CN114460622B - Novel large-area thermal neutron detector - Google Patents
Novel large-area thermal neutron detector Download PDFInfo
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- CN114460622B CN114460622B CN202210139549.3A CN202210139549A CN114460622B CN 114460622 B CN114460622 B CN 114460622B CN 202210139549 A CN202210139549 A CN 202210139549A CN 114460622 B CN114460622 B CN 114460622B
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T3/00—Measuring neutron radiation
- G01T3/06—Measuring neutron radiation with scintillation detectors
- G01T3/065—Spectrometry
Abstract
The invention relates to a novel large-area thermal neutron detector, which comprises an upper reflecting layer, a lower reflecting layer, a wave-shifting light guide and a lithium glass scintillator, wherein the wave-shifting light guide is positioned between the upper reflecting layer and the lower reflecting layer, the lithium glass scintillator is distributed in or on the surface of the wave-shifting light guide, and the wave-shifting light guide is used for transferring the wavelength of fluorescence emitted by the lithium glass scintillator to a blue-green light long wave band. By introducing wave shift technology to increase the sensitive area, high performance and large size are developed based on lithium glass scintillators 3 He tubes replace the detectors.
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 of nuclear radiation safety monitoring, in which 3 He tubes have excellent performance, and can be used at a rate of up to 75% or more in neutron detection. At present, the method is applied to the fields of fast-developing nuclear power industry, border port security, material structure research and the like 3 He tubes are widely used, e.g. in scattered neutron spectrometers, in nuclear safety monitoring systemsUsing a large scale 3 The He tube detects the array. But in recent years internationally 3 He gas has a rapid price rise due to serious shortage of resources, and development is urgent 3 Novel neutron detector replaced by He tube, wherein the novel neutron detector is based on 6 Probe development of Li glass is a hotspot of international research.
6 The Li glass scintillator is a thermal neutron detection material with very excellent performance, and the thermal neutron detection efficiency is high (75 percent: 1mm thick) 6 Li glass), short light decay time (-70 ns), and can realize n-gamma discrimination by simple pulse amplitude. Compared with other existing neutron detectors (CLYC, paint) 10 B straw pipe, 6 LiF/ZnS (Ag) detector, etc.), 6 the Li glass detector is expected to greatly improve neutron counting capacity, and can be suitable for high-low temperature and acid-base environments which cannot be applied to other detectors. However, for a long time, lithium glass has two main problems: firstly due to 6 The equivalent electron energy of the thermal neutron peak of the Li glass is about 1.5MeV, so that the sensitivity of the Li glass to high-energy gamma is higher, the particle size of the Li glass must be reduced to reduce the gamma deposition energy, and theoretically, the gamma sensitivity of the Li glass can be reduced to 10 by processing the Li glass into filaments, optical fibers or particles with the particle size of 280 mu m-1 mm -6 ～10 -3 . Secondly, it is 6 The fluorescence yield of Li glass is low (6000 pe) and the wavelength in the near ultraviolet region causes a short decay length of light transmission, limiting the increase of the sensitive area of the detector. The two disadvantages lead to the development of high performance and large size based on lithium glass 3 The technical difficulty of the He tube to replace the detector is high, and the He tube is also the key direction of research and attack at home and abroad.
Based on this, there is a need for a new high performance, large-sized large-area thermal neutron detector based on lithium glass scintillators.
Disclosure of 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 high-performance and large-size based on a lithium glass scintillator 3 He tubes replace the detectors.
In order to achieve the above object, the present invention provides the following solutions:
a novel large-area thermal neutron detector, which comprises an upper reflecting layer, a lower reflecting layer, a wave-shifting light guide and a lithium glass scintillator;
the wave-shifting light is located between the upper reflective layer and the lower reflective layer; the lithium glass scintillators are distributed in or on the surface of the wave-shifting light guide; the wavelength-shifting light guide is used to shift the wavelength of fluorescence emitted by the lithium glass scintillator to the blue-green 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-shifting light guide and a lithium glass scintillator, wherein the wave-shifting light guide is positioned between the upper reflecting layer and the lower reflecting layer, the lithium glass scintillator is distributed in or on the surface of the wave-shifting light guide, and the wave-shifting light guide is used for transferring the wavelength of fluorescence emitted by the lithium glass scintillator to a blue-green light long wave band. By introducing wave shift technology to increase the sensitive area, high performance and large size are developed based on lithium glass scintillators 3 He tubes replace the detectors.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are 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 other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a thermal neutron detector according to embodiment 1 of the present invention;
FIG. 2 is a schematic diagram of the spectrum test result of the thermal neutron detector according to embodiment 1 of the present invention;
FIG. 3 is a schematic view of the shape of the wave-shifting light guide according to embodiment 1 of the present invention;
fig. 4 is a schematic diagram showing the arrangement of a photoelectric conversion device according to embodiment 1 of the present invention;
fig. 5 is a schematic diagram of a test result of an AmLi neutron source of a 50cm long flat panel detector based on lithium glass filaments according to example 1 of the present invention.
Symbol description:
1-an upper reflective layer; 2-a lower reflective layer; 3-wave-shifting the light guide; 4-lithium glass scintillators; 5-photoelectric conversion device.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the 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 high-performance and large-size based on a lithium glass scintillator 3 He tubes replace the detectors.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1:
domestic development of high-performance and large-size lithium-based glasses 3 The research of replacing the detector by the He tube is started later, the research is focused on the preparation of lithium glass materials and the development of the lithium glass detector with small sensitive area, and some researches disclose that a crucible wire drawing method is used for preparing 20-50 mu m lithium glass fiber (bare wire), and a plurality of lithium glass fiber layers (2-5 mm) and a glass light guide are integrally poured into the detector, but the lithium glass fiber (bare wire) is attenuated rapidly in the light guide, the detector length is not more than 10cm, and the neutron-gamma pulse discrimination effect is not ideal because of dense optical fiber arrangement. The foreign related research successfully develops two lithium glass-based glasses 3 He tubes replace large area neutron detectors: phi 120 μm developed by Nucsafe corporation of America 6 A Li glass optical fiber is provided,it has high transparency and toughness, and can be longer than 2m 6 The Li glass fiber needs to control the refractive index and the conversion temperature of the 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 used by bundling into a large-area detector, and in addition, the n-gamma screening amplitude of the Li glass fiber is poor in screening effect. Another is developed in Los Alamo laboratories 6 The Li glass light guide composite detector is formed by assembling liquid light guide and lithium glass particles (1.5 mm), but the mechanical processing waste ratio of the lithium glass particles is high, the detector is complex to assemble, and the maximum length of the current detector is only 25.4cm, which is far lower than the current general purpose detector 3 Length of He tube (70 cm/90 cm).
Based on this, the current lithium glass detector still does not solve two most core problems:
1) The processing and assembling technology comprises the following steps: the mode of mechanically cutting the lithium glass flakes and particles is used, the loss of raw materials is large, the process of the multi-layer lithium glass fiber is more complex, experimental conditions are required to be strictly controlled, the cost of the final detector is high due to the fact that the multi-layer lithium glass fiber is not strong in practicability.
2) The detection performance is as follows: 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-mentioned problems, the present embodiment is used to provide a novel large-area thermal neutron detector, which includes an upper reflecting layer 1, a lower reflecting layer 2, a wave-shifting light guide 3 and a lithium glass scintillator 4, as shown in fig. 1. The wave-shifting light guide 3 is located between the upper reflective layer 1 and the lower reflective layer 2, the lithium glass scintillator 4 is distributed inside or on the surface of the wave-shifting light guide 3, and the wave-shifting light guide 3 is used for transferring the wavelength of the fluorescence emitted by the lithium glass scintillator 4 to the blue-green long wavelength band.
The working principle of the thermal neutron detector is introduced, and the thermal neutron detector realizes the neutron detection function by the following two processes:
(1) 6 luminescent process of Li glass scintillator:
thermal neutrons (or moderated fast neutrons) are incident on 6 Li glass scintillator (shown in FIG. 1 6 The Li glass scintillator is 6 Li glass filament morphology), and therein 6 Nuclear reaction of Li nuclide capture 6 Li(n，α)H 3 Charged particles alpha and H 3 Ionising in the glass matrix and transferring energy to scintillation center activator ions (typically lanthanide ions Ce 3+ ) The excitation and the backward excitation of the fluorescent lamp emit ultraviolet-visible wave band fluorescence with a certain wavelength, and the emission wavelength of the fluorescent lamp is between 350 and 450 nm. Different from 6 The central luminescence wavelengths of the Li glass scintillators are basically in the interval, and the specific difference is shown as GS20 and KG2 in the United kingdom 6 The luminescent wavelength of the Li glass scintillator is about 395nm, and the domestic CN2 is prepared 6 The emission wavelength of the Li glass scintillator is about 415nm.
(2) Wave shifting process
The thermal neutron detector of the present embodiment incorporates a wave-shifting light guide 3 (the wave-shifting light guide 3 shown in FIG. 1 is a plate-type wave-shifting light guide) having a structure in which a light source is arranged 6 The ultraviolet-visible band fluorescence (350-450 nm) of the Li glass scintillator is absorbed and then secondarily emitted to the blue-green light long band (400-580 nm), namely the wave shift light guide 3 has a wave shift mechanism, and the wavelength shift range of the wave shift light guide 3 is tens to 100nm in general. As shown in FIG. 2, FIG. 2 (a) is a conventional one 6 Absorption and emission fluorescence spectra of the Li glass detector; fig. 2 (b) shows the absorption and emission fluorescence spectra of the detector after the wave-shifting light guide 3 is introduced in this embodiment. As can be seen from fig. 2, after the wave-shifting light guide 3 is introduced, the center wavelength of the emitted fluorescence of the lithium glass scintillator 4 is shifted from the original 410nm to the long-wave 500nm. After the wavelength is moved, because the intensity attenuation of the light is in an approximately exponential attenuation law along with the length of the light guide when the light propagates in the light guide, blue-green fluorescence with longer wavelength is attenuated slowly in the light guide and can be transmitted to the two far ends through the internal total reflection of the reflecting film, and the blue-green fluorescence is converted by the photoelectric device to form pulse signals to realize detection. Therefore, the adoption of the wave shift technology principle is the key point that the embodiment breaks through a large detection sensitive area of more than 50 cm. After the wave-shifting light guide 3 is introduced in the embodiment, the sensitive area of the detector can reach more than 50cm, and the sensitivity area of the detector is developed in the Los Alamo laboratory at present 6 The maximum length of the Li glass detector is only 25.4cm, so that the thermal neutron detector of the embodiment can obviously improve the sensitivity surfaceAnd (3) accumulation.
The embodiment successfully develops the all-solid-state sensitive area with the length of up to 50cm by using the wave shift technology for the first time 6 The principle mechanisms of the preparation process and fluorescence collection of the core of the Li glass-based neutron detector are different from those of the prior art. In contrast, the thermal neutron detector of the embodiment can greatly reduce the gamma sensitivity of the detector, improve the detection efficiency and other performances, and simultaneously can effectively reduce the cost, and has obvious advantages.
Specifically, the main function of the wave-shifting light guide 3 in this embodiment is to shift the fluorescence wavelength of the lithium glass scintillator 4 to a long wave, so as to realize the absorption and secondary emission of the lithium glass fluorescence to be converted into the long wave fluorescence for transmission to the two ends of the wave-shifting light guide 3, and at this time, the wave-shifting light guide 3 can be used as a slowing body and can also improve the light collection efficiency. Unlike a general quartz or organic light guide, the wave-shifting agent containing chemical components inside the wave-shifting light guide 3 is used to shift the ultraviolet-visible light toward blue-green light, and the wave-shifting agent may include one or more chemical substances having a function of absorbing and converting fluorescence wavelengths from low to high, such as POPOPOP (1, 4-bis [2- (5-phenyloxazol) ] benzene), bis-msb (1, 4-bis (2-methylstyrene) benzene), me-msb (1, 4-bis (4-methylstyrene) benzene), dpa (9, 10-diphenylanthracene), and the like, but is not limited to the above-listed substances.
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 general light guide coated with a wave-shifting agent on the surface, that is, the wave-shifting light guide 3 of the present embodiment includes a solid wave-shifting light guide, a liquid wave-shifting light guide, and a plurality of forms such as a wave-shifting agent coated on the surface of the general light guide.
The wave-shifting light guide 3 is a plate-type wave-shifting light guide, a bar-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 plate, a bar or a ring. As shown in fig. 3, the wave-shifting light guide 3 of the present embodiment is formed by stacking one or more plate-type wave-shifting light guides; alternatively, the wave-shifting light guide 3 is formed by one or more arrays of strip-type wave-shifting light guides; alternatively, the wave-shifting light guide 3 is formed by stacking one or more ring-shaped wave-shifting light guides. Preferably, the wave-shifting light guide 3 is formed by stacking a plurality of flat-type wave-shifting light guides, as shown in fig. 3 (a), the wave-shifting light guide 3 is formed by stacking a plurality of strip-type wave-shifting light guides, as shown in fig. 3 (b), or the wave-shifting light guide 3 is formed by stacking a plurality of ring-type wave-shifting light guides, as shown in fig. 3 (c), that is, the wave-shifting light guides 3 can be arranged into a multi-layer flat-plate, a plurality of strip-type or multi-ring-shaped structure, so as to adjust the sensitive area structure of the detector, and improve the detection efficiency and the uniformity of the spatial angle 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, a proper amount of Li is taken 2 O、MgO、A1 2 O 3 、SiO 2 And Ce (Ce) 2 O 3 The precursor powder of (2) is ball-milled and mixed uniformly to obtain a first mixture, and the first mixture is calcined to obtain a second mixture containing lithium aluminum silicon solid solution oxide. Heating and melting the second mixture to obtain glass liquid, casting the glass liquid to obtain amorphous glass, and carrying out annealing treatment and crystallization heat treatment on the amorphous glass to obtain crystallized glass containing lithium aluminum silicon solid solution oxide, thereby preparing a 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 a prefabricated rod is adopted to make 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 into lithium glass particles with the diameter of 1mm, and assembling the lithium glass particles into the lithium glass wire (the particle spacing 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, can reduce the deposition capacity and sensitivity of the detector to gamma rays, is favorable for reducing the influence of gamma ray interference on neutron detection in the environment, and improves the performance of neutron detection.
The refractive index (1.56) of the wave-shifting light guide 3 of the present embodiment is close to that of the lithium glass scintillator 4, and the wave-shifting light guide 3 and the lithium glass scintillator 4 are optically coupled, specifically, the lithium glass scintillator 4 is adhered or pressed inside or on the surface of the wave-shifting light guide 3 by optical silicone grease with 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 single-ended or double-ended readout of the signal is performed by using the photoelectric conversion device 5, that is, the photoelectric conversion device 5 is located at either end of the waveshifting light guide 3 or at both ends of the waveshifting light guide 3 at the same time, so as to perform signal readout. Specifically, when the size of the detector is smaller, single-end readout is adopted, that is, one end of the detector is provided with a photoelectric conversion device 5. When the detector is large in size, for example, more than 50cm, the attenuation of light transmitted to two ends is large, and double-end reading is adopted at the moment, namely, a photoelectric conversion device 5 is simultaneously arranged at two ends of the detector, and the photoelectric conversion device depends on specific application scenes. When double-ended readout is used, the position of the incident neutron can be calculated by the pulse amplitude or time difference of the double ends, namely, 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 and the wave-shifting light guide 3 of the present embodiment have the same receiving surface, or the photoelectric conversion device 5 and the wave-shifting light guide 3 are coupled by a tapered light guide. The photoelectric conversion device 5 of the present embodiment is a photomultiplier PMT or a silicon photomultiplier SIPM. Compared with a photomultiplier PMT, the detector can be reduced in size and portability by using a semiconductor silicon photomultiplier SIPM for reading.
This embodiment discloses a novel large-area, low-cost 6 The Li glass solid-state detector adopts the preform rod wire drawing and wave shift technology 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 detection performance and the like, and has the advantages that 3 He substitution capability can be widely used in the neutron detection field. Compared with the existing neutron detector, the thermal neutron detector of the embodiment has the following advantages:
(1) The detector area is greatly increased: the fluorescence spectrum of the lithium glass scintillator 4 is shifted from the near ultraviolet band to the blue light band (400-500 nm) through the wave shift light guide 3, so that the light attenuation length is greatly improved, and the detector area is greatly increased.
(2) The n-gamma pulse amplitude discrimination effect is good: as shown in FIG. 5, FIG. 5 (a) shows the pulse amplitude spectrum of the entire 50cm detector (the neutron source irradiates the entire detector), and FIG. 5 (b) shows the different detector positions reconstructed by the two-end signals (the discrete positions of the neutron source irradiating the detector, the count difference of the different positions is due to the different irradiation times, and the detection sensitivity is not affectedRanging up to 50 cm). As can be seen from a review of FIG. 5 6 Li glass-PMMA detector 60 Co (1.3 MeV gamma) and 241 the pulse amplitude spectrum under the AmLi neutron source can form a wider platform between the high-energy gamma deposition energy and the thermal neutron peak after the deposition energy is reduced, so that the pulse amplitude spectrum can be well separated through amplitude discrimination. At the same time, the neutron counting rate is similar to that of high voltage 3 The plateau nature of He tubes suggests that the detector has good stability, both of which are critical for applications such as nuclear safety monitoring.
(3) The detector has simple equipment process, little lithium glass material loss and greatly reduced cost.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (9)
1. A large area thermal neutron detector, characterized in that the large area thermal neutron detector comprises an upper reflecting layer, a lower reflecting layer, a wave-shifting light guide and a lithium glass scintillator;
the wave-shifting light is located between the upper reflective layer and the lower reflective layer; the lithium glass scintillators are distributed in or on the surface of the wave-shifting light guide; the wave-shifting light guide is used for transferring the wavelength of fluorescence emitted by the lithium glass scintillator to a blue-green light long wave band and improving the length of a sensitive area of the large-area thermal neutron detector to 50cm or more; the fluorescence emitted by the lithium glass scintillator is ultraviolet-visible band fluorescence;
the wave-shifting light guide includes a wave-shifting agent for shifting ultraviolet-visible light to blue-green light;
the lithium glass scintillator is a lithium glass filament, and the preparation method comprises the following steps: taking a proper amount of Li 2 O、MgO、Al 2 O 3 、SiO 2 And Ce (Ce) 2 O 3 The precursor powder of the lithium aluminum silicon solid solution oxide is prepared by ball milling and mixing uniformly to obtain a first mixture, calcining the first mixture to obtain a second mixture containing lithium aluminum silicon solid solution oxide, 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 the lithium aluminum silicon solid solution oxide, drawing a 200-500-micrometer lithium glass bare wire by a preform rod, carrying out secondary processing on the lithium glass bare wire, cutting the lithium glass bare wire into lithium glass particles, and assembling the lithium glass particles to form the spaced lithium glass wire.
2. The large area 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 plain light guide surface coated with a wave-shifting agent.
3. The large area thermal neutron detector of claim 1, wherein the wave-shifting agent comprises popp, bis-msb, me-msb and dpa.
4. The large area thermal neutron detector of claim 1, wherein the wave-shifting light guide is a plate-type wave-shifting light guide, a bar-type wave-shifting light guide or a ring-type wave-shifting light guide.
5. The large area thermal neutron detector of claim 4, wherein the wave-shifting light guide is formed by stacking one or more planar wave-shifting light guides;
alternatively, the wave-shifting light guide is formed by one or more arrays of strip-type wave-shifting light guides;
alternatively, the wave-shifting light guide is laminated by one or more annular wave-shifting light guides.
6. The large area thermal neutron detector of claim 1, wherein the lithium glass scintillator is adhered to the inside or surface of the waveshifting light guide by an optical silicone grease having an adhesive property.
7. The large area thermal neutron detector of claim 1, wherein the large area thermal neutron detector further comprises a photoelectric conversion device; the photoelectric conversion device is positioned at either end of the wave-shifting light guide or at both ends of the wave-shifting light guide.
8. The large area thermal neutron detector of claim 7, wherein the photoelectric conversion device and the wave-shifting light guide are coupled using a tapered light guide.
9. The large area thermal neutron detector of claim 7, wherein the photoelectric conversion device is a photomultiplier tube PMT or a silicon photomultiplier SIPM.
Priority Applications (1)
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