Submitted by Marcele Costal de Castro (costalcastro@gmail.com) on 2017-12-08T13:39:49Z No. of bitstreams: 0 / Made available in DSpace on 2017-12-08T13:39:49Z (GMT). No. of bitstreams: 0 Previous issue date: 1973-02 / O aço inoxidável austenítico AISI 316 submetido a prótons de 5 Mev sofreu aumentos nos valores da sua microdureza variáveis com as doses de irradiação recebidas. Para os tempos de irradiação de 1,2,3,4 e 5 horas, a microdureza Vickers do material cresceu desde 180 (0 hora) até 252 kg/mm2 ( 5 horas), correspondendo a um aumento de 42% do valor original. Paralelamente, medidas da variação de dureza com a profundidade mostraram que a influência dos prótons decresceu com a diminuição do tempo de irradiação variando de 150 µm (5 horas) atem 100 µm (2 horas). Foi observado que os valores de microdureza começam a diminuir após a faixa de 40 - 80 µm. Um esforço foi feito para compreender tal efeito, bem como a ocorrência de uma constância na dureza entre 3 e 4 horas de irradiação e ao nível de 80 µm. Técnicas de microscopia ótica e difração de raios -X utilizados, não permitiram detectar a transformaçãop da austenita para fase α1.

Orientador: V.S. Sundaram / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-14T03:15:06Z (GMT). No. of bitstreams: 1 Barreto_CiclamioLeite_M.pdf: 1140110 bytes, checksum: 01c93cf69a1d4f8eb0d308125a7703da (MD5) Previous issue date: 1978 / Resumo: A técnica de Espectroscopia de Elétrons oferece uma abordagem fundamental no estudo de vários ramos da física e da química analítica. Com o auxílio de um espectrômetro MacPherson ESCA36 foram estudadas as propriedades foto-electro-emissoras de várias ligas CuxPt1-x(O < x < 1), preparadas pelas técnicas tradicionais de metalurgia cobrindo ampla gama de valores de x. A escolha de tais amostras foi determinada pela importância científica e tecnológica atribuida atualmente às ligas catalistas - um assunto sob intensiva investigação - e pelas propriedades catalíticas especialmente interessantes por elas apresentadas. Após descrever inicialmente a técnica, a aparelhagem utilizada e a preparação das amostras, os resultados são sistematicamente apresentados visando conclusões acerca da composição superficial nas ligas, da assimetria das linhas espectrais correspondentes às ligações caroçais, e dos mecanismos associados com o efeito da transferência de carga / Abstract: Not informed. / Mestrado / Física / Mestre em Física

No description available.

No description available.

No description available.

No description available.

No description available.

Synthetic hematite aggregates that result from a process that may have industrial and environmental relevance are studied by Mossbauer spectroscopy at room temperature and liquid nitrogen temperature. The Mossbauer results are compared to measurements involving chemical analysis, scanning electron microscopy, and X-ray diffraction on the same samples. Factors such as the crystalline quality of the hematite and the overall sample purity (wt%Fe$\sb2$O$\sb3)$ are followed as functions of the known synthesis conditions. Pure bulk hematite (high quality $\alpha$-Fe$\sb2$O$\sb3$) serves as a reference throughout. Mossbauer spectroscopy is useful in two ways in this problem: (i) it can detect and identify iron-bearing impurities (i.e. non-hematite Fe-compounds), and (ii) it gives much detailed microscopic information on the intra-sample hematite. We find that all of the sulphur seen by chemical analysis probably resides in an iron-bearing compound which, most often, is probably a quenstetite-like material: Fe$\sb2$(SO$\sb4)\sb3\cdot$nH$\sb2$O (n = 9-11). The synthesis conditions are understood to determine both the hematite yield (or sample purity: wt%Fe$\sb2$O$\sb3$) and the intra-hematite crystalline quality, in that these two factors are correlated. Our interpretation of the room temperature Mossbauer spectra resolves coexisting bulk-like and high-defect-density regions whose relative amounts and sample-dependent Mossbauer characteristics can be quantified accurately. On going to liquid nitrogen temperature, a Morin transition is seen to have occurred in all regions of the most bulk-like samples, to have occurred in some regions of intermediate samples, or not to have occurred at all in the samples with the highest defect-density hematites. This illustrates the intricate interplay between microstructural details and cooperative magnetism in hematite materials.

Proton-nucleus interactions, in nuclear emulsion, at incident proton energies of 200 GeV and 300 GeV are studied. The emulsion stacks were exposed with the emulsion surface perpendicular to the beam direction. The results obtained are found to be compatible with those obtained, by scanning along the track of the incident proton, in the horizontally exposed stacks. The inelastic mean-free-path is essentially the same at the two energies: 33.4+/-2.6 cm at 200 GeV 34.6+/-1.8 cm at 300 GeV. The average number of black tracks and the average number of grey tracks are also observed to be the same at both energies: &lt; Nb>=5.9+/-0.4, &lt; N g>=1.7+/-0.2 at 200 GeV and &lt; Nb>=6.1+/-0.3, &lt; Ng>=1.7+/-0.1 at 300 GeV. The average number of shower particles, &lt; ns>, increases from 13.4+/-0.6 at 200 GeV to 15.2+/-0.4 at 300 GeV. &lt; ns> may be given by &lt; n s>=1.85 s1/3, where s is the square of the C.M. energy of the nucleon-nucleon system. It is shown that the ratio of dispersion D to the averagae multiplicity in proton-nucleus collisions is independent of the target nucleus. It is also shown that the multiplicity distribution (in emulsion) obeys the KNO semi-inclusive scaling law in the energy range of 6.2 GeV to 300 GeV. The scaling function applied by Buras et al the proton-proton multiplicity distributions was used. It is argued that the proper quantity that gives the correct A dependence of the production of particles in proton-nucleus collisions is the ratio of created charges in proton-nucleus and proton-proton interactions. The predictions for the average multiplicity and the above mentioned ratio, from various models, are compared with the experimental values. The predictions of the models discussed agree reasonably well with the experimental results. The rapidity distribution provides a crucial test for the models considered. The models' prediction that there should be no difference between proton-nucleus and protonproton distributions, in the foreward region of the rapidity (in this case ln tan thetaL/2) plots is verified. It is concluded that with extensive data using various nuclear targets, it should be possible to eliminate some of the models since the models differ in the prediction of the boundary of the region where the excess number of particles (compared with proton-proton distribution at the same energy should appear.

The (n,n'gamma) reaction at En = 14.1 MeV has been studied for O16 and Ca40. Differential cross sections were obtained for the scattering by the ground states and several excited states. The excitation of the lowest 3- states was quite strong fpr each nuclide. This is evidence that the collective octupole description is valid for these 3- states. The elastic cross sections were successfully fitted using the optical model. The optical parameters which resulted were employed in DWB calculations to predict scattering cross sections for the lowest 3- states. of O16 and Ca40. For these calculations, the 3- states were represented by collective octupole vibrations. The agreement with experiment was good in the case of Ca40 but poor in the case of O16. The latter result may be due to the inadenquacy of the DWB method for such a light nucleus. Energy, yield and angular distribution measurements were made for the deexcitation gamma rays. For O16 the results were used to deduce excitation cross sections which were in good agreement with the neutron data. It was observed that states higher than the first 3- levels in O16 and Ca40 seldom decay by direct ground state transitions but rather by cascade events which proceed throught the first 3- states. This result is in accord with the assumption of a collective vibrational nature for these states if it is assumed that some of the higher states are formed on top of the 3- level.