Method for analyzing radon gas content change in closed chamber

Abstract

The invention relates to a method for analyzing the content change of radon gas in a closed chamber, the content change of radon gas (radon 222) in the closed chamber is analyzed through the content change of oxygen, and the oxygen / radon gas in the closed chamber mainly comes from oxygen / radon gas released by materials in the closed chamber and oxygen / radon gas leaked into air in the closed chamber. Compared with direct measurement of the radon gas content in the closed chamber, the oxygen content in the closed chamber can be measured by using an oxygen content sensor. The change of the content of the radon gas in the closed chamber caused by leakage can be speculated by monitoring the change of the content of the oxygen in the closed chamber in real time. Compared with the existing method for directly measuring the content of the radon gas, the method disclosed by the invention has the advantage that the change of the content of the radon gas in the closed chamber can be simply, reliably and quickly analyzed in real time at low cost. The device can be used for occasions where the radon gas content needs to be monitored in real time for a long time, such as a scale chamber of a Jiangmen neutrino experiment scale system.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear radiation detection, and in particular to a method for analyzing changes in radon gas content in a closed chamber. Background Art

[0002] Closed chambers play a key role in the field of nuclear radiation detection technology, providing a stable and controlled experimental environment to ensure the performance of detectors and the accuracy of measurement data. Nuclear radiation detection often requires isolating detectors from external interference, while controlling temperature, humidity, gas composition and other conditions to improve measurement accuracy and sensitivity. Closed chambers can calibrate detection equipment according to different application requirements, such as the Jiangmen Neutrino Experiment Calibration Room, shielding background radiation, and studying the interaction between radiation and matter.

[0003] Liquid scintillators are widely used in various particle physics experiments, such as Jiangmen Neutrino Experiment (JUNO), Borexino, and KamLand. In order to meet the requirements of physical experiments, the radioactive background in the detector needs to be strictly controlled. The natural radioactive radon gas (radon 222) and its natural radioactive daughters dissolved in the liquid scintillator in the detector, especially lead 210 with a half-life of 22.3 years, will become one of the most important background sources of the experiment. The main sources of radon gas are air leakage and material outgassing, which may diffuse into the liquid scintillator of the detector.

[0004] In addition, oxygen will reduce the luminescence yield of liquid scintillator, so the oxygen content in contact with liquid scintillator also needs to be strictly controlled. Similar to radon, the main sources of oxygen are air leakage and material outgassing, which may diffuse into the detector liquid scintillator.

[0005] For radon and oxygen produced by material outgassing, it is necessary to control the material to reduce the outgassing of the material in the experiment. For radon and oxygen that leak into the closed chamber through air, the leakage is reduced by designing the closed chamber with vacuum-grade sealing standards in the experiment. However, the closed chamber usually uses many interface flanges and vacuum feedthrough electrodes, and the sealing failure caused by installation quality or loss cannot be ignored. Therefore, the radon content and oxygen content need to be monitored in real time.

[0006] Taking the calibration room of the calibration system of the Jiangmen Neutrino Experiment as an example, the calibration room of the calibration system of the Jiangmen Neutrino Experiment serves as an auxiliary system of the calibration system, providing a platform for the installation of the calibration system subsystem and an interface for connecting the calibration system subsystem with the central detector. The flange at the bottom of the calibration room is directly connected to the central detector through a stainless steel pipe. The net size of the calibration room is 5 meters * 2.5 meters * 2 meters (length, width and height). The net weight of the calibration room is about 6 tons. There is a flange with an inner diameter of 1.25 meters on the top of the calibration room, which is used as the installation interface of the calibration subsystem and the transportation hole of large parts inside the calibration room. There is a flange with an inner diameter of 0.82 meters at the bottom, which is used as an interface with the central detector. There are also four DN150 flanges at the bottom of the calibration room, which are used as nitrogen purge interfaces and vacuum feedthrough electrode interfaces. There are ten DN150 flanges and four DN800 flanges on the side walls of the calibration room, which are used as vacuum feedthrough electrode interfaces and manholes (used to enter and exit the calibration room) respectively. The overall leakage rate of the calibration chamber is required to be less than 4×10 at working pressure (gauge pressure 1500 Pascal). -5 mbar·L / s.

[0007] The flange at the bottom of the calibration chamber is directly connected to the central detector with an inner diameter of 35.4 meters through a stainless steel pipe with an inner diameter of 0.8 meters. Since there are wiring harnesses and other pipelines in the stainless steel pipe with an inner diameter of 0.8 meters, and the stainless steel pipe serves as the overflow outlet of the central detector, there is no valve installed between the calibration chamber and the stainless steel pipe. This means that the radon and oxygen inside the calibration chamber can directly contact the liquid scintillator through the stainless steel pipe with an inner diameter of 0.8 meters, and may diffuse into the liquid scintillator of the central detector, thereby reducing the overall performance of the detector. Therefore, the oxygen and radon content in the calibration chamber needs to be strictly controlled (oxygen content is controlled at the order of 10PPM; radon content is controlled at 10mBq / m 3 The control schemes for oxygen and radon content in the calibration room are as follows: First, the overall design leakage rate of the calibration room is less than 4×10 -5 mbar·L / s (1500 Pascal), so theoretically the contribution of air leakage can be ignored; second, use materials with low outgassing rate or cover materials with high outgassing rate with epoxy resin / acrylic covers, so as to reduce the contribution of material outgassing; third, a nitrogen purge device is provided inside the calibration chamber, so as to remove the residual oxygen and radon in the initial stage of the calibration chamber, and further reduce the contribution of material outgassing, and ensure that the calibration chamber is a slightly positive pressure environment, further reducing the possibility of gas leakage into the calibration chamber.

[0008] However, considering that the calibration chamber is equipped with a large number of flanges and vacuum feedthrough electrodes, leakage may occur in extreme cases, so it is necessary to monitor the oxygen content and radon content in the calibration chamber in real time. If the oxygen content and radon content in the calibration chamber are found to increase, timely countermeasures can be taken, such as increasing the nitrogen purge flow rate, timely repairing the leak point, and reducing the impact of oxygen and radon on the normal operation of the detector.

[0009] The oxygen content in the calibration chamber can be monitored in real time (response time in seconds) using an oxygen content sensor. The radon content in the calibration chamber can be monitored using a commercial radon detector (Rad7), but real-time monitoring in seconds is not possible. Therefore, it is necessary to develop a method to quickly and real-time analyze the changes in radon content in a closed chamber such as a calibration chamber. Summary of the invention

[0010] The purpose of the present invention is to provide a method for analyzing the change of radon gas content in a closed chamber.

[0011] The purpose of the present invention can be achieved through the following technical solutions: a method for analyzing changes in radon content in a closed chamber, analyzing changes in radon content in a closed chamber by monitoring changes in oxygen content in the closed chamber.

[0012] Preferably, an increase in oxygen levels within the sealed chamber indicates an increase in radon levels.

[0013] Preferably, based on a pre-measured correlation curve of changes in oxygen and radon content over time in a closed chamber, changes in radon content are analyzed according to changes in oxygen content.

[0014] Preferably, the sealed chamber comprises a scale chamber.

[0015] Further preferably, the method for measuring the correlation curve comprises the following steps:

[0016] S1: Remove oxygen and radon from the air in the closed chamber by nitrogen purging;

[0017] S2: Make the sealed chamber connected to the outside world, so that oxygen and radon in the air can leak into the sealed chamber;

[0018] S3: Circulate the gas in the closed chamber and measure and record the oxygen and radon content over time;

[0019] S4: Draw a correlation curve based on oxygen and radon content and time.

[0020] More preferably, the method for measuring the correlation curve is performed using a correlation test system;

[0021] The associated test system includes a simulated closed chamber, an oxygen content sensor, a radon detector, a leak valve and connecting pipes;

[0022] The inlet and outlet ends of the connecting pipeline are both connected to the simulated closed chamber, an oxygen content sensor and a radon detector are arranged on the connecting pipeline, and the leakage valve is connected to the simulated closed chamber.

[0023] Preferably, the simulated closed chamber is a low-background chamber, and the background is in the order of millibecquerel / cubic meter.

[0024] Further preferably, the simulated closed chamber has a volume of 7 liters and a background of 40 millibecquerel / cubic meter.

[0025] Preferably, the radon detector is Rad7 (commercial radon detector) with a built-in circulation pump, which circulates and simulates the gas in the closed chamber.

[0026] Preferably, the connecting pipeline adopts a PU pipe and a PU pipe joint.

[0027] More preferably, in step S3, the flow rate of the gas circulating in the closed chamber is 1 liter / minute.

[0028] More preferably, step S4 records an oxygen content data every ten seconds and a radon content data every two hours.

[0029] Preferably, the method for measuring the correlation curve comprises the following steps:

[0030] S1: Remove oxygen and radon from the air in the closed chamber by purging with high-purity nitrogen;

[0031] S2: Open the leakage valve to create leakage;

[0032] S3: Use the built-in circulation pump of the radon detector to circulate the gas in the closed chamber, and measure and record the oxygen and radon content that changes over time;

[0033] S4: Draw a correlation curve based on oxygen and radon content and time.

[0034] Preferably, the oxygen / radon content contributed by the outgassing of the materials inside the sealed chamber is greater than the oxygen / radon content contributed by the air leaking into the chamber.

[0035] The oxygen content in the leaking air is higher than the radon content (the ratio of the number of oxygen atoms to the number of radon atoms is greater than 1E15), so the oxygen content is easier to measure. In addition, the penetration time of oxygen leakage or diffusion into the cavity is shorter. Therefore, for the same leakage path, oxygen will enter the cavity more easily than radon.

[0036] Preferably, the sealed chamber is connected to the oxygen content sensor via a vacuum-sealed grade pipeline.

[0037] Further preferably, the oxygen content sensor has a measuring range of 0-10000 PPM and an accuracy better than ±3% FS.

[0038] Further preferably, the response time T90 of the oxygen content sensor is better than 20 seconds.

[0039] The present invention relates to a method for analyzing the change of radon gas (radon 222) content in a closed chamber. Oxygen / radon gas in a closed chamber mainly comes from oxygen / radon gas released by materials inside the closed chamber and oxygen / radon gas in the air leaking into the closed chamber. Compared with directly measuring the radon gas content in a closed chamber, the oxygen content in a closed chamber can be measured using an oxygen content sensor. By real-time monitoring the change of oxygen content in a closed chamber, the change of radon gas content in the closed chamber caused by leakage can be inferred.

[0040] The invention provides a method for qualitatively monitoring and calibrating the change of indoor radon gas content.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention indirectly realizes low-cost, simple, reliable, rapid and real-time analysis of the change of radon content in a closed chamber through oxygen content;

[0043] 2. The present invention can be used in situations where long-term real-time monitoring of radon gas content is required, such as the closed chamber of the Jiangmen neutrino experiment calibration system;

[0044] 3. The present invention uses the correlation between oxygen and radon contributed by air leakage in a closed chamber, and uses the easily measurable oxygen content to predict the increase in radon content in the closed chamber caused by leakage, thereby solving the problem that radon content cannot be monitored in real time and for a long time;

[0045] 4. The present invention can take timely remedial measures to reduce the impact of oxygen and radon on the operation of the detector by real-time and rapid monitoring of the increase in oxygen content caused by leakage;

[0046] 5. Since the oxygen content needs to be monitored, the present invention uses the oxygen content to analyze the radon content, which can maximize the use of existing resources and reduce costs;

[0047] 6. The present invention provides a technology that utilizes the correlation between different gas contents and can predict difficult-to-measure gases by monitoring easily-measured gases. The technology can be used in monitoring scenarios of other gases, such as monitoring carbon dioxide content by oxygen content. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of oxygen content monitoring of the present invention;

[0049] Figure 2 This is the correlation curve between the oxygen content and radon content in the leaking test chamber over time. It can be seen that the radon content tends to increase with the increase of oxygen content. The oxygen content finally remains at 10000PPM because the measurement range of the oxygen content sensor is 0-10000PPM;

[0050] Figure 3 A system for testing the correlation between the oxygen content and the radon content over time in a leaky test chamber;

[0051] Figure 4 Photo of the associated test system;

[0052] In the figure: 1-simulated closed chamber, 2-oxygen content sensor, 3-radon detector, 4-leakage valve, 5-connecting pipeline, 6-closed chamber. DETAILED DESCRIPTION

[0053] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] A method for analyzing the change of radon gas content in a closed chamber, such as Figure 1 As shown, it includes a closed chamber 6 and an oxygen content sensor (MOT500-IF-02 0-10000PPM) 2; the change of the internal radon content of the closed chamber 6 needs to be analyzed in real time; the oxygen content sensor 2 is used to monitor the oxygen content in the closed chamber 6. The oxygen content sensor 2 is connected to the closed chamber 6 through a vacuum-sealed level pipeline, and can monitor the oxygen content in the closed chamber 6 in real time for a long time.

[0056] The analysis method of the change of radon content in the sealed chamber 6 of this embodiment is:

[0057] The first step is to use the oxygen content sensor 2 to monitor the oxygen content in the closed chamber 6 in real time;

[0058] Second, if the oxygen content increases, it can be inferred that the radon content is also increasing.

[0059] Example 2

[0060] A method for analyzing changes in radon content in a closed chamber includes a closed chamber 6 and an oxygen content sensor 2; changes in the radon content in the closed chamber 6 need to be analyzed in real time; the oxygen content sensor 2 is used to monitor the oxygen content in the closed chamber 6. The oxygen content sensor 2 is connected to the closed chamber 6 through a vacuum-sealed pipeline, and can monitor the oxygen content in the closed chamber 6 in real time for a long time.

[0061] The analysis method of the change of radon content in the sealed chamber 6 of this embodiment is:

[0062] The first step is to use Figures 3-4 The correlation test system shown is measured as Figure 2 The correlation curve of oxygen and radon content in the closed chamber changing with time is shown;

[0063] The second step is to use the oxygen content sensor 2 to monitor the oxygen content in the closed chamber 6 in real time;

[0064] Step 3: If the oxygen content increases, then according to Figure 2 The correlation between oxygen content and radon content shown allows one to infer that radon content is also increasing.

[0065] Specifically, the correlation test system includes a simulated closed chamber 1, an oxygen content sensor 2, a radon detector 3, a leakage valve 4 and a connecting pipe 5. The simulated closed chamber 1 has a volume of 7 liters and a background of 40 mBc / m3. The radon detector 3 is a commercial radon detector (Rad7) with a built-in circulation pump. The inlet and outlet ends of the connecting pipe 5 are both connected to the simulated closed chamber 1. The oxygen content sensor 2 and the radon detector 3 are arranged on the connecting pipe 5. The leakage valve 4 is connected to the simulated closed chamber 1.

[0066] When measuring the correlation curve, the following steps are involved:

[0067] In the first step, the test system is purged with high-purity nitrogen to remove oxygen and radon from the air in the system;

[0068] The second step is to open the leak valve and create a leak;

[0069] The third step is to use the built-in circulation pump of Rad7 (flow rate: 1 liter / minute) to circulate the gas in the simulated closed chamber and measure the oxygen (record an oxygen concentration data every ten seconds) and radon content (record a radon concentration data every two hours).

[0070] In the present invention, when the oxygen content sensor detects an increase in the oxygen content in the sealed chamber, it can be inferred that the radon content is also increasing. However, the rate of increase of the radon content is lower than that of the oxygen content, which means that there is enough time to take measures to avoid the increase of the radon content in the sealed chamber and reduce the oxygen content at the same time. The measures that can be taken include but are not limited to, first, increasing the flow rate of nitrogen purge in the chamber; second, leak detection of the chamber to find and repair the leak point.

[0071] Compared with the existing method of directly measuring the radon gas content, the present invention can realize the analysis of the change of the radon gas content in a closed chamber in a low-cost, simple, reliable, rapid and real-time manner.

[0072] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for analyzing the change of radon gas content in a closed chamber, characterized in that: The changes in radon gas content in the closed chamber are analyzed by monitoring the changes in oxygen content in the closed chamber.

2. The method for analyzing the change of radon gas content in a closed chamber according to claim 1, characterized in that: Based on the pre-measured correlation curve of the changes in oxygen and radon content in the closed chamber over time, the changes in radon content are analyzed according to the changes in oxygen content.

3. The method for analyzing the change of radon gas content in a closed chamber according to claim 2, characterized in that: The method for measuring the correlation curve comprises the following steps: S1: Remove oxygen and radon from the air in the closed chamber by nitrogen purging; S2: Make the sealed chamber connected to the outside world, so that oxygen and radon in the air can leak into the sealed chamber; S3: Circulate the gas in the closed chamber and measure and record the oxygen and radon content over time; S4: Draw a correlation curve based on oxygen and radon content and time.

4. The method for analyzing the change of radon gas content in a closed chamber according to claim 3, characterized in that: The method for measuring the correlation curve is carried out using a correlation test system; The associated test system comprises a simulated closed chamber (1), an oxygen content sensor (2), a radon detector (3), a leakage valve (4) and a connecting pipeline (5); The inlet and outlet ends of the connecting pipeline (5) are both connected to the simulated closed chamber (1), an oxygen content sensor (2) and a radon detector (3) are provided on the connecting pipeline (5), and a leakage valve (4) is connected to the simulated closed chamber (1).

5. The method for analyzing the change of radon gas content in a closed chamber according to claim 4, characterized in that: The radon detector (3) is a Rad7, which has a built-in circulation pump, and the gas in the simulated closed chamber (1) is circulated by the circulation pump.

6. The method for analyzing the change of radon gas content in a closed chamber according to claim 3, characterized in that: Step S3: The flow rate of the gas in the circulating closed chamber is 1 liter / minute; Step S4 records an oxygen content data every ten seconds and a radon content data every two hours.

7. The method for analyzing the change of radon gas content in a closed chamber according to claim 1, characterized in that: The oxygen / radon content contributed by the outgassing of the materials inside the closed chamber is greater than the oxygen / radon content contributed by the air leaking into the chamber.

8. The method for analyzing the change of radon gas content in a closed chamber according to claim 1, characterized in that: The sealed chamber is connected to the oxygen content sensor through a vacuum sealing level pipeline.

9. The method for analyzing the change of radon gas content in a closed chamber according to claim 8, characterized in that: The oxygen content sensor has a measuring range of 0-10000 PPM and an accuracy better than ±3% FS.

10. The method for analyzing the change of radon gas content in a closed chamber according to claim 8, characterized in that: The response time T90 of the oxygen content sensor is better than 20 seconds.

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