Resumo em Inglês:

We have designed and constructed an integral system that involves two electrostatic deflectors followed by a small ionization chamber with a multi-wire-proportional-counter in its entrance. The function of the former part is to separate evaporation residues from beam ions using their different electric rigidities while the latter is to detect these evaporation residues being distinguished from the beam-like particles originated in slits. Up to now, both devices have been tested and evaluated performing different experiments: the double-electrostatic deflector through scattering studies and the ionization chamber by means of scattering and fusion reactions. We present a brief description of the two devices and some results obtained in different tests.

Resumo em Inglês:

The past half century has seen an explosive growth of the discipline that is characterized by the deposition of localized high energy densities in solid matter, by means of energetic ions produced e.g. in particle accelerators. First the fundamentals of Ion-Solid Interaction are outlined. A brief overview is given about the basic energy transfer mechanisms and the consequences of ion impact into solids, such as scattering, sputtering and radiation damage. The latter gives rise to numerous changes in the material's physical and chemical properties, part of which has proven to be detrimental, and part of which is beneficial for technological applications. Though meanwhile a good general understanding of this discipline has been obtained, there are still plenty of lacks of details in our knowledge. Some representative examples are given. As a conclusion of all these points, one may say that, in spite of its age, Ion-Solid Interaction is still a challenging scientifical field, and it still offers lots of promising applications.

Resumo em Inglês:

The Monte Carlo method was employed to obtain the response of a position sensitive gamma ray detector. The basic unit consists of a scintillator bar coupled to two photon detectors. Determination of the position of interaction is obtained from the ratio of the light intensity measured at each extremity of the bar. Association of two or more detectors of this type can be used to build a system with potential use in positron emission tomography. For practical purposes, a CsI(Tl) bar with dimensions of 15×1×1 \thinspacecm³ was considered. Simulations were performed with the GEANT4 toolkit, using the physical processes of low-energy electromagnetic extension. Light attenuation coefficient and energy resolution of CsI(Tl) bars were included according to data found in the literature. Results obtained from detector irradiation with 511 keV annihilation photons indicate that the position of interaction can be determined with uncertainty of 3 mm. Simulations of positron sources placed between two detectors were also performed and two dimensional images were obtained.

Resumo em Inglês:

Concentrations of trace metallic element as well as macronutrients were measured in water and plants from pond water. The aquatic macrophyte Salvinia sp. was evaluated for its trace metals removal potential in river water under laboratory conditions. The experiment were performed using several healthy acclimatized plants Salvinia sp. The water and grown plants were collected from ponds. For the trace element removal´s test, 30-35 grams of fresh aquatic plants were grown in river water into a greenhouse for ten weeks. Control plants were also grown during the experiment. Every two weeks, both plants and water samples were collected. After the end of each experiment, the growth rate was calculated. Trace element concentrations in plants and pond water were obtained using TXRF techniques. Values for the elements (K, Ca, Ti, Fe, Cr, Mn, Cu, Zn and Sr) concentrations in plant dry weight have been obtained after deducting metal contents of control plants. For each trace element, the aquatic Salvinia sp. plant showed to possess different affinity for the incorporation of the metals in its biomass. Results suggest the use of aquatic macrophytes Salvinia sp. for metal abatement in dilute wastewaters.

Resumo em Inglês:

Although the idea of proton Computed Tomography (pCT) is not new, it is currently not available. It is still unknown if the image quality of pCT is sufficient for localizing tumors and if the accuracy of proton range calculations surpass that of X-ray CT based range calculations without significantly increasing the patient exposure. The spatial resolution of pCT is limited mainly by multiple Coulomb scattering, while the contrast resolution is affected principally by the statistical nature of the proton energy loss mechanism. Both effects are more pronounced and thus easier to study at the low proton energies available at CV-28. An experimental setup for pCT at CV-28 was elaborated by our team. The first-generation CT scheme was assumed as the most adequate for the existing CV-28 proton "pencil" beam. All equipment, which includes the collimators for the initial and outgoing proton beam, the tomographic turntable, and the ORTEC L-035-025-5 proton detector, was assembled onto the support bar of the ORTEC vacuum chamber. A water-filled glass tube of 5 mm external diameter with a 1 mm diameter polyethylene rod on the central axis was chosen as the first sample to be studied. Later, the water will be substituted by tissue-equivalent solutions of different densities to study the contrast resolution. A Monte Carlo simulation of the experiment, assuming 25 MeV monochromatic proton beam, was made using the SRIM-2003.20 code. The simulation permitted to choose the critical parameters for the setup, such as the beam collimation, the steps of translation and rotation of the turntable, and the required statistics for an accurate measurement of proton energy.

Resumo em Inglês:

One major objective of this work is to experimentally estimate the following kinetic parameters on the IPEN/MB-01 research reactor at São Paulo: the effective neutron delayed fraction, betaeff, the prompt neutron generation time, lambda, and the ratio betaeff/ lambda. In order to achieve our goal, we will use a microscopic noise technique called Rossi-alpha method. This method is based on the statistical nature of the fission-chain process. Using a coincidence acquisition system, the rationale is to experimentally determine the probability distribution of detecting neutrons from the same chain. Through a least-squares fit of this distribution we estimate the prompt neutron decay constant alpha = (betaeff-rho)/lambda. The alpha parameter will be measured for three sub-critical levels using three different source configurations, and the ratio betaeff/ lambda is obtained via a extrapolation to rho = 0. A specific acquisition system for Rossi-alpha measurements has been developed in order to achieve our objective. This system is based on a multichannel scaler controlled by virtual instruments that records the timing of all neutron events, allowing data analysis during the acquisition. The first measurements were performed using two BF3 detectors positioned at the center of IPEN/MB-01 reactor core. In the future the same measurements described above will be performed using ³He and photodiode detectors. The photodiode detectors have been developed by the Reactor Physics Division of IPEN. In this work we will present a preliminary set of Rossi-alpha measurements performed on the IPEN/MB-01 research reactor at São Paulo.

Resumo em Inglês:

Among the secondary detection effects in gamma-ray spectroscopy with HPGe detectors that reduce the peak area and must be properly taken into account in accurate measurements, the less well known is counting loss by beta and gamma-ray sum coincidence. The fraction of lost counts was estimated assuming that a photon detection event can sum either with the coincident beta-ray or its bremsstrahlung in the detector capsule or surrounding materials. The beta-ray was tracked through all the materials between source and detector. The result was calculated as a sequence of integral expressions evaluated numerically, without resorting to simulation. It is shown that the counting losses due to this effect are negligible for most calibration sources in typical detector arrangements.

Resumo em Inglês:

Trace element concentrations in water from São Francisco River using Particle Induced X-ray Emission (PIXE) and Synchroton Total Reflection X-ray Fluorescence (STXRF) techniques are measured. The main objective of this work was to characterize and to monitor the trace elements in the water of São Francisco River, as well as to provide valuable information about the levels of metallic ions pollutants. Water samples were collected monthly at five locations along the course of the river from July 2003 to April 2004. As an internal standard, 11.6 ppm of Yttrium was added to 10 ml of the water sample. The PIXE and TXRF measurements were performed at the Ion Beams and Materials Laboratory (LAMFI) and the Brazilian National Synchrotron Light Laboratory (LNLS), using a proton beam and a polychromatic X-ray beam, respectively. Si(Li) detectors were used to collect the X-ray spectra. Due to the excellent detection limits of the PIXE and STXRF analysis, up to 15 elements were quantified. The highest total content of Cr, As, Cu and Zn detected in river water are above the limits recommended by the environmental legislation.

Resumo em Inglês:

Human, bovine and swine teeth were analyzed by Proton Induced X-ray Emission (PIXE). The aim of this work was to determine the concentration of trace elements in enamel and dentine of different animal species. PIXE analysis was carried out at the Laboratório de Análise de Materiais por Feixes Iônicos da USP (LAMFI) using a 2.4 MeV proton beam to probe the samples. Healthy teeth from São Paulo region were analyzed. Thirteen elements were measured and quantified in the samples: P, S, Cl, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Sr and Ba. The measured ratio of Ca:P in dentine and enamel teeth is the same expected for hydroxyapatite: 2.13, for all three types. Trace element concentrations were found to be very similar between the three species, except for S, Cl, Fe, Cu and Sr. Ni and Cu concentrations were found to be close to 1 ppm, which is also close to the detection limits of the SP-PIXE system.

Resumo em Inglês:

A thermal neutron image acquiring system is being developed at the Instituto de Engenharia Nuclear-IEN (CNEN). This system would be capable to perform non-destructive assays after 2D images acquired on a real or quasi real time basis as well as 3D tomographic images reconstructed from the two-dimensional ones. The source-detector set is constituted by the Argonauta reactor - furnishing a thermal neutron flux of 4.46 ×10(5) n · cm-2·s-1 - and by a converter-scintillating screen for this kind of radiation. After a 90º deviation from its original path through a dark chamber provided with a properly positioned mirror, the light emitted by this screen is captured by a CCD-based video-camera coupled to a microcomputer which processes the data and supplies the final digital images. As a previous step aiming at the gathering of parameters and features to characterize the system, a conventional photo camera has been used instead of the video-camera being yet purchased. This work presents the qualitative and quantitative results obtained by using this preliminary system, such as 2D images of several objects and the Modulation Transfer Function-MTF respectively. Besides that, a comparison is made between the results achieved by using this system and those arising from a traditional neutrongraphy employing radiographic films.

Resumo em Inglês:

Ion implantation of the recoil 111In nuclei following heavy ion nuclear reactions 108Pd(7Li,4n)111In and 108Pd(6Li,3n)111In has been used to implant 111In probes in the Heusler alloys Pd2MnZ(Z=Sn,Sb,Ge,In). Perturbed Angular Correlation method was used to study the hyperfine magnetic field in these alloys. Direct implantation of 111In probe nuclei was used to great advantage in the present case resulting in large implantation efficiency. Only a few hours of irradiation time with moderate beam current of the order of 400-500 nA resulted in sufficient implanted 111In activity on the sample for good quality measurements. The hyperfine field was measured at 111In probe nuclei substituting Mn and Z sites as a function of temperature. The fraction of 111In nuclei occupying Mn atom sites was found to increases with the annealing of sample at higher temperatures.

Resumo em Inglês:

The divergence of the thermal neutron beam available at the main outlet channel of the Argonauta Reactor in the Instituto de Engenharia Nuclear has been measured by using a Position Sensitive Detector. The measurement process addressing a proper beam characterization has been conducted under several geometric arrangements, including attempts to reduce the beam divergence by using a honeycomb-type gadolinium collimator. Since the detector presents finite resolution, each measured position spectrum is a convolution of the true Rocking Curve expressing the beam divergence with the function that describes the detector response. Therefore, those spectra have been submitted to an unfolding process to recover the concealed Rocking Curve. Prior to undertake this task however, the detector Line Spread Function - LSF was determined as required by the unfolding process. This was done by taking the response of the detector to a line source simulated by a narrow slit-collimator placed at several distances from the detector window. After a Lorentzian fitting to the acquired position spectra, the related FWHM were plotted against the source-detector distance. An extrapolation to zero furnishes then the width of the unknown LSF expressed as a normalized Lorentz function, which was then incorporated to a computer program developed to perform the unfolding. The final Rocking Curve emerges then as a normalized Lorentzian function properly defined by its width and a zero offset, showing that the beam diverges about 2.2 cm in 1 meter. The honeycomb collimator could not reduce this divergence due to its low aspect ratio.

Resumo em Inglês:

Since 1985 the Argonauta Reactor at the Instituto de Engenharia Nuclear - IEN/CNEN has been used as a source of thermal neutrons to acquire transmission-generated radiographic images. From that time until the end of the last century, some Universities and Research Institutions have as well used the irradiation facilities of this reactor for that purpose and for technical and scientific training of personnel. Quite recently, a joint work program with the Laboratório de Instrumentação Nuclear - LIN/COPPE-UFRJ has been initiated addressing the research in the field of radiographic images using thermal neutrons, with special emphasis on Computer Aided Tomography. Within this frame, different tomographic systems - each one with their intrinsic features - have been developed aiming at their use in the industry field which requires the inspection of objects exhibiting different sizes and compositions. This work focuses the developed tomographs presenting their constraints and performances such as Spatial Resolution, Modulation Transfer Function and Density Resolution. The acquired images of some objects and test-bodies are as well presented for the sake of qualitative evaluation. They show a fair agreement with the performance of the tomographic system as expected from the measured quantitative parameters.

Resumo em Inglês:

We report a comparative study of two archaeological sites, Bela Vista and Serrano, located in the Araruama region of the state of Rio de Janeiro, in Brazil. The elemental geochemical compositions of the ceramics from both sites were determined by Instrumental Neutron Activation Analysis (INAA). A statistical treatment of the data, using cluster analysis and principal component analysis, indicates that there are no correlations between these sites.

Resumo em Inglês:

We report the measurement of Doppler broadening annihilation radiation in silicon, using 22Na as a positron source, and two Ge detectors arrangement. The two-dimensional coincidence energy spectrum was fitted using a model function. The model function included at rest positron annihilation with valence band, 2p, 2s, and 1s electrons. In-flight positron annihilation was also fitted. The detectors response functions included backscattering, and a combination of Compton effects, pileup, ballistic deficit, and pulse shaping problems. The obtained results agree well with the literature.

Resumo em Inglês:

Within our activities on accelerator-based boron neutron capture therapy (BNCT) carried out at the Tandar Laboratory (Comisión Nacional de Energía Atómica, Argentina) we present here the study and design of a tomographic imaging system for the measurement of the spatial distribution of the absorbed dose during a BNCT session. The 10B (n,alpha) 7Li boron neutron capture reaction produces a 478 keV gamma ray in 94 % of the cases. In BNCT a large fraction of this radiation escapes from the patient body. Its detection is thus very attractive for a noninvasive boron concentration measurement and an online absorbed dose evaluation since the dose absorbed by the tumor and healthy tissue strongly depends on the boron uptake and the neutron flux. For this purpose, a dedicated tomographic imaging system based on SPECT (Single Photon Emission Computed Tomography, a diagnostic medical imaging modality used in nuclear medicine) is proposed since standard SPECT cameras cannot be used due to the photon energy ( 478 keV ) and the particular background gamma field in BNCT. A detection system (collimator and detectors) is proposed. Monte Carlo numerical simulations are used for an implementation of a statistical algorithm used for the tomographic image reconstruction.

Resumo em Inglês:

Computed Tomography (CT) has made possible visualization of physical structures in the interior of an object in their real relative spatial position and orientation. Another important contribution of CT is to greatly improve abilities to distinguish regions with different gamma ray transmittance and to separate over-lying structures. The mathematical problem of CT imaging is that of estimating an image from its projections. In this work, the experimental setup was performed using the Mini Computerized Tomograph of Uniso (MTCU). This tomograph system operates with a gamma ray source of 241Am (photons of 60 KeV and 100 mCi of intensity) and a NaI(Tl) solid state detector. The system features translation and rotation scanning modes, a 100 mm effective field of view, 1 mm of spatial resolution and 5 % to 10 % of density resolution. The image reconstruction problem can be solved using two different algorithms: Algebraic Reconstruction Techniques (ART) or Discrete Filtered Backprojection (FBP). The three-dimensional image reconstruction method discussed in this work, involves obtaining two-dimensional (2D) gamma ray tomography images and then combining these images into a three-dimensional (3D) volume data. An opacity, shading and color is attributed to each volume element (voxel) and the resulting scene is projected in a picture plane to be display in a monitor. Our implementation was developed to be used with MTCU data and was based in the Ray casting volume rendering technique. The use of such technique for nondestructive evaluation is a powerful tool to enable a visual trip inside an object without physically opening or cutting it. Experimental and theoretical methods used are discussed and results of experiments using the 3D reconstruction techniques are presented. A particular use of this technique to study concrete properties, such as stones distributions, visualization of structural occurrences inside concrete samples is discussed.

Resumo em Inglês:

The Absolute Neutron Activation Analysis (ANAA) technique was used to estimate the reference value for Cl in whole blood of healthy group, selected from blood banks at São Paulo city, to provide information which can help in diagnosis of patients. The results show that the indicative interval obtained for Cl in serum from the nuclear analysis (3.41 - 3.69 µg ·mul-1) is in agreement with the reference value adopted (3.44 - 3.76 µg ·mul-1) in addition, an indicative interval for Cl (2.75 - 2.95 µg ·mul-1) could be proposed for whole blood. The advantages and limitations of using this nuclear methodology were discussed.

Resumo em Inglês:

The present work shows the evaluation of the flux and absorbed dose rate of neutrons in a 241AmBe Irradiator at IPEN facilities using the MCNP-4C transport code. The geometry of the 241AmBe source as well as the Irradiator design, constituted of 2 neutrons sources, were modeled. In addition, four and eight sources of 241AmBe were also considered for checking the viability to increase the Irradiator performance. The results show an increase for both flux and absorbed dose rate, mainly for the fast configuration.

Resumo em Inglês:

Intra-operative radiotherapy (IORT) using electron beams has demonstrated to be a good alternative as part of the breast-conserving surgery. Besides, as the computer processing capacity has been increasing along the years, it has become a potential auxiliary tool in radiotherapy treatment planning. In this work these streams are merged together: simulations were performed by different Monte Carlo radiation transport codes (EGS4 and MCNP in its releases 4C and 5) in an attempt to not only examine the efficacy of Al and Pb discs used in IORT procedures to protect critical regions but also to compare the performance of the forementioned codes.

Resumo em Inglês:

Prokaryote cells were exposed to ultra violet (UVc) radiation and to proton beams in order for the induced effects to be studied. Morphological and physiological alterations occurred in Escherichia coli (E. coli) cells exposed to the beams were investigated. The measurements using UVc radiation were made at the Biology Department of CEFET-PR while the measurements using proton beams were made at the Pelletron Accelerator of the Physics of the University at São Paulo. An exposition time of 3 to 15 seconds for UVc radiation and dose ranging from 0.2 to 10.0 Gy for protons was used. A cellular survival curve versus exposition time and absorbed dose was built for each case. After the irradiation the cells were submitted to a series of biochemical tests. It was observed that the E.Coli cells lost some basic biochemical properties when the received doses were in the range of 0.2 to 0.7 Gy. By microscopic observations it was noticed that the E.Coli cells elongated after irradiation with UVc as well as with proton beam.

Resumo em Inglês:

The accumulation and long term behavior of radiocesium in chili pepper trees (Capsicum fructescens) were studied. The trees to be analyzed had been cultivated at one of the sites where the Goiânia radiological accident occurred and one of them transplanted to another site with uncontaminated soil. The aim of this paper is to examine the decline of 137Cs as function of time and verify how this radionuclide and 40K were distributed throughout this tropical plant in natural environmental conditions.

Resumo em Inglês:

Stainless steel is widely employed in different areas of modern industrial production, taking advantage of its corrosion resistance. In this work we use the elastic recoil detection analysis (ERDA) to determinate the profile of nitrogen in stainless steel samples. An incident beam of 35Cl of 50 MeV was used for the analysis of sample components. The results have indicated the presence of thin films in the surface of some analyzed samples and have allowed the determination of the concentration and the thicknesses of these films.

Resumo em Inglês:

This paper describes the application of two techniques, ANAA and PIXE, used in the analyses of some available commercial food containing regular and genetically modified ingredients, as well as soybens cultivated with regular and genetically modified seeds (GMS). The aim of this work is determine their elemental composition to perform a comparative analysis. The elemental composition results of both types of food, obtained by the two techniques, were in agreement for all elements. Our results show the same elemental composition for all food samples but the quantitative analysis between soybeans seeds (regular and GM) suggested that the product made with GMS have higher concentration values, mainly for Cl, P and Zn, while for industrialized food, made with genetically modified products, a low concentration values were measured for most of the elements.

Resumo em Inglês:

Crews working on present-day jet aircraft are a large occupationally exposed group with a relatively high average effective dose from galactic cosmic radiation. Crews of future high-speed commercial flying at higher altitudes would be even more exposed. To help reduce the significant uncertainties in calculations of such exposures, the male adult voxels phantom MAX, developed in the Nuclear Energy Department of Pernambuco Federal University in Brazil, has been coupled with the Monte Carlo simulation code GEANT4. This toolkit, distributed and upgraded from the international scientific community of CERN/Switzerland, simulates thermal to ultrahigh energy neutrons transport and interactions in the matter. The high energy neutrons are pointed as the component that contribute about 70% of the neutron effective dose that represent the 35% to 60% total dose at aircraft altitude. In this research calculations of conversion coefficients from fluence to effective dose are performed for neutrons of energies from 100 MeV up to 1 GeV, irradiating MAX with mono-energetic beams in the mode Anterior-Posterior. An alternative methodology is developed too, using the atmospheric neutrons spectrum simulated with GEANT4 code at aircraft altitude instead of the traditional method that uses mono-energetic beams. To obtain the neutrons spectrum 1.5×10(5) extensive atmospheric showers are simulated by cosmic rays interactions with atmospherics atoms. The main characteristics of the spectrum are in agreement with literature confirming the validity of GEANT4. For 100 MeV energy the conversion coefficient calculated with spectrum shows a decrease of 8%, pointing out the importance of the environment influence.

Resumo em Inglês:

The odd-odd 58Co nucleus has been studied with the 51V(10B, p2n) reaction at 33-MeV incident energy and the gamma-spectrometer Saci-Pererê. Excited states up to 8.0 MeV and spin up to 11+ have been observed. The results are compared to Shell Model calculations using the GXPF1 effective interaction, developed for use in the fp shell. The pif7/2-1<FONT FACE=Symbol>Än</FONT>(p3/2²f5/2¹) configuration was assigned to the yrast levels.

Resumo em Inglês:

In this work, the escape width for nuclei with neutron excess is calculated by continuum Random Phase Approximation (RPA) with a careful treatment on the differences between the densities of neutrons and protons.

Resumo em Inglês:

The 94Mo nucleus is treated as an alpha-cluster interacting with an inert core through a phenomenological local potential. The properties of the ground state band of the alpha+90Zr system, such as the energy levels, intercluster rms radii and B(E2) transition strengths were calculated. These results are compared with previous references and available experimental data. Some predictions were made concerning the negative parity band and the excited positive parity band.

Resumo em Inglês:

The decay mechanisms of giant resonances have been revisited to investigate the isoscalar dipole resonance in 208Pb nucleus.

Resumo em Inglês:

In order to investigate the instabilities in asymmetric nuclear matter described within relativistic mean field hadron models, we build the spinodals. We have used relativistic models both with constant and density dependent couplings at zero and finite temperatures. We have seen that the main differences in the spinodals occur at finite temperature and large isospin asymmetry close to the boundary of the instability regions.

Resumo em Inglês:

We have revisited the low-energy calculation of odd Z 155Eu in the frame of a semi-microscopic formalism as a support for the interpretation of the experimental results for the multipole mixing ratios of some electromagnetic transitions. The deformation parameters were obtained through a macroscopic-microscopic method, and the proton single particle levels, calculated with realistic Woods-Saxon potential were used as input in a quasi-particle calculation of the first few rotational band heads in the Lipkin-Nogami BCS aproximation. A better agreement is found between the experimental and calculated band heads if compared with previous evaluations and RIPL recommended values.

Resumo em Inglês:

The beta decay of 155Sm (T1/2 ~ 22min) has been investigated by gamma spectroscopy measurements. The single and coincidence spectra were taken using HPGe detectors with high energy resolution. The energy and relative intensities of 42 gamma-rays have been determined, most of them with a better precision than previously. The gamma-transitions at 205.7keV and 224.8keV were observed for the first time and 40 of them were confirmed and 39 of them placed in the decay scheme. The present results, together with the results of earlier studies, allows to confirm the energy levels, in the energy range 0.05-1.6MeV, as well as the assignments of spin for most of them.

Resumo em Inglês:

The excited states in 193Ir populated by the beta- decay of 193Os were investigated via gamma-gamma coincidence analysis. Three levels at 517, 563 and 621 keV, previsouly seen only in nuclear reaction studies, were observed in the present measurements; the 487 keV transition from the 849 keV level was identified, providing good evidence that the levels at 848.93 and 849.083 keV are the same. The level at 807 keV was positively identified through both the 449 and 668 keV transitions; also, there is evidence for four new levels at 880, 882, 890 and 986 keV, and several newly-found gamma transitions were identified and placed in the decay scheme.

Resumo em Inglês:

Recent development and studies of physical and chemical properties of the conducting polymers have been calling the interest of many scientists. Among this group of materials, the polyaniline (PANI) deserves special attention because of its high chemical and thermal stability under normal conditions, simple process of polymerization and low cost. This polymer is also known due to its strongly pronounced and well studied electrochemical characteristics. In the present work, the variations of the electrical resistance of polyaniline caused by X-rays radiation have been studied. The polymer has been synthesized by electrochemical method in stainless steel and graphite electrodes. The data concerning the electrical resistance of PANI were measured just after the synthesis. This has been performed in the water solution of sulfuric acid within monomer of aniline where the polyaniline has been submitted to the applied voltages in the range from 200mV to 600mV. Polymeric samples have been irradiated using the X-rays with the energy 50keV and 100keV. After the irradiation, the electrical measurements have been repeated. The whole experimental procedure was performed several times. The obtained results have clearly shown the potential of polyaniline as a dose sensitive material that could be applied as a radiation sensor.

Resumo em Inglês:

A direct measurement of nn-scattering by colliding free neutrons has never been performed. Indirect measurements continue to provide inconsistent results, leaving the issue of charge symmetry in the nuclear force unresolved. At present the Russian pulsed reactor YAGUAR is the best neutron source for such a measurement. A neutron moderator is installed in the central through channel and the scattered neutrons are detected at a distance of 12 m from the reactor. An instantaneous value of 1.1 × 10(18)/cm²s was obtained for the thermal neutron flux density. The experiment will be performed by the DIANNA Collaboration as ISTC project No. 2286.

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I discuss recent applications of chiral effective field theory to study the properties of few-nucleon systems.

Resumo em Inglês:

We discuss macroscopic bulk properties of primordial bubbles quark matter which survived the confinement phase transition in the early universe. Electron and quark components are considered at zero temperaturemantaining beta equilibrium and charge neutrality. We analyze the possibility that a superconducting phase transition occurs,changing the initially unpaired quark matter phase to the colour-flavor locked (CFL) alternative without electrons. We had considered the gap energy and the Goldstone bosons condensation for the pressure calculation in the CFL phase.

Resumo em Inglês:

In the study of two interacting systems within the framework of microscopic theories, the correct treatment of the effective interaction between the fragments has been the most troubling problem, due to the technical difficulties in calculating the exchange terms. In the framework of the Generator Coordinate Method, and through a double projection technique, we obtain this effective interaction between two pairs of nucleons, taking into account the Coulomb exchange plus a nuclear part. Our treatment is useful in the analysis of the role of correlated nucleon pairs in photoabsorption experiments by nuclei.

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In this work we study an extension of a light-cone QCD-inspired model, where the interacting part of the mass squared operator consists of a harmonic oscillator potential as confinement, a Coulomb-like interaction and a zero-range spin interaction acting on the ³S0 states. The renormalization of the model is performed by using as a input the pion mass to fix the strength of the spin interaction. We apply the extended model to study the splitting of the ³S1 and ³S0 ground state mesons and the spectrum in the light meson sector. We show that the experimental values of the splitting between the masses of ³S1 and ³S0 ground state mesons as a function of the ground state pseudoscalar mass is reproduced by the model. In the botonium case our result is consistent with other theoretical estimates.

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In order to obtain the properties of compact stellar objects, appropriate equations of state have to be used. In the literature, strange meson fields, namely the scalar meson field sigma*(975) and the vector meson field phi(1020), had to be considered in order to reproduce the observed strongly attractive <FONT FACE=Symbol>LL</FONT> interaction. The introduction of these strange mesons makes the equations of state harder (EOS) due to the repulsive effect of the phi(1020) meson. In this work the inclusion of these mesons in the equation of state and their influence on the properties of the neutron stars are investigated.

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Short range correlations are introduced using unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. The effect of the correlations in the ground state properties of the nuclear matter is studied.

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In this communication we present results of a study of chiral symmetry in quark matter using an effective Coulomb gauge QCD Hamiltonian. QCD in Coulomb gauge is convenient for a variational approach based on a quasiparticle picture for the transverse gluons, in which a confining Coulomb potential arises naturally. We show that such an effective Hamiltonian predicts chiral restoration at too low quark densities. Possible reasons for such deficiency are discussed.

Resumo em Inglês:

A recursive subtractive renormalization of the scattering equation is applied to the nucleon-nucleon ¹S0 channel with one-pion-exchange plus derivative contact interactions. This method can be easily extended to any derivative order of the singular interaction. Although we limit this work to the singlet partial wave, the method can be used as well in higher waves and coupled channels. The ¹S0 renormalization parameters are fitted to the data.

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We obtain upper limits for the contributions of the incomplete fusion and sequential complete fusion processes to the total fusion cross section. Through those upper bounds we find that these processes are negligible in reactions induced by projectiles such as 6He and 11Li, which break up into neutrons and one fragment containing the full projectile charge.

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In order to better understand the breakup contribution to fusion, we perfomed light particle coincidence measurements for the systems 6,7Li+12C,59Co at energies near and above the barrier. A three body kinematics analysis is performed with the objective of separating the contributions of different reaction mechanisms. For small angular differences between the light particles, the sequential and direct breakup seem to dominate. On the other hand, for large detector separations, a sequential decay following transfer is likely to dominate.

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The method of fusion barrier distribution has been widely used to interpret the effect of nuclear structure on heavy-ion fusion reactions around the Coulomb barrier. We discuss a similar, but less well known, barrier distribution extracted from large-angle quasi-elastic scattering. We argue that this method has several advantages over the fusion barrier distribution, and offers an interesting tool for investigating unstable nuclei.

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This paper reviews the physics of the spallation which is a nuclear reaction in which a particle (e.g. proton) interacts with a nucleus. Given to the high energy of the incident proton, in a first stage it interacts with the individual nucleons in an intranuclear cascade which leads to the emission of secondary particles (neutrons, protons, mesons, etc.). In a secondary stage the nucleus is left in an excited state and can de-excite by evaporation and/or fission. Given to the high number of secondary neutrons produced (~ 30 n/p for proton energy of 1 GeV), this reaction can be used as a source of neutrons, for example for ADS systems as external source to drive the sub critical reactor. The main codes used in the ADS target design and an example on the utilization of one of these codes (the LAHET code) for typical ADS target are given.

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Two nuclear reactions, 11B+100Mo, (Eb=43 MeV) and 16O+51V, (Eb=70 MeV) were studied with a gamma spectrometer with a charged particle array in order to measure the correlation between gamma-rays emitted by residual nuclei produced by heavy-ion reactions in coincidence with a charged particles detected at different angles. Ratios of gamma-transition intensities in coincidence with charged particles were measured for the main products of these reactions, providing a differentiation between the exit channels, even when complete fusion is the only reaction mechanism.

Resumo em Inglês:

The detection of delayed X-rays produced by the decay that follows electron capture in the residual nuclei has been used in the past for the determination of fusion cross sections of tightly bound nuclei. In this work we applied this technique to study the effect of the break-up of a weakly bound projectile, like in the case of the 9Be + 144Sm system. Preliminary results of the complete fusion in this system at near barrier energies are presented.

Resumo em Inglês:

We obtained theoretical fusion cross sections based on a new and accurate procedure to calculate the Coulomb and nuclear interactions between deformed nuclei. The calculations were performed within the context of the barrier penetration model with zero point motion for the 64Ni + 64Ni system.

Resumo em Inglês:

We have used a parameter - free potential, obtained from data analysis at sub-barrier energies, to explain our measurements of elastic and several inelastic scattering cross sections for the 16,18O + 58Ni systems at an energy above the barrier. The data were analyzed through extensive coupled-channel calculations. Transfer cross sections could also be explained by the same interaction, which is consistent with the more fundamental São Paulo potential.

Resumo em Inglês:

One of the main applications of the Hybrid Reactors (ADS - Accelerator Driven System) is the incineration of transuranics (TRU) by fast neutrons that emerge from a spallation source in a sub critical reactor waste burner [1, 2]. For this application, an accurate description and prediction of spallation reaction is necessary, including all the characteristics concerning spatial and energetic angular distributions, spallation products and neutron multiplicity. To describe the nuclear reactions at intermediate and high energies, Monte Carlo calculations have been used. The CRISP package considers the intranuclear cascade (INC) that occurs during the spallation process in a realistic time-sequence approach in which all particles inside the nucleus can participate in the cascade and the nuclear density fluctuations are naturally taken into account during the process. The occupation number of each single particle level is considered as a function of time and a more realistic Pauli blocking mechanism can be performed. None of the existing models have effectively used all those features. The evaporation of protons and alpha particles are taken into account making possible the correct prediction of fissilities of actinides and pre-actinides [3]. Another implementation is the NN single-pion production reaction. This reaction is especially relevant if one is interested in neutron or proton multiplicities, since the creation/emission of pions is directly related with the excitation energy of the residual nucleus. We will present some results obtained with the CRISP package for proton-nucleus reaction at intermediate and high energies. This package was obtained by the coupling of the MCMC [4] and MCEF [5] codes, with the introduction of some improvements, such as better Pauli blocking mechanism, which constrains the residual nucleus energetic evolution to the Pauli Principle from the ground-state to the final compound-nucleus formed at the end of the intranuclear cascade process, and introduction of the most relevant resonant excitation and the NN single pion production channel. The results of interest for ADS development are consistent with the experimental data at different proton energies. More detailed calculations are being performed for studying other features of proton-nucleus reactions and with different targets.

Resumo em Inglês:

A new approach to evaluate nuclear photofissilities at incident photon energies above the pion photoproduction threshold has been recently developed and proved to describe successfully the fissilities of natPb and 232Th target nuclei at energies ~0.2-4.0 GeV. The method is merely a simple, semiempirical description of the photofission reactions in which fissility, f, is governed by two basic quantities, namely, i) the first-chance fission probability, $\bar{f}_1$, for the average cascade residual, and ii) the slope, $\bar{s}$, of the chance-fission probability associated with the average evaporative sequence of fissionable residuals. In the present work we have extended this approach to analyse photofissity data that have been accumulated over the past fourty years or so, measured at 1 GeV, for nearly fourty target nuclei extending from Ti up to Np. Results have shown that the variation of fissility with Z²/A could be described quite satisfactorily by the proposed model.

Resumo em Inglês:

The decay of the compound nucleus is traditionally calculated using one of two types of statistical models, either a sequential or a simultaneous emission one. The best known sequential emission models are the Weisskopf-Ewing one and the Hauser-Feshbach one. Both sequential emission models emit only one particle at a time. A well know simultaneous emission model is the Fermi breakup one, which takes into account the fragmentation of the compound nuclei into two, three or more residual nuclei/particles. We have compared the particle and residual nucleus distributions of the Weisskopf-Ewing and Fermi breakup models in the case in which only stable nuclei/particles are emitted. We find that the Weisskopf-Ewing results in larger yields of light particles and heavy residues than the Fermi breakup model, while the latter results in larger yields of intermediate mass fragments.