Geochemistry of granites and metasediments of the urban area of Vila Real (northern Portugal) and correlative radon risk |
| |
| Authors: | M E P Gomes L J P F Neves F Coelho A Carvalho M Sousa A J S C Pereira |
| |
| Institution: | (1) Departament of Geology, UTAD, Vila Real, Portugal;(2) Geosciences Centre, Coimbra, Portugal;(3) Departament of Earth Sciences, University of Coimbra, IMAR, Coimbra, Portugal |
| |
| Abstract: | Radon concentration was evaluated in dwellings of the urban area of Vila Real (Northern Portugal). The area is mainly composed
of Hercynian granites and Cambrian metasediments, and CR-39 passive detectors (n = 112) were used for the purpose. The results obtained in winter conditions suggest that the most productive geological unit
is the Hercynian granite G1 (geometric mean of 364 Bq/m3), while Cambrian metasediments of the Douro Group show the lowest average indoor radon concentration (236 Bq/m3). The geological, geochemical and radiological data obtained suggest that the most effective control on the radon concentrations
of the area is related with the uranium content of the rocks; indeed, the highest contents were observed in granite G1 (21 ppm)
and the lowest in the metasediments (3 ppm). This is also confirmed by the results obtained for groundwater, where granites
present the highest concentrations of dissolved radon (up to 938 Bq/l), uranium (5–18 ppb) and gross α activities (0.47–0.92 Bq/l). No important radiometric anomalies were found in relation with geological structures such as
faults, veins and contacts, but a moderate increase of the uranium content can occur locally in such structures. Petrographic
observations and SEM studies show that uranium is mainly contained within the rock in heavy accessory minerals (apatite, zircon,
monazite, xenotime), which reduces radon emanation. Notwithstanding, due to the high U contents granites show a significant
potential to induce indoor radon concentrations in dwellings in excess of the recommended value of 400 Bq/m3. Overall, we can conclude that the region of Vila Real presents a moderate to high radon risk in dwellings and groundwater. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
