GBZ/T 155-2002 Scintillation vial method for determination of radon concentration in air
Some standard content:
Ics13.100
National Occupational Health Standard of the People's Republic of China GBZ/T155-2002
Scintillation flask method for measuring radon concentration in the air
Ministry of Health of the People's Republic of China
Terms and definitions
Method Summary
Measuring device
Measuring steps
Measurement results
Appendix A (Informative Appendix)
Appendix B (Informative Appendix)
Calibration method
Sampling and recording
This standard is formulated in accordance with the Law of the People's Republic of China on the Prevention and Control of Occupational Diseases. In case of any inconsistency between the original standard GB/T16147-1995 and this standard, this standard shall prevail.
Appendix A and Appendix B of this standard are informative appendices. This standard is proposed and managed by the Ministry of Health.
The drafting units of this standard are: Institute of Radiation Protection and Nuclear Safety Medicine, Chinese Center for Disease Control and Prevention, and Industrial Hygiene Laboratory, Ministry of Health.
The main drafters of this standard are: Lu Yangqiao and Wang Zuoyuan. The Ministry of Health is responsible for the interpretation of this standard.
National Occupational Health Standard of the People's Republic of China GBZ/T155-2002
Scintillation flask method for measuring radon concentration in the air
1 Scope
This standard specifies the scintillation flask method for measuring radon concentration in the air
1 Scope
This standard specifies the scintillation flask method for measuring hydrogen (222Rn) concentration in the air. This standard is applicable to the measurement of hydrogen concentration in the air in indoor, outdoor and underground places. 2 Terms and Definitions
The following terms and definitions apply to this standard. 2.1 Radioactive aerosol Radioactive aerosol A dispersion system formed by solid or liquid particles containing radioactive nuclides in air or other gases. 2.2 Scintillation flask
A hydrogen detector and sampling container. Made of low-background materials such as stainless steel, copper or plexiglass. The shape is cylindrical or bell-shaped, the inner layer is coated with ZnS (Ag) powder, and there is a sealed ventilation valve on the top. 2.3 Instantaneous sampling grabsampling
The technology of collecting air samples in a short time from a few seconds to tens of minutes. 2.4 Radon chamber
A large standard device for calibrating hydrogen and its short-lived daughter detectors. It consists of equipment such as a hydrogen generator, a temperature and humidity controller, and a hydrogen and its daughter monitor. 3 Method summary
According to the prescribed procedure, the air at the test point is sucked into the scintillation bottle that has been evacuated to a vacuum state. The scintillation bottle is sealed and protected from light for 3 hours, and the α particles emitted when 2Rn, 218Po and 34Po decay are measured after the hydrogen and its short-lived daughters are balanced. They are incident on the ZnS (Ag) coating of the scintillation bottle, causing the ZnS (Ag) to emit light, which is collected by the photomultiplier tube and converted into electrical pulses. After pulse amplification and screening, it is recorded by the calibrated counting circuit. The number of pulses within a certain time is functionally related to the concentration of hydrogen in the collected air. According to the net count rate-hydrogen concentration calibration curve measured by the calibration source, the hydrogen concentration in the measured air can be obtained from the measured pulse count rate.
4 Measuring device
A typical measuring device consists of a probe, a high-voltage power supply, and an electronic analysis and recording unit. 4.1 The probe consists of a scintillation bottle, a photomultiplier tube, and a pre-unit circuit. 4.1.1 See Figure 1 for a schematic diagram of a typical scintillation bottle (2.2): 4.12 A low-noise, high-amplification photomultiplier tube must be selected, and the operating voltage must be less than 1000V. 4.13 The preamplifier circuit should be a deep feedback amplifier, and the output pulse amplitude is 0.1~10V4.14 The probe housing must have good light tightness, and the material should be made of copper or aluminum. The inner surface should be oxidized and blackened, and the housing size should be suitable for the placement of the scintillation bottle.
4.2 The output voltage of the high-voltage power supply should be continuously adjustable in the range of 0~3000V, the ripple voltage should not be greater than 0.1%, and the current should not be less than 100mA
4.3 The recording and data processing system can use a calibrator and a printer, or a multi-channel pulse amplitude analyzer and an XY plotter. Ministry of Health of the People's Republic of China XXXX-XX-XX approved XXXX-XX-XX implementation
Simplified diagram of scintillation bottle
ZnS (Ag) powder
a. The ventilation valve should be inspected by the vacuum system. After connecting to the system, under a vacuum degree of 1×10'Pa, after 12h, there is no obvious change in the vacuum degree:
b. The bottom plate is made of organic glass. Its size is consistent with the photocathode of the photomultiplier tube, the contact surface is flat, without obvious scratches, and has good optical coupling with the photocathode of the photomultiplier tube: c. ZnS (Ag) powder must be purified by potassium removal to keep its contribution to the background at a minimum level: d. During the entire sampling measurement period, the leakage of the scintillation bottle must be less than 5% of the sampling volume; when measuring the hydrogen concentration in outdoor air, the volume of the scintillation bottle should be greater than 0.5×10m2. e.
5 scale
5.1 scale source
The scale source uses a 2Ra standard source (solution or solid powder). The standard source must be calibrated by the statutory metrology department or an organization recognized by it. The standard source should have an inspection certificate, which should clearly indicate the reference date and accuracy.
5.2 Scale device
In addition to using a special hydrogen chamber (see 2.4), the scale device also often uses the glass scale system described in this article (referred to as the scale system, see Figure 2)
5.2.1 The scale system should have good airtightness. The system is under a vacuum of 1×10'Pa, and after 24 hours, the vacuum change is less than 5×10°Pa.
5.2.2 The accuracy of the pressure gauge should be better than 1%.
5.2.3 The flow meter uses a float flow meter, the accuracy should be better than 3%, and the range is 0~2×10m/min5.2.4 The cleaning and inflation gas should be hydrogen-free gas (such as nitrogen, argon or compressed air that has been stored for more than two months). 5.2.5 If a mechanical vacuum pump is used, the vacuum of the scale system must be better than 5×10\Pa. 5.3 Scale curve
5.3.1 Clean the entire scale system according to the prescribed procedures. Seal the two ends of the diffusion bottle filled with the standard radium source solution, and the accumulated hydrogen concentration reaches the standard hydrogen concentration value of the required scale point within the scale range. The scale points should cover the entire scale range, and one interval (magnitude width) should have at least 3 scale points. See Appendix A (Informative Appendix) for details. 5.3.2 The scintillation bottle in a vacuum state must be connected to the system first. Open each valve in the specified order, and use hydrogen-free gas to drive the known concentration of hydrogen gas accumulated in the diffusion bottle into the scintillation bottle. Under the determined measurement conditions, avoid light for 3 hours and perform counting measurements.
5.3.3 The calibration curve, that is, the net count rate-hydrogen concentration relationship curve, is obtained by fitting a set of standard hydrogen concentration values and their corresponding count values. And derive its function-related formula.
5.3.4 Different types of scintillation bottles and measuring devices must use different calibration curves. 6
J Mechanical vacuum pump
E Flow meter
Oil-free vacuum valve
Liquid source container
Diffusion bottle)
1 Scintillation bottle
Oil-free vacuum valve
Oil-free vacuum valve
Dry explosion agent
Oil-free vacuum valve
Figure 2 Schematic diagram of glass scale system
Measurement steps
Water pressure gauge
6.1 Under the determined measurement conditions, perform background stability determination and background measurement. Obtain the background distribution diagram and background value. 6.2 Bring the vacuumized scintillation bottle to the test point, then open the valve (in high temperature and high dust environment, it must be pre-treated for dehumidification and dust removal). After about 10 seconds, close the valve and bring it back to the measurement room for testing. Record the location, temperature and air pressure of the sampling point, etc., see Appendix B (Informative Appendix) for details.
6.3 Store the scintillation vial to be tested in the dark for 3 hours and perform counting measurement under the determined measurement conditions. The measurement time is selected according to the required measurement accuracy.
6.4 After the measurement, the scintillation vial must be cleaned with hydrogen-free gas in time to maintain the background state. 7 Measurement results
7.1 The calibration curve of a typical device is a straight line on a double logarithmic coordinate paper, and the formula is: logY=alogX+ b
-the concentration of hydrogen in the air, Bq·m3:
where: Y-
the measured net count rate, cpm;
the scale factor, which depends on the performance of the entire measuring device; a
the scale factor, which depends on the performance of the entire measuring device. b-
From formula (1), we can get:
Y=ebxa
From the net count rate, the hydrogen concentration value in the corresponding sample air can be obtained using a chart or formula. (1)
7.2 The errors of the results are mainly source error, scale error, sampling error and measurement error. When measuring the hydrogen concentration in outdoor air, the counting statistical error is the main one. According to the determined measurement procedure, the report should list the measured values and counting statistical errors. Appendix A
(Informative Appendix)
Calibration Method
This appendix mainly specifies the use of the glass calibration system. A1 Preparation of Calibration Sourcewww.bzxz.net
Dissolve the standard barium carbonate radium powder in a 2.7 mol/L hydrochloric acid solution prepared with high-grade pure hydrochloric acid and double distilled water to obtain A1.1
Liquid Ra standard source. The volume is one-third of the liquid radium source container (diffusion bottle) A1.2 The accuracy of the source is better than 5%.
A1.3 For the hydrogen concentration in the ambient atmosphere, the activity of the liquid Ra source is selected to be approximately 0.4Bq, 4Bq, 40Bq, and 400Bq. A2 Cleaning of the Calibration System
Before the scale is inflated, the entire system must be cleaned with hydrogen-free gas according to the prescribed procedures. The cleaning time should be greater than 20min. A3 Growth and accumulation of hydrogen
After cleaning the system, seal the two ends of the diffusion bottle containing the standard radium source solution, and calculate the growth time according to the hydrogen concentration required for the scale using formula (A1) A3.1
.
Where: Gm
Chm=Qna
The required\Rn concentration for the scale, Bq·m\;
QnThe activity of the liquid radium standard source, Bq;
VThe volume of the scale system, m;
-Growth time, d;
The decay constant of hydrogen.
(1e1813t)
(A1)
A3.2The scale points must be evenly distributed over the entire scale range. A concentration interval (magnitude width) takes 3 to 5 scale points. A4
Filling of scintillation vials
A4.1 The scintillation vials in a vacuum state must be connected to the system first. Open the valve according to the prescribed procedure to allow most of the generated hydrogen to enter the scintillation vials, connect the gas bottle, and use hydrogen-free gas to drive the remaining hydrogen into the scintillation vials. A4.2 The filling process is determined to be 20 minutes, and the airflow is controlled to be about 100 bubbles/min. A5 Establishment of the relationship between hydrogen concentration and net count rate According to the prescribed measurement procedure, measure the hydrogen concentration-net count rate calibration curve. The calibration curve of the above typical device is a straight line on the double logarithmic coordinate paper.
From the established hydrogen concentration-net count rate relationship, the hydrogen concentration in the air can be calculated. Appendix B
(Informative Appendix)
Sampling points must be representative
Sampling and recording
The concentration distribution of hydrogen in the air is uneven in indoor, outdoor, and underground places. The sampling point should represent the best sampling point of the space to be measured.
Sampling conditions must be standardized
Sampling conditions must take into account the ground, region, weather, living environment, population characteristics, etc. The standardization of conditions depends on the purpose of sampling.
B2.1 Sampling records depend on the purpose of sampling. B2.2 Record content
a. Sampler number:
b. Sampling time:
c. Location, time, air pressure, temperature, humidity, etc. of the sampling point: d. Other useful information related to the purpose of sampling. Such as wind direction, wind force, before and after rain, surrounding environment, etc.
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