40
soil type corresponds to fluvisol, the sod-podzolic to podsoluvizol, and the peat-bog
to histozol.
For investigation of vertical distribution of uranium in soils, the soil sections
were made on undisturbed plots using special stainless steel sampling equipment.
The soils were sampled layer by layer using increments of 5 cm to a depth of
30–40 cm. For investigation of uranium species, the soils were sampled to a depth
of 10 or 20 cm from the soil surface by a metal drill using the “envelope method”
(five subsamples of soil were taken in the corners and in the center of plots). Soil
subsamples from each plot were combined.
In laboratory conditions the soil samples were purified from plant fragments,
carefully homogenized and sieved (2 mm apertures) and dried at a temperature of
not higher than 40 °C.
The content of uranium in the samples was determined by the method of the
radiochemical analysis (MN 1497–2001; IAEA 1989). The samples of soil were
treated in a drying chamber at a temperature of 100–105 °C to constant weight and
ignited in a muffle at a temperature of 600–650 °C. After mineralization the samples
were destroyed using concentrated solutions of HF and HNO 3 and transferred into
HCl solution. Uranium separated and cleaned from other elements using ionexchange column with the AV-17 or Amberlite IRN78 (SUPELCO product) resin.
Uranium converted to nitrates and additionally cleaned from elements of the iron
group by extraction method using tributyl orthophosphoric acid (TBP). For extraction of uranium from tributyl phosphate to aqueous phase, o-xylene has been used.
After reduction of U (VI) to U (IV) by TiCl 3 , uranium was deposited on 0.1 μm pore
size membrane filters using a cerium fluoride coprecipitation technique with 50 μg
of cerium carrier. Identification of alpha-emitted isotopes of uranium was carried
out by Alpha Spectrometer SOLOIST U0450 with ULTRA-AS detector installed
and ruggedized low-background detectors 576 A-600 RV. The efficiency of the
detectors was ~30%. The ratio energy-to-channel was 5.9 and 7.8 keV channel
−1
.
The energy resolution of the detectors was 30–40 keV. The content of uranium in
the soil samples was determined in not less than four parallel subsamples.
Uncertainty of
238
U detection in soil samples was 6–11% depending on radionuclide
activity in the samples. The radiochemical yield of uranium determined using alphaemitting
232
U as a tracer.
The content of total organic matter in the soil samples was determined by ignition of the air-dry soil samples in a muffle furnace at a temperature of 1023 K. Other
soil characteristics were determined by conventional methods (Vorobyova 2006).
Interstitial (pore) solutions were extracted from water-saturated soil samples
using a high-speed SIGMA-4-10 centrifuge (Ovsiannikova et al. 2000). The separated interstitial solutions were passed through a membrane filter with a pore
diameter of 0.45 μm. The soil solutions were concentrated by evaporation in presence of a tracer
232
U and analyzed for uranium content.
The concentration of organic components and the ratio of humic acid (HA) and
fulvic acid (FA) fractions in soil solutions were determined from the optical density
of HA and FA solutions after separation of organic components into fractions
(Orlov 1990).
G. A. Sokolik et al.
soil type corresponds to fluvisol, the sod-podzolic to podsoluvizol, and the peat-bog
to histozol.
For investigation of vertical distribution of uranium in soils, the soil sections
were made on undisturbed plots using special stainless steel sampling equipment.
The soils were sampled layer by layer using increments of 5 cm to a depth of
30–40 cm. For investigation of uranium species, the soils were sampled to a depth
of 10 or 20 cm from the soil surface by a metal drill using the “envelope method”
(five subsamples of soil were taken in the corners and in the center of plots). Soil
subsamples from each plot were combined.
In laboratory conditions the soil samples were purified from plant fragments,
carefully homogenized and sieved (2 mm apertures) and dried at a temperature of
not higher than 40 °C.
The content of uranium in the samples was determined by the method of the
radiochemical analysis (MN 1497–2001; IAEA 1989). The samples of soil were
treated in a drying chamber at a temperature of 100–105 °C to constant weight and
ignited in a muffle at a temperature of 600–650 °C. After mineralization the samples
were destroyed using concentrated solutions of HF and HNO 3 and transferred into
HCl solution. Uranium separated and cleaned from other elements using ionexchange column with the AV-17 or Amberlite IRN78 (SUPELCO product) resin.
Uranium converted to nitrates and additionally cleaned from elements of the iron
group by extraction method using tributyl orthophosphoric acid (TBP). For extraction of uranium from tributyl phosphate to aqueous phase, o-xylene has been used.
After reduction of U (VI) to U (IV) by TiCl 3 , uranium was deposited on 0.1 μm pore
size membrane filters using a cerium fluoride coprecipitation technique with 50 μg
of cerium carrier. Identification of alpha-emitted isotopes of uranium was carried
out by Alpha Spectrometer SOLOIST U0450 with ULTRA-AS detector installed
and ruggedized low-background detectors 576 A-600 RV. The efficiency of the
detectors was ~30%. The ratio energy-to-channel was 5.9 and 7.8 keV channel
−1
.
The energy resolution of the detectors was 30–40 keV. The content of uranium in
the soil samples was determined in not less than four parallel subsamples.
Uncertainty of
238
U detection in soil samples was 6–11% depending on radionuclide
activity in the samples. The radiochemical yield of uranium determined using alphaemitting
232
U as a tracer.
The content of total organic matter in the soil samples was determined by ignition of the air-dry soil samples in a muffle furnace at a temperature of 1023 K. Other
soil characteristics were determined by conventional methods (Vorobyova 2006).
Interstitial (pore) solutions were extracted from water-saturated soil samples
using a high-speed SIGMA-4-10 centrifuge (Ovsiannikova et al. 2000). The separated interstitial solutions were passed through a membrane filter with a pore
diameter of 0.45 μm. The soil solutions were concentrated by evaporation in presence of a tracer
232
U and analyzed for uranium content.
The concentration of organic components and the ratio of humic acid (HA) and
fulvic acid (FA) fractions in soil solutions were determined from the optical density
of HA and FA solutions after separation of organic components into fractions
(Orlov 1990).
G. A. Sokolik et al.