Koncentracje cezu w Polsce

Ryszard Strzelecki, Stanisław Wołkowicz, Paweł Lewandowski



Studies on gamma-ray spectrometry covering the territory of Poland have been started in 1989 by the Polish Geological Institute under the national programme entitled "Protection of the Lithosphere". The main purposes of this survey are: - mapping of the cesium pollution after the ChernobyI accident; - compilation of individual radioelements distribution maps which are necessary to prepare the radon risk maps and to calculate effective dose equivalent; - estimation of the pollution of the recent river sediments by U and Ra, as the result of dropping of polluted mine-waters from the coal mines of the Upper Silesia Coal Basin. The accident at the nuclear plant in Chernobyl, disturbed very significantly the terrestrial gamma-ray radiation over a big area of Europe. The spectrometric survey conducted by the Polish Geological Institute in 1986 in the Sudetes directly before as well as after the Chernobyl accident, delivered very interesting and unique at the European scale experimental data. The results of the above mentioned field works have been used among others to work out the effective methodology of determination of in situ, total concentration of Cs isotopes. This method determines the gamma radiation dose rate related to the above mentioned radionuclides expressed as the difference between the measured total dose rate and the total dose rate from the natural gamma radiation emitters. Measurements were made along N-S oriented profile lines spaced 15' (about 17 km), each 1,000 m. In the case of TC energy of the value higher than 5,500 counts/2 minutes, measurements were made each 500 m in order to recognize the anomalies more precisely. Measurements were made using a hand held type gamma- ray spectrometer, model GS-256 produced by "Geofizyka" Brno with 3" x 3" Na (TI) detector. Two minute time of measurement was used. The detector was placed 1.5 m above the terrain in order to eliminate the influence of the tarrain geometry. The field works were carried out in the period from June till December, 1992. Out of 20 000 measurements made during this period, 19 528 was used for the map compilation. Data was collected in the Dbase system. For the map compilation the Surfer computer programme and GIS Arc/Info system were applied. Calculations were made using the SPSSIPC statistical system. Results of the field works indicate that more than 90% of the territory is characterized by low Cs concentration varying from 0 to 8 kBq/m2. The average Cs concentration calculated for Poland is 4.67 kBq/m2 (Fig. 1) with standard variation of 5.51 kBq/m2. Taking into consideration the assumption, that the average value plus the value of 2 standard variations determines the anomal concentration, 15 kBq/m2 isoline is considered as indicating the anomalies. The highest Cs pollution was noted from SW Poland (see cover photo), from E part of the Fore-Sudetes Monocline and from the Silesia Lowlands. These anomal concentrations are a part of zone characterized by higher Cs pollution running in SW-NE direction from the Kłodzko Valley area (Czech border) to the region of Warsaw. Three anomal areas can be distinguished within this zone, mainly: Opole region (surface of 4500 km2), vicinity of Radomsko and vicinity of Warsaw. The highest values of Cs pollution up to 96 kBq/m2 has been noted from the Opole region. Smaller anomalies are also observed from: - southern Poland - western Carpathians, Cs concentration up to 25 kBq/m2 - small parts of the Sudetes, Cs concentration up to 25 kBq/m2 - few anomal areas in eastern Poland, Cs concentration up to 50 kBq/m2 and their continuation in NW direction - an anomaly of Warsaw - separate Cs concentrations (15 kBq/m2) in Szczecin voivodship (NW Poland) and Elbląg voivodship (N Poland). The statistical analysis of the data did not show any correlation between Cs concentration and the type of soil and vegetation cover. Therefore it can be stated, that the meteorological conditions played the main role in the distribution of Cs pollution in Poland. Statistical frequency (Fig. 3A - F) distribution of Cs for separate voivodships characterized by higher Cs pollution show strong perturbation, positive skewness and multi-modality what suggest the multi-phase period of the deposition of pollutants. Unfortunately, lack of meteorological maps for the period of 10 days after the accident does not allow to relate the meteorological elements to the measured cesium concentration.