Aim: The study focuses on the dynamic changes in the surface concentration of cesium 137Cs in soil samples from the Opole province, which have been measured for nearly thirty years since the Chernobyl disaster.

Introduction: In 1986 there was an accident in the reactor at the Chernobyl Nuclear Power Plant in Ukraine which caused an uncontrolled release of radioactive substances. The Opole province in Poland is one of the areas which suffered the greatest accumulation of surface contamination with radionuclides. As a result of rainy weather in this area during the transition of the radioactive cloud, various radioisotopes remained in the environmental components.

Project and methods: The condition of the microenvironment is very important for the assessment of changes in 137Cs surface concentration for the soil taken from the same sampling point, so the microenvironment cannot be distorted or changed by human activity. The method of sampling must be fixed and repeatable, and the preparation of samples for measurement in the laboratory should be conducted according to strict procedures. After proper preparation, samples are measured spectrometrically on a HPGe semiconductor detector and then an analysis of gamma radiation is done with Genie-2000 software.

Results: During the gamma-radiation spectrum analysis of the soil samples, the surface concentration of natural isotopes 40K, 226Ra and 228Ac and of artificial isotopes 134Cs (reported till 1996) and 137Cs (reported to the present) was detected. The article presents the results of 137Cs surface concentration measurements, as well as the concentration of 40K, 226Ra and 228Ac natural radionuclides in the soil of the Opole province from samples measured in the period 1988–2014.

Conclusions: As expected, for the nearly 30 years since the failure of the Chernobyl NPP, the concentration of 137Cs in the soil has been gradually decreasing as a result of isotope decay and its penetration into the deeper layers of the soil. On the other hand, the concentration of natural radionuclides is at a similar level for the same sampling points. In the future it will be useful to continue measuring to see how the surface concentration of 137Cs for soil is decreasing and when its value will be below the detection threshold. It would be also good to select several sampling points (also in the Opole province) in order to investigate how 137Cs has penetrated into the deeper layers of the soil (a 25-cm layer).

Keywords: reactor accident, Chernobyl, soil radioactivity, 137Cs, 40K, 226Ra, 228Ac, 228Th, Opole province

Type of article: case study