It has been estimated that the
relative health risk of lungs cancer enhances 16% per 100 Bq/
m3 (Darby et al., 2005). According to UNSCEAR, a 1.2 mSv world
average annual effective dose is estimated due to inhalation of
radon, thoron and their decay products (Ahmad et al., 2014;
UNSCEAR., 2000a). Radon existing in rocks of the earth's
terrestrial systems diffuses continuously through water in
rocks, which leads the presence of radon in ground water.
According to USNRC,