CN115236719A - A measuring device and method for surface radon precipitation rate based on electret radon measurement - Google Patents

Abstract

The invention discloses a device and a method for measuring the exhalation rate of radon on the surface based on electret radon measurement, which relate to the technical field of radiation environment monitoring, and the device comprises: the device comprises an electret material, an ionization cavity, a filter membrane and a buffer accumulation cavity; the electret material is arranged on the ionization chamber and is used for collecting negative ions generated by alpha ions ionizing air in the decay process of radon in the ionization chamber and generating electret voltage drop according to the quantity of the collected negative ions; the upper edge of the buffer accumulation cavity is hermetically connected with the lower edge of the ionization cavity; the lower edge of the buffer accumulation cavity is contacted with the surface of the material medium to be detected; the filtering membrane is arranged between the ionization chamber and the buffer accumulation chamber and is used for filtering radon daughters; radon separated out from the surface of the material medium to be detected is fused with gas in the buffer accumulation cavity, enters the ionization cavity through the filter membrane, and decays and ionizes in the ionization cavity. The method can improve the representativeness and comparability of the radon exhalation rate data.

Description

A measuring device and method for surface radon precipitation rate based on electret radon measurement

technical field

The invention relates to the technical field of radiation environment monitoring, in particular to a measuring device and method for surface radon precipitation rate based on electret radon measurement.

Background technique

The measurement of radon precipitation rate is an identification method to test the radioactive content characteristics of new materials and building materials and to judge whether they meet the national standards.

At present, the measurement methods of radon release rate on the surface of materials and media include local static method, through-air flow method and adsorption method. The basis for the measurement of radon extraction rate is the measurement of radon concentration. Usually, a hood with a fixed volume and a fixed bottom opening area is sealed on the surface of the material medium, and the radon precipitated on the surface of the material is collected by radon in the gas collecting hood, and the change of radon concentration is detected by radon detection equipment. Among them, the local static method includes the accumulation method and the equal time measurement method. The high-voltage electrostatic collection method uses the linear growth stage of radon in the initial stage of accumulation in the gas collecting hood, and calculates the radon precipitation rate through the relationship between the measurement time and the radon concentration. Due to the influence of factors such as radon radioactive decay, air leakage and reverse osmosis, the calculation of radon precipitation rate can be divided into slope method and effective decay constant method. The effective decay constant method is to equate factors such as radon radioactive decay, gas leakage and reverse osmosis as effective decay constants.

The penetrating air flow method is to obtain the surface radon release rate by measuring the stable radon concentration established in the penetrating air flow. Because this method continuously removes the radon in the accumulation tank, thus avoiding the influence of back diffusion and leakage on the determination of radon precipitation rate caused by the increase of radon concentration in the accumulation method. The radon concentration in the gas stream is determined by using the scintillation chamber flow method or other instantaneous radon measuring equipment, and the surface radon precipitation rate is calculated from the relationship between the steady radon concentration in the gas stream and the gas flow rate.

The radon precipitation rate measured by the activated carbon box adsorption method depends on the strong adsorption characteristics of activated carbon on radon. The activated carbon box is generally cylindrical, and the box contains about 50-225g of high-quality coconut shell activated carbon of 18-28 mesh. The γ-ray peak (609keV) or peak group (294keV, 352keV, 609keV) intensity of the radon progeny characteristic of the activated carbon box is measured by a gamma spectrometer. The gamma characteristic peak group of the radon progeny is generally composed of four characteristic peaks. In order to reduce the background , when measuring radon, only the total area of the three characteristic peaks with higher energy (270 ~ 720keV) is generally taken. The radon release rate can be calculated from the peak area, accumulation time and the sampling area of the carbon box.

The above methods all need to use a radon collecting cover to collect the radon precipitated on the surface of the medium, and detect the radon concentration at different time periods through a detector. In the monitoring process of large-scale radon release rate, due to the long monitoring process of conventional radon release rate, the data acquisition efficiency is low, the monitoring time span of obtaining radon release rate before and after the same batch is large, and due to the change of natural environment in the middle, the representativeness and comparability of the same batch of data are poor. . For example, in the monitoring of radon release rate at 100 points in a site, 5 sets of equipment (usually only 2-4 sets of equipment in a unit) can be used for 10 hours a day to obtain 5-6 sets of data, which takes about 4 days to complete. Changes in the monitoring data in the morning of the first day and the weather, temperature, wind speed, humidity and other conditions in the afternoon of the third day will lead to huge changes in the radon release rate. The same batch of data is not comparable and thus loses its representativeness. Therefore, the acquisition efficiency of radon precipitation rate results is low, the field operation is complex, the monitoring environment is highly dependent, and the calculation results are not unique, which makes the data representativeness and comparability poor.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a measuring device and method for surface radon precipitation rate based on electret radon measurement, which can improve the representativeness and comparability of radon precipitation rate data.

For achieving the above object, the present invention provides the following scheme:

A measuring device for surface radon precipitation rate based on electret radon measurement, the measuring device comprises: electret material, ionization chamber, filter membrane and buffer accumulation chamber;

The electret material is arranged on the ionization chamber and is used to collect negatively charged ions generated by alpha ions ionizing air in the radon decay process in the ionization chamber, and to generate electrets according to the number of collected negatively charged ions Voltage drop;

The upper edge of the buffer accumulation cavity is sealedly connected with the lower edge of the ionization cavity; the lower edge of the buffer accumulation cavity is in contact with the medium surface of the material to be tested;

the filter membrane, arranged between the ionization chamber and the buffer accumulation chamber, is used for filtering radon progeny;

The radon precipitated on the surface of the material to be tested is fused with the gas in the buffer accumulation chamber and then enters the ionization chamber through the filter membrane, and decays and ionizes in the ionization chamber.

Optionally, the buffer accumulation cavity is a cylindrical cavity.

Optionally, the diameter of the cross section of the buffer accumulation cavity is 155.4 mm.

Optionally, the shape of the cross section of the ionization chamber is circular.

Optionally, the inner diameter of the upper edge of the buffer accumulation cavity is consistent with the inner diameter of the lower edge of the ionization cavity.

Optionally, the height of the buffer accumulation cavity ranges from 32mm to 350mm.

Optionally, the buffer accumulation chamber is fixed on the medium surface of the material to be tested by a sealing material; the sealing material is a radon isolation sealing material.

Optionally, the measuring device further includes a base plate;

When the measuring device is used to measure the background, the bottom plate is arranged between the buffer accumulation chamber and the surface of the material to be measured, and is used to prevent the radon precipitated from the surface of the medium of the material to be measured from entering the Buffer accumulation chamber.

A method for measuring the surface radon precipitation rate based on electret radon measurement, applied to the above-mentioned measuring device for the surface radon precipitation rate based on electret radon measurement, the measurement method comprising:

When the inside of the buffer accumulation chamber is communicated with the medium surface of the material to be measured, a potentiometer is used to measure the first initial voltage and the first final voltage of the electret at the measurement point;

When the inside of the buffer accumulation chamber is not in communication with the medium surface of the material to be measured, a potentiometer is used to measure the second initial voltage and the second final voltage of the electret at the measurement point;

obtaining an apparent radon concentration according to the first initial voltage, the first final voltage, the second initial voltage and the second final voltage;

From the relationship between the apparent radon concentration and the electret-based radon precipitation rate, the electret-based radon precipitation rate was calculated.

Optionally, the relationship between the apparent radon concentration and the electret-based radon precipitation rate is:

Among them, J is the radon precipitation rate of the measured dielectric material, _CR is the apparent radon concentration, λ _e is the effective decay constant, V is the volume of the buffer accumulation cavity and the ionization cavity, t is the measurement time, and A is the effective measurement process. Measure the area.

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

The measuring device for surface radon precipitation rate based on electret radon measurement provided by the present invention includes: electret material, ionization cavity, filter membrane and buffer accumulation cavity; electret material is arranged on the ionization cavity and is used for collecting The radon decay process in the ionization chamber α ions ionize the negatively charged ions generated by the air, and generate an electret voltage drop according to the number of collected negatively charged ions; the upper edge of the buffer accumulation chamber is sealed with the lower edge of the ionization chamber; the buffer accumulation chamber The lower edge is in contact with the medium surface of the material to be tested; the filter membrane is arranged between the ionization chamber and the buffer accumulation chamber to filter radon progeny; the radon precipitated on the surface of the material to be tested is fused with the gas in the buffer accumulation chamber and filtered The membrane enters the ionization chamber, where it decays and ionizes. In the present invention, the buffer accumulation chamber is sealed with the ionization chamber, and a filter membrane is arranged between the buffer accumulation chamber and the ionization chamber to isolate the radon daughter, so that the radon precipitated on the surface of the material to be tested is fused with the gas in the buffer accumulation chamber. Enter the ionization chamber through the filter membrane, and by setting the buffer accumulation chamber, the reverse osmosis and reverse diffusion of radon precipitated on the surface of the material to be tested can be reduced, the radon on the surface of the medium of the tested material can be accurately collected, and the representativeness of the radon precipitation rate data can be improved. comparability.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative labor.

Fig. 1 is the structural representation of the measuring device of the surface radon precipitation rate based on electret radon measurement provided by the present invention;

Figure 2 is a schematic structural diagram of an electret radon detector;

Fig. 3 is the structural representation of the measuring device of the surface radon precipitation rate based on electret radon measurement obtained by transforming the electret radon detector;

4 is a flow chart of a method for measuring the surface radon precipitation rate based on electret radon measurement provided by the invention.

Symbol Description:

1- electret material, 2- ionization chamber, 3- filter membrane, 4- buffer accumulation chamber, 5- air inlet with filter membrane, 6- bottom plate, 7- closed rear air inlet.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a measuring device and method for surface radon precipitation rate based on electret radon measurement, which can improve the representativeness and comparability of radon precipitation rate data.

The invention is based on the electret radon measurement technology, and proposes a measuring device and method for the surface radon precipitation rate based on the electret radon measurement, which meets the conventional radon precipitation rate measurement requirements, and is especially suitable for the radon precipitation rate of artificial materials. Measurement. The method has the advantages of simple on-site operation, low cost, greatly improved data acquisition efficiency, and simple calculation process, which overcomes the problem of non-unique data results in the cumulative radon extraction rate measurement. At the same time, because the method can carry out large-scale data collection at the same time, the representativeness and comparability of radon release rate data are improved, and it can be widely used in radiation environmental investigations.

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1, the present invention provides a measuring device for surface radon precipitation rate based on electret radon measurement, the measuring device includes: electret material 1, ionization chamber 2, filter membrane 3 and buffer accumulation chamber 4.

The electret material 1 is arranged on the ionization chamber 2 and is used to collect the negatively charged ions generated by the alpha ion ionization of the air in the radon decay process in the ionization chamber 2, and according to the number of the collected negatively charged ions An electret voltage drop occurs.

The upper edge of the buffer accumulation chamber 4 is sealedly connected with the lower edge of the ionization chamber 2; the lower edge of the buffer accumulation chamber 4 is in contact with the surface of the material to be tested; specifically, the buffer accumulation chamber 4 is cylindrical cavity; the bottom of the buffer accumulation cavity is open. The diameter of the cross section of the buffer accumulation cavity 4 is 155.4 mm. The height of the buffer accumulation cavity 4 ranges from 32mm to 350mm.

The filter membrane 3 is arranged between the ionization chamber 2 and the buffer accumulation chamber 4 for filtering radon progeny.

The radon precipitated on the surface of the material to be tested is fused with the gas in the buffer accumulation chamber 4 and then enters the ionization chamber 2 through the filter membrane 3 , and decays and ionizes in the ionization chamber 2 .

As a specific embodiment, the shape of the cross section of the ionization chamber 2 is circular. The inner diameter of the upper edge of the buffer accumulation chamber 4 is consistent with the inner diameter of the lower edge of the ionization chamber 2 .

In practical applications, as shown in Figures 2 and 3, based on the electret radon measuring device, the bottom plate 6 of the electret radon measuring device is removed, and the filter membrane air inlet around the ionization chamber 2 that communicates with the environment is sealed. Hole 5, form a closed air intake hole 7, add a buffer gas collecting cover (buffer accumulation cavity 4), adjust the air intake mode, and the buffer accumulation cavity 4 is a cylindrical cavity with the same diameter as the ionization chamber 2, and the lower edge is flat to facilitate the measurement The surface of the medium is attached and sealed, and the upper edge is connected and sealed with the ionization chamber 2 . The buffer accumulation chamber 4 is in air communication with the ionization chamber 2, and a filter membrane 3 capable of filtering radon progeny is arranged, preferably a carbon-coated high-density polyethylene synthetic paper filter membrane. More specifically, the measuring device based on the surface radon precipitation rate measured by the electret radon provided by the present invention seals the four filter-membrane air intake holes 5 where the original electret radon concentration measuring device is located in the cavity to form a closed rear air intake hole. 7. Open the bottom plate 6 of the ionization chamber 2, replace it with a carbon-coated high-density polyethylene synthetic paper filter membrane, and install a buffer accumulation chamber 4 with the same diameter as the H chamber at the lower part. The lower edge of the buffer accumulation cavity 4 is in contact with the surface of the material to be measured and sealed to carry out the measurement. The buffer accumulation cavity 4 includes a series of geometric structures, the diameter of the cavity section is 155.4mm, the minimum height is 32mm, and the maximum value is 350mm. The diameter of the inlet of the ionization chamber 2 in contact with the electret material 1 , that is, the opening at the top of the ionization chamber 2 is 99 mm. The sealing material used in the device should be a radon isolation sealing material, and radium-free clay can be used. Specifically, the buffer accumulation chamber 4 is fixed on the medium surface of the material to be tested by a sealing material; the sealing material is a radon isolation sealing material. The sealing material can be made of radium-free clay.

As a specific embodiment, the measuring device further includes a bottom plate 6 . When the measuring device is used to measure the background, the bottom plate 6 is arranged between the buffer accumulation chamber 4 and the surface of the medium of the material to be measured, to prevent the radon precipitated from the surface of the medium of the material to be measured from entering The buffer accumulation chamber 4 . Specifically, when an electret radon measuring device is improved to obtain a surface radon precipitation rate measuring device based on electret radon measurement, the bottom plate 6 is the bottom plate 6 of the electret radon measuring device.

In practical applications, the height of the buffer accumulation cavity 4 should be selected according to the expected radon release rate range of the measured medium. The purpose is to improve the accuracy of radon extraction rate measurement and reduce the waste of electret voltage. In the case where a lower radon precipitation rate is expected to be measured, a lower height buffer accumulation chamber 4 (corresponding to a smaller volume of the buffer accumulation chamber 4) is selected. Under the circumstance that a higher radon precipitation rate is expected to be measured, a higher height buffer accumulation chamber 4 (corresponding to a larger volume of the buffer accumulation chamber 4) is selected. In the case that the radon precipitation rate of the sample is completely unclear, the buffer accumulation chamber 4 with a height of 150 mm is used as the standard of this method to measure the buffer accumulation chamber 4.

The rationality judgment basis for the selection of the buffer accumulation chamber 4 . On the basis of correct operation, the reduction of the electret voltage is used as the basis for judgment. After a single measurement, if the electret voltage drops below 200V, the electret voltage drops below 10V, or the drop exceeds 300V, it can be considered that the size of the buffer accumulation cavity 4 is not suitable for the measurement selection, and the data of this measurement is invalid. Before a large-scale measurement near the point, it is necessary to reselect the buffer accumulation cavity 4 of different heights.

The measurement principle of the electret radon detector is as follows:

It consists of three parts (the voltage reading meter is not shown), the electret, the ionization chamber 2 and the voltage reading device. According to different ionization chambers, short-term accumulated radon and long-term environmental accumulated radon monitoring can be carried out. The measurement system has low requirements on the environment, and the measurement can be carried out in the environment of humidity RH% < 100% and temperature T < 50 °C. The electret radon measurement is a closed system formed by the combination of the electret material 1 and the ionization chamber 2. The ionization chamber 2 is also called the H chamber. The radon-containing air passes through the carbon-coated high-density polyethylene synthetic paper filter membrane holes on the wall of the ionization chamber 2. Diffusion into the ionization chamber where the radon progeny ²¹⁸ Po etc. are filtered. Alpha particles from the decay of radon and radon progeny ionize the air in the ionization chamber. Since the electret has a positive voltage of 700-780V, an electric field is formed in the ionization chamber 2, the secondary positive ions generated by the ionization of α particles are exported by the cavity, and the negative ions are collected by the electret under the action of the electret electric field. As a result, the surface voltage of the electret is reduced. Use a voltage reader to read the change of the electret voltage before and after. The air radon concentration can be calculated through the proportional relationship between the electret voltage change value and the radon concentration within a certain period of time. In addition, the half-life of ²²⁰ Rn is only 55.6s, and it cannot diffuse into the ionization chamber 2 in time, so the influence of thorium on the measurement results can also be excluded.

The calculation method of radon concentration measured by electret is shown in formula (S1) or (S2) and (S3):

or

Among them, I is the voltage at the beginning of the measurement of the electret, I _b is the voltage at the beginning of the measurement of the electret, and the unit is V; P is the voltage at the end of the measurement of the electret, and P _b is the end of the measurement at the end of the electret. Voltage, the unit is V; CF is the calculation factor for the combination of different electret ionization chambers, and its physical meaning is the voltage consumed per unit time when the ionization chamber is placed in a concentration environment of 1Bq/ ^m3 , the unit is (V· ^m3 )/(Bq day). D is the accumulation time, the unit is h. In the formula (S3), A and B are the inherent characteristic parameters of the electret material 1, which vary according to the combination of the electret and the ionization cavity.

As shown in FIG. 4 , a method for measuring the surface radon precipitation rate based on electret radon measurement provided by the present invention is applied to the described measuring device for the surface radon precipitation rate based on electret radon measurement. Methods include:

Step S1: when the inside of the buffer accumulation chamber is in communication with the medium surface of the material to be measured, a potentiometer is used to measure the first initial voltage and the first final voltage of the electret at the measurement point.

Step S2: when the inside of the buffer accumulation chamber is not in communication with the medium surface of the material to be measured, use a potentiometer to measure the second initial voltage and the second final voltage of the electret at the measurement point.

Step S3: Obtain the apparent radon concentration according to the first initial voltage, the first final voltage, the second initial voltage and the second final voltage.

Step S4: Calculate the radon precipitation rate based on the electret according to the relationship between the apparent radon concentration and the radon precipitation rate based on the electret. The relationship between the apparent radon concentration and the electret-based radon precipitation rate is:

Among them, J is the radon precipitation rate of the measured dielectric material, _CR is the apparent radon concentration, λ _e is the effective decay constant, V is the volume of the buffer accumulation cavity and the ionization cavity, t is the measurement time, and A is the effective measurement process. Measure the area.

In practical applications, the electret radon extraction rate measuring device includes a preparation process, a measurement process and a radon extraction rate calculation process in the radon extraction rate measurement process.

Among them, the preparation process includes:

At least two sets of parallel devices should be prepared for the measurement of radon release rate at a point, one as the background measurement device and the other as the data point measurement device. For multi-point measurement requirements, if the environmental differences of multiple measurement points are small, the same background measurement device can be shared under the condition that the air penetration γ dose rate does not change much. In addition, compressed nitrogen should be prepared on site for purging the air in the buffer accumulation chamber.

A measurement device (including a background measurement device) based on the surface radon precipitation rate measured by electret radon is arranged at the measurement point. The background measuring device should seal the contact surface between the buffer accumulation chamber and the medium surface of the material to be measured, so that radon generated by the medium surface of the material to be measured cannot enter the buffer accumulation chamber. Specifically, between the buffer accumulation chamber and the medium surface of the material to be measured Insert the base plate between the contact surfaces. The data point measurement device should seal the contact edge between the lower edge of the buffer accumulation chamber and the medium surface of the material to be measured, so that the air outside the measurement device based on the surface radon extraction rate measured by electret radon cannot enter the buffer accumulation chamber, but only allows The substances released from the surface of the medium to be measured covered by the buffer accumulation chamber enter the buffer accumulation chamber. The operation is repeated until all the measurement points and the corresponding background measurement points are arranged with the measuring device of the surface radon precipitation rate based on the electret radon measurement provided by the present invention.

Environmental conditions should be recorded, including basic information such as longitude and latitude, temperature, air pressure, wind direction, and wind speed for backup. Recording of environmental conditions facilitates finding the cause when the data is incorrect or the extraction rate cannot be measured.

The measurement process includes:

(1) Use compressed nitrogen to purge the buffer accumulation chamber and ionization chamber of the measurement device (including the background measurement device) based on the surface radon precipitation rate measured by electret radon.

(2) Take the electret material with qualified voltage (the electret material voltage should be greater than 200V) to measure the electret voltage, and install the electret material on the ionization chamber.

(3) Record the electret voltage and the placement time (the operation of the background measuring device is the same). Repeat the operation until the electret voltage at all radon extraction rate measurement points is measured, install the electret material on the ionization chamber, and record all of them.

(4) Wait for the cumulative measurement time of radon until the measurement ends. More than 4 hours should be used, and the cumulative measurement time should be within 240 hours. After the measurement, remove the electrets one by one, measure the end voltage of the electret with a potentiometer and record the voltage and time.

At this point, the measurement process ends.

It should be noted that after the end of the measurement process, due to the improper selection of the geometric size of the accumulation cavity, or the accumulation time is too long, the end voltage of the electret is lower than 200V, and the measurement point should be re-measured to improve the data accuracy.

The calculation process of radon extraction rate includes:

The local static method is used to calculate the radon precipitation rate. Since the radon buffer accumulation chamber and the ionization chamber are purged during the measurement process, C ₀ is approximately considered to be 0 at the time of t=0. For this reason:

In the formula, J is the radon precipitation rate of the measured medium material, the unit is Bq/m ² s ^-1 ; A is the effective measurement area of the measurement process, the unit is m ² ; t is the measurement time length, the unit is s; C(t ) is the radon concentration Bq/m ³ at time t; V is the effective volume of the radon accumulation cavity, including the volume of the buffer accumulation cavity and the ionization cavity, in m ³ ; λ _e is the effective decay constant.

λ _e =λ+O+L (2)

Among them, the effective decay constant λ _e is affected by the decay constant λ and O and L. λ is the decay constant of radon in s ^-1 ; O and L refer to the equivalent decay parameters of the radon concentration reduction due to back-diffusion, leakage, etc.

In actual operation, λ _e is related to the operating seal and the geometry of the buffer accumulation cavity. Specifically, due to the different geometric dimensions of the buffer accumulation cavity, the effective decay constant caused by reverse osmosis needs to be determined in advance through repeated experiments. The effective decay constant is highly dependent on the geometry of the buffered radon accumulation cavity, and for any buffered accumulation cavity conforming to the geometry described in the method, the effective decay constant λe can be determined experimentally in advance. It is necessary to repeat the above-mentioned preparation and measurement stages for more than 2 groups at the same point, and each group of data should include more than 6 radon concentration measurement data at equal time intervals.

Specifically, the calculation formula of λ _e is shown in formula (3):

Among them, x _i is n radon concentration data with equal time period T, y _j is n radon concentration data with equal time period T, n should be greater than 6, where x _i is not equal to y _j , b has no physical meaning, Refers to formula (4).

The radon concentration data measured by the measuring device for the surface radon precipitation rate based on the electret radon measurement provided by the present invention is different from the radon sample concentration at time t, but the accumulated radon decay at time t and the radon decay of linearly increasing concentration at time t. The apparent radon concentration is comprehensively expressed. For this reason, the apparent radon concentration C _R (t) measured at time t by the measuring device based on the surface radon precipitation rate measured by electret radon is obtained from formula (1) and formula (4). The relationship with the radon precipitation rate is shown in formula (5):

Among them, J is the radon precipitation rate of the measured dielectric material, _CR is the apparent radon concentration, λ _e is the effective decay constant, V is the volume of the buffer accumulation cavity and the ionization cavity, t is the measurement time, and A is the effective measurement process. Measure the area.

According to formula (5), we can get,

In the measurement, the time is t, and the apparent radon concentration is measured as _CR by the measuring device based on the surface radon precipitation rate measured by electret radon, then the radon precipitation rate of the measured dielectric material can be calculated according to (6).

Apply the measuring device and method of the surface radon precipitation rate based on electret radon measurement provided by the present invention, to measure the radon precipitation rate of a certain marble countertop and a certain new building material, as follows:

(1) Measurement of surface radon precipitation rate for a new type of sheet

The material is a white mixed material, the measured material is 100cm long and 80cm wide, and the measured surface is flat and dense. Lay the material measuring surface up, place it on the indoor bench, and prepare the measuring equipment. Including two Long-term electrets, electrostatic potentiometer, two sets of H cavities and two buffer accumulation cavities with a height of 5cm, two H cavities seal the surrounding air intake holes, one of the H cavities removes the bottom plate and installs the filter membrane The connection with the buffer accumulation chamber is sealed. The effective bottom area A of the device is 0.1863m ² , and the effective cumulative volume V of radon is 0.00188m ³ . The effect of leakage can be ignored in this cavity combination, and λ _e is approximately taken as 0.0000019s ^-1 .

Before the measurement, two sets of devices were fixed at a distance of 10 cm on the surface of the material to be measured (marble slab) near the center, and the lower edge of the cavity was sealed with the marble slab with clay. The chamber was purged with compressed nitrogen for about 1 min, after which the two electret voltages were measured, mounted immediately in the H chamber, and the time was recorded. The two electrets are numbered S255 and the electret voltage is 720V for background monitoring. The electret number is S256 and the voltage is 716V for monitoring the radon precipitation rate. The ambient air penetration γ dose rate is 85nGy/h, and the time is 8:25am. At 16:20 in the afternoon of the same day, the monitoring was ended after about 8 hours, and the two electrets were removed to measure the voltage. The two electrets S255 electret voltage is 716V, down 4V, S256 electret voltage is 551V, down 165V.

According to the calculation formula of electret radon concentration, it can be calculated, and the apparent radon concentration _CR is 1624.1Bq/m. Substituting into formula (6), the radon precipitation rate of this material can be obtained as 12.86mBqm ^-2 s ^-1 .

(2) Measurement of radon precipitation rate of a new building material

The surface radon precipitation rate was measured on a new type of plate. The material is a white mixed material. The measured material is 100cm long and 80cm wide. The measured surface is flat and dense. Lay the material measuring surface up, place it on the indoor bench, and prepare the measuring equipment. Including two Long-term electrets, electrostatic potentiometer, two sets of H cavities and two buffer accumulation cavities with a height of 5cm, two H cavities seal the surrounding air intake holes, one of the H cavities removes the bottom plate and installs the filter membrane The connection with the buffer accumulation chamber is sealed. The effective bottom area A of the device is 0.1863m ² , and the effective cumulative volume V of radon is 0.00188m ³ . The effect of leakage can be ignored in this cavity combination, and λ _e is approximately taken as 0.0000019s ^-1 .

Before the measurement, two sets of devices were fixed at a distance of 10 cm on the surface of the material to be measured near the center, and the lower edge of the cavity was sealed with the marble slab with clay. The chamber was purged with compressed nitrogen for about 1 min, after which the two electret voltages were measured, mounted immediately in the H chamber, and the time was recorded. The two electrets, numbered L234, have a voltage of 689V for background monitoring, and the electrets numbered L235 have a voltage of 700V for radon precipitation rate monitoring. The ambient air penetration γ dose rate is 90nGy/h, and the time is 8:40 am. The next day at 8:40 am at the same time, the monitoring was terminated after about 24 hours, and the two electrets were removed to measure the voltage. The two electrets L234 electret voltage is 688V, down 1V, L235 electret voltage is 615V, down 85V.

According to the calculation formula of electret radon concentration, the apparent radon concentration _CR is 3726.8Bq/m. Substituting into formula (6), the radon precipitation rate of this material can be obtained as 9.15mBqm ^-2 s ^-1 .

The invention provides a measuring device and method for surface radon precipitation rate based on electret radon measurement, which is a method and device for measuring radon precipitation rate on medium surface by using local static method. Two sets of measuring devices for surface radon precipitation rate based on electret radon measurement are arranged in parallel at the measurement point. Before measurement, the radon accumulation chamber is purged with compressed nitrogen and then sealed with the surface of the measuring medium. One set of devices can be selected to close the air inlet. As a background reference, another set is used for cumulative radon concentration measurements. Radon cumulative concentration measuring electret is installed in the ionization chamber after measuring the starting voltage and recording the time to start the measurement. The measurement process does not need to be on duty, the minimum measurement time is not less than 3 hours, and the longest measurement time is not more than 240 hours. After the measurement, remove the electret, measure the electret end voltage with a potentiometer, and record the time. The voltage and time data can be used to calculate the apparent radon concentration, which can be substituted into the calculation formula to obtain the radon precipitation rate data at this point. The device and method are particularly suitable for the investigation and measurement of the radon release rate on the surface of artificial materials. The method and equipment have the technical advantages of low cost, strong environmental applicability, simple operation, unique radon release rate calculation result, easy to carry out large data collection at the same time, etc., which improve the representativeness and comparability of radon release rate data, and can be widely used for radiation environmental investigations.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

In this paper, specific examples are used to illustrate the principles and implementations of the present invention. The descriptions of the above embodiments are only used to help understand the methods and core ideas of the present invention; meanwhile, for those skilled in the art, according to the present invention There will be changes in the specific implementation and application scope. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. A measuring device of surface radon exhalation rate based on electret radon measurement, characterized in that the measuring device includes: the device comprises an electret material, an ionization cavity, a filter membrane and a buffer accumulation cavity;

the electret material is arranged on the ionization chamber and used for collecting negative ions generated by alpha ions ionized air in the radon decay process in the ionization chamber and generating electret voltage drop according to the quantity of the collected negative ions;

the upper edge of the buffer accumulation cavity is hermetically connected with the lower edge of the ionization cavity; the lower edge of the buffer accumulation cavity is in contact with the surface of the material medium to be detected;

the filtering membrane is arranged between the ionization chamber and the buffer accumulation chamber and is used for filtering radon daughter;

and radon precipitated on the surface of the material medium to be detected is fused with gas in the buffer accumulation cavity, enters the ionization cavity through the filtering membrane, and decays and ionizes in the ionization cavity.

2. The device for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 1, wherein said buffer accumulation chamber is a cylindrical chamber.

3. The device for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 2, wherein the diameter of the cross section of said buffer accumulation cavity is 155.4mm.

4. The apparatus for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 2, wherein said ionization chamber has a cross-section with a circular shape.

5. The apparatus for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 3, wherein the inner diameter of the upper edge of the buffer accumulation chamber is identical to the inner diameter of the lower edge of the ionization chamber.

6. The device for measuring the exhalation rate of surface radon based on electret radon measurement as claimed in claim 1, wherein the height of the buffer accumulation cavity is in the range of 32mm-350mm.

7. The device for measuring the radon exhalation rate on the surface based on electret radon measurement as claimed in claim 1, wherein the buffer accumulation cavity is fixed on the surface of the material medium to be measured through a sealing material; the sealing material is radon isolation sealing material.

8. The device for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 1, further comprising a base plate;

when the measuring device is used for measuring the background, the bottom plate is arranged between the buffer accumulation cavity and the surface of the material medium to be measured and is used for preventing radon separated from the surface of the material medium to be measured from entering the buffer accumulation cavity.

9. A method for measuring the exhalation rate of radon on the surface based on electret radon measurement, which is applied to the device for measuring the exhalation rate of radon on the surface based on electret radon measurement according to any one of claims 1 to 8, wherein the method for measuring comprises:

when the interior of the buffer accumulation cavity is communicated with the surface of a material medium to be measured, measuring a first initial voltage and a first final voltage of an electret at a point by using a potentiometer;

when the interior of the buffer accumulation cavity is not communicated with the surface of the material medium to be measured, measuring a second initial voltage and a second final voltage of the electret at the measuring point by using a potentiometer;

obtaining an apparent radon concentration according to the first initial voltage, the first final voltage, the second initial voltage and the second final voltage;

and calculating the radon exhalation rate based on the electret according to the relation between the apparent radon concentration and the radon exhalation rate based on the electret.

10. The method for measuring surface radon exhalation rate based on electret radon measurement as claimed in claim 9, wherein the relationship between the apparent radon concentration and the electret-based radon exhalation rate is:

wherein J is radon exhalation rate of the measured medium material, C _R Is apparent radonConcentration, λ _e And V is the volume of the buffer accumulation cavity and the ionization cavity, t is the measurement duration, and A is the effective measurement area in the measurement process.

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