Résumé
A few elements of soil are radioactive. Soil can transfer radionuclide into plants feeding human. Sometimes their levels are as high as to be concern of human healthy. Rice has an important share for Iranian foods especially in north of Iran. Therefore we decided to obtain radionuclides concentration emitting g rays in Lahijan City [Northern Iran] rice fields using g spectroscopy. Twenty eight samples from rice field's soils and 12 samples from superficial soils were collected at a square of 10*10 m2 to get 2kg weight. To make dry samples were put into oven at 105oC for 24h. Then they were milled and 950 gr of each sample was transferred to Marinelli container with 1000cc volume, sealed and left for 40 days to get secular equilibrium. After measuring Ph, Electric conductivity and organic carbon, g spectroscopy was done to get sample gamma spectrum at 2000-6000 sec using HpGe detector. It was found 226Ra activity in rice fields of 29.273 +/- 0.72 Bqkg-1 and city soil of 31.02 +/- 1.1 Bqkg-1 and also 232Th activity of 37.47 +/- 1.12 Bqkg-1 for rice fields' soils and 40.47 +/- 1.68 Bqkg-1 for city soil were in standard mode. 40K activities mean value according to UNSCEAR; 2000 was found a little greater than standard. A little value of 137Cs was found in Lahijan rice fields and city soils that could be as a result of Chernobyl accident. In except of 137Cs, for three other under studied city soil elements, activities were greater than that of rice fields