CN106855522A - White light neutron imaging method and the material composition lossless detection method using it - Google Patents

Abstract

A white light neutron imaging method, comprising steps: a neutron source emits a pulsed neutron beam and records the emission time; a detector detects the pulsed neutron beam to obtain the position and arrival time of the neutron and transmits it to a processing unit; The energy information of neutrons can be obtained from the arrival time and the recorded emission time, and the two-dimensional neutron flux distribution can be obtained by grouping neutrons according to energy Repeat the above steps to obtain the two-dimensional neutron flux distribution when the sample is placed according to The value of and energy grouping information generate a neutron transmission image with neutron energy information. In addition, a method for non-destructive testing of material composition is proposed. The position information collected at different angles is used to reconstruct three-dimensional space information and combined with energy information to obtain the transmission information of spatial unit grid points. The value is compared with the atomic nucleus database to determine the composition of the material. The invention can accurately determine the composition of materials under non-destructive conditions, and the widest range of measured neutron energy can cover from eV to hundreds of mega eV.

Description

White-light neutron imaging method and non-destructive testing method for material composition using it

technical field

The invention belongs to the field of non-destructive testing, and more specifically relates to a white light neutron imaging method and a material composition non-destructive testing method using the same.

Background technique

Traditional neutron imaging devices usually use accelerator fission neutron sources or reactor neutron sources, and use scintillation screens to receive all incident neutrons, so the imaging process does not distinguish between particle energies, and the resulting images are actually neutrons of various energies. It is difficult to analyze the image in depth, and it is impossible to further analyze the structure and composition of the sample.

In order to solve the above problems, neutron radiography research aimed at determining neutron energy has gradually emerged in recent years. The energy information of neutrons is obtained by using pulsed accelerator neutron sources and time-of-flight measurements, and the images formed after neutrons pass through the sample are further refined, and neutron transmission pictures of different energy segments are obtained respectively; The cross-section of neutrons with different energies is different, and the composition of the material is preliminarily inferred. As shown in Figure 1, elements such as carbon, hydrogen and oxygen have significant resonance absorption structures in the fast neutron region. This technology is generally called fast neutron resonance imaging, and the corresponding neutron energy range is 1-10MeV.

There are two implementation methods in neutron resonance imaging: one method is to use quasi-monoenergetic neutron beams, for example, in 2002, Chen Gongyin et al. of MIT proposed to use D-D reaction to obtain quasi-monoenergetic neutrons distributed according to the angle beam, and image the sample point by point to obtain a series of transmission images of energy points. However, this method needs to measure neutron energies in a wide energy range one by one, which is extremely inefficient and can only reflect fast neutrons with spectral resolution. The value of photos in the field of elemental analysis and security inspection; another method is to sort neutrons or related signals with a wider energy spectrum. The resulting images are sorted. Compared with quasi-monoenergetic neutron beams, this method uses a sorting scheme to improve the utilization efficiency of the beam, shorten the imaging time, and can realize image acquisition of 4-8 fixed energy points; but this scheme is still only for image Time screening does not directly measure a single particle event. Due to the low beam intensity, the flight length of neutrons is correspondingly shortened in this scheme. Therefore, the energy range covered by neutrons intercepted through the time window is still very wide and cannot be analyzed by formants. Obtain material information. In addition, because the scheme is mechanically rotated and collected, its image collection efficiency is low, which does not meet the needs of practical applications.

Contents of the invention

Based on the above problems, the main purpose of the present invention is to propose a white light neutron imaging method and a method for non-destructive testing of material composition to solve at least one of the above technical problems.

In order to achieve the above object, as an aspect of the present invention, the present invention proposes a white light neutron imaging method, comprising the following steps:

Step 11, the pulsed accelerator neutron source emits a pulsed neutron beam with a wide energy spectrum and records the emission time;

Step 12, the detector detects and measures the pulsed neutron beam, obtains the position and arrival time of each neutron, and transmits the position and arrival time of each neutron to the processing unit;

Step 13, the processing unit obtains the energy information of each neutron according to the arrival time of each neutron and the recorded emission time, groups all neutrons by energy, and obtains the neutron flux at different positions according to the neutron position information

Step 14, place the sample between the pulsed accelerator neutron source and the detector, repeat steps 11-13, and obtain the neutron flux at different positions when placing the sample according to A series of continuous neutron transmission images with neutron energy information are generated.

Further, the above-mentioned pulsed accelerator neutron source is a small intense linear accelerator neutron source based on a large spallation neutron source or an accelerated deuterium beam.

Further, the neutron energy provided by the pulsed accelerator neutron source ranges from eV to hundreds of MeV.

Further, the above-mentioned detector is an array detector, which is composed of a neutron probe array, a photoelectric converter and an electronic readout device.

Further, the above-mentioned neutron probe array is formed by a plurality of neutron probes arranged regularly, and the measurement range of the neutron probe array matches the energy range of the pulsed neutron source.

Further, the above-mentioned neutron probe is composed of a scintillator and a conductive optical fiber, the scintillator receives neutrons and generates scintillation light, and the scintillation light is transmitted to the photoelectric converter through the conductive optical fiber.

Preferably, the above-mentioned scintillator is a fast scintillator, which is a capillary liquid scintillator, a plastic scintillator, a boron-containing scintillator or lithium glass.

Further, the above-mentioned neutron probe array receives neutrons within the detection energy range within a single pulse.

Further, the electronic readout device is used to measure the arrival time and position information of all neutrons detected by the neutron probe array in each pulse, and transmit the measured arrival time and position information of all neutrons to the processing unit.

In order to achieve the above object, as another aspect of the present invention, the present invention proposes a non-destructive testing method for material composition, using the above-mentioned white light neutron imaging method, the material sample is placed on a rotating platform, including the following steps:

Step 21. Rotate the sample on the rotating platform, use the white light neutron imaging method to obtain the neutron flux at different positions when the sample is placed at different angles, and obtain a series of continuous neutron transmission images with neutron energy information at different angles ;

Step 22, the processing unit uses a tomographic reconstruction algorithm to obtain the transmission information of the spatial unit grid points according to a series of continuous neutron transmission images with neutron energy information from different angles;

Step 23, the processing unit compares the transmission information of the spatial unit grid points with the full cross-section data of nuclides in the nuclear database to obtain the composition of the material.

Compared with other fast neutron photography methods, the white light neutron imaging method and the nondestructive testing method of material composition proposed by the present invention have the following beneficial effects:

1. The white light neutron imaging method proposed by the present invention has a fast imaging speed, can simultaneously measure neutrons in all energy segments including low energy segments, and has high data accumulation efficiency;

2. The neutron probe array in the white light neutron imaging method of the present invention can measure a single neutron and obtain the position and energy information of all neutrons, and a detailed series of continuous neutron energy information can be obtained through the processing unit. neutron transmission image;

3. The white light neutron imaging method of the present invention is combined with CT technology to form a method for non-destructive testing of material composition. This method can obtain the nuclear characteristics of the sample material, and compare it with the nuclear database to uniquely determine the nuclide composition of the sample. ;

4. When the pulsed neutron source and the neutron flight distance meet high energy resolution, this method can realize the resolution of all nuclides from light to heavy in the sample;

5. The imaging method and nondestructive testing material composition method proposed by the present invention can be used in many fields such as safety inspection, cultural relic archaeology, new energy, and new materials.

Description of drawings

Fig. 1 is the liquid scintillator used in an embodiment of the present invention to the response time curve of fast neutron;

Fig. 2 is the graph of the relationship between the neutron full cross-section and the incident energy of several elements;

Fig. 3 (a) is a schematic diagram of the device used in the white light neutron imaging method proposed by an embodiment of the present invention;

Fig. 3 (b) is the structural diagram of the neutron probe array and the conduction fiber of the detector array in Fig. 3 (a), wherein the probe adopts capillary liquid scintillator;

Fig. 3 (c) is the neutron motion schematic diagram of the device shown in Fig. 3 (a);

Fig. 4 is a graph showing the relationship between the full cross-section and incident neutron energy of the formant structure of ^{93 Nb} _proposed by an embodiment of the present invention;

Fig. 5 is a schematic diagram of the principle of a white light neutron imaging method combined with CT technology to detect material composition proposed by an embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The invention discloses a white light neutron imaging method. The white light neutron refers to a neutron beam that contains a continuous energy spectrum from eV to tens or even hundreds of mega eV and has a pulse time structure. The method includes the following steps:

Step 11, the pulsed accelerator neutron source emits a pulsed neutron beam with a wide energy spectrum and records the emission time;

Step 12, the detector detects and measures the pulsed neutron beam, obtains the position and arrival time of each neutron, and transmits the position and arrival time of each neutron to the processing unit;

Step 13, the processing unit obtains the energy information of each neutron according to the arrival time of each neutron and the recorded emission time, groups all neutrons by energy, and obtains the neutron flux at different positions according to the neutron position information

Step 14, place the sample between the pulsed accelerator neutron source and the detector, repeat steps 11-13, and obtain the neutron flux at different positions when placing the sample according to A series of continuous neutron transmission images with neutron energy information are generated.

The above-mentioned detector is an array detector, which is composed of a neutron probe array, a photoelectric converter and an electronic readout device, wherein the neutron probe array is formed by a plurality of neutron probes arranged regularly, and the measurement range of the neutron probe array is Matches the energy range of pulsed neutron sources.

Preferably, the above-mentioned neutron probe is composed of a scintillator and a conductive optical fiber, the scintillator receives neutrons and generates scintillation light, and the scintillation light is transmitted to the photoelectric converter through the conductive optical fiber.

Preferably, the above-mentioned scintillator is a fast scintillator, which may be a capillary liquid scintillator, a plastic scintillator, a boron-containing scintillator or lithium glass.

The above-mentioned neutron probe array receives neutrons in the measurement energy range in a single pulse, and measures the arrival time and position of the neutrons one by one.

The above-mentioned electronic readout device is used to measure the arrival time and position information of all neutrons detected by the neutron probe array in each pulse, and transmit the measured arrival time and position information of all neutrons to the processing unit.

The above-mentioned pulsed accelerator neutron source is a large-scale spallation neutron source based on a high-power proton accelerator, its pulse repetition frequency is several to tens of Hz, and the energy of the proton beam is above 500 MeV, or it is a small strong-current linear source based on an accelerated deuterium beam. The neutron source of the accelerator has a pulse repetition frequency of several to tens of kHz. Among them, the pulsed neutrons generated by the target are moderately moderated to form neutrons with a wide energy spectrum in the eV-MeV energy range, and then irradiate the sample after beam collimation and a suitable distance.

Among them, different methods can be used to obtain the emission time of neutrons, such as the time when a proton beam or a deuterium beam strikes a target. In some cases, scintillation detectors can also be used to simultaneously detect associated gammas from neutron sources. These associated gammas can completely reflect the emission time of neutrons. They arrive at the detector earlier than neutrons, so it is also possible to use associated gammas The arrival time of Ma inversely deduces the emission time of the neutron beam.

The above-mentioned detectors can use different scintillators to cover the extremely wide energy range of white light neutrons according to the neutron energy range. The detector measures the position and arrival time of the transmitted neutrons, and the neutron position distribution information will be used to provide the sample structure The arrival time is combined with the beam pulse hitting time provided by the pulsed accelerator neutron source (that is, the recorded emission time) to provide the neutron flight time, and the neutron flight time is completely corresponding to the neutron energy , which in turn can provide information on the nuclide composition of the sample. For large spallation neutron sources, the neutron fluence rate is high, and a longer flight distance is required to reduce the instantaneous neutron density on the detector, and a longer flight distance is also beneficial for fast neutrons and low-to-medium energy neutron energies precise measurement. For small neutron sources, the neutron fluence rate is not high, the sample and detector should be placed close to the neutron target, such as 3-10 meters, because the radio frequency linear accelerator is used, the micropulse structure of the deuterium beam can guarantee 1-10MeV The time-of-flight resolution of neutrons is controlled within a few percent, so that the resonance peaks of light nuclides can be resolved.

The reason why the above-mentioned detectors are array detectors is that neutron beams with narrow pulses are used, and the instantaneous fluence rate of neutrons passing through the sample to the detectors is very high, so an array type composed of small detection units with fast time response is required. In order to simultaneously determine the position and time information of each neutron. For the large spallation neutron source, it has a very good time structure, the repetition frequency is tens of Hz, the proton pulse width is tens of ns, and the flight distance is long, so it is relatively easy to realize the time-of-flight detection of a single neutron; while for the small The linear accelerator deuterium neutron source requires special settings for the accelerator, such as using a beam chopper to divide most of the beam in the ms-level long beam pulse into many segments to remove it, so that the beam has several ~ The macro-pulse structure of tens of kHz reduces the intensity of the neutron source, which not only reduces the shielding requirements, is convenient to use, but also facilitates the time-of-flight detection of single neutrons.

The reason why one or two groups of detectors with different scintillators can be used according to the neutron energy range is that there is currently no effective simultaneous measurement of fast neutrons (hundreds of keV to tens of MeV energy ranges) and low- and medium-energy neutron energies. Region (eV-hundred keV energy region) detectors. An effective method for measuring fast neutrons is to use a fast scintillation detector with a short pulse time structure, such as the liquid scintillator EJ-301, as shown in Figure 1, the decay time of the liquid scintillator is generally 3-5 ns, and its The time response of the neutron is less than 100ns, and the time width of the fast component of the signal pulse of the incident neutron is less than 20ns. The pulse signal generated by the incident neutron is measured by the electronic readout device, and the fastest rising edge position of the pulse signal is extracted as the center. The arrival time of the sub, its error range is less than 3ns. The measurement error of neutron energy depends on the time error and the total flight time, that is, time error, neutron energy and flight distance, from which the corresponding energy resolution can be calculated. For a fast neutron of 2.07 MeV flying 76 meters Its energy resolution is 3.2keV, which is sufficient to describe a narrow resonance peak (FWHM=12.3keV) of the C-12 nuclide as shown in Figure 2. Therefore, it is possible to distinguish whether the material contains this nuclide by means of resonance spectroscopy. .

For medium and low energy neutrons, corresponding scintillators (such as boron-10-containing scintillators, lithium glass) can also be used to distinguish the resonance peaks of medium and heavy elements. The resonance peaks of medium and heavy elements are usually in the range of several keV ~ eV level, as shown in Figure 4, the formant structure of ⁹³ N _b , due to the slow flight speed and long total flight time of low- and medium-energy neutrons, its energy resolution will be higher than that of the above-mentioned fast neutron energy region, so it also meets these nuclear requirements. Formant detection requirements for primes.

The above-mentioned neutron transmission image with neutron energy information is a spatial two-dimensional distribution image with continuous energy characteristics. Since the neutron probe has a certain probability to measure the neutrons hitting it, it is necessary to calibrate the neutron detection efficiency curve of the probe in different energy regions during the detector preparation process. Considering the non-uniformity of the neutron beam spot at the sample, the accurate neutron transmission image of the sample material can be obtained by calculating the ratio of the neutron flux at each position in the detector plane after the sample is placed and before it is placed. In the invention, a set of transmission images with energy resolution can be obtained in combination with time-of-flight measurements.

The above-mentioned white light neutron imaging method combined with CT technology can obtain the neutron cross-section information of each spatial grid point of the sample. This information is the atomic nucleus feature of the sample material. By comparing it with the atomic nucleus database, the nuclide composition of the material can be uniquely determined. , so this is a new non-destructive material analysis method.

Based on the above-mentioned white light neutron imaging method, another aspect of the present invention discloses a non-destructive testing method for material composition, the material is located on a rotating platform, comprising the following steps:

Step 21. Rotate the sample on the rotating platform, use the white light neutron imaging method to obtain the neutron flux at different positions when the sample is placed at different angles, and obtain a series of continuous neutron transmission images with neutron energy information at different angles ;

Step 22, the processing unit uses a tomographic reconstruction algorithm to obtain the transmission information of the spatial unit grid points according to a series of continuous neutron transmission images with neutron energy information from different angles;

Step 23, the processing unit compares the transmission information of the spatial unit grid points with the full cross-section data of nuclides in the nuclear database to obtain the composition of the material.

By rotating the sample on the rotating platform, imaging results from different angles can be obtained, and the processing unit can obtain the transmission information of the spatial unit grid points by using the tomographic reconstruction algorithm (the so-called CT technology). In the image analysis, different components are marked with different colors, and compared with the full-section data of nuclides in the nuclear database, the three-dimensional structure of the sample and the composition of material nuclides can be intuitively obtained.

The white light neutron imaging method proposed by the present invention will be described in detail below through specific examples.

Example

As shown in Figures 3(a) to 3(c), this embodiment provides a white light neutron imaging method, the neutrons are emitted by a pulsed accelerator neutron source and transmitted to the detector after passing through the sample, the method includes The following steps:

Step 11, the pulsed accelerator neutron source emits a pulsed neutron beam with a wide energy spectrum and records the emission time;

Step 12, the detector detects and measures the pulsed neutron beam, obtains the position and arrival time of each neutron, and transmits the position and arrival time of each neutron to the processing unit;

Step 13, the processing unit obtains the energy information of each neutron according to the arrival time of each neutron and the recorded emission time, groups all neutrons by energy, and obtains the neutron flux at different positions according to the neutron position information

Step 14, place the sample between the pulsed accelerator neutron source and the detector, repeat steps 11-13, and obtain the neutron flux at different positions when placing the sample according to A series of continuous neutron transmission images with neutron energy information are generated.

The device used in the method proposed in this embodiment is shown in Figure 3 (a), wherein the detector is composed of a neutron probe array, a multi-anode photomultiplier tube (PMT), and an electronic readout device, wherein the neutron probe array is composed of multiple Each neutron probe consists of a scintillator and a conductive fiber. For fast neutrons, the scintillator uses a fiber optic scintillator (the capillary array liquid scintillator is similar), the neutron probes are periodically densely arranged, and the signal of each conducting fiber corresponds to the multi-anode photomultiplier tube behind (such as Hamamatsu H9500) an anode. The structure of the fiber scintillator and the guiding fiber is shown in Fig. 3(b). The fiber scintillator is used to generate scintillation light signals and detect neutron incident events; the guiding fiber adopts high numerical aperture (NA>=0.5) and the same outer diameter The multi-mode optical fiber makes the critical angle of the guiding optical fiber and the optical fiber scintillator basically match, and the two are connected by all-fiber to ensure the effective collection and transmission of signal light. The conductive fiber is coated with a high-Z protective layer (such as lead) to prevent gamma signal crosstalk between scintillators. The fiber optic scintillator is coated with a metal reflective thin layer, such as 5 micron aluminum film, to collect the scintillation light emitted backwards and improve the photon collection efficiency.

For the detection of low and medium energy neutrons, lithium glass is used as the scintillator in the neutron probe array, in which lithium nuclei capture low and medium energy neutrons and then decay and emit charged particles, which excite scintillation light.

If it is necessary to improve the spatial position resolution or a larger sample, the number of probe array units can be increased, and multiple photomultiplier devices can be used for parallel processing.

As shown in Figure 3(c), the neutron source of the pulsed accelerator emits a pulsed neutron beam. The neutrons are collimated by the collimator and irradiate the sample. The neutrons transmitted through the sample are detected by the neutron probe array. After the probe array detects neutrons, a scintillation light signal is generated. The scintillation light signal is transmitted through the light guide to a photoelectric converter (such as a photomultiplier tube) and converted into an electrical pulse signal. The electrical pulse signal is processed by an electronic readout device, and the counting and flight are performed at the same time. Time measurement, and then convert the processed electrical signal into a digital signal with a certain logical relationship and send it to the computer processing system for data processing, where the image analysis software converts it into graphics and related data that can be intuitively analyzed. That is, a series of continuous neutron transmission images with neutron energy information are obtained.

As shown in Figure 5, by combining CT technology and rotating the sample stage, a series of continuous neutron transmission images with neutron energy information for each grid point are obtained, and the above steps are repeated to obtain neutron energy information at different angles. The neutron transmission image of the neutron transmission image, the computer processing system concentrates the position information collected from different angles into three-dimensional space and combines the energy information, and obtains the nuclear characteristics μ(x, y, z, E) = μ _xyz (E), this information is the nuclear characteristics of the sample material, and the nuclide composition of the material can be uniquely determined by comparing it with the nuclear database.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. A white light neutron imaging method, comprising the following steps: Step 11, the pulsed accelerator neutron source emits a pulsed neutron beam with a wide energy spectrum and records the emission time; Step 12, the detector detects and measures the pulsed neutron beam, obtains the position and arrival time of each neutron, and transmits the position and arrival time of each neutron to the processing unit; Step 13, the processing unit obtains the energy information of each neutron according to the arrival time of each neutron and the recorded emission time, groups all neutrons according to energy, and obtains different positions according to the position information of the neutrons neutron flux at Step 14, place the sample between the pulsed accelerator neutron source and the detector, repeat steps 11-13, and obtain the neutron flux at different positions when placing the sample according to the and the energy grouping information when placing the sample generate a series of continuous neutron transmission images with neutron energy information. 2. white light neutron imaging method as claimed in claim 1, is characterized in that, described pulse type accelerator neutron source is based on large-scale spallation neutron source or based on the small-scale high-current linear accelerator neutron source based on accelerated deuterium beam. 3. The white-light neutron imaging method according to claim 2, characterized in that the neutron energy range provided by the pulsed accelerator neutron source ranges from eV to hundreds of mega eV. 4. The white light neutron imaging method according to claim 3, wherein the detector is an array detector, which is composed of a neutron probe array, a photoelectric converter and an electronic readout device. 5. white light neutron imaging method as claimed in claim 4, is characterized in that, described neutron probe array is formed by the regular arrangement of many neutron probes, and the measuring range of described neutron probe array and described pulse The energy range of the sub-source is matched. 6. white light neutron imaging method as claimed in claim 5, is characterized in that, described neutron probe is made up of scintillator and conducting optical fiber, and described scintillator receives neutron and produces scintillation light, and described scintillation light is conducted An optical fiber leads to the photoelectric converter. 7. The white light neutron imaging method according to claim 6, wherein the scintillator is a fast scintillator, which is a capillary liquid scintillator, a plastic scintillator, a boron-containing scintillator or lithium glass. 8. The white light neutron imaging method according to claim 4, wherein the neutron probe array receives neutrons within a detection energy range within a single pulse. 9. white light neutron imaging method as claimed in claim 8, is characterized in that, described electronic readout device is used for measuring the time of arrival and the position information of all neutrons that neutron probe array detects in each pulse, and Transmitting arrival time and position information of all neutrons measured to the processing unit. 10. A non-destructive testing method for material composition, using the white light neutron imaging method according to any one of claims 1-9, wherein the material sample is located on a rotating platform, comprising the following steps: Step 21, rotate the sample on the rotating platform, use the white light neutron imaging method to obtain the neutron flux at different positions when the sample is placed at different angles, and obtain a series of continuous neutrons with neutron energy information at different angles transmission image; Step 22, the processing unit obtains the transmission information of the spatial unit grid points by using a tomographic reconstruction algorithm according to a series of continuous neutron transmission images with neutron energy information at different angles; Step 23: The processing unit compares the transmission information of the spatial unit grid point with the full cross-section data of nuclides in the nuclear database to obtain the composition of the material.