CN108919329B - Method and device for closed-loop measurement of emanation rate of radon in emanation medium - Google Patents
Method and device for closed-loop measurement of emanation rate of radon in emanation medium Download PDFInfo
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- CN108919329B CN108919329B CN201810487713.3A CN201810487713A CN108919329B CN 108919329 B CN108919329 B CN 108919329B CN 201810487713 A CN201810487713 A CN 201810487713A CN 108919329 B CN108919329 B CN 108919329B
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Abstract
The invention discloses a method and a device for measuring emanation rate of emanation medium radon in a closed loop manner, wherein the method comprises the following steps: (1) the gas pump is started, and the flow entering the gas pressure equalizing chamber is controlled to be Q through the flow regulator; measuring radon concentration C in external environment by radon measuring instrument0As gas-collecting hoods inTime t0Has a radon concentration of C0When the radon concentration in the gas-collecting hood is measured, the radon concentration C at the moment is recorded in sequence every time the same time interval delta T elapses1、C2、......、Cn(n is more than or equal to 5); (2) fitting a differential equation using the measurements
And then calculating the radon exhalation rate J. The method can be used for obtaining the radon exhalation rate and the equivalent decay constant before the radon concentration is balanced, and has the advantages of short time and accurate calculation.
Description
Technical Field
The invention relates to a method and a device for measuring radon exhalation rate of an emanation medium in a closed loop mode, in particular to a seepage device capable of generating controllable flow in a particle accumulation type emanation medium and a method for determining radon exhalation rate under seepage-diffusion action, and belongs to the technical field of nuclear radiation measurement.
Background
Radon is an inert radioactive gas that is colorless and odorless and widely found in rocks, soils and groundwater. The international health organization (WHO) classifies radon as 19 main environmental carcinogens, the radon exhalation rate is a physical quantity for evaluating the radon releasing capacity of an emanation medium, and the reasonable and scientific measurement of the radon exhalation rate and the exhalation rule is a research hotspot of scholars at home and abroad.
As the radon precipitation amount in a medium in a natural environment is small, scholars at home and abroad generally adopt an accumulation method to measure the radon precipitation rate on the surface of the medium, a gas collecting cover with a fixed volume is adopted to be reversely buckled on the surface of a gas emitting medium to collect radon, and then a related detection instrument and a mathematical processing method are utilized to estimate the radon precipitation rate on the surface of the medium, so that three measuring methods of open-loop radon measurement, closed-loop radon measurement and activated carbon adsorption by a local static method are developed. For closed-loop radon measurement, a gas-collecting hood is closed, radon exhalation rate calculation is carried out by monitoring radon concentration in the gas-collecting hood, and for open-loop radon measurement, on the basis of closed-loop radon measurement, the gas-collecting hood is opened, and an air inlet is arranged to balance pressure difference of the gas-collecting hood and avoid a negative pressure region generated by the gas-collecting hood. The Chinese patent document discloses an invention patent of a closed-loop type continuous measurement method for the exhalation rate of radon (application number: 201410203811.1), and the invention patent discloses the closed-loop type continuous measurement method for the exhalation rate of radon. The gas-collecting hood of the invention has no air pressure balancing port, so the seepage of radon is limited, the seepage item is ignored during calculation, the obtained experimental result is inaccurate and is not in accordance with the actual radon precipitation mechanism of the porous medium. And the method can be used when the radon concentration in the gas-collecting hood tends to be balanced, so that the effective decay constant and the radon exhalation rate cannot be quickly obtained.
Therefore, the method for calculating the radon exhalation rate under the seepage-diffusion effect can quickly determine the radon exhalation rate on the surface of the particle accumulation type emanation medium under the seepage-diffusion effect and can also determine the radon exhalation rate under the pure diffusion effect.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a seepage device capable of generating controllable flow in a particle accumulation type emanation medium and a method for calculating the radon exhalation rate under the seepage-diffusion effect.
The technical problem solved by the invention is as follows: the determination and the technical process of the radon exhalation rate are simplified; the accuracy of radon exhalation rate measurement is improved.
The technical scheme of the invention is to provide a method for measuring the radon exhalation rate of an emanation medium in a closed loop manner, which uses the following devices to measure the radon exhalation rate:
the device comprises a radon measuring instrument and a test column for containing a gas medium to be tested, wherein a gas collecting hood is arranged above the test column, the radon measuring instrument is communicated with the gas collecting hood through a gas pipe to form a closed loop, a hole communicated with the external environment is formed in the upper surface of the gas collecting hood, a gas pressure equalizing chamber is arranged below the test column, the gas pressure equalizing chamber is connected with a gas pump through a gas pipe, and a flow regulator is arranged on the gas pipe between the gas pressure equalizing chamber and the gas pump;
the method comprises the following steps:
(1) the gas pump is started, and the flow entering the gas pressure equalizing chamber is controlled to be Q through the flow regulator; measuring radon concentration C in external environment by radon measuring instrument0As gas-collecting channel at time t0(when t is 0) has a radon concentration of C0When the radon concentration in the gas-collecting hood is measured, the radon concentration C at the moment is recorded in sequence every time the same time interval delta T elapses1、C2、......、Cn(n is more than or equal to 5); preferably n-5-20, more preferably n-6-10.
(2) Fitting the following differential equation using the above measurements
Calculating the radon exhalation rate J;
wherein C is the radon concentration in the gas-collecting hood and the unit is Bq/m3(ii) a t is radon precipitation time, and the unit is s; v is the total volume of the closed loop where the emanometer and the gas collecting hood are located, and the unit is m3(ii) a S is the bottom area of the gas-collecting hood and has the unit of m2；λ1Is the decay constant of radon in units of s-1；λ2Is leakage rate in units of s-1；λ3Is the inverse diffusion coefficient, in units of s-1(ii) a Q is gas seepage flow rate, and the unit is m3S; j is the radon exhalation rate on the surface of the emanation medium and is expressed in Bq (m)-2·s-1)；
The radon concentration C in the gas-collecting hood is a variable, and a specific numerical value can be directly measured by a measuring instrument; the radon precipitation time t is variable, and the initial time is 0 s; for a particular device, both V and S are known quantitative; j is unknown quantification; λ 1+ λ 2+ λ 3 is the unknown quantification; the gas seepage flow rate Q, i.e., the gas flow rate set by the gas pump, can be directly obtained by a gas flow meter, and is generally set to a fixed amount in the experiment.
By solving the above differential equation:
let lambdae＝λ1+λ2+λ3Then, then
Order to
Then C is a + (C)0-a)e-bt；
A radon concentration value C obtained by measuring the radon concentration in the gas-collecting hood at the same time interval DeltaT1、C2、......、CnAccording to formula C (t) ═ a + (C)0-a)e-btFitting an equation to obtain values of a and b, substituting the values of a and b, and calculating lambdaeAnd (J) of a group consisting of,
wherein C (t) represents a functional relationship of C with respect to t.
The closed loop where the radon detector and the gas collecting hood are located is formed by a filtering device, a drying pipe, a gas flowmeter, the radon detector and the gas collecting hood which are sequentially connected in series by gas pipes, and the total volume V of the closed loop is the sum of the volumes of all parts (including the gas pipes).
Preferably, the emanator medium is granular; the particle diameter of the granules is 1-5 mm. The inner diameter of the test column is 150 mm and 250mm, and the height of the gas-jetting medium in the test column is 0.8-1.5 m.
Preferably, the emanator medium is uranium ore particles.
Preferably, the gas seepage flow rate Q is 150-300 ml/min.
Preferably, the time interval Δ T is between 8 and 20 minutes.
The holes are used for air pressure balance, namely the air is discharged through the holes on the upper surface of the air collecting cover after the air is pumped by the air pump, so that the air pressure balance is realized.
The invention also provides a device for closed-loop measurement of radon exhalation rate of a gas-emitting medium, which comprises a radon measuring instrument and a test column for containing the gas-emitting medium to be measured, wherein a gas-collecting hood is arranged above the test column, and the radon measuring instrument is communicated with the gas-collecting hood through a gas pipe to form a closed loop.
Preferably, the gas pipes are provided with gas flow meters.
Preferably, the gas equalizing chamber is provided with a gas inlet, the gas pump is communicated with the gas inlet through a gas pipe, and the gas inlet is positioned on the side surface or the bottom surface of the gas equalizing chamber.
Preferably, the gas pressure equalizing chamber is filled with granular packing, and the gas inlet is positioned at the bottom surface of the gas pressure equalizing chamber.
Preferably, the closed loop is formed by sequentially connecting a filtering device, a drying pipe, a gas flowmeter, a radon measuring instrument and a gas collecting hood in series by using gas pipes.
Preferably, the area of the holes accounts for 5-10% of the area of the upper surface of the gas-collecting channel.
Preferably, the test column is a column of fixed cross-sectional area.
The closed loop of the invention is a closed loop, namely, the radon detector samples from the gas-collecting hood for detection, and the gas after detection still returns to the gas-collecting hood to form a closed loop.
The invention has the advantages that: the device can generate stable and controllable gas seepage in the particle accumulation type gas-emitting medium, and under the condition of not influencing seepage, the radon exhalation rate on the surface of the particle accumulation type gas-emitting medium under the seepage-diffusion action can be rapidly determined by the method provided by the invention, and the radon exhalation rate under the pure diffusion action can also be determined by the method provided by the invention. The method can be used for obtaining the radon exhalation rate and the equivalent decay constant before the radon concentration is balanced, and has the advantages of short time and accurate calculation.
Drawings
FIG. 1 shows a diagram of an apparatus for measuring radon exhalation rate in a percolation state.
Description of reference numerals: 1-filtering device, 2-drying tube, 3-gas flowmeter, 4-hole, 5-radon detector, 6-gas collecting hood, 8-gas pressure equalizing chamber, 9-gas inlet, 10-gas pump and 11-flow regulator.
Detailed Description
The invention is further illustrated by the following figures and examples.
The embodiment provides a method and a device for measuring the radon exhalation rate of a particle accumulation type emanation medium.
The structure diagram of the device is shown in fig. 1, and the device comprises a radon measuring instrument 5 and a test column 7 for containing a gas medium to be detected, wherein a gas collecting hood 6 is arranged above the test column 7, the radon measuring instrument 5 is communicated with the gas collecting hood 6 through a gas pipe to form a closed loop, and the closed loop is formed by sequentially connecting a filtering device 1, a drying pipe 2, a gas flowmeter 3, the radon measuring instrument 5 and the gas collecting hood 6 in series through the gas pipe. The upper surface of the gas collecting hood 6 is provided with a hole 4 communicated with the outside, a gas pressure equalizing chamber 8 is arranged below the test column 7, the gas pressure equalizing chamber 8 is connected with a gas pump 10 through a gas pipe, and a flow regulator 11 is arranged on the gas pipe between the gas pressure equalizing chamber 8 and the gas pump 10. The gas pressure equalizing chamber 8 is provided with a gas inlet 9, the gas pump 10 is communicated with the gas inlet 9 through a gas pipe, and the gas inlet 9 is positioned on the side surface of the gas pressure equalizing chamber 8. The gas pressure equalizing chamber 8 is a cavity, a breathable diaphragm is arranged on the contact surface of the gas pressure equalizing chamber 8 and the test column 7, the gas-jet medium is prevented from falling, and the test column 7 is a cylinder.
The gas pressure equalizing chamber 8 is placed on the flat ground and is connected with the gas flowmeter 3, the gas pump 10 and the regulator 11 through hoses, the test column 7 with the inner diameter of 200mm is placed on the gas pressure equalizing chamber 8, the uranium ore particles which are naturally dried and have the particle size of less than 5mm are loaded into the test column 7, and the height of the filled ore particles is about 1 m. And then the filtering device 1, the drying pipe 2, the gas flowmeter 3, the radon measuring instrument 5 and the gas collecting hood 6 are connected by a hose.
Determination of radon concentration
The total volume V of the closed loop formed by the filtering device 1, the drying pipe 2, the radon measuring instrument 5, the gas collecting hood 6 and the plastic hose is measured to be about 5.41L in advance. Measuring radon concentration in indoor environment as C by radon detector0. The seepage velocity regulating device is fixed with the test column 7, the seepage flow is calculated according to the product of the seepage velocity required by the test column and the cross sectional area of the test column 7, the flow entering the gas pressure equalizing chamber 8 is controlled to be 200ml/min through the regulator 11, and the gas pump continuously and constantly pumps in the outside gas at a constant speed and generates stable gas seepage in the test column 7.
Opening a radon detector 5 to measure the radon concentration in the gas-collecting hood, and measuring the radon concentration in the gas-collecting hood every 10 minutes after the start to obtain a radon concentration value C1、C2、......、Cn(n≥5)。
Measuring to obtain the radon concentration C in the room0The value is 30Bq/m3。
Radon concentration C in the gas-collecting hoodnThe results are shown in table 1:
TABLE 1 Radon concentration C in the gas-collecting hoodn
Calculation of radon exhalation Rate
Under the gas seepage-diffusion effect, the radon concentration in the gas-collecting hood can be expressed by the following formula:
wherein: c is radon concentration in the gas-collecting hood, Bq/m3(ii) a V is the volume of the gas-collecting hood, m3. S is the bottom area of the gas-collecting hood, m2；λ1Is the decay constant of radon, s-1；λ2As leakage rate, s-1；λ3Is the inverse diffusion coefficient, s-1(ii) a Q is the gas seepage flow rate, m3S; j is the radon exhalation rate on the surface of the emanation medium and is expressed in Bq (m)-2·s-1)
The formula is simplified to obtain:
solving the above differential equation yields:
wherein: c0Is the radon concentration of the gas-collecting hood at the initial time, Bq/m3。
Let lambdae＝λ1+λ2+λ3
Then
Order to
Then C is a + (C)0-a)e-bt(5)
With gas-collecting channel at time zero (t)00) radon concentration C0Measuring the radon concentration C in the environment by a radon measuring instrument, which is the same as the radon concentration in the surrounding atmosphere0When monitoring the radon concentration in the gas-collecting hood, recording the radon concentration C at the same time every time interval delta T1、C2、......、Cn(n≥5)。
Using least square method, measuring radon concentration value C obtained by measuring radon concentration in gas-collecting hood at same time interval delta T1、C2、......、Cn(n.gtoreq.5) by the formula C (t) ═ a + (C)0-a)e-btFitting is carried out to obtain values of a and b, and the values are substituted into (5) to obtain:
data in table 1 are expressed as C (t) ═ a + (C)0-a)e-btFitting was performed and the fitting results are shown in table 2.
Parameter fitting in the formula of Table 2
| a(Bq/m3) | b(s-1) | Regression coefficient R2 |
| 23030 | 0.0011116 | 0.9781 |
Then, the data in table 2 are substituted into the formulas (6) and (7) provided by the invention to obtain the radon exhalation rate J and the equivalent decay constant lambda of the particle accumulation type emanation medium, and the result is shown in table 3. Where v represents the seepage flow rate.
TABLE 3 Radon exhalation Rate and equivalent diffusion coefficient
| J(Bq·m-2s-1) | λ(s-1) | Q(ml/min) | v(m/s) |
| 2.56 | 5.0036e-05 | 200 | 0.0001061 |
Claims (10)
1. A closed-loop method for measuring emanation medium radon exhalation rate is disclosed, which uses the following devices to measure radon exhalation rate: the device comprises a radon measuring instrument and a gas collecting hood, wherein the radon measuring instrument is communicated with the gas collecting hood through a gas pipe to form a closed loop;
the method comprises the following steps:
(1) the gas pump is started, and the flow entering the gas pressure equalizing chamber is controlled to be Q through the flow regulator; measuring radon concentration C in external environment by radon measuring instrument0The radon concentration of the gas collecting hood at zero time is C0When the radon concentration in the gas-collecting hood is measured, the radon concentration C at the moment is recorded in sequence every time the same time interval delta T elapses1、C2、……、Cn(n≥5)；
(2) Fitting the following differential equation using the above measurements
Calculating the radon exhalation rate J;
wherein C is the radon concentration in the gas-collecting hood and the unit is Bq/m3(ii) a t is radon precipitation time, and the unit is s; v is the total volume of the closed loop where the emanometer and the gas collecting hood are located, and the unit is m3(ii) a S is the bottom area of the gas-collecting hood and has the unit of m2(ii) a J is the radon exhalation rate on the surface of the emanation medium and is expressed in Bq (m)-2·s-1)；λ1Is the decay constant of radon in units of s-1；λ2Is leakage rate in units of s-1；λ3Is the inverse diffusion coefficient, in units of s-1(ii) a Q is gas seepage flow rate, and the unit is m3/s。
2. The method of claim 1, wherein solving the differential equation yields:
let lambdae＝λ1+λ2+λ3Then, then
Order to
Then C is a + (C)0-a)e-bt；
A radon concentration value C obtained by measuring the radon concentration in the gas-collecting hood at the same time interval DeltaT1、C2、……、CnAccording to formula C (t) ═ a + (C)0-a)e-btFitting an equation to obtain values of a and b, substituting the values of a and b, and calculating lambdaeAnd (J) of a group consisting of,
3. the method of claim 1, wherein the closed loop in which the emanometer and the gas collecting hood are located is formed by sequentially connecting a filtering device, a drying pipe, a gas flowmeter, the emanometer and the gas collecting hood in series by using gas pipes.
4. The utility model provides a device for measuring emanation medium radon exhalation rate of closed-loop type, including emanometer (5), a test column (7) that is used for the splendid attire emanation medium that awaits measuring, gas collecting channel (6) are established to the top of test column (7), emanometer (5) communicate and constitute closed circuit through trachea and gas collecting channel (6), a serial communication port, establish hole (4) with external intercommunication at the upper surface of gas collecting channel (6), gaseous surge-chamber (8) are established to the below of test column (7), gaseous surge-chamber (8) pass through trachea connection gas pump (10), be equipped with flow regulator (11) on the trachea between gaseous surge-chamber (8) and gas pump (10).
5. The device according to claim 4, characterized in that the gas pipes are provided with gas flow meters (3).
6. The device according to claim 4, characterized in that the gas pressure equalizing chamber (8) is provided with a gas inlet (9), the gas pump (10) is communicated with the gas inlet (9) through a gas pipe, and the gas inlet (9) is positioned on the side surface or the bottom surface of the gas pressure equalizing chamber (8).
7. The apparatus according to claim 6, characterized in that the gas pressure equalization chamber (8) is filled with a granular packing, and the gas inlet is located at the bottom of the gas pressure equalization chamber (8).
8. The device according to claim 4, characterized in that the closed loop is formed by a filtering device (1), a drying pipe (2), a gas flowmeter (3), a radon detector (5) and a gas collecting hood (6) in a mode of connecting gas pipes in series in sequence.
9. A device according to claim 4, characterized in that the area of the holes (4) is 5-10% of the area of the upper surface of the gas-collecting channel.
10. The device according to claim 4, characterized in that the test column (7) is a cylinder of constant cross-sectional area.
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| CN109655861B (en) * | 2018-12-18 | 2022-06-07 | 衡阳师范学院 | Method for measuring radium concentration in water in closed loop mode |
| CN109655860B (en) * | 2018-12-18 | 2022-06-07 | 衡阳师范学院 | Method for quickly measuring radium concentration in water in closed loop mode |
| CN109613590B (en) * | 2018-12-18 | 2022-06-07 | 衡阳师范学院 | Method for measuring radium concentration in water by closed-loop two-stage method |
| CN109655865B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for measuring radium concentration in water in closed loop mode through total counting of Po-218 and Po-214 |
| CN109655864B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for measuring radium concentration in water by Po-218 and Po-214 total counting closed-loop two-stage method |
| CN109655869B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for rapidly measuring radium concentration in water in closed-loop two-period mode |
| CN109655867B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for quickly measuring radium concentration in water through closed-loop partial integration |
| CN109655868B (en) * | 2018-12-21 | 2022-08-02 | 衡阳师范学院 | Method for rapidly measuring radium concentration in water by closed-loop electrostatic collection method |
| CN109655863B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for measuring radium concentration in water in two cycles of closed-loop electrostatic collection |
| CN109655862B (en) * | 2018-12-21 | 2022-06-21 | 衡阳师范学院 | Method for partially integrating and measuring radium concentration in water by closed-loop electrostatic collection method |
| CN109655866B (en) * | 2018-12-21 | 2022-08-12 | 衡阳师范学院 | Method for measuring radium concentration in water by closed-loop electrostatic collection two-stage method |
| CN109655874B (en) * | 2019-02-25 | 2020-04-10 | 衡阳师范学院 | Radon measuring device and method for scintillation chamber |
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| CN101644700B (en) * | 2008-12-10 | 2013-05-08 | 南华大学 | Method and device for measuring radon exhalation rate on medium surface |
| CN102426379B (en) * | 2011-11-18 | 2013-06-19 | 衡阳师范学院 | Method for measuring radon emanation rate by adopting two-stage method |
| CN103487360B (en) * | 2013-09-26 | 2016-07-06 | 衡阳师范学院 | Closed loop quickly measures the method for precipitation rate of radon |
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