LUIZ FLAVIO LOPES TEIXEIRA

LUIZ FLAVIO LOPES TEIXEIRA

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Challenges in measuring 22Na in rainfall by gamma spectrometry in the city of São Paulo, Brazil
2023 - DAMATTO, S.R.; DOMINGOS, R.M.; TEIXEIRA, L.; ISIKI, V.L.; ALENCAR, M.M.; LEONARDO, L.
Na-22 is a naturally occurring radionuclide of cosmogenic origin with half live of 2.6 years, being a beta and gamma emitter (541keV and 1274.5keV, respectively). This cosmogenic radionuclide is mainly formed when cosmic rays interact with argon nucleus, occurring a fragmentation of this nucleus. The process of production of 22Na occur continually in upper atmosphere, lower stratosphere and rainfall is the predominantly process of deposition of cosmogenic radionuclides in terrestrial surface. Na-22 together with 7Be (T1/2) = 53.3 d, gamma ray 476.7keV) can be used as tracers in studies of aerosol transport between layers of the atmosphere. At the same time 22Na is rarely used in these studies due to its extremely low abundance in rainfall. The objectives of this work were to present the first results 22Na activity concentration measured in rainfall collected at the IPEN campus located in São Paulo, Brazil. Large volumes of rainfall samples were collected from October 2022 to April 2023, totaling 20 samples, and 22Na activity concentration was measured by non-destructive gamma-ray spectrometry using a coaxial Be-layer HPGe detector with 46% relative efficiency and associated electronic devices and live counting time varying from 250,000 s to 500,000 s; the rainfall volumes ranged from 14 L to 164 L. The collection container was previously acidified with 1mol L-1 HNO3 to avoid loss of radionuclide by absorption on the container walls. The first eight rainfall samples were collected in a catchment area of 1m2, which was not enough to measure the radionuclide, since all the determined results were smaller than the detection limit of the methodology. After these results, it was decided to increase the catchment area by collecting rainfall samples from the roof of the laboratory building, in an area of 78 m2; the container used to collect samples from this area was also acidified with 1 mol L-1 HNO3. In this new area, 12 rainfall samples were collected, however, as the volume of rainfall was very large in the rains collected, only one sample was acidified, a rainfall of 2 mm and a volume of 98 L; in the other samples, the large volume of rain did not allow the water to become acidic because the collection container overflowed with water. In the acidified rainfall sample, the result of 0.725 ± 0.252 Bq L-1 was determined for the radionuclide 22Na. With this result, it is possible to prove the importance of both the catchment area and the acidulation of the sample in the determination of trace radionuclides in rainfall samples.
Study of 7Be activity concentration in rainfall as a function of sampling height
2022 - ALMEIDA NETO, J.O.; DAMATTO, S.R.; MADUAR, M.F.; LEONARDO, L.; TEIXEIRA, L.F.; DOMINGOS, R.M.
Validation of uranium and thorium determination in sediments by spectrophotometry with Arsenazo III
2017 - TEIXEIRA, L.F.L.; MAZZILLI, B.P.; NISTI, M.B.; SAUEIA, C.H.R.
The evaluation of environmental contamination is one of the most important ways to check the anthropogenic interference. Human activities next to a water body, as mining, or on the waterbody, such as transportation ships, can pour unwanted wastes, increasing the concentration of metals or radionuclides. One way to evaluate this contamination on waterbodies is the quantification of radionuclides on sediments. The evaluation of uranium and thorium contamination is an important measurement of anthropogenic interference, because these two natural radionuclides can be found in many places on earth. The are many techniques to determinate the uranium and thorium concentration in sediments samples, and the spectrophotometric method with Arsenazo III is one of the quicker and cheaper method. The Arsenazo-III reacts with both radionuclides, producing a stable complex in low pH condition. The radionuclides were extracted from the sediments samples by an acid digestion, with HNO3, HF and H2O2, on a microwave. The interferences were removed by solvent extraction process, allowing the Arsenazo III react only with the uranium and thorium. The validation process was performed to evaluate if the whole process could reach reliable results with expected quality level. The Limit of Detection (LOD), Limit of Quantification (LOQ), Accuracy (Z-Score) and Precision (Relative Standard Deviation) of each method were evaluated following the INMETRO’s guidance document. The LOD and LOQ of the uranium determination are, respectively, 0.98 and 1.11 ppm, and for thorium determination are, 0.61 and 0.81 ppm, for the analysis of 0.5g of sediments samples. The methods validations were performed using the certified reference material (CRM) IAEA SL-1, for uranium determination, and IAEA SL-3, for thorium determination. Both validations reached satisfactory results of Accuracy and Precision for the analysis of 0.5g of sediments samples.
Natural radionuclides uptake into alfalfa grown in soil amended with phosphogypsun
2015 - MAZZILLI, BARBARA; SAUEIA, C.R.; TEIXEIRA, L.F.L.; NISTI, M.B.; BERNARDI, A.C.C.; BARBOSA, G.; POLIDORO, J.C.; BALIEIRO, F.