A small β detector for particle monitoring based on MPPC

Abstract

The present invention discloses a small β detector for monitoring particulate matter based on MPPC, and its structure includes a plastic scintillator, a light guide, an MPPC, a circuit board, a housing, a shielding window, and a cable. The scintillator and the MPPC are coupled together by optical glue through the light guide; the side of the scintillator and the side of the light guide are both made with a reflective layer; the circuit board is integrated with a temperature compensation power supply circuit and a signal processing circuit; the housing includes an end cover, a main body, and a back cover, and the end cover and the front end of the main body are both provided with the shielding window. The present invention adopts a new type of semiconductor optoelectronic device MPPC, matches the β-type scintillator and the power supply and signal processing circuit suitable for MPPC, and realizes the counting detection of β rays; and by using the light guide, a larger effective detection area is realized when using an MPPC with a smaller effective photosensitive area, while ensuring a low background and high detection efficiency, which is very suitable for use in the fields of atmospheric dust particle monitoring, paper thickness measurement, etc.

Description

[0001] Technical field.

[0002] The invention relates to the technical field of beta ray detection, and in particular to a small beta detector for particle monitoring based on MPPC.

[0003] Background technology.

[0004] As the country's requirements for environmental governance become increasingly stringent, the concentration of dust / particles (PM10 and PM2.5) in the air, as a component of environmental pollution, has become an important monitoring target for environmental protection departments at all levels. Air particle monitors are important instruments and equipment used to monitor the concentration of particles in ambient air. They are widely used in automatic atmospheric monitoring stations, dust monitoring in various places, air micro stations, smart city monitoring stations, and even home or portable personal particle monitoring.

[0005] At present, there are four types of air particulate monitors according to their principles, namely, weight method, micro-oscillating balance method, β-ray method and light scattering method, each method has its own advantages and disadvantages. Among them, the particle monitor using the β-ray method uses the principle that β-rays penetrate the material and are absorbed and attenuated in intensity. The ambient air is sucked into the sampling tube by a sampling pump and discharged after passing through the filter membrane. The particles in the air are trapped on the filter membrane to form dust spots, and then the attenuation of β-rays passing through the filter membrane dust spots is measured to calculate the concentration of particles. The β-ray method has a wide range of applications, accurate measurement, and high sensitivity. It is one of the main methods for monitoring the concentration of air particulate matter, and plays an increasingly important role in various aspects such as atmospheric monitoring and construction site dust monitoring.

[0006] In the particle monitor using the β-ray method, the detector part used to realize the β-ray measurement is one of the core components. The β detectors currently used are mainly Geiger counters and β-scintillation detectors based on photomultiplier tubes (PMTs). Geiger counters are designed based on the ionization properties of radiation on gases. The operating voltage is about several hundred volts, the service life is relatively short, the dead time is long, and the detection efficiency of high-energy β-rays is not high. Nowadays, they have been gradually replaced by β-scintillation detectors based on PMTs. β-scintillation detectors based on PMTs use the luminescence of scintillators when they are exposed to ionizing radiation for detection. They have the advantages of long life, fast response, high detection efficiency, and good temperature characteristics. However, the PMTs used generally need to provide a high operating voltage of thousands of volts, are easily affected by magnetic fields, are large in size, and have high power consumption, which is not conducive to the application of portable devices. In addition, the manufacturing process of PMTs is complex, and it is difficult to reduce costs, which is not conducive to the application of monitoring equipment that needs to be widely deployed.

[0007] Multi-Pixel Photon Counter (MPPC), also known as Silicon photomultiplier (SiPM), is a new type of photoelectric conversion device with the advantages of low operating voltage, small size, high sensitivity, resistance to magnetic field interference, strong resistance to mechanical shock and low mass production cost. It is not only conducive to reducing the size of the detector, improving the stability and safety of the detector, but also conducive to reducing costs. It has broad application prospects in high-energy physics experiments, cosmic ray observations, nuclear medicine imaging, nuclear safety and environmental monitoring.

[0008] In recent years, MPPC has received more and more attention in various nuclear radiation measurement fields, and has begun to replace PMT in some applications, especially in gamma detection of nuclear medicine imaging equipment, where it has been maturely applied. It has also gradually begun to be studied and used in other fields such as environmental radiation safety and nuclear safety inspections. However, its application in particulate matter monitoring is still blank.

[0009] The lower limit, upper limit and detection limit of the β-ray air particle monitor are related to the size of the dust spot on the filter membrane. Accordingly, the β detector is required to have a sufficiently large effective detection area and a sufficiently high detection efficiency. The β-ray air particle monitor usually uses a low-energy 14C radioactive source with a long half-life. The activity range is generally below the exemption value. It has good stability, safety and durability. However, due to the relatively weak energy of its β-rays, it is very easy to be blocked and absorbed. The luminescence after interaction with the plastic scintillator is also very weak. The β detector is also required to have a high detection efficiency. In order to ensure a high detection efficiency, on the one hand, the detector window needs to minimize the blocking of β-rays while meeting the light-shielding requirement. On the other hand, the luminescence of the plastic scintillator needs to be collected on the photosensitive surface as little as possible without loss. The volume of MPPC is significantly smaller than that of PMT, but the photosensitive area is also relatively small. Moreover, the size of its photosensitive area is related to the cost of the device. On the premise of ensuring that the detector has a large effective detection area, it is necessary to use a relatively low-cost MPPC device with a small effective photosensitive area, which is critical for the effective collection of scintillation light.

[0010] The application of the beta-ray method for particle monitoring is to detect the weak light generated by low-energy beta rays. The circuit design and threshold parameter setting of the corresponding detector should not only effectively remove noise and ensure a low background count rate, but also effectively detect the ray signal to further ensure high detection efficiency. In particular, atmospheric particulate monitoring requires high measurement accuracy and the ability to adapt to a certain range of ambient temperature changes. Therefore, the detector is required to have good temperature characteristics so that the output can remain stable even when the ambient temperature changes. This can avoid requiring the monitoring instrument itself to perform very precise constant temperature control, which is relatively difficult and costly. Generally, the PMT itself has good temperature characteristics. The scintillation counting detector using the PMT can also be set according to the plateau characteristics of the PMT to make the PMT work in the plateau area through appropriate parameter settings, so that the output scintillation counting signal is not easily affected by temperature changes. The temperature coefficient of the MPPC device itself is significantly higher than that of the PMT, and its temperature characteristics are relatively poor. It cannot work in the plateau area like the PMT. Therefore, it is relatively technically difficult to realize a β-ray counting detector with excellent performance based on MPPC. It is necessary to design an adapter circuit according to the characteristics of the MPPC, and to obtain low background and high detection efficiency by setting the appropriate MPPC working voltage, extracting, amplifying and distinguishing the appropriate MPPC signal, and ensuring effective detection of the ray signal and removal of the noise signal. It is also necessary to perform accurate working voltage compensation according to the MPPC temperature characteristics to ensure that the detector has good temperature stability.

[0011] Contents of the invention.

[0012] The technical problem to be solved by the present invention is: in view of the problems of large size, high power consumption, difficult cost control and inconvenience for use in portable devices of PMT-based β scintillation detectors, the present invention adopts a new MPPC photoelectric sensor with smaller size and lower price to replace the traditional PMT, and designs a light guide between the larger scintillator and the smaller photosensitive MPPC to optimally collect and conduct the scintillation light. In addition, a temperature compensation power supply circuit that can accurately adjust the temperature coefficient and an adaptive MPPC signal extraction, amplification and discrimination circuit are designed. On the basis of ensuring excellent detection performance, a small-sized, low-power β scintillation detector that can significantly reduce costs in batches and can be applied to portable devices is realized.

[0013] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a small β detector for monitoring particulate matter based on MPPC of the present invention comprises a shielding window, a scintillator, a light guide, an MPPC, a circuit board, a shell, a cable, an upper circular plate, a first long strip plate, a second long strip plate, a lower circular plate, an end cover, a main body, and a back cover; the shell comprises an end cover, a main body and a back cover, the main body is cylindrical, the end cover and the main body are connected by threads, and the back cover and the main body are fixed by screws; the scintillator, the light guide, the MPPC, and the circuit board are installed in the shell; the shielding window is arranged on the inner side of the end cover and the front end of the shell main body; one end of the scintillator is connected to the shielding window, and the other end is coupled to the end face of the light guide; the other end face of the light guide is connected to the MPP C coupling; the circuit board includes an upper circular plate, a lower circular plate, a first long strip plate and a second long strip plate, the upper circular plate, the lower circular plate, the first long strip plate and the second long strip plate are connected and fixed to each other by pins, the upper circular plate and the lower circular plate are parallel to each other, the first long strip plate and the second long strip plate are parallel to each other, forming a "Ⅱ" shape; the MPPC is welded on the upper circular plate; the circuit board integrates the power supply circuit and signal processing circuit adapted by the MPPC; the first long strip plate is a power supply circuit, which provides the working voltage for the MPPC; the second long strip plate is a signal processing circuit, which amplifies, identifies and shapes the output signal of the MPPC; the lower circular plate has a through hole, and a cable is led out to input a low-voltage power supply and output a standard TLL signal.

[0014] Preferably, the MPPC is a non-array device having an effective photosensitive area that is smaller than the surface area of ​​the scintillator.

[0015] Preferably, the scintillator is a plastic scintillator sheet.

[0016] Preferably, the light guide is made of optical glass or optical organic glass.

[0017] Preferably, the light guide is a frustum structure, the surface of the larger end has the same shape and area as the surface of the scintillator, and the diameter of the end face with a smaller area of ​​the light guide is the same as the side length of the effective area of ​​the MPPC, so as to collect the light emitted by the larger area of ​​the scintillator and transmit it to the smaller area of ​​the MPPC detection window.

[0018] Preferably, the height of the light guide is between greater than (S1-S2) / 2 and less than (S1-S2), wherein S1 is the diameter or side length of the larger end face of the light guide, and S2 is the diameter or side length of the smaller end face of the light guide; the height that can achieve optimal light collection and light conduction is preferably determined after actual measurement and comparison of light guides of different heights by using an amplitude spectrum test plus a count rate test method.

[0019] Preferably, the larger end face of the light guide is coupled to the plastic scintillator sheet by using optical glue.

[0020] Preferably, the smaller end face of the light guide and the photosensitive surface of the MPPC are coupled together and fixed using optical glue.

[0021] Preferably, after the scintillator is coupled to the light guide, the whole is manufactured with a light reflecting layer having full side coverage and high reflectivity to reduce light loss as much as possible.

[0022] Preferably, the material, geometric shape and size of the light guide, the coupling of the scintillator and the light guide, and the high-reflectivity light reflecting layer that fully covers the sides together ensure the light collection efficiency to the greatest extent, thereby ensuring the detection efficiency of the weak scintillation light generated by low-energy beta rays.

[0023] Preferably, the circuit board includes an upper circular plate, a lower circular plate, a first long strip plate and a second long strip plate. The sub-plates are connected and fixed to each other by pins. The upper circular plate and the lower circular plate are parallel to each other, and the first long strip plate and the second long strip plate are parallel to each other, forming an "Ⅱ" shape, which is designed according to the slender cylindrical shell structure.

[0024] Preferably, the circuit board integrates a power supply circuit and a signal processing circuit adapted for the MPPC; the MPPC is welded on the upper circular plate; the first long strip is a power supply circuit, which provides a working voltage for the MPPC; the second long strip is a signal processing circuit, which amplifies, identifies and shapes the output signal of the MPPC, and the parameter settings of the signal amplification circuit and the identification threshold set according to the characteristics of the MPPC used balance the low background count rate and high detection efficiency, while also ensuring the anti-interference performance of the detector; the lower circular plate leads out a cable / connector for inputting a low-voltage power supply and outputting a standard TLL signal.

[0025] Preferably, the power supply circuit is a temperature compensated circuit, which is designed to be able to finely adjust the temperature coefficient and the output voltage, and can provide a suitable operating voltage for the MPPC according to the ambient temperature, so that the output gain of the MPPC and the output count rate of the detector are stable within a certain temperature variation range.

[0026] Preferably, the shell includes an end cover, a main body and a back cover, and is made of aluminum alloy; the main body is cylindrical, the end cover and the middle cylinder are connected by threads, and the back cover and the middle cylinder are fixed by screws.

[0027] Preferably, the shielding window is a double-sided aluminum-plated polyester film. The double-sided aluminum-plated polyester film shielding window consists of two layers, which are respectively arranged on the inner side of the end cover and the front end of the main body, and are bonded and fixed with sealant. Under the premise of minimizing the blocking of β rays as much as possible, the light shielding and sealing of the front end of the detector are achieved at the same time.

[0028] Preferably, the scintillator, the light guide, the MPPC and the circuit board are housed in the housing.

[0029] Preferably, the front end surface of the scintillator is close to the shielding window at the front end of the main body, and the shielding window also plays a role of light reflection, reflecting the photons emitted from the front end surface of the scintillator back and collecting them to the MPPC via the light guide, thereby reducing the light loss at the front end surface of the scintillator and further ensuring the detection efficiency of the detector.

[0030] Preferably, the lower circular plate is fixed to the outer shell with black glue, thereby achieving light protection and sealing of the rear end of the detector.

[0031] Preferably, the ground of the circuit board is electrically connected to the housing, which further ensures the excellent anti-interference performance of the detector.

[0032] Preferably, in one of the embodiments, the MPPC is a device with an effective area of ​​3 mm×3 mm.

[0033] Preferably, in one of the embodiments, the MPPC is a device with an effective area of ​​4 mm×4 mm.

[0034] Preferably, in one of the embodiments, the MPPC is a device with an effective area of ​​6 mm×6 mm.

[0035] Preferably, in one embodiment, the light reflecting layer is made of Teflon wrapped and coated with aluminum foil.

[0036] Preferably, in one embodiment, the light reflecting layer is a titanium dioxide reflective coating.

[0037] Preferably, in one embodiment, the light reflecting layer is a nano-reflective coating.

[0038] The beneficial effects of the present invention are as follows: 1. A new type of semiconductor photoelectric device MPPC is used to replace the traditional PMT, and a plastic scintillator and a power supply and signal processing circuit designed by the inventor to adapt to MPPC are matched, so as to realize a low-energy β-ray scintillation counting detector suitable for particulate matter monitoring; 2. The preferred light guide shape and specification design verified by experiments enable the detector to achieve a larger effective detection area and high detection efficiency when using MPPC with a smaller effective photosensitive area, which is conducive to low-cost control; 3. The setting of power supply, signal amplification and discrimination parameters adapted to MPPC ensures the low background, high detection efficiency and good temperature characteristics of the detector, and the output count rate is stable and not easily affected by temperature; 4. On the basis of achieving excellent detection performance, the detector has high integration, compact structure and small appearance, and can convert the detected β-rays into standard TTL signal output, with low power consumption, high safety, easy use, and can be suitable for portable devices; 5. The detector also has the advantages of good light shielding, good sealing, not being easily affected by magnetic fields, and strong anti-electromagnetic interference ability.

[0039] Description of the drawings.

[0040] Figure 1 It is a schematic diagram of the working principle of the present invention.

[0041] Figure 2 It is a schematic diagram of the structure of the present invention.

[0042] On the figure: shielding window 1, scintillator 2, light guide 3, MPPC 4, circuit board 5, housing 6, cable 7, upper circular plate 51, first long strip plate 52, second long strip plate 53, lower circular plate 54, end cover 61, main body 62, back cover 63.

[0043] Specific implementation method.

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods, but the examples given are not intended to limit the present invention.

[0045] See attached Figure 1 The working principle of the small β scintillation detector for particulate matter monitoring in this embodiment is schematically shown. β rays pass through the detector shielding window, and the luminescence of the scintillator is collected on the MPPC photosensitive surface to effectively collect the scintillation light. The adapter circuit is designed according to the characteristics of the MPPC. By setting the appropriate MPPC working voltage, the appropriate MPPC signal is extracted, amplified and identified, and the effective detection of the ray signal and the removal of the noise signal are guaranteed at the same time, so as to obtain low background and high detection efficiency. It is also necessary to perform accurate working voltage compensation according to the MPPC temperature characteristics to ensure that the detector has good temperature stability. The rear end leads to a cable from the circuit board for low-voltage power input and TTL signal output.

[0046] See attached Figure 1 and attached Figure 2 The small β scintillation detector for monitoring particulate matter in this embodiment includes: a shielding window 1, a scintillator 2, a light guide 3, an MPPC4, a circuit board 5, a housing 6 and a cable 7. The MPPC4 is welded on the circuit board 5, the scintillator 2 and the MPPC4 are respectively coupled with the two end faces of the light guide 3, the scintillator 2, the light guide 3, the MPPC4 and the circuit board 5 are installed in the housing 6, the front end of the housing 6 is fixed with a shielding window 1, and the rear end is led out of the circuit board to the cable 7 for low-voltage power input and TTL signal output.

[0047] In this embodiment, the scintillator 2 is a plastic scintillator sheet with a specification of φ14mm×0.5mm, which can achieve an effective detection area of ​​φ12mm. The thickness of 0.5mm has sufficient blocking effect on the lower energy β rays of the detected 14C radiation source, and can ensure detection efficiency.

[0048] In this embodiment, MPPC4 is a non-array product developed by Hamamatsu Photonics Co., Ltd. of Japan, and its effective photosensitive area is 3 mm*3 mm.

[0049] In this embodiment, the light guide 3 is made of optical organic glass material and has a truncated cone structure; the diameter of the end face of the light guide 3 with a larger area is the same as the surface diameter of the scintillator 2, and is coupled to the scintillator 2 using optical silicone; the diameter of the end face of the light guide 3 with a smaller area is the same as the side length of the effective area of ​​the MPPC4, and is coupled to the photosensitive surface of the MPPC4 using optical silicone; the overall side of the light guide 3 and the scintillator 2 is made of a fully covered light reflection layer with a certain thickness, which has a good light reflection effect; the height of the light guide 3 is between 5.5mm and 11mm, and the height that can achieve the best light collection and light transmission is selected through experimental comparison; such a geometric structure allows most of the light reaching the side to be collected on the photosensitive surface of the MPPC4 quickly through reflection, thereby reducing light loss as much as possible. In this way, a larger detection area and high detection efficiency can be achieved while using a relatively low-cost MPPC4 with a small effective photosensitive area.

[0050] In this embodiment, the light reflection layer uses a nano-reflective coating with a certain thickness and a reflectivity of 95% or more, which reduces the light transmission loss on the sides of the scintillator 2 and the light guide 3.

[0051] In this embodiment, the coupling between the light guide 3 and the MPPC 4 is reinforced by using fixing glue to prevent decoupling due to force.

[0052] In this embodiment, the circuit board 5 includes an upper circular plate 51, a first long strip plate 52, a second long strip plate 53 and a lower circular plate 54. The sub-plates are connected and fixed to each other by pins. The upper circular plate and the lower circular plate are parallel to each other, and the first long strip plate and the second long strip plate are parallel to each other, forming an "Ⅱ" shape, which is suitable for being installed in a slender cylindrical shell structure and fixed, and is also suitable for circuit division according to different functions. MPPC4 is welded on the upper circular plate 51; the first long strip 52 is provided with a power supply circuit with a temperature compensation function, and its temperature coefficient and output voltage are designed to be finely adjusted, so that a suitable working voltage can be provided for MPPC4 according to the real-time feedback temperature of the temperature sensor near MPPC4 and the temperature coefficient of MPPC4, ensuring that the output gain of MPPC4 remains stable within the temperature range of -10°C to +45°C, thereby keeping the output count rate of the detector stable; the second long strip 53 is a signal processing circuit, which leads out a pulse signal according to the characteristics of the MPPC used, and then amplifies, discriminates, and shapes it into a standard TTL level signal. The parameter settings of the amplification and discrimination circuits are preferably set by actual measurements, so that the detector can strike a balance between a low background count rate and a high detector efficiency; the lower circular plate 54 is an input and output circuit board, which leads out a cable 7 to the outside of the housing 6, provides a low-voltage power input for the circuit board 5 and outputs a TTL signal.

[0053] In this embodiment, the housing 6 is composed of an end cap 61, a main body 62 and a rear cover 63, and is cylindrical in shape and made of aluminum alloy. A shielding window 1 is fixed to the front ends of the end cap 61 and the main body 62 with sealant; the shielding window 1 is a double-sided aluminum-plated polyester film, and the design of the two layers of shielding windows satisfies the requirement of complete light protection while minimizing the influence on the passage of low-energy β rays; the end cap 61 and the main body 62 are fixed by threaded connection and have good electrical conduction, and the rear cover 63 and the main body 62 are fixed by screw connection and have good electrical conduction; there is a through hole on the rear cover 63 for the cable 7 to pass through.

[0054] In this embodiment, the scintillator 2, the light guide 3, the MPPC4, and the circuit board 5 are installed in the housing 6; the front end surface of the scintillator 2 is close to the aluminum foil film shielding window 1 at the front end of the main body. This structure enables the shielding window 1 to not only meet the light-shielding function but also play a role of light reflection, reducing the loss of scintillation light from the front end surface of the scintillator 2, thereby providing further guarantee for the detector to obtain high detection efficiency; the lower circular plate 54 and the main body 62 are fixed with black glue, and at the same time, the light shielding and sealing of the rear end of the detector are realized, so that when the detector is used in the particle monitor equipment, there is no need to make excessively high requirements on the light shielding of the equipment, and the measurement accuracy problem caused by leakage in the gas path is avoided as much as possible.

[0055] In this embodiment, the ground of the circuit board 5 is connected to the rear cover 63 through the ground wire led out from the lower circular plate 54, so as to achieve electrical connectivity and form a good shielding, further ensuring the excellent anti-interference ability of the detector.

[0056] In summary, the small β scintillation detector in this scheme adopts a new type of semiconductor photoelectric sensor MPPC4, utilizes a truncated cone-shaped light guide 3, matches a thin-sheet plastic scintillator 2, and adds a power supply and signal processing circuit design and circuit parameter setting suitable for MPPC, a reasonable and compact structure and shell design. While using the MPPC4 with a small effective photosensitive area and relatively low cost, it achieves a large effective detection area and high detection efficiency, converts the detected β rays into a standard TTL signal, and has a compact shape (φ20mm*75mm) and low power consumption (0.2W), is very easy to use and suitable for portable devices, and also has the characteristics of good temperature characteristics, good light protection, good sealing, not easily affected by magnetic fields, and strong anti-electromagnetic interference ability, and is very suitable for atmospheric dust particle monitoring, dust monitoring in various occasions, paper thickness measurement and other fields.

[0057] The above description is only a preferred embodiment to fully illustrate the present invention. The features described in the description are still satisfied or partially satisfied in other embodiments; any local modifications or equivalent substitutions made under the spirit and principles of the present invention will be deemed to be within the scope of protection of the present invention.

Claims

1. A small β scintillation detector for particle monitoring based on MPPC, comprising a shielding window, a scintillator, a light guide, an MPPC, a circuit board, a housing, a cable, an upper circular plate, a first long strip plate, a second long strip plate, a lower circular plate, an end cover, a main body, and a rear cover; characterized in that: The shell comprises an end cover, a main body and a back cover, the main body is cylindrical, the end cover and the main body are connected by threads, and the back cover and the main body are fixed by screws; the scintillator, light guide, MPPC and circuit board are installed in the shell; the shielding window is arranged on the inner side of the end cover and the front end of the shell main body, the shielding window is a double-sided aluminum-plated polyester film, and the double-sided aluminum-plated polyester film shielding window has two layers, which are respectively arranged on the inner side of the end cover and the front end of the main body; one end of the scintillator is connected to the shielding window, and the other end is coupled to the end face of the light guide, and the front end surface of the scintillator is close to the shielding window at the front end of the main body; The other side end face of the light guide is coupled with the MPPC; the circuit board includes an upper circular plate, a lower circular plate, a first long strip plate and a second long strip plate, the upper circular plate, the lower circular plate, the first long strip plate and the second long strip plate are connected and fixed to each other by pins, the upper circular plate and the lower circular plate are parallel to each other, the first long strip plate and the second long strip plate are parallel to each other, forming a "Ⅱ" shape; the MPPC is welded on the upper circular plate; the circuit board integrates the power supply circuit and signal processing circuit adapted by the MPPC; the first long strip plate is a power supply circuit, which provides the working voltage for the MPPC; the second long strip plate is a signal processing circuit, which amplifies, identifies and shapes the output signal of the MPPC; the lower circular plate has a through hole, and a cable is led out to input a low-voltage power supply and output a standard TLL signal; the scintillator is a plastic scintillator sheet.

2. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The MPPC is a non-array device with an effective photosensitive area that is small compared to the surface area of ​​the scintillator.

3. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The material of the light guide is one of optical glass or optical organic glass.

4. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The light guide is a frustum structure, the surface of the larger end has the same shape and area as the surface of the scintillator, and the diameter of the end face with a smaller area of ​​the light guide is the same as the side length of the effective area of ​​the MPPC, and is used to collect the light from the larger area of ​​the scintillator and transmit it to the smaller area of ​​the MPPC detection window.

5. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The height of the light guide is between greater than (S1-S2) / 2 and less than (S1-S2), wherein S1 is the diameter or side length of the larger end face of the light guide, and S2 is the diameter or side length of the smaller end face of the light guide; the height that can achieve optimal light collection and light transmission is determined by measuring and comparing light guides of different heights using an amplitude spectrum test plus a count rate test method.

6. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The larger end surface of the light guide is coupled with the plastic scintillator sheet by using optical glue.

7. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The smaller end face of the light guide and the photosensitive surface of the MPPC are coupled together and fixed by using optical glue.

8. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: After the scintillator is coupled to the light guide, the whole is manufactured with a light reflecting layer having a high reflectivity and fully covering the sides, so as to reduce light loss as much as possible.

9. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The material, geometric shape and size of the light guide, the coupling of the scintillator and the light guide, and the high-reflectivity light reflecting layer that fully covers the sides together ensure the light collection efficiency to the greatest extent, thereby ensuring the detection efficiency of the weak scintillation light generated by low-energy beta rays.

10. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The power supply circuit is a temperature compensation circuit, which is designed to be able to finely adjust the temperature coefficient and the output voltage. It can provide a suitable operating voltage for the MPPC according to the ambient temperature, and stabilize the output gain of the MPPC and the output count rate of the detector within a certain temperature variation range.

11. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The shell is made of aluminum alloy material.

12. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The two layers of shielding windows are bonded and fixed to the inner side of the end cover and the front end of the main body by using sealant.

13. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The lower circular plate and the housing are fixed with black glue, which simultaneously realizes light protection and sealing of the rear end of the detector.

14. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: The ground of the circuit board is electrically connected to the housing, which further ensures the excellent anti-interference performance of the detector.

15. The small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: In one embodiment, the MPPC is a device with an effective area of ​​3 mm×3 mm.

16. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: In one embodiment, the MPPC is a device with an active area of ​​4 mm×4 mm.

17. A small β scintillation detector for particle monitoring based on MPPC according to claim 1, characterized in that: In one embodiment, the MPPC is a device with an effective area of ​​6 mm×6 mm.

18. The small β scintillation detector for particle monitoring based on MPPC according to claim 8, characterized in that: In one embodiment, the light reflecting layer is made of Teflon wrapped and coated with aluminum foil.

19. The small β scintillation detector for particle monitoring based on MPPC according to claim 8, characterized in that: In one embodiment, the light reflecting layer is a titanium dioxide reflective coating.

20. The small β scintillation detector for particle monitoring based on MPPC according to claim 8, characterized in that: In one embodiment, the light reflecting layer is a nano-reflective coating.

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