Characteristics of radioactivity and radiological risk indices in beach sediments from northern Vietnam

The beach sediments in northern Vietnam were analysed for grain size, minerals and radionuclides in 24 samples. Grain size was measured by sieving, minerals by XRD and radionuclides by gamma-ray spectrometry. The radiological risk indices Ra_eq, ADR, AEDE, I_γr, AUI, H_ex, AGDE and ELCR were evaluated. There were three types of sediment: very fine sand, fine sand and medium sand. Very fine sand with a mean diameter (Md) of 105 µm, fine sand with an Md of 192 µm and medium sand with an Md of 330 µm were used. The percentages of minerals with quartz, illite, feldspar, kaolinite, chlorite, goethite, gibbsite and amphibole contents were 80.6, 5.4, 3.3, 2.4, 2.0, 2.0, 0.2 and 0.8 %, respectively. The average radioactivity of ²³⁸U, ²²⁶Ra, ²³²Th and ⁴⁰K was 23.3, 23.1, 27.1 and 214.9 Bq/kg, respectively. The radiological risk indices, including Ra_eq, ADR, AEDE, I_γr, AUI, H_ex, AGDE and ELCR, were 78.38 Bq/kg, 38.8 nGy/h, 0.04 mSv/yr, 0.57, 0.56, 0.21, 256.1 µSv/y and 0.16 × 10^-3, respectively. The origin of radioisotopes is mainly in sediments and from mainland, which are influenced by minerals and grain sizes. Additionally, another source from seawater or the atmosphere plays a minor role. The average radioactivity and radiological risk indices were lower than the global average and the recommendation of UNSCEAR, so sediments were safe for humans and organisms.