Titan, the largest moon of Saturn, is the only known moon with a fully developed nitrogen-rich atmosphere, its ionosphere is detectable as high as 2200 km above its surface and hosts complex organic chemistry. Titan’s atmosphere and ionosphere has striking similarities to current theories of these regions around Earth 3.5 billion years ago. The Cassini spacecraft has been in orbit around Saturn since 2004 and carries a wide range of instruments for investigating Titan’s ionosphere, among them the Langmuir probe, a “space weather station”, manufactured and operated by the Swedish Institute of Space Physics, Uppsala. This thesis presents studies of positive ions, negative ions and negatively charged dust grains (also called aerosols) in Titan’s ionosphere using the in-situ measurements by the Cassini Langmuir probe, supplemented by the data from particle mass spectrometers. One of the main results is the detection of significant (up to about 4000 cm-3) charge densities of heavy (up to about 13800 amu/charge) negative ions and dust grains in Titan’s ionosphere below 1400 km altitude. The dust is found to be the main negative charge carrier below about 1100 km on the nightside/terminator ionosphere, forming a dusty plasma (also called “ion-ion” plasma). A new analysis method is developed using a combination of simultaneous observations by multiple instruments for a case study of four flybys of Titan’s ionosphere, further constraining the ionospheric plasma charge densities. This allows to predict a dusty plasma in the dayside ionosphere below 900 km altitude (thus declaring it a global phenomenon), as well as to empirically estimate the average charge of the negative ions and dust grains to between -2.5 and -1.5 elementary charges. The complete Cassini dataset spans just above 13 years, allowing to study effects of the solar activity on Titan’s ionosphere. From solar minimum to maximum, the increase in the solar EUV flux increases the densities by a factor of ~2 in the dayside ionosphere and, surprisingly, decreases by a factor of ~3-4 in the nightside ionosphere. The latter is proposed to be an effect of the ionospheric photochemistry modified by higher solar EUV flux. Modelling photoionization also reveals an EUV trend (as well as solar zenith angle and corotational plasma ram dependencies) in the loss rate coefficient.

Beryllium-7 (Be-7) only decays by electron capture into lithium-7 (Li-7) with a half life of 53 days. We study the effect of ionization on this decay rate. We do so by trapping a Be-7 ion plasma in a cylindrical Malmberg-Penning trap and measuring Be-7 and Li-7 concentrations as functions of time by using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). We have simulated these signals in a 2-dimensional electrostatic particle-in-cell (PIC) code. The two spectrum peaks merge at high ion densities whereas at low ion densities they can be resolved. The merged peak shifts linearly according to the relative abundances of these species. We have also simulated singly-ionized beryllium-7 hydride (BeH+) and Li-7 ion plasmas at high densities. These two separate peaks shift according to their relative abundances. We describe an analytical model that explains how these peaks shift.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T12:34:18Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T12:34:18Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T12:34:18Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T12:34:18Z (GMT). No. of bitstreams: 0 / O entendimento dos mecanismos de degradação que agem sob os nanocompósitos poliméricos frente ao intemperismo (luz UV, calor, oxigênio, chuva ácida, entre outros), é o ponto chave para o desenvolvimento de novos aditivos e novas aplicações. Para este trabalho a síntese do nanocompósito foi realizada no estado fundido, utilizando-se uma extrusora de dupla rosca. A matriz polimérica utilizada foi o HMS-PP (polipropileno com alta resistência do fundido) sintetizado por irradiação gama e a argila Montmorilonita. Para melhor compatibilização entre a matriz e a nanocarga, foi utilizada o agente compatibilizante andrido maléico. Para os ensaios de envelhecimento ambiental e acelerado em estufa, os corpos de prova foram confeccionados por meio de termoprensagem. A caracterização dos efeitos da adição de argila e do envelhecimento nos nanocompósitos, presupôs o emprego das técnicas de ensaios mecânicos, Calorimetria Diferencial Exploratória (DSC), Termogravimetria (TGA), Espectroscopia no Infravermelho por Transformada de Fourier (FT-IR), Espectrometria de Fluorescêcia de Raios X por Dispersão de Comprimento de Onda (WDXRF), Microscopia Eletrônica de Varredura (MEV), Índice de Fluidez (IF), Difração de Raios-X (DRX) e Espectroscopia de Energia Dispersiva (EDS). Foram ensaiadas amostras com 0,1; 1; 3; 5 e 10% de argila. A amostra com porcentagem de 5% de argila demonstrou uma melhor estabilidade frente ao ensaio de envelhecimento ambiental e no envelhecimento acelerado em estufa. Por outro lado na amostra com maior porcentagem de argila (10%) ocorreu o inverso, sob ensaio ambiental houve maior degradação e sob envelhecimento acelerado em estufa, manteve-se resistente até 56 dias de envelhecimento. Nas porcentagens estudas (menor que ≤ 3%) de argila, pode-se constatar um equilíbrio entre o efeito barreira da argila e a ação dos íons metálicos que aceleram o processo degradativo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP