“…Several studies have been carried out in different countries: Algeria (Ziane et al, 2014), Austria (Bossew et al, 2007), Brazil (Alberigi et al, 2011), China (Song et al, 2011), Croatia (Radolić et al, 2005), Greece (Nikolopoulos et al, 2010), Hungary (Hámori et al, 2006), Serbia (Nikolov et al, 2012), Spain (Ródenas et al, 2008), Poland (Walczac et al, 2016 and Turkey (Tarim et al, 2012) to measure the radon concentration in indoor air and in natural mineral water of thermal spas in order to estimate the doses of natural radiation received by the workers. In the majority of these studies and due to several reasons, radon concentration can reach worrying levels.…”