Element distribution imaging device and method based on rotation modulation collimator

Abstract

The present invention discloses an element distribution imaging device and method based on a rotary modulation collimator. The measuring device comprises a neutron generator, a rotary modulation collimator, a gamma ray detector and a data acquisition and processing system. The rotary modulation collimator comprises two encoding plates, a cylinder, a synchronous belt and a motor. The sample to be tested is placed in a neutron field between the neutron generator and the rotary modulation collimator. The elements to be tested in the sample to be tested react with the neutrons in the neutron field and emit characteristic gamma rays of different energies through capture reaction and inelastic scattering. The characteristic gamma rays change in flux after passing through the encoding plate. The gamma ray detector measures the characteristic gamma rays after the flux changes. The gamma ray detector is connected to the data acquisition and processing system. The gamma ray detector can send the measured characteristic gamma ray data to the data acquisition and processing system. The present invention has the advantages of high detection accuracy, high detection efficiency and short measurement time.

Description

Technical Field

[0001] The invention belongs to the technical field of sample element content detection, and in particular relates to an element distribution imaging device and method based on a rotation modulation collimator. Background Art

[0002] Nondestructive testing and analysis of precious cultural relics, space samples, alloy samples and other samples have always been the focus of attention. At present, in the field of measurement and analysis, nuclear technology, especially neutron technology, has become a routine technology. Prompt gamma neutron activation imaging (PGAI) is an imaging analysis method derived from prompt gamma neutron activation analysis (PGNAA) technology. It can not only perform qualitative and quantitative analysis of the element content inside the sample, but also obtain the distribution information of the elements in the sample. PGNAA technology uses neutron capture and inelastic scattering reactions with radionuclides in the sample to obtain a quantitative analysis of the element content in a very short time (less than 10 -13 s) emits characteristic gamma rays, and the energy and intensity of the gamma rays are detected to perform qualitative and quantitative analysis of the nuclides in the sample. On this basis, PGAI technology generally adopts a double-collimated layer-by-layer scanning method. Through highly collimated neutron beams and gamma-ray detection devices, the detected volume is continuously reduced, so the spatial information of the element distribution at different positions in the sample can be obtained through scanning. At present, PGAI technology has been experimentally applied to the analysis and research of the internal elemental composition distribution of objects such as cultural relics and meteorites, which is of great significance to the dating, protection and restoration of cultural relics.

[0003] The traditional layer-by-layer scanning method requires highly collimated neutron beams and gamma collimation devices, which brings an insurmountable problem that the detection efficiency is very low. A possible solution is to increase the neutron beam width and obtain element distribution information through a position-sensitive gamma detector. However, the maximum energy of gamma rays in PGAI exceeds 10 MeV, which exceeds the maximum range of 300 keV~ 2 MeV of commonly used position-sensitive scintillator detectors. Detectors that meet this energy range and high energy resolution (such as high-purity germanium HPGe, BGO) do not have position resolution capabilities. Therefore, it is very necessary to propose a method for using a high-energy resolution detector to achieve position resolution and element distribution detection to solve this problem. Summary of the invention

[0004] The purpose of the present invention is to provide a new detection method and device for the distribution of nuclides inside a sample, so as to enable the detector to obtain and image the element distribution information inside the sample, thereby overcoming the difficulties of the traditional seed activation imaging method, and utilizing the characteristics of rotational modulation to simplify the imaging device while making the imaging have a higher resolution.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] An element distribution imaging device based on a rotary modulation collimator comprises a neutron generator, a rotary modulation collimator, a gamma ray detector and a data acquisition and processing system, wherein: the rotary modulation collimator comprises two encoding plates, a cylinder, a synchronous belt and a motor, the encoding plates are respectively fixed at two ends of the cylinder, the synchronous belt is wound between the cylinder and the motor, the motor can drive the cylinder to rotate through the synchronous belt, thereby rotating the encoding plate and changing the angle of the encoding hole on the encoding plate, the neutron generator can emit neutrons to the rotary modulation collimator, and the emission direction is coaxial with the central axis of the cylinder, the sample to be tested is placed in the neutron field between the neutron generator and the rotary modulation collimator, the elements to be tested in the sample to be tested react with the neutrons in the neutron field and inelastic scatter to emit characteristic gamma rays of different energies, the flux of the characteristic gamma rays changes after passing through the encoding plate, the gamma ray detector measures the characteristic gamma rays after the flux changes, the gamma ray detector is connected to the data acquisition and processing system, and the gamma ray detector can send the measured characteristic gamma ray data to the data acquisition and processing system.

[0007] To optimize the above technical solutions, the specific measures taken also include:

[0008] A device shielding device is arranged around the coding plate on the side close to the neutron generating device, and the device shielding device is used to shield the gamma rays that have not entered the rotating modulation collimator.

[0009] The gamma-ray detector is provided with a detector shielding device around its periphery, and the detector shielding device is used to shield the gamma rays that have not passed through the rotation modulation collimator from entering the gamma-ray detector.

[0010] The device shielding device and the detector shielding device are both made of lead, tungsten or bismuth.

[0011] The above-mentioned neutron generating device is a neutron generator or an isotope neutron source. When the neutron generating device is a neutron generator, the neutron generating device is a DD neutron generator emitting 2.5 MeV neutrons or a DT neutron generator emitting 14 MeV neutrons; when the neutron generating device is an isotope neutron source, the neutron generating device is an Am-Be neutron source or a californium-252 neutron source.

[0012] The above-mentioned coding plate is a tungsten steel coding plate, and a plurality of parallel strip openings are provided on the coding plate.

[0013] The cylindrical body is a polytetrafluoroethylene cylinder.

[0014] The gamma-ray detector is a BGO scintillator detector, a NaI detector or a high-purity germanium detector.

[0015] The present invention has the following effects:

[0016] 1. The present invention breaks through the limitations of traditional neutron activation imaging technology, such as high collimation accuracy requirements, low detection efficiency, and time-consuming measurement. It uses PGNAA technology, Monte Carlo method simulation, and a rotating modulated collimator to provide the internal nuclide distribution information of the sample. It can be applied to sample nuclide distribution detection in the fields of industry, materials, and archaeology, and has important application value.

[0017] 2. The present invention uses a rotation modulation method to enable the coding plate to obtain multiple coding information using projection technology during rotation. The number of coding times can be determined by the rotation angle / number of times, so the device structure is simpler while obtaining a higher resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a top view of the device of the present invention;

[0019] Figure 2 It is the structural diagram of the coding plate of the present invention;

[0020] Figure 3 is a system response function of an embodiment of the present invention;

[0021] Figure 4 is a modulation curve of an embodiment of the present invention;

[0022] Figure 5 This is a measurement diagram of the spatial distribution of chlorine element in an embodiment of the present invention.

[0023] The reference numerals in the drawings are: neutron generating device 1, sample to be tested 2, encoding plate 3, cylinder 4, motor 5, synchronous belt 6, device shielding device 7, detector shielding device 8, gamma ray detector 9, industrial control computer 10. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0025] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0026] refer to Figure 1 The example shown is an element distribution imaging device based on a rotary modulation collimator, including a neutron generating device 1, a coding plate 3, a cylinder 4, a motor 5, a synchronous belt 6, a device shielding device 7, a detector shielding device 8, a gamma ray detector 9, an industrial control computer 10 and other structures.

[0027] The neutron generating device 1 is a set of electrically controllable DD neutron generator.

[0028] The rotary modulation collimator consists of two tungsten steel code plates with a radius of 44.4 mm and a thickness of 2.5 mm, a polytetrafluoroethylene cylinder with a radius of 45 mm and a length of 20 cm, and a drive structure consisting of a 3M model drive wheel, a synchronous belt 6 and a stepper motor. The code plate has 12 strip openings with a width of 4.44 mm. The specific parameters are shown in Figure 2 .

[0029] The device shielding device 7 uses two lead blocks with a size of 10 cm×15 cm and a thickness of 5 cm to shield the rotary modulation collimator in the up, down, left and right directions. The detector shielding device 8 is a lead block with a size of 15 cm×15 cm, a thickness of 10 cm, a circular through hole in the middle, and a hole diameter of 12 cm. It is used to be placed on the top, bottom, left and right of the gamma-ray detector 9 to shield the sides of the gamma-ray detector 9.

[0030] The basic principles of the present invention are as follows:

[0031] Prompt gamma-ray neutron activation analysis technology uses neutron capture (n, γ) and inelastic scattering (n, n' γ) reactions with nuclides in the sample to generate a rapid and accurate neutron emission tomography (TEM) analysis in a very short time (less than 10 -13 s) emit characteristic gamma rays, such as the capture reactions of H, B and Cl emit characteristic gamma rays of 2.22 MeV, 0.478 MeV and 1.951 MeV, respectively, and the inelastic scattering reactions of Pb, C and O emit characteristic gamma rays of 2.61 MeV, 4.44 MeV and 6.13 MeV, respectively. The emission position of gamma rays of each characteristic energy in the sample essentially reflects the spatial distribution of the corresponding nuclide in the sample.

[0032] The basic structure of the rotary modulated collimator is to place the detector under a pair of separated coding plates with several strip openings on the coding plates. The rays can be received by the detector when they can pass through the openings of the two coding plates at the same time, otherwise they will be shielded by the non-opening parts of the coding plates. The rotary modulated collimator can be modulated and rotated to a certain angle. At different angles, the two aperture plates show different transmittances to rays in different positions and directions, and the flux of the rays changes. The rotary modulated collimator is divided into I angles, and the sample element distribution is divided into J regions. Through Monte Carlo simulation, when the rotary modulated collimator is at different rotation angles i, the counting rate of the characteristic peak of the unit intensity radiation source at different positions j of the target sample is recorded as the response function R i (j). Theoretically, the number of regions J is limited by the single rotation angle of the rotary collimator, that is, the resolution of sample imaging is related to the number of modulation structures of the encoding plate. Under the condition that the sample distribution is unknown, after the rotary modulation collimator rotates by angle i, the characteristic peak count rate N of the detector is i =∑Φ j Ri (j), the detector counts N under the rotation angle of group I i It is called the modulation curve. Combined with the modulation curve N i and the system response function R i (j), we can get an equation about the characteristic peak ray counts in each area. Through data processing, the maximum likelihood expectation maximization algorithm (MLEM) is used to solve the radiation source position information, thereby obtaining the nuclide distribution of the sample.

[0033] Example:

[0034] Measuring the distribution of chlorine inside an inhomogeneous sample:

[0035] In this example, a 12×12×2 cm 3 The volume of the sodium chloride sample is measured, which is 2×2×2cm 3 As a unit, divided into 36 blocks, select a position to place sodium chloride solid powder (for example Figure 5 The sample was placed at (5,2) in the middle, and the rest of the positions were left empty and placed in organic glass containers of unit size. The sample was placed 30 cm away from the DD neutron generator and 30 cm away from the rotating modulation collimator. Figure 2 The example rotation modulation collimator coding aperture structure. Modulation starts from 0°, with an interval of 6°, to 354°. Figure 3 The detector response N at each angle is recorded. It is obtained by Monte Carlo simulation Figure 4 The system response curve R is obtained by solving the equations according to the maximum likelihood expectation maximization method. Figure 5 To measure and obtain the spatial distribution results of chlorine element in the sample.

[0036] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. An element distribution imaging device based on a rotation modulation collimator, comprising a neutron generating device (1), a rotation modulation collimator, a gamma ray detector (9) and a data acquisition and processing system, characterized in that: The rotary modulation collimator comprises two encoding plates (3), a cylinder (4), a synchronous belt (6) and a motor (5); the encoding plates (3) are respectively fixed at two ends of the cylinder (4); the synchronous belt (6) is wound between the cylinder (4) and the motor (5); the motor (5) can drive the cylinder (4) to rotate through the synchronous belt (6), thereby rotating the encoding plates (3) and changing the angle of the encoding holes on the encoding plates (3); the neutron generating device (1) can emit neutrons to the rotary modulation collimator, and the emission direction is coaxial with the central axis of the cylinder (4); the sample to be tested (2) is placed in a neutron field between a neutron generator (1) and a rotating modulation collimator, and the elements to be tested in the sample to be tested (2) undergo a capture reaction with the neutrons in the neutron field and inelastic scattering to emit characteristic gamma rays of different energies. The characteristic gamma rays pass through a coding plate (3), and the flux changes. The gamma ray detector (9) measures the characteristic gamma rays after the flux changes. The gamma ray detector (9) is connected to a data acquisition and processing system, and the gamma ray detector (9) can send the measured characteristic gamma ray data to the data acquisition and processing system.

2. The element distribution imaging device based on the rotation modulation collimator according to claim 1 is characterized in that: A device shielding device (7) is arranged around the coding plate (3) on one side close to the neutron generating device (1), and the device shielding device (7) is used to shield the gamma rays that have not entered the rotating modulation collimator.

3. The element distribution imaging device based on the rotation modulation collimator according to claim 2 is characterized in that: A detector shielding device (8) is arranged around the gamma ray detector (9), and the detector shielding device (8) is used to shield gamma rays that have not passed through the rotation modulation collimator from entering the gamma ray detector (9).

4. The element distribution imaging device based on the rotation modulation collimator according to claim 3 is characterized in that: The device shielding device (7) and the detector shielding device (8) are both made of lead, tungsten or bismuth.

5. The element distribution imaging device based on the rotation modulation collimator according to claim 4 is characterized in that: The neutron generating device (1) is a neutron generator or an isotope neutron source. When the neutron generating device (1) is a neutron generator, the neutron generating device (1) is a DD neutron generator emitting 2.5 MeV neutrons or a DT neutron generator emitting 14 MeV neutrons; when the neutron generating device (1) is an isotope neutron source, the neutron generating device (1) is an Am-Be neutron source or a Californium-252 neutron source.

6. The element distribution imaging device based on the rotation modulation collimator according to claim 5 is characterized in that: The coding plate (3) is a tungsten steel coding plate, and a plurality of parallel strip openings are provided on the coding plate (3).

7. The element distribution imaging device based on the rotation modulation collimator according to claim 6 is characterized in that: The cylindrical body (4) is a polytetrafluoroethylene cylinder.

8. The element distribution imaging device based on the rotation modulation collimator according to claim 7 is characterized in that: The gamma-ray detector (9) is a BGO scintillator detector, a NaI detector or a high-purity germanium detector.

9. The element distribution imaging device based on the rotation modulation collimator according to claim 8, characterized in that: The data acquisition and processing system is an industrial control computer (10).

10. The element distribution imaging measurement method based on a rotation modulation collimator according to any one of claims 1 to 9, characterized in that: The following steps are involved: 1) Monte Carlo simulation is designed according to the actual geometric arrangement. The rotation modulated collimator is divided into I angles, and the element distribution of the sample to be tested (2) is divided into J regions. Through Monte Carlo simulation, the counting rate of the characteristic peak of the unit intensity radiation source at different positions j of the target sample at different rotation angles i of the rotation modulated collimator is recorded as the response function R i (j); 2) Use a gamma detector to measure the characteristic peak count rate N of the detector after the sample is rotated by an angle i through the rotary modulated collimator. i , whose counting rate can be expressed as N i =∑Φ j R i (j) Count the detectors under the rotation angle N of group I i It is called the modulation curve; 3) Combined modulation curve N i and the system response function R i (j) We obtain an equation about the characteristic peak ray counts in each region. Through data processing, we use the maximum likelihood expectation maximization algorithm to solve the equation and obtain the location information of the radiation source, thereby obtaining the nuclide distribution of the sample.

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