Avaliação da concentração de radônio em casas pré-fabricadas e determinação da camada emissora de radônio em argamassa de cimento

Abstract

Radon-related research is required because of the carcinogenic potential of this gas, and the reference limits are subject of recommendations. For this research, radon concentrations were measured inside and outside of two prefabricated houses, built in an experimental environment, in UTFPR/Ecoville. One of these houses was built with building materials from the Czech Republic (1) and the other (2) with materials from Brazil. Whith this proposal, 40 CR-39 detectors were used. The average concentration for house (1) was 10,1±1,3 Bq/m³, for house (2) was 7,8±1,1 Bq/m³ and for the exterior was 11,5±2,9 Bq/m³. The values obtained were below 300 Bq/m³, thus, no mitigating measures were necessary. Besides, measurements were made of the number of thacks of alpha particles coming from common cement paste samples and from sand with high radon activity samples in order to identify the value of the emitting layer. For common cement paste samples of 1.5, 2.6, 3.8 and 4.6 cm of thickness, the number os tracks was 762±25, 799±51, 814±31, 791±45 e 798±27, respectively. The analysis showed that there ir no statistical difference between the data, which indicates that the thickness of 1.5 cm is already configured as a limit for a randon exhalation. For the active sand samples of 1.4, 2.3, 2.9, 3.5 and 4.2 cm, the number of tracks was 380±18, 322±15, 298±5, 548±25 e 446±83, respectively. In a general analysis, it was concluded that there is no expressive increase of the exhalation with the increase of the thickness, só that the thickness of 1.4 cm is already configured as a limit for the exhalation of radon. In order to determine the concentration of radon exhaled by the samples made of common cement past and active sand, were analyzed samples in flasks where the secular equilibrium had already occured. The results showed that, for common cement past samples, the values do not represent and expressive growth. However, for the test samples with high radon activity and increase in the concentration with increasing the thickness was observed. To determine the contribution of the concentrations in an indoor environment, radon exhalation flux measurement was performed. These results were extrapolated to the standard room and varies from 15 to 60 Bq/m³. This contribution can be considered expressive, but not of concern, só the results were considered close to normality.