L. J. P. F. Neves

On the influence of faulting on small-scale soil-gas radon variability: a case study in the Iberian Uranium Province

In order to evaluate the influence of faulting on the variability of geogenic radon at detailed scale (1:2000), data on gamma ray fluxes, U and Th concentrations in rocks, radon in soil-gas and radon in groundwater were collected in three target areas on the Oliveira do Hospital region (Central Portugal). This region stands on the Iberian Uranium Province, and is dominantly composed of Hercynian granites and metasedimentary rocks of pre-Ordovician age, crosscut by faults with dominant strike N35 degrees E, N55 degrees E and N75 degrees E. Radiometric anomalies are frequent, associated with faults of the referred systems and metasedimentary enclaves; the analytical data confirms that these anomalies are produced by local high uranium contents in rocks and fault-filling materials (n=34, range 13-724 ppm), while other radiogenic elements are relatively constant (e.g. Th 4-30 ppm). Radon concentration in soil can be extremely high, up to 12,850 kBq m(-3) (n=215), with a large proportion of results above 100 kBq m(-3). Unsurprisingly, groundwater also shows high radon concentrations, with observed values in the range 150-4850 Bq.L(-1) (n=17). From the results it is concluded that metasedimentary enclaves, as well as faults, can accumulate uranium from circulating fluids, and as a consequence, strongly locally enhance geogenic radon potential. Due to this fact, for the purpose of land use planning in such uranium-enriched regions, very detailed geological mapping is needed to precisely recognize radon high risk areas. A correlation between radon concentration in soil or in groundwater and gamma ray fluxes was established pointing to the possible use of these fluxes as a first step in assessing geogenic radon potential, at least to geological setting similar to the study area.

Indoor radon periodicities and their physical constraints: a study in the Coimbra region (Central Portugal)

Indoor radon activities were measured during a period of 6 months, as well as several physical environmental variables (temperature, pressure, humidity and rainfall). The location was a small room at an administrative building of the University of Coimbra, usually undisturbed by human activities and situated over bedrock of low-uranium Triassic red sandstones. A low average activity of radon was observed (36 Bq m(-3)), however showing a very well marked daily periodicity (10+/-5 Bq m(-3)), with maximum values occurring more frequently between 9 and 10 a.m. Daily variations are shown to have no relation with earth tides, and their amplitudes exhibit a significant correlation with outdoor temperature; no dependence on barometric pressure was found. Rainfall disturbs the observed daily radon cycles through a strong reduction of their amplitude, but has no effect on the long-term variability of the gas concentration.

Evidence for the Unroofing History of Hercynian Granitoids in Central Portugal Derived from Late Palaeozoic and Mesozoic Sedimentary Zircons

The Lusitanian Basin on the western Iberian margin comprises Mesozoic and Cenozoic sediments derived from the surrounding Precambrian to Lower Palaeozoic and Hercynian basement. Apatite fission-track data from Hercynian granitoids to the east of the basin show that the intrusives were being actively eroded throughout the Jurassic and Cretaceous; however, exactly when these rocks first became exposed and eroded is not clear. In this study we have attempted to reconstruct the erosional history of the granitoids of Central Portugal by examining the detrital zircon fission-track signatures contained within post-granite emplacement sediments.

Students’ Final Projects: An Opportunity to Link Research and Teaching

The final project that students have to complete before finishing their degree in the new adapted system to Bologna in Spain is an opportunity to link research and teaching. This experience has been ongoing for several years now within our research group and the engineering geology course. These studies had a final project in the non-adapted system, and this will serve as experience for the system to come. Teaching staff must be aware of the current lack of independence that students have when working on their own and how the new system will attempt to remedy this failure by working the different competencies. The involvement of students in research groups has shown that they feel more confident if their opinion is taken into account when they are carrying out a research project, leading them to feel gratified if they appear in the authorship of papers and abstracts concerning their work presented at international congress. This helps to increase their motivation as professionals in the last stages of their university studies.

Structural lineaments in a volcanic island evaluated through remote sensing techniques The case of Santiago Island (Cape Verde)

The remote sensing data (optical and radar) was used with the purpose of identify the structural lineaments that crosscut the geological formations that composed the bedrock of the south part of Santiago island (Cape Verde). Besides tectonics, this study also provided new insights to the understanding of the hydrogeological system of the volcanic island.