Background Gamma Radiation Mapping in Bangladesh: Radioactivity in the Surface Soil of 'BhawalGahr' Area of Gazipur

The total background radiation in the earth's environment is due to the contributions from natural (cosmic and terrestrial) as well as artificial (fall-out from nuclear weapon test, nuclear accidents, discharge from nuclear reactors etc.) radiation sources. It comes mainly from uranium 238 U series, thorium 232 Th series and radioisotope of potassium, 40 K. Moreover, fission products such as 134 Cs, 137 Cs, 90 Sr etc. may spread as fall- out radiation in the environment. Natural environmental radioactivity depends on the geological and geographic conditions, and appears at different levels in the soils of each different geological region.Therefore, it is worthy of investigating background radioactivity originating from natural and probable artificial radioactive sources. Country-wide background gamma radiation mapping program has been initiated in Bangladeshby dividing the whole country primarily into ~5 km×~5 km (1'× 1' in GPS scale) systematic square grids. About 30 km × 30 km area of forest land of Gazipur district called the 'BhawalGahr' (including the Bhawal National Park) bordering Mymensinghand Tangail districts was selected for sampling for this study. Soil samples at 0-5 cm depth were collected from the grid-node points of the squaregrids.Gamma ray spectrometry technique using a High Purity Germanium (HPGe) detector of 20% relative efficiency was used to detect the probable radionuclides and calculate of their activity concentrations in the samples. The activity concentrations of 226 Ra, 232 Th and 40 K in these soil samples varied from 49.928.83 to 83.446.09Bq/kg, 76.83 5.44 to 126.458.33Bq/kg and 363.7192.33 to 585.91106.12 Bq/kg, respectively.As Bangladesh is actively considering embarking upon nuclear power programto improve its energy mix and neighbouring countrieshave a number of nuclear power plants in operation, therefore, this background radioactivity database would be useful as a baseline data in time of any nuclear incidentin this region.