Eotvos Lorand Geophysical Institute of Hungary Budapest, Hungary
5. FIELD MEASURING POSSIBILITIES
In addition to the laboratory analysis a car mounted radioactive gamma spectra measuring system was established in the Geophysical Institute. It is also suitable for the measurement of the natural (U-Ra, Th, K-40) and artificial (e.g. Cs-137 of Cheraobyl) gamma spectra in field circumstances.
The measuring car is a four-wheel-driven air-conditioned van. The basis of the measuring system is a portable, liquid nitrogen cooled, high purity germanium semiconductor detector. By the help of the built-in professional computer system, there is the possibility of the prompt analysis and report of the locally obtained spectra. This is independent of the electric network. In case of nuclear accidents this system can also work as a monitoring unit.
F/G. 5. Cs -137. Estimated intensity values (nGy/h) - 1987-88. 1) 0- 40, 2) 40-80, 3) 80-170.
FIG. 6. Distribution ofCs-137 (nGy/h) in the flood-plain sediments of Hungary. (Sampling interval:
0-10 cm). 1) <1.0, 2) 1.0-1.78, 3) >1.78, 4) catchment basins.
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Fig. 7. Distribution of Cs-137 (nGy/h) in the flood-plain sediments of Hungary. (Sampling interval:
50-60 cm). 1) <0.7, 2) 0.7-1.5, 3) >1.5, 4) catchment basins.
6. CONCLUSIONS
The prime factor in low density surveys determining the geochemical pattern in Hungary is the surface predominance of young (Pleistocene or Miocene) clastic sediments over the older formations and basement rocks. The geochemical method used has the advantage to give regional surface background data outlining at the same time the areas of possible contamination. It also has the disadvantage of not being contrasty enough to differentiate geologically dissimilar areas.
At certain regions, the rate of sedimentation was fairly fast: the environmental effects of ore mining in Transylvania and in southern Slovakia as well as those of the heavy industry in northern Hungary can be observed even in the lower (50-60 cm) samples.
For the radioelements investigated highly reliable abundance data can be obtained for the surface environment. This approach gives no definite contrast in the distribution of the radioelements, only areas covered by the andesitic rocks can be outlined.
Catchment basins with anomalous values of e.g. Pb, Zn, As and Cd have been delineated but potentially dangerous concentration of radioelements have not so far been found in the investigated sediments.
ACKNOWLEDGEMENTS
This publication is partly sponsored by the U.S.-Hungarian Science and Technology Joint Fund in co-operation with the U. S. Geological Survey and the Hungarian Geological Survey under Project: J. F. No. 415.
REFERENCES
[1] DARNLEY, A.G., International geochemical mapping: a new global project, Journal of Geochemical Exploration (1990) 39, 1-3.
[2] XIE XUEJING, Some problems, strategical and tactical, in international geochemical mapping, Journal of Geochemical Exploration (1990) 39, 15-33.
[3] DEMETRIADES, A., OTTESEN, R.T., LOCUTURA, J. (eds.), Geochemical Mapping of Western Europe towards the Year 2000, Pilot Project Report, NGU Report (1990) 90-105, 9 pages and 10 appendices.
[4] DARNLEY, A.G. (CANADA), BJORKLUND, A. (FINLAND), BOLVIKEN, B.
(NORWAY), GUSTAVSSON, N. (FINLAND), KOVAL, P.V. (RUSSIA), PLANT, J. A.
(UK), STEENFELT, A. (GREENLAND), TAUCHID, M. (IAEA), XIE XUEJING (CHINA), with contributions by Garett, R.G. and Hall, G.E.M. (Canada), A Global Geochemical Database for Environmental and Resource Management, Recommendations for International Geochemical Mapping, Final Report of IGCP Project 259, UNESCO Publishing (1995) Earth Sciences 19.
[5] ODOR, L., HORVATH, I., FUGEDI, U., Low-density geochemical survey of Hungary.
Environmental Geochemical Baseline Mapping in Europe, Abstracts (1996) May 21-24,1996 Spisska Nova Ves, Slovakia.
[6] WEBER, B., Az ur£n es torium eloszlasa az Eszaki Kozephegyseg foldtani kepzodmenyeiben legi gamma-spektrometriai meresek alapjan, The distribution of U and Th in the geological formations of northern Hungary on the basis of air-borne gamma spectrometric measurements, Foldtani Kozlony, (1975) 105/3., 309-319 (in Hungarian).
JeftBLA^KJ
133
XA9745943
SPATIAL DISTRIBUTION OF
40K,
228Ra, ^Ra, ^U AND
137Cs
IN SURFACE SOIL LAYER OBSERVED AT SMALL AREAS D. BARISIC, S. LULIC
Ministry of Agriculture and Forestry Zagreb, Croatia
Abstract
The main goal of this study is to give a more detailed insight into spatial radionuclide distribution in soils.
It had been necessary in order to plan the future soil sampling procedure that would assure the representative soil samples for brother areas that are usually covered by in situ gamma-spectrometry measurements or aerial gamma-ray spectrometry. The spatial distributions of natural radionuclides and 137Cs activity in surface soil layer were studied in five regular grids, consisting of 9 points each. The distances between sampled points were 30 cm (A grid), 2.45 m (B grid), 19.5 m (C grid), 156 m (D grid) and 312 m (E grid), respectively. Soil samples were dominantly taken at agricultural ploughed fields from areas of ca. 315 cm2 (circle of a. 20 cm diameter), from surface up to 15 cm depth. The fraction of air-dried material that passed through a 0.5 mm sieve was reduced by quartering and dried at 105 °C to the constant weight. The activities of *)K, ^Ra, 226Ra, 238U and 137Cs were determined by the gamma-spectrometry method. The highest variations of "°K activities are found in the E grid: 312-573 Bq/kg, the lowest are in the B grid: 318-338 Bq/kg. "°K activities are found in ranges of 310-408 Bq/kg in 9 samples taken in the A grid, in an area of less than 0.65 m2. Very high variations in 228Ra activities are found in the E grid: 22-32 Bq/kg, while the lowest are in the A and B grid (22-24 Bq/kg). A very similar range of 226Ra and ^U activities are found in all observed grids; the lowest are in the A, B, and C grid (23-24 or 25 Bq/kg for 226Ra, 22-24 or 25 Bq/kg for 238U, respectively); the highest are in the D and E grid (21 or 22-31 Bq/kg for 226Ra, 23-30 Bq/kg for 238U, respectively).
137Cs activities are found in a range of 17-37 Bq/kg in the E grid, a very high range was observed in the B grid (18-31 Bq/kg) and the lowest range (20-22 Bq/kg) in the A grid. It seems that variations of potassium concentration could be very high in areas of less than one square metre. The Average of *°K activity in 38 taken samples was 368 Bq/kg: 359 in the A, 327 in the B, 340 in the C, 412 in the D and 414 Bq/kg in the E grid. Distribution of other observed natural radionuclides is relatively homogenous in areas which covered approximately 1500 m2. The representative soil sample must cover the broader area to provide data that could be compared with data collected by aerial gamma-spectrometry. The average sample on each locality must be prepared from several point samples. It seems that the central point and four points, each at approximately 50-100 m N, S, E, and W from the central point, could be enough.
1. INTRODUCTION
The UNESCO International Geological Correlation Programme (IGCP) Project 259 — International Geochemical Mapping (IGM) was launched to address the problem of distribution of chemical elements, including radioactive ones, in the earth's surface materials. Airborne gamma survey has been applied and recommended for radiometric mapping of most national territories.
Current researches are mostly based on aerial gamma-ray spectrometry measurements and data conversion into radionuclide concentration in soil. In the context of IGM project, the main function of ground gamma-ray spectrometry measurements is to provide a link between data gathered by conventional geochemical sampling and related airborne gamma-ray profiles. Many useful details
about aerial gamma-ray spectrometry measurements have been published [1, 2], and regional
geochemical maps of some primordial radionuclides are presented elsewhere.Radiation from soil is the most important contributor to the external terrestrial radiation because bedrock is covered with soil in most areas of the world. It is a well-known fact that the