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HJ 1212-2021: Measurement methods for determination of radon in environmental air
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Measurement methods for determination of radon in environmental air
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Basic data | Standard ID | HJ 1212-2021 (HJ1212-2021) | | Description (Translated English) | Measurement methods for determination of radon in environmental air | | Sector / Industry | Environmental Protection Industry Standard | | Classification of Chinese Standard | Z33 | | Word Count Estimation | 23,238 | | Issuing agency(ies) | Ministry of Ecology and Environment | HJ 1212-2021: Measurement methods for determination of radon in environmental air---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
(Measurement method of radon in ambient air (release draft))
National Ecological Environment Standard of the People's Republic of China
Methods of measuring radon in ambient air
Measurement methods for determination of radon in environmental air
This electronic version is the official standard text, which is reviewed and typeset by the Environmental Standards Institute of the Ministry of Ecology and Environment.
Published on 2021-11-26
2022-01-15 Implementation
Released by the Ministry of Ecology and Environment
directory
Foreword...ii
1 Scope...1
2 Normative references...1
3 Terms and Definitions...1
4 Overview...2
5 Measurement method...3
6 Quality Assurance and Quality Control...14
Appendix A (Normative Appendix) Selection of Measurement Methods for Radon in Ambient Air...16
Appendix B (Informative) Typical Relative Standard Uncertainty of Different Measurement Methods...17
Appendix C (Normative Appendix) Indoor Standard Sampling Conditions...18
Methods of measuring radon in ambient air
1 Scope of application
This standard specifies four common measurement methods for radon in ambient air, namely track etching method, activated carbon box method, pulse ionization chamber method, static
Electric collection method.
This standard applies to the determination of radon concentration in ambient air, including outdoor and indoor environments.
2 Normative references
This standard refers to the following documents or clauses thereof. For dated references, only the dated version applies to this standard.
For undated references, the latest edition (including all amendments) applies to this standard.
GB/T 8170 Numerical Rounding Rules and Representation and Judgment of Limit Values
GB/T 13163.1 Radiation Protection Instruments Radon and Radon Progeny Measuring Instruments Part 1.General Principles
HJ 61 Radiation Environment Monitoring Technical Specification
JJG 825 Radon Tester
3 Terms and Definitions
The following terms and definitions apply to this standard.
3.1
radon
The isotope 222Rn of the element with atomic number 86 is an intermediate product of the decay of the uranium series. Radon in nature has 219Rn, 220Rn, 222Rn
Three isotopes, radon in this standard ambient air only refers to 222Rn.
3.2
radon concentration
The radioactive activity of radon per unit volume of air, the SI unit is Bq/m3.
3.3
spot measurement
A method of obtaining the concentration value at a certain moment in a relatively short time range.
3.4
continuous measurement
An uninterrupted measurement that takes place at a certain time interval and can obtain results for each time interval.
3.5
integrating measurement
An integral measurement made over a specific time period, the result of which is the average concentration over that time period.
3.6
standard radon chamber
A special sealed radon-containing container can stably and uniformly regulate the radon concentration and related environmental conditions inside it, and control the radon concentration.
Accurately determined value. For the verification or calibration of radon concentration measuring instruments.
3.7
Scale calibration
Determine the scale factor (sensitivity) or correction factor of the measuring device given the known radon concentration.
3.8
sampling strategy
According to the sampling purpose and environment, select the sampling point location and density, measurement method, and technical principles of sampling or measurement time.
4 Overview
4.1 Purpose of measurement
The purpose of the measurement is to collect enough representative samples to obtain useful measurement results. In actual measurement, the radon concentration in the air will generally be
Over time, there may even be an order of magnitude change in some regions. Therefore, it should be based on different measurement purposes and uncertainty requirements.
Seek to choose a sampling strategy and measurement method.
4.2 Sampling strategy
4.2.1 Analyze the historical survey situation of sampling points.
4.2.2 On-site survey (in some cases, preliminary measurements of the survey area can be carried out with the aid of portable radiometric instruments).
4.2.3 Determine the migration path and accumulation area of radon in the survey area.
4.2.4 Carefully investigate the area of the sampling site and select the sampling site and density.
4.2.5 Select measurement methods according to different measurement purposes, see Appendix A for details.
4.2.6 Determine the sampling or measurement time according to the measurement uncertainty requirements. Typical values of each measurement method at different sampling or measurement times
See Appendix B for relative standard uncertainty.
4.3 Measurement method
4.3.1 According to the different sampling time, the measurement methods are divided into instantaneous measurement, continuous measurement and cumulative measurement. obtained by different measurement methods
The characteristics of the measurement results are shown in Table 1.
4.3.2 According to the different sampling methods, the measurement methods are divided into active measurement and passive measurement.
5 Measurement method
5.1 Track etching method
5.1.1 Method overview
This method is cumulative sampling, and the measurement result is the average concentration of radon during the sampling period. Adopt passive measurement method, if the measurement period is 90 d,
The detection limit of this method can reach at least 5 Bq/m3.
5.1.2 Measurement principle
The detector adopts solid nuclear track material (such as Kodak Alpha Film LR-115 or Carbonic Acrylic Acetate CR-39), placed in a certain shape
The track-etching radon sampler (hereinafter referred to as "sampler") is composed of the sampling box, as shown in Figure 1.
The radon gas enters the sampling box through the diffusion window. When the alpha particles emitted by radon and its newly decayed daughter bombard the detector, it generates a submerged path.
trace. The detector is chemically or electrochemically etched under certain conditions to expand the damage track, so that a microscope or automatic counting device can be used
Make observational statistics or counts. The number of tracks per unit area is proportional to the product of radon concentration and exposure time. Use the scale factor to convert the track density
Converted to radon concentration. This method can be used for cumulative measurements.
5.1.3 Equipment or materials
5.1.3.1 Detectors
Select solid core track materials sensitive to alpha particles, such as LR-115, CR-39, etc.
5.1.3.2 Sampling box
Most of the cavity boxes are made of conductive plastic or metal, and their dimensions should meet the actual measurement requirements.
5.1.3.3 Etching device
Used to etch detectors bombarded by alpha particles to expand damage tracks for measurement by counting devices. Mostly by NaOH or KOH
solution for chemical etching or electrochemical etching.
5.1.3.4 Counting device
A device used to read the number of tracks per unit area of the etched detector, generally through an optical magnifying device such as an optical microscope.
number of traces.
5.1.4 Measurement steps
5.1.4.1 Sampler Preparation
5.1.4.1.1 Put the detector into the sampling box and fix it to form a sampler.
5.1.4.1.2 Seal the sampler from outside air.
5.1.4.2 Deployment Principles
5.1.4.2.1 Remove the outer sealed packaging of the sampler at the measurement site.
5.1.4.2.2 Indoor measurements. Place the sampler on the measurement site, and its sampling conditions should meet the requirements of C.2 in Appendix C. The sampler can be suspended
Hang it with no other objects within 20 cm of its diffusion window, and the sampler is at least 1 m from the wall.
5.1.4.2.3 Outdoor measurements. The sampling point should be far away from roads, chimneys and other pollutant discharge facilities, the terrain is open, and there are no buildings within 10 m around it.
Avoid hollows and wet areas where air deposits are deposited. The height of the sampler is generally not more than 1.5 m, and measures such as waterproofing should be taken when placing the sampler. the above
The principle of deployment does not apply to measurement activities for the purpose of surveying pollution source items.
5.1.4.2.4 When sampling is terminated, remove the sampler, seal the package, and return it to the laboratory. The sampling time is generally not less than 30 d.
5.1.4.2.5 Details to be recorded during sampling are detailed in C.3 in Appendix C.
5.1.4.2.6 Determine the sampling time according to the radon concentration level at the deployment point. For areas with high radon concentration, the sampling time should be shortened to avoid detectors.
Saturated; for areas with low radon concentrations, the sampling time should be extended.
5.1.4.3 Measurement
5.1.4.3.1 The sampler shall be measured as soon as possible after it is brought back to the laboratory.
5.1.4.3.2 Take the detector out of the sampling box and put it into the etching device (the typical etching conditions for CR-39 sheets are
Degree. c(KOH) = 6.5 mol/L; etching temperature. 70 °C; etching time. 10 h).
5.1.4.3.3 Take out the etched detector, wash it, and dry it.
5.1.4.3.4 Use a counting device to read out the number of tracks per unit area of the detector after processing.
5.1.4.4 Scale
5.1.4.4.1 Put the assembled sampler in a standard radon room (specific requirements shall be implemented in accordance with the relevant provisions of JJG 825), and expose it for a certain period of time.
Handle the detector according to the prescribed measurement procedure, and calculate the scale factor according to formula (1).
bN
5.2 Activated carbon box method
5.2.1 Method overview
This method is cumulative sampling, and the measurement result is the average concentration of radon during the sampling period. Using passive measurement method, the detection limit of this method is
At least up to 6 Bq/m3.
5.2.2 Measuring principle
The activated carbon box is generally made of plastic or metal, with a diameter of 6 cm to 10 cm and a height of 3 cm to 5 cm, and contains 25 g to 100 g of activated carbon.
The open side of the box is sealed with a filter membrane (to filter the radon progeny), which immobilizes the activated carbon and allows radon to enter the carbon box. Activated carbon box and activated carbon form activated carbon
Box method radon sampler (hereinafter referred to as "sampler"), as shown in Figure 2.
The air diffuses into the carbon bed, and the radon in it is adsorbed by the activated carbon and decays at the same time, and the new daughters are deposited in the activated carbon. with a gamma spectrometer
The intensity of the characteristic gamma ray peak (or peak group) of the radon progeny of the sampler is measured, and the radon concentration is calculated according to the characteristic peak area. This method can be used to accumulate
Measurement.
Setting a diffusion barrier between the activated carbon and the measured air helps to reduce the desorption of the adsorbed radon on the activated carbon. The presence of a diffusion barrier also reduces the
The charcoal absorbs water vapour, so even in locations with humidity greater than 75%, the sampler can be exposed for more than 7 days.
5.2.3 Equipment or materials
5.2.3.1 Activated carbon
Activated carbon with excellent radon adsorption performance should be selected, such as coconut shell activated carbon, generally 8 mesh to 16 mesh.
5.2.3.2 Activated carbon box
It is made of plastic or metal, the size can refer to the provisions of 5.2.2, or can be selected according to the actual measurement requirements of users.
5.2.3.3 Oven
Used for baking activated charcoal before use.
5.2.3.4 Balance
For the weighing of activated carbon.
5.2.3.5 Gamma spectrometer
Use HPGe or NaI(Tl) spectrometers.
5.2.4 Measurement steps
5.2.4.1 Sampler Preparation
5.2.4.1.1 Put the selected activated carbon in an oven, bake at 120 ℃ for 5 h to 6 h, and then put it into a sealed bag for use.
5.2.4.1.2 Sample loading. Weigh a certain amount of baked activated carbon into a carbon box and cover with a filter membrane.
5.2.4.1.3 Reweigh the total weight of the sample box.
5.2.4.1.4 Seal the activated carbon box from outside air by sealing the box lid with additional tape (eg vinyl tape).
5.2.4.2 Deployment Principles
5.2.4.2.1 Open the lid of the sealed box at the site to be tested, and lay it for 3 to 7 days.
5.2.4.2.2 Indoor measurements. Place the sampler on the sampling point, and its sampling conditions should meet the requirements of C.2 in Appendix C. The sampler can be suspended
Hang it with no other objects within 20 cm of its diffusion window, and the sampler is at least 1 m away from the wall.
5.2.4.2.3 Outdoor measurements. The sampling point should be far away from roads, chimneys and other pollutant discharge facilities, the terrain is open, and there are no buildings within 10 m around it.
Avoid hollows and wet areas where air deposits are deposited. The height of the sampler is generally not more than 1.5 m, and measures such as waterproofing should be taken when placing the sampler. the above
The principle of deployment does not apply to measurement activities for the purpose of surveying pollution source items.
5.2.4.2.4 When sampling is terminated, replace the sealing cap of the sampler and return it to the laboratory promptly.
5.2.4.2.5 The contents to be recorded during sampling are detailed in the requirements of C.3 in Appendix C.
5.2.4.2.6 For areas with high humidity, samplers with diffusion barriers should be selected as far as possible.
5.2.4.3 Measurement
5.2.4.3.1 Measure as soon as possible after sampling stops for 3 hours, and weigh again before measurement to calculate the amount of water absorbed.
5.2.4.3.2 Place the sampler on the gamma spectrometer for counting, and measure the characteristic gamma ray all-energy peaks of radon daughters (214Pb. 295 keV, 352 keV; 214Bi.
609 keV) net count rate. The geometrical conditions of the measurement are consistent with those of the calibration.
5.2.4.4 Scale
The scale factor is the ratio of the net count rate of the characteristic γ-ray Omnipotent peak of radon progeny to the standard radon concentration value, and the unit is s-1/(Bq/m3). scale
Its scale factor should be calculated at different humidity levels (at least three humidity levels. 30%, 50%, 80%). If accurate measurement results are required,
The scale coefficients should be calculated at different sampling times and under different humidity conditions, and the obtained scale coefficients can be summarized into a scale coefficient table.
5.2.5 Quantitative calculations
5.2.5.1 Radon concentration calculation
The radon concentration is calculated according to Equation (8), Equation (9), Equation (10), Equation (11) and Equation (12).
5.3 Pulse ionization chamber method
5.3.1 Method overview
This method is continuous sampling, which can continuously measure the concentration of radon in ambient air. Using active measurement, the detection limit of this method is up to
as little as 5 Bq/m3.
5.3.2 Measuring principle
After the air is filtered, it diffuses into the ionization chamber or is pumped into the ionization chamber. In the sensitive area of the ionization chamber, the alpha emitted by radon and its decay daughter decays
The particles ionize the air and generate a large number of electrons and positive ions.
Voltage pulses or current pulses are formed on the surface, and these pulses are recorded after being amplified by the electronic measuring unit. The number of recorded pulses is proportional to the number of alpha particles.
That is proportional to the radon concentration, as shown in Figure 3.This method can be used for instantaneous or continuous measurements.
5.3.3 Equipment or materials
5.3.3.1 Pulse ionization chamber radon tester
It is mainly composed of ionization chamber, sampling pump, amplifier, pulse amplitude analyzer and counter.
5.3.3.2 Thermohygrometer
Used to record the temperature and humidity of the environment during measurement.
5.3.3.3 Flowmeter
It is mainly used to indicate the working state of the instrument during active sampling.
5.3.3.4 Diffusion window
Used to filter radon progeny.
5.3.4 Measurement procedure
5.3.4.1 Inspection before measurement
The instrument should be checked before measurement, such as the flow rate of the flowmeter, battery voltage, instrument parameters, measurement mode, time interval, etc.
measurement requirements. The instrument should be handled with care.
5.3.4.2 Deployment Principles
5.3.4.2.1 Indoor measurements
Arrangement principles and sampling conditions should meet the requirements of C.2 in Appendix C.
5.3.4.2.2 Outdoor measurements
The sampling point should be far away from roads, chimneys and other pollutant discharge facilities, the terrain is open, there are no buildings within 10 m around it, and air deposits should be avoided.
Depressed and wet areas. The measurement height is generally not more than 1.5 m, and the instrument should take measures such as waterproofing and sun protection. Should not be used in rainy days, 24 hours after rain
Measurements within 12 hours after high winds. The above-mentioned distribution principles do not apply to measurement activities for the purpose of surveying pollution source items.
5.3.4.3 Measurement
5.3.4.3.1 Place the instrument in the selected measurement position, and start the measurement according to the operating procedures of the instrument.
5.3.4.3.2 If continuous measurement for 24 hours is not possible, generally select sampling measurement from 8.00 am to 12.00 am, and measure continuously for at least 2 days.
5.3.4.3.3 Details to be recorded during the measurement are detailed in C.3 in Appendix C.
5.3.4.4 Scale
The calibration of the instrument is carried out in accordance with the relevant provisions of JJG 825.
5.3.5 Quantitative calculation
5.3.5.1 Radon concentration calculation
Radon concentration was calculated according to equation (17).
/()
Rn i
CQ n R
(17)
In the formula. CRn - the average value of radon concentration during the measurement, Bq/m
3;
n--measurement times;
R - volume activity response, given by the instrument calibration or verification unit;
Qi--Indication value of the instrument for a single measurement, Bq/m
3.
5.3.5.2 Standard uncertainty calculation
Standard uncertainty is calculated according to Equation (18) and Equation (19).
twenty two
() (/()) () ()
Rn i rel rel
u CQ n R u R u Q
(18)
In the formula. u(CRn) - standard uncertainty of radon concentration measurement;
Qi--Indication value of the instrument for a single measurement, Bq/m
3;
n--measurement times;
R - volume activity response, given by the instrument calibration or verification unit;
urel(R)--relative standard uncertainty of verification coefficient;
urel(Q) - Relative standard uncertainty of multiple measurements.
()/()
()
(/())
rel n
u Q n R
u Q
Q n R
(19)
In the formula. urel(Q)--relative standard uncertainty of multiple measurements;
urel (Qi) - the standard uncertainty of the instrument indication for a single measurement, given by the measuring instrument;
Qi--Indication value of the instrument for a single measurement, Bq/m
3;
n--measurement times;
R - volume activity response, given by the instrument calibration or verification unit.
5.3.5.3 Calculation of detection lower limit
The lower detection limit is calculated according to formula (20).
4.66b
Rn
LLD C
(20)
In the formula. LLD (CRn)--the detection limit of radon concentration measurement, Bq/m
3;
Nb--the background count of the instrument;
w--conversion factor, including sensitivity, measurement time, etc.
5.4 Electrostatic collection method
5.4.1 Method overview
This method is continuous sampling, which can continuously measure the concentration of radon in ambient air. Using active measurement, the detection limit of this method is up to
as little as 5 Bq/m3.
5.4.2 Measuring principle
After the air is dried, the radon progeny is filtered out through the filter membrane and then enters the collection chamber. The collection chamber is generally hemispherical or cylindrical, and is installed in the center.
There are alpha energy spectrum detectors. The radon in the collection chamber will decay into nascent radon daughters (mainly positively charged 218Po), and 218Po is under the action of the electrostatic field
It is collected on the surface of the detector, and the radon concentration is calculated by measuring the alpha particles emitted by the radon progeny, as shown in Figure 4.This method is available
for instantaneous or continuous measurements.
5.4.3 Equipment or materials
5.4.3.1 Radon meter by electrostatic collection method
It is mainly composed of detector, collection chamber, amplifier and energy spectrum analyzer.
5.4.3.2 Thermohygrometer
Used to record the temperature and humidity of the environment during measurement.
5.4.3.3 Flowmeter
It is mainly used to indicate the working state of the instrument during active sampling.
5.4.3.4 Desiccant or drying tube
Drying of gases for active sampling.
5.4.4 Measurement steps
Same as 5.3.4.
5.4.5 Quantitative calculation
Same as 5.3.5.
6 Quality Assurance and Quality Control
6.1 Verification/calibration of measuring instruments
6.1.1 Active measuring instruments (such as radon measuring instruments using pulse ionization chamber method or electrostatic collection method) should be approved by the national metrology department or its authorized
The standard radon should be verified or calibrated indoors, and ensured to be used within the validity period (recommended verification or calibration cycle is one year). After the instrument is repaired, it should be re-
For new verification or calibration, the verification or calibration factor should be used correctly.
6.1.2 Passive measuring devices (such as track etching method radon sampler or activated carbon box method radon sampler) should be in the national metrology department or its
The authorized standard radon is exposed indoors for a period of time (to ensure that the radon concentration inside and outside the sampler reaches a balance), and then returned to the laboratory for analysis and measurement.
6.2 Verification of measuring instruments
6.2.1 Short-term stability verification of measuring instruments. For active measuring instruments, the measurement shall be carried out under the conditions of pure nitrogen or radon-free air.
Bottom value. For passive measuring devices, randomly select not less than 5% of the samplers (and at least 10) as blanks when preparing the samplers
The sampler and blank sampler should be treated the same as the field sampler (such as mailing at the same time) except that they are not exposed to the sampling point.
The result is used as the background value for this verification. After measuring the background value, carry out the Poisson distribution test according to the procedure in Appendix E of HJ 61.
6.2.2 Long-term stability verification of measuring instruments. Collect 20 measurements at intervals of a certain period of time (such as one year) under normal working conditions
Above the background value, calculate the mean and standard deviation, and draw the quality control chart. After each measurement of a background value, point it on the graph, if the data
If it falls within the upper and lower warning lines (mean ± 2 times standard deviation), it means that the measuring instrument is working properly. If the data falls on the upper and lower warning lines and
Between the upper and lower control lines (average ± 3 times standard deviation), it means that although the measuring instrument is working normally, it may be out of control, which should be paid attention to. Such as
If the data falls outside the control line, it indicates that the measuring instrument may be faulty, and a series of repeated measurements should be immediately carried out and judged.
interrupt and process. If most of the data points fall on the same side of the centerline, this indicates a slow drift in the performance of the meter, and the
The status is adjusted and the quality control chart is redrawn.
6.3 Parallel sample measurement
Randomly select 10% to 20% of the total measurement points for parallel sample measurement. For the measurement points with parallel sample measurement, the measured value of
The relative deviation should be no more than 20%.
6.4 Blank measurement
6.4.1 For active measuring instruments, the background value shall be measured with pure nitrogen or radon-free air before each measurement.
6.4.2 For passive measuring devices, when preparing each batch of samplers, randomly select no less than 5% of the samplers (and at least 10)
As a blank sampler, except that the blank sampler is not exposed to the sampling point, it is treated the same as the field sampler (such as mailing at the same time, etc.), and
Use this measurement as the background value for the batch of samplers.
6.5 Laboratory comparison
Should regularly participate in inter-laboratory comparisons or proficiency testing organized by authoritative institutions to check whether there is a relationship between laboratories or between measurement methods.
system error.
...
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