Radioactive Aerosols of Chernobyl Accident - Aerosols: Measurement, Dosimetry, and Health Effects - page 479

4

Zr-95
Nb-95
Ru-103
Ru-106
I-131
Cs-137
Ba-140
La-140
Ce-141

3

2

1

0

-1

-2

8 14 15 16 17 19

May 1986

FIGURE 18.3 Concentration of the aerosols containing gamma-radioactivity above the fourth block of the
Chernobyl NPP in May 1986.

distance of 15 km from the reactor, the portion of fuel particles depending on azimuth were from
50% to 100%. In the far zone, including beyond borders of the USSR, to the contrary, particles of
fuel origin were measured only in a small number of cases (see, e.g., [12]).
Radioactive aerosol particle sizes directly above the destroyed reactor were measured for the irst
time on May 14, 1986. For this purpose, the gondola of aircraft An-24 was supplied with a package
of ilters for disperse analysis composition.
It was shown that the smallest size had particle carriers of 131 I, 132 Te, and 103,106 Ru. The activity
median aerodynamic diameter (AMAD) of aerosols was 0.3-0.4 μm with geometric standard devia-
tion σ = 2.3-2.5. The sizes of carriers of refractory radionuclides Zr, Nb, La, and Ce were larger:
AMAD = 0.7 (σ = 1.6-1.8). On the same carriers, 134, 137 Cs were discovered. In some countries of
the northern hemisphere, at the beginning of May [13-19] practically similar values of AMAD of
radionuclides carriers of Chernobyl origin were measured. In these measurements, different types
of impactors were used.
In the summer of 1986, the surface of the soil, buildings, vegetable layer, rods, etc., polluted with
primary fallout became comparable to or even more important sources of contamination closest to
the surface layer of the atmosphere. In this period, it was impossible even quantitatively to describe
all mechanisms of forming aerosols, because in the atomic station area and around a 30 km zone
very intense deactivation took place, often resulting in aerosol formation. An additional source was
the intense transport movement near the Chernobyl NPP.
Figure 18.4 presents the dynamics of aerosol concentration in the summer of 1986.
This correlation was based on measurements of the total gamma-activity of samples provided by
scientists of Khlopin Radium Institute from military vehicles, which traveled over Chernobyl NPP
by perimeter [20]. As we can see, average aerosol concentrations near the station in the background
of substantial variations were comparable with measured concentrations above the destroyed reactor
in the second half of May (Figure 18.2).
Measurements provided in July-September 1986 demonstrated that practically all radionuclides
were disposed on the same particle carriers. AMAD values of aerosols, averaging for the period
of observation, were 2.95 ± 0.60 μm for 95 Zr, 2.89 ± 0.37 μm for 95 Nb, 2.93 ± 0.62 μm for 134 Cs and