Synteza, modyfikacja powierzchni i charakterystyka fizykochemiczna wielofunkcyjnych nanomateriałów luminescencyjnych zawierających jony pierwiastków ziem rzadkich

Wydział Chemii: Zakład Ziem Rzadkich

Measurement of picosecond lifetimes in neutron-rich Xe isotopes

Background: Lifetimes of nuclear excited states in fission fragments have been studied in the past following isotope separation, thus giving access mainly to the fragments' daughters and only to long-lived isomeric states in the primary fragments. For the first time now, short-lived excited states in the primary fragments, produced in neutron-induced prompt fission of U-235 and Pu-241, were studied within the EXILL&FATIMA campaign at the intense neutron-beam facility of the Institute Laue-Langevin in Grenoble. Purpose: We aim to investigate the quadrupole collective properties of neutron-rich even-even Xe-138,Xe-140,Xe-142 isotopes lying between the double shell closure N = 82 and Z = 50 and a deformed region with octupole collectivity. Method: The gamma rays emitted from the excited fragments were detected with a mixed array consisting of 8 HPGe EXOGAM Clover detectors (EXILL) and 16 LaBr3(Ce) fast scintillators (FATIMA). The detector system has the unique ability to select the interesting fragment making use of the high resolution of the HPGe detectors and determine subnanosecond lifetimes using the fast scintillators. For the analysis the generalized centroid difference method was used. Results: We show that quadrupole collectivity increases smoothly with increasing neutron number above the closed N = 82 neutron shell. Our measurements are complemented by state-of-the-art theory calculations based on shell-model descriptions. Conclusions: The observed smooth increase in quadrupole collectivity is similar to the evolution seen in the measured masses of the xenon isotopic chain and is well reproduced by theory. This behavior is in contrast to higher Z even-even nuclei where abrupt change in deformation occurs around N = 90.

On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an SN2-ET dichotomy in alkylation reactions

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c-C3H5CH2F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative SN2 concerted mechanism, discerning thus this mechanistic SN2-ET dichotomy.

Simulazione Monte Carlo del muon veto dell'esperimento XENON1T

Numerose osservazioni astrofisiche e cosmologiche compiute a partire dagli anni '30 confermano che circa il 26% dell'Universo è costituito da materia oscura. Tale materia ha la particolarità di interagire solo gravitazionalmente e, forse, debolmente: essa si presenta massiva e neutra. Tra le numerose ipotesi avanzate riguardanti la natura della materia oscura una delle più accreditate è quella delle WIMP (Weakly Interacting Massive Particle). Il progetto all'avanguardia nella ricerca diretta delle WIMP è XENON presso i Laboratori Nazionali del Gran Sasso (LNGS). Tale esperimento è basato sulla diffusione elastica delle particelle ricercate su nuclei di Xeno: il rivelatore utilizzato è una TPC a doppia fase (liquido-gas). La rivelazione diretta di materia oscura prevede l'impiego di un rivelatore molto grande, a causa della piccola probabilità di interazione, e di ambienti a bassa radioattività naturale, per ridurre al minimo il rumore di fondo. Risulta necessario inoltre l'utilizzo di uno schermo attivo che individui particelle di alta energia, in particolare muoni cosmici, che possono produrre falsi segnali. È stato realizzato a tale scopo un sistema di Muon Veto composto da un grande cilindro d'acqua posto attorno alla TPC, equipaggiato con 84 fotorivelatori atti ad osservare i fotoni ottici emessi per effetto Čherenkov dai raggi cosmici. Il presente lavoro di tesi si colloca nell'ambito di un programma di simulazione Monte Carlo, creato per realizzare virtualmente l'esperimento XENON1T e per effettuare studi preliminari. Lo scopo di tale lavoro è stato quello di contribuire alla scrittura e alla verifica del codice di simulazione e allo studio di eventi di muoni cosmici da esso generati. L'analisi dati è stata effettuata scrivendo un programma in C++ in grado di analizzare i risultati forniti dal simulatore e di generare degli Event Display statici e dinamici per una visualizzazione efficace degli eventi.

Moléculas simples com aplicação na medicina

O trabalho apresentado, foi realizado no âmbito do mestrado em Química para o ensino, da Universidade de Évora e tem como tema " Moléculas Simples de Aplicação na Medicina". A abordagem deste tema deve-se à necessidade cada vez maior de um ensino que motive os alunos e lhes proporcione um gosto maior pelo estudo das ciências, uma vez que cada vez mais os jovens estudantes revelam pouca motivação e gosto pelo estudo das áreas científicas quer ao nível do ensino secundário quer ao nível do ensino superior. Pretende-se também tentar compreender e explicar o porquê das suas desmotivações e tentar adaptar novas abordagens a temas que suscitem nos jovens um maior interesse, uma melhor compreensão da importância das ciências, da tecnologia na vida quotidiana de todos nós no que respeita ao nosso bem-estar e à nossa saúde. Numa primeira parte é feita uma revisão sobre os principais conteúdos propostos a desenvolver em sala de aula, conteúdos esses que sustentam o estudo do xénon como anestésico e dos perfluorocarbonetos como substitutos do sangue. A segunda parte integra um programa orientador, seguindo as metodologias e estrutura do programa homologado pelo ME para o 12º ano de escolaridade, e protocolos de algumas actividades de carácter experimental laboratorial propostas. Estas actividades têm como finalidade estimular a curiosidade e facilitar a consolidação das matérias. ABSTRACT: The present study was carried out under the Master's Degree in Chemistry for Teaching, taught at the University of Évora under the theme "lmplementation of Simple Molecules in Medicine". The approach to this issue is due to an increasing need for teaching that motivates students and sharpen their senses for the study of science because, increasingly, young students show little motivation and passion for the study of science, both at secondary school and higher education terms. The aim is also trying to understand and explain the reason of their discouragement and try new approaches to issues that raise young in a better understanding of the importance of science and technology in everyday life for all of us in what concerns to our welfare and our health. ln the first part there is an overview of the major content areas to develop in the classroom. These contents support the study of xenon as an anesthetic and perfluorocarbons as blood substitutes. The second part includes the syllabus, following the methodologies and structure of the curriculum approved by the ME to the 12th grade and protocols of some activities for an experimental laboratory. These activities intend to stimulate curiosity and facilitate the consolidation of materials.

Development of numerical tools for the simulation, design and optimization of a Helicon Plasma Thruster

This work thesis focuses on the Helicon Plasma Thruster (HPT) as a candidate for generating thrust for small satellites and CubeSats. Two main topics are addressed: the development of a Global Model (GM) and a 3D self-consistent numerical tool. The GM is suitable for preliminary analysis of HPTs with noble gases such as argon, neon, krypton, and xenon, and alternative propellants such as air and iodine. A lumping methodology is developed to reduce the computational cost when modelling the excited species in the plasma chemistry. A 3D self-consistent numerical tool is also developed that can treat discharges with a generic 3D geometry and model the actual plasma-antenna coupling. The tool consists of two main modules, an EM module and a FLUID module, which run iteratively until a steady state solution is converged. A third module is available for solving the plume with a simplified semi-analytical approach, a PIC code, or directly by integration of the fluid equations. Results obtained from both the numerical tools are benchmarked against experimental measures of HPTs or Helicon reactors, obtaining very good qualitative agreement with the experimental trend for what concerns the GM, and an excellent agreement of the physical trends predicted against the measured data for the 3D numerical strategy.