Radioactive Aerosol Standards - Aerosols: Measurement, Dosimetry, and Health Effects - page 532

The highly dispersed aerosols are generated by means of two methods. The irst one consists of
obtaining a primary NaCl aerosol with the particle size of ∼0.005 μm by means of the spontaneous
condensation with a subsequent consolidation of particles up to the required size in the instrument,
whose principle of operation is based on condensing the vapors of given substances on nuclei. The
aerosol-particle sizes are adjusted in this method by varying the instrument mixture temperature or
changing the ration of the air lows with the NaCl particles and the consolidating-substance vapors.
The interaction of the hydrochloric acid vapors with the ammonia vapor low is used in the
second method. As a result of this reaction ammonium chloride aerosol particles are produced.
The size of the generated particles is adjusted by varying the concentration of ammonia vapors in
an excessive concentration of hydrochloric acid vapors, or vice versa. This method is suitable for
obtaining aerosols with ∼0.002-0.2 μm particles.
Aerosols with 0.2-10 μm particles are generated by the method of diffusing monodisperse sus-
pensions. Coarsely dispersed aerosols with particle sizes of 5-200 μm are generated by means of a
disk pulverizer whose principle of operation consists of the following. The original liquid is fed to
the center of a rapidly rotating disk. Under the effect of the centrifugal force the liquid is displaced
toward the disk edge and is ejected from it in the form of monodispersed drops. The particle size is
adjusted by changing the disk rotation speed. The disk pulverizer serves to obtain aerosols with a
liquid dispersed phase from the type VM-4 oil and with a solid dispersed phase from a rosin solu-
tion in alcohol from steric acid melts. The described generators are suitable for obtaining virtually
monodispersed aerosols with particle sizes of 0.002-200 μm.
The disperse composition of highly dispersed aerosols as well as medium-dispersed aerosols up
to 0.5 μm. is determined by means of the diffusion method. For this purpose 13 diffusion batteries
are used with a total channel length of 0.5-5600 m in each battery. The error in measuring the aver-
age size of particles by means of the diffusion method does not exceed 20%.
For certifying suspensions with particles smaller than 1 μm. and also for studying the dis-
persed composition of ammonium chloride aerosols the electron microscope type EM-9 was
used. Suspensions with particles exceeding 1 μm are certiied and the dispersed composition of
coarsely dispersed aerosols is studied by means of optical microscope type MBI-11. Medium dis-
persed aerosol particles in the range of 0.25-10 μm are also determined by means of photoelectric
aerosol-particle counters type AZ-4.
The counted concentration of aerosols is measured after preliminary consolidation is diluted (if
required) with AZ-4 instrument, whose measurement-result MSD does not exceed 20%. Counted
concentrations of particles with diameter 2-4 μm. are measured by means of the sedimentation
method with an error not exceeding 7%. Aerosols with particles sizes exceeding 10 μm are mea-
sured (owing to their rapid sedimentation) by a newly developed technique for determining the
number of particles entrapped in instrument sampler with an error not exceeding 10%.
The GERA-5 installation was used for studying the dispersed composition of aerosols generated
by the GERA-1 and GERA-2 installations and also for metrological investigation of instruments
used in measuring the parameters of inactive aerosols.
The GERA-6 installation serves to generate aerosols and electroaerosols and for measuring
electrical characteristics of aerosols. Its generating unit consists of light-ion and electroaerosol
generators. The light-ion generator is provided with air ionization by means of 239 Pu radionuclides.
The volumetric density of the charge is adjusted by varying the voltage across the generator
electrodes. Pneumatic pulverization of liquid forced through a nozzle and the charging of particles
in the ield of the indexing electrode is used in electroaerosol generator. The volumetric density of
the charge is measured by means of aspiration condenser method based on depositing the charged
aerosol particles in the electric ield of the condenser.
The GERA-6 installation serves to reproduce the volumetric density units of positive and nega-
tive aerosol and aeroion electric charges with a random error characterized by the measurement-
result MSD not exceeding 10% and a nonexcluded systematic error also not exceeding 10%. The
range of reproduced charge volumetric densities amounts to 2 × 10 −11 -2 × 10 −7 C m −3 for light ions