Multi-scale approach to assess total porosity and pore size in four different kinds of carbonate rocks.

Petroleum is, at present, still the main energy source in the world. Most of it is stored in carbonate rock reservoirs with complex inner structures and pores ranging from nanometers to dozens of meters. Knowing the rock's entire pore network is indispensable to perform an effective petroleum extraction. X-ray microtomography, a technique that generates images from samples' inner structure and a powerful tool to evaluate the 3D pore network, was employed in this scientific research to scan four kinds of carbonate rocks (Dolomite, Desert Pink, Indiana, and Winterset) in five different pore scales (90 µm, 13 µm, 5.5 µm, 1.0 µm, and 65 nm). A multi-scale approach based on the number of pores was applied to integrate different pore scale data and assess the total porosity as well as each sample pore size distribution. The results were compared to classical Mercury Injection Capillary Pressure (MICP) results, demonstrating a fair agreement in total porosity in the two samples. Multi-scale porosity of the Dolomite sample was 17.7% against (18.9 ± 2.1)% of the MICP porosity. The Winterset sample had multi-scale porosity of 26.2%, while MICP porosity was (31.2 ± 0.6)%. Pore size distribution results were rather satisfactory, especially when overlapping regions in different scales were compared. In general, the multi-scale approach showed good potential. It still needs further evaluation to fine-tune some procedures and fluid flow simulation tests but might become a useful tool to study reservoir rocks with a wide range of pore sizes, such as carbonate rocks.

40K, 226Ra AND 228Ra SERIES IN BOVINE AND POULTRY FEED AND IN DICALCIUM PHOSPHATE (DCP) SAMPLES BY GAMMA-RAY SPECTROMETRY

The aim of this study is to determine the amounts of radionuclides' activity present in samples of feed for young and adult chicken and feed for dairy and beef cattle, as well as in dicalcium phosphate (DCP) (CaHPO4), used as a nutritional supplement for animal feed. Radioactivity in these samples is due to the presence of the 238U and 232Th radioactive series, as well as their daughter. In addition, as it is for environmental samples, the activity of 40K should be an important source of radioactivity in all analyzed samples. Gamma rays were measured using a standard spectroscopy system, with a high-resolution HPGe detector. Measured activities in feed samples ranged from 0.23 to 1.51 Bq.kg-1, 0.67 to 4.21 Bq.kg-1, 0.29 to 1.63 Bq.kg-1 and 236 to 402 Bq.kg-1 for 226Ra, 228 Ra, 228 Th and 40K, respectively. Measured activities in DCP samples were 46.6 Bq.kg-1, 83 Bq.kg-1, 4.20 Bq.kg-1 and 16.61 Bq.kg-1 for 40 K, 226 Ra, 228 Ra and 228 Th, respectively. Although 40K activity has reached hundreds of Becquerel in feed samples, it should not represent a risk to human health, not even to animals, since potassium is an essential mineral to living organisms.

Brazil nuts: determination of natural elements and aflatoxin / Castanha do Brasil: determinação de elementos naturais e aflatoxinas

A study was carried out to evaluate the association of levels of radioactivity, selenium and aflatoxin in shelled Brazil nuts, which were classified in different sizes, for export. The selenium determinations were performed by inductively coupled plasma optical emission spectrometry (LOQ = 3.0 µg g-1), and aflatoxins were detected by Liquid chromatography-mass spectrometry (LOQ = 0.85 µg kg-1), recovery rates were between 92 and 100 percent. Radioactivity was measured by high-resolution gamma spectrometry. The selenium mean concentration was (22.7 ± 7.4) µg g-1. (n = 30). Mean activities determined for the following radium isotopes were: 15.77 Bq kg-1 for 224Ra, 104.8 Bq kg-1 for 226Ra and 99.48 Bq kg-1 for 228Ra. For 226Ra, the levels did not vary significantly with nut sizes, although such differences were observed for 224Ra and 228Ra. There was no statistically significant association between the level of selenium and the activity of radionuclides, however, there was correlation between the radionuclides. Aflatoxins above the quantification limit were not found.

Um estudo foi realizado para avaliar a associação dos níveis de radioatividade, selênio e aflatoxinas em castanha-do-Brasil descascada, que foram classificadas em diferentes tamanhos, para exportação. As determinações de selênio foram realizadas por espectrometria de emissão óptica com plasma indutivamente acoplado (LOQ=3,0 µg kg-1) e aflatoxinas foram detectadas por LC-MSMS (LOQ=0,85 µg kg-1), as taxas de recuperação ficaram entre 92 e 100 por cento. A radioatividade foi medida por espectrometria gama de alta resolução. A concentração média de selênio foi de (22,7 ± 7,4) µg g-1. (n = 30). A atividade média determinada para os radioisótopos foram: 15,77 Bq kg-1 para o 224Ra, 104,8 Bq kg-1 para 226Ra e 99,48 Bq kg-1 para 228Ra. Para 226Ra, os níveis não variaram significativamente com o tamanho das nozes, embora tais diferenças foram observadas para 224Ra e 228Ra. Não houve associação estatisticamente significativa entre o nível de selênio e a atividade de radionuclídeos, no entanto, houve correlação entre os radionuclídeos. Não foi encontrado aflatoxinas acima do limite de quantifcação.