Spatial analysis of natural radionuclides in peat overlying a lithological contact in Co. Donegal, Ireland

The Cronamuck Valley lies on the north-eastern contact of the Barnesmore pluton in Co. Donegal and has been identified as a region with elevated levels of natural radionuclides during a programme of uranium prospecting in the region, conducted in the 1970s. As part of a radiological survey of the area carried out by the Institute of Technology, Sligo the spatial distribution of 238U, 226Ra, 228Ra and 40K in the valley was investigated using geostatistical methods. Radionuclide levels in sixty soil samples were determined using high-resolution gamma-ray spectrometry. 238U levels ranged from 2.7 to 788 Bq kg-1 with a mean value of 79 Bq kg-1, 226Ra levels ranged from 4 to 479 Bq kg-1, with a mean value of 104 Bq kg-1, 228Ra levels ranging from 3 to 135 Bq kg-1 with a mean of 35 Bq kg-1 and 40K activities ranged from 8 to 1088 Bq kg-1 with a mean value of 526 Bq kg-1. Standard deviations for the radionuclide distributions were 149.9, 125.5, 25.1 and 278.1 Bq kg-1, respectively. Isopleth maps of the radionuclide activities were constructed using geostatistical techniques. These indicate strong geological control over soil radionuclide levels in the region, the highest activity values occurring in the granite area, and provide evidence of the immobility of natural radionuclides in organic soils.