Preliminary studies on the spatial distribution of artificial ¹³⁷Cs and natural gamma radionuclides in the region of the Ojców National Park, Poland

The aim of the research is to obtain preliminary information about the spatial distribution of gamma radionuclides in the soils taken from the Ojców National Park with emphasis on the behaviour of artificial radionuclides, with ¹³⁷Cs as a representative. The natural radionuclides ⁴⁰K, ²²⁶Ra (uranium series), and ²²⁸Th (thorium series), which are considered as background radiation, were also determined. In total, 18 soil samples were collected during the summer periods in 2015-2017, while the sampling points were selected with respect to differences in rainfall and local topography gradient. The method was based on gamma-ray spectrometry performed on high-purity germanium (HPGe) gamma detector (relative efficiency 34%). ¹³⁷Cs was mostly deposited in the top soil layers, with activity in the range of 27.9÷586.6 Bq·kg^-1. We found strong positive correlation of the ¹³⁷Cs activity with the soil organic matter content, and at the same time, its dependence on the rainfall amount. Consequently, the soil types and local climate can control the spatial distribution of 137Cs on a small spatial scale. The quantity of natural radionuclides was highly similar in all samples with the following mean values: 38.0 Bq·kg^-1for ²²⁸Th, 33.1 Bq·kg^-1for ²²⁶Ra, and 479.9 Bq·kg^-1for ⁴⁰K.