Showing papers by "National Nuclear Energy Commission published in 1999"

Study of Correlations between Microstructure and Conductivity in a Thermoplastic Polyurethane Electrolyte

Abstract: Micro-Raman and positron annihilation lifetime spectroscopy (PALS) have been used to investigate the structure of a thermoplastic polyurethane/LiClO4 solid flexible polymer electrolyte at room temperature. Correlation between the free volume and carrier concentration with ionic conductivity was observed. The polyurethane soft phase consisted of a poly(tetramethylene glycol-co-ethylene glycol) copolymer reinforced by condensation with hexamethyldiisocianate. The range of salt concentration between 5 and 35 wt %, which attained the beginning of phase segregation, was also studied by differential scanning calorimetry (DSC), which showed the presence of three thermal events; the soft-phase Tg, a change in heat capacity suggested as the hard-phase Tg, and a hard-phase ordering endotherm. The total ionic conductivity was found to be approximately 4 × 10-6 S cm-1 at 23 °C up to 27 wt % salt, whereas there were pronounced changes observed by the spectroscopic techniques. The PALS measurements indicated a decrease...

Radiation damage studies on the optical and mechanical properties of plastic scintillators

Abstract: This paper describes the radiation damage studies on a large volume plastic scintillator based in polystyrene doped with PPO and POPOP. The consequences on their mechanical and scintillation properties were evaluated before and after irradiation with different dose rates of 60 Co gamma radiation, in several doses. The optical results show a significant difference in the radiation susceptibility, when the plastic scintillator is irradiated at low rate (0.1 kGy/h) with that irradiated at high dose rate (85 kGy/h). The losses in the optical and mechanical properties increase as the irradiation dose is increased. The damage evaluated by the transmittance, emission intensity, pulse height and tensile strength was normalized as a damage fraction and fitted by a bi-exponential function. It was observed that the damage for irradiation is not permanent and it obeys a bi-exponential function.

Radioactivity in and committed effective dose from some Brazilian foodstuffs.

Abstract: Thirty-eight types of food including fruits, vegetables, cereals, and meat have been analyzed by gamma-ray spectrometry. Clove and black pepper were found to have the highest concentration of 137Cs. The annual intake of 40K, 228Ra, 226Ra, and 137Cs were found to be 14 kBq, 53.2 Bq, 17.5 Bq, and 3.2 Bq, respectively, taking into account the typical diet of Sao Paulo City, Brazil. The annual committed effective doses from these radionuclides for adults were estimated to be 87.4 microSv, 36.7 microSv, 4.9 microSv, and 0.04 microSv, respectively.

The inversion point of the isothermal reactivity coefficient of the IPEN/MB-01 reactor-1 : Experimental procedure

Abstract: A new experimental quantity is presented to serve as a benchmark to verify the adequacy of the newly released 235 U thermal and subthermal cross sections for the determination of the reactivity coefficients of light water reactors. Such a quantity is denominated the inversion point, and by definition it is the temperature for which the isothermal reactivity coefficient of a reactor system becomes positive. The experimental bases for its determination are discussed. The experiment has been performed in the IPEN/ MB-01 reactor facility. Instead of heating the reactor system as usual in experiments considering temperature variations, the reactor system is cooled to ∼8.5°C. By means ofa heating/cooling system, the temperature is allowed to increase slowly in a stepwise manner. For each step, the control bank critical position is recorded, and by analyzing its behavior as a function of temperature, the inversion point is inferred. The inversion point has been found to be an adequate experimental quantity to validate the thermal and subthermal 235 U cross section because it does not require any sort of calculated correction factors or any quantity that comes either from the calculational methodologies or from another experiment. In addition, the inversion point is an experimental quantity that can be measured with an excellent level of accuracy due mainly to the very precise characteristics of the control bank system of the IPEN/MB-01 reactor. The final value obtained for the IPEN/MB-01 reactor is 14.99 ± 0.15°C.

Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy in alkali niobium tellurite glasses

Abstract: Alkali niobium tellurite glasses have been prepared and some of their properties measured by differential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO2–Nb2O5–(0.5K2O–0.5Li2O). Raman scattering shows that for samples in the TeO2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO4) units connected by the vertices, as in the α-TeO2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed essentially of (TeO3) and (NbO6) units. Samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing up to 10% mol Nd3+. The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd3+ sample amorphous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd–Ofelt Ωλ intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd3+ concentration, we suggest that these glasses could be utilized in optical amplifying devices.

Natural convection inside two‐dimensional cavities: the integral transform method

Abstract: The Integral Transform Method is employed in the hybrid numerical-analytical solution of laminar natural convection inside rectangular enclosures. The hybrid nature of this approach allows for the establishment of benchmark results in the solution of non-linear partial differential systems, including the coupled set of heat and fluid flow equations that govern the steady natural convection problem under consideration. Therefore, numerical results under user prescribed accuracy are obtained for different values of the governing parameters, and the convergence behaviour of the proposed eigenfunction expansions is illustrated. Critical comparisons against previously reported benchmark solutions are then performed

An enhanced pipe elbow element : application in plastic limit analysis of pipe structures

Abstract: In this paper, we present a new pipe elbow element based on a previous simplified model proposed by Bathe and Almeida [1, 2] and modified by Militello and Huespe [3]. It is really a beam-type element but it describes the ovalization, warping, radial expansion and non-symmetric deformation of cross-section of curved pipe with Fourier series. Therefore, it could model precisely enough a real pipe elbow structure but remains simple. The extensive loading cases are effectively implemented by the proposed numerical techniques and displacement model. The developed element is used in this paper in plastic limit analysis of pipe elbow structures. This is realized by means of a direct mathematical programming technique. Various elastic and plastic limit state analyses of straight pipes and elbow structures are presented, which illustrates the efficiency of the element and the numerical method. Copyright © 1999 John Wiley & Sons, Ltd.

Relationship between thermomechanical treatment, microstructure and α′ martensite in stainless Fe-based shape memory alloys

Abstract: This work presents some preliminary results relating training treatment, training temperature and the formation of α′ martensite to the shape recovery effect of stainless shape memory alloys. For the composition tested, the sample shows some mechanical memory (constant tensile stress at 4% strain and constant yield stress throughout the training cycles) with a very good shape recovery (95% after 4% tensile strain) at a training temperature of 873 K. Its residual strain is related to the generation of perfect dislocations only. For the sample trained at 723 K, the residual strain could be attributed to incomplete reversion of stress-induced e martensite, in part due to the blocking effect of α′ martensite and also to the generation of perfect dislocations. The influence of α′ martensite on shape recovery is relative and is dependent on training temperature, and the preferential growth of α′ martensite is shown to occur for large grain size.

Instrumental neutron activation analysis of rib bone samples and of bone reference materials.

Abstract: The instrumental neutron activation analysis method was used for the determination of trace elements in rib bone samples taken from autopsies of accident victims. The elements Br, Ca, Cl, Cr, Fe, Mg, Mn, Na, P, Sr, Rb, and Zn were determined in cortical tissues by using short and long irradiations with thermal neutron flux of the IEA-R1m nuclear reactor. The reference materials NIST SRM 1400 Bone Ash and NIST SRM 1486 Bone Meal were also analyzed in order to evaluate the precision and the accuracy of the results. It was verified that lyophilization is the most convenient process for drying bone samples because it does not cause any element losses. Comparisons were made between the results obtained for rib samples and the literature values as well as between the results obtained for different ribs from a single individual and for bones from different individuals.

Synthesis of nanocrystalline tetragonal zirconia by a polymeric organometallic method

Abstract: A polymeric precursor method based on the Pechini process was successfully used to synthesize zirconia-12 mol% ceria ceramic powders. The influence of the main process variables (citric acid-ethylene glycol ratio, citric acid-total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investigated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystalline tetragonal zirconia single-phase, with crystallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m 2 g 1 . Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions.

Application of radiochemical methods and dispersion model in the study of environmental pollution in brazil

Abstract: Methodologies for analysis of anthropogenic and natural radionuclides in marine samples were developed and applied in environmental samples. Results of systematic measurements of these radionuclides have showed that artificial radioactivity levels are in agreement with the values from the regions not affected directly by nuclear accidents or nuclear reprocessing plant discharges and are due to the global fallout. The average concentration of137Cs is of 1.4 Bq·m−3 in seawater, ranges from 13 to 220 mBq·kg−1 in fish, and from 0.4 to 1.8 Bq·kg−1 for sediments.90Sr levels in seawater are of 1.8 Bq·m−3 and in fish vary from 19 to 75 mBq·kg−1. Sediments present concentrations of90Sr lower than 0.8 Bq·kg−1 and for239+240Pu of 0.03 to 0.18 Bq·kg−1.210Po levels in fish range from 0.5 to 5.3 Bq·kg−1. The data generated represent reference values for our country and are used to estimate the intake levels of these radionuclides by consuming of marine products.

Determinação da composição mineral de subprodutos agroindustriais utilizados na alimentação animal, pela técnica de ativação neutrônica

Abstract: This study aimed to analyze some agroindustrial by-products used to feed animals in order to identify the presence of the main minerals. Samples of cotton seed meal, rice, canola, soybean and wheat; fish meal, feather meal, meat meal, feather plus viscera meal; rinds of cotton, rice, orange; citrus pulp and tomato residue were collected in different sites of production of the by-products. The method of analysis used was the neutron activation followed by gamma ray spectrometry. The levels of minerals found in all samples were compared with the levels commonly found in forages. The mineral concentration, even those of the toxic elements, as As, Cd and Hg, was at low level and did not exceed the maximum tolerable levels for domestic animals.

New valleys of cold fission and cluster radioactivity processes from nuclei far from the β-stability line

Abstract: The present work provides new results for the half-life of cluster radioactivity and cold fission processes from neutron-deficient nuclei of atomic number near proton shell closure. Results are also reported for the half-life of possible decays leading to the neutron-deficient, doubly magic island near ${}^{100}\mathrm{Sn}.$ The model reproduces the well-established experimental systematics of Geiger-Nuttall diagrams for alpha decay, as well as predicting similar diagrams for heavy cluster emission and cold fission processes.

Microstructural studies on Pr-Fe-B-Cu magnets produced by upset forging of cast ingot

Abstract: Recent work has shown that Pr–Fe–B–Cu-type permanent magnets have been produced from cast ingot materials using upset forging and that intrinsic coercivity can be enhanced substantially by a post forging heat treatment at 1000°C for 5 h plus 500°C for 3 h. In the present work, the microstructures of both as-upset forged and heat treated magnets have been investigated by optical and by scanning electron microscopy (SEM) in an attempt to explain the origin of this increase in the intrinsic coercivity. Backscattered electron images on the SEM, energy dispersive X-ray analysis (EDX) and thermomagnetic analysis confirm the presence of Pr2Fe17 (Fe/Pr≈8.2) after the upset forging process and heat treatment at l000°C. The quantity of this phase is substantially reduced after the second heat treatment at 500°C. In addition a Pr34Fe62Cu4 (Pr6Fe13Cu) phase has also been observed by SEM and EDX analysis after the anneal at 500°C. The increase in the coercivity on annealing has been attributed to the grain boundary improvement isolation and to the reduction in the amount of the Pr2Fe17 phase after heat treatment at 500°C.

Use of radioiodine urinalysis for effective thyroid blocking in the first few hours post exposure.

Abstract: A useful correlation between maximum thyroid uptake and radioiodine urine levels at different times after exposure was developed in order to determine when the intervention with an adequate blocking agent might still be effective. In an animal model (dog), six different doses were administered in the range of 100-600 kBq. The best correlation was found between the 125 I uptake after 48 h (T-48) and urine radioactivity 4-6 h (U-4, U-5, U-6) after exposure. For the case of U-4, the equation Y T-48 = 0.790 X U-4 + 2.973 (r = 0.974 with a level of significance of p < 0.001) was obtained. An analogous study, carried out in humans (n = 20) to whom 131 I was administered, showed a similar correlation and level of significance: Y T-24 = 1.162 X U-4 + 3.263 (r = 0.926; p < 0.001). The validity of this correlation was confirmed in four volunteers who received small doses of 125 I (25-100 kBq), with good agreement between measured and extrapolated thyroid uptake and a mean difference of less than 10% (CV = 16.2%). Three different blocking agents were then tested in the same dog: potassium iodide, potassium perchlorate, and a thionamide (Tapazole ) . The blocking action of the first two compounds was about 90%, as opposed to only 48% for the third compound. Potassium iodide was chosen for its limited side effects and more universal utilization. The final study, carried out with four different doses, indicated that 25 mg of KI is the ideal amount to be administered to the dog. This corresponds to approximately 100 mg for a 70 kg human being (i.e., 1.4 mg kg -1 ). This dose, when administered to a volunteer 4 h after exposure, provided a thyroid blocking of 68%.

Determinação de elementos essenciais e não essenciais em palmito de pupunheira.

Abstract: Considerando-se a atual situacao epidemiologica do Brasil em que a obesidade e as doencas cronico-degenerativas (doencas cardiovasculares, diabetes mellitus e câncer) passam a ser destaque em saude publica, parece prudente a preocupacao quanto a caracterizacao quimica dos alimentos regionais com potencial economico e nutricional, em especial os de baixo teor calorico, como o palmito. Sendo assim, determinou-se a composicao centesimal, fitato e elementos minerais (macro e micro) no palmito de pupunheira in natura e cozido. O palmito de pupunheira utilizado foi o da raca Pampa Hermosa, da Estacao Experimental de Fruticultura da Coordenacao de Pesquisas em Ciencias Agronomicas (CPCA) do Instituto Nacional de Pesquisas da Amazonia (INPA), em Manaus (AM), coletado no periodo chuvoso, em janeiro de 1995. Tomou-se aleatoriamente 3,5 kg de palmito de 110 progenies de pupunha inerme, com 2 anos de idade, por ocasiao do primeiro corte. As palmeiras foram cultivadas em Latossolo Amarelo, isento de adubacao. As analises quimicas foram efetuadas no Laboratorio de Nutricao e Fisico-Quimica dos Alimentos do INPA e IPEN-CNEN. De acordo com os resultados obtidos, verificou-se que o palmito, in natura e cozido, apresentou em 100g da parte comestivel respectivamente, alto teor de umidade, em torno de 90%; 1,5 g de proteinas; baixo teor de lipidio (0,3 e 0,2 g) e; concentracoes importantes de fibra alimentar (3,8 e 2,2 g). Em relacao aos elementos minerais nutricionalmente importantes sobressairam, tambem em 100g da parte comestivel, K (194,0 mg; 128,0 mg); Ca (42,4 mg ; 42,9 mg); Mg (3,4 mg; 2,2 mg); Fe (237,7 µg; 265,2 µg), Se (2,1 µg; 2,8 µg), respectivamente no palmito in natura e cozido. Dos elementos minerais nao essenciais na alimentacao, destacaram-se o bromo (830,4 ±5,8 µg%; 434±5,8 µg%) e o rubidio (315,2±3,2 µg%; 433,5±34,0 µg%) respectivamente para palmito in natura e cozido. A concentracao de fitato (hexafosfato de mioinositol) foi de 554,7 mg% para o palmito in natura e 379,1 mg%, para o palmito cozido. Apesar do palmito ser um alimento dietetico sob o ponto de vista nutricional, devido a baixa concentracao em calorias e a presenca de fibra, o mesmo pode contribuir no aporte de minerais essenciais na alimentacao da populacao Amazonica.

Resinas quelantes amidoxímicas

Abstract: Resinas quelantes com grupos amidoxima foram sintetizadas por copolimerizacao em suspensao de acrilonitrila (AN) e divinilbenzeno (DVB) e subsequente modificacao quimica dos grupos ciano por reacao com hidroxilamina. Na copolimerizacao, a proporcao de divinilbenzeno e o grau de diluicao foram variados. Gelatina e carbonato de calcio foram usados como estabilizadores de suspensao e sulfato de sodio foi adicionado para reduzir a solubilidade da acrilonitrila em agua, por meio do efeito salting out. Os copolimeros de AN/DVB e as resinas amidoximicas obtidos foram caracterizados por meio de densidade aparente, area especifica, volume de poros e teor de nitrogenio. As resinas amidoximicas foram tambem avaliadas em relacao a capacidade de complexacao de ions cobre.

Measurements of neutron photoproduction cross sections for 232Th and 238U using capture gamma rays

Abstract: Neutron photoproduction studies for {sup 232}Th and {sup 238}U were carried out from 5.61 to 10.83 MeV, by using up to 30 neutron capture gamma rays with high resolution in energy (4 to 20 eV), produced in an experimental arrangement at the IPEN-IEA-R12-MW research reactor. Samples of U{sub 3}O{sub 8} depleted to 0.34% in {sup 235}U and natural ThO{sub 2} were irradiated inside a 4{pi} sr long-counter neutron detector system, 520.5 cm away from the capture target. The gamma-ray flux was determined by means of a coaxial solid state Ge(Li) detector (EG and G ORTEC, 25 cm{sup 3}, 5%) previously calibrated with capture gamma rays from a standard target of nitrogen (melamine). The compound neutron photoproduction cross section was measured for the gamma-ray spectrum produced by each capture target. Two methods to unfold the set of experimental data were proposed in order to obtain the differential cross sections at the main gamma line energies: the iterative and the least-squares methods. The calculated neutron photoproduction cross sections for {sup 232}Th and {sup 238}U were compared with experimental data reported by other authors who have employed different gamma-ray sources. A good overall agreement was observed among the experimental data, however, marked discrepancies more » were identified for some data points, indicating the possibility of narrow structures showing up at these excitation energies. « less