J. A. S. Barata

University of Coimbra, Coímbra, Coimbra, Portugal

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Publications (25)17.68 Total impact

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    ABSTRACT: In this paper we present the results of the ion mobility measurements made in gaseous mixtures of argon (Ar) and methane (CH4) for pressures ranging from 5 to 8 Torr and for low reduced electric fields (in the 17 Td to 43 Td range), at room temperature. The time of arrival spectra of the several mixture ratios studied revealed that the relative abundance of the ions formed depend on the mixture ratios. For CH4 concentrations in the 2.5–10% range three well defined peaks were observed which were attributed to single-carbon ions (CH5+), 2-carbon ions (C2H4+ and C2H5+), and 3-carbon ions (C3H4+, C3H5+, C3H6+ and C3H7+). The time of arrival spectra for CH4 concentrations of 2.5% (P-2.5), 5% (P-5), 10% (P-10) and the reduced mobilities of the ions obtained from the peaks observed are presented in this paper. The ion mobility study was performed for typical reduced electric fields used in gaseous detectors (E/N > 15 Td).
    Journal of Instrumentation 06/2014; 9(06):P06003. · 1.66 Impact Factor
  • Journal of Instrumentation 12/2013; 8(P12012). · 1.66 Impact Factor
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    ABSTRACT: A recent experimental technique was used for measuring the mobility of positive ions originated from ethane in their parent gas. In this particular experiment, measurements were made in pure ethane (C2H6) for pressures ranging from 6 to 10 Torr and for reduced electric fields varying from 6 to 42 Td. The time of arrival spectra revealed two peaks and their reduced mobilities were determined. Extrapolation to zero field led to the values of 1.58 cm2V-1s-1 and 1.47 cm2V-1s-1, which are likely to belong to a 3-carbon ions group which includes C3H5+, C3H7+, C3H8+ and C3H9+ and to a 4-carbon ions group which includes C4H9+ and C4H10+ ions. For typical reduced electric fields used in gaseous detectors (E/N > 15 Td), the mobilities were 15% smaller than the Langevin limit [1].
    Journal of Instrumentation 07/2013; 8(07):P07013. · 1.66 Impact Factor
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    ABSTRACT: A recently used experimental technique for measuring the mobility of positive ions in their parent gases is applied to methane (CH4 purity ⩾99.995%), where ion reduced mobility values K0 are deduced from the analysis of measured time-of-arrival spectra of the ions produced by a GEM. For CH4 pressures in the range 3 to 10 Torr, two peaks could be observed when reduced applied fields E/N were varied from 10 to 60 Td, where E/N is the ratio of electric-field strength to gas-number density. The corresponding extrapolated zero-field mobility values in CH4 were found to be K0 = 2.58 cm2 V−1 s−1 and K0 = 2.42 cm2 V−1 s−1, belonging likely to CH5+ ions on the 1st peak and to C2H5+ and C3H7+ ions, with similar mobility values and falling both under the 2nd peak.
    Journal of Instrumentation 01/2012; 7(06). · 1.66 Impact Factor
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    ABSTRACT: We measured the reduced mobilities of the atomic, Ne+, and dimer, Ne-2(+), ions in Ne, under different pressures and reduced electric fields, at 300 K. Extrapolation to zero field yields values of 4.4 cm(2)V(-1)s(-1) for Ne+ and 6.2 cm(2)V(-1)s(-1) for Ne-2(+), which are in relative good agreement with other published data. The Ne+ ions are converted to Ne-2(+) by a three-body reaction with a rate constant that was also measured. Its average value for reduced electric fields in the 8 to 12 Td range was (5.6 +/- 0.1) x 10(-32)cm(6)s(-1) at 300 K, also agreeing with the results from other authors using other techniques.
    IEEE Transactions on Nuclear Science 08/2011; 58(4):2060-2063. · 1.22 Impact Factor
  • J. A. S. Barata, C. A. N. Conde
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    ABSTRACT: Monte Carlo simulations are preformed to calculate ion transport parameters. Results are presented for the calculated reduced mobilities, K0, and longitudinal, DL, and transverse, DT, diffusion coefficients, for Xe+ ions in gaseous Xe-Ne mixtures, at atmospheric pressures, for Ne concentrations between 1 and 10%, and reduced electric field strengths, E/N, from about 5 to 500 Td, corresponding to values of E/p, from about 1.66 to 166 V cm−1 Torr−1 at 293 K. Reduced mobility, K0, peaks at about 50 Td with values of about 0.50 cm2V−1s−1 and increases slightly with the Ne concentration. The diffusion coefficients remain approximately constant and equal to 0.013 or 0.014 cm2s−1 for E/p values up to about 100 Td. The Monte Carlo simulations use a set of integral and differential elastic collision cross sections for Xe+ ions with neutral Xe and Ne atoms. Integral and differential elastic collision cross-sections for Xe+ ions with neutral Ne atoms are also calculated, and reported for center-of-mass energies in the 1 meV to 10 eV range, using a Tang and Toennies ion-atom interaction potential model to describe ab initio spectroscopic data for the Xe+-Ne molecular ion, and the phase shifts are calculated by the JWKB approximation.
    01/2011;
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    ABSTRACT: The photopeak shift in High Pressure Xe (HPXe) gamma ray detectors due to the energy acquired/lost by the photoelectric and Compton electrons, from the electric field applied in the drift region, is calculated using the PENELOPE code for gamma rays from several radioactive sources. The implications of this effect in HPXe detectors are discussed, namely for TPCs for double beta decay of 136Xe studies.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 01/2010
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    ABSTRACT: We measured the reduced mobilities of the atomic, Ne+, and dimer, Ne2+, ions in Ne, under different pressures and reduced electric fields, at 300 K. The value obtained for the atomic ion, 4.1 cm2V-1 s-1, is in good agreement with other values published in the scientific literature. The value obtained for the mobility of the dimer ion, 7.3 cm2 V-1 s-1, is not in accordance with other published data. We discuss the most probable sources of error.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 01/2010
  • J. A. S. Barata, C. A. N. Conde
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    ABSTRACT: Integral and differential cross-sections for elastic collisions of He+ ions in the ground state (2S) with neutral He atoms are calculated, for centre-of-mass energies between 0.001 and 10 eV, using the partial waves method. The scattering phase shifts are calculated using the JWKB semi-classical approximation, with modified Tang-Toennies ion-atom (TTIA) potential energy curves, that describe spectroscopic data, dissociation energies and equilibrium internuclear distances, and the long-range interaction potentials. These cross-sections are used in a detailed three-dimensional Monte Carlo simulation model to calculate the main transport coefficients describing the ion drift through the neutral gas, as a function of the gas temperature and the reduced uniform electric field. Calculated drift velocities, ion mobilities, as well as longitudinal and transverse diffusion coefficients for He+ atomic ions in gaseous He, at temperature T=293 K and reduced electric fields, E/N, in the 1 to 300 Td (1 Td=10-17 V cm2) range, are reported and compared with the limited experimental data available in the scientific literature. The calculated drift velocities range from 28.31 m s-1 at 1 Td to 3685.0 m s-1 at 300 Td.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; 619:21-23. · 1.14 Impact Factor
  • J. A. S. Barata, C. A. N. Conde
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    ABSTRACT: The drift velocities and the longitudinal and transverse diffusion coefficients for Ar+ ions in gaseous Ar/Ne mixtures, at atmospheric pressures, for Ar concentrations between 1 and 20%, and reduced electric field strengths, E/N, from 1 to 100 Td, corresponding to E/p, from about 0.329 to 32.9 V cm−1 Torr−1 at 293 K, are calculated by Monte Carlo simulation. The Monte Carlo simulations use a set of integral and differential elastic collision cross-sections for Ar+ ions with neutral Ar and Ne atoms. Differential and integral elastic collision cross-sections for Ar+ ions with neutral Ne atoms are calculated, and reported for center-of-mass energies between 1 meV and 10 eV, using a modified Tang and Toennies ion-atom interaction potential model to describe ab initio spectroscopic data for the ArNe+ molecular ion and the long-range interaction potentials. The phase shifts were calculated with the JWKB approximation. The cross-sections for the collision of Ar+ ions with Ar atoms used were the ones calculated before by the authors.
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2010;
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    ABSTRACT: Neutrinoless double beta decay measurements are the most promising experiments both to reveal the Majorana nature of the neutrino and to set a value for its mass. The NEXT project propose to build a High pressure Xenon TPC in the Canfranc Underground Laboratory (Huesca, Spain) to measure double-beta decay of 136Xe, both normal and neutrinoless, with a source mass of 100 kg of enriched xenon.
    Journal of Physics Conference Series 07/2009; 179(1):012005.
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    ABSTRACT: We propose a novel detection concept for neutrinoless double-beta decay searches. This concept is based on a Time Projection Chamber (TPC) filled with high-pressure gaseous xenon, and with separated-function capabilities for calorimetry and tracking. Thanks to its excellent energy resolution, together with its powerful background rejection provided by the distinct double-beta decay topological signature, the design discussed in this Letter Of Intent promises to be competitive and possibly out-perform existing proposals for next-generation neutrinoless double-beta decay experiments. We discuss the detection principles, design specifications, physics potential and R&D plans to construct a detector with 100 kg fiducial mass in the double-beta decay emitting isotope Xe(136), to be installed in the Canfranc Underground Laboratory. Comment: Letter of Intent to the LSC Scientific Committee 115 pages
    07/2009;
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    01/2009;
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    ABSTRACT: We measured the reduced mobilities (k0 in cm2V-1s-1) of the ions that are formed in P-10 mixtures under different pressures and various reduced electric fields. Two types of ions were identified. We then used the extrapolated values of k0 when E/N¿0 (2.41 and 2.76 cm2V-1s-1), the Langevin formula and the Blanc's law, to calculate the masses of these ions. Calculations indicate that the two ions have masses of 41 a.u. and 25 a.u., respectively. We propose hypothesis to explain the nature and origin of those ions.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 01/2009
  • J. A. S. Barata, C. A. N. Conde
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    ABSTRACT: Integral and differential elastic collision cross-sections for Ne+ ions with neutral Ne atoms are calculated, for center of mass collision energies from 1 meV to 10 eV, using modified Tang and Toennies ion-atom interaction potentials models, TTIA and TTIA-wb, to fit experimental accurate spectroscopic data for the Ne2+ molecular ion and to describe the long-range interaction potentials. The effect of the spin-orbit interaction is included through a semi empirical model and the scattering phase shifts are calculated using the JWKB approximation.
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2008;
  • J.A.S. Barata, C.A.N. Conde
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    ABSTRACT: The drift velocities and the longitudinal and transverse diffusion coefficients for Xe<sup>+</sup> ions in gaseous Xe/<sup>3</sup>He mixtures, at atmospheric pressures, for Xe concentrations between 1 and 30%, and reduced electric field strengths, from about 3 to 70 Td, corresponding to E/p, from about 1 to 22.5 V cm<sup>-1</sup>Torr<sup>-1</sup> at 300 K, are calculated by simulation using a detailed Monte Carlo computer programme. This programme uses a set of integral and differential elastic collision cross sections for Xe ions with neutral He and Xe atoms, previously calculated by the authors using a modified Tang-Toennies ion-atom interaction potential and the JWKB approximation to calculate the phase shifts. The calculated drift velocities of Xe<sup>+</sup> ions depend strongly on the concentration of Xe in the mixtures.
    IEEE Transactions on Nuclear Science 07/2007; · 1.22 Impact Factor
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    J. A. S. Barata, C. A. N. Conde
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    ABSTRACT: Results are presented for the calculated drift velocities and diffusion coefficients for Ar+ ions in helium at atmospheric pressure, temperature T=300 K and for reduced electric fields E/N from about 1 Td up to about 150 Td, using Monte Carlo techniques. The drift velocities range from 5.94×103 to 559.0×103 cm s−1 for the Ar+ ions in the ground state 2P3/2 and from 5.85×103 to 545.0×103 cm s−1 for the Ar+ ions in the metastable excited state 2P1/2. These values are in good agreement (within about 5%) with the few experimental values available. The mobilities and diffusion coefficients for atomic Ar+ ions in helium gas show no significant dependence on the spin state of the ion.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2007; 580:18-21. · 1.14 Impact Factor
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    J. A. S. Barata
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    ABSTRACT: Integral and differential elastic collision cross-sections for Ar+ ions with neutral Ar atoms are calculated using modified Tang and Toennies ion–atom interaction potential models, TTIA and TTIA-wb, to describe experimental spectroscopic data for the Ar2+ molecular ion, and the phase shifts are calculated by the JWKB approximation. Results are presented for center-of-mass energies in the 1meV to 10eV range. In our calculations, the effects of the spin–orbit interaction are included through a semi-empirical model. The results obtained agree with the scarce data available in the scientific literature.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2007; 580(1):14-17. · 1.14 Impact Factor
  • J.A.S. Barata, C.A.N. Conde
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    ABSTRACT: Drift velocities and longitudinal and transverse diffusion coefficients for Ar<sup>+</sup> ions in gaseous Ar, at atmospheric pressures p = 160 Torr, T = 293 K and reduced electric fields, E/N, in the 1 to 500 Td range, are calculated using a three-dimensional Monte Carlo simulation model. The integral and differential elastic collision cross-sections used were the ones calculated before by the authors, for center-of-mass energies in the 1 meV to 10 eV range, using a modified Tang-Toennies ion-atom potential and a semi-classical approximation with phase shifts calculated by the JWKB approximation. The calculated reduced mobilities, K<sub>0</sub>, for Ar<sup>+</sup> ions in Ar, range from 1.431 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at 1 Td to 0.759 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at 500 Td for Ar<sup>+</sup> ions in the <sup>2</sup>P<sub>3/2</sub> ground state and from 1.414 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at 1 Td to 0.758 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at 500 Td, for the <sup>2</sup>P<sub>frac12</sub> metastable state. The results obtained for the drift velocities and diffusion coefficients are compared with the experimental data available and discussed.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
  • J.A.S. Barata, C.A.N. Conde
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    ABSTRACT: Elastic collision cross-sections for Xe<sup>+</sup> ions with neutral Xe atoms are calculated using a modified Tang-Toennies ion-atom potential and a semi-classical approximation with phase shifts calculated by the Jeffreys-Wentzel-Kramers-Brillouin approximation. Results are presented for integral and differential cross sections at center-of-mass energies in the 1 meV to 10 eV energy range. The cross sections were then used to calculate the drift velocities and diffusion coefficients of Xe<sup>+</sup> ions in gaseous xenon at atmospheric pressures and reduced electric fields, E/N, in the 3 to 300 Td range (N is the neutral gas number density and 1 Td=10<sup>-17</sup> Vcm<sup>2 </sup>) using Monte Carlo technique. The results obtained are compared and discussed with limited experimental data available from previous studies
    IEEE Transactions on Nuclear Science 01/2006; · 1.22 Impact Factor