Search Results

You are looking at 1 - 10 of 18 items for

  • Author or Editor: D. Melo x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Internal contamination with radioactive materials of mining workers is a common problem in Brazil. This is caused by the presence of uranium, thorium, and their natural decay series associated with the mined ore. The clear examples are the workers at the niobium mine located in the state of Goiás. The niobium is associated with considerable quantities of uranium and thorium, but the mine is not legally subject to radiation protection requirements.Twenty mine workers were evaluated using in vitro bioassay techniques (urine and feces). The fecal samples were analyzed by alpha spectrometry using the method developed in the Bioassay Laboratory of the Instituto de Radioproteção e Dosimetria/CNEN which evaluates thorium and uranium isotopes simultaneously. Minor modifications were introduced to measure a higher level of activity, around 1 Bq of uranium per sample. The urine samples were analyzed by alpha spectrometry for thorium and by fluorimetry for uranium. The results obtained show that a control of the occupationally-exposed workers is necessary.

Restricted access

Abstract  

The decay products of uranium and thorium natural series are widely distributed in all the terrestrial crust. Their concentrations are considerable in the phosphates utilized as fertilizer in the Brazilian agriculture. In this work analysis was performed on238U,234U,232Th,238Th,226Ra and210Po in 22 Brazilian tobacco samples. The results showed238U and234U are in isotopic activity equilibrium (0.5±0.2 mBq/g). The equilibrium was not reached in the case of thorium isotopes: the228/232Th ratio was about 6.4. The average values obtained were 34.3 mBq/g for228Th and 5.4 mBq/g for232Th. The226Ra values were higher than its radioactive precursor,238U. This can be explained by the high affinity of radium to tobacco plant and the uranium removal during physical and chemical processes. The high concentration of210Po (20 mBq/g) in tobacco samples may be due to radon daughter products being electrically charged and then attaching themselves to inert dusts, which then become attached to tiny hairs on tobacco leaves. The results of this work are consistent with values presented in specialized literature.

Restricted access

Abstract  

ZnS(1-x)MSx(x=0.01 and M=Mn2+, Cu2+ and Eu2+) compounds have been obtained by precipitation from homogeneous solutions of zinc, copper, manganese and europium salts, with S2- as the precipitating anion, formed by the decomposition of thioacetamide. The thermal study of the milled zinc acetate, thioacetamide, copper acetate, manganese acetate and europium nitrate, respectively, was studied for thermal analyis TG/DSC. XRD respect exhibits a zinc blend crystal structure.

Restricted access

Abstract  

The thermal decomposition reactions of crystalline chelates of general formula Ln(thd)3 (Ln=La,Pr, Nd, Sm and Gd; thd=2,2,6,6-tetramethyl-3,5-heptanedione) have been studied by isothermal thermogravimetry. Several models were proposed initially to calculate the kinetic parameters by isothermal method, thus the time reduced method was used to define the best kinetic models. The Avrami–Erofeev (Am=2, 3 and 4) and R1 and R2 models presented good agreement with experimental data, as well as, linear correlation coefficient (r) and standard deviation (s).

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: A. Garrido Pedrosa, P. Pimentel, D. Araújo Melo, H. Scatena, F. Borges, A. Souza, and L. Zinner

Abstract  

Ln(TFA)3⋅3AZA (Ln=La, Sm, Er; TFA=trifluoroacetate and AZA=2-azacyclononanone)compounds were synthesized and characterized by microanalytical procedures, IR spectroscopy, X-ray powder diffraction, and thermal analysis. A kinetic study using La, Sm and Er thermogravimetric curves was carried out aiming to proposing a mechanism for the thermal decomposition of such complexes.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: D. Melo, F. Borges, F. Lima, H. Scatena, L. Zinner, V. Fernandes, W. Souza, and Z. Silva

Abstract  

In this work, a cobalt complex with dmit (1,3-dithiol-2-thione-4,5-dithiolate) as ligand was prepared and its thermal stability was studied by thermogravimetric analysis and kinetics by means of the Zsak method and a non-linear method. For both methods, numerical binomial and polynomial filters were used, where points in the central interval were utilized.

Restricted access

Abstract  

The reason of comparing thermal behaviour and kinetics of some nickel compounds, is justified by the influence of anion on it, besides supplying information on the stability of the salts. In this work, Ni(TMS)2·6H2O, Ni(TFA)2·3H2O and Ni(Ac)2·2H2O, were synthesized and characterized by microanalysis, atomic absorption molar, conductance and thermal analysis. Thermogravimetric curves indicate that the decomposition of the salts occurs in the range 295–1169 K and the NiO is the final residue. Non-isothermal kinetic evaluation from thermogravimetric data was used to determine energies of activation and pre-exponential factors.

Restricted access
Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: L. Julião, A. Azeredo, M. Santos, D. Melo, B. Dantas, and J. Lipsztein

Abstract  

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.

Restricted access

Abstract

The thermo-programmed reduction study of Pt/WOx–ZrO2 materials prepared with different tungsten loading were performed by thermogravimetry. The samples were synthesized by impregnation method and calcined at 600, 700 and 800°C. The characterizations of both un-calcined and calcined materials were carried out using different techniques: thermal analysis (TG and DTA), X-ray diffraction (XRD) and thermo-programmed reduction (TPR). TG and DTA analysis of un-calcined were used to determination of calcination temperatures of the samples. XRD diffractograms were useful to help us in the determination of phase presents. TPR profiles showed between three and four events at different temperatures attributed to platinum reduction and the different stages of tungsten specie reduction.

Restricted access