Effect of lower grain sized particles on natural radiation level of the Ponnaiyar river sediments

River sediment depositions on the bottom of rivers most frequently consist of sand and gravel particles with different grain sizes, which make them particularly valuable for the building construction. Knowledge of radioactivity present in building material enables one to assess any possible radiological hazard to mankind by the use of such materials. The natural radionuclide (238U, 232Th and 40K) contents have been analyzed for the sediment samples of Ponnaiyar River with an aim of evaluating the radiation hazard nature. To know the radiological characteristics of the sediment, dose rate is calculated and are compared with recommended values. Mineral characteristics of the sediments have been analyzed through FTIR and XRD techniques. Extinction coefficient and Crystallinity index is calculated to know the relative distribution of major minerals and crystalline nature of quartz, respectively. Multivariate statistical analyses were carried to find the relationship between the radioactivity characteristics and minerals, the results obtained in the study suggest that the level of natural radioactivity of the present sediments mainly depends upon the amount of kaolinite (clay). Mineral characterization of various grain sized sediments show clay and magnetic minerals are rich in lower grain sized (≤120 μm) samples. The level of radioactivity has also been measured for >120 μm sediments and results show that both activity concentrations and dose rate are considerably lowered when compared with the respective values of the bulk samples. The removal of ≤120 μm particles from the sediments of the river make it safer to use these materials for building construction.

► River sediment natural radioactivity mainly depends upon kaolinite (clay).
► Minerals in various grain sized sediments have been characterized.
► Radioactivity of >120 μm grain sized sediments considerably decrease.
► Removal of ≤120 μm grain sized sediments may be safer for building construction.