4-hydroxybenzoic acid methyl ester organic single crystal and preparation method and application thereof

Abstract

The application discloses a kind of 4-methyl 4-hydroxybenzoate organic single crystals and preparation method and application thereof, and relates to the technical field of organic crystal.The method comprises uniformly dispersing 4-methyl 4-hydroxybenzoate polycrystal material in acetone, then removing impurities and insoluble substances by filtration to obtain a filtered solution;the filtered solution is placed at 0-5℃ for 12-48 hours to obtain 4-methyl 4-hydroxybenzoate organic single crystals.The application effectively overcomes the problems of poor crystalline quality, small crystal size, complex process and high equipment requirement in the growth of existing 4MHB crystals by combining low-temperature solvent evaporation method with low-temperature seed crystal method, thereby realizing the growth of large-size and high-quality 4MHB single crystals.

Description

Technical Field

[0001] This invention relates to the field of organic crystal technology, specifically to an organic single crystal of methyl 4-hydroxybenzoate, its preparation method, and its application. Background Technology

[0002] In recent years, fast neutron detection technology has received widespread attention for its applications in nuclear energy, radiation protection, and medical imaging. However, existing neutron detectors still face some challenges, particularly in meeting the need for efficient and accurate detection of fast neutrons. Fast neutron detection typically relies on the interaction between materials and neutrons, detecting secondary particles (such as recoil protons and electrons). Ideal detection materials should possess high hydrogen density, low dark current, good charge carrier mobility, fast response speed, and high radiation stability.

[0003] Organic semiconductor materials, due to their high hydrogen density and low manufacturing cost, have shown great application potential in radiation detection, especially in fast neutron detection. Methyl 4-hydroxybenzoate (4MHB), as a novel organic semiconductor material, possesses a high hydrogen density (2 × 10⁻⁶). 22 n·cm -3 It exhibits excellent performance in fast neutron detection. Furthermore, the 4MHB single crystal possesses a high carrier mobility (μ=15.62 cm⁻¹). 2 ·V -1 ·s -1 ) and low dark current (less than 10 at 100 V) -12 A) It also has good radiation stability, showing great potential as a fast neutron detection material.

[0004] Increasing the size of 4MHB single crystals helps improve neutron detection efficiency, but as the crystal size increases, internal defects also increase, affecting electrical transport performance. Currently, common 4MHB single crystal growth methods include the Czochralski method, physical vapor transport (PVT), slow cooling, and solvent evaporation. While the Czochralski method can grow single crystals with a maximum diameter of 25 mm, the crystal quality is poor and cannot meet the requirements of high-performance detectors. The PVT method requires precise control of growth conditions, involves complex equipment operation, has a long growth cycle, and struggles to stably grow large-size, high-quality single crystals. The slow cooling method successfully grew crystals with dimensions of 45×42×62 mm by suspending the seed crystal. 3 Large-sized single crystals can be grown, but crystallization defects are easily generated during the cooling process, resulting in low crystal quality. The solvent evaporation method uses acetone as a solvent at room temperature to grow centimeter-sized single crystals. Although it can obtain large-sized single crystals, its quality has significant problems, with many macroscopic defects and ultraviolet transmittance of less than 70%, failing to meet the high-quality standard.

[0005] Therefore, in order to realize the widespread application of 4MHB single crystals in fields such as fast neutron detection, it is urgent to develop a method for growing large-size, high-quality 4MHB single crystals stably. Summary of the Invention

[0006] To address the shortcomings of the aforementioned background technology, this invention primarily solves the problems of low crystal quality, small crystal size, complex processes, and high requirements for crystal growth equipment in existing 4MHB crystal growth processes. This invention provides an organic single crystal of methyl 4-hydroxybenzoate, its preparation method, and its applications. This method, through low-temperature solvent evaporation and low-temperature seed crystal methods, effectively overcomes problems such as poor crystal quality and uncontrollable growth, achieving large-size, high-quality 4MHB single crystal growth.

[0007] The first objective of this invention is to provide a method for preparing organic single crystals of methyl 4-hydroxybenzoate, comprising the following steps:

[0008] 4-hydroxybenzoate polycrystalline material was uniformly dispersed in acetone, and then filtered to remove impurities and insoluble matter, resulting in a filtered solution.

[0009] The filtered solution was left to stand at 0-5℃ for 12-48 hours to obtain organic single crystals of methyl 4-hydroxybenzoate.

[0010] Preferably, the ratio of the methyl 4-hydroxybenzoate polycrystalline material to the acetone is 2.0~2.5 g: 10~15 mL.

[0011] Preferably, the filtered solution is sealed through a sealing membrane, and after creating pores in the sealing membrane, it is allowed to stand.

[0012] Preferably, the ratio of the methyl 4-hydroxybenzoate polycrystalline material to the acetone is 8.85~9.0 g: 30~32 mL.

[0013] Preferably, the filtered solution is sealed and then allowed to stand.

[0014] After settling, it also includes:

[0015] Select a defect-free seed crystal, fix it at the bottom of the container, pour in the solution after it has settled, seal it with a sealing film, and place it in the growth device again to obtain a large-sized organic single crystal of methyl 4-hydroxybenzoate.

[0016] Preferably, during filtration, an organic filter head with a pore size of 0.22 μm is used to filter the solution to remove impurities and insoluble substances.

[0017] Preferably, the methyl 4-hydroxybenzoate polycrystalline material is obtained by purifying methyl 4-hydroxybenzoate powder raw material three times. Each purification step includes: soaking the methyl 4-hydroxybenzoate raw material in petroleum ether, shaking and discarding the petroleum ether, heating it to 55~60°C on a heating table, evaporating it to dryness, and then dissolving it in acetone and filtering, drying and recrystallizing it.

[0018] The second objective of this invention is to provide an organic single crystal of methyl 4-hydroxybenzoate, wherein the transmittance of the single crystal in the ultraviolet-visible-near-infrared band above 400 nm is as high as 90%.

[0019] The third objective of this invention is to provide an application of methyl 4-hydroxybenzoate organic single crystal in fast neutron detection.

[0020] Preferably, methyl 4-hydroxybenzoate organic single crystals are used to detect fast neutrons with different fluxes, achieving a sensitivity of 6.19 cps·nv. -1 .

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides an organic single crystal of methyl 4-hydroxybenzoate, its preparation method, and its applications. Acetone is used as the solvent in this invention. Acetone has moderate solubility, which effectively controls crystallite stacking, and its relatively fast evaporation rate facilitates precise control of the crystal growth process, ultimately achieving efficient preparation of large-size, high-quality single crystals. Compared with existing technologies, the growth method of this invention is simple and economical, and can obtain high-performance single crystals while reducing production costs.

[0023] This invention employs a solvent evaporation method combined with a low-temperature seed crystal method. By adjusting the solution to near saturation, partial surface re-dissolves the seed crystal. At this point, the seed crystal acts as a template, promoting uniform crystal growth. This effectively avoids defects caused by excessively high nucleation rates or excessively rapid growth rates in traditional methods, thus ensuring stable crystal growth and ultimately obtaining high-quality, large-size 4MHB single crystals.

[0024] Furthermore, the detector based on this technology shows great potential in the field of radiation detection. It can effectively detect neutrons, possesses excellent fast neutron energy identification capabilities, and its response to neutron sources is verified through experiments and simulated spectra. It exhibits high linearity to different fluxes of neutrons, with a sensitivity of 6.19 cps·nv. -1 It can be used for fast neutron flux testing. Attached Figure Description

[0025] Figure 1 The growth process for 4MHB crystals.

[0026] Figure 2This is a constant-temperature ice-water bath apparatus for seed crystal growth.

[0027] Figure 3 These are seed crystals and single crystals after growth is complete.

[0028] Figure 4 4MHB crystals grown under different conditions: (a) 0℃, 0.20 g / ml; (b) 30℃, 0.20 g / ml; (c) 15℃, 0.20 g / ml; (d) -5℃, 0.20 g / ml; (e) 0℃, 0.10 g / ml; (f) 0℃, 0.30 g / ml.

[0029] Figure 5 The ultraviolet-visible-near-infrared transmission spectrum of a 4MHB single crystal is shown.

[0030] Figure 6 The X-ray diffraction pattern is for a 4MHB single crystal.

[0031] Figure 7 Experimental neutron energy spectrum for the 4MHB detector: (a) Background spectrum, alpha particle energy spectrum and neutron energy spectrum under the same test conditions; (b) Comparison of simulated spectrum and experimental spectrum.

[0032] Figure 8 The results represent the linear response characterization of the 4MHB detector. Detailed Implementation

[0033] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0034] This invention provides a method for preparing large-size methyl 4-hydroxybenzoate (4MHB) organic semiconductor single crystals using a combination of low-temperature solvent evaporation and low-temperature seed crystal growth, and its applications. This method aims to solve the problems of poor crystal quality, small crystal size, complex processes, and high equipment requirements in existing 4MHB crystal growth processes. By controlling the solution saturation state, temperature, and evaporation rate, this method successfully achieves the preparation of large-size, high-quality 4MHB single crystals. Based on this single crystal, direct detection of fast neutrons was successfully achieved, exhibiting excellent energy identification and linear response capabilities, providing a new technical solution for the field of fast neutron detection.

[0035] This invention achieves large-size and high-quality 4MHB single crystal growth through a combination of low-temperature solvent evaporation and low-temperature seed crystal methods. The method involves dissolving 4MHB polycrystalline material in acetone and filtering it, followed by low-temperature evaporation crystallization and seed crystal-induced growth to obtain a large-size single crystal. Detectors based on this 4MHB single crystal exhibit excellent energy recognition capability and linear response in fast neutron detection, with a sensitivity as high as 6.19 cps·nv. -1 .

[0036] The first aspect of this invention provides a method for preparing organic single crystals of methyl 4-hydroxybenzoate, comprising the following steps:

[0037] 4-hydroxybenzoate polycrystalline material was uniformly dispersed in acetone, and then filtered to remove impurities and insoluble matter, resulting in a filtered solution.

[0038] The filtered solution was left to stand at 0-5℃ for 12-48 hours to obtain organic single crystals of methyl 4-hydroxybenzoate.

[0039] The ratio of the polycrystalline 4-hydroxybenzoate to the acetone is 2.0~2.5 g: 10~15 mL.

[0040] The filtered solution is sealed through a sealing membrane, and pores are made in the sealing membrane before it is allowed to stand.

[0041] According to the present invention, the ratio of the polycrystalline 4-hydroxybenzoate to the acetone is 8.85~9.0 g: 30~32 mL.

[0042] After the filtered solution is sealed, it is allowed to stand; after standing, the process also includes:

[0043] Select a defect-free seed crystal, fix it at the bottom of the container, pour in the solution after it has settled, seal it with a sealing film, and place it in the growth device again to obtain a large-sized organic single crystal of methyl 4-hydroxybenzoate.

[0044] During filtration, an organic filter head with a pore size of 0.22 μm is used to filter the solution to remove impurities and insoluble substances.

[0045] The polycrystalline 4-hydroxybenzoate (4MHB) is obtained by purifying 4-hydroxybenzoate powder raw material three times. Each purification step includes: soaking the 4-hydroxybenzoate raw material in petroleum ether, shaking and discarding the petroleum ether, heating it to 55~60°C on a heating table, evaporating it to dryness, and then dissolving it in acetone and filtering, drying and recrystallizing it.

[0046] The purification process specifically includes: weighing 20-25 g of methyl tetrahydroxybenzoate powder with a purity ≥99.0%, soaking it thoroughly in petroleum ether (AR ≥99.0%), shaking for 20 seconds, discarding the petroleum ether, and placing the raw material on a heating table, heating at 55-60℃ for 10 minutes, evaporating to dryness, and then drying. Next, using 100-120 mL of acetone with a purity AR ≥99.7% as a solvent, adding the raw material to the acetone, and stirring magnetically to completely dissolve it, followed by filtration, drying, and recrystallization.

[0047] An exemplary method for preparing an organic single crystal of methyl 4-hydroxybenzoate includes:

[0048] Weigh 2.0~2.5 g of 4MHB polycrystalline material, add 10~15 mL of acetone, and stir with a magnetic stirrer until the 4MHB is completely dissolved.

[0049] The solution was filtered using an organic filter head with a pore size of 0.22 μm to remove impurities and insoluble matter, resulting in a filtered solution.

[0050] Wrap the filtered solution in plastic wrap and tie it tightly with a rubber band, making two small holes. Place it in the refrigerator and let it stand for 36-48 hours to allow the acetone to slowly evaporate and the solution to gradually reach a supersaturated state. 4MHB crystals will precipitate out during this process.

[0051] The refrigerator temperature is 0~5℃ to ensure that the solution evaporates slowly during the standing process, promoting the effective growth of crystals.

[0052] An exemplary method for preparing an organic single crystal of methyl 4-hydroxybenzoate includes:

[0053] Weigh 8.85~9.0 g of 4MHB polycrystalline material, add 30~32 mL of acetone, and stir with a magnetic stirrer until the 4MHB is completely dissolved;

[0054] The solution was filtered using an organic filter head with a pore size of 0.22 μm to remove impurities and insoluble matter.

[0055] Transfer the filtered solution to a sealed container and keep it in a refrigerator for 12-16 hours; the temperature should be 0-5℃.

[0056] A defect-free seed crystal was selected, fixed at the bottom of a beaker, and the solution after heat preservation was slowly poured in. The beaker was then quickly sealed with a sealing film and placed back into the growth device to finally obtain a large-size and high-quality 4MHB single crystal.

[0057] The filtration step, which takes place after magnetic stirring, is performed by combining a syringe booster and an organic filter tip to ensure that impurities and insoluble substances in the solution are completely removed.

[0058] The refrigerator temperature is set to 0~5℃ to ensure that the solution evaporates slowly during the standing process, promoting the effective growth of crystals.

[0059] The second aspect of the present invention provides an organic single crystal of methyl 4-hydroxybenzoate, wherein the transmittance of the single crystal in the ultraviolet-visible-near-infrared band above 400 nm is as high as 90%.

[0060] The molecular formula of the 4MHB organic crystal is C8H8O3, and its structural formula is:

[0061] .

[0062] A third aspect of this invention provides an application of methyl 4-hydroxybenzoate organic single crystals in fast neutron detection. Specifically, the methyl 4-hydroxybenzoate organic single crystals are used to detect fast neutrons with different fluxes, achieving a sensitivity of 6.19 cps·nv. -1 The 4MHB single crystal is used for the direct detection of fast neutrons and has excellent energy identification and linear response capabilities.

[0063] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0064] Example 1

[0065] See Figure 1 As shown, a method for preparing methyl 4-hydroxybenzoate seed crystals includes the following steps:

[0066] S1. Raw material preparation and preliminary processing:

[0067] Weigh 20 g of methyl 4-hydroxybenzoate (4MHB) powder with a purity AR ≥ 99.0%. Immerse the powder in petroleum ether (purity AR ≥ 99.0%), shake for about 20 seconds, and then discard the petroleum ether. Place the powder on a heating plate at a temperature of 55~60℃ and heat for about 10 minutes until the solvent in the powder evaporates, and then perform a drying process.

[0068] S2. Solution preparation:

[0069] Measure 100 mL of acetone with a purity of AR ≥ 99.7% as the solvent, and add the pre-treated raw material to the acetone. Stir with a magnetic stirrer until the raw material is completely dissolved.

[0070] S3, First Filter:

[0071] After stirring, the solution is filtered using a syringe plunger combined with a 0.22 μm organic filter to remove impurities and insoluble substances, resulting in a pure solution after the first filtration.

[0072] S4. Recrystallization operation:

[0073] The solution after the first filtration was wrapped in two layers of plastic wrap and secured with a rubber band, with three small holes punched in the wrap. It was then allowed to stand at room temperature for 24 hours to evaporate, yielding crystals after the first recrystallization. The crystals from the first recrystallization were then subjected to the same dissolution and filtration steps (using the same amount of acetone and the same filtration method) to obtain the solution before the second recrystallization. The solution before the second recrystallization was then subjected to a second recrystallization to obtain crystals after the second recrystallization. Finally, the crystals after the second recrystallization were subjected to the same dissolution and filtration steps to obtain the solution before the third recrystallization.

[0074] S5, Low-temperature volatilization crystallization:

[0075] Divide the recrystallized solution into ten equal portions, place each portion in a beaker, and wrap each portion with two layers of plastic wrap. Secure the plastic wrap tightly with rubber bands, and poke two small holes in the plastic wrap. Place these beakers in a 0°C refrigerator for 48 hours. During this time, the acetone slowly evaporates under low temperature conditions, promoting crystal precipitation. Figure 4 As shown in (a), the formed size is approximately 5×4×2 mm. 3 A 4MHB single crystal was obtained. The obtained single crystal can be used as a seed crystal for subsequent crystal growth.

[0076] The system uses an ice-water bath to maintain a constant temperature. The equipment consists of a glass water tank, a mercury thermometer, and a beaker rack. (See [link]). Figure 2 As shown. Place it in a refrigerator with the temperature set to 0°C, continuously test the temperature of the ice-water bath using a mercury thermometer, and constantly add ice to maintain a constant temperature.

[0077] Example 2

[0078] See Figure 1 As shown, a method for preparing large-size single crystals of methyl 4-hydroxybenzoate includes the following steps:

[0079] S1. Solution preparation:

[0080] Weigh 8.85 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 30 mL of acetone with an AR purity ≥ 99.7% and add it to the beaker. Stir with a magnetic stirrer until the raw materials are completely dissolved and a homogeneous mixture is formed.

[0081] S2, Filtration:

[0082] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0083] S3, Insulation:

[0084] Quickly transfer the filtrate to a well-sealed special container and place it in the growth device to keep it warm for 12 hours.

[0085] S4. Seed crystal implantation and solution injection:

[0086] The selected seed crystals are attached to the bottom of the beaker, the insulated solution is slowly poured into the beaker and quickly sealed with a sealing film, and then placed in a growth device at 0°C.

[0087] S5, Crystal growth:

[0088] Under the above conditions, due to the slight re-dissolution of the seed crystal, the solution reaches saturation. The solute in the solution will grow gradually with the seed crystal as the core, using the existing crystal nuclei. After 24 hours, the maximum size of the harvested crystal will reach 20×15×10mm. 3 High-quality 4MHB single crystal. See also Figure 3 As shown in (b), the seed crystal and the single crystal after growth are completed.

[0089] Comparative Example 1

[0090] S1. Solution preparation:

[0091] Weigh 0.20 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 10 mL of acetone with an AR purity of ≥99.7% and add it to the beaker. Stir with a magnetic stirrer until the crystals are completely dissolved to obtain a homogeneous solution with a concentration of 0.20 g / mL.

[0092] S2, Filtration:

[0093] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0094] S3, Volatile crystallization:

[0095] Wrap the beaker in two layers of plastic wrap and secure it tightly with a rubber band, making two small holes in the plastic wrap. Place the beaker in a 30°C water bath and let it stand for 36 hours. During this time, acetone will evaporate, the solution will gradually reach a supersaturated state, and crystals will begin to precipitate. See [link to relevant documentation]. Figure 4 As shown in (b).

[0096] Comparative Example 2

[0097] S1. Solution preparation:

[0098] Weigh 0.20 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 10 mL of acetone with an AR purity of ≥99.7% and add it to the beaker. Stir with a magnetic stirrer until the crystals are completely dissolved, resulting in a homogeneous solution with a concentration of approximately 0.20 g / mL.

[0099] S2, Filtration:

[0100] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0101] S3, Volatile crystallization:

[0102] Wrap the beaker in two layers of plastic wrap and secure it tightly with a rubber band, making two small holes in the plastic wrap. Place the beaker in a water bath at 15°C and let it stand for 36 hours. During this time, acetone will evaporate, the solution will gradually reach a supersaturated state, and crystals will begin to precipitate. See [link to relevant documentation]. Figure 4 As shown in (c).

[0103] Comparative Example 3

[0104] S1. Solution preparation:

[0105] Weigh 0.20 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 10 mL of acetone with an AR purity of ≥99.7% and add it to the beaker. Stir with a magnetic stirrer until the crystals are completely dissolved, resulting in a homogeneous solution with a concentration of approximately 0.20 g / mL.

[0106] S2, Filtration:

[0107] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0108] S3, Volatile crystallization:

[0109] Wrap the beaker in two layers of plastic wrap and secure it tightly with a rubber band, making two small holes in the plastic wrap. Place the beaker in a refrigerator at -5°C for 48 hours. During this time, acetone slowly evaporates at low temperature, the solution gradually reaches a supersaturated state, and crystals begin to precipitate. See [link to relevant documentation]. Figure 4 As shown in (d).

[0110] Comparative Example 4

[0111] S1. Solution preparation:

[0112] Weigh 0.10 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 10 mL of acetone with an AR purity of ≥99.7% and add it to the beaker. Stir with a magnetic stirrer until the crystals are completely dissolved, resulting in a homogeneous solution with a concentration of approximately 0.10 g / mL.

[0113] S2, Filtration:

[0114] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0115] S3, Volatile crystallization:

[0116] Wrap the beaker in two layers of plastic wrap and secure it tightly with a rubber band, making two small holes in the plastic wrap. Place the beaker in a 0°C growth apparatus and let it stand for 36 hours. During this time, acetone evaporates, the solution gradually reaches a supersaturated state, and crystals begin to precipitate. See [link to documentation]. Figure 4 As shown in (e).

[0117] Comparative Example 5

[0118] S1. Solution preparation:

[0119] Weigh 0.30 g of 4MHB crystals that meet the purity requirements and place them in a clean, dry beaker. Measure 10 mL of acetone with an AR purity of ≥99.7% and add it to the beaker. Stir with a magnetic stirrer until the crystals are completely dissolved, resulting in a homogeneous solution with a concentration of approximately 0.30 g / mL.

[0120] S2, Filtration:

[0121] Select an organic filter head with a pore size of 0.22 μm and install it correctly on the filtration device, ensuring no leakage. Slowly pour in the solution, using the pressure difference to force the solution through the filter head, trapping impurities and insoluble matter to obtain a pure filtrate.

[0122] S3, Volatile crystallization:

[0123] Wrap the beaker in two layers of plastic wrap and secure it tightly with a rubber band, making two small holes in the plastic wrap. Place the beaker in a 0°C growth apparatus and let it stand for 36 hours. During this time, acetone evaporates, the solution gradually reaches a supersaturated state, and crystals begin to precipitate. See [link to documentation]. Figure 4 As shown in (f).

[0124] To illustrate the relevant performance of the 4MHB single crystal provided by this invention, the accompanying drawings are provided.

[0125] Figure 1This document describes the process flow for growing methyl 4-hydroxybenzoate (4MHB) crystals, encompassing multiple steps from raw material preparation, dissolution and filtration, recrystallization, to seed crystal growth. First, petroleum ether is mixed with 4MHB, followed by washing and drying. Next, 4MHB is dissolved in acetone using magnetic stirring and then filtered. Subsequently, the crystals are purified through evaporation crystallization and three recrystallizations. Finally, large-size single crystals are obtained through seed crystal growth. Throughout the entire process, the temperature is strictly controlled at 0°C to ensure the quality and efficiency of crystal growth.

[0126] Figure 2 This is a schematic diagram of an ice-water bath temperature control device used for low-temperature seed crystal growth, including a glass water bath, a mercury thermometer, and a beaker rack. The device is placed in a refrigerator set at 0°C, with the mercury thermometer continuously monitoring the temperature and ice added periodically to maintain a constant temperature.

[0127] Figure 3 Using acetone as a solvent, the seed crystal (a) grown by the low-temperature solvent evaporation method in Example 1 and the large-sized single crystal (b) grown in Example 2 are shown.

[0128] Figure 4 4MHB crystals grown under different conditions: (a) 0℃, 0.20 g / ml; (b) 30℃, 0.20 g / ml; (c) 15℃, 0.20 g / ml; (d) -5℃, 0.20 g / ml; (e) 0℃, 0.10 g / ml; (f) 0℃, 0.30 g / ml. The growth of 4MHB single crystals showed significant differences under different temperatures and concentrations. At 30℃ and 0.20 g / ml, the solution evaporated rapidly, leading to rapid solute precipitation, uncontrollable nucleation numbers, poor crystal quality, and a tendency to form clusters. At 15℃ and 0.20 g / ml, crystal growth was relatively stable, with fewer nuclei and moderate size, but the crystals were not transparent and of poor quality. At -5℃ and 0.20 g / ml, crystal growth was slow, and defects appeared inside large single crystals, affecting transparency. Regarding the effect of concentration, at 0℃ and 0.10 g / ml, the crystal size is small and the growth is slow; at 0℃ and 0.20 g / ml, the crystal size is moderate, the quality is good, and the crystallization is uniform; while at 0℃ and 0.30 g / ml, under high concentration conditions, crystal crowding occurs, grain boundaries increase, and the quality is poor. In summary, the crystal growth is most ideal at 0℃ and 0.20 g / ml, resulting in moderate size and good quality.

[0129] Figure 5 The image shows the ultraviolet-visible-near-infrared spectrum of the 4MHB single crystal in Example 2. Figure 5 In the middle (a), the 4MHB single crystal has a light transmittance of up to 90% in the wavelength range above 400nm, indicating that it has excellent crystal quality. Figure 5In (b), the band gap is 4.12 eV and the band gap is 4MHB.

[0130] Figure 6 The X-ray diffraction pattern of the 4MHB single crystal in Example 2 is shown. After comparing the position and intensity with the simulated spectrum, it can be seen that the maximum exposed plane is the {021} crystal plane.

[0131] Figure 7 Experimental neutron energy spectrum of the 4MHB detector fabricated in Example 2: Figure 7 Figure (a) shows the neutron energy spectrum of the 4MHB detector (chemical source, 10.8 MeV) and compares it with the background noise and the alpha source (5.5 MeV) energy spectrum. Under the same test conditions, the highest address of the measured alpha particle energy spectrum is 2240. Calculations show that the address corresponding to the 10.8 MeV alpha particle is 4400, and the actual measured highest address is 4500. The two values ​​are extremely close, verifying the accurate response of the 4MHB detector to different particle energies. The neutron energy spectrum is concentrated in the range of 1000 to 4000 addresses, and the average count at each address is greater than 100, fully demonstrating the excellent neutron response performance of the detector. Figure 7 (b) further verifies the good response characteristics of the 4MHB detector to neutrons by comparing the experimental spectrum with the simulated spectrum, and further confirms its application potential in fast neutron detection.

[0132] Figure 8 These are experimental results used to characterize the linear response capability of the 4MHB detector fabricated in Example 2. Figure 8 In (a), the measured neutron energy spectrum counts differed significantly for 2.5 MeV neutrons emitted from the neutron tube at different fluxes. As the neutron flux increased, the energy spectrum remained a typical rectangular shape without distortion. Figure 8 (b) After statistical analysis and linear fitting of the total counts of the energy spectrum under different fluxes, a clear and good linear relationship is shown, with a sensitivity of 6.19 cps·nv. -1 .

[0133] In summary, this invention presents a 4MHB single crystal fabrication process and its application in the field of fast neutron detection. A low-temperature solvent evaporation method combined with a seed crystal method is used to grow large-size single crystals. Compared to some existing technologies, this method eliminates the need for complex equipment and harsh environments, effectively avoiding problems such as poor crystal quality and uncontrollable growth found in existing technologies. The detector fabricated based on this method can effectively detect neutrons and has excellent fast neutron energy identification capabilities. Experimental and simulated spectra verify its good response to neutron sources. It exhibits excellent linear response to different fluxes of neutrons, with a sensitivity of 6.19 cps·nv. -1 It can be used for fast neutron flux testing and has great potential in the field of radiation detection.

[0134] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0135] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an organic single crystal of methyl 4-hydroxybenzoate, characterized by, Includes the following steps: 4-hydroxybenzoate polycrystalline material was uniformly dispersed in acetone, and then filtered to remove impurities and insoluble matter, resulting in a filtered solution. The filtered solution was left to stand at 0-5℃ for 12-48 hours to obtain organic single crystals of methyl 4-hydroxybenzoate. The ratio of the polycrystalline 4-hydroxybenzoate to the acetone is 2.0~2.5 g: 10~15 mL.

2. The method for preparing organic single crystals of methyl 4-hydroxybenzoate according to claim 1, characterized in that, The filtered solution is sealed through a sealing membrane, and pores are made in the sealing membrane before it is allowed to stand.

3. The method for preparing organic single crystals of methyl 4-hydroxybenzoate according to claim 2, characterized in that, After filtering, seal the solution and let it stand. After settling, it also includes: Select a defect-free seed crystal, fix it at the bottom of the container, pour in the solution after it has settled, seal it with a sealing film, and place it in the growth device again to obtain a large-sized organic single crystal of methyl 4-hydroxybenzoate.

4. The method for preparing organic single crystals of methyl 4-hydroxybenzoate according to claim 1, characterized in that, During filtration, an organic filter head with a pore size of 0.22 μm is used to filter the solution to remove impurities and insoluble substances.

5. The method for preparing organic single crystals of methyl 4-hydroxybenzoate according to claim 1, characterized in that, The polycrystalline 4-hydroxybenzoate was obtained by purifying 4-hydroxybenzoate powder raw material three times. Each purification step included: soaking the 4-hydroxybenzoate raw material in petroleum ether, shaking and discarding the petroleum ether, heating it to 55~60°C on a heating table, evaporating it and drying it, then dissolving it in acetone and filtering, drying and recrystallizing it.

6. An organic single crystal of methyl 4-hydroxybenzoate prepared by the method according to any one of claims 1 to 5, characterized in that, The transmittance of this single crystal in the ultraviolet-visible-near-infrared band is as high as 90% above 400 nm.

7. The application of the methyl 4-hydroxybenzoate organic single crystal as described in claim 6 in fast neutron detection.

8. The application of the methyl 4-hydroxybenzoate organic single crystal according to claim 7 in fast neutron detection, characterized in that, 4-methyl 4-hydroxybenzoic acid organic single crystal for detecting fast neutrons with different fluxes, with a sensitivity of 6.19 cps·nv -1 .

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