A μBq / cm 2 of 210 Po activity detection device

Abstract

The present invention discloses a μBq / cm 2 Level 210 Po activity detection device, belonging to the field of radionuclide detection technology, is used for detecting radionuclides on the surface of materials in low background experiments. 210 Highly sensitive detection of Po activity. This system includes a glove box, sample chamber, SiPIN detector array, electronics box, and vacuum system. The glove box is purged with nitrogen to maintain a low-radon environment. The sample chamber is sealed with a KF200 flange and connected to a vacuum pump. Nine SiPIN detectors are arranged in parallel in a 3×3 array, with a total sensitive area of ​​29.2 cm. 2 The electronics box integrates an amplifier circuit based on LMH6629, replacing the commercial preamplifier module. Through the collaborative design of multiple small-area detectors in parallel, a closed low-background environment and self-developed electronics, a single-day 210 Po activity detection sensitivity ≤ 1μBq / cm 2 , background ≤ 3cpd, suitable for surface contamination monitoring in neutrino and dark matter detection experiments.

Description

Technical Field

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

[0002] 210 Po is a radioactive nuclide. 222 Rn via 218 Po, 214 Pb, 214 Bi, 214 Po, 210 Pb, 210 Decay daughters after Bi, 210 The half-life of Po is 138.4 days. 210 Po is a very important background source in neutrino detection and dark matter detection experiments. 210 Po can undergo α decay, and α particles can produce neutrons through α-n reaction. For neutrino experiments using liquid scintillators as target materials or dark matter experiments using liquid xenon, liquid argon, high-purity germanium, etc. as target materials, the neutron background is more difficult to remove than the conventional γ or β background. In order to remove the neutron background on the detector surface, the neutron background is generated by the α-n reaction. 210 Po, different international experiments have different treatment methods for different detector materials used. The GERDA experiment is to remove oxygen-free copper and stainless steel surfaces. 222 The Rn daughter was treated by etching and electrolytic polishing. DEAP3600 experiment was used to remove the surface of organic glass. 222 Rn daughter specially developed a set of robotic devices to cut the entire inner surface by about 500μm. In addition to taking necessary removal measures, it is also necessary to 210 The present invention mainly satisfies the low background experiment on the surface of the detector material. 210 Developed for the detection of Po activity to achieve μBq / cm 2 of 210 The main goal is to detect Po activity.

[0003] Currently, the closest product to this project is a surface alpha contamination detector. The Alpha Analyst, manufactured by Mirion Technologies (Canberra), Inc. in the United States, uses a 450-18AM PIPS detector to detect alpha particles, along with related electronics and computer software. The detector has a maximum sensitivity volume of 12 cm. 2, the background count is about 1 count per hour (cph). According to the sensitivity calculation formula: L=1.64×σ BG / C F , when the detection efficiency is 100%, that is, C F =1, if the measurement is for one day, the measurement sensitivity of the device is about 7μBq / cm 2 . Alpha Analyst can be used to 210 Po activity detection, but the sensitivity is nearly several times lower than that of the present invention. As a commercial instrument produced in the United States, Alpha Analyst is expensive, costing hundreds of thousands or even millions of dollars. In addition, it is difficult for Alpha Analyst to maintain a background of 1 cph for a long time. According to its design, when the sample is replaced, the sample chamber will be exposed to the air, and the dust in the air will adhere to the inside of the sample chamber. After a long period of accumulation, the change will cause the measurement background to rise. Alphaanalyst uses a single-chip 450-18AM PIPS detector for Alpha particle detection, and its effective area is 12cm 2 ,The large area Si detector is relatively expensive, which is also one of the factors contributing to the high price of the ,instrument. Summary of the Invention

[0004] In order to solve the technical problems raised in the background technology, 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 The Po activity detection device comprises:

[0007] The glove box includes 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 independent air inlet and air outlet for nitrogen purging.

[0008] The sample chamber is sealed to the main chamber through a KF200 flange and contains a sample stage and a detector support plate made of PTFE material.

[0009] Nine parallel SiPIN detector arrays are arranged in a 3×3 square pattern and fixed on the detector support plate. Each detector has a sensitive area of ​​18 mm×18 mm, with a total sensitive area of ​​29.2 cm 2 ;

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

[0011] Vacuum pump, connected to the sample chamber through a 1 / 4 VCR valve to maintain the vacuum environment;

[0012] Oscilloscope, used to acquire 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, and the transition chamber is purged with evaporated nitrogen before transferring the sample, 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 which are used for vacuum pumping and signal transmission respectively.

[0015] In the above technical solution, the SiPIN detector is fixed by a PTFE support plate. The support plate is provided with 9 25mm×25mm square grooves, and a 1.5mm step is provided under the groove to prevent the detector from displacement. The support plate is connected to the pressure plate by M5 bolts.

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

[0017] Input terminal A is connected to the SiPIN anode and loaded with a 50V bias voltage;

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

[0019] The output terminal Signal is connected to the oscilloscope through the SMA connector.

[0020] In the above technical solution, the amplifier circuit of the electronic box is shielded in an aluminum box body, includes a ±2.5V power supply interface, and the signal noise is ≤1mV.

[0021] In the above technical solution, the sample stage is a disc with a diameter of 150 mm, and the sample to be tested 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 pump has an exhaust time of ≥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 is ≤3cpd, 210 Po detection sensitivity ≤1μBq / cm 2 .

[0025] Beneficial effects:

[0026] First, high sensitivity and low background. The purpose of this invention is to 210 Po is tested and analyzed to measure 210 The 5.3MeV Alpha particles produced by Po decay are the detection target, and radon gas and dust in the air are the main background sources. The present invention uses a KF200 high vacuum flange coupler as the detector chamber. The KF200 coupler is a standard product that does not require customization and is inexpensive. In addition, to prevent environmental radon gas, i.e., dust, from entering the sample chamber during sample placement and contaminating the detector, the present invention uses a glove box as a low-background environment. The glove box is protected by evaporated nitrogen, which can ensure that the background of the measuring device does not increase after repeated use.

[0027] Second, large area and low cost. The existing measurement devices use large-area semiconductor detectors to detect alpha particles. The present invention uses a solution of connecting multiple small-area SiPIN detectors in parallel, which significantly reduces the cost of the detectors.

[0028] Third, uniquely designed electronics. In electronics, the present invention uses circuit design to enable nine SiPIN detectors to operate simultaneously without interfering with each other, successfully replacing the preamplifier and main amplifier conventionally required for SiPIN detectors, reducing device costs while ensuring performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 Schematic diagram of the sample chamber structure.

[0031] Figure 3 This 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. DETAILED DESCRIPTION

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

[0034] Example

[0035] The device structure of the present invention is as follows Figure 1 As shown, it mainly includes six parts: liquid nitrogen tank 1, glove box, sample chamber 5, vacuum pump 2, oscilloscope 6 and electronics box. Among them, liquid nitrogen tank 1, vacuum pump 2 and oscilloscope 6 are conventional commercial equipment, and the remaining parts are designed by the present invention. The specific functions are as follows:

[0036] 1. Glove box: The glove box is divided into two parts: the main chamber 3 and the transition chamber 4. The function of the main chamber 3 is to hold the measurement sample chamber 5 and continuously provide a low-background, 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 possible during the sample transfer process, while ensuring operational safety and experimental reliability. The transition chamber 4 is equipped 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 needs to be purged with evaporated nitrogen to prevent air from entering the main chamber 3. The left side of the main chamber 3 is an outer door. Its main function is to place the sample chamber 5 inside the main chamber 3 at the beginning of the equipment operation. An inner door is provided between the main chamber 3 and the transition chamber 4. Its main function is to connect the main chamber 3 and the transition chamber 4 to achieve sample transfer. The main chamber 3 also features an inlet and outlet, each equipped with a quick-connect valve. The inlet valve is the third valve 9, and the outlet valve is the fourth valve 10. The inlet is permanently connected to the gas phase port of the liquid nitrogen tank 1 to maintain a nitrogen atmosphere within the chamber. The outlet is connected to the atmosphere via a single-phase valve. In addition, the main chamber 3 also features a ¼ VCR bulkhead connector. One end of the connector connects to the sample chamber 5 via a stainless steel bellows and a ¼ VCR valve (second valve 8), and the other end connects to the vacuum pump 2 via a stainless steel bellows and a ¼ VCR valve (first valve 7). The sample chamber 5 can be evacuated using the vacuum pump 2 before measurement. The main chamber 3 also features two SMA bulkhead connectors, both of which connect to the electronics box. One connector is used to apply voltage to the SiPIN detector 15 in the sample chamber 5, and the other connector is used to read the SiPIN detector 15 signal.

[0037] 2. Sample Chamber 5: The main body of Sample Chamber 5 consists of a KF200 flanged union, approximately 200mm high. The lower end of the chamber is sealed with a KF200 blind plate. At the upper end, the KF200 flange is connected to a stainless steel pipe that connects to three KF40 adapters. One end of each KF40 adapter is connected to a KF200-KF40 adapter, and the other end is connected to a 1 / 4VCR valve via a KF40-1 / 4VCR adapter. This is then connected to 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 via SMA bulkhead connectors on the main chamber 3: one for loading the SiPIN detector 15 signal and the other for reading it. The sample chamber 5 is equipped with a sample stage 16 and a SiPIN detector 15. The sample stage 16 is used to place the sample for measurement. The SiPIN detector 15 is placed on a SiPIN detector support plate 14 made of PTFE. A SiPIN detector pressure plate 13 is provided on the SiPIN detector 15. The SiPIN detector pressure plate 13 and the SiPIN detector support plate 14 are connected with screws to fix the position of the SiPIN detector 15. The specific structure is as follows: Figure 2 shown.

[0038] The M5 screws connecting the SiPIN detector support plate 14 and the SiPIN detector pressure plate 13 are 15 mm long, ensuring a 5 mm gap between the SiPIN detector support plate 14 and the sample stage 16. To increase the detector's sensitive area and save costs, the present invention uses nine Hamamatsu s3204-09 SiPIN detectors for alpha signal detection. These SiPIN detectors have ceramic housings with outer dimensions of 25 mm x 25 mm and a central sensitive area of ​​18 mm x 18 mm. All nine SiPIN detectors are connected in parallel, with only one voltage input and one voltage output. To better secure the nine SiPIN detectors, the PTFE support frame has nine 25 mm x 25 mm square slots, each with a 1.5 mm wide step below it to support the SiPIN and prevent it from falling. To further secure the SiPIN detectors, a SiPIN detector pressure plate 13 is provided at the top, secured to the SiPIN detector support frame 14 with M5 bolts. The sample stage 16, SiPIN detector support frame 14, and SiPIN detector pressure plate 13 are all disk structures with an outer diameter of 150 mm. The total sensitive volume of the Alpha detector is 29.2 cm 2, 9 SiPINs are arranged in a 3×3 square array with a side length of 75mm. Therefore, this device recommends that the size of the sample to be tested should be a 75mm×75mm square, and the size should not exceed a 150mm diameter disk.

[0039] 3. Electronics Box: This invention uses a self-made electronic readout board for signal readout. The self-made electronic board uses the LMH6629 operational amplifier produced by Ti Company as the core device. The specific design circuit diagram is as follows Figure 3 As shown. Point A in the schematic is connected to the anode of the SiPIN detector 15, which is used to bias the SiPIN detector. Point B is connected to the cathode of the SiPIN detector 15 for signal readout. The circuit board, fabricated according to this schematic, is placed in an aluminum shielding box. The shielding box has six SMA connectors. Connector 1 connects to the DC power supply from the outside, and the HV port from the inside. Connector 2 connects to the anode of the SiPIN detector from the outside, and the A connector on the electronics board from the inside. Connectors 1 and 2 are used to bias the SiPIN detector. Connector 3 connects to the cathode of the SiPIN detector from the outside, and the B connector on the circuit board from the inside for signal readout. Connectors 4 and 5 power the amplifier board. The internal connector connects to the ±2.5V port, and the external connector connects to the DC power supply. Connector 6 is used for signal readout. The internal connector connects to the Signal port of the preamplifier board, and the external connector connects to the input port of an oscilloscope.

[0040] The sample to be tested by this device must be a flat thin plate with a sample area of ​​75mm×75mm square. The usage is as follows:

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

[0042] (2) When measuring the sample, the outer door on the right side of the transition chamber 4 needs to be opened, and the sample to be measured needs to be placed in the transition chamber 4. Then, the fifth valve 11 and the sixth valve 12 are opened to purge the transition chamber 4 with nitrogen. The purge time should be no less than 5 minutes, and the purge flow rate should be no less than 2L / min.

[0043] (3) After the transition chamber 4 is purged, the fifth valve 11 and the sixth valve 12 are closed, the inner doors of the glove box main chamber 3 and the transition chamber 4 are opened, and the sample is then placed into the main chamber 3;

[0044] (4) Open the KF200 flange at the bottom of the sample chamber 5, place the sample to be tested on the sample stage 16 in 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 position with screws, then install the KF200 flange, and seal the chamber with a clamp and bracket;

[0045] (5) After the sample chamber is sealed, 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 50V bias voltage to the SiPIN detector 15, and apply ±2.5V operating voltage to the amplifier;

[0047] (7) Open the oscilloscope 6 to collect data, and perform data analysis after the data collection is completed.

[0048] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. μBq / cm 2 Level 210 The Po activity detection device is characterized in that: include: The glove box comprises 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 independent air inlet and air outlet for nitrogen purging. An inner door is provided between the main chamber and the transition chamber of the glove box. The transition chamber is purged with evaporated nitrogen before transferring samples. The purge time is ≥5 minutes and the purge flow rate is ≥2L / min. The sample chamber is sealed to the main chamber through a KF200 flange and contains a sample stage and a detector support plate made of PTFE material. Nine parallel SiPIN detector arrays are arranged in a 3×3 square pattern and fixed on the detector support plate. Each detector has a sensitive area of ​​18 mm×18 mm, with a total sensitive area of ​​29.2 cm 2 ; An electronics box, containing a signal amplification circuit based on the LMH6629 operational amplifier, used to bias the SiPIN detector and read out the signal; Vacuum pump, connected to the sample chamber through a 1 / 4 VCR valve to maintain the vacuum environment; Oscilloscope, used to collect and analyze alpha particle signals; The background count of the device is ≤3 cpd, 210 Po detection sensitivity ≤1μBq / cm 2 .

2. The device according to claim 1, characterized in that: 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, which are used for vacuum pumping, signal transmission, and voltage loading respectively.

3. The device according to claim 1, characterized in that: The SiPIN detector is fixed by a PTFE support plate, which is provided with 9 25mm×25mm square slots, with a 1.5mm step below the slot to prevent the detector from moving, and is connected to the pressure plate by M5 bolts.

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

5. The device according to claim 4, characterized in that: The amplifier circuit of the electronic box is shielded in an aluminum box body, includes a ±2.5V power supply interface, and the signal noise is ≤1mV.

6. The device according to claim 1, characterized in that: The size of the sample stage is a disc with a diameter of 150 mm, and the sample to be tested is a flat thin plate with an area not exceeding this size.

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

8. 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 10 mm to continuously maintain the nitrogen purity ≥ 99%.

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