12.3.3 Soil Radioactivity After Chernobyl
Top soil (0–5 cm) was sampled from each NERSN station and analysed annually
for gamma-ray emitting radionuclides in ERL. Natural radionuclides like
40
K,
226
Ra,
234
Th,
214
Pb,
214
Bi,
228
Ac,
212
Pb,
210
Pb,
212
Bi,
208
Tl,
235
U, cosmogenic radionuclide
7
Be
and artificial radionuclides, mainly
137
Cs, were determined by direct gamma-ray
spectrometry by counting around 150 g on a HPGe detector. More than 300 soil
samples from NERSN were measured and the range of data obtained for
137
Cs
between 1986 and 1992 is from 2 Bq/kg to 2133 Bq/kg (see Fig. 12.2).
Apart from regular measurements of the soil samples from NERSN stations,
some hotspots were identified based on measurements of samples collected for
various other research, for example Semenic Mountains in the SW part of Romania
(1816 Bq/kg dry
137
Cs) and Axente Sever (Sibiu county) with 660 Bq/kg dry
137 Cs.
The highest level measured by ERL was 4 kBq/kg dry
137 Cs (or equivalent of 48.5
kBq/m
2 of
137 Cs), in soil sampled in 1993 at the Toaca mountain station (1907 m
altitude) (see Table 12.2).
Other hotspots for Romanian soils, having more than 50 kBq/m
2 , were reported
in the extensive study on migration of
137
Cs in the Romanian soils (Toro and
Galeriu 1991a, b), mainly for the SW part of Romania (Novaci, Sadova Noua etc).
Compared with the time dependence of deposition rates (which depend on the
rate of unavailability of Caesium for resuspension), top soil concentrations decrease
more slowly with time by migration processes or washout. Based on available
measurements a total of about 1.7–2.7 PBq was estimated for the
137 Cs deposited on
Romania’s territory. This figure could be improved by increasing the density of the
sampling points.
Table 12.1 Comparison of
deposition velocities (cm s
À1
)
Radionuclide
Romanian stations
Neuherberg
137
Cs
0.22 Æ 0.16
0.27
134
Cs
0.18 Æ 0.13
136
Cs
0.19 Æ 0.14
141
Ce
1.6 Æ 1.1
144
Ce
1.6 Æ 1.2
95
Zr
2.8 Æ 2.6
110m Ag
0.33 Æ 0.07
0.37
131
I
0.35 Æ 0.37
0.13
132
Te
0.16 Æ 0.23
0.08
129m Te
0.21 Æ 0.19
140
Ba
0.34 Æ 0.33
0.15
103
Ru
0.33 Æ 0.23
0.08
106
Ru
0.29 Æ 0.21
0.1
125
Sb
0.35 Æ 0.18
0.07
212
C. Dovlete et al.
Top soil (0–5 cm) was sampled from each NERSN station and analysed annually
for gamma-ray emitting radionuclides in ERL. Natural radionuclides like
40
K,
226
Ra,
234
Th,
214
Pb,
214
Bi,
228
Ac,
212
Pb,
210
Pb,
212
Bi,
208
Tl,
235
U, cosmogenic radionuclide
7
Be
and artificial radionuclides, mainly
137
Cs, were determined by direct gamma-ray
spectrometry by counting around 150 g on a HPGe detector. More than 300 soil
samples from NERSN were measured and the range of data obtained for
137
Cs
between 1986 and 1992 is from 2 Bq/kg to 2133 Bq/kg (see Fig. 12.2).
Apart from regular measurements of the soil samples from NERSN stations,
some hotspots were identified based on measurements of samples collected for
various other research, for example Semenic Mountains in the SW part of Romania
(1816 Bq/kg dry
137
Cs) and Axente Sever (Sibiu county) with 660 Bq/kg dry
137 Cs.
The highest level measured by ERL was 4 kBq/kg dry
137 Cs (or equivalent of 48.5
kBq/m
2 of
137 Cs), in soil sampled in 1993 at the Toaca mountain station (1907 m
altitude) (see Table 12.2).
Other hotspots for Romanian soils, having more than 50 kBq/m
2 , were reported
in the extensive study on migration of
137
Cs in the Romanian soils (Toro and
Galeriu 1991a, b), mainly for the SW part of Romania (Novaci, Sadova Noua etc).
Compared with the time dependence of deposition rates (which depend on the
rate of unavailability of Caesium for resuspension), top soil concentrations decrease
more slowly with time by migration processes or washout. Based on available
measurements a total of about 1.7–2.7 PBq was estimated for the
137 Cs deposited on
Romania’s territory. This figure could be improved by increasing the density of the
sampling points.
Table 12.1 Comparison of
deposition velocities (cm s
À1
)
Radionuclide
Romanian stations
Neuherberg
137
Cs
0.22 Æ 0.16
0.27
134
Cs
0.18 Æ 0.13
136
Cs
0.19 Æ 0.14
141
Ce
1.6 Æ 1.1
144
Ce
1.6 Æ 1.2
95
Zr
2.8 Æ 2.6
110m Ag
0.33 Æ 0.07
0.37
131
I
0.35 Æ 0.37
0.13
132
Te
0.16 Æ 0.23
0.08
129m Te
0.21 Æ 0.19
140
Ba
0.34 Æ 0.33
0.15
103
Ru
0.33 Æ 0.23
0.08
106
Ru
0.29 Æ 0.21
0.1
125
Sb
0.35 Æ 0.18
0.07
212
C. Dovlete et al.