A eutectic scintillator and its preparation method and application

Abstract

The present invention discloses a eutectic scintillator and a preparation method and application thereof, which relate to the technical field of scintillator materials. The preparation method comprises the following steps: mixing raw materials LiF, CaF2, AlF3, and EuF2 in a molar ratio of (100-x-y-z): x:y:z; wherein x>0, y>0, z>0, and x+y+z<100; placing the obtained mixed powder in a crucible and placing the mixed powder in a quartz tube, evacuating the tube and sealing the tube; placing the sealed quartz tube in a descending furnace so that the temperature at the location of the crucible is equal to or higher than the melting point of each raw material, maintaining the temperature for a preset time, and then descending the crucible at a preset descending speed to grow EuF2. 2+ and Al 3+ Co-doped LiF-CaF2 eutectic scintillator. The eutectic scintillator prepared by the present invention can achieve a light yield of 16,700 photons / thermal neutron under thermal neutron irradiation, the highest value among fluoride eutectic scintillators.

Description

Technical Field

[0001] The present invention relates to the technical field of scintillator materials, and in particular to a eutectic scintillator and a preparation method and application thereof. Background Art

[0002] Neutron scattering and neutron imaging technologies have important applications in materials science, biology and medicine, geology and environmental science, energy research, and homeland security. The ultimate realization of these applications relies on thermal neutron detection. Scintillator materials can convert high-energy particles into pulsed visible light photons. Photoelectric devices such as photomultiplier tubes and charge-coupled devices then convert the optical signals into electrical signals for detection. Detection methods based on inorganic scintillators have become one of the main approaches. Traditional inorganic scintillator materials can be categorized by their mesoscopic structure into single crystals, glass, and powder bonds.

[0003] At present, the commercial products of scintillation single crystals used for thermal neutron detection are mainly: Cs2LiLaBr6:Ce (CLLB) and NaI:Li (NaIL) produced by Saint-Gobain of France, and Cs2LiYCl6:Ce (CLYC) produced by Radiation Monitoring Devices of the United States. Although these scintillation single crystals have a very high light yield, they are very easy to absorb moisture. The entire process from raw materials to crystal growth to final processing into crystals needs to strictly avoid moisture. In addition, the growth process of this type of crystal is complicated, and it is difficult to prepare large-sized single crystals. The main representative product of scintillation glass is GS20 produced by Scintacor of the United Kingdom. This material is lithium silicate glass. It was developed in the 1960s and is one of the earliest scintillator materials used in neutron detection. Although glass materials are easy to prepare on a large scale, their light yield is low, which is not conducive to achieving high-resolution and high-sensitivity thermal neutron detection. The powder adhesive is mainly EJ-426 ( 6 LiF / ZnS:Ag). This material has a high light yield, is not easy to absorb moisture, and is relatively stable. However, because it is made by combining powder with an organic binder, the material is a completely opaque scintillating screen, which greatly limits the detection efficiency.

[0004] In the early 1920s, Japan's Tokuyama Corporation and Tohoku University jointly developed fluoride eutectic scintillating ceramics and reported the performance of this type of material in thermal neutron detection. 2+ / Ce 3+Doped LiF-CaF2 and LiF-SrF2 materials exhibit excellent stability and a layered eutectic structure, which is believed to have optical waveguide properties, reducing photon scattering during transmission. However, the highest light yield reported at the time was only 10,000 photons per thermal neutron, still low compared to single crystals.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a eutectic scintillator and a preparation method and application thereof, aiming to solve the problem of low light yield of the existing LiF-CaF2 eutectic scintillator.

[0007] The technical solutions of the present invention are as follows:

[0008] A first aspect of the present invention provides a method for preparing a eutectic scintillator, comprising the steps of:

[0009] The raw materials LiF, CaF2, AlF3, and EuF2 are mixed in a molar ratio of (100-xyz):x:y:z to obtain a mixed powder; wherein x>0, y>0, z>0, and x+y+z<100;

[0010] The mixed powder is placed in a crucible, and the crucible containing the mixed powder is placed in a quartz tube, which is then vacuumed and sealed;

[0011] The sealed quartz tube is placed in a descending furnace so that the temperature of the crucible in the sealed quartz tube is equal to or higher than the melting point of each raw material. After maintaining the temperature for a preset time, the crucible in the sealed quartz tube is lowered at a preset descending speed to grow Eu. 2+ and Al 3+ Co-doped LiF-CaF2 eutectic scintillator.

[0012] Optionally, the crucible is a platinum crucible or a graphite crucible; and / or,

[0013] The bottom shape of the crucible is flat, conical or capillary.

[0014] Optionally, the vacuum degree in the quartz tube after vacuuming is 10 -4 ~10 -3 Pa.

[0015] Optionally, the temperature zones of the descending furnace include a high temperature zone, a transition temperature zone and a low temperature zone from top to bottom;

[0016] The sealed quartz tube is placed in a descending furnace, and a heating program is set so that the temperature of the high temperature zone is 1000-1050° C., the temperature of the low temperature zone is 300-400° C., and the temperature gradient of the transition temperature zone is 2.4-3.0° C. / mm.

[0017] Optionally, the position of the sealed quartz tube in the descending furnace is adjusted so that the temperature at the position of the crucible in the sealed quartz tube is 800-850°C.

[0018] Optionally, the preset time is 1 to 10 hours.

[0019] Optionally, the preset descending speed is 1 to 50 mm / h.

[0020] Optionally, the method for preparing the eutectic scintillator further comprises the steps of:

[0021] After the growth is completed, the furnace is cooled to room temperature at a rate of 50-100℃ / h, the crucible is taken out, and the grown Eu 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0022] A second aspect of the present invention provides a eutectic scintillator, wherein the eutectic scintillator is prepared by the preparation method of the present invention as described above.

[0023] A third aspect of the present invention provides an application of the eutectic scintillator as described above in the field of neutron detection, neutron imaging or neutron positioning.

[0024] Beneficial effect: The present invention adopts the crucible descending method combined with Eu 2+ 、Al 3+ The co-doping of LiF-CaF2 eutectic scintillator can improve the light yield of LiF-CaF2 eutectic scintillator and the luminous intensity of LiF-CaF2 eutectic scintillator. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator has good transparency and a layered eutectic structure. Under thermal neutron irradiation, the light yield can reach 16,700 photons / thermal neutron, which is the highest value among fluoride eutectic scintillators. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of the device used in the direct solidification method in an embodiment of the present invention.

[0026] Figure 2 Schematic diagram of the preparation process of the eutectic scintillator in an embodiment of the present invention.

[0027] Figure 3Schematic diagram of the structure of the crucible in an embodiment of the present invention.

[0028] Figure 4 Schematic diagram of the structure of the descending furnace in an embodiment of the present invention.

[0029] Figure 5 Eu prepared in Example 1 and Comparative Example 1 of the present invention 2+ and Al 3+ Actual image of the co-doped LiF-CaF2 eutectic scintillator.

[0030] Figure 6 Eu prepared in Example 2 of the present invention 2+ and Al 3+ Actual image of the co-doped LiF-CaF2 eutectic scintillator.

[0031] Figure 7 Eu prepared in Example 2 of the present invention 2+ and Al 3+ Scanning electron microscopy image of co-doped LiF-CaF2 eutectic scintillator.

[0032] Figure 8 Eu prepared in Example 2 of the present invention 2+ and Al 3+ Schematic diagram of the optical waveguide of the co-doped LiF-CaF2 eutectic scintillator.

[0033] Figure 9a LiF-CaF2:0.5mol%Eu in Example 5 of the present invention 2+ ,1mol%Al 3+ , LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ Emission spectrum under X-ray excitation; Figure 9b LiF-CaF2:1mol%Al in Comparative Example 3 3 + , Emission spectrum of LiF-CaF2 in Comparative Example 4 under X-ray excitation.

[0034] Figure 10 GS20, LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ , LiF-CaF2:0.5mol%Eu in Comparative Example 5 2+ ,1mol%Al 3+ , LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ Pulse height spectrum under thermal neutron irradiation.

[0035] Figure 11 CaF2:Eu commercial single crystal, LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ , LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ Thermoluminescence spectrum of .

[0036] Figure 12 GS20 and the pulse height spectra of the eutectic scintillator with different doping amounts in Example 6.

[0037] Figure 13 The different doping amounts of Eu in Comparative Example 6 2+ and Al 3+ Pulse height spectrum of co-doped LiF-SrF2 eutectic scintillator. DETAILED DESCRIPTION

[0038] The present invention provides a eutectic scintillator and its preparation method and application. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only for the purpose of explaining the present invention and are not intended to limit the present invention.

[0039] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] Unless otherwise specified, LiF in the present invention refers to 6 LiF, Li refers to 6 Li.

[0041] In the inventor's previous research, the direct solidification method was used to prepare the fluoride eutectic scintillator, specifically Figure 1As shown, each raw material is placed in a crucible 1, and then the crucible 1 containing the raw materials is placed in a heating device 31 (such as a tubular furnace), and a mixed gas of Ar and CF4 or nitrogen is introduced to play a protective role. The heating device 31 is heated to melt the raw materials, and then the temperature is reduced at a certain rate. After complete cooling, a fluoride eutectic scintillator is obtained. The characteristic of the direct solidification method is that after the raw materials are melted, they are cooled in the heating device according to a set cooling program, and the crucible or raw materials do not move during the melting or cooling process. However, this method cannot achieve the control of eutectic growth, resulting in the inability to fully discharge the gas, and then the prepared eutectic scintillator has more pores inside and a ring-shaped part with low transparency appears on the edge. At the same time, this method cannot effectively improve the light yield of the fluoride eutectic scintillator (light yield is also called light output, which is the main performance parameter of the scintillator material and determines the spatial resolution of the scintillator detector). Furthermore, the inventor adopted a traditional directional solidification growth method, that is, the raw materials are placed in a vacuum drop furnace, and then a fluorine-containing gas is introduced for protection. The characteristic of directional solidification is that after the raw material is melted, it is cooled according to a set cooling program. During the cooling process, the crucible or the raw material is controlled to move in a directional manner, thereby guiding and controlling the growth of the eutectic, which is conducive to obtaining a microscopically ordered eutectic structure (layered, rod-shaped). However, since this method requires a vacuum furnace combined with fluorine-containing gas protection, it increases production costs. Based on this, an embodiment of the present invention provides a method for preparing a eutectic scintillator, such as Figure 2 As shown, the following steps are included:

[0042] S1. Mix raw materials LiF, CaF2, AlF3, and EuF2 in a molar ratio of (100-xyz):x:y:z to obtain a mixed powder; wherein x>0, y>0, z>0, and x+y+z<100;

[0043] S2, placing the mixed powder in a crucible, then placing the crucible containing the mixed powder in a quartz tube, evacuating the tube and sealing the tube;

[0044] S3, placing the sealed quartz tube in a descending furnace so that the temperature of the crucible in the sealed quartz tube is equal to or higher than the melting point of each raw material, and after maintaining the temperature for a preset time, lowering the crucible in the sealed quartz tube at a preset descending speed to grow Eu 2+ and Al 3+ Co-doped LiF-CaF2 eutectic scintillator.

[0045] The present invention adopts the crucible descent method combined with Eu 2+ 、Al 3+ The co-doping of LiF-CaF2 eutectic scintillator can improve the light yield of LiF-CaF2 eutectic scintillator and the luminous intensity of LiF-CaF2 eutectic scintillator. 2+ and Al3+ The co-doped LiF-CaF2 eutectic scintillator has excellent transparency and a layered eutectic structure. Under thermal neutron irradiation, its light yield can reach 16,700 photons / thermal neutron, which is 2.75 times that of commercial scintillator glass and the highest value among fluoride eutectic scintillators. The present invention prepares the eutectic scintillator by combining a quartz tube vacuum seal with a crucible drop method. The crucible drop method effectively solves the problem that the direct solidification method cannot effectively improve the light yield of the eutectic scintillator, and the resulting eutectic scintillator is uneven and has internal holes (i.e., poor quality). The quartz tube vacuum seal method overcomes the high cost problem of traditional directional solidification growth methods due to the requirements of the internal furnace atmosphere.

[0046] In the present invention, LiF and CaF2 form a eutectic scintillator, Al 3+ and Eu 2+ Entering the CaF2 lattice to replace Ca 2+ The position of Eu 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator consists of two crystalline phases, one of which is LiF (containing nuclides 6 Li), plays the role of absorbing thermal neutrons, generating nuclear reactions with thermal neutrons, and generating secondary charged particles. The other phase is Eu 2+ and Al 3+ Co-doped CaF2 (denoted as CaF2:Eu,Al) is a luminescent body used to achieve luminescence and generate light signals. Specifically, the secondary charged particles generated by the reaction of LiF and thermal neutrons cause ionization inside CaF2 to achieve luminescence, while Eu 2+ Entering into the CaF2 lattice, it generates 4f-5d transition and emits light. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator is a luminescent material that converts thermal neutrons into visible photons.

[0047] However, for Eu 2+ Doped LiF-CaF2 eutectic scintillator, part of Li + Will enter the CaF2 lattice, replacing Ca 2 + In order to balance the charge, fluorine vacancies are generated. Fluorine vacancies are also called color centers. They are a typical point defect. They are low-frequency shallow-level electron traps that absorb the thermalized electrons generated by ionization, reducing the number of thermal electrons that should be used for scintillation and luminescence, thereby reducing the light yield. Therefore, Eu 2+ There are defects inside the doped LiF-CaF2 eutectic scintillator. 3+ Further doping can eliminate Eu2+ The doped LiF-CaF2 eutectic scintillator has internal defects (defects inside CaF2), thereby improving the light yield and luminous intensity of the eutectic scintillator.

[0048] In step S1, the present invention does not limit the specific ratio of each raw material, the ratio of the fluoride raw materials (i.e., the ratio of LiF to CaF2) and the specific doping amount (i.e., the amount of EuF2 and AlF3 added). The ratio of the raw materials LiF, CaF2, EuF2, and AlF3 can be set according to actual needs. For example, the molar ratio of LiF, CaF2, AlF3, and EuF2 is 80mol:19.7mol:0.2mol:0.1mol, 80mol:18.5mol:1mol:0.5mol or 70mol:28mol:1mol:1mol, etc.

[0049] In some embodiments, the raw materials LiF, CaF2, AlF3, and EuF2 are mixed in a certain proportion and ground in an agate mortar for 30 to 60 minutes to obtain a mixed powder.

[0050] In step S2, in some embodiments, the crucible is a platinum crucible or a graphite crucible. Eutectic scintillator is a polycrystalline ceramic obtained by melting powdered raw materials in a crucible and then slowly cooling them, resulting in the precipitation of two or more separate crystalline phases from the melt. Therefore, the crucible material must be high-temperature resistant, non-reactive with the melt, and relatively inert. Therefore, in this embodiment, a graphite crucible or a platinum crucible is used. However, since platinum crucibles are relatively expensive, a high-purity graphite crucible is preferred.

[0051] In some embodiments, as Figure 3 As shown, the bottom shape of the crucible is flat, conical, or capillary, that is, the crucible is a flat-bottom crucible, a conical-bottom crucible, or a capillary-bottom crucible, but is not limited thereto. The eutectic scintillator prepared using a capillary-bottom crucible has higher quality than that prepared using a flat-bottom crucible or a conical-bottom crucible (the eutectic scintillator prepared using a capillary-bottom crucible is essentially pore-free). This is mainly because the crucible-descent method relies primarily on spontaneous crystallization to form the eutectic, which grows upward from the bottom of the crucible, that is, solidification begins from the bottom of the crucible. The capillary-shaped bottom of the crucible has a geometric elimination effect, which allows the eutectic scintillator to grow on a single crystal plane, effectively eliminating pores and obtaining a high-quality eutectic scintillator.

[0052] In some embodiments, the vacuum degree in the quartz tube after vacuuming is 10 -4 ~10 -3 Pa, for example, the vacuum degree can be 10 -4 Pa, 1×10 -4 Pa, 2×10 -4Pa, 3×10 -4 Pa, 4×10 -4 Pa, 5×10 -4 Pa, 6×10 -4 Pa, 7×10 - 4 Pa, 8×10 -4 Pa, 9×10 -4 Pa or 10 -3 Pa et al.

[0053] In step S2, the crucible containing the mixed powder is placed in a quartz tube, evacuated, and then sealed. This completely isolates the raw materials from oxygen and moisture during the growth process. This also overcomes the high cost associated with conventional directional solidification growth methods, which require a high furnace atmosphere.

[0054] In step S3, in some embodiments, the temperature zones of the descending furnace include a high temperature zone, a transition temperature zone, and a low temperature zone from top to bottom;

[0055] The sealed quartz tube is placed in a descending furnace, and then a temperature ramp is set so that the temperature of the high temperature zone is 1000-1050°C, the temperature of the low temperature zone is 300-400°C, and the temperature gradient of the transition temperature zone is 2.4-3.0°C / mm. For example, the temperature of the high temperature zone can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, or 1050°C; the temperature of the low temperature zone can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, or 400°C, and the temperature gradient of the transition temperature zone can be 2.4°C / mm, 2.5°C / mm, 2.6°C / mm, 2.68°C / mm, 2.7°C / mm, 2.8°C / mm, 2.9°C / mm, or 3.0°C / mm.

[0056] In some embodiments, the position of the sealed quartz tube in the descending furnace is adjusted so that the temperature at the crucible in the sealed quartz tube is 800-850°C, for example, 800°C, 810°C, 820°C, 830°C, 840°C, or 850°C, which ensures that the raw materials melt without volatilizing. Specifically, by adjusting the position of the sealed quartz tube in the descending furnace, the position of the crucible in the quartz tube is also adjusted accordingly, thereby ensuring that the temperature at the bottom vertex of the crucible in the sealed quartz tube is 800-850°C.

[0057] In some embodiments, the preset time is 1 to 10 hours, that is, the melting time of the raw material is 1-10 hours. For example, the preset time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0058] In some embodiments, the preset descending speed is 1 to 50 mm / h, for example, 1 mm / h, 5 mm / h, 10 mm / h, 15 mm / h, 20 mm / h, 25 mm / h, 30 mm / h, 35 mm / h, 40 mm / h, 45 mm / h, or 50 mm / h. In this embodiment, the preset descending speed (i.e., the growth speed of the eutectic scintillator) can achieve the growth of a eutectic scintillator with good transparency and a layered eutectic structure.

[0059] In some embodiments, the method for preparing the eutectic scintillator further comprises the steps of:

[0060] After the growth is completed, the furnace is cooled to room temperature at a rate of 50-100℃ / h, the crucible is taken out, and the grown Eu 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0061] In this embodiment, the cooling rate is 50 to 100° C. / h. For example, the cooling rate may be 50, 60, 70, 80, 90, or 100° C. / h.

[0062] The following combination Figure 4 , for Eu 2+ and Al 3+ The preparation method of the co-doped LiF-CaF2 eutectic scintillator is described in detail.

[0063] The raw materials after grinding and mixing are placed in a crucible 1, and then the crucible 1 containing the raw materials is placed in a quartz tube 2, and the quartz tube 2 is vacuumed and sealed;

[0064] A descending furnace 32 is provided, which includes a furnace body 321, a lifting device 322 located at the lower part of the furnace body, and a control cabinet 323 for controlling the temperature of the furnace body 321 and controlling the lifting and lowering of the lifting device 322; the temperature zones of the furnace body 321 include a high temperature zone, a transition temperature zone and a low temperature zone from top to bottom.

[0065] The sealed quartz tube 2 is placed vertically in the furnace body 321 of the descending furnace 32 and placed on the lifting device 322. The temperature rise program is set through the control cabinet 323 so that the temperature of the high temperature zone of the furnace body 321 is 1000-1050°C, the temperature of the low temperature zone is 300-400°C, and the temperature gradient of the transition temperature zone is 2.4-3.0°C / mm;

[0066] The lifting device 323 is controlled by the control cabinet 323 to adjust the position of the sealed quartz tube 2 in the furnace body 321, so that the temperature at the position of the crucible 1 in the sealed quartz tube 2 is 800-850°C. At this time, the raw materials in the crucible begin to melt. After melting for 1-10 hours, the crucible is lowered at a rate of 1-50 mm / h to grow crystals. After the growth is completed, the furnace body 321 is cooled to room temperature at a rate of 50-100°C / h, the quartz tube 2 is taken out, and the crucible 1 is taken out from the quartz tube 2, and the grown Eu is placed in the furnace body 321. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator is peeled off from the crucible 1.

[0067] The present invention also provides a eutectic scintillator, wherein the eutectic scintillator is prepared by the preparation method of the present invention as described above. The eutectic scintillator provided by the present invention is Eu 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator has a light yield of 16,700 photons / thermal neutron, which is 2.75 times that of commercial scintillating glass and the highest value among fluoride eutectic scintillators.

[0068] The embodiment of the present invention further provides an application of the eutectic scintillator as described above in the field of neutron detection, neutron imaging or neutron positioning. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator has a light yield of up to 16,700 photons / thermal neutron, which enables it to have high spatial resolution in neutron detection, neutron imaging or neutron localization.

[0069] Specifically, the eutectic scintillator is used to convert high-energy particles into pulsed visible photons, and then convert the optical signals into electrical signals through photoelectric devices such as photomultiplier tubes and charge couplers to achieve detection.

[0070] The eutectic scintillator can be used as a detection material in a scintillation camera (Anger camera) to convert thermal neutrons into visible photons, and can be combined with a photodetector and an electronic system to form a thermal neutron detector for use in spallation neutron sources and nuclear reactors.

[0071] The eutectic scintillator can be used as a scintillator material for a neutron camera (CCD + scintillator combination) for neutron imaging, and is applied to imaging of light element substances and industrial non-destructive testing. In addition, the eutectic scintillator can also be used as a material for detecting other high-energy rays.

[0072] The following describes it in detail through specific examples.

[0073] Example 1

[0074] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 14 mm. 2+ and Al 3+ Doping a LiF-CaF2 eutectic scintillator comprises the following steps:

[0075] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:19.7:0.2:0.1 and ground thoroughly in an agate mortar for 60 minutes to obtain 10 g of mixed powder.

[0076] The mixed powder is transferred into a conical bottom graphite crucible, the conical bottom graphite crucible is placed in a quartz tube, and after vacuuming, the tube is sealed using a tube sealing device to protect the capillary bottom graphite crucible and the raw materials.

[0077] Place the sealed quartz tube vertically on Figure 4 In the descending furnace shown, the temperature of the high temperature zone of the furnace body is set to 1050°C, the temperature of the low temperature zone is set to 400°C, and the temperature gradient of the transition temperature zone is 2.7°C / mm.

[0078] The position of the sealed quartz tube in the descending furnace body was adjusted using the descending furnace's lifting system so that the temperature at the bottom vertex of the conical-bottomed graphite crucible in the sealed quartz tube was 830°C. After the raw materials were melted for 5 hours, the conical-bottomed graphite crucible was lowered at a speed of 10 mm / h using the descending furnace's lifting system to grow crystals, and the growth ended when it descended to 400°C.

[0079] After the furnace body was cooled to room temperature at a cooling rate of 50℃ / h, the quartz tube was taken out, and the conical bottom graphite crucible was taken out from the quartz tube. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0080] Example 2

[0081] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 14 mm. 2+ and Al 3+The preparation method of the doped LiF-CaF2 eutectic scintillator is basically the same as that of Example 1, with the only difference being that the conical bottom graphite crucible in Example 1 is replaced by a capillary bottom graphite crucible.

[0082] Example 3

[0083] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 25 mm. 2+ and Al 3+ Doping a LiF-CaF2 eutectic scintillator comprises the following steps:

[0084] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:19.7:0.2:0.1 and ground thoroughly in an agate mortar for 60 minutes to obtain 50 g of mixed powder.

[0085] The mixed powder is transferred into a capillary bottom graphite crucible, the capillary bottom graphite crucible is placed in a quartz tube, and after vacuuming, the tube is sealed using a tube sealing device to protect the capillary bottom graphite crucible and the raw materials.

[0086] Place the sealed quartz tube vertically on Figure 4 In the descending furnace shown, the temperature of the high temperature zone of the furnace body is set to 1000°C, the temperature of the low temperature zone is set to 400°C, and the temperature gradient of the transition temperature zone is 2.4°C / mm.

[0087] The position of the sealed quartz tube in the descending furnace body was adjusted using the descending furnace's lifting system so that the temperature at the top of the bottom of the capillary bottom graphite crucible in the sealed quartz tube was 850°C. After the raw materials were melted for 3 hours, the capillary bottom graphite crucible was lowered at a speed of 10 mm / h using the descending furnace's lifting system to grow crystals, and the growth ended when it descended to 400°C.

[0088] After the furnace body was cooled to room temperature at a cooling rate of 100℃ / h, the quartz tube was taken out, and the capillary bottom graphite crucible was taken out from the quartz tube. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0089] Example 4

[0090] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 50 mm. 2+ and Al 3+ Doping a LiF-CaF2 eutectic scintillator comprises the following steps:

[0091] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:19.7:0.2:0.1 and ground thoroughly in an agate mortar for 60 minutes to obtain 100 g of mixed powder.

[0092] The mixed powder is transferred into a capillary bottom graphite crucible, which is placed in a quartz tube. After vacuuming, the tube is sealed using a tube sealing device to protect the capillary bottom graphite crucible and the raw materials.

[0093] Place the sealed quartz tube vertically on Figure 4 In the descending furnace shown, the temperature of the high temperature zone of the furnace body is set to 1050°C, the temperature of the low temperature zone is set to 300°C, and the temperature gradient of the transition temperature zone is 3.0°C / mm.

[0094] The position of the sealed quartz tube in the descending furnace body was adjusted using the descending furnace's lifting system so that the temperature at the top of the bottom of the capillary bottom graphite crucible in the sealed quartz tube was 850°C. After the raw materials were melted for 3 hours, the capillary bottom graphite crucible was lowered at a speed of 10 mm / h using the descending furnace's lifting system to grow crystals, and the growth ended when it descended to 400°C.

[0095] After the furnace body was cooled to room temperature at a cooling rate of 100℃ / h, the quartz tube was taken out, and the capillary bottom graphite crucible was taken out from the quartz tube. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0096] Example 5

[0097] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 50 mm. 2+ and Al 3+ The preparation method of the doped LiF-CaF2 eutectic scintillator is basically the same as that of Example 4, except that:

[0098] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:18.5:1:0.5 and ground thoroughly in an agate mortar for 60 minutes to obtain 100 g of mixed powder;

[0099] The obtained product is recorded as LiF-CaF2:0.5mol%Eu 2+ ,1mol%Al 3+ .

[0100] Example 6

[0101] A series of Eu with different doping amounts and a diameter of 50 mm were prepared using the crucible descent method (also known as directional solidification method). 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator has a molar ratio of LiF to the sum of the molar ratios of CaF2, AlF3, and EuF2 of 80:20. For the specific method, see Example 4, wherein Eu 2+ The doping amount is 0.5 mol%, Al 3+ The doping amounts are 0.50 mol%, 0.75 mol%, 1.0 mol%, 3.0 mol%, 5.0 mol%, 10 mol% and 15 mol% respectively.

[0102] Comparative Example 1

[0103] Eu with a diameter of 12 mm was prepared by direct solidification method. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator comprises the following steps:

[0104] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:19.7:0.2:0.1 and ground thoroughly in an agate mortar for 60 minutes to obtain 10 g of mixed powder;

[0105] Transfer the mixed powder into a flat-bottomed graphite crucible and place Figure 1 The tube furnace shown in the figure was evacuated and sintered at 400℃ for 5h to completely dehydrate the raw materials. Then nitrogen was filled into the tube furnace and melted at 850℃ for 1h. Then the temperature was cooled to room temperature at a rate of 4℃ / min. 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

[0106] Comparative Example 2

[0107] The crucible descent method (also known as directional solidification method) was used to prepare Eu with a diameter of 50 mm. 2+ The preparation method of the doped LiF-CaF2 eutectic scintillator is basically the same as that of Example 5, except that the raw materials LiF, CaF2, and EuF2 are mixed in a molar ratio of 80:19.5:0.5, and ground in an agate mortar for 60 minutes to obtain 100 g of mixed powder; the obtained product is recorded as LiF-CaF2:0.5mol%Eu 2+ .

[0108] Comparative Example 3

[0109] The crucible descent method (also known as directional solidification method) was used to prepare Al with a diameter of 50 mm. 3+The preparation method of the doped LiF-CaF2 eutectic scintillator is basically the same as that of Example 5, except that the raw materials LiF, CaF2, and AlF3 are mixed in a molar ratio of 80:19:1, and ground in an agate mortar for 60 minutes to obtain 100 g of mixed powder; the obtained product is recorded as LiF-CaF2:1mol%Al 3+ .

[0110] Comparative Example 4

[0111] A LiF-CaF2 eutectic scintillator with a diameter of 50 mm was prepared by the crucible drop method (also known as the directional solidification method). The preparation method is basically the same as that in Example 5, except that the raw materials LiF and CaF2 were mixed in a molar ratio of 80:20 and ground in an agate mortar for 60 minutes to obtain 100 g of mixed powder; the obtained product was recorded as LiF-CaF2.

[0112] Comparative Example 5

[0113] Eu with a diameter of 50 mm was prepared by direct solidification method. 2+ and Al 3+ The doped LiF-CaF2 eutectic scintillator is basically the same as that in Comparative Example 1, except that:

[0114] The raw materials LiF, CaF2, AlF3, and EuF2 were mixed in a molar ratio of 80:18.5:1:0.5 and ground in an agate mortar for 60 minutes to obtain 100 g of mixed powder. The product was recorded as LiF-CaF2:0.5 mol% Eu 2+ ,1mol%Al 3+ .

[0115] Comparative Example 6

[0116] Preparation of Eu with different doping amounts 2+ and Al 3+ Co-doped LiF-SrF2 eutectic scintillator, see the preparation method above, wherein Eu 2+ The doping amount is 0.05 mol%, Al 3+ The doping amounts are 0 mol%, 0.05 mol%, 0.10 mol%, 0.50 mol%, 1.00 mol% and 5.00 mol%, respectively.

[0117] According to actual needs, the products in the examples and comparative examples were cut and polished before testing.

[0118] Related tests:

[0119] (1) Eu prepared in Example 1 and Comparative Example 1 2+ and Al3+ The actual picture of the co-doped LiF-CaF2 eutectic scintillator is as follows Figure 5 As shown, the eutectic scintillator prepared by the direct solidification method in Comparative Example 1 has more pores inside and a ring-shaped part with low transparency on the edge, and the quality of the eutectic scintillator is poor. The eutectic scintillator prepared by the crucible descent method (conical bottom graphite crucible) in Example 1 has fewer pores, no ring-shaped part with low transparency on the edge, and the quality of the eutectic scintillator is better.

[0120] (2) The Eu prepared by the crucible descent method (using a capillary bottom graphite crucible) in Example 2 2+ and Al 3+ The actual picture of the co-doped LiF-CaF2 eutectic scintillator is as follows Figure 6 As shown, the prepared eutectic scintillator has no pores, uniform texture and good quality. Figure 6 The upper right part of the middle picture shows the actual picture after the capillary part is polished off, and the lower right part shows the actual picture after cutting and polishing. Figure 5 and 6 It can be seen that compared with the conical-bottom graphite crucible, the eutectic scintillator prepared using the capillary-bottom graphite crucible has no pores and better quality. This is because the crucible descent method relies on spontaneous crystallization to form the eutectic, which grows upward from the bottom of the crucible, that is, solidification begins from the bottom of the crucible. The crucible with a capillary bottom has a geometric elimination effect, which allows the eutectic scintillator to maintain one crystal plane growth, effectively eliminating pores.

[0121] (3) Eu prepared in Example 2 2+ and Al 3+ The electron scanning microscopy image of the co-doped LiF-CaF2 eutectic scintillator is shown in Figure 2. Figure 7 As shown, it can be seen that it has a clear layered structure (specifically, alternating layers of LiF and Eu 2+ and Al 3+ Co-doped CaF2 layer). This structure has optical waveguide properties, which can reduce the scattering of photons during transmission. 2+ and Al 3+ Schematic diagram of the optical waveguide of the co-doped LiF-CaF2 eutectic scintillator Figure 8 As shown, photons in Eu 2+ and Al 3+ Directed transport in co-doped CaF2 layers.

[0122] (4) LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ , LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+, LiF-CaF2:1mol%Al in Comparative Example 3 3+ , the emission spectrum of LiF-CaF2 in Example 4 was tested under X-ray excitation, and the results were as follows Figure 9a and 9b As shown by Figure 9a It can be seen that compared with LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ , LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ With higher luminous intensity; Figure 9b It can be seen that compared with the LiF-CaF2 in Comparative Example 4, the LiF-CaF2:1mol%Al in Comparative Example 3 3+ Has a higher luminous intensity. Figure 9a and 9b It can be explained that Al 3+ Doping can increase LiF-CaF2 and LiF-CaF2:0.5mol%Eu 2+ luminous intensity.

[0123] (5) Commercial thermal neutron scintillating glass (GS20), LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ , LiF-CaF2:0.5mol%Eu in Comparative Example 5 2+ ,1mol%Al 3+ (prepared by direct solidification method), LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ (Prepared by crucible descent method) Pulse height spectrum test was carried out under thermal neutron irradiation, and the results were as follows Figure 10 As shown, it can be seen that LiF-CaF2:0.5mol%Eu in GS20 and Comparative Example 2 2+ , LiF-CaF2:0.5mol%Eu in Comparative Example 5 2+ ,1mol%Al 3+ (prepared by direct solidification method), LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ The light yields of the samples prepared by the crucible descent method are 6000 photons / thermal neutron, 10000 photons / thermal neutron, 15580 photons / thermal neutron, and 16700 photons / thermal neutron respectively (using the same equipment and under the same test conditions, the higher the number of channels corresponding to the peak value, the higher the light yield). 2+ 、Al 3+Co-doping can effectively improve the light yield of eutectic scintillators. In addition, under the same doping conditions, the crucible drop method plus a capillary-shaped graphite crucible is more conducive to improving light yield than the direct solidification method.

[0124] (6) The CaF2:Eu commercial single crystal (Eu doping amount is 0.1mol%, purchased from Shanghai Shuojie Crystal Materials Co., Ltd., epic-crystal) and LiF-CaF2:0.5mol%Eu in Comparative Example 2 were tested. 2+ , LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ A low-temperature thermoluminescence spectrum experiment was conducted, and the thermoluminescence spectrum results were as follows: Figure 11 The results show that LiF-CaF2:0.5mol%Eu in Comparative Example 2 2+ A strong thermoluminescence peak appears around 127K, indicating the presence of a corresponding defect. At the same time, it was observed that CaF2:Eu commercial single crystals do not have this defect, so it is speculated that this defect is caused by Li + Part of it enters the CaF2 lattice, replacing Ca 2+ In order to balance the charge, a fluorine vacancy (also known as a color center, a typical point defect) is generated. The general thermoluminescence model is used for fitting, and the fitting results show that ( Figure 11 The defect is a low-frequency shallow-level electron trap that absorbs the thermalized electrons generated by ionization, reducing the number of thermal electrons that should be used for scintillation, thereby reducing the light yield. The thermoluminescence spectrum shows that the LiF-CaF2:0.5mol%Eu in Example 5 2+ ,1mol%Al 3+ There is no obvious thermoluminescence peak, indicating that the Al 3+ Doping, defects are significantly reduced, Al 3+ Co-doping improves the light yield of eutectic scintillators. The process of defect generation is expressed as: , the process of defect elimination is expressed as: Among them, Ca ca Indicates the normal position of Ca when not doped, Li′ Ca It means that Li replaces the position of Ca, and Li replaces the position of Ca with a negative charge compared to the original position. It means that Al replaces the position of Ca, and Al replaces the position of Ca with a positive charge compared to the original position. represents a fluorine vacancy, which is equivalent to a positive charge.

[0125] (7) Pulse height spectrum test was performed on commercial thermal neutron scintillation glass (GS20) and eutectic scintillators with different doping amounts in Example 6. The results are as follows: Figure 12 As shown, the results show that the fixed Eu 2+ The doping concentration is 0.5 mol%, and different amounts of Al are doped 3+ Both can increase the light yield. When Al 3+ The doping concentration is 1mol%, and the effect is best.

[0126] (8) Comparative Example 6 with different doping amounts of Eu 2+ and Al 3+ The pulse height spectrum of the co-doped LiF-SrF2 eutectic scintillator was tested, and the results are as follows Figure 13 As shown, the results show that different Al 3+ Eu doping concentration 2+ and Al 3+ The light yield of co-doped LiF-SrF2:Eu samples is lower than that of Eu 2+ The sample doped alone shows that Al 3+ Doping to increase light yield is not effective for all fluoride eutectic scintillators but only for LiF-CaF2.

[0127] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a eutectic scintillator, characterized in that: Including steps: The raw materials LiF, CaF2, AlF3, and EuF2 are mixed in a molar ratio of (100-xyz):x:y:z to obtain a mixed powder; wherein x>0, y>0, z>0, and x+y+z<100; The mixed powder is placed in a crucible, and the crucible containing the mixed powder is placed in a quartz tube, which is then vacuumed and sealed; The sealed quartz tube is placed in a descending furnace so that the temperature of the crucible in the sealed quartz tube is equal to or higher than the melting point of each raw material. After maintaining the temperature for a preset time, the crucible in the sealed quartz tube is lowered at a preset descending speed to grow Eu. 2+ and Al 3+ Co-doped LiF-CaF2 eutectic scintillator; the Eu 2+ and Al 3+ Co-doped LiF-CaF2 eutectic scintillator includes LiF and Eu 2+ and Al 3+ Co-doped CaF2; The bottom shape of the crucible is capillary; The temperature zones of the descending furnace include a high temperature zone, a transition temperature zone and a low temperature zone from top to bottom; The sealed quartz tube is placed in a descending furnace, and a temperature program is set so that the temperature of the high temperature zone is 1000-1050° C., the temperature of the low temperature zone is 300-400° C., and the temperature gradient of the transition temperature zone is 2.4-3.0° C. / mm; The position of the sealed quartz tube in the descending furnace is adjusted so that the temperature of the crucible in the sealed quartz tube is 800-850°C.

2. The preparation method according to claim 1, characterized in that The crucible is a platinum crucible or a graphite crucible.

3. The preparation method according to claim 1, characterized in that The vacuum degree in the quartz tube after vacuuming is 10 -4 ~10 -3 Pa.

4. The preparation method according to claim 1, characterized in that The preset time is 1 to 10 hours.

5. The preparation method according to claim 1, characterized in that The preset descending speed is 1 to 50 mm / h.

6. The preparation method according to claim 1, characterized in that The method for preparing the eutectic scintillator further comprises the steps of: After the growth is completed, the furnace is cooled to room temperature at a rate of 50-100℃ / h, the crucible is taken out, and the grown Eu 2+ and Al 3+ The co-doped LiF-CaF2 eutectic scintillator was peeled off from the crucible.

7. A eutectic scintillator, characterized in that: The eutectic scintillator is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the eutectic scintillator according to claim 7 in the fields of neutron detection, neutron imaging or neutron positioning.

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