In this research work, the activity concentrations of 40K, 226Ra and 232Th in soil and rice samples from Kogi State of Nigeria have been determined. Soil and rice samples taken from rice producing areas Lokoja and Ibaji in Kogi were analysed by means of Gamma-ray Spectroscopy using NaI(Tl) detector. The mean activity concentrations of 40K, 226Ra and 232Th in Lokoja soil samples were found to be 508.86 ± 54.02, 41.27 ± 9.31 and 18.90 ± 4.21 Bqkg-1 respectively; those of Lokoja rice samples were 41.15 ± 5.41, 12.73 ± 3.77 and 10.36 ± 1.72 Bqkg-1 respectively. The concentrations of the three radionuclides for Lokoja market rice sample were 38.00 ± 10.23, 7.45 ± 2.37 and 9.08 ± 3.04Bqkg-1 respectively. Mean activity concentrations in Ibaji soil samples were 639.52 ± 64.97, 9.81 ± 3.13 and 11.95 ± 3.79 Bqkg-1 respectively; those of Ibaji rice samples were 61.01 ± 18.05, 7.28 ± 0.83 and 9.89 ± 2.59 Bqkg-1 respectively. The concentrations for Ibaji market rice sample were 38.71 ± 10.25, 7.94 ± 2.27 and 8.65 ± 2.01 Bqkg- 1 respectively. These results are fairly higher than those of other literature [3,12,4]; these could be due to differences in agricultural practices and geology of the areas. Also, when compared with the world mean values of 400, 35 and 30 Bqkg-1 respectively[16], the results showed significantly high values for 40Kand 226Ra in Lokoja soil samples and 40K in Ibaji soil samples. This is due to the mechanised rice cultivation system and agricultural practices of fertilizer application and artificial irrigation method employed in Lokoja and Ibaji farms. Also, the predominant presence of mountains of sedimentary and igneous origins in Lokoja, as against the lowland nature of Ibaji area, contributed to the high concentration levels in Lokoja soil samples. The Mean Transfer Factors of the three radionuclides for Lokoja samples were 0.0808, 0.3090 and 0.5912 respectively, and those of Ibaji soil samples were 0.0975, 0.8052, and 0.8710 respectively, with the transfer being highest in Thorium followed by Uranium. These low values indicate slow transport of these radionuclides to the rice grains.
