Lithium-doped plastic scintillator with thermal neutron discrimination capability and preparation method thereof

Abstract

The invention provides a lithium-doped plastic scintillator with thermal neutron discrimination capability and a preparation method thereof, and relates to the technical field of radiation detection materials, the scintillator comprises a styrene monomer, a cross-linking agent divinylbenzene, and a luminescent substance 2, 2 '-divinylbenzene which are fused through a polymerization reaction, the initiator is 2, 5-diphenyloxazole, the wave shifting agent is 7-diethylamino-4-methylcoumarin, and the initiator is azodiisobutyronitrile and lithium isobutyrate. According to the invention, the problem that a common plastic scintillator does not have the thermal neutron-fast neutron-gamma pulse shape discrimination capability and is poor in thermal neutron-fast neutron-gamma pulse shape discrimination capability is solved.

Description

Technical Field

[0001] This specification relates to the field of radiation detection materials technology, and in particular to a lithium-doped plastic scintillator with thermal neutron discrimination capability and its preparation method. Background Technology

[0002] Plastic scintillator detectors are widely used as neutron detectors in fields such as nuclear power generation, nuclear medicine, security inspection, oil well logging, high-energy physics, national defense and security, and nuclear energy applications. Compared to other scintillators, plastic scintillators have advantages such as high neutron detection efficiency, fast time response, high count rate, non-toxicity, non-hygroscopicity, good radiation resistance, low cost, and the ability to be mass-produced. However, because neutron radiation fields coexist with gamma radiation, conventional plastic scintillator detectors cannot distinguish between neutron and gamma-ray signals, which can significantly affect the accuracy of neutron measurements. Plastic scintillators are mainly composed of three parts: a substrate, a primary luminescent material, and a wave-shifting agent. The principle of luminescence in plastic scintillators is that the large π electrons in organic molecules de-excite and release a large number of photons each time they are excited by ionizing radiation. Each luminescence consists of fast-decaying fluorescence and slow-decaying phosphorescence. The ratio of fluorescence to phosphorescence determines the decay time of each luminescence. The luminescence intensity is proportional to the radiation energy. The photomultiplier device and subsequent circuitry convert the collected photons into pulse waveform electrical signals with time and amplitude information.

[0003] Pulse shape discrimination (PSD) capability is commonly found in liquid scintillators or organic crystals. It is based on the fact that different types of ionizing radiation have different ionization modes in the scintillator, resulting in different luminescence decay times and different pulse waveform fall rates. Different types of ionizing radiation can be distinguished by differentiating the pulse fall edges.

[0004] Thermal neutron detection methods are limited, typically employing detectors containing high thermal neutron cross-section isotopes such as He-3, B-10, and Li-6. Higher isotope content leads to higher thermal neutron detection efficiency. Plastic scintillators with pulse shape discrimination require a primary luminescent material (PPO) mass percentage of at least 15% to ensure sufficiently close intermolecular spacing and enhance delayed fluorescence emission. Higher primary luminescent material content results in better pulse shape discrimination. Therefore, doping plastic scintillators with lithium compounds can impart thermal neutron discrimination. Furthermore, since the secondary particles generated by the Li-6 reaction excite more particles in the plastic than those generated by the B-10 reaction, higher light output, stronger neutron signal, easier detection, and better signal-to-noise ratio can be achieved, contributing to a lower detection threshold and improved detection efficiency. Summary of the Invention

[0005] To address the aforementioned shortcomings in the prior art, this invention provides a lithium-doped plastic scintillator with thermal neutron discrimination capability and its preparation method, which solves the problems of ordinary plastic scintillators lacking thermal neutron-fast neutron-gamma pulse shape discrimination capability and having poor thermal neutron-fast neutron-gamma pulse shape discrimination capability.

[0006] To achieve the aforementioned objectives, the present invention employs the following technical solution: a lithium-doped plastic scintillator with thermal neutron discrimination capability, comprising: The polymer consists of styrene monomer, crosslinking agent divinylbenzene, luminescent material 2,5-diphenyloxazole, wave-shifting agent 7-diethylamino-4-methylcoumarin, initiator azobisisobutyronitrile, and lithium isobutyrate.

[0007] High yield and high discrimination capability coexist: Under the action of the crosslinking agent, the successful doping of high-concentration PPO results in excellent pulse shape discrimination (FoM value) performance of the scintillator. Superior physical properties: The introduction of the crosslinking network significantly improves the hardness, heat distortion temperature, and durability of the scintillator. The product maintains shape stability and normal operation even at 60℃, overcoming the shortcomings of traditional highly doped scintillators being soft and easily deformable. Thermal neutron detection capability: Based on the 6Li(n,α)3H reaction, the incorporated lithium element enables the scintillator to detect thermal neutrons. By optimizing the doping concentration (2%), thermal neutron clusters that are well separated from fast neutrons and gamma rays can be clearly observed in the PSD spectrum.

[0008] Further, the crosslinking agent divinylbenzene has a volume percentage of 2.5% to 5%, the lithium salt lithium isobutyrate has an added mass of 1% to 3% of the styrene monomer mass, the luminescent material is 2,5-diphenyloxazole (PPO), which has a mass percentage of 20% to 40% of the styrene monomer mass, the wave-shifting agent is 7-diethylamino-4-methylcoumarin, which has a mass percentage of 0.1% to 0.5% of the styrene monomer mass, and the initiator is azobisisobutyronitrile (AIBN), which has a mass percentage of 0.1% to 0.2% of the styrene monomer mass.

[0009] This invention provides a method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability, comprising: S1: Styrene monomer and crosslinking agent divinylbenzene are purified by vacuum distillation to remove polymerization inhibitors, and purified styrene monomer and purified divinylbenzene monomer are obtained. S2: The purified styrene monomer and the purified divinylbenzene monomer are passed through dry nitrogen to remove oxygen, and styrene monomer and divinylbenzene monomer after removing oxygen are obtained respectively. S3: In an oxygen-free glove box, the luminescent material, wave-shifting agent, initiator, lithium salt, and styrene monomer and divinylbenzene monomer (after removing oxygen) are mixed in a certain proportion to obtain a mixed solution. In this process, the lithium salt must first be dissolved in isobutyric acid, stirred and mixed thoroughly, and then mixed with other components. S4: The mixed solution is subjected to ultrasonic treatment under heating conditions to homogenize it and start prepolymerization to obtain the ultrasonicated solution; S5: Seal the ultrasonicated solution and carry out a programmed temperature-increasing thermal polymerization reaction in an oxygen-free environment to obtain the polymerization result; S6: Based on the polymerization results, the obtained solid scintillator is cut and polished to a predetermined shape to obtain a polished scintillator; S7: The polished scintillator is encapsulated using polytetrafluoroethylene raw material tape to obtain a lithium-doped plastic scintillator with thermal neutron discrimination capability, thus completing the preparation of the lithium-doped plastic scintillator with thermal neutron discrimination capability.

[0010] Further, S1 includes: Styrene and divinylbenzene were purified by vacuum distillation. Styrene and divinylbenzene were placed in a rotary evaporator condenser in sequence, and the styrene monomer and crosslinking agent divinylbenzene were purified by vacuum distillation using a water bath heating pot. The rotary evaporator was evacuated to a vacuum by a vacuum pump and the polymerization inhibitor was removed by rotating the rotary flask to obtain purified styrene and divinylbenzene monomers.

[0011] Further, S5 includes: The ultrasonically treated solution was sealed and subjected to a programmed temperature-increasing thermal polymerization reaction in an oxygen-free environment. The temperature was maintained at the first preset temperature for a certain period of time, then slowly increased to the second preset temperature and maintained for a period of time. Finally, the temperature was cooled down to room temperature to obtain the polymerization result.

[0012] This invention provides a method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability. By adding an appropriate amount of crosslinking agent, the plastic scintillator simultaneously possesses good hardness, plasticity, and light transmittance, and significantly increases the solubility of the first luminescent material. By selecting a suitable second luminescent material based on the principle of molecular luminescence, excellent thermal neutron-fast neutron-gamma pulse shape discrimination effect is achieved. The energy detection range of neutrons and gamma rays that can be discriminated is from tens of keV to several MeV, while still retaining the advantages of plastic scintillators. This overcomes the problems of ordinary plastic scintillators lacking thermal neutron-fast neutron-gamma pulse shape discrimination capability and having poor thermal neutron-fast neutron-gamma pulse shape discrimination capability. It has a shape discrimination PSD capability equivalent to or better than that of commercially available EJ-276 plastic scintillator. Attached Figure Description

[0013] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein: Figure 1 This is an exemplary flowchart illustrating a method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability according to some embodiments of this specification; Figure 2 This is an exemplary schematic diagram of a lithium-doped plastic scintillator with thermal neutron discrimination capability, as shown in some embodiments of this specification. Figure 3 This is an exemplary schematic diagram of a Cs-137 light yield test according to some embodiments of this specification; Figure 4 This is an exemplary schematic diagram illustrating the fast neutron-thermal neutron-gamma signal PSD discrimination capability according to some embodiments of this specification; Figure 5 This is an exemplary schematic diagram illustrating the use of FOM factor evaluation according to some embodiments of this specification. Detailed Implementation

[0014] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0015] Example Figure 1 This is an exemplary flowchart illustrating a method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability, according to some embodiments of this specification. Figure 1 As shown, the process includes the following steps. In some embodiments, the process may be executed by a processor.

[0016] Figure 2 This is an exemplary schematic diagram of a lithium-doped plastic scintillator with thermal neutron discrimination capability, shown according to some embodiments of this specification. Figure 2 As shown, a lithium-doped plastic scintillator with thermal neutron discrimination capability comprises: styrene monomer fused by polymerization reaction, crosslinking agent divinylbenzene, luminescent material 2,5-diphenyloxazole (PPO), wave-shifting agent 7-diethylamino-4-methylcoumarin, initiator azobisisobutyronitrile (AIBN), and lithium isobutyrate.

[0017] This invention discloses a lithium-doped plastic scintillator with excellent thermal neutron-fast neutron-gamma ray pulse shape discrimination (PSD) capability. The plastic scintillator uses styrene as a monomer, adds divinylbenzene as a crosslinking agent to form a polymer substrate, and is doped with a high concentration of the luminescent material 2,5-diphenyloxazole (PPO), a wave-shifting agent, and lithium salt. By introducing the crosslinking agent, this invention successfully solves the problems of softening and turbidity in plastic scintillators caused by high-concentration luminescent material and lithium salt doping, significantly improving the physical stability, heat resistance, and solubility of the luminescent material. The prepared lithium-doped plastic scintillator exhibits high light yield and excellent thermal neutron-fast neutron-gamma ray pulse shape discrimination (PSD) capability. Its quality factor (FOM) is significantly superior to the commercial product EJ270 over a wide energy range, making it particularly suitable for high-precision detection of neutron-gamma mixed radiation fields.

[0018] In a lithium-doped plastic scintillator with thermal neutron discrimination capability, the crosslinking agent divinylbenzene accounts for 2.5% to 5% by volume, the lithium salt lithium isobutyrate is added at 1% to 3% of the mass of styrene monomer, the luminescent material is 2,5-diphenyloxazole (PPO) at 20% to 40% of the mass of styrene monomer, the wave-shifting agent is 7-diethylamino-4-methylcoumarin at 0.1% to 0.5% of the mass of styrene monomer, and the initiator is azobisisobutyronitrile (AIBN) at 0.1% to 0.2% of the mass of styrene monomer.

[0019] In some embodiments, the processor can use a styrene-divinylbenzene crosslinked polymer as a substrate, allowing the doping concentration of the luminescent material PPO to be as high as 20%-40% (preferably 36%), while incorporating an isobutyric acid solution containing 1%-5% (preferably 2%) lithium isobutyrate, with a mass ratio of isobutyric acid solution to isobutyric acid of 4:1. This formulation ensures high thermal neutron detection efficiency while maintaining the excellent physical properties of the material through the crosslinked structure.

[0020] Preferably, the proportion of lithium isobutyrate is changed to 2% and the proportion of isobutyric acid is changed to 8% during operation.

[0021] Preferably, the proportion of lithium isobutyrate is changed to 2.5% and the proportion of isobutyric acid is changed to 10% during operation.

[0022] like Figure 2As shown, from right to left, these correspond to lithium isobutyrate doping amounts of 1.5% wt., 2% wt., and 2.5 wt., respectively. After the radiation interacts with the scintillator, fluorescence is generated. The fluorescent photons interact with the photomultiplier tube (PMT) to generate an electrical signal. Therefore, the maximum amplitude of the electrical signal is proportional to the incident particle energy and the fluorescence yield. In the experiment, we took the half-height of the falling edge of the Compton plateau region as the standard for measuring the light yield, as indicated by the gray dashed line in the figure. To test the effect of the lithium doping content on the gamma spectrum, this invention tested the pulse amplitude spectra of lithium-doped plastic scintillators at 1.5% wt., 2% wt., and 2.5% wt. under the same conditions using a 137Cs radiation source. The results are shown below. Figure 3 It can be seen that as the concentration of the wave shifter increases, the relative light yield gradually decreases. The change is not significant at doping ratios of 1.5% wt. and 2% wt., but a significant decrease occurs at 2.5% wt. Therefore, if it is necessary to increase the lithium content while maintaining the light yield, the optimal lithium isobutyrate doping ratio is 2% wt.

[0023] In some embodiments, the processor may employ a strict oxygen-free operation, heating and ultrasonic homogenization, and programmed temperature-increasing thermal polymerization process. A reasonable mixture of solvents ensures the uniform distribution of each component, especially the lithium salt, in the polymer matrix, thereby obtaining an optically uniform and stable scintillator.

[0024] S1: Styrene monomer and crosslinking agent divinylbenzene are purified by vacuum distillation to remove polymerization inhibitors, resulting in purified styrene monomer and purified divinylbenzene monomer.

[0025] In some embodiments, the processor can perform vacuum distillation of styrene and divinylbenzene. Styrene and divinylbenzene are placed sequentially in a rotary evaporator condenser, and a water bath is used for heating to purify the styrene monomer and crosslinking agent divinylbenzene through vacuum distillation. A vacuum pump is used to evacuate the rotary evaporator to a vacuum level, and the rotating flask is rotated to remove the polymerization inhibitor, resulting in purified styrene and divinylbenzene monomers. Specifically, the processor can perform vacuum distillation of styrene and divinylbenzene. Styrene and divinylbenzene are placed sequentially in a rotary evaporator condenser, and a water bath is used for heating and distillation purification. During the purification process, the rotary evaporator is first evacuated to a vacuum level, and the rotating flask is rotated at a speed of 20 rpm. The temperature of the water bath is then set to 50°C–80°C, thereby obtaining pure styrene and divinylbenzene without the polymerization inhibitor through distillation purification in a vacuum environment.

[0026] S2: The purified styrene monomer and the purified divinylbenzene monomer are passed through dry nitrogen to remove oxygen, and styrene monomer and divinylbenzene monomer after removing oxygen are obtained respectively.

[0027] In some embodiments, the processor can pour the purified styrene and divinylbenzene monomers into an anaerobic flask and purge oxygen with dry nitrogen for 40 minutes. Simultaneously, the glove box valve is opened, and nitrogen is introduced into the glove box until the oxygen content inside the glove box is below 1%, at which point nitrogen introduction is stopped and the valve is closed.

[0028] S3: In an oxygen-free glove box, the luminescent material, wave-shifting agent, initiator, lithium salt, and styrene monomer and divinylbenzene monomer after removing oxygen are mixed in a certain proportion to obtain a mixed solution. In this process, the lithium salt must first be dissolved in isobutyric acid, stirred and mixed thoroughly, and then mixed with other components.

[0029] In some embodiments, the processor can sequentially place the pharmaceutical product (including the luminescent substance 2,5-diphenyloxazole, the wave-shifting agent 7-diethylamino-4-methylcoumarin, the cross-linking agent divinylbenzene, the initiator azobisisobutyronitrile, and the lithium-containing compound) and the styrene that has been purged with nitrogen in step 2) into the transition chamber of the glove box after slightly opening the bottle cap to balance the pressure. The transition chamber is first evacuated to a vacuum to remove the original oxygen in the bottle, and then nitrogen is introduced until the pressure is balanced before transferring the pharmaceutical product into the glove box.

[0030] In some embodiments, the processor can weigh and bottle the pharmaceuticals in a glove box. The mass of the pharmaceuticals is calculated according to the following criteria: the volume of the plastic scintillator to be made by styrene and divinylbenzene is directly calculated based on the density of styrene and divinylbenzene. In this example, each pharmaceutical is added according to the mass ratio of styrene, and the proportions of each pharmaceutical are as follows: divinylbenzene 5.2%, 2,5-diphenyloxazole 20%-40%, 7-diethylamino-4-methylcoumarin 0.1%-0.5%, initiator azobisisobutyronitrile 0.1%-0.2%, divinylbenzene 1-10%, lithium isobutyrate 1.5%, and isobutyric acid 6%.

[0031] S4: The mixed solution is subjected to ultrasonic treatment under heating conditions to homogenize it and start prepolymerization to obtain the ultrasonicated solution.

[0032] In some embodiments, the ultrasonic treatment temperature is 45°C to 55°C, and the treatment time is 30 minutes.

[0033] S5: Seal the ultrasonicated solution and carry out a programmed temperature-increasing thermal polymerization reaction in an oxygen-free environment to obtain the polymerization result.

[0034] In some embodiments, after weighing, lithium isobutyrate is first poured into isobutyric acid and mixed until fully dissolved. Then, the solution is mixed with the remaining reagents and solutions, and ultrasonically heated to 50°C for prepolymerization. Simultaneously, the oven is preheated to 50°C. After ultrasonic heating is completed, the oven is directly placed in the solution, vacuumed, and then nitrogen is introduced, repeated at least five times until the oxygen content is below 1%. Finally, heating is performed in a vacuum environment. During the heating process, the oven program is set as follows: after the initial oven temperature reaches 50°C, it is first maintained at 50°C for 1 day, then slowly increased to 70°C over 5 days and maintained for 4 days. After maintaining 70°C for 3 days, cooling can begin, preferably at a rate of 2°C / h to room temperature.

[0035] In some embodiments, the processor can seal the ultrasonicated solution and perform a programmed temperature-increase thermal polymerization reaction in an anaerobic environment. The solution is maintained at a first preset temperature for a certain period, then slowly increased to a second preset temperature and maintained for a period thereafter, and finally cooled to room temperature to obtain the polymerization result. For example, the processor can seal the ultrasonicated solution and perform a programmed temperature-increase thermal polymerization reaction in an anaerobic environment, maintaining the temperature at 50°C for one day, then slowly increasing the temperature to 70°C over five days and maintaining it for four days, and finally cooling to room temperature to obtain the polymerization result.

[0036] S6: Based on the polymerization results, the obtained solid scintillator is cut and polished to a predetermined shape to obtain a polished scintillator.

[0037] In some embodiments, the processor may remove the plastic scintillator from the container, cut and polish it to the required size, and then encapsulate it with PTFE raw material tape until only one bottom surface is exposed to prevent fogging.

[0038] S7: The polished scintillator is encapsulated using polytetrafluoroethylene raw material tape to obtain a lithium-doped plastic scintillator with thermal neutron discrimination capability, thus completing the preparation of the lithium-doped plastic scintillator with thermal neutron discrimination capability.

[0039] In some embodiments, to quantify the quality of the PSD value, the processor can introduce a Figure of Merit (FOM) factor to quantitatively evaluate the separation quality of n-γ discrimination. The FOM factor is the difference between the peak positions of the neutron and γ peaks divided by the sum of the full width at half maximum (FWHM) of the two peaks.

[0040] In the formula These are the central peak positions of the neutron peak and the γ peak, respectively, obtained from double Gaussian fitting. The full width at half maximum (FWHM) of the neutron peak and the gamma peak are measured separately; the larger the FWHM value, the higher the n-γ discrimination ability.

[0041] In some embodiments, the present invention conducted n-γ discrimination performance tests on an americium-beryllium neutron source platform, and the results are as follows: Figure 4 As shown in the figure. Serial number ① corresponds to 1.5% wt., serial number ② corresponds to 2% wt., and serial number ③ corresponds to 2.5% wt. The figure clearly shows that the PSD diagram has two energy bands: the upper band is the neutron band, and the lower band is the γ band. The part circled in red, located near the energy of 350 keVee, is the thermal neutron cluster. As can be seen from the figure, the thermal neutron cluster technology becomes more pronounced with increasing lithium isobutyrate concentration. The FoM value is a performance parameter used to determine the n-γ discrimination ability of plastic scintillators. A higher FoM value in the low-energy range indicates better n-γ discrimination ability of the plastic scintillator. This invention selects the low-energy region of 100 keVee to 400 keVee for calculation, with a step size of 100 keVee. The results are as follows. Figure 5 As shown in the figure, the results indicate that the n-γ discrimination ability decreases with increasing lithium isobutyrate concentration, but good discrimination performance is still maintained.

[0042] In some embodiments of this specification, a method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability is provided. By adding an appropriate amount of crosslinking agent, the plastic scintillator simultaneously possesses good hardness, plasticity, and light transmittance, and also significantly increases the solubility of the first luminescent material. By selecting a suitable second luminescent material based on the principle of molecular luminescence, a good thermal neutron-fast neutron-gamma pulse shape discrimination effect is obtained. The energy detection range of neutrons and gamma rays that can be discriminated is from tens of keV to several MeV, while still retaining the advantages of plastic scintillators. This overcomes the problems of ordinary plastic scintillators lacking thermal neutron-fast neutron-gamma pulse shape discrimination capability and having poor thermal neutron-fast neutron-gamma pulse shape discrimination capability. It has a shape discrimination PSD capability equivalent to or better than that of commercially available EJ-276 plastic scintillators.

Claims

1. A lithium-doped plastic scintillator with thermal neutron discrimination capability, characterized in that, include: The polymer consists of styrene monomer, crosslinking agent divinylbenzene, luminescent material 2,5-diphenyloxazole, wave-shifting agent 7-diethylamino-4-methylcoumarin, initiator azobisisobutyronitrile, and lithium isobutyrate.

2. The lithium-doped plastic scintillator with thermal neutron discrimination capability according to claim 1, characterized in that, The crosslinking agent divinylbenzene has a volume percentage of 2.5% to 5%, the lithium salt lithium isobutyrate has an added mass of 1% to 3% of the styrene monomer mass, the luminescent material is 2,5-diphenyloxazole (PPO), which has a mass percentage of 20% to 40% of the styrene monomer mass, the wave-shifting agent is 7-diethylamino-4-methylcoumarin, which has a mass percentage of 0.1% to 0.5% of the styrene monomer mass, and the initiator is azobisisobutyronitrile (AIBN), which has a mass percentage of 0.1% to 0.2% of the styrene monomer mass.

3. A method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability, applied to the lithium-doped plastic scintillator with thermal neutron discrimination capability as described in any one of claims 1 to 2, characterized in that, include: S1: Styrene monomer and crosslinking agent divinylbenzene are purified by vacuum distillation to remove polymerization inhibitors, and purified styrene monomer and purified divinylbenzene monomer are obtained. S2: The purified styrene monomer and the purified divinylbenzene monomer are passed through dry nitrogen to remove oxygen, and styrene monomer and divinylbenzene monomer after removing oxygen are obtained respectively. S3: In an oxygen-free glove box, the luminescent material, wave-shifting agent, initiator, lithium salt, and styrene monomer and divinylbenzene monomer (after removing oxygen) are mixed in a certain proportion to obtain a mixed solution. In this process, the lithium salt must first be dissolved in isobutyric acid, stirred and mixed thoroughly, and then mixed with other components. S4: The mixed solution is subjected to ultrasonic treatment under heating conditions to homogenize it and start prepolymerization to obtain the ultrasonicated solution; S5: Seal the ultrasonicated solution and carry out a programmed temperature-increasing thermal polymerization reaction in an oxygen-free environment to obtain the polymerization result; S6: Based on the polymerization results, the obtained solid scintillator is cut and polished to a predetermined shape to obtain a polished scintillator; S7: The polished scintillator is encapsulated using polytetrafluoroethylene raw material tape to obtain a lithium-doped plastic scintillator with thermal neutron discrimination capability, thus completing the preparation of the lithium-doped plastic scintillator with thermal neutron discrimination capability.

4. The method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability according to claim 3, characterized in that, S1 includes: Styrene and divinylbenzene were purified by vacuum distillation. Styrene and divinylbenzene were placed in a rotary evaporator condenser in sequence, and the styrene monomer and crosslinking agent divinylbenzene were purified by vacuum distillation using a water bath heating pot. The rotary evaporator was evacuated to a vacuum by a vacuum pump and the polymerization inhibitor was removed by rotating the rotary flask to obtain purified styrene and divinylbenzene monomers.

5. The method for preparing a lithium-doped plastic scintillator with thermal neutron discrimination capability according to claim 3, characterized in that, S5 includes: The ultrasonically treated solution was sealed and subjected to a programmed temperature-increasing thermal polymerization reaction in an oxygen-free environment. The temperature was maintained at the first preset temperature for a certain period of time, then slowly increased to the second preset temperature and maintained for a period of time. Finally, the temperature was cooled down to room temperature to obtain the polymerization result.

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