Hazard indices and annual effective dose due to terrestrial radioactivity in Northern Kerala, India Reshma Bhaskaran 1,2 • C. D. Ravikumar 1 • A. M. Vinodkumar 1 • I. Vijayalakshmi 3 • B. Danalakshmi 3 • N. Chitra 3 • S. Bala Sundar 3 • M. T. Jose 3 • B. Venkatraman 3 Received: 28 August 2017 Ó Akade ´miai Kiado ´, Budapest, Hungary 2017 Abstract Kerala is listed among the six highest back- ground radiation areas of the world. The west coast of Kerala is very well studied. However, no data is available regarding the high ranges. This study reports measurement of terrestrial concentration of radionuclides in Wayanad district (altitude range 700–2100 m above mean sea level), a known tourist place of Kerala, India having a sizeable tribal population. Activities of 40 K, 226 Ra and 232 Th in soil samples measured using gamma ray spectrometry were found to be 265 ± 334, 21 ± 15 and 39 ± 38 Bq kg -1 respectively. Similar studies were done for rock samples. The average indoor and outdoor hazard indices were found to be 0.24 and 0.20 for soil and 0.5 and 0.4 for rocks, respectively. The indoor radon and thoron concentrations were measured using solid state nuclear track detector. The annual average radon concentration was found to be 31 Bq m -3 and the annual average thoron concentration was 96 Bq m -3 . Out of the samples, one house showed elevated thoron concentration with an annual average value of 621 Bq m -3 . Keywords Terrestrial radioactivity  Gamma ray spectrometry  Hazard indices  Inhalation dose  Solid state nuclear track detector Introduction Radiation is omnipresent in varying forms in the environ- ment. Natural sources contribute significantly in total radiation exposure to mankind. Cosmic rays and the ter- restrially occurring radionuclides are the main components of natural radioactivity. Understanding the dose from nat- ural sources and its comparison with manmade sources is essential in devising remedial measures if situation warrants. The main contribution of external terrestrial exposure comes from gamma-emitting radionuclides present in trace amounts in soil, mainly 40 K and 238 U and 232 Th families [1]. Puranik and Ramachandran [2] estimated the average natural radiation exposure to the Indian population to be around 2.3 mSv year -1 which is at par with the global average. However, in India, Chavara and Manavalakurichi were identified with high natural background radiation areas (HNBRA) of the world inhabited by large population along with Guarapari in Brazil, Yangjiang in China and Ramsar in Iran [3]. The south west coast of India is known for the high levels of background radiation. Chavara–Neendakara belt in Kerala and Manavalakurichi–Kadiapattanam–Midalam belt in Tamil Nadu are among the well documented areas, the source of radiation being the monazite sand deposits [2, 4, 5]. It has been reported that the presence of monazite sands in the coastal region of Kerala and Tamil Nadu is due to the weathering of rocks in the Western Ghats [6]. Even though Wayanad is part of the Western Ghats, no study of background radioactivity has so far been reported. Waya- nad district is the place of origin for many rivers like Valapattanam, Chaliyar, Kabani etc. Kabani River is a tributary of the river Kaveri, which supplies water to many parts of Karnataka. It has been found that the level of 210 Po & Reshma Bhaskaran bhaskaran_reshma@yahoo.co.in 1 Department of Physics, University of Calicut, Malappuram, Kerala, India 2 Government Medical College, Kozhikode, Kerala, India 3 Radiological Safety Division, Indira Gandhi Center for Atomic Research, Kalpakkam, TN, India 123 J Radioanal Nucl Chem DOI 10.1007/s10967-017-5583-5