GB/T 16143-1995 Activated carbon measurement method for radon exhalation rate on building surfaces
Some standard content:
National Standard of the People's Republic of China
Charcoel canister method for measuring2Rn exhalation rate from building surface1Subject content and scope of application
GB/T16143-1995Www.bzxZ.net
This standard specifies the method for measuring the oxygen evolution rate from building surface by cumulative adsorption of activated carbon and spectrum analysis. This standard is applicable to the determination of hydrogen evolution rate from flat surfaces of buildings (including building components). The determination of chlorine evolution rate from various soil and rock surfaces can be used as a reference.
2Terms
2.1Building surfaceBuilding surface in this standard refers to the flat surfaces of the building's ceiling, floor, ground, inner wall and outer wall. 2.2 Chlorine and its daughters In this specification, oxygen refers only to +Rn, and hydrogen daughters refer to "the short-lived decay products of Rn, Pu, Pb, Bi and 2*Po. 2.3 Area hydrogen exhalation rate Area adon exhalation rate The activity of hydrogen exhaled from the surface of a unit building and entering the air in a unit time, and its unit is expressed in Ba-m-·-1. 3 Instruments and equipment
3.1 Activated carbon box
3.1.1 Container
The activated carbon box is a cylindrical container made of low-radioactive materials (such as polyethylene, organic glass, stainless steel, etc.) and filled with activated carbon. The bottom diameter should be equal to or slightly smaller than the diameter of the detector, and the height should be one-third to one-third of the diameter. 3.1.2 Active effect
Use high-quality coconut shell granular activated carbon with developed microporous structure, large specific surface area and particle size of 18 to 28 months. 3.1.3 Mesh cover
Use materials with good air permeability, such as nylon mesh, gold screen mesh or gauze, to cover the opening surface of the activated carbon box. The mesh cover grid density should match the activated carbon particle size.
3.1.4 Vacuum seal
Use to seal the gap between the activated carbon box and the surface of the medium to be tested and fix their relative position. 3. 2 Energy Spectrometer
3.2.1 Detector
a. Flash detector Nal(TI) is composed of a cylindrical Nal(TI> crystal of not less than .5cm×7.5cm and a low-noise photomultiplier tube. The resolution of the detector for 661.6keV7 rays of urCs should be better than 9%. b. Semiconductor detector Li or high purity Ge (HPGe) with a sensitive volume greater than 50tn\ The resolution for 1332.5keV characteristic gamma rays of Co should be better than 2.2keV. Approved by the State Administration of Technical Supervision on December 15, 1995 and implemented on July 1, 1996
3.2.2 Screen drum chamber
CB/I 16143-1995
The shielding material with low radioactive nuclei content and no surface contamination should be selected. The detector should be placed in the center of the shielding room with a wall thickness of not less than 10cm lead equivalent. The minimum distance between the inner wall of the shielding room and the detector surface should be greater than -13c11. The inner lining of the lead chamber should be composed of multiple layers of shielding materials with gradually decreasing atomic numbers. From the outside to the inside, it can be composed of 1.6mm, 0.4mm saw and 2~3mm organic glass materials. The shielding room should have a door for easy access to samples. 3.2.3 High power supply
There should be a high-voltage power supply to ensure the stable operation of the detector, and its ripple voltage should not exceed =0.01%. The high voltage of the semi-conductor detector should be continuously adjustable in the range of 0~5 kV.
3.2.4 Spectrum amplifier
There should be an amplifier with waveform adjustment that matches the preamplifier and pulse height analyzer. 3.2.5 Pulse height analyzer
Nal(T1)7 spectrometer has no less than 256 channels. For high resolution semiconductor spectrometer, the number of channels is no less than 4096. 3.2.6 Data printer
3.2.7 Data processing device
?The spectrometer can be connected with a dedicated or microcomputer to process the spectrum data online, or it can be processed manually by a calculator. 4 Collection and measurement of precipitated chlorine
4.1 Preparation of activated carbon box
4.1.1 Place the activated carbon in an oven and bake it at 120℃ for 7~-8h to remove the residual gas in the activated carbon. 4.1.2 Fill the activated carbon box container with the baked activated carbon and weigh it. The weight difference between each carbon box should be less than 0.5%. Then add a mesh cover and a cover. Seal it.
4.1.3 Keep 1-2 newly prepared activated carbon boxes (referred to as fresh carbon boxes) exposed to oxygen and protons in the laboratory for background counting measurement.
4.2 Collection of precipitated oxygen
4.2.1 Remove dust and sand from the surface of the actual microstructure, open the activated carbon box, turn it upside down on the surface, fix and seal it with vacuum mud, and record the time when the precipitated chlorine begins to be collected. The precipitated chlorine collection lasts for 5-7 days. 4.2.2 At the end of the collection, remove the vacuum mud, carefully remove the activated carbon box, seal the lid, record the end time, and bring it back to the laboratory. 4.3 Hydrogen plate
4.3.1 Check and adjust the spectral source to normal working state. 4.3.2 Under the same conditions as the sample display mother, in? The background spectrum of the "fresh\active" box is measured on the harmonic analyzer. 4.3.3 After the collection, the activated carbon box is placed on Si to L. When the H high-resolution spectrum is double, the base\Bi's 0. R59M:V, 214Pb's 0.241, 0.295 and 0.352Mr:V are measured; when the NaI (T1) spectrometer is used, the counting efficiency of the virtual energy zone of the fast energy base phase is measured
5 Calculation of the precipitation rate
The oxygen precipitation rate on the building surface is calculated according to formula (1): (n. - n) -exp(,).A
expt-A)
where: R—oxygen precipitation rate, Bg·mg; the counting rate of the selected oxygen-ray peak energy zone in the activated carbon box, Ih:
and the corresponding counting rate of the "fresh" activated carbon box, the time interval between the active intercalation and the precipitation of ammonia,
the time interval from the end of collection to the beginning of measurement, 3! GB/T 16143 1995
and the detection efficiency at the corresponding gamma-ray barrier energy or energy zone: S—the area of the measured surface, m
A.---radioactive decay constant of hydrogen, 2. 1 ×10-s-1 6 Detection efficiency scale
6.1 Preparation of body standard source
6.1.1 The standard source matrix should be the same type and weight as the activated carbon used in the activated carbon box. 6.1.2 Use a 10,000 ppm balance to accurately weigh the standard powder of indium iodide with known specific activity approved by the national law department. The total activity should be 52~500 The relative standard deviation of specific activity is within the range of Prl, and the relative standard deviation is greater than 4%. 6.1.3 Place the standard powder in a 50ml beaker and dissolve it with 1mol hydrochloric acid solution. Then dilute it with 0.1mol of acid to the required volume (so that the activated carbon matrix can be fully incorporated), pour in the activated carbon particles, and stir continuously. 6.1.4 Bake the activated carbon under an infrared lamp to evaporate its water continuously. When it is almost constant weight, transfer it to another clean beaker. Wash the used 100mL beaker with a small amount of 100ml hydrochloric acid washing solution, pour the washing solution into the activated carbon (be careful not to contact the clean beaker wall that previously contained the activated carbon), and then bake it with an infrared lamp, stirring continuously until constant weight. 6.1.5 Transfer the radioactive material into an empty activated fluorescent box, flatten it, add the required amount, seal it, and place it for 30 days. The radioactive material Ra is in radioactive equilibrium with oxygen and its body. 6.1.6 Comprehensive uncertainty of standard source ( - standard deviation), or control it within ±1%. 6.2 Calibration
6.2.1 According to the requirements of the user manual, correctly install and adjust the spectrometer system, including the detector, source, preamplifier, spectrometer amplifier, pulsed spectrometer and computer system, so that it is in the best working state. 6.2.2 Under the same conditions as the sample measurement, obtain the above-mentioned standard source energy spectrum of known Rn activity and the background spectrum of fresh active source.
6.2.3 Select one or more full energy peaks of the daughter of hydrogen, 0.241, 0.295, 0.3352 MeV of Pb and 0.509 MeV of 1Bi from the net spectrum, and calculate its net peak count. If a NaI(TI) scintillation detector is used, when the above-mentioned several ray peaks cannot be clearly separated, the net count of the energy region containing more than one of the above-mentioned peaks can also be calculated: 6.2.4: Calculate the detection efficiency according to the net count rate of the full energy peak (or selected energy range) of the selected gamma-ray. 7. The relative standard deviation of the measured oxygen evolution rate is o.ru = Voall - c. Formula: w. Total relative standard deviation, %. Relative standard deviation of efficiency scale, %;
- Relative standard deviation of measured counts, %. It can be calculated by the following formula:
VN./E+N/E
N,hh.N/tr
Where: N.
Integral count of the selected hydrogen proton ray peak or energy range in the activated carbon box: N, the integral count of the "fresh" activated carbon box corresponding to the sample counting time,
t. - background counting time.
Interference and influencing factors
B. 1 The result obtained by hitting the activated carbon box on the surface of the building does not represent the oxygen precipitation rate under natural conditions. It is equivalent to the hydrogen precipitation rate when the chlorine concentration in the outside air is 0, that is, the maximum precipitation rate. This method does not consider the influence of the wind speed and exchange rate of the outside air. However, it may cause changes in the local water content of the irrigated material where the activated carbon plate is buckled, which will cause a slight interference to the oxygen precipitation rate. 8.2 During the period of chlorine precipitation, the area hydrogen precipitation rate is actually affected by the surrounding environment, such as meteorology, temperature, humidity, air pressure, wind speed changes, etc. Therefore, the measurement results only represent the average value of the area oxygen precipitation rate during the period of collection under the corresponding environmental conditions. B.3 When using a Na1(T1) gamma spectrometer to determine the oxygen activity collected by the activated carbon box, the 0.242 MeV ray peak of the oxygen daughter Pb is interfered by the 0.238 MeV gamma ray peak of the Th daughter 22Pb. The interference has less than 1% effect on the measurement result. When using a high-resolution semiconductor detector for measurement, there is no such interference. 8.4 The detection limit of this method mainly depends on the detection limit of the gamma spectrometer used. See Appendix A (reference). 272
GB/T 16143—1995
Appendix A
Detection limit of chlorine evolution rate on the surface of buildings (reference)
A1 The detection limit of oxygen evolution rate on the surface of buildings is mainly determined by the detection limit of the gamma spectrometer used. The detection limit is the lowest activity that can be measured by the system under a given confidence level. A2 The lower limit of detection in counts can be expressed as LD(K.+K.)
where LLD-
lower limit of detection;
the upper percentile value of the standard normal variable corresponding to the selected risk probability of misjudging the presence of radioactivity (n); the value corresponding to the pre-selected confidence level (1-) for detecting the presence of radioactivity; α-the standard deviation of the counting statistics of the net sample radioactivity measurement. For various levels of K and β, the values of K are shown in Table AI. Table A1
.0. 02
If the values of α and β are at the same level, such as K-Rs=K. LLD2Ko
A3 The lower limit of detection in counting rate units is the minimum detectable counting rate under given conditions. If the radioactivity of hydrogen in the carbon box is close to the background, the minimum detectable counting rate is ULD-2/2.KVN/t
or: LLD
Minimum detectable yield rate:
Background spectrum measurement time:
Background counts corresponding to a certain full energy peak energy extraction area in the background spectrum. A4 According to the minimum detectable counting rate, the minimum detectable surface hydrogen precipitation rate can be calculated according to formula (1). Additional notes:
This standard was proposed by the Ministry of Health of the People's Republic of China. This standard was drafted by the Beijing Institute of Radiation Health and Protection. The main drafter of this standard is Lin Lianqing.
This standard was entrusted by the Ministry of Health to the technical coordination unit Industrial Hygiene Laboratory of the Ministry of Health for interpretation. (A3)
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