Repositório RCAAP

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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.

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.