A radon exhalation rate measuring instrument calibration device and radon exhalation rate control method

Abstract

The present invention relates to a radon exhalation rate measuring instrument calibration device and a radon exhalation rate control method thereof, and relates to the field of radon exhalation rate measurement. The device comprises a diffuse solid radon source, a solid radon source placement cavity, a radon accumulation cavity, a diffusion medium, an air pressure balance device, a support frame and a fixing frame; a circular cone at the bottom of the radon accumulation cavity is connected to the solid radon source placement cavity, and the top of the radon accumulation cavity is sealed by a diffusion medium, the diffusion medium comprises a gypsum board and a high-density board, and the high-density board is above the gypsum board; the air pressure balance device is connected to the radon accumulation cavity, and the air pressure balance device is used to maintain a dynamic balance between the radon accumulation cavity and the ambient atmospheric pressure; and the radon exhalation rate on the surface of the diffusion medium is determined according to the thickness of the diffusion medium layer and the activity of the solid radon source in the solid radon source placement cavity. The invention improves the stability and uniformity of radon exhalation rate measurement and realizes calibration of different radon exhalation rate measuring instruments to be tested by adjusting the radon exhalation rate of a radon exhalation rate measuring instrument testing device.

Description

Technical Field

[0001] The present invention relates to the field of radon exhalation rate measurement, in particular to a radon exhalation rate measuring instrument calibration device and a radon exhalation rate control method. Background Art

[0002] Radon is ubiquitous and is second only to smoking as a risk factor for lung cancer. It is listed by the World Health Organization as one of the 19 most carcinogenic substances. The harm radon poses to human health, as well as its monitoring and prevention (especially indoor radon), are receiving increasing public attention. Radon in the environment primarily emanates from surface radon. To ensure both ecological and human safety, radon source monitoring and control imposes technical requirements on the reliability of surface radon exhalation rate measurements. This necessitates the development of a test and calibration device for radon exhalation rate measuring instruments, known as a radon exhalation rate standard device.

[0003] Patent application number 201810557524.9 provides a reference device and method for stably regulating radon exhalation rates. This device utilizes a water platform, a flow-type radon source, an air pump, and a regulating chamber to regulate the radon exhalation rate. This is achieved primarily by varying the volume of the regulating chamber, eliminating the need to purchase a large number of standard radon sources of varying strengths. This reduces both the device's procurement and subsequent maintenance costs. However, this invention suffers from shortcomings such as an inability to eliminate the influence of ambient air pressure inside and outside the device, and poor uniformity and stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a radon exhalation rate measuring instrument calibration device and a radon exhalation rate control method, which improves the stability and uniformity of the radon exhalation rate of the medium surface of the radon exhalation rate measuring instrument calibration device, so as to improve the accuracy of the radon exhalation rate measuring instrument calibration.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A radon exhalation rate measuring instrument calibration device includes a diffusion type solid radon source, a solid radon source placement cavity, a radon accumulation cavity, a diffusion medium and an air pressure balance device;

[0007] The radon accumulation cavity is in an inverted cone shape, the circular cone at the bottom of the radon accumulation cavity is connected to the solid radon source placement cavity, the top of the radon accumulation cavity is connected to the diffusion medium, the diffusion medium includes a gypsum board and a high-density board, the gypsum board is located above the radon accumulation cavity, and the high-density board covers the gypsum board, the air pressure balancing device is connected to the radon accumulation cavity, and the air pressure balancing device is used to maintain a dynamic balance between the air pressure of the radon accumulation cavity and the ambient atmosphere;

[0008] determining a radon exhalation rate on the surface of the diffusion medium according to a diffusion coefficient of radon in the diffusion medium, a thickness of the diffusion medium layer, and an activity of a solid radon source in the solid radon source placement cavity;

[0009] The radon exhalation rate is adjusted by changing the activity of the solid radon source in the solid radon source placement cavity and the thickness of the diffusion medium layer.

[0010] Optionally, the device further comprises a support frame and a fixing frame, wherein the fixing frame is used to fix the diffusion medium layer; the fixing frame comprises an upper fastening flange, a lower fastening flange, a fastening screw and a clamping plate, wherein the clamping plate is used to clamp the edge of the diffusion medium layer, and the fastening screw is used to pass through the clamping plate, and the length of the fastening screw is adjustable; the upper fastening flange and the lower fastening flange are respectively located at both ends of the fastening screw and are used to fasten the clamping plate;

[0011] The support frame is connected to the bottom of the fixing frame, and the support frame is used to support the radon accumulation cavity. The support frame and the radon accumulation cavity are both made of stainless steel;

[0012] The bottom of the support frame is provided with universal wheels.

[0013] Optionally, it further includes an outer cover, which is cylindrical and is sleeved on the outside of the support frame and the diffusion medium. The material of the outer cover is stainless steel.

[0014] Optionally, the radon accumulation cavity and the solid radon source placement cavity are connected by a flange connection, and a silicone sealing gasket is provided between the radon accumulation cavity and the solid radon source placement cavity.

[0015] Optionally, a silicone sealing gasket is provided between the high-density board and the gypsum board.

[0016] Optionally, the air pressure balance device includes a U-shaped connecting tube and an air pressure balance bottle, the air pressure balance bottle is connected to the radon accumulation cavity through the U-shaped connecting tube, and the liquid in the air pressure balance bottle includes a salt water mixture exceeding a set salt concentration.

[0017] Optionally, a first inlet and a second inlet are provided on the side wall of the radon accumulation cavity, and the first inlet and the second inlet are symmetrically distributed on the side wall of the radon accumulation cavity. The first inlet and the second inlet are used for the flow-type solid radon source to quickly fill a predetermined amount of radon into the radon accumulation cavity.

[0018] Optionally, a cross support frame is provided at the top opening of the radon accumulation cavity.

[0019] The present invention also discloses a radon exhalation rate control method, which is applied to the radon exhalation rate measuring instrument calibration device. The radon exhalation rate control method includes:

[0020] Adjusting the radon exhalation rate of the radon exhalation rate measuring instrument verification device by changing the activity of a fixed radon source and the thickness of a diffusion medium layer in a radon accumulation cavity of the radon exhalation rate measuring instrument verification device, and calibrating different radon exhalation rate measuring instruments to be verified by adjusting the radon exhalation rate of the radon exhalation rate measuring instrument verification device;

[0021] The adjustment process of the radon exhalation rate to be adjusted specifically includes:

[0022] Step 1: Determine the thickness of the gypsum board and high-density board in the diffusion medium;

[0023] Step 2: Determine the relationship between diffuse solid radon sources of different activities and the radon exhalation rate and radon concentration in the radon-accumulating cavity;

[0024] Step 3: Based on the relationship between the diffusible solid radon sources with different activities and the radon exhalation rate and the radon concentration in the radon-accumulated cavity, a diffusible solid radon source is selected according to the radon exhalation rate to be adjusted;

[0025] Step 4: Determine the stable radon concentration of the radon-accumulating cavity based on the selected diffuse solid radon source;

[0026] Step 5: Place the selected diffusion-type solid radon source in the solid radon source placement cavity, use the gas-flow solid radon source to fill a predetermined amount of radon into the radon accumulation cavity, and wait for the radon concentration in the radon accumulation cavity to reach an equilibrium state;

[0027] When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium does not change, repeat steps 3 to 5 to adjust the radon exhalation rate;

[0028] When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium changes, repeat steps 1 to 5 to adjust the radon exhalation rate.

[0029] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0030] The present invention adopts gypsum board and high-density board with adjustable thickness as diffusion media, utilizes the uniformity of radon diffusion in the high-density board and the radon-blocking ability of the gypsum board, and adopts a pressure balancing device to eliminate the influence of atmospheric pressure changes on the radon exhalation rate of the device, thereby achieving the uniformity and stability of the radon exhalation rate on the surface of the device; by filling the radon accumulation cavity with radon activity matching the solid radon source, the device can quickly reach a steady state and produce a stable and uniform expected radon exhalation rate, thereby improving the efficiency of radon exhalation rate regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 This is a structural schematic diagram of a radon exhalation rate measuring instrument calibration device of the present invention;

[0033] Figure 2 This is a schematic diagram of the upper and lower fastening flanges of the diffusion medium of the present invention;

[0034] Figure 3 This is a schematic diagram of the connection of the diffusion medium of the present invention;

[0035] Figure 4 Schematic diagram of the air pressure balancing device of the present invention;

[0036] Figure 5 A side view of the cavity for placing the solid radon source of the present invention;

[0037] Figure 6 This is a top view of the cavity where the solid radon source of the present invention is placed;

[0038] Figure 7 This is a schematic diagram of the peripheral pores of the radon accumulation cavity of the present invention;

[0039] Figure 8 This is a schematic diagram of the radon accumulation cavity of the present invention;

[0040] Figure 9 Schematic diagram of parameters for the diffusion of radon in a double-layer medium according to the present invention;

[0041] Figure 10 It is a placement point map of the activated carbon box of the present invention;

[0042] Figure 11 is the relationship between the radon exhalation rate and the activity of the solid radon source of the present invention;

[0043] Explanation of symbols:

[0044] a-solid radon source placement cavity, b-radon accumulation cavity, c-gypsum board, d-high-density board, e-fastening flange, f-fastening screw, g-positioning flange, h-outer cover, i-support frame, j-universal wheel, k-air pressure balancing device, l-air hole, m-fixing frame. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] The purpose of the present invention is to provide a radon exhalation rate measuring instrument verification device and a radon exhalation rate control method, which improves the stability and uniformity of the radon exhalation rate measuring instrument verification device and improves the accuracy of the radon exhalation rate measuring instrument verification.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] Figure 1 This is a schematic diagram of the structure of a radon exhalation rate measuring instrument calibration device of the present invention, as shown in FIG. Figure 1 As shown, a radon exhalation rate measuring instrument calibration device includes a diffusion type solid radon source, a solid radon source placement cavity, a radon accumulation cavity, a diffusion medium and an air pressure balance device.

[0050] Diffused solid radon source is referred to as solid radon source.

[0051] The radon accumulation cavity is in an inverted cone shape, the circular cone at the bottom of the radon accumulation cavity is connected to the solid radon source placement cavity, the top of the radon accumulation cavity is connected to the diffusion medium, the diffusion medium includes a gypsum board and a high-density board, the gypsum board is located above the radon accumulation cavity, and the high-density board covers the gypsum board, the air pressure balancing device is connected to the radon accumulation cavity, and the air pressure balancing device is used to maintain a dynamic balance of air pressure between the radon accumulation cavity and the ambient atmosphere.

[0052] Solid radon source placed in the cavity Figure 5 and Figure 6 shown.

[0053] The radon exhalation rate on the surface of the diffusion medium is determined according to the diffusion coefficient of radon in the diffusion medium, the thickness of the diffusion medium layer and the activity of the solid radon source placed in the radon cavity.

[0054] The radon exhalation rate is adjusted by changing the activity of the solid radon source in the solid radon source placement cavity and the thickness of the diffusion medium layer.

[0055] A radon exhalation rate measuring instrument calibration device also includes a supporting frame and a fixing frame.

[0056] The fixing frame is used to fix the diffusion medium layer; Figure 3 As shown, the fixing frame includes an upper fastening flange, a lower fastening flange, a fastening screw and a clamping plate. The clamping plate is used to clamp the edge of the diffusion medium layer. The fastening screw is used to pass through the clamping plate. The length of the fastening screw is adjustable. The upper fastening flange and the lower fastening flange are respectively located at both ends of the fastening screw and are used to fasten the clamping plate.

[0057] The support frame is connected to the bottom of the fixing frame, and is used to support the radon accumulation cavity. The support frame and the radon accumulation cavity are both made of stainless steel.

[0058] The bottom of the support frame is provided with universal wheels.

[0059] A radon exhalation rate measuring instrument calibration device further comprises an outer cover, which is cylindrical and sleeved on the outer sides of the support frame and the diffusion medium. The material of the outer cover is stainless steel.

[0060] In addition to stainless steel, the support frame, radon accumulation cavity and outer cover can also be made of other metals that are impermeable to radon.

[0061] The radon accumulation cavity and the solid radon source placement cavity are detachably connected, and the radon accumulation cavity and the solid radon source placement cavity are connected by a flange type, such as Figure 2 and Figure 3 As shown, a silicone sealing gasket is provided between the radon accumulation cavity and the solid radon source placement cavity, and 1 to N fastening screws flange-connect the radon accumulation cavity and the solid radon source placement cavity.

[0062] The radon accumulation cavity is made of radon-impermeable metal material by integral stamping. Figure 8 shown.

[0063] A silicone sealing pad is provided between the high-density board and the gypsum board.

[0064] like Figure 4 As shown, the air pressure balancing device includes a U-shaped connecting pipe and an air pressure balancing bottle. The air pressure balancing bottle is connected to the radon accumulation cavity through the U-shaped connecting pipe. The liquid in the air pressure balancing bottle includes a high-concentration salt water mixture (a salt water mixture exceeding a set salt concentration). The liquid in the air pressure balancing bottle can also be other liquids that are impermeable to radon.

[0065] The side wall of the radon accumulation cavity is provided with a first inlet and a second inlet, and the first inlet and the second inlet are symmetrically distributed on the side wall of the radon accumulation cavity. The first inlet and the second inlet are used for the solid radon source to quickly fill a predetermined amount of radon into the radon accumulation cavity. Figure 7 shown.

[0066] The thickness of the high-density board and the thickness of the gypsum board are adjustable.

[0067] As a specific implementation, the thickness of the high-density board is 30 mm, and the thickness of the gypsum board is 60 mm.

[0068] A cross support frame is provided at the top opening of the radon accumulation cavity.

[0069] The air pressure balancing device of the present invention can maintain dynamic balance between the radon accumulation cavity and the ambient atmospheric pressure, and can minimize the influence of the seepage effect caused by the pressure gradient.

[0070] The diffusion medium is made of a material with moderate radon permeability, thereby slowing down the migration rate of radon in the medium and forming a stable radon exhalation rate on the surface of the medium. The present invention uses a diffusion medium (diffusion component) composed of high-density board and gypsum board.

[0071] The present invention utilizes a top-down combination of high-density board and gypsum board as the diffusion medium, resolving the issue of high-density board's weak radon barrier but excellent uniformity, and the relatively dense gypsum board, which offers some radon barrier but poor uniformity. The integrated diffusion assembly of these two components achieves excellent stability and uniformity.

[0072] The present invention uses high-performance sealant to seal all connections and diffusion medium edges. Combined with the inverted conical design of the radon-accumulating cavity, this device achieves one-dimensional upward diffusion of radon. The radon exhalation rate measurement device is simple and portable, easy to operate, and capable of on-site measurements, meeting the engineering needs of rapid radon exhalation rate measurement.

[0073] The solid radon source with high emissivity coefficient of the present invention is placed in a cavity. A diffusion type solid radon source with high emissivity coefficient and good stability is placed in the cavity. The activity of the solid radon source can be achieved. 3 Bq~10 8 It can be adjusted within the Bq range. Under the conditions of ambient temperature of 10℃~45℃ and relative humidity of 1~100%, its emanation coefficient reaches (96±2)%.

[0074] The present invention utilizes a first inlet and a second inlet provided on the side wall of the radon accumulation cavity, and uses a flow-type radon source to fill the radon accumulation cavity with the radon concentration required for device equilibrium, thereby quickly establishing the equilibrium radon concentration of the radon accumulation cavity, greatly shortening the time for establishing radon concentration equilibrium by relying solely on a diffusion source.

[0075] The present invention provides a radon exhalation rate measuring instrument calibration device, which is composed of a diffusion-type solid radon source with high emission coefficient and good stability, a radon accumulation cavity, a diffusion medium, an air pressure balance device, a support frame, a fixing frame and an outer cover. By changing the activity of the radon source, the thickness of the radon diffusion medium and the rapid establishment of the radon concentration in the radon accumulation cavity, the radon exhalation rate of the device can be regulated, thereby expanding the adjustment range of the radon exhalation rate. The radon exhalation rate of the device can be adjusted within 5mBq / (m 2 ·s)~20000mBq / (m 2 The radon exhalation rate uniformity is less than 5%, and the stability is less than 5%. It is used for performance verification and calibration of radon exhalation rate measuring instruments.

[0076] Example 2

[0077] In the solid radon source placement cavity of a radon exhalation rate measuring instrument calibration device of the present invention, 17000Bq and 100000Bq of diffusion-type solid radon sources are placed respectively. The radon accumulation cavity is in the shape of an inverted cone, and is made of stainless steel by integral punching. The inner and outer surfaces are flat and smooth without grooves. Two radon source quick filling inlets and a pressure balance device connection port are provided. Two mutually perpendicular strip cross support frames are designed on the upper part of the radon accumulation cavity. 30mm high-density board and 60mm gypsum board are selected as the preferred diffusion media. The pressure balance device adopts a U-shaped tube connection method. The pressure balance device is filled with salt water with a concentration of about 90%, and a high humidity environment is formed at the outlet of the pressure balance bottle. The support frame and the outer cover are made of brand-new stainless steel as a whole. The bottom of the support frame is equipped with a universal wheel, and the surface of the outer cover is painted. After testing, the radon exhalation rates of the device surface (diffusion medium surface) are 21.57±1.02mBq / (m 2 ·s) and 197.28±2.32mBq / (m 2 ·s).

[0078] (1) Radon exudation mechanism

[0079] Radon is released from the surface of the medium into the atmosphere, which is called radon precipitation from the surface of the medium. Radon is a monatomic gas at room temperature. It migrates by atomic thermal motion and convection. Radon atoms can move freely through the connecting gaps inside the medium and precipitate from the surface of the medium. The migration of radon in porous media obeys Fick's first diffusion law, that is,

[0080]

[0081] The second-order differential equation for the diffusion and migration of radon through the medium is as follows:

[0082]

[0083] Considering the inherent diffusion coefficient of the material itself, we have formula (3):

[0084]

[0085] Where, J is the radon exhalation rate of the device surface, Bq / (m 2 ·s), D is the diffusion coefficient of radon in the medium, cm 2 / s, is the radon concentration gradient in the medium, in one-dimensional direction, x represents the coordinate of the medium surface with the normal as the axis, and t represents time. Since the diffusion coefficient of radon in the medium is determined by the medium material, the radon exhalation rate is affected by the radon concentration gradient in the medium.

[0086] (2) Measurement of the diffusion coefficient of radon in the medium

[0087] When a diffuse solid radon source is placed in a radon accumulation cavity, the volume of the radon accumulation cavity is V1, and the radon concentration in the radon accumulation cavity is recorded as C1, a radon collection cover is placed on the surface of the medium to continuously test the change in radon concentration, the volume of the radon collection cover is recorded as V2, the radon concentration in the radon collection cover is recorded as C2, the surface area of the precipitation medium is recorded as S, and the thickness of the medium is recorded as H. When the solubility coefficient of radon in the material is regarded as 1, then

[0088]

[0089] When D / H 2 When is large enough, formula (4) can be simplified to:

[0090]

[0091]

[0092] Formula (6) can be used to calculate the radon diffusion coefficient of various media.

[0093] Table 1 below shows the calculated radon diffusion coefficients of gypsum board and high-density board.

[0094] Table 1 Radon diffusion coefficients of gypsum board and high-density board

[0095]

[0096] (3) Radon diffusion in double-layer media

[0097] When there is no pressure gradient in the space environment, the migration of radon in the double-layer medium is pure diffusion migration. Based on the radon diffusion theory, when the radon concentration reaches a stable equilibrium state in space, the differential equation for the diffusion of radon in the double-layer medium is:

[0098]

[0099] The diffusion parameters of radon in a double-layer medium are as follows: Figure 9 shown.

[0100] In formula (7),

[0101] C1: Radon concentration in gypsum board, Bq / m 3 ;

[0102] C2: Radon concentration in high-density board, Bq / m 3 ;

[0103] D1: Radon diffusion coefficient of gypsum board, m 2 / s;

[0104] D2: Radon diffusion coefficient of high-density board, m 2 / s;

[0105] λ: radon decay constant, 2.1×10 -6 s -1 ;

[0106] x: coordinate of the axis with the normal line inside the medium surface, m;

[0107] Solving equation (7), we get:

[0108]

[0109] In formula (8), A1, B1, A2 and B2 are all intermediate parameters, h1 represents the thickness of the gypsum board, and h2 represents the thickness of the high-density board.

[0110]

[0111]

[0112]

[0113]

[0114] in, It represents the radon concentration on the surface of the medium when the medium thickness is h1. C0 represents the radon concentration on the surface of the medium when the medium thickness approaches 0. The C0 value is an ideal case and is not used for calculation. It indicates the radon concentration on the medium surface when the medium thickness is h1+h2.

[0115] When x=0, C1=A1-B1=C0;

[0116] When x=h1+h2,

[0117] When x=h1,

[0118] The radon exhalation rate of the lower surface of the optimal diffusion medium can be obtained as follows:

[0119]

[0120] Right now

[0121]

[0122] Similarly, the radon exhalation rate on the upper surface of the optimal diffusion medium of the device can be obtained as follows:

[0123]

[0124] The ratio of the radon exhalation rate on the lower surface of the diffusion component to the radon exhalation rate on the upper surface is preferably:

[0125]

[0126] That is, J1=kJ2 (17)

[0127] in,

[0128]

[0129] D1 = 2.94 × 10 -9 m 2 / s, D2=1.42×10 -8 m 2 / s, h1=0.06m, h2=0.03m, λ=2.1×10 - 6 s -1 Substituting into formula (18), we get

[0130]

[0131] when When it is small enough, k≈1, that is, J1≈J2.

[0132] k is an intermediate parameter.

[0133] (4) Rapidly establish equilibrium radon concentration in radon accumulation cavity

[0134] All radon in the radon accumulation cavity is generated by solid radon sources, and it takes too long to reach equilibrium. In order to quickly establish the equilibrium state of radon concentration in the radon accumulation cavity, a method is adopted in which radon is filled into the radon accumulation cavity from a gas-flow solid radon source in the initial state. The change of radon concentration in the radon accumulation cavity is shown in formula (20):

[0135]

[0136] When the radon concentration in the radon accumulation cavity reaches equilibrium, let the left side of equation (20) be 0, and the radon concentration in the radon accumulation cavity is obtained, that is, the concentration of radon filled into the radon accumulation cavity in the initial state is C e.

[0137]

[0138] Since J1≈J2, Equation (14) is optimized as

[0139]

[0140] Formula (22) is transformed to

[0141]

[0142] It can be seen from formula (23) that when any two parameters among the activity of the placed solid radon source, the radon concentration quickly filled into the radon-accumulating cavity, and the radon exhalation rate on the device surface are known, the third unknown quantity can be calculated, and the functional relationship of any two parameters among the three parameters can be fitted.

[0143] (5) Activated carbon-γ spectrum method for measuring radon exhalation rate

[0144] Place the activated carbon box upside down on the surface of the precipitation medium and seal it with plasticine. Note the time to start the radon accumulation process. The accumulation time is set as t1. After the accumulation is completed, remove the activated carbon box and seal it. After the waiting time t2, use a high-purity germanium spectrometer to measure the activated carbon box. After the measurement is completed, record the net count N and background count rate B, and substitute them into the following formula to calculate

[0145]

[0146] J: Radon exhalation rate, Bq / (m 2 s);

[0147] N: Net count rate of the γ characteristic peak at 609 keV, cps;

[0148] B: background count rate, cps;

[0149] t1: accumulation time (h);

[0150] t2: the time interval from the end of accumulation to the start of measurement, i.e., the waiting time (h);

[0151] λ: radon decay constant, 7.55×10 -3 h -1 ;

[0152] S: cross-sectional area of activated carbon box, 0.006359m 2 ;

[0153] K: Conversion factor, 0.007cps / Bq.

[0154] The present invention measures the radon exhalation rate on the surface of a reference device through an activated carbon adsorption method. The activated carbon adsorption method utilizes the adsorption of precipitated radon by activated carbon. The radon exhalation rate is calculated by measuring the gamma spectrum generated by the decay of radon adsorbed in the activated carbon. The stability and uniformity of the measurement of the radon exhalation rate measuring instrument calibration device can be verified at the same time.

[0155] Example 3

[0156] A method for measuring radon exhalation rate by a radon exhalation rate measuring instrument calibration device of the present invention comprises:

[0157] Step 101: Place the activated carbon box upside down on the diffusion medium, and seal the activated carbon box and the diffusion medium.

[0158] Step 102: After a first set time has passed, the activated carbon box is removed and sealed.

[0159] Step 103: After the second set time, the activated carbon box is measured using a high-purity germanium spectrometer to obtain the net count rate and background count rate of the γ characteristic peak at 609 keV.

[0160] Step 104: Determine a radon exhalation rate according to the first set time, the second set time, the net count rate, and the background count rate.

[0161] Step 104 specifically includes calculating the radon exhalation rate according to formula (24).

[0162] The present invention adopts the activated carbon adsorption method to measure the radon exhalation rate of the radon exhalation rate measuring instrument calibration device. The placement point of the activated carbon box on the diffusion medium is as follows: Figure 10 The radon exhalation rate measurement results are shown in Table 2.

[0163] Table 2100000Bq diffusion source stability and uniformity measurement

[0164]

[0165]

[0166] As shown in Table 2, using a diffuse solid radon source with an activity of 100,000 Bq, the stability of the radon exhalation rate is less than 5%, and the uniformity is less than 5%. The theoretical and measured values agree well, demonstrating the excellent performance of the radon exhalation rate measurement instrument and the verification device.

[0167] Example 4

[0168] A radon exhalation rate control method of the present invention uses the radon exhalation rate measuring instrument calibration device disclosed in Example 1, and the radon exhalation rate control method includes:

[0169] By changing the fixed radon source activity and the thickness of the diffusion medium layer in the radon accumulation cavity of the radon exhalation rate measuring instrument verification device, the radon exhalation rate of the radon exhalation rate measuring instrument verification device is adjusted, and different radon exhalation rate measuring instruments being verified are calibrated by adjusting the radon exhalation rate of the radon exhalation rate measuring instrument verification device.

[0170] The adjustment process of radon exhalation rate specifically includes:

[0171] Step 1: Determine the thickness of the gypsum board and high-density board in the diffusion medium.

[0172] Step 2: Determine the relationship between diffuse solid radon sources of different activities and the radon exhalation rate and radon concentration in the radon-accumulating cavity.

[0173] The relationship between diffuse solid radon sources of different activities and radon exhalation rate and radon concentration in radon-accumulated cavities includes the relationship between radon exhalation rate and activity of diffuse solid radon sources, as well as the relationship between activity of diffuse solid radon sources, radon exhalation rate and radon concentration in radon-accumulated cavities.

[0174] Using the radon exhalation rate measuring instrument calibration device, by changing the activity of the solid radon source, we can form different levels of uniform and stable radon exhalation rates on the surface of the precipitation medium. By placing them in the calibration device and filling the radon accumulation cavity with the source, the radon exhalation can be quickly stabilized. The radon exhalation rate at the middle point of the precipitation medium is measured using the activated carbon-gamma spectrum method, thereby obtaining the relationship between the radon exhalation rate and the activity of the diffuse solid radon source. The results are as follows: Figure 11 shown.

[0175] Depend on Figure 11 It can be seen that through the linear fitting of the data, the linear fitting equation between the radon exhalation rate J in the calibration device and the activity A0 of the placed diffuse solid radon source is obtained.

[0176] J=0.002A0-5.854.

[0177] R 2 Indicates the degree of data dispersion, measures the overall fit of the regression equation, and expresses the overall relationship between the dependent variable and all independent variables. 2 It is equal to the ratio of the regression sum of squares to the total sum of squares, that is, the percentage of the dependent variable variability that the regression equation can explain. 2 The closer the value is to ±1, the better the equation fitting effect is. 2 = 0.99, close to 1, indicating a reasonable linear fit. If the activity of the radon source placed in the calibration device is known, the radon exhalation rate of the reference device can be quickly determined using the fitting equation. This radon exhalation rate measurement device can be used to provide the required solid radon source activity reference value for achieving higher radon exhalation rates, significantly improving experimental efficiency.

[0178] According to formula (23), when the activity of the placed diffuse solid radon source and the radon exhalation rate are known, the radon concentration in the cumulative radon cavity can be calculated.

[0179] Step 3: Based on the relationship between diffuse solid radon sources of different activities and the radon exhalation rate and the radon concentration in the radon-accumulated cavity, select a diffuse solid radon source according to the radon exhalation rate to be adjusted.

[0180] Step 4: Determine the stable radon concentration of the radon-accumulating cavity based on the selected diffuse solid radon source.

[0181] Step 5: Place the selected diffuse solid radon source in the solid radon source placement cavity, use the gas flow solid radon source to fill a predetermined amount of radon into the radon accumulation cavity, and wait for the radon concentration in the radon accumulation cavity to reach equilibrium.

[0182] When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium does not change, repeat steps 3 to 5 to adjust the radon exhalation rate.

[0183] When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium changes, repeat steps 1 to 5 to adjust the radon exhalation rate.

[0184] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. The methods disclosed in the embodiments are described briefly because they correspond to the devices disclosed in the embodiments. For relevant details, refer to the method section.

[0185] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A radon exhalation rate measuring instrument calibration device, characterized in that: It includes a diffuse solid radon source, a solid radon source placement cavity, a radon accumulation cavity, a diffusion medium layer and an air pressure balancing device; The radon accumulation cavity is in an inverted cone shape, the circular cone at the bottom of the radon accumulation cavity is connected to the solid radon source placement cavity, the top of the radon accumulation cavity is connected to the diffusion medium layer, the diffusion medium layer includes a gypsum board and a high-density board, the gypsum board is located above the radon accumulation cavity, and the high-density board covers the gypsum board, the air pressure balancing device is connected to the radon accumulation cavity, and the air pressure balancing device is used to maintain a dynamic balance between the air pressure of the radon accumulation cavity and the ambient atmosphere; determining a radon exhalation rate on a surface of the diffusion medium layer according to a diffusion coefficient of radon in the diffusion medium layer, a thickness of the diffusion medium layer, and an activity of a solid radon source in the solid radon source placement cavity; Adjusting the radon exhalation rate by changing the activity of the solid radon source in the solid radon source placement cavity and the thickness of the diffusion medium layer; The air pressure balance device includes a U-shaped connecting pipe and an air pressure balance bottle, wherein the air pressure balance bottle is connected to the radon accumulation cavity through the U-shaped connecting pipe, and the liquid in the air pressure balance bottle includes a salt water mixture exceeding a set salt concentration; A first inlet and a second inlet are provided on the side wall of the radon accumulation cavity. The first inlet and the second inlet are symmetrically distributed on the side wall of the radon accumulation cavity. The first inlet and the second inlet are used for rapidly charging a predetermined amount of radon into the radon accumulation cavity from a gas-flowing solid radon source.

2. The radon exhalation rate measuring instrument calibration device according to claim 1, characterized in that: The support frame and the fixing frame are further included. The fixing frame is used to fix the diffusion medium layer. The fixing frame includes an upper fastening flange, a lower fastening flange, a fastening screw and a clamping plate. The clamping plate is used to clamp the edge of the diffusion medium layer. The fastening screw is used to pass through the clamping plate. The length of the fastening screw is adjustable. The upper fastening flange and the lower fastening flange are respectively located at both ends of the fastening screw and are used to fasten the clamping plate. The support frame is connected to the bottom of the fixing frame, and the support frame is used to support the radon accumulation cavity. The support frame and the radon accumulation cavity are both made of stainless steel; The bottom of the support frame is provided with universal wheels.

3. The radon exhalation rate measuring instrument calibration device according to claim 2, characterized in that: The device further comprises an outer cover which is cylindrical and is sleeved on the outer sides of the support frame and the diffusion medium layer. The material of the outer cover is stainless steel.

4. The radon exhalation rate measuring instrument calibration device according to claim 2, characterized in that: The radon accumulation cavity and the solid radon source placement cavity are connected by a flange type, and a silicone sealing gasket is provided between the radon accumulation cavity and the solid radon source placement cavity.

5. The radon exhalation rate measuring instrument calibration device according to claim 1, characterized in that: A silicone sealing pad is provided between the high-density board and the gypsum board.

6. The radon exhalation rate measuring instrument calibration device according to claim 1, characterized in that: A cross support frame is provided at the top opening of the radon accumulation cavity.

7. A method for controlling radon exhalation rate, characterized in that: The radon exhalation rate control method is applied to the radon exhalation rate measuring instrument calibration device according to any one of claims 1 to 6, and the radon exhalation rate control method includes: Adjusting the radon exhalation rate of the radon exhalation rate measuring instrument verification device by changing the activity of a fixed radon source and the thickness of a diffusion medium layer in a radon accumulation cavity of the radon exhalation rate measuring instrument verification device, and calibrating different radon exhalation rate measuring instruments to be verified by adjusting the radon exhalation rate of the radon exhalation rate measuring instrument verification device; The adjustment process of the radon exhalation rate to be adjusted specifically includes: Step 1: Determine the thickness of the gypsum board and high-density board in the diffusion medium layer; Step 2: Determine the relationship between diffuse solid radon sources of different activities and the radon exhalation rate and radon concentration in the radon-accumulating cavity; Step 3: Based on the relationship between the diffusible solid radon sources with different activities and the radon exhalation rate and the radon concentration in the radon-accumulated cavity, a diffusible solid radon source is selected according to the radon exhalation rate to be adjusted; Step 4: Determine the stable radon concentration of the radon-accumulating cavity based on the selected diffuse solid radon source; Step 5: Place the selected diffusion-type solid radon source in the solid radon source placement cavity, use the gas-flow solid radon source to fill a predetermined amount of radon into the radon accumulation cavity, and wait for the radon concentration in the radon accumulation cavity to reach an equilibrium state; When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium layer does not change, repeat steps 3 to 5 to adjust the radon exhalation rate; When the radon exhalation rate to be adjusted changes, if the thickness of the gypsum board and the high-density board in the diffusion medium layer changes, repeat steps 1 to 5 to adjust the radon exhalation rate.

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