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as the results of [26]. After the irst days of the accident, both aerosol and gaseous forms of
137
Cs were also found [31].
So in the process of monitoring the products of the Chernobyl accident and the new previously
unknown data on physicochemical forms of existence in the atmosphere, some radionuclides such
as Te, Ru, Cs, and I isotopes were found.
18.7 CHARACTERISTICS OF RADIOACTIVE AEROSOLS
NEAR THE EARTH'S SURFACE
Extensive territories were polluted as a result of fallout on the earth's surface of gaseous-aero-
sol products of the accident at Chernobyl NPP. The most polluted territories were close to the
Chernobyl station, where the density of pollution by
137
Cs was more than 3.7 MBq/m
2
(100 Ci/km
2
).
After fallout was stopped from the reactor, the main mechanism of producing aerosol was the sec-
ondary raising (resuspension) from polluted surfaces of the soil, trees, buildings, etc. Concentration
of these secondary aerosols depends on many factors. Among them are meteorological situation,
characteristics of the surfaces (presence of vegetable layer, buildings, surface humidity and type of
soil, intensity of mechanical activity on the surface, presence of the snow layer), physicochemical
properties of pollution, time after forming of primary pollution, etc.
The value that characterizes the danger of radioactive fallout, as a source of aerosols, is the
resuspension coeficient:
C
S
K
r
=
where
C
is aerosol concentration (Bq/m
3
)
S
is the density of pollution (Bq/m
2
)
Because
S
depends only on the decay constant of radionuclides, the value of
C
is in the same way
as informative as
K
r
(in the case of absence of aerosol transport from other regions).
As a result of extensive studies on secondary aerosols of Chernobyl origin, it was found that
•
The concentration of secondary aerosols decreases three to four times approximately lin-
early at a height of up to 15 m above the soil [32].
•
137
Cs and
144
Ce concentrations change in the region by more than an order of magnitude,
and concentration decrease takes place faster than it should according to radioactive decay.
•
The intensity of fallout decreases with increasing distance from roads and sites of agricul-
tural activity [33].
•
Aerosol concentration increases linearly with the speed of wind [34].
•
Values of
K
r
decrease with time after primary fallout according to exponential law with a
time constant of 0.02-0.12/month [35].
•
Strong winds resulted in aerosol transport from the zone of pollution by hundreds of
kilometers, which resulted in an increase in aerosol concentration on remote territories by
tens-hundreds of times [36].
•
The values of
K
r
measured in the same periods, but at different points of Europe, differ
from Chernobyl data in the range of order of magnitude, and variations are accidental in
nature. In 1994,
K
r
was around 2.33 × 10
−10
/month [35].
After completion of the “Shelter” building, measurement of aerosol disperse composition around
the Chernobyl NPP continued at some points in a radius of 0.5-5 km around the reactor. All samples
were taken at a height of 1.5 m from the surface. The MMF was used for sampling [37].
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