SUMMARY

Localizing natural radioactivity and external hazard index (Hf) from ground gamma spectrometry data in Yên Hợp - Quỳ Hợp, Nghệ An province

Nguyễn Văn Nam, Lê Văn Đạt

The radioactivity in the growing soil layers from rare earth - bearing locations of Yên Hợp commune, Quỳ Hợp district, Nghệ An province was determined on the basis of the ground gamma spectrum measurements in an area of 6 km², with the network grid of 100 m x 50 m. The total gamma absorbed dose calculated from the radioactivity of ⁴⁰K, and the range of ²³⁸U- ²³²Th varied from 45 to 750 nGy/h, with an average value of 300 nGy/h. The isometric map of gamma-absorbed dose showing three areas relating to geological formation of the Sông Cả, Bù Khạng and Quaternary sediment, which have the absorbed doses at the height of 1.0 m are 0.3, 0.5, and 0.7 nGy/h, respectively. This map aims to warning of natural radioactivity in the air. The calculated results of the external hazardous index (H_f) of the surface soil layers according to TCVN 7879/2011 indicated that: H_f values vary from 0.5 to 4.5 and isometric map of external hazardous index in the study area allowed us to localize the areas which have H_f index of ≤ 0.7; 0.7-1.0; 1.0-2.0 and > 2.0 to warning of danger for using rock and soil as construction materials.

Keywords: gamma radiation spectrum; gamma-absorbed dose; external hazardous index (Hf).