviation between the neutron transmission intensities at each spatial location on the target object exceed a preset threshold. As another optional implementation, the imaging results of the target object can be used to obtain a pre-trained deep learning model to obtain the non-destructive testing results of the target object. The non-destructive testing results can be the presence or absence of defects, or the type of defects.

[0044] The one-dimensional time-coded laser neutron source imaging device in this embodiment can also complete the size measurement of laser neutron source 1 with an extremely simple experimental configuration. In laser-driven neutron source experiments, the size of the laser neutron source is a key parameter, reflecting the size information of the neutron emission source. The knife-edge method is a traditional method for measuring the size of neutron sources. Similar to neutron radiography, in the knife-edge method, the knife edge (which can be a tungsten block) partially blocks some of the neutrons emitted by the neutron source, thus forming a shadow edge on the detector. By extracting the edge region (i.e., the edge spread function) information of the knife-edge shadow in the detector image, the size information of the neutron source can be analyzed. Therefore, this embodiment also provides a source size measurement method, including the following steps: S101, the knife edge is used as the target object of the one-dimensional time-coded laser neutron source imaging device and placed between the laser neutron source 1 and the neutron visible light converter 21, as shown. Figure 13 As shown; in this embodiment, a 10 cm thick tungsten block is used as the cutting edge; S102, neutrons are emitted towards the target object through the laser neutron source 1, and the one-dimensional time series signal output by the photodetector 3 when neutrons are emitted towards the target object through the laser neutron source 1 is obtained as the imaging result of the knife edge; An ideal, infinitely sharp knife edge, after obtaining the neutron intensity distribution using neutron imaging technology, will exhibit a transition region from dark to light at the boundary between the absence of a knife edge and the projection of the knife edge, due to the size limitation of the neutron source. This transition region, from completely black (neutrons are completely blocked) to completely white (neutrons are completely transmitted), carries the size information of the neutron source. The edge spread function is the mathematical function of the gray-scale change in this transition region, which describes the response of the imaging system to an ideal "step" signal (i.e., the knife edge). S103, an edge expansion function is generated by fitting the transition region from dark to light in the imaging result of the knife edge; S104, Differentiate the edge spread function to extract the full width at half maximum (FWHM) of the edge spread function; S105, the size of the laser neutron source 1 is obtained by dividing the full width at half maximum (FWHM) of the edge spread function by the magnification of the one-dimensional time-coded laser neutron source imaging device; the magnification of the one-dimensional time-coded laser neutron source imaging device is the ratio of the distance L1 between the blade edge and the neutron visible light converter 21 to the distance L2 between the blade edge and the laser neutron source 1, such as... Figure 13 As shown, in this embodiment, the distance L1 between the blade edge and the neutron visible light converter 21 is 135cm, the distance L2 between the blade edge and the laser neutron source 1 is 65cm, and the magnification of the one-dimensional time-coded laser neutron source imaging device is about 2.1 times.

[0045] Since the transition region of the edge spread function is only on the order of millimeters—for example, the measured transition region from dark to light in the existing technology is approximately 8 millimeters—the maximum spacing D between the fibers in the fiber array 22 must be larger than the transition region in order to measure this 8-millimeter transition region. As an optional implementation, such as... Figure 14 As shown, in this embodiment, the collecting ends of each optical fiber in the fiber array 22 are uniformly arranged along the vertical direction of the blade edge to form a one-dimensional fiber array. Here, a design scheme with 7 optical fibers is shown. In fact, the required number can be selected as needed. The maximum spacing D between the optical fibers should be greater than the transition area. In this embodiment, the maximum spacing D between the optical fibers is selected as 9 mm, the fiber end spacing is 1.5 mm, and the optical fiber adopts a typical multimode silica fiber with a core diameter R of 100 micrometers.

[0046] In step S103, when fitting the transition region from dark to light in the imaging result of the knife edge to generate the edge expansion function, this embodiment records the recording points of the transition region from dark to light, such as... Figure 15 As shown, normalized intensity refers to the intensity normalized according to the maximum relative intensity of the edge spread function. The normalized intensity is the relative intensity divided by the maximum relative intensity. In this embodiment, seven discrete recording points were selected ( Figure 15The edge extension function is fitted using a circular annotation. Considering the form of the transition region, and for the case of fitting the edge extension function with a small number of data points, the function expression for fitting the edge extension function for the transition region from dark to light in the imaging result of the knife edge in step S103 of this embodiment is as follows: ; in, For edge expansion function, To normalize the intensity distribution in the imaging results, , and , where are the fitting coefficients, and e is the natural constant. Ultimately, in this embodiment, the model is obtained by fitting data from seven discrete recording points. =1.0059, =1.4656, =-0.0140, Figure 16 This diagram illustrates the fit between the edge diffusion function obtained in this embodiment and the original curve, where the dashed lines represent sampling points and the solid lines represent the fitted edge diffusion function. In this embodiment, the goodness of fit R of the edge diffusion function fitted based on 7 discrete recording points is... 2 The value is 0.9996, which proves the effectiveness of using the source size measurement method of this embodiment to measure the size of the laser neutron source 1.

[0047] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A one-dimensional time-coded laser neutron source imaging device, characterized in that, The system includes a laser neutron source (1), a time-series signal encoder (2), and a photodetector (3). The laser neutron source (1) is used to emit neutrons toward a target object. The time-series signal encoder (2) includes a neutron-visible light converter (21), an optical fiber array (22), and an optical fiber combiner (23). The neutron-visible light converter (21) is used to convert neutrons that have passed through the target object into visible light. The optical fiber array (22) includes multiple optical fibers with their collection ends fixed in an array shape. The multiple optical fibers are of unequal length to convert the light signals with different spatial coordinates after conversion by the neutron-visible light converter (21) to different time coordinates. The optical fiber combiner (23) is used to combine the light signals converted to different time coordinates to form a one-dimensional time-series signal, which is then converted into an electrical signal output by a single-pixel photodetector (3).

2. The one-dimensional time-coded laser neutron source imaging device according to claim 1, characterized in that, The different time coordinates are t0, t0+Δt, ..., t0+(n-1)Δt, where t0 is the time coordinate of the first optical fiber, Δt is the time required for the optical signal to travel through the optical fiber of length L0, n is the number of optical fibers in the fiber array (22), L0 is the length difference of the optical fibers in the fiber array (22), and the lengths of the optical fibers in the fiber array (22) are L... g ,L g +L0,…,L g +(n-1)L0,L g This is the length of the first optical fiber.

3. The one-dimensional time-coded laser neutron source imaging device according to claim 2, characterized in that, The collection ends of each optical fiber in the laser neutron source (1), neutron visible light converter (21) and optical fiber array (22) are arranged in the shielded target chamber. Each optical fiber passes through the optical fiber light guiding window on the outer wall of the shielded target chamber and is connected to the optical fiber combiner (23). The optical fiber combiner (23) and photodetector (3) are arranged outside the shielded target chamber.

4. The one-dimensional time-coded laser neutron source imaging device according to claim 1, characterized in that, The neutron visible light converter (21) is a scintillator, which is a whole scintillator or multiple scintillators located at the light input end of each optical fiber in the optical fiber array (22).

5. The one-dimensional time-coded laser neutron source imaging device according to claim 4, characterized in that, The constant parameter M between the decay time constant τ of the scintillator and the length difference L0 of the optical fibers in the fiber array (22) satisfies the preset range [M]. min M max To ensure that the optical signals received by the fiber combiner (23) at different time coordinates do not alias, where M min and M max These are the preset minimum and maximum values ​​of the constant parameter M, respectively. The functional expression of the constant parameter M is: ； Where n0 is the refractive index of the optical fiber for the scintillator's emission band, c is the speed of light in vacuum, and τ is the decay time constant of the scintillator.

6. The one-dimensional time-coded laser neutron source imaging device according to claim 1, characterized in that, The collecting ends of each optical fiber in the optical fiber array (22) are evenly arranged on the same straight line.

7. The one-dimensional time-coded laser neutron source imaging device according to claim 1, characterized in that, The neutron-visible light converter (21) is in direct contact with the collecting end of each fiber in the fiber array (22); or a distance L is provided between the neutron-visible light converter (21) and the collecting end of each fiber in the fiber array (22), and a fiber collimator is provided at the collecting end of each fiber in the fiber array (22). The spatial resolution of the neutron imaging of the one-dimensional time-coded laser neutron source imaging device is thus achieved. for ,in denoted as the numerical aperture of the optical fiber.

8. The one-dimensional time-coded laser neutron source imaging device according to claim 1, characterized in that, The output terminal of the photodetector (3) is connected to an oscilloscope (4) or an electrical signal processing terminal for non-destructive testing.

9. A source dimension measurement method, characterized in that, Includes the following steps: S101, the knife edge is placed between the laser neutron source (1) and the neutron visible light converter (21) of the one-dimensional time-coded laser neutron source imaging device as the target object of the one-dimensional time-coded laser neutron source imaging device according to any one of claims 1 to 8. S102, neutrons are emitted towards the target object through the laser neutron source (1), and the one-dimensional time series signal output by the photodetector (3) when neutrons are emitted towards the target object through the laser neutron source (1) is obtained as the imaging result of the knife edge; S103, an edge expansion function is generated by fitting the transition region from dark to light in the imaging result of the knife edge; S104, Differentiate the edge spread function to extract the full width at half maximum (FWHM) of the edge spread function; S105, the size of the laser neutron source (1) is obtained by dividing the full width at half maximum (FWHM) of the edge spread function by the magnification of the one-dimensional time-coded laser neutron source imaging device.

10. The source dimension measurement method according to claim 9, characterized in that, The magnification of the one-dimensional time-coded laser neutron source imaging device is the ratio of the distance between the knife edge and the neutron visible light converter (21) to the distance between the knife edge and the laser neutron source (1).

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