Radioactive Aerosols of Chernobyl Accident - Aerosols: Measurement, Dosimetry, and Health Effects - page 476

in India, and May 5 and 6 in Canada and the United States. On the North American continent,
products of the Chernobyl accident came practically simultaneously from the west and east. All this
conirms that the intermix of aerosols in the horizontal and vertical direction was substantial, and
also that the transfer of activity took place mostly on submicrometer-sized particles. No substantial
amount of radionuclides was detected in the southern hemisphere. Thus, the distribution of aerosols
after the Chernobyl accident took place in the earth's atmosphere according to ideas formulated
earlier based on the examples of volcano eruption and tests of nuclear weapons.
18.4 SAMPLING DEVICES
In the initial period after the accident and during the building of the “Shelter,” measurements of
aerosol characteristics (mainly for radiation reconnaissance and dosimetry) were taken almost con-
tinuously at different sampling points. After the “Shelter” was built, the main goal became the study
of the temporary and spatial evolution of radionuclides and the disperse composition of aerosols,
and also the study of secondary sources of aerosols (wind raising dust, forest ires, etc.). Sampling
became more focused and related to meteorological conditions. For sampling, usually ilter materi-
als AFA-RMP and also packages from different ilter materials were used.
Three-layer packages, consisting of ilter materials FPA-70-0.15, FPA-70-0.25, and FPA-15-1.5,
were used for the simultaneous measurement of the concentration and disperse composition of aero-
sols (with the help of the so-called method of multilayer ilters [MMF], see Chapter 17).
For simultaneously sampling aerosol and gaseous substances with I, Te, Ru, and Cs, sorption-
ilter material SFM-I was used [6]. This material consists of two sorption layers, covered from above
and below with FPP-70-0.2, and the frontal layer of FPP-15-1.5 is only for aerosol deposition. Each
sorption layer was developed from FPP-70-0.3 material, on the iber of which was ine-grained car-
bon with AgNO 3 . The quantity of sorbent was some mg/cm 2 , and the eficiency of molecular iodine
catching was not less than 90%. All used ilter materials and analytical ilters were developed in the
Karpov Institute of Physical Chemistry.
The areas of ilter materials, depending on sampler devices, were in the range of 3 cm 2 -3 m 2 .
Such variety was needed for the operational assessment of radiation contamination of the air, taking
a great number of air samples at different sites and times.
All the sampler devices used, both ground and aircraft, were variations of the measurement
technique widely used in the system of routine and research aerosol monitoring in Russia. All
measurements were provided by means of standard methods of spectrometry and radiometry of
ionizing radiation. In some cases, radiochemical methods were used for the preliminary separation
of studied substances from the samples.
18.5 AEROSOL CHARACTERISTICS IN THE FIRST
HALF YEAR AFTER THE ACCIDENT
The irst aerosol sample of “Chernobyl origin” was taken on April 26 above the western portion of
the European part of the Soviet Union. These data were used for the assessment of the ejection of
radioactive substances from the destroyed fourth block of Chernobyl NPP in the irst day after the
accident. Regular sampling above the breakdown reactor began at night from April 27 and 28 from
aircraft An-24, which belonged to the Ministry of Defense of the USSR. In addition, for the same
purpose, a helicopter was used [7].
Aerosol sampling from the aircraft above the fourth block continued until the beginning of
August 1986 [8]. In Figure 18.2, the values of concentrations of beta-radioactive aerosols for this
period are shown. As we can see from these data, the concentration of radioactive isotopes in the
atmosphere, despite some variations, decreased by 5-6 orders of magnitude after 100 days.
This took place due to decreasing temperature in the destroyed reactor, radioactive decay of short-
lived radionuclides, deactivation of the territory, measures for decreasing dust concentration, etc.