Assessment of natural radioactivity in the Higher and Tethys Himalayan Rocks along Manali-Leh Highway, India

The Higher and Tethys Himalayan region of NW-Himalaya is less explored from the natural radioactivity mapping assessment, though geologically and tectonically, this region is still active. The concentration of primordial radionuclides (²²⁶Ra, ²³²Th, and ⁴⁰ K) in rock samples of the Manali-Leh Highway region of the Himalayas is determined in the present study using the HPGe detector. The radiological hazard parameters are also estimated in terms of radium equivalent activity (Ra_eq), annual effective dose (E_in and E_out), hazard indices (H_in, H_ex, H_α, and H_γ), and gamma absorbed dose rate. SEM-EDS analysis was used to understand the mineralogical composition of the rocks. The activity concentration of ²²⁶Ra, ²³²Th, and ⁴⁰ K radionuclides varies from 1.4 ± 0.9 to 25.3 ± 1.2, 0.7 ± 0.5 to 59.6 ± 1.6, and BDL (below detection limit) to 830.3 ± 45.7 Bq kg^-1, with an average value of 13.0 ± 1.0, 21.7 ± 1.0, and 243.7 ± 25.2 Bq kg^-1, respectively. The average of Ra_eq in the study region lies within the safe limit of 370 Bq kg^-1. The hazard indices have values < 1, indicating no radiological hazards to the population from the rocks. The annual effective dose also has values less than the global average value. This study revealed that the rocks of the Higher Himalayan region have a higher concentration of natural radioactivity, while the Tethys Himalayan rocks have lower concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰ K radionuclides. The origin of rocks from different lithologies may be the reason for the natural radioactivity variation. The average concentrations of primordial radionuclides in the region are within the world average indicating that the rocks of the region are safe to be used for different purposes.