Acessibilidade / Reportar erro
Brazilian Journal of Physics, Volume: 36, Número: 2b, Publicado: 2006
  • XIX International seminar on ion-atom collisions - XIX ISIAC Foreword

    Montenegro, Eduardo Chaves; Sigaud, Geraldo Monteiro
  • Production of 1s2s2p4P states by transfer-loss cascades in O5+ collisions with he and H2 targets

    Zouros, T. J. M.; Sulik, B.; Gulyás, L.; Orbán, A.

    Resumo em Inglês:

    Single differential cross-sections for transfer-loss (TL) leading to the production of O5+(1s2s³S)nl4L states were computed for 0.2-1.2 MeV/u collisions of O5+(1s²2s) ions with He and H2 targets. At these collision energies, 1s loss is significant and electron transfer to n = 3-4 levels is dominant. Furthermore, due to spin conservation, quartet states can only be populated by TL. Within the independent particle model (IPM), the probability of 1s electron loss from O5+(1s²2s) projectiles was calculated using the semi-classical approach, while the probability for electron transfer to the O5+(1s2s³S)nl4L states (n > 2) was computed using the continuum distorted wave (CDW) approximation. The majority of states with n > 2 can be assumed to have sufficient time to eventually decay with an almost 100% probability to the long-living metastable 1s2s2(4)P level via a much faster sequence of electric dipole transitions, thus establishing an upper limit to such cascade contributions. The inclusion of this cascade feeding is found to lead to a strong enhancement in the production of the 1s2s2p4P states, particularly for collisions with the H2 target, thus reducing dramatically the existing two-order of magnitude discrepancy between older TL calculations (for n = 2 only) and existing zero-degree Auger projectile electron spectroscopy measurements.
  • Mechanisms of one-electron capture by slow He2+, C4+ and O6+ ions in collisions with CH4

    Seredyuk, B.; McCullough, R. W.; Gilbody, H. B.

    Resumo em Inglês:

    Translational energy spectroscopy (TES) has been used to study one-electron capture by He2+, C4+, and O6+ ions in collisions with CH4 within the range 200 - 2000 eV amu-1. In each case the main collisions mechanisms and product channels have been identified. The measurements reveal significant differences in the way the dissociative and non-dissociative mechanisms contribute to electron capture. However, in all cases, the highly selective nature of the charge transfer process is confirmed in spite of the wide range of energy defects associated with possible product channels.
  • Interference effects in the ionization of diatomic molecules

    Nagy, L.; Borbély, S.; Póra, K.

    Resumo em Inglês:

    Interference effects in the ionization of H2 by charged particle and photon impact have been investigated. For the charged particle impact the influence of the residual molecule on the final state has been taken into account in a perturbative way. In case of the photoionization various final-state wavefunctions have been used. The effects of the molecular orientation on the differential photoionization cross sections and the contribution of different partial waves have been also analyzed.
  • Projectile electron loss in nitrogen

    Santos, A. C. F.; Melo, W. S.; Sant'Anna, M. M.; Sigaud, G. M.; Montenegro, E. C.

    Resumo em Inglês:

    The projectile electron loss channel plays an important role in modeling several processes connected to the penetration of swift ions in gases, such as radiation damage, energy loss, upper atmosphere studies, storage lifetimes of low-charge state heavy ions, etc. In this paper we have used recent measurements of projectile electron loss of He+ ions in N2 together with previous data for higher charged ions in order to shed light on the role played by the projectile electron loss in the heating and ionization of Titan's atmosphere.
  • Dominant screening process in the projectile electron loss for F- + Ar collisions

    Sant'Anna, M. M.

    Resumo em Inglês:

    A comparison between projectile electron loss cross sections for negative, F-, and positive, He+, projectiles is presented for collisions with Ar target. The behavior of the two collision systems is similar for the projectile electron loss with target ionization. For projectile electron loss without target ionization (the so-called screening electron-loss process), quite different situations are presented for the studied positive and negative projectiles. For He++ Ar, the loss without target ionization collision channel is negligible for intermediate-to-low energies. On the other hand, for F-+ Ar, this collision channel is the dominant one in the total projectile electron loss at intermediate-to-low velocities. The roles played by coupling with the electron capture by the projectile collision channel and by the very different binding energies for negative and positive projectiles are discussed.
  • Differential ionization studies for positron impact

    DuBois, R. D.; Lucio, O. G. de; Gavin, J.

    Resumo em Inglês:

    Recent studies of differential ionization by positron impact being performed at the University of Missouri-Rolla are described. Recoil ion-scattered positron and recoil ion-scattered positron-ejected electron coincidences are measured to provide doubly and triply differential ionization data (DDCS and TDCS) for e+ - Ar collisions. The DDCS and TDCS studies are for 750 and 200 eV impact respectively. For the TDCS studies the positron scattering angles are between approximately ± 5º and electrons ejected with energies less than 15 eV and angles between 90º ± 50º with respect to the beam direction are detected. Examples of TDCS data for the scattered positron and the ejected electron are presented.
  • CDW and CDW-EIS calculations for FDCSs in highly charged ion impact ionization of helium

    Ciappina, M.; Cravero, W. R.

    Resumo em Inglês:

    In this work we present fully differential cross sections (FDCS) calculations using CDW and CDW-EIS theories for helium single ionization by 100 MeV/amu and 2 MeV/amu C6+ and 3.6 MeV/amu Au24+ and Au53+ ions. We performed our calculations for different momentum transfers and ejected electron energies. We study the influence of the internuclear potential on the ejected electron spectra. We discuss different regimes where the internuclear interaction can or cannot be neglected. We compare our calculations with experimental data available. It is shown that for high impact energy and small momentum transfer, internuclear potential effects can be neglected in FDCSs.
  • Ionization potentials, dissociation energies and statistical fragmentation of neutral and positively charged small carbon clusters

    Díaz-Tendero, S.; Sánchez, G.; Hervieux, P.-A.; Alcamí, M.; Martín, F.

    Resumo em Inglês:

    Dissociation energies, ionization potentials and fragmentation dynamics of neutral, singly- and doubly charged small carbon clusters have been theoretically studied with a combination of the density functional theory, the coupled cluster method and the the statistical model microcanonical Metropolis Monte Carlo. The second ionization potential decreases with the cluster size and is larger than the first one, which also decreases with the size showing oscillations. Dissociation energies also oscillate with the cluster size, being those with an odd number of atoms more stable. C3 cluster has the largest dissociation energy. The combination of a statistical treatment for the cluster fragmentation with experimental results has allowed us to evaluate the energy distribution in collisions experiments.
  • Ionic desorption in valence- and core- excited polymers: poly(vinyl chloride) and poly(vinylidene chloride)

    Rocco, M. L. M.; Faraudo, G. S.; Pontes, F. C.; Souza, G. G. B. de; Pinho, R. R.; Ferreira, M.

    Resumo em Inglês:

    Photon stimulated ion desorption (PSID) studies have been performed in poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDC) using synchrotron radiation, covering from valence to core electron (Cl 2p and C 1s) energy ranges. Data acquisition was performed at the TGM beam line from the Brazilian Synchrotron Light Source (LNLS), operating in a multi-bunch mode and using a time-of-flight mass spectrometer (TOF-MS). A new pulsed system developed uses as a trigger for the TOF-MS experiments the pulsed extraction high voltage applied to the sample. Ionic desorption from PVC and PVDC shows strong selectivity in the formation of chlorine ions around the Cl 2p-edge while very similar fragmentation patterns are observed for the other energies studied.
  • Ionization and dissociation of the formic acid molecule by protons and electrons

    Pilling, S.; Santos, A. C. F.; Boechat-Roberty, H. M.; Souza, G. G. B. de; Sant' Anna, M. M.; Barros, A. L. F.; Wolff, W.; Faria, N. V. de Castro

    Resumo em Inglês:

    Ionization and dissociation of the formic acid molecule (HCOOH) by energetic charged particles have been studied for 1 keV electrons and nearly equivelocity 2 MeV protons. Whereas the fragmentation pattern induced by impact of electron and proton show close similarities, some distinctions in the fragmentation yields were observed for these equivelocity projectiles.
  • High resolution zero degree electron spectroscopy of argon ions through carbon foil

    Imai, M.; Sataka, M.; Kawatsura, K.; Takahiro, K.; Komaki, K.; Shibata, H.

    Resumo em Inglês:

    Electrons emitted from high Rydberg states formed by penetration of 2.0 MeV/u Ar6, 13, 14, 15+ ions through C-foil targets of various thicknesses (4.0 - 20 µg/cm²) have been measured with high resolution utilizing zero-degree electron spectroscopy. Intense series of Coster-Kronig peaks due to Ar14+ 1s²2p(²P3/2,1/2)nl - 1s²2s(²S1/2)epsilonl' and Ar13+ 1s²2s2p(³P2,1,0)nl - 1s²2s² (¹S0)epsilonl' transitions, in which the principal quantum number, n, starts at 10 and increases with increasing peak energy, have been observed for every combination of initial charge state and foil thickness, and quite a few number of other peaks remain unassigned in the electron energy region investigated. Intensities of each series of Coster-Kronig electron peaks follow the n-3 law. The mean charge states after the foil penetration have been found to be the same within 10% uncertainty and the total intensity of the Coster-Kronig transitions including Ar15+ 1s²2p(²P) and Ar14+ 1s²2s2p(³P) cores have also been found to remain constant for all the collision systems investigated. The total Ar15+ 1s²2p(²P) population derived from n = 10 transition peaks is found to be almost the same as those of Ar14+ 1s²2s2p(³P), which is in contrast to the ratio of Ar15+ to Ar14+ fractions measured downstream the foil.
  • Multiple ionization effects in x-ray emission induced by heavy ions

    Czarnota, M.; Pajek, M.; Banas, D.; Dousse, J.-Cl.; Maillard, Y.-P.; Mauron, O.; Raboud, P. A.; Berset, M.; Chmielewska, D.; Rzadkiewicz, J.; Sujkowski, Z.; Hoszowska, J.; Slabkowska, K.; Polasik, M.

    Resumo em Inglês:

    The x-ray satellite structure of Pd Lalpha1,2(L3M4,5) transition excited by an impact of O7+ and Ne6+ ions with energies 279 and 178 MeV, respectively, which were measured using a high-resolution von Hamos crystal spectrometer, is discussed in terms of the multi-configuration Dirac-Fock (MCDF) calculations. We demonstrate, by using the arguments of the general central limit theorem (GCLT), that a structure of complex M-shell satellites of Pd Lalpha1,2(M-m) transitions for a higher number of spectator vacancies (m > 4), which consists of hundreds of thousands of individual x-ray transitions as obtained from the MCDF calculations, can be well described by a single Voigtian profile. The Lorentzian width of such Voigtian line can be well modeled by using the results of the MCDF calculations for simpler configurations with a number of vacancies m < 4 . This method allows one to describe realistically a complex structure of M-shell satellites, thus extending the applicability of the MCDF calculations, which are limited by an increasing complexity of numerical calculations.
  • Mapping the intrinsic stochasticity of tokamak divertor configuration Regular Articles

    Barocio, S. R.; Chávez-Alarcón, E.; Gutierrez-Tapia, C.

    Resumo em Inglês:

    Poloidal divertors are, more than ever before, a crucial topic for the advancement of magnetic fusion technology. Due to the often non linear and stochastic nature of the plasma edge phenomena, canonical mapping has provided a powerful method at modelling their characteristics, albeit many authors rely on heuristically adapted schemes. Thus, it is reported here a specific and physically consistent map model of the tokamak single null magnetic configuration, assuming plasma-field equilibrium, based on the construction of a fundamental Hamiltonian form. Then, the magnetohydrodynamically non ideal perturbations are introduced through the Rayleigh function of the system. As an illustration, the resulting compact canonical map is applied to the analysis of some of the most relevant features of the edge magnetic topology.
  • Phase diagrams of the Blume-Emery-Griffiths thin films Regular Articles

    Ez-Zahraouy, H.; Bahmad, L.; Benyoussef, A.

    Resumo em Inglês:

    We study the spin-1 Blume-Emery-Griffiths model with bilinear and biquadratic exchange interactions and single-ion crystal field, using the mean field theory. In addition to the four usual phases: The disordered phase D, the ferromagnetic phase F, the staggered quadrupolar phase SQ and The ferrimagnetic phase I, we found two new phases, in the case of a thin magnetic film, namely: the sublattice (A or B) non magnetic phase NM and the global non magnetic phase G. These phases are studied, for each layer of the film in the temperature-crystal field plane (T/J,delta/J) for different film thicknesses. It is found that the ferrimagnetic and sublattice phases are absent for a monolayer film. Whereas, these phases appear for increasing film thicknessses N > 2. On the other hand, the thermal behaviour of the layer quadrupolar moments qA, qB and layer magnetisations mA, mB are investigated for negative values of the biquadratic coupling and crystal field. It is also shown that for fixed values of the biquadratic coupling, the temperature and the crystal field, each layer of the film can belong to a different phase. To illustrate this situation, an example is given for d/J = -1.5, delta/J = -3.0 and T/J = 1.3.
  • On a gravitational cutoff for the vacuum energy Regular Articles

    Culetu, Hristu

    Resumo em Inglês:

    A possible connection between the energy W of the vacuum fluctuations of quantum fields and gravity in "empty space" is conjectured in this paper using a natural cutoff of high momenta with the help of the gravitational radius of the vacuum region considered. We found that below some "critical" length L = 1 mm the pressure sigma is one third of the energy density epsilon, but above 1 mm the equation of state is sigma = -epsilon as for dark energy). In the case of a massive field, W does not depend on the mass of the field for L << 1mm but for L >> 1 mm it does not depend on h. In addition, when the Newton constant tends to zero, W becomes infinite. The energy density is also a function of the volume V of the vacuum region taken into account.
  • A new inflaton model beginning near the Planck epoch Regular Articles

    Opher, Reuven; Pelinson, Ana

    Resumo em Inglês:

    The Starobinsky model predicts a primordial inflation period without the presence of an inflaton field. The modified version of this model predicts a simple time dependence for the Hubble parameter H(t), which decreases slowly between the Planck epoch and the end of the inflation, H(t) = M Pl -betaM²Pl t, where beta is a dimensionless constant to be adjusted from observations. We investigate an inflaton model which has the same time dependence for H(t). A reverse engineered inflaton potential for the time dependence of H is derived. Normalization of the derived inflaton potential is determined by the condition that the observed density fluctuations, <FONT FACE=Symbol>dr</FONT>/<FONT FACE=Symbol>r »</FONT> 10-5, are created at ~ 60 e-folds before the end of inflation. The derived potential indicates an energy (mass) scale, Mend ~ 10(13) GeV, at the end of inflation. Using the slow roll parameters, which are obtained from this potential, we calculate the spectral index for the scalar modes nS and the relative amplitude of the tensor to scalar modes r. A tensor contribution, r ~ 0.13, and an approximately Harrison-Zeldovich density perturbation spectrum, nS ~ 0.95, are predicted.
  • Electron collisons with cyclobutane Regular Articles

    Bettega, M. H. F.; Lopes, A. R.; Lima, M. A. P.; Ferreira, L. G.

    Resumo em Inglês:

    We report integral, differential, and momentum transfer cross sections for elastic scattering of low-energy electrons by cyclobutane (c-C4H8), which is an isomer of the C4H8 molecule and has a closed chain. Our calculations were performed with the Schwinger multichannel method with pseudopotentials at the static-exchange level of approximation, for energies up to 50 eV. We compare the cross sections of cyclobutane with the cross sections of other three isomers of C4H8, namely, isobutene, cis-2-butene, and skew-1-butene. These isomers have open chain and were the subject of a previous study by our group [Lopes et al. J. Phys. B 37, 997 (2004)]. We also show previous calculated integral and momentum transfer cross sections for isomers of C3H4, C3H6 and C4H6, which have open and closed chains. For each isomeric group we discuss the isomer effect focusing on the closed chain isomer. The isomer effect is related to differences in the isomers cross sections due to differences in their geometries.
  • Interior problem in a ponsymmetric theory of gravitation Regular Articles

    Ragusa, S.; Bosquetti, D.

    Resumo em Inglês:

    The field equations of a previous metric nonsymmetric theory of gravitation are considered for the interior of a static spherically symmetric perfect fluid with a view to a study of stellar equilibrium. The equations are put into a form of four first-order differential equations which are ready for numerical integration.
  • The temperature dependence of the QCD running coupling Regular Articles

    Steffens, F. M.

    Resumo em Inglês:

    We study the running of the QCD coupling with the momentum squared (Q²) and the temperature scales in the high temperature limit (T > Tc), using a mass dependent renormalization scheme to build the Renormalization Group Equations. The approach used guaranty gauge invariance, through the use of the Hard Thermal Loop approximation, and independence of the vertex chosen to renormalize the coupling. In general, the dependence of the coupling with the temperature is not logarithmical, although in the region Q² ~ T² the logarithm approximation is reasonable. Finally, as known from Debye screening, color charge is screened in the coupling. The number of flavors, however, is anti-screened.
  • Influence of fabrication process on the final properties of natural-rubber latex tubes for vascular prosthesis Regular Articles

    Neves-Junior, W. F. P.; Ferreira, M.; Alves, M. C. O.; Graeff, C. F. O.; Mulato, M.; Coutinho-Netto, J.; Bernardes, M. S.

    Resumo em Inglês:

    We report a process of fabrication of latex tubes using the dip-coating technique. We investigated centrifuged latex, with different original viscosities, extracted from the Hevea brasiliensis. The influence of the main deposition parameters (dip-coating velocity, mold material, mold diameter and number of coatings) and post-deposition drying process parameters (temperature and time) on the properties of the final samples are investigated and discussed. Additional investigation about the elastic behavior of the tubes is presented for strain values up to rupture. The rupture occurred at 120 mm for tubes 15 mm-long, which represents an elongation of 800%. The tubes presented two distinct elastic mechanisms, with the most elastic one being observed below an elongation of about 500%. During a cycled strain experiment with strain values below the rupture point, a hysteretic-like curve was observed, which was related to the uncurling and recurling of the polymeric chains.
  • An overview of the interatomic correlation moments and the mean square relative atomic displacements in anharmonic crystals Review Article

    Rodrigues, C. G.; Rabelo, J. N.Teixeira; Zubov, V. I.

    Resumo em Inglês:

    We present an overview of a method developed for the calculation of dynamic interatomic correlations in anharmonic crystals based on the correlative method of unsymmetrized self-consistent field (CUSF). The quadratic correlation momenta and the mean square relative displacements have been calculated for one-, two- and three-dimensional classical models.
Sociedade Brasileira de Física Caixa Postal 66328, 05315-970 São Paulo SP - Brazil, Tel.: +55 11 3091-6922, Fax: (55 11) 3816-2063 - São Paulo - SP - Brazil
E-mail: sbfisica@sbfisica.org.br