Abstract Information on the distribution and emission patterns of natural and artificial radionuclides and their radiation level in the environment is very important for assessing the health effects of people living in a given region. In this study, the specific activity of radionuclides was measured using high purity germanium detector and a map of their distribution was drawn. The samples were collected from the Gaz River sediment in northern Iran, in the mountains of Golestan Province, and sediments on the middle and southern side of Gorgan Bay. The average of specific activities of 226Ra, 232Th, 40K, and 137Cs was 17.61, 35.91, 398.65, and 4.01 Bq/kg, respectively, which for natural radioactive nuclei are lower than the global average. The highest concentration of 40K was obtained in the sediments of the Gaz River estuary due to the use of potassium fertilizers for agriculture in this region. The highest concentration of 137Cs was obtained in the sediments of Gorgan Bay because 137Cs is injected both directly through the atmosphere and transfer by river water from upstream points to the Gorgan Bay. The diffusion pattern of 137Cs in the Gorgan Bay was
