Natural radionuclides from different sources in the environment, even in our bodies can be originated from weathering of the earth’s crust (rocks, soils, ores), food consumption, mining activity, and fertilizer materials (Nguyen et al. 2016; Azeez et al. 2019; Querfeld et al. 2019; Takagi et al. 2019; Cwanek et al. 2020; Duong et al. 2020; Van Hao et al. 2020 a,b,c; Loat et al. 2021; Van-Hao et al. 2019; 2021a,b,c). In the air, radionuclides such as 222Rn and 220Rn initiate from the alpha decay of 226Ra in the 238U series and 224Ra in the 232Th decay series in respective (Omori et al. 2016). The half-lives of 222Rn and 220Rn are 3.8 days and 55.6s, respectively. The lung cancer risk of 222Rn radioactive exposure and its decay products through inhalation are well known (e.g., Tomášek and Plaček 1999; Al-Zoughool and Krewski 2009; Clement et al. 2010). One of the most main causes of lung cancer in the population is the inhalation of 222Rn and 220Rn (UNSCEAR 2006). Thus, the human is always exposed to a wide range of natural radionuclides (Sonkawade et al. 2008). Therefore, investigation of 222Rn and 220Rn dispersion in the environment plays an important role in public health, which can be used to assess the population exposure to radiation and estimate the radiological hazard.
The concentration and radiation dose due to inhalation of 222Rn and 220Rn have been also extensively investigated worldwide (e.g., Iida et al. 1996; Chung and Tokonami 1998; Wang 2002; Bochicchio et al. 2003; Magalhães et al. 2003; Oikawa et al. 2003; Mohammad and Abumurad 2008; Le Khanh et al. 2015; Omori et al. 2016; Ramola et al. 2016; Thu et al. 2019). In general, the 222Rn and 220Rn concentration in soil and air depends on the types of rocks, their migration from rock to soil, the release of 222Rn and 220Rn from the soil, rock to the atmosphere, and the weathering characteristics, thus it varies from one site to another.
There are many mines in northern Vietnam, which contain a high content of natural radionuclides such as rare earth mines in NX, DP (Lai Chau), MH (Lao Cai), YP (Yen Bai); polymetallic mine (contain high uranium concentration) in NP (Thai Nguyen); uranium ore in BY (Son La); TS (Phu Tho), NB (Cao Bang) (Figure. 1). These mines were recently reported to have a high radioactive background by Vietnam Geological division for Radioactive and Rare elements. Therefore, the surrounding environments and local communities of those areas can be exposed to a high 222Rn and 220Rn concentration. In this study, the baseline of natural radiological hazard assessment of 222Rn and 220Rn in the areas surrounding REE and uranium mines will be presented. This paper will also provide baseline data to evaluate the radioactive pollution during the exploitation of these mines and supply information for local stakeholders to reduce the impacts of the radioactivity risks in further.