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Os efeitos químicos do recuo do 51Cr formado pela reação (n,y) foram investigados nos compostos: [Cr(NH3) 5ONO] (NO3)2, [Cr(NH3) 5NO3] (NO3)2 e [Cr(NH3)5 NCS] (NO3)2, irradiados no estado sólido. Após dissolução dos cristais, os fragmentos resultantes da irradiação foram analisados por cromatografia com resina trocadora de íons e eletroforese em papel. A distribuição inicial das espécies é discutida em termos da formação de complexos polinucleares e da não ocorrência de conversão interna em compostos de cromo (III). Os efeitos de reversão térmica indicam uma considerável influência do oxigênio atmosférico e de defeitos cristalinos no comportamento químico das espécies. / The chemical effects of recoiling 51Cr formed by (n,y) reactions in the solid compounds [Cr (NH3)5 ONO] (NO3)2, [Cr(NH3)5 NO3] and [Cr(NH3)5 NCS] (NO3)2 has been investigated. The fragments resulting from neutron irradiation were analysed by ion-exchange chromatography and paper electrophoresis after dissolution of the crystals. The initial distribution of the species is discussed in terms of polynuclear complexes formation and non-ocurrence of internal conversion in trivalent chromium compounds. Thermal annealing effects show a considerable influence of atmospheric oxygen and crystal deffects in the chemical behavior of the species.

Made available in DSpace on 2018-07-27T18:26:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-03-23. Added 1 bitstream(s) on 2018-07-27T18:30:01Z : No. of bitstreams: 1 000722927.pdf: 549168 bytes, checksum: f805267ee895e64b69cdde777e44d404 (MD5) / Neste trabalho nós analisamos a influência da troca de um méson sigma sobre alguns dos principais observáveis do processo de decaimento hipernuclear fraco não-mesônico. Para isso discutimos em detalhe o formalismo baseado no modelo de camadas extremo para tratar as taxas do processo de decaimento fraco não-mesônico. O potencial de transição para o processo com mudança de estranheza ('delta'S =1), 'lâmbda'nü' 'SETA'nü'nü', foi construído a partir de diversos modelos de troca de um méson incluindo, além da troca dos mésosns pseudoescalares ('pi', 'capa', 'eta') e dos mésons vetoriais ('rô', 'ômega', 'capa'*), uma nova contribução devido ao méson escalar-isoescalar 'sigma'. Apresentamos tmbém os resultados numéricos obtidos para a taxa não mesônica total 'gama IND. nm='gama IND.n' + 'gama IND. p' e para a razão 'gama IND. n'/'gama IND. p' no decaimento do 'INTPOT. 5 ANTIND. 'LÂMBDA' He'. Esses resultados comprovam que a influências do méson 'sigma' é significativa e vai na direção de aumentar a razão 'gama IND. n'/'gama IND. p' / In this work we investigate the influence of the exchange of a scalar-isoscalar sigma meson on some of the main observables in the nonmesonic hypernuclear weak decay. We discuss in detal the formalism based on the extreme shell model for the computation of the nonmesonic weak decay rates. The weak transition potential for the strangeness changing ('delta'S =1) process 'lâmbda'nü' 'SETA'nü'nü' is constructed based on several one-meson-exchange models, that include, beyond of the pseudoscalar ('pi', 'capa', 'eta') and the vector ('rô', 'ômega', 'capa'*) mesons, a ew contribution due to the scalar-isoscalar 'sigma' meson. We also present the numerical results obtained for the total nonmesonic rate, 'gama IND. nm='gama IND.n' + 'gama IND. p', and for the ration 'gama IND. n'/'gama IND. p' in the decay of 'INTPOT. 5 ANTIND. 'LÂMBDA' He'. We show that the influence of the 'sigma' meson is significant and goes in the direction of increasing the 'gama IND. n'/'gama IND. p'ratio.

Orientador: Sérgio Ferraz Novaes / Doutor