Electron and gamma-ray spectrometer based on a gradient magnetic field

Abstract

An electron and gamma-ray spectrometer based on a gradient magnetic field includes a conversion target, a shielding part, a spectrometer main body, and a detector. By adopting a gradient magnetic field, the convergence points of the deflection trajectories of electrons with different energies can be made to be almost on a straight line. The detector is inserted into the main body of the spectrometer along the straight line to collect positive and negative electron signals generated by electrons or gamma rays after passing through the conversion target, thereby realizing high-resolution detection. The present invention has the characteristics of online detection, high resolution, large dynamic range, and flexible use.

Description

Technical Field

[0001] The invention relates to electron and gamma ray detection, in particular to an electron and gamma ray spectrometer based on a gradually varying magnetic field. Background Art

[0002] With the rapid development of laser technology, especially the proposal and implementation of chirped pulse amplification (CPA), the peak intensity of lasers has been continuously improved. After more than 20 years of development of high-field lasers, laser devices at home and abroad have broken through the PW limit. In recent years, a series of large scientific plans have begun to build 10PW laser devices. In 2020, the Shanghai Institute of Optics and Fine Mechanics took the lead in completing the construction and acceptance of 10PW laser devices and physical experimental platforms, and has started the construction of 100PW laser devices. An important application direction of PW-level high-field lasers is to generate gamma rays through a variety of mechanisms: high-energy electrons accelerated by strong lasers bombard high-Z targets and produce gamma rays through Bremsstrahlung; high-energy electron beams accelerated by lasers interact with secondary laser pulses to produce high-energy gamma rays through inverse Compton scattering; high-energy electrons accelerated by strong laser tail fields produce high-brightness gamma rays through cyclotron radiation under the action of the transverse electrostatic field in the tail field; when strong field lasers interact with plasma and enter the radiation-dominated region (10PW-level lasers), electrons moving in the laser field can produce extremely strong gamma radiation.

[0003] Compared with traditional gamma rays, gamma rays produced by strong field lasers have unique properties. Since strong field lasers are ultrafast in time, the gamma ray sources they produce are usually also ultrafast, generally less than picoseconds. The time resolution of commonly used gamma ray detectors, such as scintillators and semiconductor detectors, is generally in the sub-nanosecond or nanosecond range, that is, the time interval between two adjacent incident gamma photons needs to be more than nanoseconds to be distinguished. The gamma ray pulse width generated by femtosecond relativistic laser drive is short, and all gamma photons arrive at the detector almost at the same time. They will instantly produce a large number of fluorescent photons, causing "channel blockage", so these detectors cannot be used to directly measure the ultrafast gamma ray energy spectrum. The mechanisms of gamma ray interaction with matter include photoelectric effect, Compton scattering, positron-electron pair generation, photonuclear reaction, etc. The detection of ultrafast gamma rays also mainly uses the above mechanisms to achieve indirect measurement. Compton scattering is a commonly used detection method, which is mainly based on the similar energy spectrum distribution of electrons after Compton scattering and incident gamma rays. High-energy gamma rays are incident on the conversion target, and electrons are generated through Compton scattering. The electron energy spectrum is measured by a magnetic spectrometer, and the spectrum of the incident light is inferred based on the energy spectrum of the scattered electrons. This method is suitable for the detection of gamma rays below tens of MeV. Compton scattering spectrometers usually use a uniform magnetic field (Rev. Sci. Instrum. 85, 065119 (2014)) or a step-changing magnetic field (Matter Radiat. Extremes 6, 014401 (2021)) to deflect electrons. The former has a lower resolution, and the latter requires the detector to be bent to obtain a higher resolution, which is not conducive to real-time detection. The prior art (CN213635562U) proposes a permanent magnetic device that can generate a gradient magnetic field, proving that the generation of a gradient magnetic field is feasible. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of existing measurement technologies and propose an electron and gamma-ray spectrometer based on a gradient magnetic field, which can realize laser-driven ultrafast gamma-ray energy spectrum detection. The device can be used in experimental environments such as vacuum and air, and has the characteristics of online detection, high resolution, large dynamic range and flexible use.

[0005] The technical solution of the present invention is as follows:

[0006] An electron and gamma-ray spectrometer based on a gradient magnetic field is characterized in that it includes a conversion target, a shielding part, a spectrometer main part and a detector, and their positional relationship is: along the direction of gamma ray travel, they are the conversion target, the shielding part, the spectrometer main part in sequence, and the detector is inserted into the inside of the spectrometer main part.

[0007] The shielding part is composed of a plurality of lead bricks with central holes of the same diameter and a tungsten tube inserted into the central holes of the lead bricks.

[0008] The main part of the spectrometer is composed of an injection hole, a magnetic steel group, an assembly shell and a rear end collimator. The magnetic steel group generates a gradient magnetic field with linearly enhanced magnetic field strength. Under the action of the gradient magnetic field, the incident electrons are deflected, and the deflection trajectories of electrons with different energies converge on almost a straight line. The assembly shell is used to encapsulate the magnetic steel group, fix the injection hole and the rear end collimator, and has a certain magnetic field shielding and noise shielding effect. The injection hole and the rear end collimator are used for spectrometer alignment.

[0009] The detector is inserted into the main part of the spectrometer along the straight line where the convergence points of the deflection trajectories of electrons with different energies are located. The detector is composed of a detector plug-in board, an imaging board or a fluorescent screen, and the imaging board or the fluorescent screen is installed on the detector plug-in board.

[0010] The conversion target is a low-Z target material, such as LiF, C, etc., which is used to convert incident gamma rays into electrons.

[0011] The inner diameter of the tungsten tube has a variety of sizes to choose from, which are used to adjust the size of the limiting hole, and the number of lead bricks can be adjusted according to demand.

[0012] The imaging plate is mainly used for detecting electron and gamma ray energy spectra under non-repetitive laser conditions; the fluorescent screen is used together with a camera to realize real-time detection under repetitive laser conditions.

[0013] Compared with the prior art, the technical effects of the present invention are as follows:

[0014] 1. High resolution. The invention uses a gradual magnetic field to make the deflection trajectories of electrons with different energies and incident positions basically converge on a straight line, so that the entire energy spectrum detection range has high resolution.

[0015] 2. It can realize real-time detection and offline detection in vacuum or non-vacuum conditions. The detector seat can be used to place the fluorescent screen and imaging board for real-time and offline detection. When using the fluorescent screen for real-time detection, the detector seat is slotted, and the CCD camera can directly image the fluorescent screen.

[0016] 3. Large dynamic range. The present invention can detect ultrafast gamma rays and electron energy spectra from hundreds of keV to tens of MeV.

[0017] The invention can be used in experimental environments such as vacuum and air, and has the characteristics of online detection, high resolution, large dynamic range and flexible use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the electron and gamma-ray spectrometer based on a gradient magnetic field;

[0019] Figure 2 Trajectory diagram of electrons with different energies incident from different positions into a gradually changing magnetic field with a magnetic field gradient of 11 T / m;

[0020] Figure 3 Dimensions of a 20MeV electron and gamma-ray spectrometer based on a gradient magnetic field;

[0021] Figure 4 Measured magnetic field intensity gradient of a 20MeV electron and gamma-ray spectrometer based on a gradient magnetic field.

[0022] In the figure:

[0023] 1-conversion target, 2-shielding part, 3-spectrometer main part, 4-detector, 301-injection hole, 302-magnetic steel group, 303-assembly shell, 304-rear end collimator. DETAILED DESCRIPTION

[0024] In order to make the above advantages of the present invention clear and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. It should be noted that the present invention should not be limited to the following specific implementation contents, and those skilled in the art should understand the present invention from the spirit embodied in the following implementation methods, and each technical term can be understood in the broadest sense based on the spirit of the present invention.

[0025] Please refer to Figure 1 , Figure 1 It is a structural schematic diagram of the electron and gamma-ray spectrometer based on a gradient magnetic field of the present invention. As can be seen from the figure, the electron and gamma-ray spectrometer based on a gradient magnetic field of the present invention includes a conversion target 1, a shielding part 2, a spectrometer main part 3 and a detector 4, and their positional relationship is: along the direction of gamma ray travel, they are the conversion target 1, the shielding part 2, the spectrometer main part 3 in sequence, and the detector 4 is inserted into the interior of the spectrometer main part 3.

[0026] When the spectrometer is used for electron detection, the conversion target 1 does not need to be added. When used for gamma ray detection, the conversion target 1 needs to be added to convert the incident gamma rays into electrons; low-Z targets such as LiF and C are usually used. The shielding part 2 is composed of multiple lead bricks with holes and tungsten tubes, and the diameter of the tungsten tube has various sizes; according to the detection needs, the number of lead bricks can be adjusted, and tungsten tubes with different inner diameters can be selected and inserted into the lead bricks to adjust the size of the limiting hole. The main part 3 is composed of an injection hole 301, a magnetic steel group 302, an assembly shell 303 and a rear end collimator 304. During alignment, the laser pen is inserted into the rear end collimator 304, and the laser passes through the center of the main part 3 of the spectrometer from the rear end collimator 304, passes through the injection hole 301, passes through the center of the limiting hole of the shielding part 2, and hits the target point, thereby adjusting the position and direction of the spectrometer. The magnetic steel group 302 is composed of multiple magnetic steels, which can generate a magnetic field with a linearly enhanced magnetic field intensity along the incident direction. The assembly shell 303 is used to encapsulate the magnetic steel group 302, fix the injection hole 301 and the rear end collimator 304, and has a certain magnetic field shielding and noise shielding effect. When using a fluorescent screen for detection, the shielding shells on both sides need to be removed to facilitate the fluorescence generated by the positive and negative electrons hitting the fluorescent plate to be detected by the camera. The detector 4 is composed of a detector plug-in plate, an imaging plate or a fluorescent screen. The detector plug-in plate has two types: non-slotted and slotted. The non-slotted plug-in plate is used to install the imaging plate. After the signal acquisition is completed, the imaging plate is taken out and the signal is read by the imaging plate scanner; therefore, the imaging plate is suitable for non-repetitive laser conditions. The slotted plug-in plate is used to install the fluorescent screen, and the light-emitting surface of the fluorescent screen faces the slot. The camera is used to collect the fluorescence signal generated by the electrons hitting the fluorescent screen, which is suitable for real-time detection of electron and gamma-ray energy spectra under repetitive laser conditions.

[0027] See the examples Figure 3 and Figure 4:A gradient magnetic field electron and gamma ray spectrometer with an energy range of 0.2 to 20 MeV. The conversion target of the spectrometer is a carbon target. The shielding part consists of 5 lead plates with a thickness of 20 mm. The center of the lead plate is opened, and the base size of the hole is 10 mm in diameter. The center hole is equipped with a tungsten tube with an outer diameter of 10 mm, a length of 20 mm, and an inner diameter of 8, 5, 2 or 1 mm, which can be flexibly replaced as needed. Magnetic field working area (length * width * air gap): 120*192*8mm, the center magnetic field intensity gradient is 11T / m, and the high-end magnetic field intensity is 1.3T. The front injection port is a square hole with a size of 10*20mm, and the diameter of the rear collimator is 10mm. Insert the laser pen into the rear collimator, adjust the position of the spectrometer, and aim the beam at the target through the front injection port of the spectrometer. The detector is inserted into the magnetic field through a plug-in plate, and there is a plug-in fixing slot inside the magnetic field. The positions of the detectors on both sides (IP1, IP2) are: y = -0.14 + 0.81*x. The trajectory convergence point of electrons with different energies after entering the spectrometer of this embodiment is near this straight line, ensuring that the spectrometer of this embodiment has high resolution in the energy range of 0.2 to 20 MeV. The front end face of the rear-end detector IP3 is 120 mm away from the front end of the magnetic field as shown in the figure. It is used to detect electrons with energy greater than 20 MeV, and the resolution is relatively low. The spectrometer adopts a linear gradient magnetic field to achieve high-resolution detection of high-energy electrons. The volume and weight are also relatively small, and it can be moved and adjusted by one person.

[0028] Experiments show that the device of the present invention can be used in experimental environments such as vacuum and air, and has the characteristics of online detection, high resolution, large dynamic range and flexible use.

[0029] The above embodiments are only preferred embodiments of the present invention and do not limit the protection scope of the present invention. The present invention can be modified and varied in various ways. Any modification, equivalent substitution, improvement, etc. based on the design principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electron and gamma ray spectrometer based on a gradient magnetic field, characterized in that: It comprises a conversion target (1), a shielding part (2), a spectrometer main part (3) and a detector (4), wherein the positional relationship is as follows: along the advancing direction of the gamma ray, the conversion target (1), the shielding part (2) and the spectrometer main part (3) are arranged in sequence, and the detector (4) is inserted into the inside of the spectrometer main part (3); The shielding part (2) is composed of a plurality of lead bricks with center holes of the same diameter and a tungsten tube inserted into the center holes of the lead bricks; The spectrometer main body (3) is composed of an injection hole (301), a magnetic steel group (302), an assembly shell (303) and a rear collimator (304). The magnetic steel group (302) generates a gradient magnetic field with a linearly enhanced magnetic field strength. Under the action of the gradient magnetic field, incident electrons are deflected, and the deflection trajectories of electrons with different energies converge on a nearly straight line. The assembly shell (303) is used to encapsulate the magnetic steel group (302), fix the injection hole (301) and the rear collimator (304), and has a certain magnetic field shielding and noise shielding effect. The injection hole (301) and the rear collimator (304) are used for spectrometer alignment. The detector (4) is inserted into the interior of the spectrometer main body (3) along the straight line where the convergence points of the deflection trajectories of electrons with different energies are located. The detector (4) is composed of a detector plug-in board, an imaging board or a fluorescent screen, and the imaging board or the fluorescent screen is mounted on the detector plug-in board.

2. The electron and gamma ray spectrometer based on a gradient magnetic field according to claim 1, characterized in that: The conversion target (1) is a low-Z target material, used to convert incident gamma rays into electrons.

3. The electron and gamma ray spectrometer based on a gradient magnetic field according to claim 1, characterized in that: The inner diameter of the tungsten tube has a variety of sizes to choose from, which are used to adjust the size of the limiting hole, and the number of lead bricks can be adjusted according to demand.

4. The electron and gamma ray spectrometer based on a gradient magnetic field according to claim 1, characterized in that: The imaging plate is mainly used for detecting electron and gamma ray energy spectra under non-repetitive laser conditions; the fluorescent screen is used together with a camera to realize real-time detection under repetitive laser conditions.

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