A μBq / m 3 Gas radon concentration measurement device

Abstract

The present invention discloses a μBq / m 3 A gas radon concentration measuring device of magnitude includes a liquid nitrogen tank, a gas dehumidification device, a radon enrichment device and a radon detector; the liquid nitrogen tank is provided with a liquid nitrogen outlet; the liquid nitrogen outlet pipeline is divided into two paths, one path is sequentially connected to the first solenoid valve and the first dewar tank, and the other path is sequentially connected to the second solenoid valve and the second dewar tank; the water storage tank is in the first dewar tank; the water storage tank is provided with a first air inlet pipe and a first air outlet pipe; the activated carbon chamber is in the second dewar tank; the activated carbon chamber is provided with a second air inlet pipe and a second air outlet pipe; the first valve inlet is a sampling port; the first valve outlet is sequentially connected to the first mass flowmeter, the first air inlet pipe of the water storage tank, the first air outlet pipe of the water storage tank, the second air inlet pipe of the activated carbon chamber, the second air outlet pipe of the activated carbon chamber and the radon detector. The present invention realizes a zero-background dehumidification device; efficient radon enrichment and highly sensitive radon concentration detection, and the entire device can be combined to achieve μBq / m 3 The detection of gas radon concentration at this level has many advantages, such as high sensitivity, high measurement accuracy and short measurement time.

Description

Technical Field

[0001] The present invention relates to a μBq / m 3 The invention discloses a gas radon concentration measuring device of magnitude, belonging to the field of radon concentration measurement. Background Art

[0002] Radon is a colorless, odorless, inert gas that is soluble in water and easily soluble in organic solvents. The main isotopes of radon are 222 Rn, 220 Rn and 219 Rn, these three are unstable nuclides, among which 220 Rn and 219 Rn has a half-life of only seconds and cannot exist for a long time. Its half-life is 3.8 days. 222 Rn is the main component of radon gas in nature. 222 Rn is 238 U via 226 The decay products of Ra, 226 Ra and 238 U is commonly found in soil and rocks. 222 Rn is everywhere; 222 Rn will further decay into 218 Po, and eventually decays into a stable 206 Pb, during its decay, emits several alpha and beta particles and a large number of gamma rays. Radon is an important background source in low-background experiments. Many low-background experiments in the world have been "troubled" by radon. For example, the Kamland experiment, a neutrino experiment, had to distill its target material liquid scintillator to reduce the background introduced by radon gas. The neutrinoless double beta decay experiment Nemo-3 added an online radon removal device to remove the radon background. The dark matter direct detection experiment DEAP-3600 removed 500μm of the surface layer of organic glass to remove the radon background. Whether radon protection can be done well will directly affect whether the physical goals of the experiment can be achieved.

[0003] At present, there is no μBq / m 3 The most sensitive device is the patent CN206876605U authorized by the project team in 2018: mBq / m 3 The specific structure of the device is as follows: Figure 1 The main principle is to use activated carbon at room temperature to enrich a certain volume of radon gas, and then decompose it at high temperature into the detector chamber to detect the radon concentration, mBq / m 3The main devices of the radon concentration measuring device 100 include: a sampling container 110, a desiccant 150, a mass flow meter 142, a circulation pump 141, an activated carbon chamber 120 and a heating temperature control device and a radon detection chamber 131. The gas circulation system 140 for gas circulation includes the following components: a circulation pump 141 and a mass flow meter 142. mBq / m 3 The method of using the radon concentration measuring device 100 is as follows: first, a certain amount of radon-containing gas is placed in the sampling chamber, then the circulation pump 141 and the mass flow meter 142 are turned on, and valves 143B and 143C are opened at the same time, and valves 143A and 143D are closed. A closed circulation gas path can be formed between the sampling container 110 and the enrichment chamber 120. At this time, the heating device outside the enrichment chamber 120 does not work, and the activated carbon inside the enrichment chamber 120 will circulate to the gas to be measured in the enrichment chamber 120. When the mass flow meter 142 is closed, valves 143A, 143B and 143D are opened, and valve 143C is closed, another closed circulating gas path can be formed between the enrichment chamber 120 and the α particle detection device 130. At this time, the heating device outside the enrichment chamber 120 is heated and stabilized at 300°C, and the activated carbon inside the enrichment chamber 120 will desorb the adsorbed radon gas at high temperature and transfer the radon gas to the detection chamber 131 for subsequent detection work. The sensor chamber 132 may include a temperature sensor and a humidity sensor, which are used to sense the temperature and humidity of the gas to be measured, respectively. The device has the following defects:

[0004] First, the device uses activated carbon at room temperature to enrich radon gas, and the adsorption coefficient and adsorption efficiency of activated carbon at room temperature for radon gas are low, so it is impossible to adsorb all the radon gas in the gas passing through the activated carbon at one time. Therefore, it is necessary to make the gas to be tested pass through the activated carbon chamber multiple times under the action of a circulating pump.

[0005] Second, the device uses a solid desiccant, which will also release a certain amount of radon gas, which is the background of the measurement device. Currently, all solid desiccants on the market cannot be applied to μBq / m 3 Among the radon measurement devices of the order of magnitude.

[0006] Third, the device uses a cylindrical radon detector chamber, which reduces the detector's collection efficiency of radon progeny and affects the measurement sensitivity of the entire device.

[0007] Fourth, based on the requirement of gas circulation, the device uses a sampling chamber of a certain volume, which limits the volume of the sample and makes it difficult to further improve the measurement sensitivity of the device. Summary of the invention

[0008] In order to solve the above technical problems and improve the detection sensitivity of radon in gas, the present invention provides a μBq / m 3 The present invention is mainly used to measure the concentration of extremely small amounts of radon in the gas in low-background experiments. 222 Developed for the detection of Rn content to achieve μBq / m 3 The measurement of radon concentration is the main goal.

[0009] The present invention adopts the following technical solutions:

[0010] A μBq / m 3 A gas radon concentration measuring device of magnitude, comprising a first valve, a first mass flow meter, a water storage tank, a second valve, a third valve, an activated carbon chamber, a fifth valve, a radon detector, a liquid nitrogen tank, a first solenoid valve, a first liquid nitrogen inlet pipe, a second solenoid valve, a second liquid nitrogen inlet pipe, a first dewar tank, a second dewar tank, a first temperature controller, a second temperature controller, a first temperature sensor, and a second temperature sensor;

[0011] A liquid nitrogen outlet is provided on the top of the liquid nitrogen tank; the liquid nitrogen outlet pipeline is divided into two routes, one route is sequentially connected to the first solenoid valve, the first liquid nitrogen inlet pipe and the first dewar tank, and the other route is sequentially connected to the second solenoid valve, the second liquid nitrogen inlet pipe and the second dewar tank;

[0012] One end of the first temperature controller is connected to the first solenoid valve, and the other end is connected to the first temperature sensor in the first Dewar tank; one end of the second temperature controller is connected to the second solenoid valve, and the other end is connected to the second temperature sensor in the second Dewar tank;

[0013] The water storage tank and the first temperature sensor are located in the first Dewar tank; the water storage tank is provided with a first air inlet pipe and a first air outlet pipe;

[0014] The activated carbon chamber, the heating belt and the second temperature sensor are located in the second Dewar tank; the activated carbon chamber is provided with a second air inlet pipe and a second air outlet pipe;

[0015] The inlet of the first valve is the sampling port; the outlet of the first valve is connected in sequence to the first mass flow meter, the first air inlet pipe of the water tank, the first air outlet pipe of the water tank, the second valve, the third valve, the second air inlet pipe of the activated carbon chamber, the second air outlet pipe of the activated carbon chamber, the fifth valve and the radon detector.

[0016] Furthermore, a nitrogen outlet is provided on the top of the liquid nitrogen tank, which is connected to the second mass flow meter and the fourth valve inlet in sequence; the fourth valve outlet is divided into two paths, one path is connected to the second valve and the water storage tank in sequence, and the other path is connected to the third valve and the activated carbon chamber in sequence.

[0017] Furthermore, the first liquid nitrogen inlet pipe extends into the interior of the first Dewar tank.

[0018] Furthermore, the second liquid nitrogen inlet pipe extends into the interior of the second Dewar tank.

[0019] Further, a heating tape is wrapped around the activated carbon chamber.

[0020] Furthermore, the radon detector is provided with a third air inlet, a third air outlet and a vacuum exhaust port, and the vacuum exhaust port is connected to a high vacuum angle valve, a bellows and a vacuum pump in sequence.

[0021] Furthermore, a sixth valve and a pressure gauge are respectively connected to the third gas outlet of the radon detector.

[0022] Furthermore, the radon detector comprises a stainless steel container and a Si-PIN semiconductor detector, and the Si-PIN semiconductor detector is located in the middle of the top of the stainless steel container.

[0023] Furthermore, the lower half of the stainless steel container is a hemispherical structure.

[0024] Furthermore, the inner wall of the radon detector and the inner walls of all pipelines are electrolytically polished to a roughness better than 0.1 μm.

[0025] First, the present invention uses low-temperature activated carbon to first enrich the low-concentration radon-containing gas, and then transfers the enriched radon-containing gas to the radon detector for measurement, converting the low-concentration radon detection into high-concentration radon detection, which makes μBq / m 3 In addition, enrichment can also shorten the measurement time and improve the measurement accuracy. According to the actual measurement of the project team, the adsorption capacity of activated carbon used in this project for radon gas increases significantly with the decrease of temperature. When the temperature drops to -180℃, 1g of activated carbon can adsorb more than 2000m3 of radon. 3 Radon gas in radon-containing nitrogen;

[0026] Second, the present invention designs the first hemispherical radon detector. Compared with the traditional cylindrical detector, the present device greatly improves the detector's collection efficiency of radon progeny. The research group used a radon detector with a concentration of 10Bq / m 3 The detector was calibrated with standard radon-containing gas and the calibration factor was 67 cph / (Bq / m 3 ), considering the 50% detection efficiency of Si-PIN detector for α particles and the 41.5L detector chamber volume, it can be concluded that the detector 222 The collection efficiency of Rn daughters reaches 90%;

[0027] Third, the present invention designs a simple and economical temperature control system, which can achieve stable temperature control of -196-200°C using liquid nitrogen, heating belts and temperature control devices, and the temperature stability is better than ±5°C;

[0028] Fourthly, the low-temperature dehumidification device designed in the present invention can achieve "zero background" introduction, which has great advantages in the field of low background research compared to desiccant dehumidification.

[0029] The advantages of the present invention are:

[0030] First, we developed a low-temperature activated carbon radon enrichment device by taking advantage of the fact that activated carbon can significantly enhance its radon adsorption capacity at low temperatures. This device can absorb 2000 m3 of radon with 1 gram of activated carbon. 3 The radon gas in the radon-containing gas greatly reduces the amount of activated carbon used compared to the normal temperature activated carbon adsorption device, while relaxing the background requirements for activated carbon and reducing the impact of the radioactive content of the activated carbon itself on the measurement results.

[0031] Second, a low-temperature dehumidification device was proposed and used, realizing a zero-background dehumidification device and eliminating the background caused by traditional desiccants.

[0032] Third, the use of a hemispherical detector improves the collection efficiency of radon progeny, increases the measurement sensitivity of the radon detector itself, and increases accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 mBq / m 3 Schematic diagram of the structure of the radon concentration measurement equipment;

[0034] In the figure, mBq / m 3 Magnitude radon concentration measuring device 100, sampling container 110, enrichment chamber 120, alpha particle detection device 130, radon detection chamber 131, sensor chamber 132, gas circulation system 140, circulation pump 141, mass flow meter 142, valve 143A, valve 143B, valve 143C, valve 143D, desiccant 150.

[0035] Figure 2 The figure is a schematic diagram of the structure of a device for measuring the gas radon concentration at the μBq / m3 level according to the present invention.

[0036] Figure 3 This is a schematic diagram of the structure of a low-temperature dehumidification device.

[0037] Figure 4 This is a schematic diagram of the structure of the activated carbon radon enrichment device.

[0038] Figure 5 Schematic diagram of the internal structure of a radon detector.

[0039] In the figure, 1-liquid nitrogen tank; 2-nitrogen outlet; 3-liquid nitrogen outlet; 4-second mass flow meter; 5-first solenoid valve; 6-first mass flow meter; 7-first liquid nitrogen inlet pipe; 8-second solenoid valve; 9-second liquid nitrogen inlet pipe; 10-first Dewar tank; 11-second Dewar tank; 12-first temperature controller; 13-second temperature controller; 14-radon detector; 15-vacuum exhaust port; 16-high vacuum angle valve; 17-bellows; 18-vacuum pump; 19-pressure gauge ; 20-first valve; 21-second valve; 22 third valve; 23-fourth valve; 24-fifth valve; 25-sixth valve; 26-first air inlet pipe; 27-first air outlet pipe; 28-second air inlet pipe; 29-second air outlet pipe; 30-third air inlet pipe; 31-third air outlet pipe; 32-water storage tank; 33-first temperature sensor; 34-activated carbon chamber, 35-heating belt, 36-second temperature sensor, 37-Si-PIN detector. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are limited to explaining the present invention, and the protection scope of the present invention should include the entire contents of the claims, and 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.

[0041] The present invention μBq / m 3 The gas radon concentration measuring device of this magnitude has a reserved sampling port. When in use, the sample to be tested only needs to be placed in a high-pressure container, and then the gas in the high-pressure container passes through the device. 3 The main structure of the gas radon concentration measurement device is as follows: Figure 2-5 As shown, the main advantages are high sensitivity and high accuracy.

[0042] like Figure 2-5 As shown, a μBq / m 3 The invention discloses a gas radon concentration measuring device of the order of magnitude, comprising a liquid nitrogen tank 1, a nitrogen outlet 2, a liquid nitrogen outlet 3, a second mass flowmeter 4, a first solenoid valve 5, a first mass flowmeter 6, a first liquid nitrogen inlet pipe 7, a second solenoid valve 8, a second liquid nitrogen inlet pipe 9, a first dewar tank 10, a second dewar tank 11, a first temperature controller 12, a second temperature controller 13, a radon detector 14, a vacuum exhaust port 15, a high vacuum angle valve 16, a bellows 17, a vacuum pump 18, a pressure gauge 19, a first valve 20, a second valve 21, a third valve 22, a fourth valve 23, a fifth valve 24, a sixth valve 25, a first air inlet pipe 26, a first air outlet pipe 27, a second air inlet pipe 28, a second air outlet pipe 29, a third air inlet pipe 30, a third air outlet pipe 31, a water storage tank 32, a first temperature sensor 33, an activated carbon chamber 34, a heating belt 35, a second temperature sensor 36 and a Si-PIN detector 37.

[0043] A nitrogen outlet 2 and a liquid nitrogen outlet 3 are provided at the top of the liquid nitrogen tank 1. The nitrogen outlet 2 is connected to the second mass flow meter 4 and the inlet of the fourth valve 23 in sequence; the outlet of the fourth valve 23 is divided into two paths, one of which is connected to the second valve 21 and the water storage tank 32 in sequence, and the other is connected to the third valve 22 and the activated carbon chamber 34 in sequence. The liquid nitrogen outlet 3 pipeline is divided into two paths, one of which is connected to the first solenoid valve 5, the first liquid nitrogen inlet pipe 7 and the first Dewar tank 10 in sequence, and the other is connected to the second solenoid valve 8, the second liquid nitrogen inlet pipe 9 and the second Dewar tank 11 in sequence. One end of the first temperature controller 12 is connected to the first solenoid valve 5, and the other end is connected to the first temperature sensor 33 in the first Dewar tank 10. One end of the second temperature controller 13 is connected to the second solenoid valve 8, and the other end is connected to the second temperature sensor 36 in the second Dewar tank 11.

[0044] The water storage tank 32 and the first temperature sensor 33 are located in the first dewar tank 10, and the first liquid nitrogen inlet pipe 7 extends into the first dewar tank 10. The water storage tank 32 is provided with a first air inlet pipe 26 and a first air outlet pipe 27.

[0045] The activated carbon chamber 34, the heating belt 35 and the second temperature sensor 36 are located in the second Dewar tank 11. The second liquid nitrogen inlet pipe 9 extends into the second Dewar tank 11. The heating belt 35 is wrapped around the activated carbon chamber 34, and the activated carbon chamber 34 is provided with a second air inlet pipe 28 and a second air outlet pipe 29.

[0046] The inlet of the first valve 20 is a sampling port; the outlet of the first valve 20 is connected in sequence to the first mass flow meter 6, the first air inlet pipe 26 of the water tank, the first air outlet pipe 27 of the water tank, the second valve 21, the third valve 22, the second air inlet pipe 28 of the activated carbon chamber, the second air outlet pipe 29 of the activated carbon chamber, the fifth valve 24 and the radon detector 14. The top of the radon detector 14 is provided with a third air inlet pipe 30, a third air outlet pipe 31 and a vacuum suction port 15, and the third air inlet pipe 30 is connected to the fifth valve 24; the third air outlet pipe 31 is divided into two paths, one path is connected to the sixth valve 25, and the other path is connected to the pressure gauge 19; the vacuum suction port 15 is connected in sequence to the high vacuum angle valve 16, the bellows 17 and the vacuum pump 18.

[0047] μBq / m 3 The gas radon concentration measuring device of the present invention mainly comprises a low-temperature dehumidification device, a radon enrichment chamber and a radon concentration measuring device.

[0048] 1. Low temperature dehumidification device, used to reduce the absolute humidity of the gas to be tested to 0.1g / m 3, because below this humidity, the detection efficiency of the radon detector device will no longer change significantly with the decrease of humidity. The low-temperature dehumidification device mainly includes a water storage tank 32, a first dewar tank 10, a first temperature controller 12, a first temperature sensor (Pt100) 33, a first solenoid valve 5, a first liquid nitrogen inlet pipe 7 and a liquid nitrogen tank 1. The water storage tank 32 and the first temperature sensor 33 are placed in the first dewar tank 10. The specific internal structure of the first dewar tank 10 is as follows: Figure 3 As shown. The device dehumidifies the gas to be tested by low temperature. The gas to be tested flows through the device from the water storage tank 32, and the first dewar tank 10 is only used as a heat preservation container without direct contact with the gas to be tested. The water storage tank 32 and the first temperature sensor 33 are placed in the first dewar tank 10. The first temperature sensor 33 can detect the temperature in the first dewar tank 10 in real time and input it into the first temperature controller 12 as an input. If the measured temperature is higher than the set temperature of the first temperature controller 12, the first temperature controller 12 will control the first electromagnetic valve 5 to open. At this time, the liquid nitrogen in the liquid nitrogen tank 1 will be sprayed into the first dewar tank 10 through the first liquid nitrogen inlet pipe 7, thereby reducing its internal temperature. If the temperature measured by the first temperature sensor 33 is lower than the set temperature of the first temperature controller 12, the first temperature controller 12 will control the closing of the first electromagnetic valve 5, and stop spraying liquid nitrogen into the first dewar tank 10. Since there is heat leakage in the first dewar tank 10, the temperature in the first dewar tank 10 will slowly rise. Through the cooperation of the first temperature sensor 33, the first temperature controller 12, the first solenoid valve 5 and the liquid nitrogen tank 1, the temperature in the first Dewar tank 10 can be controlled at any temperature from the liquid nitrogen temperature (-196°C) to the room temperature. After testing, when the gas flow rate is 1L / min, the humidity of the gas to be tested can be reduced to 0.1g / m 3 If the gas flow rate increases, the set temperature needs to be lowered. The most prominent advantage of this dehumidification device over conventional desiccant is that the background is low and will not affect subsequent measurements.

[0049] 2. Radon enrichment chamber, which is mainly used to enrich the radon concentration of the gas to be tested, mainly includes the second Dewar tank 11, the activated carbon chamber 34, the second temperature sensor 36, the second solenoid valve 8, the heating belt 35 and the liquid nitrogen tank 1. The activated carbon chamber 34, the second temperature sensor 36 and the heating belt 35 are placed in the second Dewar tank 11. The internal structure of the second Dewar tank 11 is as follows: Figure 4 The radon enrichment chamber and the low-temperature dehumidification device share the same liquid nitrogen tank 1. The activated carbon chamber 34 is a stainless steel tube with a length of 15 cm and an outer diameter of 1 / 4 inch, which can hold the low-background activated carbon preferred in this project (low-background activated carbon refers to the internal 226Special activated carbon with Ra content less than 10mBq / kg. According to the research and test of the project team, only Carboact and Saratech brands of activated carbon currently meet this condition. Saratech activated carbon is used in this experiment. )1g. The adsorption capacity of activated carbon for radon gas is characterized by the adsorption coefficient, which is negatively correlated with the temperature of the activated carbon, that is, the lower the temperature, the higher the adsorption coefficient. According to actual measurements, 1g of activated carbon can adsorb 2000mBq / kg at a temperature of -180℃. 3 Radon gas in radon-containing nitrogen, and the adsorption efficiency is greater than 99%. Activated carbon can efficiently adsorb radon gas in radon-containing gas at low temperature, and can desorb all adsorbed radon gas at a high temperature of 200°C. Using this principle, we can achieve the enrichment of radon gas, that is, first pass a large amount of low-concentration radon-containing gas through activated carbon at low temperature, and then desorb the radon gas adsorbed by activated carbon into the detector at high temperature, thereby converting low-concentration radon measurement into high-concentration radon measurement. The activated carbon chamber 34, the second temperature sensor 36 and the heating belt 35 are placed in the second dewar tank 11, wherein the heating belt 35 is wrapped around the activated carbon chamber 34. Since cooling and heating are divided into two stages of the experiment, that is, cooling is the radon adsorption stage, and heating is the radon desorption stage, the cooling process and the heating process do not affect each other. The temperature in the second dewar tank 11 is measured by the second temperature sensor 36 and input into the second temperature controller 13. During the cooling process, the second temperature controller 13 controls the second solenoid valve 8, and liquid nitrogen is sprayed into the second Dewar tank 11 through the second liquid nitrogen inlet pipe 9, thereby maintaining the interior of the second Dewar tank 11 at a low temperature. During the heating process, the second temperature controller 13 controls the heating belt 35. When the measured temperature is lower than the set temperature, the heating belt 35 works, and when the temperature reaches the set temperature, the heating belt 35 stops working. Through this device, the temperature in the second Dewar tank 11 can be controlled at any temperature between -196°C and 200°C during the test.

[0050] 3. A radon concentration measuring device. The main function of the device is to measure the radon content inside the chamber. The radon concentration measuring device is a radon detector 14. The internal structure of the radon detector 14 is as follows: Figure 5 As shown. It mainly includes two parts, one is a stainless steel container, and the other is a Si-PIN semiconductor detector 37. The Si-PIN semiconductor detector is located in the center of the top of the stainless steel container. Radon ( 222 Rn) is an unstable nuclide with a half-life of 3.8 days, which can undergo alpha decay. When decay occurs, 222 Rn emits an alpha particle with an energy of 5.49 MeV, which itself transforms into 218 Po, because the energy of the α particles released is high, the daughter nucleus 218 Po will gain a larger recoil energy, which will cause 218Po loses several electrons in its outer layer and becomes positively charged. During the specific measurement, a negative potential is added to the surface of the Si-PIN semiconductor detector 37 through an external circuit and the stainless steel cavity container is grounded. In this way, an external electric field is formed from the stainless steel shell to the Si-PIN detector 37. 222 Rn decay daughter ( 218 Po, etc.) are collected on the surface of the Si-PIN detector. When the daughter decays again, the Si-PIN detector can detect the α particles produced by the decay. Since the α particles have weak penetration ability in the air, 222 The α produced by Rn cannot be detected. In addition, since the sensitive part of the Si-PIN detector is only on the order of μm, the gamma rays in the environment and the electrons produced during the decay process cannot form detectable signals on it. The signal detected by this device is 222 Rn daughter 218 Po and 214 Alpha particles produced by Po decay. In order to improve the collection efficiency of the detector for radon progeny, the lower half of the stainless steel container is optimized into a hemispherical structure. In addition, the device will be evacuated during use. In order to enhance its mechanical strength and reduce its weight, a head design is used for the upper half of the chamber. The radon concentration measuring device is equipped with a pressure gauge 19, which can monitor the internal pressure during the process of vacuum gauge inflation. The chamber is connected to an external vacuum pump 18 through a high vacuum angle valve 16, and its function is to evacuate the gas inside the detector before the experiment begins and before the gas is transferred. The main function of evacuating the gas before the experiment is started is to reduce the background of the detector. The detector is evacuated before the gas transfer because the detector needs to work at normal pressure. The purpose of evacuating the detector is to bring the gas adsorbed by the activated carbon into the detector through the carrier gas.

[0051] In addition to the above main devices, this device also needs Figure 2 The pipelines and valves shown in the figure. Since the radon content to be measured in this project is μBq / m 3 of radon-containing gas, and the radon content in the air is ~10Bq / m 3 , 10 higher than the detection target 7 Therefore, the device must ensure that the system leakage rate is less than 10 -9 Pa*m 3 / s, so the valves and pipe joints used in the gas circuit of this device must use vacuum connection radial sealing joints (i.e. VCR joints), the water tank 32 of the dehumidification device and the stainless steel chamber flange of the radon concentration measuring device are sealed with knife-edge flanges, and the vacuum exhaust port, high vacuum angle valve and vacuum pump bellows connection joints also need to use knife-edge flange seals. The vacuum pressure gauge 19 also needs to use a pressure gauge with a VCR joint. In addition, for the consideration of the detector background, all containers and gas pipelines of this device are electrolytically polished, and the inner wall surface roughness after electrolytic polishing is better than 0.1μm.

[0052] The gas sample to be tested in this device must be placed in a high-pressure container with a valve, and the interface of the high-pressure container must match this device. The usage is as follows:

[0053] (1) Connect the high-pressure container containing the gas to be tested to the first valve 20 of the device, then open the first valve 20, the second valve 21, the third valve 22, the fifth valve 24 and the high vacuum angle valve 16, set the flow rate of the first mass flow meter 6 to the fully open state, set the temperature of the first temperature controller 12 to room temperature, set the temperature of the second temperature controller 13 to 200 degrees Celsius, close the fourth valve 23 and the sixth valve 25, and turn on the vacuum pump 18 after the temperature in the second Dewar tank 11 stabilizes to 200°C, and evacuate the chamber and pipeline of the radon detector 14. When the pressure gauge shows a pressure of -101 kPa, continue to evacuate for 10 minutes, and then close the high vacuum angle valve 16 and the vacuum pump 18 in turn.

[0054] (2) Set the flow rate of the first mass flow meter 6 to 1L / min, set the first temperature controller 17 to -60°C, and set the second temperature controller 13 to -150°C (the temperature can be adjusted according to the amount of activated carbon and the amount of gas to be treated. The less the amount of activated carbon and the larger the amount of gas to be treated, the lower the set temperature should be, but it cannot be set below the liquefaction temperature of the carrier gas). After the temperatures of the first dewar tank 10 and the second dewar tank 11 are stable, open the valve of the high-pressure container containing the gas to be tested, and let the gas to be tested pass through the dehumidification device, the activated carbon radon enrichment device and the radon detector in turn. At the same time, observe the internal pressure of the radon detector. When the pressure is higher than 10kPa, open the sixth valve 25 to discharge the gas (if the carrier gas is a harmful gas, it should be treated before being discharged), and then maintain this state until the sampling is completed. This stage is the low-temperature radon adsorption stage of the gas to be tested.

[0055] (3) After the sampling of the sample to be tested is completed, the first valve 20, the second valve 21, the third valve 22, the fifth valve 24 and the sixth valve 25 are closed, the temperature of the second temperature controller 13 is set to 200°C, and the high vacuum angle valve 16 and the vacuum pump 18 are opened at the same time to evacuate the radon detector chamber. When the pressure gauge shows a pressure of -101 kPa, continue to evacuate for 10 minutes, and then close the high vacuum angle valve 16 and the vacuum pump 18 in turn.

[0056] (4) After the temperature in the second Dewar tank 11 stabilizes to 200°C, open the fourth valve 23, the third valve 22, and the fifth valve 24, and set the flow rate of the second mass flowmeter 4 to 1L / min. At the same time, observe the pressure change inside the detector chamber. When the pressure reaches 5kPa, close the fifth valve 24, and then successively close the fourth valve 23 and the third valve 22. At this time, the radon desorption process of the activated carbon is completed.

[0057] (5) The radon concentration of the gas in the chamber is measured using a radon detector, and the radon concentration in the sample to be tested can then be obtained based on the volume of the detector and the volume of the gas sample.

[0058] The present invention does not elaborate on some of the common technologies of those skilled in the art. The above-described embodiments are only descriptions of preferred implementations of the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementations described. Without departing from the design spirit of the present invention, various modifications and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A μBq / m 3 A gas radon concentration measuring device of the order of magnitude, characterized in that: The invention comprises a first valve (20), a first mass flow meter (6), a water storage tank (32), a second valve (21), a third valve (22), an activated carbon chamber (34), a fifth valve (24), a radon detector (14), a liquid nitrogen tank (1), a first solenoid valve (5), a first liquid nitrogen inlet pipe (7), a second solenoid valve (8), a second liquid nitrogen inlet pipe (9), a first dewar tank (10), a second dewar tank (11), a first temperature controller (12), a second temperature controller (13), a first temperature sensor (33) and a second temperature sensor (36); A liquid nitrogen outlet (3) is provided at the top of the liquid nitrogen tank (1); the liquid nitrogen outlet (3) pipeline is divided into two paths, one path is sequentially connected to the first solenoid valve (5), the first liquid nitrogen inlet pipe (7) and the first Dewar tank (10), and the other path is sequentially connected to the second solenoid valve (8), the second liquid nitrogen inlet pipe (9) and the second Dewar tank (11); One end of the first temperature controller (12) is connected to the first solenoid valve (5), and the other end is connected to the first temperature sensor (33) in the first dewar tank (10); one end of the second temperature controller (13) is connected to the second solenoid valve (8), and the other end is connected to the second temperature sensor (36) in the second dewar tank (11); The water storage tank (32) and the first temperature sensor (33) are located in the first Dewar tank (10); the water storage tank (32) is provided with a first air inlet pipe (26) and a first air outlet pipe (27); The activated carbon chamber (34), the heating belt (35) and the second temperature sensor (36) are located in the second Dewar tank (11); the activated carbon chamber (34) is provided with a second air inlet pipe (28) and a second air outlet pipe (29); The inlet of the first valve (20) is a sampling port; the outlet of the first valve (20) is sequentially connected to a first mass flow meter (6), a first air inlet pipe (26) of a water storage tank (32), a first air outlet pipe (27) of the water storage tank, a second valve (21), a third valve (22), a second air inlet pipe (28) of an activated carbon chamber (34), a second air outlet pipe (29) of the activated carbon chamber, a fifth valve (24) and a radon detector (14).

2. The gas radon concentration measuring device according to claim 1, characterized in that: A nitrogen outlet (2) is also provided at the top of the liquid nitrogen tank (1), and the nitrogen outlet (2) is sequentially connected to a second mass flow meter (4) and an inlet of a fourth valve (23); the outlet of the fourth valve (23) is divided into two paths, one path is sequentially connected to the second valve (21) and a water storage tank (32), and the other path is sequentially connected to the third valve (22) and an activated carbon chamber (34).

3. The gas radon concentration measuring device according to claim 1, characterized in that: The first liquid nitrogen inlet pipe (7) extends into the interior of the first Dewar tank (10).

4. The gas radon concentration measuring device according to claim 1, characterized in that: The second liquid nitrogen inlet pipe (9) extends into the interior of the second Dewar tank (11).

5. The gas radon concentration measuring device according to claim 1, characterized in that: A heating tape (35) is wrapped around the activated carbon chamber (34).

6. The gas radon concentration measuring device according to claim 1, characterized in that: A third air inlet pipe (30), a third air outlet pipe (31) and a vacuum air pumping port (15) are provided on the top of the radon detector (14); the third air inlet pipe (30) is connected to a fifth valve (24); the third air outlet pipe (31) is divided into two paths, one path is connected to a sixth valve (25), and the other path is connected to a pressure gauge (19); the vacuum air pumping port (15) is sequentially connected to a high vacuum angle valve (16), a bellows (17) and a vacuum pump (18).

7. The gas radon concentration measuring device according to claim 1, characterized in that: The radon detector (14) comprises a stainless steel container and a Si-PIN detector (37), wherein the Si-PIN detector (37) is located at the center of the top of the stainless steel container.

8. The gas radon concentration measuring device according to claim 7, characterized in that: The lower half of the stainless steel container is a hemispherical structure, and the inner wall of the chamber is electrolytically polished, with a roughness better than 0.1 μm.

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