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  • Author or Editor: M. Bacchi x
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Abstract  

Soil is usually carried to the mills, as an impurity in sugar cane, leading to economic drawbacks for the industry. The quantification of this dirt is important to identify its causes and for routine quality control. Several methods have been used for this purpose, however, no single one has been pointed out as an industrial standard. The use of a γ-ray emitting radionuclide of natural occurence was investigated and, after several soil and cane radioactivity analyses,212Pb was chosen as the best tracer. Calibration curves developed with the addition of soil in clean cane, from 0 to 10% (dry mass), demonstrated the linearity of the method. Analyses of eleven samples taken from consignments showed that the procedure was consistent and reliable when compared to the traditional ash method.

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Abstract  

This work shortly describes the main steps involved in the design and development of the software package Quantu, created to conduct k 0-standardized NAA. The package comprises a database as well as two individual programs. Quantu-MCA is dedicated to (g-ray spectrum analysis and Quantu-INAA is the interface for the database administration, also dealing with k 0-method calculations.

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Abstract  

Selenium detection limits of INAA are normally above its concentration in most biological materials. Gamma-gamma coincidence methodology can be used to improve the detection limits and uncertainties in the determination of selenium. Here, some edible parts of plants were measured using a HPGe detector equipped with a NaI(Tl) active shielding, producing spectra both in normal and coincidence modes. The results presented the reduction of the detection limits of selenium by a factor of 2 to 3 times and improvement in the uncertainty of up to 2 times.

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Abstract  

After more than ten years working with multicomparator instrumental neutron activation analysis, mainly applied to the characterization of environmental samples, the Radioisotopes Laboratory (CENA/USP) started changing gradually to the k 0-method in 1997. The main activities developed, as well as some of the results obtained, are presented here. Even though there is much more work to be done, the good quality of the results and the possibility of elemental determinations without the co-irradiation of standards may lead to the definitive adoption of the k 0-method in a near future.

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Abstract  

Brazil has become the largest producer of biomass ethanol derived from sugar cane. The industrial production is based on the fermentation of sugar cane juice by yeast, inside of large volume vats, in a fed-batch process that recycles yeast cells. To study the dynamics of chemical elements in each operating cycle, five stages of the fementation process were considered: must, yeast suspension, wine, non-yeast wine and yeast cream. For this, a mass balance of the terrigenous elements, Ce, Co, Cs, Eu, Fe, Hf, La, Na, Sc, Sm, and Th, and the sugar cane plant elements, Br, K, Rb, and Zn, were established in fementation vats of an industrial scale unit, with sampling undertaken during different climatic conditions (dry and rainy periods). A similar distribution of the sugar cane characteristics elements was found for the stages analysed, while for the terrigenous elements a trend of accumulation in the yeast cream was observed. Preferential absorption of Br, K, Rb, and Zn by yeast cells was indicated by the smaller concentrations observed in yeast suspension than in yeast cream.

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Abstract  

The experimental work involved the efficiency determination of three coaxial hyperpure Ge detectors, using point-like sources placed at various distances from the top cover of the detectors. Curves were fitted to the experimental data and a microcomputer routine was developed to calculate the efficiencies of cylindrical sources, including self-attenuation correction. Tested at various source and distance conditions, the procedure showed results sufficiently consistent for routine k 0-INAA.

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Abstract  

New software was developed to assist users of the k 0-approach in NAA to harmonize their results. The k 0-IAEA software uses the holistic approach developed at the Delft Interfaculty Reactor Institute and incorporates the latest k 0 data catalogue together with additional information on coincidence and sum peaks, which together are used in the joint evaluation of samples. Multiple irradiations as well as multiple measurements of samples are treated simultaneously. Flux parameter determination as well as efficiency calibrations of detectors are accommodated using a single-measurement approach as developed at the Interfaculty Reactor Institute, Delft. The standard Windows software will stimulate the application of the k0 approach through the free distribution and updates of the program.

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Abstract  

This work presents a comparison of analytical results obtained for U, Th, K, and Fe in solid material from tailings pond, carried out within the CIPC's Tailings Management Program, with those achieved by instrumental neutron activation analysis. The validity of the techniques applied for dissolution and determination of elements in high silicate grade material, as the present case, can be assured by good agreement of the resulst.

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Abstract  

Aiming at the determination of toxic and essential elements in Brazilian commercial bovine milk, 25 ultra high temperature (UHT) milk samples were acquired in the local market of Piracicaba, SP. The samples were freeze-dried and analyzed by instrumental neutron activation analysis (INAA) allowing the determination of Br, Ca, Co, Cs, Fe, K, Na, Rb and Zn. When the results were expressed as concentration (mg·l−1) no significant differences were found. However, considering the dry matter, results showed a clear difference between the mass fractions (mg·kg−1 d.w.) of skim milk and whole milk for the elements Br, Ca, K, Na, Rb and Zn, indicating that the removal of fat caused a concentration effect in the dry matter of skim milks. Discrepancies were found between the concentrations of Ca and Na measured by INAA and the values informed in the labels. Ca showed variations within 30% for most samples, while concentrations of Na were up to 190% higher than informed values. The sample preparation and the INAA procedure were appropriate for the determination of Br, Ca, Co, Cs, Fe, K, Na, Rb and Zn in milk samples.

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Abstract  

This study investigated the representativeness of samples for assessing chemical elements in milk bulk tanks. Milk samples were collected from a closed tank in a dairy plant and from an open top tank in a dairy farm. Samples were analyzed for chemical elements by instrumental neutron activation analysis (INAA). For both experiments, Br, Ca, Cs, K, Na, Rb and Zn did not present significant differences between samples thereby indicating the appropriateness of the sampling procedure adopted to evaluate the analytes of interest.

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