Resumo em Inglês:

The experiment E93-026 at the Thomas Jefferson National Accelerator Facility (JLab) determined the electric form factor of the neutron <IMG SRC="/img/revistas/bjp/v34n3a/a02img03.gif">through quasielastic <IMG SRC="/img/revistas/bjp/v34n3a/a02img01.gif">(<IMG SRC="/img/revistas/bjp/v34n3a/a02img02.gif">; e'n)p scattering using a longitudinally polarized electron beam and a frozen polarized 15ND3 target. The knocked out neutrons were detected in a segmented plastic scintillator detector in coincidence with the scattered electrons. The <IMG SRC="/img/revistas/bjp/v34n3a/a02img03.gif">was extracted by comparing the experimental beam-target asymmetry with full theoretical calculations based on different values of <IMG SRC="/img/revistas/bjp/v34n3a/a02img03.gif">. Preliminary results of the Fall 2001 run are reported.

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The population and the mode of decay of the low-lying excited levels of 193Ir have been investigated by single and <FONT FACE=Symbol>gg</FONT> coincidence spectroscopy using 192Os enriched to 99% and several HPGe detectors. From singles spectra analysis the energies of 71 gamma rays have been determined with a better overall precision than previously, 17 of them for the first time. The energies at 1043.244(15) and 1316.628(18)keV , observed for the first time in this work, as well as some preliminary coincidence relationships, suggest that the end point energy Qbetamax(<FONT FACE=Symbol>»</FONT>1.14MeV) must be further investigated.

Resumo em Inglês:

A method of analysis for gamma angular correlation experiments was developed for the case of a multi-detector setup, tested with several known sources of radiation, and applied in the decay of the 155Eu nucleus. The method has shown good reliability. This method was applied for five cascades for the transitional nucleus 155Eu and produced the following results: delta(65 keV) = 0.09(11), delta(203 keV) = -0.44(17), delta(246 keV) = 0.281(22), delta(664 keV) = -0.231(21), delta(1002 keV) = -0.35(6).

Resumo em Inglês:

We investigate the properties of mixed stars formed by hadronic and quark matter in beta-equilibrium described by appropriate equations of state (EOS) in the framework of relativistic mean-field theory. We use the non-linear Walecka model for the hadron matter and the MIT Bag and the Nambu-Jona-Lasinio models for the quark matter. The calculations were performed for T = 0 and for finite temperatures in order to describe neutron and proto-neutron stars. The star properties are discussed. Both the Bag model and the NJL model predict a mixed phase in the interior of the star.

Resumo em Inglês:

Compaction processes can influence soil physical properties such as soil density, porosity, pore size distribution, and processes like soil water and nutrient movements, root system distribution, and others. Soil porosity modification has important consequences like alterations in results of soil water retention curves. These alterations may cause differences in soil water storage calculations and matric potential values, which are utilized in irrigation management systems. Because of this, soil-sampling techniques should avoid alterations of sample structure. In this work soil sample compaction caused by core sampling devices was investigated using the gamma ray computed tomography technique. A first generation tomograph with fixed source-detector arrangement and translation/rotational movements of the sample was utilized to obtain the images. The radioactive source is 241Am, with an activity of 3.7 GBq, and the detector consists of a 3 in. x 3in. NaI(Tl) scintillation crystal coupled to a photomultiplier tube. Soil samples were taken from an experimental field utilizing cylinders 4.0 cm high and 2.6 cm in diameter. Based on image analyses it was possible to detect compacted regions in all samples next to the cylinder wall due to the sampling system. Tomographic unit profiles of the sample permitted to identify higher values of soil density for deeper regions of the sample, and it was possible to determine the average densities and thickness of these layers. Tomographic analyses showed to be a very useful tool for soil compaction characterization and presented many advantages in relation to traditional methods.

Resumo em Inglês:

We describe the use of the 14C-AMS technique to study the influence of upwelling waters to the local biological production, at Arraial do Cabo, Brazil. Results on delta14C from seaweed tissues incubated into three different types of water mass show the association of primary production with the upwelling waters. We also discuss the importance of high- precision 14C-AMS measurements for this kind of study, and the properly application of isotopic fractionation corrections on radiocarbon results.

Resumo em Inglês:

We give an overall picture of our present understanding of the effect of the break-up of stable weakly bound nuclei on their fusion cross section with light, medium and heavy mass nuclei, at energies above the Coulomb barrier. The discussion is based mostly on recent data obtained by our group in collaborative experiments with ANU, USP and Tandar Laboratories. We conclude that there is complete fusion suppression for heavy targets, due to the loss of flux, corresponding to the occurrence of incomplete fusion of one of the break-up fragments. For medium and light mass targets, the incomplete fusion is negligible and therefore is no complete fusion suppression.

Resumo em Inglês:

We use a modified version of the Skyrme model in which the stabilizing fourth-order term is separated in two parts with different parameters that are introduced in the Lagrangian and could vary independently. The predictions for the static properties of baryons are calculated and results are compared with the respective experimental values and those of other authors. We show that it possible to improve in an expressive way the results for the set of the important quantities at the same time.

Resumo em Inglês:

The availability of radioactive beams has produced great opportunities for advances in our understanding of the nucleosynthesis occurring in stellar explosions such as novae, X-ray bursts, and supernovae. At the HRIBF, we have used proton-rich beams such as 17;18F and neutron-rich beams such as 82Ge to study astrophysicallyimportant reaction rates. Large-area detector arrays and kinematically-complete measurements have been used to overcome the challenges of low beam currents and beam impurities. The experimental methods and results are discussed.

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Only 300 out of thousands of isotopes are stable and exist in nature. The others are unstable and decay within a wide range of lifetimes. The properties of most of these rare isotopes are unknown and can only be inferred, with considerable uncertainty, from theoretical calculations. The proposed Rare Isotope Accelerator (RIA) will make it possible to produce and study more than a thousand new rare isotopes in the laboratory. RIA will be driven by a highly flexible superconducting linear accelerator which will be capable of delivering intense beams of all elements from hydrogen to uranium. The RIA facility will be the most powerful rare isotope research facility in the world.

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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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

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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.

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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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

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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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

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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.

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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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

Resumo em Inglês:

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.

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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.

Resumo em Inglês:

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.

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PHOBOS is one of the four heavy ion experiments currently running at the Relativistic Heavy Ion Collider (RHIC). In this paper we will present some of the current results from PHOBOS: the study of charged multiplicity distribution as function of pseudorapidity and centrality at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 19.6, 130 and 200 GeV, a discussion of multiplicity scaling, and a measurement of transverse momentum spectra (pT) of charged hadrons produced in d+Au and Au+Au interactions at <IMG SRC="/img/revistas/bjp/v34n3a/a32img01.gif" > or = 200 GeV. The dependence of the Au+Au yields as function of centrality is found to be independent of pT. A strong suppression in the Au+Au hadron spectra relative to p<IMG SRC="/img/revistas/bjp/v34n3a/a32img05.gif"> at high pT is observed. The spectral shape for d+Au collisions is significantly different from the observations in Au+Au, the yield suppression is not observed in d+Au.

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In this work we study the effects of temperature on the equations of state within a relativistic model, with the inclusion of the baryons of the octet over a wide range of densities. We compare the results of the equation of state, effective mass and strangeness fraction for the TM1, NL3 and GL sets of parameters.

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The spectra and the beta decay of the Ni-Cu-Zn isotopes with A=58, 59 and 60 are studied by using the pseudo-SU(4) model.

Resumo em Inglês:

This paper presents results of 137Cs concentration measured from a guava tree cultivated after the first decontamination work of one of the sites where the worst Brazilian radiological accident occurred. The present work aims to verify how the 137Cs is transported and distributed along the tropical trees. Bi-dimensional analyses of the radial distribution of 137Cs in the main trunk are also presented. Neither symmetrical nor homogeneous behaviors of the specific activity distribution in the tree rings were observed.

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Recent developements in our understanding of the fundamental nucleon-nucleon interaction are reviewed. Among the topics considered are (1) the so-called high-precision nucleon-nucleon potentials that emerged in the mid 1990s, (2) progress in the microscopic description of the intermediate-range part of the nucleon-nucleon interaction in terms of correlated pion-pion and rho-pion exchange and (3) efforts towards a quantitative descripton of the nucleon-nucleon interaction utilizing methods based on effective field theory.

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This paper describes two beta decay experiments performed at the CERN/ISOLDE mass separator. The structure of 74Kr has been studied using a total absorption gamma spectrometer (TAgS). The measured Gamow-Teller strength is presented and compared to HFBCS+QRPA calculations. The 33Na decay is also presented. The structure of the 33Mg daughter nucleus is compared to shell-model calculations, showing for the first time an inversion of states in the A~35 mass region.

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The methodology for simulating all detection processes in a 4<FONT FACE=Symbol>pb-g</FONT> coincidence system by means of the Monte Carlo technique is described. The goal is to predict the behavior of the observed activity as a function of the 4<FONT FACE=Symbol>pb</FONT> detector efficiency. In this approach, the information contained in the decay scheme is used for determining the contribution of all radiations emitted by the selected radionuclide, to the measured spectra by each detector. This simulation yields the shape of the coincidence spectrum, allowing the choice of suitable gamma-ray windows for which the activity can be obtained with maximum accuracy. The simulation can predict a detailed description of the extrapolation curve, mainly in the region where the 4<FONT FACE=Symbol>pb</FONT> detector efficiency approaches 100%, which is experimentally unreachable due to self absorption of low energy electrons in the radioactive source substrate. The theoretical work is being developed with MCNP Monte Carlo code, applied to a gas-flow proportional counter of 4pi geometry, coupled to a pair of NaI(Tl) crystals. The calculated efficiencies are compared to experimental results. The extrapolation curve can be obtained by means of another Monte Carlo algorithm, being developed in the present work, to take into account fundamental characteristics of a complex decay scheme, including different types of radiation and transitions. The present paper shows preliminary calculated values obtained by the simulation and compared to predicted analytical values for a simple decay scheme.

Resumo em Inglês:

We have extended the Dirac-Hartree-Bogoliubov (DHB) approximation developed in a previous work [1] with the inclusion of blocking terms in order to study the pairing properties of both even and odd nuclei. We have concentrated our attention in the isotope chains of 12-26O, 34-56Ca, 48-78Ni and 100-132Sn as well as on the alpha-decay of the new superheavy element (277)112.

Resumo em Inglês:

Coulomb excitation matrix elements are often expressed in terms of the scalar electric potential and the electromagnetic fields. We show that, through an appropriate gauge transformation, the excitation matrix elements can always be expressed in terms of the electromagnetic fields alone. This change in representation becomes important when the widths of the excited states are taken into account.

Resumo em Inglês:

The neutrino-nucleus cross-section and the muon capture rate are discussed within a simple formalism which facilitates the nuclear structure calculations. The corresponding formulae only depend on four types of nuclear matrix elements, which are currently used in the nuclear beta decay. We have also considered the non-locality effects arising from the velocity-dependent terms in the hadronic current. We show that for both observables in 12C the higher order relativistic corrections are of the order of ~ 4% only, and therefore do not play a significant role.

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Within the instanton liquid model, we study the dependence of the gauge invariant two-point quark correlator on the path used to perform the color parallel transport between two points in the Euclidean space.

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Fusion cross-sections were measured for the 6Li+27 Al,64 Zn and 9Be+64Zn systems at energies around the Coulomb barrier, in order to study the influence of the break-up of weakly bound nuclei on the fusion process.

Resumo em Inglês:

We show that the systematic inconsistence found in the simultaneous fit of the neutron and proton magnetics moments in light-front models, disappears when one allows an asymmetry in the constituent quark masses. The difference between the constituent quarks masses is an effective way to include in the nucleon model the effect of the attractive short ranged interaction in the singlet spin channel.

Resumo em Inglês:

Topological charge screening in the QCD vacuum is found to provide crucial nonperturbative contributions to the short-distance expansion of the pseudoscalar (0-+) glueball correlator. The screening contributions enter the Wilson coefficients and are an indispensable complement to the direct instanton contributions. They restore consistency with the anomalous axial Ward identity and remedy several flaws in the 0-+ glueball sum rules caused by direct instantons in the absence of screening (lack of resonance signals, violation of the positivity bound and of the underlying low-energy theorem). The impact of the finite width of the instanton size distribution and the (gauge-invariant) renormalization of the instanton contributions are also discussed. New predictions for the 0-+ glueball mass and decay constant are presented.

Resumo em Inglês:

A phenomenological model which has had some success in explaining polarization phenomena and left-right asymmetry in inclusive proton-proton scattering is considered for reactions involving photons. In particular, the reactions (a) gamma + p -> H + X; (b) gamma + p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) <FONT FACE=Symbol>® p</FONT>± + X and (c) p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) -> + p <FONT FACE=Symbol>® g</FONT> + X are considered where gamma = resolved photon and hyperon H = lambda, sigma, xi etc. Predictions for hyperon polarization in (a) and the asymmetry (in (b) and (c)) provide further tests of this particular model. Feasibility of observing (b) at HERA and the effect of the polarization of the sea in the proton in p(<IMG SRC="/img/revistas/bjp/v34n3a/a46img01.gif">) + p <FONT FACE=Symbol>® p</FONT>± + X is briefly discussed.

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The electromagnetic current of spin-1 composite particles does not transform properly under rotations if only the valence contribution is considered in the light-front model. In particular, the plus component of the current, evaluated only for the valence component of the wave function, in the Drell-Yan frame violates rotational symmetry, which does not allow a unique calculation of the electromagnetic form-factors. The prescription suggested by Grach and Kondratyuk [Sov. J. Nucl. Phys. 38, 198 (1984)] to extract the form factors from the plus component of the current, eliminates contributions from pair diagrams or zero modes, which if not evaluated properly cause the violation of the rotational symmetry. We address this problem in an analytical and covariant model of a spin-1 composite particle.

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A new experiment to measure differential cross sections as a function of the bombarding energy and scattering angle for the 16O + 28Si system in order to discriminate regular and chaotic regimes, was performed using the particle spectrometer CHICO combined with the multidetector array Gammasphere. In this contribution we summarize the characteristics of the method developed to analyze the experimental data and present the preliminary results.

Resumo em Inglês:

In the present work we discuss the contribution of the vacuum polarization on the nuclear pairing, in the context of the relativistic Hartree-Fock-Bogoliubov (HFB) approximation. The polarization effects on the pairing, as a function of Fermi momentum, is shown with the scalar and vector meson-nucleon coupling constants scaled by a parameter x. We have obtained that the nuclear pairing is affected by the vacuum polarization.

Resumo em Inglês:

We develop a Dirac-Hartree-Fock-Bogoliubov description of nuclear matter pairing in ¹S0 and ³S¹-³ D¹ channels. Here we investigate the density dependence ot the ¹S0 and ³S¹-³ D¹ pairing fields in asymmetric nuclear matter, using a Bonn meson-exchange interaction between Dirac nucleons. In this work, we present preliminary results.

Resumo em Inglês:

Results which have been recently obtained with the Boltzmann master equation and the FLUKA code in the analysis of heavy ion interactions at relative energies ranging from Coulomb barrier up to a few GeV/n are discussed.

Resumo em Inglês:

Our group at the Laboratorio do Acelerador Linear (IFUSP- USP) is currently developing several studies related to the interaction of different kinds of radiation with DNA. Initially, our plan is to study the interactions proton-DNA, gamma-DNA and neutron-DNA. In this work we describe the most important features of the neutron-DNA study, which we plan to perform by selecting thermal, epithermal and fast neutrons. To improve the information about radiation-DNA interaction is important in order to achieve more secure and efficient cancer treatments by using radiation therapy. Nowadays, one important technique is the boron neutrons capture therapy, where neutrons are used to initiate a nuclear reaction at the tumor site. The effects of the neutrons on the health tissue, however, must be better understood. The study of neutron-DNA interaction, in this scenario, is of great importance. The research facility for Boron Neutron Capture Therapy (BNCT) in the IEA-R1 Reactor of the IPEN-CNEN/SP[1] will be used for studying the neutron-induced DNA damage. At present, we are evaluating the characteristics of the neutron flux at the biological sample, and we are carrying out simulations of the experimental procedure through Monte Carlos N Particle transport code system version 4C (MCNP-4C)[2] to find the experimental conditions necessary to minimize such contamination, and also verify the effects of those gamma's on the DNA molecule. The first step is the selection of filters configurations, which will allow us to irradiate the DNA sample with thermal, epithermal and fast neutrons. We present the results of our simulations, and describe the experimental setup show the best sets of materials necessary to obtain neutron spectra for different neutrons energies.

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Experimental studies have obtained the caloric curve of nuclear matter from heavy ion collisions as well as its dependence on the size of the fragmenting source. In particular it has been determined that smaller systems have caloric curves with higher plateau temperatures than larger systems. This work uses molecular dynamics simulations to study the thermodynamics of heavy ion collisions and to identify the main factors that determine the caloric curve. The simulations indicate that the reaction is composed of three stages: 1) an initial collision that transforms the nuclei from normal density and zero temperature and entropy, to a hot and dense blob of matter with higher values of density, temperature and entropy; 2) this is followed by a constant-entropy expansion that takes the system to the spinodal of the phase diagram; 3) where the system rapidly disassembles into fragments by the process of spinodal decomposition, and not by nucleation. These findings indicate that the plateau temperature of the caloric curve is nothing more than the temperature of the phase change and it is set by the intersection of the isentropic expansion and the spinodal. In other words, the plateau temperature is simply the temperature at which the system breaks as it enters the spinodal. This transition temperature is thus set by the entropy generated during the initial part of the collision.

Resumo em Inglês:

Fusion cross section excitation functions were measured for the 6;7Li+59Co systems (12 < Elab < 26 MeV)aiming the investigation of the effect of the breakup process on the fusion cross section. The experimental method consisted on the detection of gamma-rays from the evaporation residues. Coupled channels calculations have been performed for both systems. The comparison to the experimental results support the conclusion that there is neither supression nor enhancement at energies above the coulomb barrier. A slight enhancement at energies below the barrier is observed for the 6Li+59Co cross section over the one for 7Li+59Co. In order to better quantify the effect of the breakup process, coincidence measurements for the breakup products are being performed.

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Precision measurements of the structure of nucleons and nuclei in the regime of strong interaction QCD are now possible with the availability of high current polarized electron beams, polarized targets, and recoil polarimeters, in conjunction with modern spectrometers and detector instrumentation. The physics at JLab will be highlighted using two recent measurements of general interest. The ratio of the proton electric to magnetic form factors indicates the importance of the role of angular momentum in the structure of the nucleon. The existence of 5-quark configurations in the ground state wavefunctions of hadrons is confirmed by a narrow peak attributed to an exotic baryon with strangeness S=+1. These and other examples will be used to illustrate the capabilities and focus of the experimental program at JLab.

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A small-mass system has been developed for monitoring the flux of neutrons with energy up to 1 MeV at the new time-of-flight facility at CERN, n_TOF. The monitor is based on a thin Mylar foil with a 6Li deposit, placed in the neutron beam, and an array of Silicon detectors, placed outside the beam, for detecting the products of the 6Li(n, alpha)³H reaction. The small amount of material on the beam ensures a minimal perturbation of the flux and minimizes the background related to scattered neutrons. Moreover, a further reduction of the gamma-ray background has been obtained by constructing the scattering chamber hosting the device in carbon fibre. A detailed description of the flux monitor is here presented, together with the characteristics of the device, in terms of efficiency, resolution and induced background. The use of the monitor in the measurement of neutron capture cross-sections at n_TOF is discussed

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The probability of a compound residual hot hypernucleus formation at the end of pre-equilibrium phase of high energy photonuclear reactions is calculated with a time dependent Monte Carlo Multicollisional Cascade (MCMC) approach. The emission of hadrons during the rapid phase of the reaction is discussed and characteristics of the residual nucleus are obtained. Results for mass and charge distributions of the formed hot hypernucleus are shown and its excitation energy is discussed.

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A simple approach to evaluate nuclear photofissilities at energies above the pion photoproduction threshold has been developed. It is based on the current, two-step model for intermediate-energy photonuclear reactions, i.e. a photon-induced intranuclear cascade followed by a fission-evaporation competition process for the excited, post-cascade residual nucleus. The calculation method (semiempirical by nature) shows that fissility (i.e., total fission probability) is governed by two basic quantities, namely, the first-chance fission probability for the average cascade residual, and a parameter which defines an evaporative sequence of residuals in which the average, equivalent chance-fission probabilities of nuclides belonging to the same generation are located. The natPb photofissility data measured recently in the range ~ 0.2 - 3.8 GeV at the Thomas Jefferson Laboratory could be explained very satisfactorily by the present approach.

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From the study of the Ni+Ni,Ag 30 MeV/nucleon dissipative midperipheral collisions, it has been possible to detect events in which Intermediate Mass Fragments (IMF) are emitted by two different sources with different mechanisms. The sources are: a) a quasi-projectile (QP) (and a quasi-target (QT)), with an excitation energy that leads to multifragmentation totally described in terms of a statistical disassembly of a thermalized system (T <IMG SRC="/img/revistas/bjp/v34n3a/a59img01.gif">4. MeV, E*<IMG SRC="/img/revistas/bjp/v34n3a/a59img01.gif"> 4 MeV/nucleon); b) an intermediate source, emitting both light particles and IMF. In this second case, fragments are more neutron rich than the average matter of the overall system, and have a very different charge distribution, with respect to those statistically emitted from the QP. The above features can be considered as a signature of the dynamical origin of the midvelocity emission. The results of this analysis show that IMF can be produced via different mechanisms simultaneously present within the same collision. They also show that the probability of IMF production via dynamical reaction increase with the size of the target nucleus.

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The spectroscopic study of unbound states in the 6Li nucleus was performed by measuring the energy spectrum of the alpha-particles emitted from the transfer reaction ³He(7Li, alpha)6Li. The 7Li beam at E Lab = 31.2MeV was produced at the São Paulo Pelletron accelerator. A ³He gas cell was used as target. alpha-Particle spectra were measured from thetaLab = 8º up to thetaLab = 20º with steps of 1º. Due to its positive Q = +13.3MeV, the ³He(7Li, alpha)6Li reaction favours the population of states in 6Li at high excitations energies up to about 20MeV. We observed resonances at 17.29MeV, 15.31MeV, and a new state at 12.45MeV, in addition to all previously known states of 6Li. An <FONT FACE=Symbol>Â</FONT>-Matrix analysis was performed and the positions and widths of these states were extracted.

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In this work we describe the results obtained with S3590-06 and ion-implanted diodes for alpha particle spectrometry. Satellite peaks were also investigated in order to identify not only the origin of these phenomena, but also the importance of the guard ring region on their relative intensities. The preliminary results indicate that the true cause of the spurious satellite peaks might be associated with the weak electric fields around the guard rings region and changes on the entrance window absorption near the edge of the diodes. Further steps are needed to clear up this problem.

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The procedure followed by the Laboratório de Metrologia Nuclear (LMN) at the IPEN, in São Paulo, for the standardization of the 45Ca is described. The activity measurement was carried out in a 4<FONT FACE=Symbol>pb</FONT>-gamma coincidence system, by the tracing method. The radionuclide chosen as the beta-gamma emitting tracer nuclide was 60Co because of its end-point beta-ray energy which is close to 45Ca. Six sources were prepared using a 1:1 ratio (beta-pure and beta-gamma) dropped directly on the Collodion film, and other two solutions of 45Ca + 60Co were mixed previously using a 1:1 and 1:2 ratio before making the radioactive sources. The activity of the solution was determined by the extrapolation technique. The events were registered using a Time to Amplitude Converter (TAC) associated with a Multi-channel Analyzer.

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The effect of nuclear fragmentation in the passage of 180MeV protons through the human body tissue is discussed. Prostate cancer protontherapy with these intermediate-energy protons is discussed in light of model calculation.

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In the framework of the QCD parton model, we study unpolarized scattering of high energy real photons from a proton target into lepton pairs and a system of hadrons. For a given parametrization of parton distributions in the proton, we calculate the cross section of this process and show the cancellation of the interference terms.

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The polymers Tetrafluoroethylene- hexa- fluoropropylene (FEP) and Tetrafluoroethylene- per- fluoromethoxyethelene (PFA) are normally used as anti-adherent coatings and can also be applied for several applications in research. For example, they can be used as radiation dosimeters for X-ray and gamma photons, electrons, protons and other ionazing particles. In order to determine radiation induced damage, that can compromise applications in dosimetry, FEP and PFA films were bombarded with protons of 1 MeV at fluences from 1 × 10(11) protons/cm² to 1 × 10(16) protons/cm². During the bombardment, the chemical species emission was monitored with a Residual Gas Analyzer (RGA), and results show that the CF3 radical is the specie preferentially emitted. The bombarded films were also analyzed with Optical Absorption Photospectrometry (OAP) which shows quantitative chemically specific evidence of the damage caused by the proton bombardment. Our results show that damage to polymers is detectable for all fluences used in this work, but damage that can compromise applications in dosimetry occurs only for fluences greater than 1 × 10(14) protons/cm².

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In this paper we summarize the status of the racetrack microtron that is under construction at IFUSP, showing the achievements obtained in the transport, RF, control and vacuum systems. A description of the experimental equipment that will be available to the users is also presented.

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This report describes a method for calculating fusion and decay probabilities in reactions leading to the production of transfermium elements. The competition between quasi-fission and fusion is described on the basis of the Dinuclear System Concept (DNSC). Both the competition between fusion and quasi-fission and statistical decay of heavy highly fissionable excited compound nuclei is described in an approach based on the Monte-Carlo method.

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We developed a model to describe the radiation-DNA interaction in water solution. The model is based on some important aspects of the Bethe Theory for the ionizing process, and on the assumption that the direct interaction between the incident particle and the DNA molecule is negligible in comparison with the indirect effect. This assumption can always be true under controlled conditions. The results show that the number of damages induced by radiation depends on the accumulated dose, on parameters related only to the medium properties, and on the DNA structure, but not on the incident particle. A few applications of the model are discussed, and results are successfully compared with experimental data. New experiments are proposed.

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Experimental data on light nuclei close to dripline suggests that as the nucleon number asymmetry increases, the shell structure from stability line is not preserved. In contrast with spherical shell model, Elliott's SU(3) model, uses a deformed multi-nucleon basis to describe nuclear states. The SU(3) symmetry is a strong feature of 1p shell nuclei, where symmetry breaking spin-orbit force is rather weak. We have calculated the binding energies and low-lying energy spectra of Be isotopes (A=6 to A=14), within the framework of Elliott's SU(3) model, with special emphasis on effects due to the presence of intruder orbit 1S1/2 in the region. The model space includes SU(3) basis states that maximize the quadrupole-quadrupole interaction (-chiQ.Q). An extended model space includes, in addition, a set of 2p-2h excitations, with excited nucleons occupying lowest energy SU(3) states in harmonic oscillator shell N=2. Group theoretical methods have been used to classify the states and calculate the nuclear interaction matrix elements. Good angular momentum states are projected out from intrinsic deformed SU(3) states by using standard angular momentum projection techniques. The interaction used contains the monopole-monopole, quadrupole-quadrupole and isospin dependent terms. Interaction parameters are fixed so as to reproduce the binding of 4 nucleons in N=1 orbit for the N=Z isotope-8Be in ground state and first excited 2+ state, along with the known systematics of single neutron separation energies for Be isotopes. The calculated energy espectra are compared with available experimental data. The calculated excitation energies of intruder states in 8Be and 10Be, are discussed in the light of available experimental evidence and theoretical results from shell model as well as deformed oscillator model calculations of Fayache et al..

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The progress of nuclear physics had allowed a better understanding of nuclear structure and reaction mechanisms, but also enables important applications of nuclear energy in our modern way of life. We can point out those ones related to power generation from nuclear reactors, providing an almost inexhaustive power source due to the huge quantities of nuclear fuel existent in our planet, which guaranties its utilization for thousands of years. The main interest is the so-called Hybrid Reactors (ADS - Accelerator Driven System), in which the reactor has a sub critical core and the chain reaction is sustained by an external source that comes from spallation reactions induced by high energy protons (about 1 GeV) from an accelerator, producing a large number of secondary particles (mainly neutrons). For those applications, precise knowledge about nuclear structure and nuclear reaction characteristics is needed.

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Three different substrates for the analysis of liquid samples by Total Reflection X-Ray Fluorescence with Synchrotron Radiation (SR-TXRF) were investigated and compared: Lucite (Perspex), Kimfoil and Mylar. Dry targets were prepared by pipetting 5 mul aliquotes of the liquid samples (synthetic standards and fresh water samples) on the different substrates. A five fold reduction of the continuous background and a corresponding reduction of the elementary detection limits were observed when thin polymer film substrates were used instead of the common thick Perspex substrate.

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In this work we have studied the direct detection and spectrometric capabilities for internal conversion electrons of an ion-implanted diode, developed in the framework of R&D programs at CERN, envisaging its use in an electron-gamma coincidence system for nuclear parameters measurements. The best energy resolution obtained until now, 12.6 keV (FWHM) for the 133Ba 320.32 keV electron emission, is sufficiently good to justify the use of this diode for spectrometry of low energy electrons.

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I present in this talk the latest results of the neutron spin physics program at Jefferson Laboratory in Hall A using the highly polarized electron beam and a high pressure polarized ³He target. This program includes among others experiment E99-117 in which the neutron spin asymmetry <IMG SRC="/img/revistas/bjp/v34n3a/a74img01.gif">was measured in the deep inelastic region with high precision. This asymmetry is observed, for the first time, to change sign from negative to positive values between 0.3 < x < 0.6. Furthermore we perform a flavor decomposition of the spin-dependent to spin-independent quark distributions ratios in the nucleon and find that relativistic quark models are in better agreement than pQCD fits using the hadron helicity conservation constraint as x -> 1.

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The PARRNe (Production d'Atomes Radioactifs Riches en Neutrons) experimental program has been part of the recent R&D efforts for the design of the SPIRAL2 project at GANIL. The PARRNe2 set-up installed at IPNOrsay allows the use of the Tandem as a deuteron driver in order to produce mass separated fission fragment beams. The measured fission fragment yields proved to be high enough to undertake a series of beta-decay experiments dedicated at studying the structure of proton-deficient nuclei close to N=50. We report here on two such experiments, the first being dedicated at the observation of the decay of 83Ga->83Ge (Z=32, N=51), 84Ga->84Ge (Z=32, N=52) and the second of the decay of 81Zn->81Ga (Z=31, N=50) allowing for the fist time the identification of a few gamma lines with transitions in the daughter nuclei thus providing the material for a preliminary glimpse of their structure.

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The PrimEx (Primakoff Experiment) Collaboration is currently preparing to perform a high precision (1.4%) measurement of the two photon decay width of the neutral pion, <img id="_x0000_i1026" src="../../../../img/revistas/bjp/v34n3a/a76img05.gif" align=absmiddle>. The proposed 12 GeV upgrade of the CEBAF accelerator will enable a significant enlarging of the scope of these studies to include measurements of the two photon decay widths of the h and h' mesons, as well as of the transition form factors of all the light pseudoscalar mesons (pº; h; h'). These precision measurements would have a significant impact on the experimental determination of the ratios of the light quark masses (m u;m d;m s), and on our understanding of some fundamental issues in QCD.

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The set of experiments forming the g8a run took place in the summer of 2001 in Hall B of Jefferson Lab. The g8a run was the commissioning experiment for the linearly-polarized photon beam at CLAS. The aim of these experiments is to improve the understanding of the underlying symmetry of the quark degrees of freedom in the nucleon, the nature of the parity exchange between the incident photon and the target nucleon, and the mechanism of associated strangeness production in electromagnetic reactions. A beam of tagged and collimated linearly polarized photons (energy range 1.8-2.2 GeV) in conjunction with the large solid angle coverage of CLAS make possible the extraction of the differential cross-sections and polarization observables for the photoproduction of vector mesons and kaons. The reaction channels -<img id="_x0000_i1026" src="../../../../img/revistas/bjp/v34n3a/a77img01.gif" align=absmiddle>p ® r0p ® p+p-p and <img id="_x0000_i1027" src="../../../../img/revistas/bjp/v34n3a/a77img01.gif" align=absmiddle>p ® K+L0 ® K+p-p are under investigation to search for possibly missing nucleon resonances. An overview of the experiment and preliminary results on the measurement of the photon asymmetries of the aforementioned reactions will be presented in this paper.

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The study of the baryon spectrum is a fundamental part of the scientific program in Hall B at Jefferson Laboratory. The so called N* program indeed concerns the measurement of the electromagnetic production of exclusive hadronic final states, with the purpose of extracting information on baryon excited states. CLAS, the CEBAF Large Acceptance Spectrometer, is explicitly designed for conducting a broad experimental program in hadronic physics, using the continuous electron beam provided by the laboratory. An overview of the most recent results is presented.

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New accelerator facilities for radioactive-ion beams and high-intensity stable beams will start operation in a few years. Although these beams will provide interesting opportunities for exploring unknown territories of the nuclear landscape, the experimental conditions will be very challenging and, indeed, the nuclear structure community has realized that a new generation of powerful arrays for gamma-ray spectroscopy has to be built in order to cope with them. As a result of years of experience with Compton suppressed germanium arrays and of intensive R&D work targeted to extend their limits, it is now clear that the next 4<FONT FACE=Symbol>p g</FONT>-ray spectrometers will be built fully from germanium detectors and will be based on the technique of gamma-ray tracking. The "Advanced GAmma Tracking Array" (AGATA), proposed in Europe, will be an instrument of major importance for nuclear structure studies at the very limits of nuclear stability. It will be built out of 120/180 highly segmented Ge crystals operated in position sensitive mode by means of digital data techniques and pulse shape analysis of the segment signals. AGATA will be able to measure gamma radiation in a large energy range (from ~ 10 keV to ~ 10 MeV), with the largest possible photopeak effi ciency (25 % at Mgamma = 30) and with a good spectral response. In particular, its very good Doppler correction and background rejection capabilities will allow to perform "standard" gamma-ray spectroscopy experiments using fragmentation beams with sources moving at velocities up to beta ~ 0.5.

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The 105Rh nucleus has been studied by in-beam gamma spectroscopy with the heavy-ion fusion-evaporation reaction 100Mo(11B, <FONT FACE=Symbol>0</FONT>2ngamma) at 43 MeV. A rich variety of structures was observed at high and low spin, using gamma - gamma - t and gamma - gamma - particle coincidences and directional correlation ratios. Four magnetic dipole bands have also been observed at high spin. Two of them are nearly degenerate in excitation energy and could be chiral partners, as predicted by Tilted Axis Cranking calculations.

Resumo em Inglês:

The neutron deficient 141Tb nucleus has been studied with the 92Mo (54Fe, alphap) reaction at 240-MeV incident energy and the multidetector array GASP. For the yrast pih11/2 decoupled band, excited states up to 6.7 MeV and spin up to 47/2- have been observed. This band presents an upbend at rotational frequency of <IMG SRC="/img/revistas/bjp/v34n3a/a69img04.gif">omega = 0.38 MeV due to the alignment of h11/2 protons. The results are discussed in terms of the Cranking model.

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The 108Pd nucleus has been studied with the 100Mo(11B, p2ngamma) reaction at 43 MeV incident energy. gamma -gamma - t, gamma -gamma - charged particle coincidences and directional correlation ratios were measured using the gamma spectrometer formed by four Compton suppressed HPGe detectors and a 4pi charged-particle ancillary detector system. The struture of the bands was interpreted within the framework of the cranked shell model and total Routhian calculations.

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Based on the LINAG Phase 1 conceptual design, a two years detailed study on a ISOL-type facility for the production of high intensity exotic beams, named SPIRAL2, has been launched. The radioactive isotope beams are produced via the fission process, with the aim of 10(13) fissions/s at least, induced in a UCx target either by fast neutrons from a C converter or by direct bombardment of fissile material. Fusion-evaporation residues, using heavy ions beams in different targets can also be produced in this facility. The driver, with an acceleration potential of 40 MV will accelerate deuterons (5 mA) and q/A =1/3 ions (1mA). Even heavier ions will be possible in a later stage. The driver consists in high-performance ECR sources, an RFQ cavity and independent phase superconducting resonators. As it is a linear accelerator, further upgrade will be possible in future.

Resumo em Inglês:

Spectroscopic investigation, on exotic nuclei, performed in two different experiments with secondary radioactive boron beams are discussed. Spectroscopic factors for the 13B+n bound-states are obtained by measuring momentum distribution of the 13B residual nucleus from knockout reaction of the 14B beam at intermediate energy. The momentum distributions are measured in coincidence with the emited gamma-rays from the excited residual 13B nucleus allowing spin-parity assignment and partial cross section determination. In the other experiment, a deuteron transfer, ²H(8B,alpha)6Be, reaction with low energy 8B beam are used to search for resonances in the unbound 6Be nucleus. The ANC - Asymptotic Normalization Coefficient method are presented and astrophysical implications of these two experiments are discussed.

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Positron annihilation radiation profi le in aluminum was observed with a pair of Ge detectors in coincidence. 22Na was used as a source of positron and the two-dimensional gamma energy spectrum wasfi tted using a model function. Annihilation components of positron at rest with conduction band, 1s, 2s, and 2p electrons were observed. The in-flight positron annihilation was also observed. The model function also took into account the detector response function, relative effi ciency corrections and the gamma backscattering. Coincidences involving a combination of Compton effect, pileup, ballistic defi cit, and pulse shaping problems were treated as well.

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Computerized Tomography (CT) refers to the cross sectional imaging of an object from both transmission or reflection data collected by illuminating the object from many different directions. The most 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 the CT imaging is that of estimating an image from its projections. These projections can represent, for example, the linear attenuation coefficient of gamma-rays along the path of the ray. In this work we will present some new results obtained by using tomographic techniques to analyze column samples of concrete to check the distribution of various materials and structural problems. These concrete samples were made using different proportions of stone, sand and cement. Another set of samples with different proportions of sand and cement were also used to verify the outcome from the CT analysis and the differences between them. Those samples were prepared at the Material Laboratory of Faculdade de Engenharia de Sorocaba, following the same procedures used in real case of concrete tests. The projections used in this work was obtained by Mini Computerized Tomograph of Uniso (MTCU), located at the Experimental Nuclear Physics Laboratory at University of Sorocaba. This tomograph 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, and 1 mm spatial resolution. The image reconstruction problem is solved using Discrete Filtered Backprojection (FBP).

Resumo em Inglês:

The high momentum transfer electron-nucleus scattering cross section is evaluated within the plane wave impulse approximation (PWIA) supplemented by the relativistic Hartree approximation (RHA). Binding effects on the struck nucleon are introduced through the scalar and vector meson-exchange fields within the framework of quantum hadrodynamics. This model naturally satisfies the current conservation, with the off-shell nucleons behaving as being on the mass shell but having an effective mass. The nucleon inelastic response is included via different parameterizations of the structure function measured at SLAC, while the smearing of the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on 56Fe are well reproduced for all measured geometries by the first time. Scaling effects are analyzed as well, and the scaling properties of the nuclear response in terms of the y variable associated to the PWIA within the RHA framework are discussed. The theoretical scaling function obtained in our approach also significantly improves previous PWIA calculations within the multi-GeV electron scattering regime, and describes properly the CEBAF scaling data.

Resumo em Inglês:

The biggest constraint in the RPCs operation is the drop of their efficiency with the counting rate, consequence of charge gain decrease. This effect is normally attributed to the voltage drop on the dielectrics, although not supported by quantitative measurement. In this work we present the first results of a two-parameter analysis of the charge pulse height time variation from a cylindrical resistive detector, operating in proportional regime, under high irradiation rates. The dynamic behaviour of this detector was investigated through the determination of the time decay constants related to its stationary condition, where the charge gain becomes constant. To perform this study, a data acquisition system, which allows the users to observe in real-time the temporal variation of the energy spectrum, was specially designed. The fitting of the peak centroid position as a function of time, obtained for rates range from 220Hz up to 1230Hz, showed it can be described by a sum of two exponentials plus a constant term, what is in accordance to the dielectric delayed polarization processes.

Resumo em Inglês:

A new neutron facility has recently been constructed and became available at CERN. The high instantaneous neutron flux, high resolution and low background make this facility well suited for high quality neutron cross section measurements. The scientific program, together with the description of the facility and the main features of the experimental apparatus will be mentioned. The results of the first measurements campaign, which have confirmed the innovative aspects of the facility are presented.