Repositório RCAAP

The propagation of the struck proton through the nuclear medium is studied in the semi-classical multicolli-sional internuclear cascade approach. The probability of formation of various residual nucleus configurations and the corresponding excitation energies were obtained as a function of the energy omega transferred to the proton by the knockout.

The utilization of a position sensitive detector in tomographic systems is an attractive possibility because it is capable of furnishing the position where the ionizing event occurs. This feature can reduce significantly the image acquiring time, since a sample translation is no longer required. In this work the performance of a gaseous position sensitive detector equipping a thermal neutron tomographic system has been improved by a stepwise increase of the filling-gas (³He-enriched helium) pressure from 3 to 6 atm. Important quantitative detector parameters such as resolution, linearity and homogeneity have been measured for that pressure range, and compared with the tomographic images of test-samples. Several test-samples have been studied, all of them constituted by an aluminum cylinder containing inserts of different materials. Besides that, the modulation transfer function-MTF for the system has been experimentally obtained and compared with the expected theoretical curve. An improvement of both detector efficiency and resolution has been observed, as theoretically expected from an increase of the filling-gas pressure.

The study of the odd 99;101Ru nuclei complements the investigation of the collectivity of the first quadrupolar excitations in 100;102;104Ru. Angular distributions for the 99;101Ru(d, d') reactions at 13 MeV were obtained in the Pelletron Laboratory using nuclear emulsion plates on the focal plane of the Enge spectrograph. A Coulomb-Nuclar Interference analysis employing DWBA-DOMP predictions with global optical potential parameters was applied to the excitation of states which could belong to the multiplet built on the first quadrupolar excitation of the core. In the analysis, three states were identified for each of the isotopes and associated, respectively, with adopted levels in the Nuclear Data Sheets Compilation of Jpi= 5=2+, 7=2+ and 9=2+. Through the comparison of experimental and predicted cross section angular distributions, the values of (<IMG SRC="/img/revistas/bjp/v34n3a/a14img01.gif">)² and of the ratio C = <IMG SRC="/img/revistas/bjp/v34n3a/a14img01.gif" >/ <IMG SRC="/img/revistas/bjp/v34n3a/a14img02.gif" >were obtained.

A linear realization of flavor SU (3) × SU (3) symmetry is developped with scalar and pseudoscalar mesons coupled to baryons and massive vector fields. This system may be also coupled to colored quarks and gluons, which are expected to be deconfined above a critical range of energy densities and seemingly inside baryons. The coupling to vector fields may lead to finite density baryonic and also anti-baryonic matter. Prescriptions for the stability equation which yields bound systems is verified. A qualitative discussion of the possible resulting (QCD - type) phase diagram is discussed including the possibility of finding several kinds of superfluid (and eventually superconductive) states. Some bosonic fields are assumed to have non zero expected values, at least at low energies, corresponding to dynamical symmetry breakings. A generalized symmetry radius is found and the masses of the particles are found to vary with density. Possible relevance to relativistic heavy ion collision is pointed out.

A computer program to simulate tomographic images generated by transmitted radiation was developed. The algorithm uses a deterministic approach to generate the projections, which supply an existing image reconstruction software. A dispersion associated with the counting statistics is also incorporated into the algorithm, in order to simulate the influence of the detector efficiency and counting time on the final image quality. The detector resolution is also included in the algorithm by assuming a gaussian shape for its line spread function - LSF. The program deals with cylindrical objects containing any desired number of cylindrical rods inside and requires their positions, dimensions and attenuation properties as input data. Images of such objects, acquired with a thermal neutron tomograph equipped with a position sensitive detector, have been compared with those simulated by the developed program in order to evaluate its ability to reproduce those images.

Using a relativistic nuclear optical potential consisting of a Lorentz scalar, Vs, and the time-like component of a four-vector potential, V0, with a Gaussian form factor, we have calculated elastic scattering differential sections and polarizations for p+ 6,8He at intermediate energies. We compare our results with those of the Relativisitic Impulse Approximation (RIA) and with the available experimental data in the range of 0 < t < 0.22 (GeV/c)².

Angular distributions for the inelastic scattering of 13.0 MeV deuterons on 104;106;108;110Pd were measured with the Sao Paulo Pelletron-Enge-Spectrograph facility in the range of 12(0) < thetalab < 64(0). A Coulomb-Nuclear Interference analysis, employing the Distorted Wave Born Approximation with the Deformed Optical Model as transition potential, under well established global optical parameters, was applied to the first quadrupolar excitations. The values of C = <IMG SRC="/img/revistas/bjp/v34n3a/a14img02.gif">/ <IMG SRC="/img/revistas/bjp/v34n3a/a14img01.gif">, the ratio of charge to isoscalar deformation lengths, and of (<IMG SRC="/img/revistas/bjp/v34n3a/a14img01.gif">)² were extracted through the comparison of experimental and predicted cross section angular distributions. The ratios of reduced charge to isoscalar transition probabilities, B(EL) to B(ISL) respectively, are related to the square of the parameter C and were thus obtained with the advantage of scale uncertainties cancellation. For 104Pd, and preliminary for 108Pd, the respective values of C = 1.18(3) and C = 1.13(4) reveal an enhanced contribution of the protons relative to the neutrons to the excitation, while a smaller effect is found for 106Pd, C = 1.06(3) and for 110Pd, C = 1.07(3), in comparison with the value C = 1.00 expected for homogenous collective excitations.

We address the description of nuclear dynamics at intermediate energies within the DYWAN model. New fluctuation-dissipation aspects are discussed and confronted with experimental results in nucleus-nucleus and in nucleon-nucleus reactions. We show that the implemented treatment of fluctuations provides with a convenient tool to investigate the main characteristics of particle and light clusters emission in the intermediate energy range.

The potentialities of coherent X-radiation for investigation of structural features of self-assembled systems and liquid crystals was studied using Monte Carlo techniques. The radiation spectra were simulated for the case of interaction of 20 MeV electrons with a liquid crystal, and the influence of the various crystal parameters was studied. The simulations show that coherent X-radiation spectra are almost free of background, and that such measurements could be considered as an alternative to those where Synchrotron sources are used.

This paper describes the IPEN Cyclotron CV-28, and its utilization in basic and applied physics and to drive a zero power lead Accelerator Driven System (ADS), as a milestone in a road map for a phrogram or network on the utilization of accelerators. Preliminary results for a conceptual lead sub critical cubic matrix with square or hexagonal metallic U pins driven by a proton beam (24 MeV; 50 muA) are shown. These results demonstrate the feasibility to use the CV-28 to drive the zero power ADS.

High spin states in the neutron rich 188Os and 190Os nuclei have been populated using the 82Se + 192Os deepinelastic reaction. The level schemes are extended up to spin I <FONT FACE=Symbol>»</FONT>21. The observed new structures are tentatively interpreted as fragments of rotational bands built on multi-quasiparticle configurations.

Symmetries and statistical properties in nuclei are closely related. The most striking example is the extremely large enhancement of parity violation in neutron resonances. Statistical distributions can provide information about the underlying character of nuclear properties. Level statistics and electromagnetic transition distributions have been used successfully to provide unique tests of predictions of random matrix theory.

With the nuclear fission discovery and development of nuclear weapons in 1940s, artifi cial radioisotopes were introduced in the environment. This contamination is due to worldwide fallout by superfi cial nuclear tests realized from early 1950s to late 1970s by USA, former URSS, UK, France and China. One of theses radioisotopes that have been very studied is cesium-137. Cesium-137 has a half-life of 30.2 years and its biological behavior is similar to the potassium. The behavior in soil matrix, depth distribution, spatial variability and inventories values of cesium-137 has been determinate for several regions of the world. In Brazil, some research groups have worked on this subject, but there are few works published about theses properties of cesium-137. The aim of this paper was study the depth distribution, spatial variability, and inventory of cesium-137 in native forest. Two native forests (Mata 1 and Mata UEL) were sampling in region of Londrina, PR. The results shows that there is a spatial variability of 40% for Mata 1 and 42% for Mata UEL. The depth distribution of cesium-137 for two forests presented a exponential form, characteristic to undisturbed soil. Cesium-137 inventory determinate for Mata 1 was 358 Bq m-2 and for Mata UEL was 320 Bq m-2.

The use of protons instead of X-rays for computerized tomography (CT) studies has potential advantages, especially for medical applications in proton treatment planning. However, the spatial resolution of proton CT is limited by multiple Coulomb scattering (MCS). We used the Monte Carlo simulation tool GEANT4 to study the resolution achievable with different experimental arrangements of a proton CT scanner. The passage of a parallel 200MeV proton beam through a virtual cylindrical aluminum phantom with 50mm external diameter was simulated. In our study, the phantom contained a set of cylindrical holes with diameters ranging from 4mm to 0.5mm. The GEANT4 simulation consisted of a series of 180 projections at 2 degree intervals with 350 proton track histories for each one. The fi ltered back projection algorithm was used to reconstruct a 2D tomographic image of phantom.

We studied the double-charge-exchange reaction on 93Nb and 56Fe targets. The energy dependence of forward transition was calculated based on an optical model with the nuclear structure described in the pseudo-SU(4) model.

The absolute neutron activation analysis (ANAA) technique was used for the determination of some elements on body organs, such as, kidney, heart, muscles and spleen of small-sized animals used on experiments in health area. The advantages and limitations of using this nuclear methodology were discussed.

In the framework of studies concerning new fuel cycles and nuclear wastes produced by reactors, we have undertaken a number of measurements in order to determine the radiative capture and/or the fi ssion cross sections of neutron induced reactions on several nuclei (232Th 233Pa, 233U) which play an important role in the Th-U cycle.

Partial wave analysis and the decoupling of the wave equations based on potential barriers modifi ed by coupling effects are applied in the study of the fusion process in medium heavy nuclei. Several relevant physical quantities are calculated in order to provide evidence of underline reaction mechanisms that determine characteristics of fusion excitation functions and barrier distributions. The influence of Q- values is especially considered. The method is applied for the neutron transfer reaction in the 17O +144Sm system.

We report the preliminary result of an exact calculation of the asymmetry parameter, alambda, in the nonmesonic hypernuclear decay, based on a one-meson-exchange (OME) model. For the case of <IMG SRC="/img/revistas/bjp/v34n3a/a30img02.gif">He and including one-pion-exchange only, the result is shown not to differ considerably from the one obtained with the approximate formula widely used in the literature. In particular, the sign of alambda remains negative, in disagreement with its most recent experimental determination. Whether these facts remain true for heavier hypernuclei and in a more complete OME model is still under investigation.

Anions with atomic number lower than 18 had their total electron detachment cross sections measured in the 0.3-1.5 a.u. velocity range (40 keV-1.4 MeV) for He, Ne, and Ar targets with a experimental method developed in our laboratory. Several universal trends were observed: (a) each cross section can be described as the product of a target-dependent curve by a projectile-dependent constant; (b) for a given target all cross sections present a maximum at almost the same velocity; (c) the cross section ratios taken between different periods in a given column are target-independent.