Formar científicos en condiciones de adversidad

Esta reseña de mi trayectoria, con cuya solicitud me ha honrado la AAPC, intenta transmitir algunas reflexiones sobre cómo facilitar la investigación científica. La preparación de la misma me ha permitido reconocer algunas ideas que han surgido a partir de mis experiencias como investigador y docente a lo largo de mi quehacer universitario y que vale la pena compartir. No abundaré en detalles demasiado particulares que probablemente no tengan un valor general que sí tienen otros. Excepto algunas menciones ineludibles, estas cuestiones son complementarias de lo que muchos investigadores ya han expuesto en las excelentes reseñas que pueden encontrarse en las páginas de la AAPC sobre las condiciones políticas y sociales en las décadas que nos ha tocado desarrollar la investigación en la Argentina.Instituto de Física La Plat

Formar científicos en condiciones de adversidad

Esta reseña de mi trayectoria, con cuya solicitud me ha honrado la AAPC, intenta transmitir algunas reflexiones sobre cómo facilitar la investigación científica. La preparación de la misma me ha permitido reconocer algunas ideas que han surgido a partir de mis experiencias como investigador y docente a lo largo de mi quehacer universitario y que vale la pena compartir. No abundaré en detalles demasiado particulares que probablemente no tengan un valor general que sí tienen otros. Excepto algunas menciones ineludibles, estas cuestiones son complementarias de lo que muchos investigadores ya han expuesto en las excelentes reseñas que pueden encontrarse en las páginas de la AAPC sobre las condiciones políticas y sociales en las décadas que nos ha tocado desarrollar la investigación en la Argentina.Instituto de Física La Plat

Activities of 232Th, 226Ra, 40K, and 137Cs in surface soil and external dose assessment at two zones of Buenos Aires Province, Argentina

In the frame of establishing the radiological baseline of the Buenos Aires Province, Argentina, this work assesses the total outdoor external dose and the activity values of 40K, 226Ra, 232Th and 137Cs in superficial soils of La Plata and Lima cities. In the latter, the most important nuclear emplacement of the country is located. At La Plata, 49 sites were analyzed, which correspond to the green public spaces of the city while at Lima 6 sites around the nuclear power plants were studied. For La Plata, the external dose contribution and activity distribution maps of 40K, 226Ra, 232Th and 137Cs were obtained using the Kriging geo-statistical method. Activity values of 226Ra and 232Th resulted lower than their worldwide average ones, while the 40K levels were higher than the corresponding one. The activity dataset was analyzed together with the activity values determined previously in unperturbed soils of the region. The Pearson correlation coefficient was re-calculated, obtaining correlations more significant when all activity data were considered. No correlation between activity superficial distributions and the height above sea level or the geomorphological units was found. The activity values obtained in Lima soils lie in the range of the values determined for La Plata soils. Like in La Plata, 137Cs activity around the nuclear facility could be associated only with the nuclear power tests. The average total external annual dose for La Plata inhabitants are in the range of 0.19 to 0.25 mSv/year, similar to those determined for Lima residents. The present work complements previous reports contributing to the establishment of the radiological baseline for soils of Buenos Aires Province, Argentina, the province with the most important nuclear activities of the country.Instituto de Física La Plat

Lattice-dynamics of the intermediate oxide of tin

The lattice-dynamical properties of the intermediate oxide of tin (IO) have been investigated over the temperature range 80–295 K. The logarithm of the recoil-free fraction varied linearly with temperature. However, a Debye model does not give a good account of this dependence. By comparison with the other oxides of the Sn-O system, the recoil-free fraction for tin atoms with 2+ and 4+ oxidation states of the IO were estimated. At room temperature, they are 0.463 and 0.323 for 4+ and 2+ states respectively.Facultad de Ciencias Exacta

Phase transformations induced by implantation of ¹²C⁻ ions into α-Fe and AISI 304 and 316 stainless steels studied by CEMS and SEM

Samples of AISI 304 and 316 stainless steels, initially in austenitic (first set) and martensitic states (second set) and α-Fe (third set), were implanted with 180 keV¹²C⁻ to a dose of 10¹⁷ atoms/cm² at room temperature. Surfaces were examined by SEM (scanning electron microscopy) and the crystalline-phase fractions were estimated through CEMS (conversion electron Mossbauer spectroscopy). Different grades of etching were produced by sputtering during the implantations on the stainless steel samples depending on the previous crystallographic states. CEMS data reveal the γ → α′ transformation in the initially martensitic samples and no noticeable modifications as a result of the implantation on α-Fe and austenitic samples.Facultad de Ciencias Exacta

Excitation functions for the production of 90 Nb and 88 Y by irradiation of zirconium with deuterons

Excitation functions for reactions induced by deuterons on natural zirconium and90Zr targets have been measured radiochemically with the stacked foil technique between ≈9 and 27 MeV. The observed reactions are Zr(d,xn)90 Nb, Zr(d,axn)88Y,90Zr(d, 2n)90Nb and90Zr(d, α)88Y. The excitation functions for the reactions91Zr(d, 3n)90Nb and91Zr(d, αn)88Y have been deduced from the results mentioned above. Calculations of the excitation function for the (d, 2n) reaction have been performed with two different treatments, each one taking into account two competitive mechanisms. The compound-statistical model plus Hittmair's stripping theory accounts quite well for the (d, 2n) cross sections observed. However, the agreement obtained with Peaslee-Otozai's theory is excellent and the set of parameters used more reasonable. It has been assumed that the stripping mechanism can have no contribution to the (d, α) reaction. Accordingly, calculations for this reaction have been done using the compound-statistical model and the entire absorption process followed by the evaporation of an α particle. No good agreement is obtained with either theory.Facultad de Ciencias Exacta

Microscopic spheroidal particles obtained by laser cutting

In this work we study the characteristics of the particles ejected from the cutting zone of a SAE 1010 steel while using a CO2 gaseous laser with the purpose of determining the feasibility to use this technique in the production of microscopic particles for nuclear applications [2] as well as for other scientific and technological uses [1].Instituto de Física La Plat

Estudio de superficie de α - FE y aceros inoxidables implantados con ¹²C⁻

Se han implantado iones ¹²C⁻ con una energía de 180 keV y una dosis del orden de 10¹⁷ at / cm² en a - Fe y en aceros inoxidables AISI304 y 316 en distintas fases en equilibrio. Se estudian las modificaciones superficiales que tienen lugar atendiendo a sus anteriores estados cristalinos. Se observaron cambios importantes en las superficies de las muestras implantadas tales como la formación de ampollas (blisters), escamas (flakes), y ataque preferencial producidos por el impacto de los iones sobre la superficie. Se relacionan las modificaciones superficiales con las estructuras cristalinas de las muestras previas a la implantación.Facultad de Ciencias Exacta

The origin of gley colors in hydromorphic vertisols: the study case of the coastal plain of the Río de la Plata estuary

This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Río de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Río de la Plata estuary were analyzed using routine and chemical analyses, Mössbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite).Fil: Gómez Samus, Mauro Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Ambientales y Recursos Naturales; ArgentinaFil: Comerio, Marcos. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Montes, María Luciana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Boff, Laura Daniela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geomorfología y Suelos; ArgentinaFil: Loffler, Julia. Universidad Nacional de La Plata; ArgentinaFil: Mercader, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Bidegain, Juan Carlos. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentin

Estudio sistemático de la interacción de intercambio en óxidos y haluros de metales de transición

Se presenta un estudio de las interacciones de superintercambio en óxidos y haluros de metales de transición con el método de Heitler-London a partir de una base de orbitales moleculares. Se halló un fuerte superintercambio en la cadena lineal Cu-O-Cu, aproximadamente un orden de magnitud mayor a los otros compuestos, lo que avala recientes teorías de interacciones mediadas por spin en superconductores de alta temperatura crítica a base de óxidos de cobre.Instituto de Física de Líquidos y Sistemas Biológico