Laboratorio TANDAR

San Martín, Argentina

Laboratorio TANDAR

San Martín, Argentina

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Timmers H.,Australian Defence Force Academy | Gladkis L.G.,Australian Defence Force Academy | Warner J.A.,Australian Defence Force Academy | del Grosso M.F.,Laboratorio Tandar | And 4 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

Radionuclide tracers were ion implanted with three different techniques into the ultra-high molecular weight polyethylene polymer. Tracer nuclei of 7Be were produced with inverse kinematics via the reaction p(7Li,7Be)n and caught by polymer samples at a forward scattering angle with a maximum implantation energy of 16 MeV. For the first time, 97Ru, 100Pd, and, independently, 111In have been used as radionuclide tracers in ultra-high molecular weight polyethylene. 97Ru and 100Pd were recoil-implanted following the fusion evaporation reactions 92Zr(12C,α3n) 97Ru and 92Zr(12C,4n)100Pd with a maximum implantation energy of 8 MeV. 111In ions were produced in an ion source, mass-separated and implanted at 160 keV. The tribology of implanted polymer samples was studied by tracing the radionuclide during mechanical wear. Uni-directional and bi-directional sliding apparatus with stainless steel actuators were used. Results suggest a debris exchange process as the characteristic feature of the wear-in phase. This process can establish the steady state required for a subsequently constant wear rate in agreement with Archard's equation. The nano-scale implantation of mass-separated 111In appears best suited to the study of non-linear tribological processes during wear-in. Such non-linear processes may be expected to be important in micro- and nanomachines. © 2010 Elsevier B.V. All rights reserved.


Garcia F.,CONICET | Garcia F.,National University of La Plata | Aguilera D.N.,Laboratorio Tandar | Aguilera D.N.,CONICET | And 3 more authors.
Astronomy and Astrophysics | Year: 2014

Context. In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assumed to produce relativistic jets only if their surface magnetic field is weak enough (B ∼ 108 G). However, the most common manifestation of neutron stars are pulsars, whose magnetic field distribution peaks at B ∼ 1012 G. If the neutron star magnetic field has at least this strength at birth, it must decay considerably before jets can be launched in binary systems. Aims. We study the magnetic field evolution of a neutron star that accretes matter from the wind of a high-mass stellar companion so that we can constrain the accretion rate and the impurities in the crust, which are necessary conditions for jet formation. Methods. We solved the induction equation for the diffusion and convection of the neutron star magnetic field confined to the crust, assuming spherical accretion in a simpliflied one-dimensional treatment. We incorporated state-of-the-art microphysics, including consistent thermal evolution profiles, and assumed two different neutron star cooling scenarios based on the superfluidity conditions at the core. Results. We find that in this scenario, magnetic field decay at long timescales is governed mainly by the accretion rate, while the impurity content and thermal evolution of the neutron star play a secondary role. For accretion rates ? ≥ 10-10M· yr-1, surface magnetic fields can decay up to four orders of magnitude in ∼10 7 yr, which is the timescale imposed by the evolution of the high-mass stellar companion in these systems. Based on these results, we discuss the possibility of transient jet-launching in strong wind-accreting high-mass binary systems like supergiant fast X-ray transients. © 2014 ESO.


Negri A.E.,Laboratorio TANDAR | Fernandez Niello J.O.,Laboratorio TANDAR | Fernandez Niello J.O.,National University of San Martín of Argentina | Wallner A.,University of Vienna | And 3 more authors.
Science of the Total Environment | Year: 2012

129I and 127I concentrations in animal thyroids coming from several regions of Argentina were determined by accelerator mass spectrometry (AMS) and gas chromatography (GC), respectively. The measured 129I/ 127I ratios, ranging from 3×10 -12 to 4×10 -10, are significantly lower than those typical for areas in the northern hemisphere (10 -10-10 -7). The 129I concentrations show a clear dependence with latitude and season, which can be understood considering tropospheric circulation patterns, possible 129I sources and regional precipitation rates. © 2012 Elsevier B.V.


Niello Fernandez J.,Laboratorio TANDAR | Niello Fernandez J.,National University of San Martín of Argentina | Negri A.,Laboratorio TANDAR | Wallner A.,Australian National University | And 3 more authors.
EPJ Web of Conferences | Year: 2013

Total iodine and129-iodine in rivers and lakes of Argentina were measured by means of inductively coupled plasma mass spectrometry and accelerator mass spectrometry respectively. The obtained isotopic ratios, higher than the natural level, are explained as the delayed signal from nuclear weapon atmospheric tests. Besides, deposition fluences in catchment areas of the lakes are analyzed. Their latitudinal dependence, similar to the dependence of annual precipitation rates, favours wet deposition as the main 129I fallout mechanism for this region. © Owned by the authors, published by EDP Sciences, 2013.


Negri A.E.,Laboratorio TANDAR | Fernandez Niello J.O.,Laboratorio TANDAR | Fernandez Niello J.O.,National University of San Martín of Argentina | Wallner A.,Australian National University | And 3 more authors.
Environmental Science and Technology | Year: 2013

Measurements of total iodine (I) and iodine-129 (129I) concentrations in rivers and lakes of Argentina are presented. Their latitudinal distribution can be explained by taking into account their main sources (oceanic emissions and biomass burning for I, and atmospheric nuclear tests for 129I), transport mechanisms, and fallout patterns. From the measured 129I concentrations in the studied lakes, deposition fluences for their catchment areas were estimated. These results agree with a model of the global deposition pattern due to the 129I released by atmospheric nuclear weapon tests and with other fluences reported for the southern hemisphere. In addition, the first measurements of 129I in shallow seawater from the South Atlantic Ocean are presented and discussed. © 2013 American Chemical Society.


Negri A.E.,Laboratorio TANDAR | Fernandez Niello J.O.,Laboratorio TANDAR | Fernandez Niello J.O.,National University of San Martín of Argentina | Wallner A.,University of Vienna | And 3 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

129I/127I ratios and iodine concentrations in bovine thyroids stemming from Argentina were determined by accelerator mass spectrometry (AMS) and gas chromatography (GC), respectively. From these measurements, a relationship of the 129I/127I ratio with iodine content in the gland was obtained. A weak correlation between the two isotopes was found, suggesting that 129I re-emission from the ocean is not the only process for the 129I deposition in Argentina. Moreover, contributions to the total 129I inventory in the Southern hemisphere from both natural and anthropogenic sources were theoretically studied. Surface compartments present similar contribution from natural sources and nuclear explosions fallout. © 2012 Elsevier B.V. All rights reserved.


Mohr P.,Diakonie Klinikum Schwabisch Hall GGmbH | Mohr P.,Institute of Nuclear Research ATOMKI | de Faria P.N.,University of Sao Paulo | Lichtenthaler R.,University of Sao Paulo | And 8 more authors.
Physical Review C - Nuclear Physics | Year: 2010

Cross sections of 120Sn(α,α)120Sn elastic scattering have been extracted from the α-particle-beam contamination of a recent 120Sn(6He,6He)120Sn experiment. Both reactions are analyzed using systematic double-folding potentials in the real part and smoothly varying Woods-Saxon potentials in the imaginary part. The potential extracted from the 120Sn(6He,6He)120Sn data may be used as the basis for the construction of a simple global 6He optical potential. The comparison of the 6He and α data shows that the halo nature of the 6He nucleus leads to a clear signature in the reflexion coefficients ηL: The relevant angular momenta L with ηL ≫ 0 and ηL ≪ 1 are shifted to larger L with a broader distribution. This signature is not present in the α-scattering data and can thus be used as a new criterion for the definition of a halo nucleus. © 2010 The American Physical Society.


Szybisz L.,Laboratorio TANDAR | Szybisz L.,University of Buenos Aires | Szybisz L.,CONICET | Sartarelli S.A.,National University of General Sarmiento
AIP Advances | Year: 2011

Adsorption on single planar walls and filling of slits with identical planar walls are investigated in the frame of the density functional theory. In this sort of slits the external potential is symmetric with respect to its central plane. Calculations were carried out by applying both the canonical and grand canonical ensembles (CE and GCE, respectively). The behavior is analyzed by varying the strength of the adsorbate-substrate attraction, the temperature T, and the coverage Results obtained for physisorption of Xe on alkaline surfaces are reported in the present work. Prewetting (PW) lines and wetting temperatures, T w, are determined from the analysis of adsorption on single walls. The filling of slits is analyzed for temperatures T T w. It is found that whenever for a given Xe-substrate combination the adsorption on a single wall exhibits a first-order wetting transition then asymmetric profiles that break the left-right symmetry of the external potential appear in the filling of an equivalent slit. These spontaneously symmetry breaking (SSB) solutions occur in a restricted range of with a T-dependent width. In the case of closed slits analyzed in the CE scheme, the obtained asymmetric profiles exhibit lower Helmholtz free energies than the symmetric species and, therefore, could be stabilized in this geometry. For open slits, the GCE scheme yields all the symmetric and SSB states in the corresponding convex regimes of the free energy. It is shown that both the CE and the GCE frames yield three coexistent states, two symmetric and one asymmetric twofold degenerate. Both a PW line and the related SSB effect terminate at the same temperature. For rather strongly attractive surfaces reentrant SSB states are found at a fixed value of T. © Copyright 2011 Author(s).


PubMed | Laboratorio TANDAR
Type: Journal Article | Journal: Environmental science & technology | Year: 2013

Measurements of total iodine (I) and iodine-129 ((129)I) concentrations in rivers and lakes of Argentina are presented. Their latitudinal distribution can be explained by taking into account their main sources (oceanic emissions and biomass burning for I, and atmospheric nuclear tests for (129)I), transport mechanisms, and fallout patterns. From the measured (129)I concentrations in the studied lakes, deposition fluences for their catchment areas were estimated. These results agree with a model of the global deposition pattern due to the (129)I released by atmospheric nuclear weapon tests and with other fluences reported for the southern hemisphere. In addition, the first measurements of (129)I in shallow seawater from the South Atlantic Ocean are presented and discussed.


PubMed | Laboratorio TANDAR
Type: | Journal: The Science of the total environment | Year: 2012

(129)I and (127)I concentrations in animal thyroids coming from several regions of Argentina were determined by accelerator mass spectrometry (AMS) and gas chromatography (GC), respectively. The measured (129)I/(127)I ratios, ranging from 3 10(-12) to 4 10(-10), are significantly lower than those typical for areas in the northern hemisphere (10(-10)-10(-7)). The (129)I concentrations show a clear dependence with latitude and season, which can be understood considering tropospheric circulation patterns, possible (129)I sources and regional precipitation rates.

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