CN114460622A - Novel large-area thermal neutron detector - Google Patents
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Abstract
The invention relates to a novel large-area thermal neutron detector which comprises an upper reflecting layer, a lower reflecting layer, a wave-shift light guide and a lithium glass scintillator, wherein the wave-shift light guide is positioned between the upper reflecting layer and the lower reflecting layer, the lithium glass scintillator is distributed in the wave-shift light guide or on the surface of the wave-shift light guide, and the wave-shift light guide is used for transferring the wavelength of fluorescence emitted by the lithium glass scintillator to a blue-green light long wave band. Development of high performance, large size based on lithium glass scintillators by introducing a wave-shift technique to increase the sensitive area3He tube replaces the detector.
Description
Technical Field
The invention relates to the technical field of neutron detection, in particular to a novel large-area thermal neutron detector based on a lithium glass scintillator and a wave shift technology.
Background
Neutron detection technology has long been an important means for nuclear radiation safety monitoring, among others3He tube relies onExcellent performance, and the utilization rate in neutron detection is up to more than 75%. At present, the method is in the fields of rapidly developing nuclear power industry, border port security, material structure research and the like3He tube is widely applied, such as scattering neutron spectrometer and nuclear safety monitoring system which use large scale3He tube probe array. But in recent years internationally3He gas has a rising price due to a serious shortage of resources, and is urgently under development3He tube substituted neutron detector based on6The development of detectors for Li glass is a hotspot of international research.
6The Li glass scintillator is a thermal neutron detection material with excellent performance, and the thermal neutron detection efficiency is high (75%: 1mm thick)6Li glass), short light attenuation time (70 ns), and can realize n-gamma discrimination by simple pulse amplitude. Compared with other conventional neutron detectors (CLYC, coating)10B straw tube,6LiF/zns (ag) detectors, etc.),6the Li glass detector is expected to greatly improve the neutron counting capacity, and can be suitable for high-low temperature and acid-base environments which cannot be suitable for other detectors. However, for a long time, lithium glass has two major problems: firstly, due to the fact that6The Li glass has the thermal neutron peak equivalent electron energy of about 1.5MeV, so that the sensitivity to high-energy gamma is higher, the particle size of the lithium glass must be reduced to reduce the gamma deposition energy, and theoretically, the gamma sensitivity of the lithium glass can be reduced to 10 by processing the lithium glass into 280 mu m-1 mm of wires, optical fibers or particles-6～10-3. Second one6The Li glass has a low fluorescence yield (6000pe) and the wavelength in the near ultraviolet region results in a short attenuation length of light transmission, limiting the increase of the sensitive area of the detector. The above two disadvantages lead to the development of high-performance, large-size lithium glass-based glass3The process technology difficulty of replacing the detector by the He pipe is high, and the He pipe is also a key direction for domestic and foreign research and attack and customs.
Based on this, a need exists for a new large-area thermal neutron detector based on lithium glass scintillator with high performance and large size.
Disclosure of Invention
The invention aims to provide a novel bracketAn area thermal neutron detector, a wave shift technology is introduced to improve the sensitive area, so that high-performance and large-size lithium glass scintillator-based development is realized3He tube replaces the detector.
In order to achieve the purpose, the invention provides the following scheme:
a novel large-area thermal neutron detector comprises an upper reflecting layer, a lower reflecting layer, a wave-shift light guide and a lithium glass scintillator;
the wave-shifting light guide is positioned between the upper reflective layer and the lower reflective layer; the lithium glass scintillator is distributed in the interior or on the surface of the wave-shift light guide; the wavelength shifting light guide is used for shifting the wavelength of the fluorescence emitted by the lithium glass scintillator to a blue-green light long wavelength band.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a novel large-area thermal neutron detector which comprises an upper reflecting layer, a lower reflecting layer, a wave-shift light guide and a lithium glass scintillator, wherein the wave-shift light guide is positioned between the upper reflecting layer and the lower reflecting layer, the lithium glass scintillator is distributed in the wave-shift light guide or on the surface of the wave-shift light guide, and the wave-shift light guide is used for transferring the wavelength of fluorescence emitted by the lithium glass scintillator to a blue-green light long wave band. Development of high performance, large size based on lithium glass scintillators by introducing a wave-shift technique to increase the sensitive area3He tube replaces the detector.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic structural view of a thermal neutron detector provided in embodiment 1 of the present invention;
fig. 2 is a schematic diagram illustrating a spectrum test result of the thermal neutron detector provided in embodiment 1 of the present invention;
FIG. 3 is a schematic view of the shape of a wave-shifting light guide provided in embodiment 1 of the present invention;
fig. 4 is a schematic view of an arrangement of a photoelectric conversion device provided in embodiment 1 of the present invention;
fig. 5 is a schematic diagram of a test result of a 50cm long flat panel detector AmLi neutron source based on a lithium glass filament provided in embodiment 1 of the present invention.
Description of the symbols:
1-an upper reflective layer; 2-a lower reflective layer; a 3-wave shifting light guide; 4-lithium glass scintillator; 5-photoelectric conversion device.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a novel large-area thermal neutron detector, which introduces a wave shift technology to improve the sensitive area, thereby developing a high-performance large-size thermal neutron detector based on a lithium glass scintillator3He tube replaces the detector.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1:
domestic development of high-performance, large-size lithium-based glasses3Research on replacing a detector with a He tube is started late, the research is concentrated on lithium glass material preparation and small-sensitive-area lithium glass detector development at present, some researches disclose that 20-50 mu m lithium glass fiber (bare wire) is prepared by a crucible wire drawing method, and the detector is integrally cast by adopting a plurality of lithium glass fiber layers (2-5 mm) and a glass light guide, but because the lithium glass fiber (bare wire) is quickly attenuated in the light guide, the length of the detector is not more than 10cm, and because the optical fiber is densely arranged, the detector is closely conductiveThe neutron-gamma pulse discrimination effect is not ideal. Two lithium glass-based methods are successfully developed in foreign related research3He tube replaces a large area neutron detector: one is phi 120 mu m developed by Nucsafe corporation of America6Li glass optical fiber has high transparency and good toughness, and the length can exceed 2m, but6The Li glass fiber needs to control the refractive index and the conversion temperature of a cladding, so that the preparation process is complex, the duty ratio of a sensitive area is large, the cost is high when the Li glass fiber is bundled into a large-area detector for use, and in addition, the n-gamma discrimination effect is poor. The other is developed by Los Alamo laboratory6The Li glass light guide composite detector is assembled by liquid light guide and lithium glass particles (1.5mm), but the waste ratio of lithium glass particle machining is high, the detector assembly is complex, and the maximum length of the current detector is only 25.4cm, which is far lower than that of the current general detector3The length of the He tube (70cm/90 cm).
Based on this, the current lithium glass detector still does not solve two most core problems:
1) the processing and assembling process comprises the following steps: the mode of mechanically cutting lithium glass sheets and particles is used, raw material loss is large, the process of the multilayer lithium glass fiber is more complex, experimental conditions need to be strictly controlled, and the final detector is high in cost and low in practicability.
2) Detection performance: the fluorescent light collection mode of the common light guide is adopted, the sensitive area of the detector is very limited, and the gamma sensitivity and the detection efficiency are insufficient.
In order to solve the above problems, the present embodiment is configured to provide a novel large-area thermal neutron detector, as shown in fig. 1, including an upper reflective layer 1, a lower reflective layer 2, a wave-shift light guide 3, and a lithium glass scintillator 4. The wave-shift light guide 3 is positioned between the upper reflecting layer 1 and the lower reflecting layer 2, the lithium glass scintillator 4 is distributed in the wave-shift light guide 3 or on the surface of the wave-shift light guide 3, and the wave-shift light guide 3 is used for transferring the wavelength of the fluorescent light emitted by the lithium glass scintillator 4 to a blue-green light long wavelength band.
The working principle of the thermal neutron detector is introduced here, and the neutron detection function of the thermal neutron detector is divided into the following two processes:
(1)6luminescence process of Li glass scintillator:
thermal neutrons (or moderated fast neutrons) are incident on6In Li glass scintillator (shown in FIG. 1)6Li glass scintillator of6Li glass filament morphology), and of6Trapping nuclear reaction of Li nuclide6Li(n，α)H3Charged particles alpha and H3Ionizes in a glass matrix and transfers energy to a scintillation center activator ion (typically the lanthanide ion Ce)3+) The fluorescence is excited and retreated to excite and emit ultraviolet-visible band fluorescence with a certain wavelength, and the emission wavelength is 350-450 nm. Is different in that6The central emission wavelengths of Li glass scintillators are substantially all in this interval, with specific differences, such as those of U.S. GS20 and British KG26The luminescent wavelength of the Li glass scintillator is about 395nm, the product of Chinese CN26The emission wavelength of the Li glass scintillator is about 415 nm.
(2) Wave shifting process
The thermal neutron detector of the present embodiment incorporates a wave-shift light guide 3 (the wave-shift light guide 3 shown in fig. 1 is a flat-plate type wave-shift light guide) having a structure in which a plurality of light emitting elements are arranged in a matrix6The Li glass scintillator has the function of secondarily emitting ultraviolet-visible band fluorescence (350-450 nm) absorbed and then to blue-green band long wavelength (400-580 nm), namely, the wave-shifting light guide 3 has a wave-shifting mechanism, and generally, the wavelength shifting range reaches dozens to 100 nm. As shown in FIG. 2, FIG. 2(a) is a conventional one6Absorption and emission fluorescence spectra of a Li glass detector; FIG. 2(b) shows the absorption and emission fluorescence spectra of the detector after the wavelength-shifting light guide 3 is introduced in this embodiment. As can be seen from FIG. 2, the central wavelength of the fluorescence emitted from the lithium glass scintillator 4 was shifted from 410nm to 500nm in the long wavelength range after the introduction of the wavelength shift light guide 3. After the wavelength is shifted, because the intensity attenuation of light is approximately exponential attenuation rule along with the length of the light guide when the light is transmitted in the light guide, the blue-green fluorescence with longer wavelength is attenuated in the light guide and becomes slow, and the blue-green fluorescence can be transmitted to two far ends through the internal total reflection of the reflecting film, and is converted by the photoelectric device to form a pulse signal to realize detection. Therefore, the key point of the embodiment breaking through the large detection sensitive area of more than 50cm is to adopt the wave shift technical principle. The true bookAfter the wave-shift light guide 3 is introduced, the sensitive area of the detector can reach more than 50cm, which is developed by Los Alamo laboratory at present6The maximum length of the Li glass detector is only 25.4cm, and therefore the thermal neutron detector can obviously improve the sensitive area.
The embodiment successfully develops the all-solid-state with the sensitive region length of up to 50cm for the first time by utilizing the wave shift technology6The Li glass-based neutron detector has different core preparation process and fluorescence collection principle and mechanism from the prior art. Compared with the prior art, the thermal neutron detector of the embodiment can greatly reduce the gamma sensitivity of the detector, improve the detection efficiency and other performances, effectively reduce the cost and has obvious advantages.
Specifically, the main function of the wavelength-shifting light guide 3 of the present embodiment is to shift the fluorescence wavelength of the lithium glass scintillator 4 to a long wavelength, so as to realize absorption and secondary emission of the lithium glass fluorescence and convert the lithium glass fluorescence into long-wavelength fluorescence, so as to transmit the long-wavelength fluorescence to both ends of the wavelength-shifting light guide 3, and at this time, the wavelength-shifting light guide 3 can be used as a moderator, and can also improve light collection efficiency. Unlike ordinary quartz or organic light guides, the inside of the wave-shifting light guide 3 contains a chemical component wave-shifting agent for shifting ultraviolet-visible light toward blue-green light, and the wave-shifting agent may include one or more chemical substances having a function of absorbing fluorescence from low to high and converting emission, such as popp (1, 4-bis [2- (5-phenyloxazole) ] benzene), bis-msb (1, 4-bis (2-methylstyrene) benzene), me-msb (1, 4-bis (4-methylstyrene) benzene), and dpa (9, 10-diphenylanthracene), but is not limited to the above-listed ones.
The wave-shifting light guide 3 of the present embodiment is a solid wave-shifting light guide, a liquid wave-shifting light guide, or a common light guide coated with a wave-shifting agent on the surface, that is, the wave-shifting light guide 3 of the present embodiment includes various forms such as a solid wave-shifting light guide, a liquid wave-shifting light guide, and a wave-shifting agent coated on the surface of a common light guide.
The wave-shifting light guide 3 is a slab-type wave-shifting light guide, a strip-type wave-shifting light guide, or a ring-type wave-shifting light guide, i.e., the wave-shifting light guide 3 may be shaped as a slab, a strip, or a ring. As shown in fig. 3, the wave-shift light guide 3 of the present embodiment is formed by stacking one or more flat plate-type wave-shift light guides; alternatively, the wave-shifting light guide 3 is formed by one or more strip-shaped wave-shifting light guide arrays; alternatively, the wave-shifting light guide 3 is formed by stacking one or more ring-type wave-shifting light guides. Preferably, the wave-shift light guide 3 is formed by stacking a plurality of flat wave-shift light guides, as shown in fig. 3(a), the wave-shift light guide 3 is formed by stacking a plurality of strip wave-shift light guides, as shown in fig. 3(b), or the wave-shift light guide 3 is formed by stacking a plurality of ring wave-shift light guides, as shown in fig. 3(c), that is, the wave-shift light guide 3 may be arranged in a multi-layer flat plate, a plurality of strip or multi-ring structures, so as to adjust the structure of the sensitive region of the detector, and improve the detection efficiency and the uniformity of the spatial angular response.
The lithium glass scintillator 4 of the present embodiment is a lithium glass filament, a lithium glass particle, or a lithium glass flake. Specifically, taking a proper amount of Li2O、MgO、A12O3、SiO2And Ce2O3The precursor powder is ball-milled and mixed evenly to obtain a first mixture, and the first mixture is calcined to obtain a second mixture containing lithium, aluminum and silicon solid-solution oxides. Heating and melting the second mixture to obtain glass liquid, casting the glass liquid to obtain amorphous glass, annealing and crystallizing the amorphous glass to obtain crystallized glass containing lithium aluminum silicon solid solution oxide, and further preparing the lithium glass raw material, wherein the main luminescence wavelength of the lithium glass raw material is in a near ultraviolet band of 350-420 nm, and the softening temperature is about 1000 ℃. And then drawing the preform into a lithium glass bare wire with the diameter of 200-500 mu m. And (3) carrying out secondary processing on the lithium glass bare wire, cutting the lithium glass bare wire into lithium glass particles with the diameter of 1mm, and assembling the lithium glass particles into the lithium glass wire (the spacing between the particles is more than 2 mm). Compared with the lithium glass fiber, the lithium glass particles can further reduce the gamma sensitivity by about 100 times, so that the deposition capacity and sensitivity of the detector to gamma rays can be reduced, the influence of gamma ray interference on neutron detection in the environment can be reduced, and the performance of neutron detection can be improved.
The refractive index (1.56) of the wave-shift light guide 3 and the lithium glass scintillator 4 of the present embodiment are close, the wave-shift light guide 3 and the lithium glass scintillator 4 are optically coupled, and specifically, the lithium glass scintillator 4 is adhered or pressed inside or on the surface of the wave-shift light guide 3 by an optical silicone grease having a viscosity.
In order to realize signal readout of the detector, as shown in fig. 4, the thermal neutron detector of the present embodiment further includes a photoelectric conversion device 5, and the photoelectric conversion device 5 is used for single-ended or double-ended readout of signals, that is, the photoelectric conversion device 5 is located at either end of the wavelength-shifting light guide 3 or at both ends of the wavelength-shifting light guide 3 for signal readout. Specifically, when the detector is small in size, single-ended readout is adopted, that is, a photoelectric conversion device 5 is arranged at one end of the detector. When the size of the detector is large, for example, more than 50cm, the attenuation of light transmitted to two ends is large, and double-end reading is adopted, namely, a photoelectric conversion device 5 is simultaneously placed at two ends of the detector, which depends on the specific application scene. When double-end reading is used, the position of an incident neutron can be calculated through the pulse amplitude or the time difference of the double ends, namely, the position information is obtained according to signals at the two ends, and the pulse amplitude spectrum of the detector is corrected.
Specifically, the photoelectric conversion device 5 of the present embodiment is the same as the receiving surface of the wave-shifting light guide 3, or the photoelectric conversion device 5 and the wave-shifting light guide 3 are coupled using a tapered light guide. The photoelectric conversion device 5 of the present embodiment is a photomultiplier tube PMT or a silicon photomultiplier tube SIPM. Compared with a photomultiplier tube PMT, the silicon photomultiplier tube SIPM reading device using the semiconductor can reduce the volume of the detector and enhance the portability.
This embodiment discloses a low-cost novel large tracts of land6The Li glass solid detector adopts the technology of preform drawing and wave shift to solve the problems of small area, high gamma sensitivity and high cost of the lithium glass detector for a long time, has obvious advantages in the aspects of detection performance and the like, and has the advantages of3The capability of He replacement can be widely applied to the field of neutron detection. Compared with the existing neutron detector, the thermal neutron detector of the embodiment has the following advantages:
(1) the area of the detector is greatly increased: the fluorescence spectrum of the lithium glass scintillator 4 is moved from a near ultraviolet band to a blue light band (400-500nm) through the wave-shift light guide 3, so that the light attenuation length is greatly improved, and the area of the detector is greatly increased.
(2) The n-gamma pulse amplitude discrimination effect is good: FIG. 5(a) shows the pulse width of the whole 50cm detector as shown in FIG. 5The spectra (neutron source irradiates the whole detector), fig. 5(b) shows different detector positions (neutron source irradiates discrete positions of the detector, and the counting difference of different positions is due to different irradiation time, which does not affect and proves that the detection sensitive region range reaches 50cm) reconstructed by using signals at two ends. As can be seen from an examination of FIG. 56Li glass-PMMA detector in60Co (1.3 MeV. gamma.) and241in the pulse amplitude spectrum under the AmLi neutron source, a wider platform is formed between the energy and the thermal neutron peak after the deposition energy of high-energy gamma is reduced, so that the high-energy gamma can be well separated through amplitude discrimination. At the same time, the neutron counting rate is similar to that of high pressure3The plateau characteristic of the He tube shows that the detector has good stability, and the two characteristics are very important for applications such as nuclear safety monitoring.
(3) The detector has simple equipment process, small loss of the lithium glass material and greatly reduced cost.
The principle and the embodiment of the present invention are explained by applying specific examples, and the above description of the embodiments is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (10)
1. A novel large-area thermal neutron detector is characterized by comprising an upper reflecting layer, a lower reflecting layer, a wave-shift light guide and a lithium glass scintillator;
the wave-shifting light guide is positioned between the upper reflective layer and the lower reflective layer; the lithium glass scintillator is distributed in the interior or on the surface of the wave-shift light guide; the wavelength shifting light guide is used for shifting the wavelength of the fluorescence emitted by the lithium glass scintillator to a blue-green light long wavelength band.
2. The thermal neutron detector of claim 1, wherein the wave-shifting light guide is a solid wave-shifting light guide, a liquid wave-shifting light guide, or a common light guide with a wave-shifting agent coated on a surface thereof.
3. The thermal neutron detector of claim 1, wherein the wave-shifting light guide comprises wave-shifting agents, the wave-shifting agents comprising popp, bis-msb, me-msb, and dpa.
4. The thermal neutron detector of claim 1, wherein the wave-shift light guide is a slab wave-shift light guide, a strip wave-shift light guide, or a ring wave-shift light guide.
5. The thermal neutron detector of claim 4, wherein the wave-shift light guide is laminated by one or more flat plate-shaped wave-shift light guides;
or the wave-shift light guide is formed by one or more strip-type wave-shift light guide arrays;
alternatively, the wave-shifting light guide is formed by stacking one or more ring-type wave-shifting light guides.
6. The thermal neutron detector of claim 1, wherein the lithium glass scintillator is lithium glass filaments, lithium glass particles, or lithium glass flakes.
7. The thermal neutron detector of claim 1, wherein the lithium glass scintillator is bonded inside or on the surface of the wave-shifting light guide by an optical silicone grease with adhesive properties.
8. The thermal neutron detector of claim 1, wherein the thermal neutron detector further comprises a photoelectric conversion device; the photoelectric conversion devices are located at either end of the wavelength shifting light guide or at both ends of the wavelength shifting light guide.
9. The thermal neutron detector of claim 8, wherein the photoelectric conversion device and the wave-shifting light guide are coupled using a tapered light guide.
10. The thermal neutron detector of claim 8, wherein the photoelectric conversion device is a photomultiplier tube (PMT) or a silicon photomultiplier tube (SIPM).
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| CN202210139549.3A CN114460622B (en) | 2022-02-16 | 2022-02-16 | Novel large-area thermal neutron detector |
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| CN202210139549.3A CN114460622B (en) | 2022-02-16 | 2022-02-16 | Novel large-area thermal neutron detector |
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