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Ver el documento (formato PDF)   Baró, Gregorio Bonifacio.  "Estado químico del arsénico formado por transformaciones nucleares en compuestos inorgánicos de germanio, selenio, bromo y arsénico"  (1961)
Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
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Abstract:
The distribution of radioactive arsenic among trivalent and pentavalent states of arsenic produced by nuclear transformations has been investigated in simple inorganic compounds of germanium, selenium, bromine and arsenic. In some cases we have studied the change of this distribution by annealing processes. The nuclear transformations we have studied are the following: Ge77-—β—> As77 Se76 (n,p) As76 Br81 (n,α) As78 Br79 (n,α) As76 As75 (n,γ) As76 The compounds were irradiated with neutrons in the RAI reactor in Buenos Aires and later with neutrons obtained by bombarding beryllium with 26 MeV deuterons in the Philips synchrocyclotron of Amsterdam. The chemical separations used consisted of the dissolution of the irradiated compound in a solution containing AsIII and AsV carriers. The arsenate fractions were separated from the arsenite fractions by precipitation as magnesium ammonium arsenate. The arsenite was then oxidized to arsenate which in turn was precipitated as magnesium ammonium arsenate. All fractions were converted to magnesium piro-arsenate. The radioactive samples were counted with an end-window G.M. counter under conditions of standard geometry. Annealing was carried out in constant-temperature baths during specified periods of time. It is evident from our experimental results that chemical conditions in the aqueous medium, and specially the pH, have little or no influence on the distribution of the arsenic activity among the two oxidation states. This suggests that the final form in which the radioactive arsenic will be found is already determined inside the target lattice. It is even more striking that the distribution observed in GeO2 is very nearly equal to that in SeO2. This suggests that the structure of the oxide is the determining factor for the distribution of the arsenic activity among arsenite and arsenate fractions. It is very curious that the AsV: total As of radioactive arsenic in the oxides of germanium and selenium and in the oxides of arsenic may be represented as a linear function of the oxygen: parent element ratio for the irradiated compound. This is true for some other compounds as Na2Se04 and Na2Ge03. In the other compounds that we have investigated the linear relationship does not hold very well. In part this maybe the reflection of the differences in the lattice arrangement, but reducing and oxidizing tendencies of the irradiated compounds may also possibly play a role. The differences found between Na2Se03 and H2Se03 can be ascribed to bound hydrogen present inside the latter compound. The results in the bromine compounds indicate that the distribution of radioactive arsenic among the arsenite and arsenate fractions depends on the amount of oxygen contained in the irradiated compounds. Even in the bromides the percentage of radioarsenic is fairly directly correlated with the oxygen present as water in the crystal. Annealing turned out to be quite slow, even at temperatures appreciably higher than those required to increase the retention in most neutron irradiated solid salts. The first part of this thesis presents a survey of the field of Szilard-Chalmers and similar phenomena with emphasis on inorganic systems. It will not cite all the literature published until now, but will try to review some of the most significant recent work.
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Título : Estado químico del arsénico formado por transformaciones nucleares en compuestos inorgánicos de germanio, selenio, bromo y arsénico    
Autor : Baró, Gregorio Bonifacio
Director : Aten Junior, A. H. W.
Año : 1961
Editor : Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Filiación : Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales
Instituto de Investigaciones Nucleares de Amsterdam (Instituut voor Kernphysisch Onderzoek)
Grado obtenido : Doctor en Ciencias Químicas
Ubicación : Preservación - http://digital.bl.fcen.uba.ar/gsdl-282/cgi-bin/library.cgi?a=d&c=tesis&d=Tesis_1096_Baro
Idioma : Español
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