< 210 > Po activity detection device of [mu] Bq / cm < 2 >

Abstract

The invention discloses a [mu] Bq / cm < 2 > level < 210 > Po activity detection device, belongs to the technical field of radionuclide detection, and is used for high-sensitivity detection of radionuclide < 210 > Po activity on the surface of a material in a low background experiment. Comprising a glove box, a sample cavity, a SiPIN detector array, an electronics box and a vacuum system. The glove box maintains a low-radon environment through nitrogen purging, and the sample cavity is sealed by adopting a KF200 flange and is connected with a vacuum pump; the nine SiPIN detectors connected in parallel are arranged in a 3 * 3 array, and the total sensitive area is 29.2 cm < 2 >; the electronics box is integrated with an LMH6629-based amplification circuit to replace a commercial pre-amplification module. Through the collaborative design of parallel connection of a plurality of small-area detectors, a closed low-background environment and self-research electronics, the single-day 210Po activity detection sensitivity is less than or equal to 1 mu Bq / cm < 2 >, the background is less than or equal to 3cpd, and the detector is suitable for surface pollution monitoring in neutrino and dark substance detection experiments.

Description

Technical Field

[0001] The present invention belongs to the technical field of radionuclide detection, and particularly relates to a 2 Po activity detection device with 210 μBq / cm Background Art

[0002] 210 Po is a radionuclide, which is 222 the decay daughter of 218 Rn through 214 Po, 214 Pb, 214 Bi, 210 Po, 210 Pb, 210 Bi, and the half-life of 210 Po is 138.4 days. 210 Po can undergo α decay, and α particles can generate neutrons through the α-n reaction. For neutrino experiments using liquid scintillator as the target material or dark matter experiments using liquid xenon, liquid argon, high-purity germanium, etc. as the target material, neutron background is more difficult to remove than conventional γ or β background. In order to remove 210 Po on the detector surface, different experiments internationally have different treatment methods for different detector materials they use. The GERDA experiment uses etching and electropolishing to remove 222 Rn daughters on the surface of oxygen-free copper and stainless steel. The DEAP3600 experiment specifically developed a set of robotic devices to shave off about 500 μm of the entire inner surface to remove 222 Rn daughters on the surface of plexiglass. In addition to necessary removal measures, it is also necessary to detect the residual 210 Po activity on the surface. The present invention is mainly developed to meet the detection of 210 Po activity on the surface of detector materials in low-background experiments, with the main goal of realizing the detection of 2 Po activity with 210 μBq / cm

[0003] Currently, the device closest to the function of this project is the surface alpha contamination meter. In terms of surface alpha contamination meters, the product currently closest to this project is the Alpha Analyst device produced by Mirion Technologies (Canberra), Inc. in the United States. Alpha Analyst uses a 450-18AM PIPS detector to detect alpha particles, and is equipped with relevant electronics and computer software. The maximum sensitive volume of the detector of this device is 12 cm 2, the background count is about 1 count per hour (cph). According to the formula for sensitivity: L = 1.64×σ BG / C F , when the detection efficiency is 100%, that is, C F = 1, if measured for one day, the measurement sensitivity of the device is about 7 μBq / cm 2 . Alpha Analyst can be used for 210 the detection of Po activity, but the sensitivity is nearly several times different from that of the present invention. As a commercial instrument produced in the United States, Alpha Analyst is expensive, in the hundreds of thousands or even millions of yuan. In addition, it is very difficult for Alpha Analyst to maintain a background of 1 cph for a long time. According to its design, when changing samples, the sample chamber will be exposed to the air, and then dust in the air will adhere to the inside of the sample chamber, and after long-term accumulation, it will cause an increase in the measurement background. Alphaanalyst uses a single-chip 450-18AM PIPS detector in the detection of alpha particles, and its effective area is 12 cm 2 . The large-area Si detector is relatively expensive, which is also one of the factors contributing to the high price of this instrument. SUMMARY OF THE INVENTION

[0004] In order to solve the technical problems raised in the background art, the present invention proposes a μBq / cm 2 level 210 Po activity detection device.

[0005] The technical solution of the present invention is as follows:

[0006] A μBq / cm 2 level 210 Po activity detection device, comprising:

[0007] A glove box, including a main chamber and a transition chamber. The main chamber is connected to the gas-phase interface of the liquid nitrogen tank through an air inlet to maintain a nitrogen environment. The transition chamber is provided with an independent air inlet and an air outlet for nitrogen purging;

[0008] A sample chamber, hermetically connected to the inside of the main chamber through a KF200 flange, and is internally provided with a sample stage and a detector support plate made of PTFE material;

[0009] An array of 9 parallel-connected SiPIN detectors, arranged in a 3×3 square and fixed on the detector support plate. Each sensitive area is 18 mm×18 mm, and the total sensitive area is 29.2 cm 2 ;

[0010] An electronics box, containing a signal amplification circuit based on the LMH6629 operational amplifier, is used to apply a bias voltage to the SiPIN detector and read out signals.

[0011] A vacuum pump is connected to the sample chamber through a 1 / 4 VCR valve to maintain a vacuum environment.

[0012] An oscilloscope is used to collect and analyze alpha particle signals.

[0013] In the above technical solution, an inner door is provided between the main chamber and the transition chamber of the glove box. The transition chamber transfers the sample after being purged with evaporated nitrogen, and the purging time is ≥ 5 minutes.

[0014] In the above technical solution, the sample chamber is a KF200 flange two-way structure with a height of 200 mm. The bottom is sealed by a KF200 blind plate, and the top is connected to three KF40 adapters. Two of the adapters are respectively used for vacuum pumping by the vacuum pump and signal transmission.

[0015] In the above technical solution, the SiPIN detector is fixed by a PTFE support plate. The support plate is provided with 9 square slots of 25 mm × 25 mm. There is a 1.5 mm step below the slots to prevent the displacement of the detector, and it is connected to the pressing plate by M5 bolts.

[0016] In the above technical solution, the circuit design of the electronics box includes:

[0017] Input terminal A is connected to the SiPIN anode to apply a 50V bias voltage.

[0018] Input terminal B is connected to the SiPIN cathode and the signal is amplified by the LMH6629.

[0019] Output terminal Signal is connected to the oscilloscope through an SMA connector.

[0020] In the above technical solution, the amplification circuit of the electronics box is shielded in an aluminum box body, including ±2.5V power supply interfaces, and the signal noise is ≤ 1 mV.

[0021] In the above technical solution, the sample stage is a disc with a diameter of 150 mm, and the sample to be measured is a flat thin plate with an area not exceeding this size.

[0022] In the above technical solution, the air outlet of the main chamber is connected to the atmosphere through a one-way valve. The vacuum pumping time of the vacuum pump is ≥ 5 minutes, and the vacuum degree is ≤ 10 -3 Pa.

[0023] In the above technical solution, the liquid nitrogen tank is connected to the air inlet of the main chamber through a PU tube with an outer diameter of 10 mm to continuously maintain the nitrogen purity ≥ 99%.

[0024] In the above technical solution, the background count of the device ≤ 3 cpd, 210 Po detection sensitivity ≤ 1 μBq / cm 2 .

[0025] Beneficial effects:

[0026] First, high sensitivity and low background. The purpose of the present invention is to detect and analyze 210 Po on the surface of the material, and use the 5.3 MeV Alpha particles generated by the decay of 210 Po as the detection target. Radon gas and dust in the air are the main background sources. The present invention uses a KF200 high-vacuum flange two-way as the detector chamber. The KF200 two-way is a standard product, which does not need to be customized and is cheap. In addition, in order to avoid environmental radon gas and dust from entering the sample chamber during the sample placement process and contaminating the detector, the present invention uses a glove box as a method to obtain a low-background environment, and uses evaporated nitrogen to protect the glove box, which can ensure that the background of the measuring device does not increase after multiple uses.

[0027] Second, large area and low cost. The measurement devices in the prior art use large-area semiconductor detectors to detect Alpha particles. The present invention uses a scheme of paralleling multiple small-area SiPIN detectors, which significantly reduces the cost of the detector.

[0028] Third, uniquely designed electronics. In the electronics, the present invention can achieve the simultaneous operation of 9 SiPIN detectors through circuit design without interference, successfully replacing the preamplifier and main amplifier conventionally required for SiPIN detectors, and reducing the cost of the device while ensuring performance. Description of the drawings

[0029] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0030] Figure 2 It is a schematic diagram of the sample chamber structure.

[0031] Figure 3 It is the circuit diagram of the electronics box.

[0032] Among them, 1 is a liquid nitrogen tank, 2 is a vacuum pump, 3 is a main chamber, 4 is a transition chamber, 5 is a sample chamber, 6 is an oscilloscope, 7 is a first valve, 8 is a second valve, 9 is a third valve, 10 is a fourth valve, 11 is a fifth valve, 12 is a sixth valve, 13 is a SiPIN detector pressure plate, 14 is a SiPIN detector support plate, 15 is a SiPIN detector, and 16 is a sample stage. Specific implementation manners

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the protection scope of the present invention should cover all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0034] Embodiment

[0035] The device structure of the present invention is as Figure 1 shown, mainly including a liquid nitrogen tank 1, a glove box, a sample chamber 5, a vacuum pump 2, an oscilloscope 6 and an electronics box. Among them, the liquid nitrogen tank 1, the vacuum pump 2 and the oscilloscope 6 are conventional commercial devices, and the rest are devices designed by the present invention. The specific functions are as follows:

[0036] I. Glove box: The glove box is divided into a main chamber 3 and a transition chamber 4. The function of the main chamber 3 is to hold the measurement sample chamber 5 and continuously provide a low-background and ultra-clean experimental environment for the sample chamber 5. The main function of the transition chamber 4 is to maintain the purity and stability of the internal environment to the greatest extent during the sample transfer process, while ensuring operation safety and experimental reliability. The transition chamber 4 is provided with an air inlet and an air outlet. The valve of the air inlet is the fifth valve 11, and the valve of the air outlet is the sixth valve 12. After placing the sample in the transition chamber 4, it is necessary to use evaporated nitrogen for purging to avoid air entering the main chamber 3. The left side of the main chamber 3 is an outer door, whose main function is to place the sample chamber 5 into the main chamber 3 at the beginning of the equipment operation. There is an inner door between the main chamber 3 and the transition chamber 4, whose main function is to connect the main chamber 3 and the transition chamber 4 to realize sample transfer. The main chamber 3 is also provided with an air inlet and an air outlet on it. Each of the air inlet and the air outlet is equipped with a valve with a quick-connect interface. The valve of the air inlet is the third valve 9, and the valve of the air outlet is the fourth valve 10. The air inlet is long-term connected to the gas-phase interface of the liquid nitrogen tank 1 to maintain the nitrogen environment inside the chamber. The air outlet is connected to the atmosphere through a one-way valve. In addition, there is a 1 / 4VCR through-board joint on the main chamber 3. One end of the joint is connected to the sample chamber 5 through a stainless steel bellows and a 1 / 4VCR valve (the second valve 8), and the other end is connected to the vacuum pump 2 through a stainless steel bellows and a 1 / 4VCR valve (the first valve 7). Before measurement, the vacuum pump 2 can be used to evacuate the sample chamber 5. In addition, there are two SMA through-board joints on the main chamber 3. Both joints are connected to the electronics box. One path is used to apply voltage to the SiPIN detector 15 in the sample chamber 5, and the other path is used to read out the signal of the SiPIN detector 15.

[0037] II. Sample Chamber 5: The main body of the sample chamber 5 is a KF200 flange two-way, with a height of approximately 200 mm. The lower end of the chamber is sealed with a KF200 blind plate, and the upper end KF200 flange is connected to three KF40 adapters through a stainless steel pipe. One end of the three KF40 adapters is connected to the KF200-KF40 adapter, and the other end is connected to a 1 / 4VCR valve through a KF40-1 / 4VCR adapter, and then linked to the vacuum pump 2 for evacuating the chamber; the other two KF40 connectors are connected to two SMA KF40 vacuum electrodes. Both SMA connectors are connected to the electronics box through the SMA feedthrough connectors on the main chamber 3, one for loading the signals of the SiPIN detector 15 and the other for reading out the signals of the SiPIN detector 15. Inside the sample chamber 5, there is a sample stage 16 and a SiPIN detector 15. The sample stage 16 is used for placing the sample to be measured, and the SiPIN detector 15 is placed on a SiPIN detector support plate 14 made of PTFE. There is a SiPIN detector pressure plate 13 on the SiPIN detector 15. The SiPIN detector pressure plate 13 and the SiPIN detector support plate 14 are connected by screws to fix the position of the SiPIN detector 15. The specific structure is as Figure 2 shown.

[0038] The length of the M5 screw used for connecting between the SiPIN detector support plate 14 and the SiPIN detector pressure plate 13 is selected to be 15 mm, which can keep a 5-mm spacing between the SiPIN detector support plate 14 and the sample stage 16. In order to increase the sensitive area of the detector and save costs, 9 s3204-09 type SiPIN detectors produced by Hamamatsu Corporation are used in the present invention to detect Alpha signals. The SiPIN detector has a ceramic package housing, with an outer dimension of 25 mm × 25 mm and a middle sensitive area of 18 mm × 18 mm. The 9 SiPIN detectors are all connected in parallel. After parallel connection, the 9 detectors have only one voltage input and one voltage output. In order to better fix the 9 SiPIN detectors, there are 9 square slots of 25 mm × 25 mm on the PTFE support frame, and there is a step with a width of 1.5 mm under each slot to support the SiPIN to prevent it from falling. In order to better fix the SiPIN detector, a SiPIN detector pressure plate 13 is also provided at the upper end. The SiPIN detector pressure plate 13 and the SiPIN detector support frame 14 are fixed by M5 bolts. The sample stage 16, the SiPIN detector support frame 14, and the SiPIN detector pressure plate 13 are all disc structures with an outer diameter of 150 mm. The total sensitive volume of the Alpha detector is 29.2 cm 2, Nine SiPINs are arranged in a 3×3 square array with a side length of 75 mm. Therefore, the size of the test sample recommended for this device is a square with dimensions of 75 mm×75 mm, and the size shall not exceed a disc with a diameter of 150 mm.

[0039] III. Electronics Box: The present invention uses a self-made electronics readout board for signal readout. The self-made electronics board uses the LMH6629 operational amplifier produced by Texas Instruments as the core device, and the specific design circuit diagram is as Figure 3 shown. In the circuit diagram, the standard point A is connected to the anode of the SiPIN detector 15 for applying a bias voltage to the SiPIN detector, and point B is connected to the cathode of the SiPIN detector 15 for signal readout. The circuit board components made according to this schematic diagram are placed in an aluminum shielding box. There are 6 SMA connectors on the shielding box. Among them, the external interface of the No. 1 connector is connected to the DC power supply, and the internal interface is connected to the HV port. The external interface of the No. 2 connector is connected to the anode of the SiPIN detector, and the internal interface is connected to the A connector of the electronics board. The No. 1 and No. 2 connectors are used to provide a bias voltage for the SiPIN detector; the external interface of the No. 3 connector is connected to the cathode of the SiPIN detector, and the internal interface is connected to the B connector of the circuit board for signal reading of the SiPIN; the No. 4 and No. 5 connectors are used to supply power to the amplifier board. The internal connectors are connected to the ±2.5V ports, and the external connectors are connected to the DC power supply; the No. 6 connector is used for signal readout. The internal connector is connected to the Signal port of the preamplifier board, and the external connector is connected to the input port of the oscilloscope.

[0040] The test sample of this device needs to be in the shape of a flat thin plate, and the sample area is a square with dimensions of 75 mm×75 mm. The usage method is as follows:

[0041] (1) After the equipment is installed, it is necessary to connect the nitrogen gas pipeline to purge the main chamber 3 of the glove box with evaporated nitrogen. During the operation of the equipment, it is necessary to ensure that the main chamber 3 of the glove box is always in the state of nitrogen purging. The main purpose is to maintain a clean and low-radon environment inside the glove box. Except when replacing the liquid nitrogen tank, the third valve 9 and the fourth valve 10 need to be kept open at other times;

[0042] (2) When measuring the sample, it is necessary to open the outer door on the right side of the transfer chamber 4, place the test sample inside the transfer chamber 4, and then open the fifth valve 11 and the sixth valve 12 to purge the transfer chamber 4 with nitrogen. The purging time shall not be less than 5 minutes, and the purging flow rate shall not be lower than 2 L / min;

[0043] (3) After purging the transfer chamber 4, close the fifth valve 11 and the sixth valve 12, open the inner doors of the glove box main chamber 3 and the transfer chamber 4, and then send the sample into the main chamber 3;

[0044] (4) Open the KF200 flange port at the lower part of the sample chamber 5, place the sample to be measured on the sample stage 16 inside the sample chamber, then place the SiPIN detector support frame 14 and the SiPIN detector pressure plate 13 on the sample stage 16, fix the positions with screws, and then install the KF200 flange and seal the chamber with clamps and brackets;

[0045] (5) After completing the sealing of the sample chamber, open the first valve 7, the second valve 8 and the vacuum pump 2 to evacuate the sample chamber 5 for more than 5 minutes;

[0046] (6) Connect the preamplifier box to the DC power supply, apply a 50V bias voltage to the SiPIN detector 15, and apply a ±2.5V operating voltage to the amplifier;

[0047] (7) Turn on the oscilloscope 6 for data acquisition, and perform data analysis after completing the data acquisition.

[0048] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A Po activity detection device at the level of μBq / cm 2 level 210 , characterized in that Comprising: A glove box, including a main chamber and a transition chamber. The main chamber is connected to the gas-phase interface of a liquid nitrogen tank through an air inlet to maintain a nitrogen environment, and the transition chamber is provided with an independent air inlet and an air outlet for nitrogen purging; A sample chamber, hermetically connected to the inside of the main chamber through a KF200 flange, with a sample stage and a detector support plate made of PTFE material inside; A 9-chip parallel SiPIN detector array is fixed on the detector support plate in a 3×3 square arrangement. Each chip has a sensitive area of 18mm×18mm, and the total sensitive area is 29.2cm 2 ; An electronics box, including a signal amplification circuit based on an LMH6629 operational amplifier, used to apply a bias voltage to a SiPIN detector and read out signals; A vacuum pump, connected to the sample chamber through a 1 / 4VCR valve to maintain a vacuum environment; An oscilloscope, used to collect and analyze α-particle signals.

2. The device according to claim 1, characterized in that: An inner door is provided between the main chamber and the transition chamber of the glove box. After purging the transition chamber with evaporated nitrogen, the sample is transferred. The purging time is ≥5 minutes, and the purging flow rate is ≥2L / min.

3. The device according to claim 1, characterized in that: The sample chamber is a KF200 flange two-way structure, with a height of 200mm, sealed at the bottom by a KF200 blind flange, and connected to three KF40 adapters at the top. The three adapters are respectively used for vacuum pumping of the vacuum pump, signal transmission, and voltage loading.

4. The device according to claim 1, characterized in that: The SiPIN detector is fixed by a PTFE support plate. The support plate is provided with 9 square grooves of 25mm×25mm. There is a 1.5mm step below the grooves to prevent the displacement of the detector, and it is connected to a pressure plate through an M5 bolt.

5. The device according to claim 1, characterized in that: The circuit design of the electronics box includes: Input terminal A is connected to the anode of the SiPIN to apply a 50V bias voltage; Input terminal B is connected to the cathode of the SiPIN and the signal is amplified by an LMH6629; The output terminal is connected to the oscilloscope through an SMA connector.

6. The device according to claim 5, characterized in that: The amplification circuit of the electronics box is shielded in an aluminum box body, including ±2.5V power supply interfaces, and the signal noise is ≤1mV.

7. The device according to claim 1, characterized in that: The size of the sample stage is a disc with a diameter of 150mm. The sample to be measured is a flat thin plate, and its area does not exceed this size.

8. The device according to claim 1, characterized in that: The air outlet of the main chamber is communicated with the atmosphere through a one-way valve. The air extraction time of the vacuum pump is ≥ 5 minutes, and the vacuum degree is ≤ 10 -3 Pa.

9. The device according to claim 1, characterized in that: The liquid nitrogen tank is connected to the air inlet of the main chamber through a PU air pipe with an outer diameter of 10mm, continuously maintaining the nitrogen purity ≥99%.

10. The device according to claim 1, wherein: The background count of the said device ≤ 3 cpd, 210 The detection sensitivity of Po ≤ 1 μBq / cm 2 .

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