MeV-level wide-energy-spectrum gamma energy selection amplification imaging system and design method thereof

Abstract

The invention discloses a MeV-level wide-energy-spectrum gamma energy selection amplification imaging system and a design method thereof. The technical problem that an existing gamma ray beam energy selection imaging device is low in detection efficiency is solved. The imaging system comprises a radiation conversion unit, an energy selection beam amplification unit and an imaging unit, the radiation conversion unit is a radiation conversion target and is used for converting gamma rays from a to-be-detected target into electron beams; the energy selection beam amplification unit comprises a collimator, a first magnet and a second magnet which are sequentially arranged along the transmission path of the electron beam; the collimator is used for limiting the collection angle of the electron beam; the parameter specifications of the first magnet and the second magnet are different, the first magnet and the second magnet are respectively used for changing a transmission path of an electron beam through a magnetic field, and a first beam limiting device is arranged between the first magnet and the second magnet and is used for removing electrons which can be dispersed in the y direction and are large in angle; and a second beam limiting device is arranged between the imaging unit and the second magnet and is used for removing electrons which can be dispersed in the x direction and have large angles.

Description

Technical Field

[0001] The present invention relates to a gamma energy selection imaging system, and particularly to an MeV-level wide energy spectrum gamma energy selection and amplification imaging system and its design method. Background Art

[0002] In inertial confinement fusion (ICF) implosion diagnosis, different from neutron and X-ray diagnoses, gamma-ray images are helpful for characterizing information on the inertial confinement fuel and ablator components at stagnation. Moreover, energy-selective imaging for 4.44 MeV gamma rays can effectively determine the volume and symmetry of the ablation of indirect-drive DT implosions. Therefore, gamma-ray imaging diagnosis has important application value for improving inertial confinement fusion devices.

[0003] Existing high-energy ray measurement methods mainly measure the energy spectrum, which can generally be achieved by measurement devices such as gas Cherenkov detectors, gamma-ray reaction history diagnostics, scintillator decay spectrometers, stepped filter spectrometers, and filter stack spectrometers. The above measurement devices have different advantages and disadvantages in terms of measurement accuracy, accuracy, complexity, time resolution, etc.

[0004] In addition, researchers found that the gamma energy spectrum can be measured by the method of combining forward Compton electrons and a deflection magnetic field, and the energy spectrum measured by this method can reflect the key physical parameters of the fusion process. However, this method cannot achieve spatial distribution diagnosis. Chinese invention patent with publication number CN 116774269A discloses a pulsed gamma-ray beam energy selection imaging device, which combines forward Compton electrons and magnetic lens charged particle imaging. First, gamma rays are converted into Compton electrons, and then the imaging of the electron motion trajectory is realized by the magnetic field provided by a dipole magnet. However, the detection efficiency of this imaging system is relatively low, only 2.5×10 -6 , which cannot meet the minimum requirement of the detection efficiency of inertial confinement fusion (7.1×10 -4 ). Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that the existing gamma-ray beam energy selection imaging device has a relatively low detection efficiency and cannot meet the minimum requirement of the detection efficiency of inertial confinement fusion, and to provide an MeV-level wide energy spectrum gamma energy selection and amplification imaging system and its design method.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] An MeV-level wide energy spectrum gamma energy selection and amplification imaging system, characterized in that:

[0008] It includes a radiation conversion unit, an energy selection beam amplification unit, and an imaging unit;

[0009] The radiation conversion unit is a radiation conversion target, which is used to convert gamma rays from the target to be measured into an electron beam;

[0010] The energy selection beam amplification unit includes a collimator, a first magnet, and a second magnet arranged in sequence along the transmission path of the electron beam; the collimator is arranged close to the radiation conversion target, and the incident end of the collimator is attached to the rear end face of the radiation conversion target. The collimator is used to limit the collection angle of the electron beam; both the first magnet and the second magnet are fan-shaped ring structures, and their parameter specifications are different; the incident end of the first magnet is connected to the exit end of the collimator, and the exit end is connected to the incident end of the second magnet through a vacuum pipe; the first magnet and the second magnet are respectively used to change the transmission path of the electron beam through a magnetic field. The transmission path of the electron beam is represented by a 6×6 first-order transmission matrix M, and it needs to satisfy:

[0011]

[0012] where M 11 is the element in the first row and the first column, M 12 is the element in the first row and the second column, M 16 is the element in the first row and the sixth column, M 33 is the element in the third row and the third column, M 34 is the element in the third row and the fourth column;

[0013] A first beam limiter is arranged in the vacuum pipe between the first magnet and the second magnet. It is located at the Fourier plane in the y direction of the electron beam transmission path and is used to remove electrons with energy dispersion in the y direction and large angles;

[0014] The imaging unit is located at the exit end of the second magnet and is connected to the exit end of the second magnet through a vacuum pipe. A second beam limiter is arranged in this vacuum pipe. The second beam limiter is located at the Fourier plane in the x direction of the electron beam transmission path after passing through the second magnet and is used to remove electrons with energy dispersion in the x direction and large angles.

[0015] Further, the first magnet is a dipole electromagnet, its deflection radius is 450 - 650 mm, the deflection angle is 45 - 65°, and the edge angle is dynamically adjusted according to the corresponding deflection angle;

[0016] The second magnet is a dipole electromagnet, its deflection radius is 450 - 650 mm, the deflection angle is smaller than that of the first magnet, and the edge angle is dynamically adjusted according to the corresponding deflection angle.

[0017] Further, the length of the vacuum pipe between the exit end of the first magnet and the incident end of the second magnet is 0.7 - 1.0 m;

[0018] The length of the vacuum pipe between the exit end of the second magnet and the imaging system is 2 ± 0.5 m.

[0019] Further, the radiation conversion target selects a Be target with a mass thickness of 150-180 mg / cm 2 , and its electron collection angle is greater than 0.1-0.15 rad.

[0020] Further, the collimator is a cylindrical structure, and its two bottom surfaces are respectively the incident end and the exit end. The length of the cylindrical structure is 0.6-0.8 m, and the diameters of the two bottom surfaces are respectively less than or equal to 100 mm.

[0021] Further, the cross sections of the beam limiting holes of the first beam limiter and the second beam limiter are both rectangular structures. Among them, the length of the beam limiting hole of the first beam limiter is 10 cm, and the width is less than 2.5 cm; the length of the beam limiting hole of the second beam limiter is less than 2.5 cm, and the width is 10 cm.

[0022] Further, the imaging unit is composed of a scintillator and a CCD camera;

[0023] Alternatively, the imaging unit is an IP imaging plate.

[0024] In addition, the present invention also provides a design method for a gamma energy selection and magnification imaging system, including the following steps:

[0025] S1. Prepare the first beam limiter, the second beam limiter and the imaging unit in advance;

[0026] S2. According to the target detection efficiency, use Geant4 software to determine the thickness of the radiation conversion target, as well as the shape and size of the collimator by means of simulation;

[0027] S3. Select the first magnet and the second magnet with different parameter specifications, and calculate and adjust through beam optics design software to obtain the relative parameters of the first magnet and the second magnet, the distance between the two, and the distance between the second magnet and the imaging unit; the transmission path of the electron beam between the first magnet and the second magnet is represented by a 6×6 first-order transmission matrix M and satisfies:

[0028]

[0029] wherein, M 11 is the element in the first row and the first column, M 12 is the element in the first row and the second column, M 16 is the element in the first row and the sixth column, M 33 is the element in the third row and the third column, M 34 is the element in the third row and the fourth column; the relative parameters include the deflection radius, the deflection angle and the edge angle;

[0030] S4. Assemble the radiation conversion target and collimator determined in step S2, the first magnet and second magnet determined in step S3, and the imaging unit prepared in advance in step S1 in sequence;

[0031] S5. On the basis of step S4, place the first beam limiter prepared in advance in step S1 at the y-direction Fourier plane of the electron beam movement trajectory between the first magnet and the second magnet, and place the second beam limiter at the x-direction Fourier plane of the electron beam movement trajectory between the second magnet and the imaging unit, and respectively adjust the sizes of the beam limiting holes of the first beam limiter and the second beam limiter, so as to obtain a gamma energy selection magnification imaging system.

[0032] Further, in step S2, the collimator is of a cylindrical structure, with a length of 0.6 - 0.8 m and a bottom diameter less than or equal to 100 mm.

[0033] Further, in step S5, the length and width of the beam limiting hole of the first beam limiter are respectively adjusted according to the matrix coefficients at the y-direction Fourier plane; the length and width of the beam limiting hole of the second beam limiter are adjusted according to the matrix coefficients at the x-direction Fourier plane.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. A MeV-level wide energy spectrum gamma energy selection magnification imaging system provided by the present invention, wherein the radiation conversion unit is a radiation conversion target for converting gamma rays from a target to be measured into electron beams; the energy selection beam current magnification unit includes a collimator, a first magnet, and a second magnet sequentially arranged along the transmission path of the electron beam. Among them, the parameter specifications of the first magnet and the second magnet are different. The control of the electron beam transmission path is achieved through the first magnet and the second magnet, and at the same time, energy and angle selection are performed through the first beam limiter and the second beam limiter. Finally, achromatic aberration and point-to-point imaging are achieved at the imaging end while magnification imaging is performed, improving the detection efficiency while meeting the spatial resolution, so as to meet the requirements of inertial confinement fusion detection efficiency.

[0036] 2. The overall structure of a MeV-level wide energy spectrum gamma energy selection magnification imaging system provided by the present invention is compact and easy to assemble.

[0037] 3. A design method of a MeV-level wide energy spectrum gamma energy selection magnification imaging system provided by the present invention can determine the thickness of the radiation conversion target and the shape and size of the collimator through simulation, so as to meet the detection requirements under different imaging fields of view. In addition, the thickness of the radiation conversion target can be adjusted according to the target detection efficiency to further improve the detection efficiency.

[0038] 4. In the design method of the MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system provided by the present invention, the sizes of the collimation holes of the first collimator and the second collimator can be adjusted according to the matrix coefficients at the Fourier plane in the corresponding directions, so as to meet the requirements of the target detection efficiency, energy resolution, and spatial resolution. Description of the Drawings

[0039] Figure 1 is a schematic structural diagram of an embodiment of the MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system of the present invention.

[0040] Figure 2 is a schematic diagram of the positional relationship between the first magnet and the second magnet in an embodiment of the MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system of the present invention.

[0041] The reference numerals are as follows:

[0042] 1 - Radiation conversion target, 11 - Gamma source, 2 - Energy selection beam amplification unit, 21 - Collimator, 22 - First magnet, 23 - First collimator, 24 - Second magnet, 25 - Second collimator, 3 - Imaging unit. Detailed Embodiments

[0043] To make the objectives, advantages, and features of the present invention clearer, the following further describes the present invention in detail with reference to the drawings and specific embodiments. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0044] As Figure 1 shown, this embodiment provides an MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system, including a radiation conversion unit, an energy selection beam amplification unit 2, and an imaging unit 3.

[0045] The radiation conversion unit is a radiation conversion target 1, which is used to convert gamma rays with an energy distribution from a target to be measured into an electron beam (Compton electron beam). In this embodiment, the radiation conversion target 1 selects a Be target with a mass thickness of 150 - 180 mg / cm 2 and an electron collection angle of 0.1 - 0.15 rad. Preferably, the mass thickness of the radiation conversion target 1 is 150 mg / cm 2 , and the electron collection angle is about 0.1 rad. This thickness and electron collection angle can meet the minimum requirements of the detection efficiency and ensure the performance of energy and spatial resolution.

[0046] The energy selection beam amplification unit 2 includes a collimator 21, a first magnet 22, and a second magnet 24 sequentially arranged along the transmission path of the electron beam.

[0047] The collimator 21 is arranged close to the radiation conversion target 1, and the incident end of the collimator 21 is in contact with the rear end face of the radiation conversion target 1. The collimator 21 is used to limit the collection angle of the electron beam. The collimator 21 in this embodiment has a cylindrical structure, and its two bottom surfaces are respectively the incident end and the exit end. The length of the cylindrical structure is 0.6 - 0.8 m, and the diameters of the two bottom surfaces are respectively less than or equal to 100 mm. Increasing the electron collection angle will improve the detection efficiency but will cause a decrease in spatial resolution. Therefore, to limit the electron collection angle to be greater than about 0.1 rad, the length of the cylindrical structure in this embodiment is 600 mm (i.e., Figure 2 L1 in

[0048] ), and the bottom surface diameter is 100 mm, so as to obtain an effective electron collection angle range of 0.083 rad - 0.166 rad.

[0049] Both the first magnet 22 and the second magnet 24 have a fan-shaped ring structure. Their parameter specifications are different, but the magnet itself is symmetric, and its own incident and exit edge angles are the same. Using two magnets with different specifications can achieve magnified imaging while meeting the compact layout of the system, and further reduce the high-order transfer matrix coefficient.

[0050]

[0051] Among them, M 11 is the element in the first row and the first column, M 12 is the element in the first row and the second column, M 16 is the element in the first row and the sixth column, M 33 is the element in the third row and the third column, M 34 is the element in the third row and the fourth column.

[0052] This embodiment utilizes the idea of magnified imaging and combines the first magnet 22 and the second magnet 24 with different parameter specifications to achieve electron achromatic magnified imaging, that is, on the basis of point-to-point imaging, reduce the high-order transfer matrix coefficient, further reduce the high-order aberration, and improve the spatial resolution performance of the system. While improving the detection efficiency, this embodiment still maintains a horizontal spatial resolution of about 1 mm and a vertical spatial resolution of 2.5 mm within a field of view of 60×60 mm.

[0053] Such as Figure 2As shown, the preferred parameter combinations of the first magnet 22 and the second magnet 24 in this embodiment are: the deflection radius R1 of the first magnet 22 is 500 mm, the deflection angle θ1 is 65°, and the edge angle α1 is 26.80°; the deflection radius R2 of the second magnet 24 is 650 mm, the deflection angle θ2 is 40°, and the edge angle α2 is 3.29°.

[0054] The length L2 of the vacuum pipe between the exit end of the first magnet 22 and the entrance end of the second magnet 24 in this embodiment is 0.7174 m. The length L3 of the vacuum pipe between the exit end of the second magnet 24 and the receiving end of the imaging unit 3 is 1.8969 m. The vacuum pipe is made of stainless steel.

[0055] A first beam limiter 23 is provided in the vacuum pipe between the first magnet 22 and the second magnet 24. It is located at the y-direction Fourier plane of the electron beam transmission path and is used to remove electrons with large energy dispersion and large angles in the y direction.

[0056] The imaging unit 3 is located at the exit end of the second magnet 24 and is connected to the exit end of the second magnet 24 through a vacuum pipe. A second beam limiter 25 is provided in this vacuum pipe. The second beam limiter 25 is located at the x-direction Fourier plane of the electron beam transmission path after passing through the second magnet 24 and is used to remove electrons with large energy dispersion (large deviation from the central energy) and large angles in the x direction. In this embodiment, the xy plane where the x direction and the y direction are located is defined as the beam trajectory cross-section, which is perpendicular to the electron beam transmission direction.

[0057] The pore length-width dimensions of the first beam limiter 23 and the second beam limiter 25 can be flexibly adjusted according to the full-system simulation method of gamma incident on the imaging receiver. Generally, the smaller the pore, the better the spatial resolution and energy resolution performance, but the detection efficiency will decrease. In this embodiment, the cross-sections of the beam-limiting holes of the first beam limiter 23 and the second beam limiter 25 are both rectangular structures. Among them, the length of the beam-limiting hole of the first beam limiter 23 is 10 cm, and the width is less than 2.5 cm; the length of the beam-limiting hole of the second beam limiter 25 is less than 2.5 cm, and the width is 10 cm. It should be noted that the length and width here respectively represent the length and width of the rectangular structure, and the depth of the beam-limiting hole is the thickness of the corresponding beam limiter, which is determined according to the maximum electron energy and the material of the corresponding beam limiter.

[0058] The imaging unit 3 of this embodiment is composed of a scintillator and a CCD camera. Alternatively, the imaging unit 3 can also choose an IP imaging plate, which is mainly used to receive information from the target to be measured and form an image.

[0059] The detection efficiency of the imaging system provided by this embodiment for 4.44 MeV gamma rays (a circular planar gamma ray source with a diameter of 60 mm) is greater than 7.1×10 -4 , and in ICF diagnosis, it can satisfy that at least one electron is captured by each pixel.

[0060] The working principle of this embodiment is to perform electron energy selection imaging based on gamma-electron conversion. First, MeV-level gamma rays mainly undergo Compton scattering after passing through the low atomic number radiation conversion target 1 and are converted into electrons. The electrons enter the energy selection beam amplification unit 2, and the magnetic field provided by the dipole electromagnet is used to control the electron motion trajectory, and energy and angle selection are performed. Finally, an image is obtained on the image plane through the imaging unit 3. The electron beam generated by the interaction between gamma rays and matter has the characteristics of a wide energy spectrum and a large divergence angle. According to the target detection efficiency, the radiation conversion target 1 and the collimator 21 can be optimized. At the same time, in order to control the spatial resolution, the idea of magnified imaging can be adopted to reduce higher-order aberrations.

[0061] Preferably, an imaging restoration algorithm can also be combined to further process the information received by the imaging unit 3, thereby improving the system spatial resolution performance.

[0062] In addition, the imaging system of this embodiment may further include a gamma source 11, which is located at the front end of the radiation conversion target 1. During use, the object to be measured can be placed between the gamma source 11 and the radiation conversion target 1 to measure the energy spectrum of the object to be measured. Alternatively, the gamma source 11 can also be regarded as the object to be measured to achieve the test and diagnosis of the energy spectrum of the gamma source.

[0063] This embodiment also provides a design method for an MeV-level wide energy spectrum gamma energy selection magnified imaging system, including the following steps:

[0064] S1. Prepare a first collimator 23, a second collimator 25 and an imaging unit 3 in advance.

[0065] S2. According to the target detection efficiency, use Geant4 software to determine the thickness of the radiation conversion target 1, and the shape and size of the collimator 21 through simulation. The process of simulation is to count the number of effective electrons within a certain angle and energy range, and then use the ratio obtained by dividing the number of effective electrons by the number of incident gamma rays to select and determine the thickness of the radiation conversion target 1. In addition, by optimizing the radiation conversion target 1 and the collimator 21, adjusting the electron collection angle and increasing the proportion of effective Compton forward electrons, the detection efficiency can be further improved.

[0066] In this embodiment, the collimator 21 generally selects a cylindrical structure, with a length of 0.6 - 0.8 m and a bottom diameter less than or equal to 100 mm. Of course, the specific shape and size can also be designed according to the design requirements.

[0067] S3. Select the first magnet 22 and the second magnet 24 with different parameter specifications, and calculate and adjust them through beam optics design software (COSY infinity) to obtain the relative parameters of the first magnet 22 and the second magnet 24, the distance between the first magnet 22 and the second magnet 24, and the distance between the second magnet 24 and the imaging unit 3. The transmission path of the electron beam between the first magnet 22 and the second magnet 24 is represented by a 6×6 first-order transmission matrix M, and satisfies:

[0068]

[0069] where M 11 is the element in the first row and first column, M 12 is the element in the first row and second column, M 16 is the element in the first row and sixth column, M 33 is the element in the third row and third column, M 34 is the element in the third row and fourth column; the relative parameters include deflection radius, deflection angle, and edge angle.

[0070] In this process, the above parameters can also be iteratively optimized according to the actual situation to ensure that the detection efficiency of the imaging system meets the expected requirements, and at the same time to meet the compact layout of the implementation system for magnified imaging.

[0071] S4. Assemble the radiation conversion target 1 and the collimator 21 determined in step S2, the first magnet 22 and the second magnet 24 determined in step S3, and the imaging unit 3 prepared in advance in step S1 in sequence.

[0072] S5. On the basis of step S4, place the first beam limiter 23 prepared in advance in step S1 at the y-direction Fourier plane of the electron beam movement trajectory between the first magnet 22 and the second magnet 24, and place the second beam limiter 25 at the x-direction Fourier plane of the electron beam movement trajectory between the second magnet 24 and the imaging unit 3, and respectively adjust the sizes of the beam limiting holes of the first beam limiter 23 and the second beam limiter 25, so as to obtain a gamma energy selection magnified imaging system.

[0073] In this embodiment, the length and width of the beam limiting hole of the first beam limiter 23 are respectively adjusted according to the matrix coefficients at the y-direction Fourier plane; the length and width of the beam limiting hole of the second beam limiter 25 are adjusted according to the matrix coefficients at the x-direction Fourier plane, so that the method has flexible adjustability, thus meeting the requirements of target detection efficiency, energy resolution, and spatial resolution.

[0074] In this embodiment, the detection efficiency is improved by optimizing the designs of the radiation conversion target 1 and the collimator 21; meanwhile, the design of the magnet is optimized, and the idea of magnified imaging is adopted to reduce the high-order coefficients of the transfer matrix and maintain the spatial resolution performance. In addition, the parameters to be optimized mainly include the deflection angle θ, the deflection radius R, the edge angle α, and the vacuum pipes L2 and L3. By adjusting the values of these parameters, the transfer matrix meets the conditions of achromatic magnified imaging, and it is required that the high-order transfer matrix coefficients be as small as possible.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. An MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system, characterized in that: It includes a radiation conversion unit, an energy selection beam amplification unit (2) and an imaging unit (3); The radiation conversion unit is a radiation conversion target (1), which is used to convert gamma rays from the target to be measured into an electron beam; The energy selection beam amplification unit (2) includes a collimator (21), a first magnet (22) and a second magnet (24) arranged in sequence along the transmission path of the electron beam; the collimator (21) is arranged close to the radiation conversion target (1), and the incident end of the collimator (21) is attached to the rear end face of the radiation conversion target (1), and the collimator (21) is used to limit the collection angle of the electron beam; both the first magnet (22) and the second magnet (24) are fan-shaped ring structures, and their parameter specifications are different; the incident end of the first magnet (22) is connected to the exit end of the collimator (21), and the exit end is connected to the incident end of the second magnet (24) through a vacuum pipeline; the first magnet (22) and the second magnet (24) are respectively used to change the transmission path of the electron beam through a magnetic field. The transmission path of this electron beam is represented by a 6×6 first-order transmission matrix M, and it is required to satisfy: Among them, M 11 is the element in the first row and the first column, M 12 is the element in the first row and the second column, M 16 is the element in the first row and the sixth column, M 33 is the element in the third row and the third column, M 34 is the element in the third row and the fourth column; A first beam limiter (23) is arranged in the vacuum pipeline between the first magnet (22) and the second magnet (24). It is located at the Fourier plane in the y direction of the electron beam transmission path and is used to remove electrons with energy dispersion in the y direction and relatively large angles; The imaging unit (3) is located at the exit end of the second magnet (24) and is connected to the exit end of the second magnet (24) through a vacuum pipeline. A second beam limiter (25) is arranged in this vacuum pipeline. The second beam limiter (25) is located at the Fourier plane in the x direction of the electron beam transmission path after passing through the second magnet (24) and is used to remove electrons with energy dispersion in the x direction and relatively large angles.

2. The MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system according to claim 1, characterized in that: The first magnet (22) is a dipole electromagnet, its deflection radius is 450 - 650 mm, the deflection angle is 45 - 65°, and the edge angle is dynamically adjusted according to the corresponding deflection angle; The second magnet (24) is a dipole electromagnet, its deflection radius is 450 - 650 mm, the deflection angle is smaller than that of the first magnet (22), and the edge angle is dynamically adjusted according to the corresponding deflection angle.

3. The MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system according to claim 2, characterized in that: The length of the vacuum pipeline between the exit end of the first magnet (22) and the incident end of the second magnet (24) is 0.7 - 1.0 m; The length of the vacuum pipeline between the exit end of the second magnet (24) and the imaging system (3) is 2 ± 0.5 m.

4. The MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system according to claim 1 or 2 or 3, characterized in that: The radiation conversion target (1) selects a Be target with a mass thickness of 150 - 180 mg / cm 2 , and its electron collection angle is greater than 0.1 - 0.15 rad.

5. The MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system according to claim 4, characterized in that: The collimator (21) has a cylindrical structure, with its two bottom surfaces being the incident end and the exit end respectively. The length of the cylindrical structure is 0.6 - 0.8 m, and the diameters of the two bottom surfaces are less than or equal to 100 mm.

6. The MeV - level broad - energy - spectrum gamma energy - selective amplification imaging system according to claim 5, characterized in that: The cross - sections of the beam - limiting holes of the first beam - limiting device (23) and the second beam - limiting device (25) are both rectangular structures. Among them, the length of the beam - limiting hole of the first beam - limiting device (23) is 10 cm, and the width is less than 2.5 cm; the length of the beam - limiting hole of the second beam - limiting device (25) is less than 2.5 cm, and the width is 10 cm.

7. The MeV - level broad - energy - spectrum gamma energy - selective amplification imaging system according to claim 1, characterized in that: The imaging unit (3) is composed of a scintillator and a CCD camera; Alternatively, the imaging unit (3) is an IP imaging plate.

8. A design method for the MeV-level wide-energy-spectrum gamma energy selection and amplification imaging system according to any one of claims 1-7, characterized in that, Including the following steps: S1. Prepare the first beam - limiting device (23), the second beam - limiting device (25) and the imaging unit (3) in advance; S2. According to the target detection efficiency, use Geant4 software to determine the thickness of the radiation conversion target (1), as well as the shape and size of the collimator (21) through simulation; S3. Select the first magnet (22) and the second magnet (24) with different parameter specifications, and calculate and adjust through beam - optics design software to obtain the relative parameters of the first magnet (22) and the second magnet (24), the distance between the two, and the distance between the second magnet (24) and the imaging unit (3); the transmission path of the electron beam between the first magnet (22) and the second magnet (24) is represented by a 6×6 first - order transfer matrix M and satisfies: Among them, M 11 is the element in the first row and the first column, M 12 is the element in the first row and the second column, M 16 is the element in the first row and the sixth column, M 33 is the element in the third row and the third column, M 34 is the element in the third row and the fourth column; the relative parameters include the deflection radius, the deflection angle, and the edge angle; S4. Assemble the radiation conversion target (1) and the collimator (21) determined in step S2, the first magnet (22) and the second magnet (24) determined in step S3, and the imaging unit (3) prepared in advance in step S1 in sequence; S5. On the basis of step S4, place the first beam - limiting device (23) prepared in advance in step S1 at the y - direction Fourier plane of the electron - beam movement trajectory between the first magnet (22) and the second magnet (24), place the second beam - limiting device (25) at the x - direction Fourier plane of the electron - beam movement trajectory between the second magnet (24) and the imaging unit (3), and respectively adjust the sizes of the beam - limiting holes of the first beam - limiting device (23) and the second beam - limiting device (25), so as to obtain the gamma energy - selective amplification imaging system.

9. The design method of the MeV - level broad - energy - spectrum gamma energy - selective amplification imaging system according to claim 8, characterized in that: In step S2, the collimator (21) has a cylindrical structure, with a length of 0.6 - 0.8 m and a bottom - surface diameter less than or equal to 100 mm.

10. The design method of the MeV - level broad - energy - spectrum gamma energy - selective amplification imaging system according to claim 8 or 9, characterized in that: In step S5, the length and width of the collimator aperture of the first collimator (23) are adjusted according to the matrix coefficients at the Fourier plane in the y direction; the length and width of the collimator aperture of the second collimator (25) are adjusted according to the matrix coefficients at the Fourier plane in the x direction.

Images