SU1644055A1 - Aerosol characteristics determination method - Google Patents

Description

(21) 4732760/25 (22) 08.22.89 (46) 04.23.91. Bul № 15 (72) P.P. Poluektov, G.V. Nadyrnykh, V.G. Shatunov, A.N. Semykin, V.A. Maslnkin and G.Yu. Kolomeytsev (53) 621.387.424 (088.8)

(56) Muraveva S. I., Kaznina N. I., Prokhorova E. K, Handbook for the Control of Harmful Substances in the Air. - M .: Himi, 1988, p. 28. US Patent ISfe 4277682, cl. G 01 T 1/18, 1981.

Bad VV and others. The study of the dispersion composition of aerosols in the emissions of nuclear power plants with RBMK.- In coll .: Radiation safety and protection of nuclear power plants / Ed. Yu A Egorova - M .: Energoizdat, 1985, № 9, p. 282.

(54) METHOD FOR DETERMINING THE CHARACTERISTICS OF AEROSOLS

(57) The invention relates to methods for controlling the dispersed composition and properties of aerosols and can be used to quickly determine the dispersion and radioactivity of aerosols during emergency restoration works in the zone of radioactive contamination. The aim of the invention is to determine the radioactive and inactive components of the aerosol fractions. To do this, measure the size and electric charge of each aerosol particle, as well as the concentration of ions in the sampled gas. The measurement results and the dependence of the electric charge induced on the aerosol particle on the type of radioactive decay determine the level of radioactivity for each particle 1

The invention relates to methods for monitoring the dispersion composition and properties of aerosols and can be used to quickly determine the dispersion and radioactivity of aerosols during emergency restoration work in the zone of radioactive contamination.

The purpose of the invention is to obtain additional information about the radioactivity levels of individual aerosol particles and, therefore, in determining the radioactive and reactive components of aerosol fractions.

The charge and size of each aerosol particle and the concentration of ions in the sampled gas are measured, and the radioactive component of the aerosol fraction is determined by the ratio

A K g p.

where A is the radioactivity of the aerosol particle;

q is the charge of a particle;

n is the concentration of negative ions in the gas;

K is the coefficient depending on the particle size and type; radioactive decay.

The proposed method is based on that. that during radioactive decays in the substance of aerosols, electrons are knocked out of the surface layer of particles. As a result of this process, radioactive aerosol particles accumulate

About 4 О About JV SL

a positive charge, the value of which depends on the radioactivity level of the aerosol particle and the type of radioactive decay in the particle matter.1 On the other hand, due to the larger diffusion coefficient of negative ions in the gas, negative charge accumulates on aerosol particles. Therefore, in the case of radioactive aerosols, it is necessary to take into account both processes, i.e., the process of aerosol charging due to radioactive decays and the process of their diffusion discharge. The flow of charges emitted from the particle due to radioactive decays is compensated by the ion flow from the environment, as a result of which stabilization of the positive charge of the radioactive aerosol particle is achieved. The particle charge increases linearly with activity on the aerosol particle; on the other hand, the dependence of the charge on the concentration of negative ions in the atmosphere is inversely proportional. Since the number of electrons emitted by a particle during each decay depends on the size of the particle, there is a weak dependence of the charge of the radioactive particle on its size. The concentration of ions in the surrounding gas is formed as a result of the ionization of the gas under the action of radiation of radioactive aerosols, external ionizing radiation (for example, radiation of contaminated soil), as well as the drain of ions on the aerosols and nearby surfaces; since the activity (A) of the aerosol particle is proportional to the concentration of ions, the latter is to be measured according to this method.

The drawing shows a block diagram of an apparatus for carrying out the method.

The device contains a particle charge meter 1, a particle size meter 2, a gas concentration meter 3, a synchronization unit 4, an information processing unit 5 and a sampling device including a gas flow booster and a sampling channel 7.

The device works as follows.

A sample of the gas containing the analyzed aerosols, with the help of the booster 6 of the gas flow through the sampling channel 7, is successively fed to the charge meter 1 and the particle size 2. Signals from meters 1 and 2 are fed to block 4 of synchronization, in which the signal from meter 1 of particle charges is delayed by a time equal to the time spent by the particles of the distance between two meters.

From the output of block 4 of synchronization, a signal containing information about the size and charge of each aerosol particle is fed to the input of block 5 of information processing, where

From these data, taking into account the magnitude of the signal from the ion concentration meter in gas 3, the level of radioactivity of the particles is calculated.

The form of implementation of the meter 2 particle sizes can be different, for example, optical sensors of various types can be used. The main restriction on the design of meters imposes a condition for their compatibility

5 speeds of pumping sample and speed. The sampling path between gauges 1 and 2 should be as short as possible and should not change the dispersion composition of aerosols.

0 in the sample.

Example. The method was implemented in a device containing an inductive meter 1 of particle charges with an annular sensor 0.5 mm thick, the diameter of the sampling channel 5 in the sensor 1 mm. The signals from the sensor were amplified using an electrometric amplifier and fed to an analog-to-digital converter (ADC). The minimum logged value for the order was 150 elementary charges. The meter 2 particle size was made on the basis of the known scheme of the optical particle counter. The sensor was a resonator of a non-laser (output

5 power of 2 mW), through which a sample of gas was pumped out of the particle charge meter 1 1. The light scattered by particles into the region of small angles (5 °) relative to the optical axis of the laser, using

0 focusing lens on a photodetector (PMT). The signals from the photodetector were processed using a logarithmic amplifier and fed to the ADC. The meter provided registration of particles in the range of 5–3–10 µm in size (in diameter) with a maximum aerosol concentration of not more than 10b particles / l. At high aerosol concentrations, the sensor is pre-calibrated.

0 dilution of the sample.

The sensor of the particle charge meter was installed at the minimum possible distance from the measuring volume of the particle size meter (5 mm).

5 Digital signals from both ADCs corresponding to the maximum signal levels of the detectors were applied to a synchronization unit, which is a buffer memory that provides a signal delay from the meter.

particle charges for a time of 0.5 ms, corresponding to the transit time of particles between the sensors. The issuance of a complete digital code from the synchronization unit to the signal processing unit, which was used for the DVK-3 microcomputer, was performed at the moment the data were received from the particle size meter.

An ion concentration meter in a gas was made on the basis of an ionization chamber. A part of the sampled gas was passed through an aerosol filter (in order to exclude the effect of the radioactivity of the particles on the meter readings) and was fed into the ionization chamber. The current signal from the camera was amplified by an electrometric amplifier and fed to an ADC. A digital code with an ADC corresponding to the concentration of ions in the gas was periodically read into the information processing unit (1 time in 5-10 s).

The coefficient K was determined by calibrating the device on aerosols containing known quantities of ft and y-active isotopes (salt

131

radioactive aerosols containing J or S). The radioactivity of the particles was controlled after their fractionation in the importer by an autoradiographic method. The operability of the device was tested on a series of aerosol samples containing particles with different levels of radioactivity. The results obtained by the proposed method were checked by independent methods — by measuring the total radioactivity of individual aerosol fractions and autoradiographically. Experiments showed a good agreement between the results obtained by various methods in cases where there was an uneven distribution of radioactivity among particles (i.e., when a relatively small number of particles with a high level of radioactivity were contained in the aerosol sample). In the case of a uniform distribution of radioactivity in the particles and a low specific activity of the particles, the proposed method gave underestimated results.

This is due to the fact that the minimum measurable level of radioactivity in

This device variant has Bq / particle. Therefore, particles that had lower levels of radioactivity were not taken into account in the results obtained by the proposed method. However, this limit can be lowered by increasing the sensitivity of the charge and particle size gauges.

Thus, the use of the proposed method allows rapid (the processing time of a signal from a single particle is 10 ms, the total time for obtaining information on the dispersed composition and radioactivity of particles is determined by the concentration of aerosols and averages 0.5-10 minutes) to determine the level of radioactivity of aerosols . Since there is information on its size for each particle, it is possible to calculate the specific activities of particles in different size ranges, determine the proportion of radioactive particles among the total amount of aerosols, etc. The method can be used for the operative control of radioactive air pollution during emergency -recovery, during radiation survey of the area, to assess the amount and form of radioactive substances entering the lungs of personnel,

engaged in works, etc.

Claims (1)

Claims A method for determining the characteristics of aerosols, including sampling a gas and measuring the radioactivity of an aerosol in a sample, characterized in that, to determine the radioactive and inactive component aerosol fractions, the charge and size of each aerosol particle are measured, the concentration of ions in the sample taken gas, and the radioactive component A of the aerosol fraction is determined by the ratio A q q p, where q is the charge of a particle; n is the concentration of negative ions in the gas; K is a coefficient depending on the particle size and decay type. Test tsarosol