Assessment of Natural Radioactivity in a Residence in Belo Horizonte

Natural radioactivity comes from natural radionuclides present in rocks and soil and from cosmic rays. In addition to gamma-emitting radionuclides, radon stands out, which is a carcinogenic gas. In nature, radon occurs as radioisotopes: 222Rn (half-life time, t1/2,of 3.83 d), 219Rn (t1/2 = 3.92 s) and 220Rn (or thoron, t1/2 = 54.5 s). The World Health Organization (OMS) recommends that it be measured in homes, with the recommended limit being 100 Bq/m3 and the maximum limit being 300 Bq/m3. This work evaluates the origin of natural radiation in a residence in Belo Horizonte, Minas Gerais, Brazil, in which was observed radon concentrations above the limits established by the OMS. The detectors used were: nuclear trace detectors type CR-39, electrets (E-PERM), AlphaGUARD (AG) and the detector RS-230. The result of the 222Rn concentration measured in the electrets in the rooms of the residence varied from 14,8 Bq/m3 to 932 Bq/m3. At this highest point, the result of the average concentration of AlphaGUARD was from 4.78 kB/m3, with a maximum value of 8.5 kBq/m3. The concentration of 220Rn varied Bq/m3  Bq/m3. As this is a basement-type room, the bedroom next door was investigated, in which it is highlighted that the radon concentration of the detector CR-39 was from 445 Bq/m3, AG of 198.2 Bq/m3 with a maximum value of 350 Bq/m3, and electret of 29.6 Bq/m3. Gamma scanning with the RS-230 indicates higher counts on uncoated walls. Measurements of radon in the water showed background concentrations. It is concluded that poor ventilation of the location must be the biggest contributor to the high concentration of 222Rn, which originates mainly from the soil. The thoron concentration was higher in construction materials due to the measurement method. The instrumentation used allows a complete and comparative study between detectors in order to find the origin of natural radionuclides and subsequently suggest appropriate mitigation measures. In future studies, radon concentration in the soil and radon progeny will be measured.