Thoron (220Rn) is a gaseous decay product of232Th decay chain which becomes a potential source of internal contamination for individuals who handle significant amounts of ores and raw materials containing thorium. With the objective of establishing an occupational control of such workers, a methodology which permits, by means of in-vivo measuremens, the determination of the level of internally deposited220Rn daughters (212Pb,212Bi, and208TI), was developed at the Institute of Radiation Protection and Dosimetry/Brazilian Nuclear Energy Commission (IRD/CNEN) whole body counter. Previous calibration of an 8×4 NaI(Tl) detector was carried out using the lawrence Livermore National Laboratory (LLNL) thorax phantom with the lung cavity filled withi plastic bags containing28Th standard solution. After sealing, the bags are stored until radioactive equilibrium is reached. Patients are measured for I h in two steps, at an interval of approximately 20 h, Positioning the detector over the thorax. A comparison of the activities determined at each measurement allows the distrimination of the contribution of the internally deposited shoret-and longlived radionuclides. This technique was recently applied to a group of workers at a gas mantle industry in Rio de Janeiro. Results of these measurements will be shown.
Authors:J. Lipsztein, D. Grynspan, B. Dantas, L. Bertelli, and M. Wrenn
The main objective of this paper is to point out problems associated with interpretation of bioassay monitoring in view of the existing biokinetic models. The exposure to thorium in Brazil is given in this paper as an example of the seriousness of the problem.
Authors:M. Lourenço, B. Dantas, E. Lucena, and C. Oliveira
The construction of reliable bone phantoms to calibrate whole body counting facilities for bone-seeking radionuclides has been a challenge for several research institutes. Different techniques have been applied to get uniform distribution of those nuclides in bone tissue. A241Am skull phantom was developed at the Institute of Radiation Protection and Dosimetry/Brazilian Nuclear Energy Commission's (IRD/CNEN) Whole Body Counting facility, using a dipping procedure. Preliminary tests were performed using non-radioactive ink solution. The first step was to choose the appropriate solvent to be used, since it was observed that acid solutions attack bone tissue. At the second step, pieces of skull were dipped into those solutions to check the extent and homogeneity of the penetration. The third step consisted of verifying the dipping time using a241Am standard solution. The homogeneity was checked with a high-purity germanium detector. Tissue-equivalent material was used to cover the skull surface and to simulate the low energy X and gamma radiation attenuation. The calibration factor and the detection limit were calculated for two phoswich detectors positioned at each side of the head, which is the standard geometry for this kind of measurement.
Authors:F. L. Macedo, R. A. Candeia, L. L. M. Sales, M. B. Dantas, A. G. Souza, and M. M. Conceição
Searching for other alternative sources, which are not part of the food chain, and which are able to supply the biofuel market is a promising option. In this context, it has been searched to investigate the oiticica oil, approaching its availability to the biodiesel synthesis, as well as its thermal stability. Few works retreat parameters such as: the optimization of the biodiesel synthesis, its physical–chemical properties, and thermal parameters etc. The characterization results revealed that the oil showed very high kinematic viscosity, and acidity value around 13 mg KOH/g, requiring a pre-treatment. To reduce the acid in the oil, it has been done the esterification of oil, which was studied in different molar ratios oiticica oil/ethanol (1:9) and 2.0% catalyst, in order to get the best reduction the index of acidity. The lowest level of acidity of the oil obtained after the esterification was 4.4 mg KOH/g. The reaction rate for the synthesis of biodiesel, compared to the initial mass of oiticica oil ester was 85%. This income can be overcome by pursuing an even smaller reduction of acid value of biodiesel oiticica. The acid value of biodiesel was 1.8 mg KOH/g. The results have revealed that the oiticica oil and biodiesel are stable at 224 and 179 °C, respectively.
Authors:L. Julião, A. Azeredo, M. Santos, D. Melo, B. Dantas, and J. Lipsztein
This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between232Th and228Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between232Th and228Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because228Ra is more efficiently taken up from the soil by plants, in comparison to228Th or232Th, and subsequently,228Th grows in from its immediate parent,228Ra.
Authors:A. Souza, H. Danta, M. Silva, I. Santos, V. Fernandes, F. Sinfrônio, L. Teixeira, and Cs. Novák
The biodiesel obtained by transesterification by reaction between ester and an alcohol in the presence of catalyst. The purpose
of this work is to evaluate the thermal and kinetic behavior of the methanol biodiesel derived from cotton oil. The quality
analysis was done by gas chromatography and proton nuclear magnetic resonance spectrometry (1H NMR) in order to examine if the product meets with the requirements of the European Standard EN 1403. The thermogravimetric
profile of the cotton biodiesel indicated that the decomposition steps are associated to the volatilization and/or decomposition
of the methyl esters. Kinetic data was also obtained by thermal analysis.
Authors:A. Vasconcelos, M. Dantas, M. Filho, R. Rosenhaim, E. Cavalcanti, N. Antoniosi Filho, F. Sinfrônio, I. Santos, and A. Souza
The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained
from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical
(anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying
efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm−1 range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree,
except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation
of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence
of the drying process on the oxidative stability of biodiesel.
Authors:H. Dantas, R. Mendes, R. Pinho, L. Soledade, C. Paskocimas, B. Lira, M. Schwartz, A. Souza, and Iêda Santos
Gypsum is a dihydrated calcium sulfate, with
the composition of CaSO4⋅2H2O,
with large application interest in ceramic industry, odontology, sulfuric
acid production, cement, paints, etc. During calcination, a phase transformation
is observed associated to the loss of water, leading to the formation of gypsum
or anhydrite, which may present different phases. The identification of the
phases is not so easy since their infrared spectra and their X-ray diffraction
patterns are quite similar. Thus, in this work, temperature modulated differential
scanning calorimetry (TMDSC) was used to identify the different gypsum phases,
which can be recognized by their different profiles.
Authors:M. Dantas, Marta Conceição, V. Fernandes Jr, Nataly Santos, R. Rosenhaim, Aldalea Marques, Iêda Santos, and A. Souza
This work evaluates the thermal and kinetic
behaviour of corn biodiesel obtained by the methanol and ethanol routes. As
to the TG curves, in air three thermal decomposition steps are for the methanol
biodiesel and two steps are for the ethanol biodiesel. These steps are related
to the evaporization and/or combustion of the methyl and ethyl esters, respectively.
The corn oil presented four thermal decomposition steps in air, and only one
step in nitrogen. These steps were attributed to the evaporization and/or
decomposition of triglycerides. The TG and DTA profiles of the biodiesel approach
the mineral diesel oil ones.