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200
North
Nort-West
South
150
100
50
0
January
March
May
July
September
November
FIGURE 18.16
Ratio of activity
137
Cs/
241
Am in aerosols of ground level of atmosphere near the “Shelter”
in 2000.
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
1993
1996
1999
2002
2005
2008
FIGURE 18.17
Average annual aerosol concentration Σβ of radiating nuclides in the area of the northern
(\\\), the northwestern (◻) and the southern (◼) installations in 1993-2008.
half-life time of less than 300 days had practically disappeared by 1993, Σβ comprises
90
Sr +
90
Y,
137
Cs and
241
Pu only.
As it is apparent from Figure 18.17, a systematic decrease with the course of time of beta-active
aerosol carriers of Chernobyl accident products took place. The sharpest drop (approximately, three
times) happened in 1993-1995. In the subsequent 13 years, the concentration in the areas AU-1
and AU-2 did not exceed 0.01 Bq/m
3
and did not descend below 0.005 Bq/m
3
. A more sophisticated
dynamic was observed in the area of AU-3. Here the concentration increased again to 0.03 Bq/m
3
after a drop in 1996-1997. Then in 2001 it again dropped down to 0.005-0.007 Bq/m
3
and stayed at
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