Neste trabalho calculamos taxas de captura de elétrons e decaimento beta no estágio de pré-supernova, para espécies nucleares da camada fp que são fundamentais nessa etapa da evolução estelar. Enfatizamos as transições entre estados de baixa energia. No cálculo dos elementos de matriz nucleares foram utilizados modelos microscópicos. Dados experimentais e densidades de níveis foram empregados na construção da função de partição nuclear. Foi avaliado o impacto de nossos cálculos nas abundâncias isotópicas e na derivada temporal da fração de elétrons, comparando o nossos resultados com cálculos mais simples. Concluímos de nosso trabalho que um cálculo mais detalhado das taxas de captura de elétrons e decaimento beta dando ênfase nas transições entre ~estados de baixa energia, pode conduzir a variações importantes nas predições sobre o posterior colapso e explosão da supernova. / ln this work we carry out calculations of electron capture and beta decay rates, at presupernova stages, from several nuclei of the fp region that are important in this stages of stellar evolution. We emphasize transitions between low energy states. The nuclear matrix elements was calculated using microscopic models. We used experimental data and level densities in the construction of the nuclear partition function. We estimated the influence of ours calculations in the isotopic abundances and in the temporal variation of the electron fraction. We compared ours results with nives calculations. We conclude that a more detailed calculation of the electron capture and beta decay rates giving emphasize to the transition between low energy states can lead importants variations to predictions about the subsequent collapse and supernova explosion.

Foram estudados os decaimentos BETA-, BETA+ e por captura de elétrons do 132 Cs. Foram medidas misturas multipolares E2/M1 de transições pelo método de correlação angular direcional gama-gama. Foi aplicado o modelo de Bohr na formulação K. Kumar e M. Baranger ao 132 Xe e os resultados são discutidos. / The 132 Cs BETA-, BETA+ and electron capture decays have been studied. New gamma transitions and electron capture feedings were determined. Some E2/M1 multipole mixings of gamma transitions in 132 Xe and 132Ba were measured with the gamma-gamma angular directional correlation method. The Bohr\'s collective model with K. Kumar and M. Baranger\'s solution was applied to 132 Xe and the results were discussed.

O estado fundamental e propriedades térmicas de um sistema de bosons não relativísticos interagentes por uma interação repulsiva de dois corpos, são investigados através de uma aproximação Gaussiana auto-consistente que consiste em escrevermos o operador densidade variacionalmente determinado como o funcional Gaussiano mais geral dos operadores de campo. Resultados a temperatura finita são obtidos, incluindo transições de fase, no contexto do ensemble grand-canônico. Através de truncamentos na aproximação Gaussiana completa podemos reproduzir resultados tradicionais de Bogolyubov e de Lee, Yang e Huang. A aproximação Gaussiana completa fornece uma fase condensada que é termodinamicamente instável e uma fase não condensada que não difere essencialmente de uma teoria livre quando forças de contato e um esquema de renormalização padrão são usados. Como alternativa, uma teoria dependente do cut-off no momento é desenvolvida para um sistema diluído de bosons interagentes. A aproximação Gaussiana gera um espectro de quasi-partículas que contém um gap na energia, em conflito com os resultados perturbativos. Para investigar o espectro de excitações na teoria efetiva, é desenvolvida uma formulação dependente do tempo e o regime de pequenas oscilações para os parâmetros variacionais é estudado. São obtidas então as mesmas energias utilizadas no cálculo das ocupações estáticas. / The ground-state and thermal properties of a system of non-relativistic bosons interacting through repulsive two-body interactions are investigated using a self-consistent Gaussian mean-field approximation which consists in writing the variational determined density operator as the most general Gaussian functional of the quantized field operators. Finite temperature results are obtained, including phase transitions, in the grand canonical framework. Contact is made with the results of Bogolyubov and Lee, Yang and Huang in terms of particular truncations of the full Gaussian approximation. The full Gaussian approximation gives a condensate phase which is thermodinamically unstable and a non-condensate phase that does not differ essentially from a free phase when contact forces and standard renormalization scheme are used. As an alternative an effective cut-off dependent theory is developed for a dilute interacting bose system. The Gaussian approximation generates a quasi-particle spectrum having an energy gap, in conflict with perturbation theory results. In order to investigate the excitation spectrum of the effective theory, a time-dependent formulation is developed and the small oscillation regime for the variational parameter is studied. The same energies used in the calculus of the static occupations are obtained.

eng Distribuições angulares, referentes ao espalhamento inelástico de dêuterons nos isótopos de ANTPOT 94,98 Mo e à excitação dos primeiros estados coletivos 2 POT.+ E 3 POT.-, foram obtidas com dêuterons incidentes de 13,2 MeV e 16,0 MeV, utilizando o acelerador Pelletron da Universidade de São Paulo. Os dêuterons emergentes da reação foram analisados por um espectrógrafo magnético tipo polo-partido de Enge e registrados em placas de emulsão posicionadas na sua superfície focal. As seções de choque diferenciais, na energia incidente de 13,2 MeV, foram medidas em 18 ângulos de espalhamento, detalhando, particularmente para as excitações quadrupolares de ambos os isótopos, a região de máxima interferência nuclear-coulombiana (CNI) e também aquela onde a excitação nuclear predomina. A análise foi feita na aproximação de Born com ondas distorcidas e potencial óptico deformado (DWBA-DOMP), utilizando parâmetros ópticos globais. O ajuste das previsões sobre as medidas de CNI com dêuterons, que interagem isoescalarmente com o núcleo, foi realizado pelo método dos mínimos quadrados, permitindo a extração dos parâmetros correlacionados delta POT.N IND.L e C = delta POT.C IND.L/DELTAPOT.N IND.L , com suas incertezas experimentais, onde deltaPOT.N IND.L é o comprimento de deformação nuclear e deltaPOT.C IND.L., o comprimento de deformação de carga. Esses parâmetros possibilitaram, dentro dos modelos adotados, a determinação da razão dos momentos quadrupolares e octupolares das distribuições de nêutrons e prótons,M IND.n/M IND.p, bem como os respectivos valores das probabilidades reduzidas de transição elétrica, B(EL), e isoescalar, B(ISL). O parâmetro C, que é diretamente proporcional à [B(EL)/B(ISL)] POT.1/2, foi obtido com precisão da ordem de 2% para as excitações quadrupolares e de aproximadamente 7% para as octopolares, para ambos os isótopos, nos estudos de CNI aqui apresentados. ) Os resultados experimentais indicam, de forma coerente, que as transições para os estados 2 POT.+ IND.1 e 3 POT.- IND.1nos núcleos de ANTPOT 94 Moe ANTPOT 98 Mo são mais influenciadas pelos prótons do que pelos nêutrosn, em relação à previsão do modelo coletivo homogêneo N/Z. / eng Experimental angular distributions for deuteron inelastic scaterring by 94,98Mo excitating the first 2+ and 3- collective states were obtained using the deuteron beam of the São Paulo Pelletron accelerator, at incident energies of 13.2 MeV and 16.0 MeV. The ejectiles of the reactions were momentum analyzed by an Enge split-pole magnetic spectrograph and detected in nuclear emulasion plates exposed at the focal plane. The differential cross sections, corresponding to the incident energy of 13.2 MeV, were measured for both isotopes at 18 scattering angles, detailing, in particular for the quadrupolar excitations, not only the region of maximum Coulomb-nuclear interference (CNI), but also the region where the nuclear interaction is predominant. The analysis was performed in the framework of the collective distorted wave Born approximation (DWBA) within a deformed optical model potential (DOMP) approach, using well tested global optical model parameters for deuterons. Since the deuteron is a projectile of isoscalar character, the fit of the DWBA-DOMP predictions to the CNI measurements, by means of the least squares method, allowed the simultaneous extractions of the correlated parameters NL and C= CL/NL, with their experimental uncertainties, where NL and CL are, respectively, the nuclear (mass) and charge deformation lengths. These experimental quantities yielded, within the adopted models, values of the ratio Mn/Mp for the quadrupolar and octupoular moments of the neutron and proton distributions, and also for the corresponding electric [B(EL)] and isoscalar [B(ISL)] reduced transition probabilities. The C parameters, which are proportional to the ratio [B(EL)/B(ISL)]1/2, were determined in the present CNI studies, for both 94,98Mo, within a 2% statistical uncertainty level for the 2+1 excitations and within ~ 7% for the 3-1 ones. The experimental results reveal, in a consistent way for both isotopes, protons to contribute more than neutrons to the first quadrupolar and octupolar excitations, with respect to the homogeneous collective model expectation of N/Z.

Foram realizadas medidas de espectroscopia gama simples, de espectroscopia. gama-gama em coincidência e de correlação angular para o estudo de \'ANTPOT 194 PT\', a partir do decaimento por \'beta POT. +\' e por captura eletrônica de \'ANTPOT 194 AU\'. Foram determinadas, utilizando um cálculo covariante, as energias e as intensidades de 167 transições gama, das quais 31 pela primeira vez: 212 keV, 243 keV, 304 keV, 338 keV, 363 keV, 366 keV, 373 keV, 398 keV, 421 keV, 436 keV, 500 keV, 602 keV, 627 keV, 699 keV, 807 keV, 814 keV, 857 keV, 901 keV, 1121 keV, 1262 keV, 1346 keV, 1388 keV, 1474 keV, 1488 keV, 1535 keV, 1541 keV, 1565 keV, 1665 keV, 1675 keV, 1775 keV e 1780 keV. O esquema de níveis obtido contém 45 estados; destes estados, 4 foram determinados pela primeira vez: 1373 keV, 1737 keV, 2003 keV e 2140 keV. Foram determinados os valores para as razões de mistura multipolar \'delta\'(E2/M1) das transições mais intensas utilizando o método de correlação angular direcional gama-gama. Utilizando elipses de correlação, foi possível determinar ou restringir os valores do spin e/ou paridade de 7 níveis: 1373 keV, 1737 keV, 1778 keV, 1930 keV, 2052 keV, 2134 keV e 2157 keV. Cálculos usando o formalismo de Kumar e Baranger para a resolução do Hamiltoniano de Bohr foram realizados para o núcleo \'ANTPOT 194 PT\'. Foram então determinados níveis e propriedades eletromagnéticas e os resultados, discutidos. / Single gamma ray spectroscopy, gamma-gamma spectroscopy and gamma-gamma directional angular correlation have been performed to study the \'ANTPOT 194 PT\', following the \'beta POT. + \' decay and electron capture of \'ANTPOT 194 AU\'. We have determined, using covariant calculations, energies and intensities of 167 gamma transitions, 31 of them for the first time: 212 keV, 243 keV, 304 keV, 338 keV, 363 keV, 366 keV, 373 keV, 398 keV, 421 keV, 436 keV, 500 keV, 602 keV, 627 keV, 699 keV, 807 keV, 814 keV, 857 keV, 901 keV, 1121 keV, 1262 keV, 1346 keV, 1388 keV, 1474 keV, 1488 keV, 1535 keV, 1541 keV, 1565 keV, 1665 keV, 1675 keV, 1775 keV and 1780 keV. The decay scheme contains 45 levels; 4 of these states have been determined for the first time: 1373 keV, 1737 keV, 2003 keV and 2140 keV. We have also determined values for the multipole rnixing ratios \'delta\'(E2/M1) in the case of the strongest transitions, using directional gamma-gamma angular correlation. With the angular correlation ellipses, it was possible to determine or to restrict the spin and/or parity values of 7 levels: 1373 keV, 1737 keV, 1778 keV, 1930 keV, 2052 keV, 2134 keV and 2157 keV.

Magister Scientiae - MSc / The odd – odd Tl nuclei with A ≥ 190 have moderate oblate nuclear deformation and show rotational bands built on different quasiparticle excitations. Several phenomena, not yet fully understood, were observed in these nuclei, such as large signature splitting in the yrast band (built on a πh9/2⊗νi13/2 configuration), possible non – axiality of the nuclear shape, etc. In this work the high – spin states in 194Tl were studied. The 194Tl nuclei were produced in the 181Ta (18O, 5n) 194Tl reaction at a beam energy of 93 MeV and the γ - rays were detected using the AFRODITE array. The obtained extended level scheme of 194Tl is presented and discussed in this work. CSM (Cranking shell model) and TRS (Total Routhians Surface) models were both applied to interpret the results for band 1. The results were compared with the neighboring isotone 193Hg. / South Africa

The accurate replication of the mammalian genome is a complex and logistically challenging process. The entirety of the genome must undergo a single duplication with as little error as possible. This must occur in a coordinated fashion and over suitably short time scale so as to allow timely cellular division within a cell cycle that is typically around 24 hours in a human cell. A great wealth of knowledge already exists describing various aspects of the S phase, during which this replication of the genome occurs. This data has been gathered over a variety of model systems, ranging from inferences from the replicative mechanics of SV40 through to direct observations of replication in mammalian cells.In order integrate this data and determine the value of inferences from different data sources, quantitative models of the mammalian cell S phase are required. This study documents the development of several such models and the exploration of the influences that experimentally determined parameters and different mechanistic theories can have on the behaviour of a simulated S phase. Of particular exploratory interest were the modes of activating replication of replicon clusters, with the aim of simulating experimentally observed dynamics. Additionally, the study also aimed to investigate the variation of replication fork rates and the density of origins of replication, along with the relationship that occurs between the two during both replicational stress and during a normal S phase. Through an iterative series of models, relevant parameters and key theories are sequentially explored so as to better understand the S phase. Particularly influential parameters were identified and studied in detail, with experimental determination where necessary in order to more accurately inform the model system. Conclusions concerning the behaviour of the system and the potential impact of the results were drawn upon the completion of each level of modelling and experimental work.To conclude the study, a linear model simulating the genome of the MRC5 cell line was used to estimate the modes activation of DNA replication along chromosomes in order to recreate experimentally observed replication dynamics. Experimentally determined profiles of replication fork rates and the density of origin firing were also determined for the MRC5 cell line, and were used to populate the model with accurate and appropriate data. Using the model to simulate S phase through a variety of behavioural parameters, realistic S phase dynamics were found to occur through a combination of de novo activation of replicon clusters and a specific probability of neighbour activation by completed clusters. These derived mechanics, when performed on a system correctly parameterised with suitable data, can simulate experimentally observed phenomena. The development of the model highlighted the requirements of data fit for purpose, and the study also stresses the need for critical consideration of inferences made between different model systems.

La structure du noyau N = Z doublement magique 56Ni (N = 28, Z = 28) a été étudiée en mesurant les réactions de transfert á un et deux nucléons. Le transfert nous donne des informations sur deux aspects physiques différents: la fermeture de couche N=28 et l’intensité de l’appariement neutron-proton. Le nombre magique N=28 est particulier, car c’est le premier créé par le spin-orbit. La double magicité permet la détermination de la nature de particule indépendante des voisins N±1 par réaction de transfert d’un nucléon. De plus, en tant que noyau N=Z a couches fermeés, le 56Ni est un noyau clé pour l’étude de l’apparement np dans la plus grande couche accessible expérimentalement. L’apparement np se manifeste dans le canal isoscalaire (T=0) et isovecteur (T=1). L’intensité relative de chaque canal révèle la nature collective des états. L’expérience de ce travail a eu lieu au GANIL-Caen, en France, avec un faisceau radioactif de 56Ni á 30MeV / u produit par frag- mentation de 58Ni et purification avec le spectromètreLISE. Les mesures ont été effectuées en cinématique inverse sur des cibles CH2 et CD2. Les détecteurs MUST2 et TIARA ont été utilisés pour la détection de éjectiles légers et couvraient presque 4π. En outre, quatre détecteurs germanium d’EXOGAM ont été utilisés pour les coïncidences de particules-gamma afin d’identifier l’état peuplé du résidu de réaction. Pour étudier le gap de N=28, nous étudions la spectroscopie du 55Ni par les réactions de transfert de nucléons (d, t) et (p, d) sur le 56Ni. Le spectre en énergie d’excitation est déduit de la mesure des éjectiles légers seulement. Ensuite,les coincidences particule-gamma sont utilisées pour améliorer la résolution et identifier les principaux états peuplés. La comparaison des distributions angulaires ainsi obtenues avec des calculs DWBA permet d’extraire les facteurs spectroscopiques pour les états de particules et de trous ainsi peuplés. En ce qui concerne l’appariement np, nous avons analysé la réaction 56Ni(d,α)54Co qui réalise un transfert de paires neutron-proton. Un affaiblissement du canal T=0 á cause de l’effet du spin-orbite est attendu. La sélectivité en ∆T=0 de la réaction (d, α) permet d’étudier plus en détail le canal isoscalaire T = 0. / The structure of the unstable doubly ma- gic nucleus 56Ni has been investigated by measuring one- and two-nucleon transfer reactions. Each trans- fer reaction provides information for two different physical aspects: the robustness of the N=28 shell gap and the strength of the neutron-proton pairing. 56Ni is a self-conjugate doubly magic nucleus with N=28 and Z=28. The magic number 28 is a peculiar shell closure created by spin-orbit splitting effects. The double magicity makes the determination of the single-particle nature of their N±1 neighbors by one-neutron transfer reaction of major interest to test both the robustness of shell closures as well as the evolution of particle and/or valence orbitals. Moreover 56Ni, as a N=Z nucleus with fully closed shells, is a key nucleus to investigate neutron-proton pairing in the largest shell accessible experimentally, the fp shell. Neutron-proton pairing can occur both in the isoscalar (T=0) and in the isovector (T=1) channels. The relative intensity of both channels reveals the collective nature of the states. The radioactive beam of 56Ni was produced at GANIL-Caen, France at 30 MeV/u by fragmentation of 58Ni and purification with the LISE spectrometer. The experimental set-up used, consists of the TIARA- MUST2-EXOGAM combination which provides an al- most 4π coverage and the ability to perform particle- γ coincidences. To probe the N=28 gap, we studied the spectroscopy of 55Ni through one-nucleon trans- fer reactions on 56Ni. The excitation energy spectrum is deduced by measuring the light ejectiles only, while particle-γ coincidences are used to improve the re- solution of the populated states and select the main ones. Comparison in between the extracted angular distributions and DWBA calculations allow the extraction of the spectroscopic strength of the hole- and particle- states populated by these one neutron pick- up reactions. As for neutron-proton pairing, a weakening of the strength is expected in the T=0 channel from previous results. The selectivity in ∆T=0 of the 56Ni(d,α)54Co reaction enables further investigation of the isoscalar channel contribution.

Previously developed Zn decay schemes were limited by a number of factors including low production rates and detector efficiencies making it impossible to place weak transitions. Furthermore, most of the published results are from initial exploratory measurements while subsequent studies in this region either ignored the data obtained from the Zn decays or was not analyzed due to the focus on more exotic nuclei. In the current experiments, a nearly pure beam of the Cu isotope was provided by the Holifield Radioactive Ion Beam Facility (HRIBF) for the study of the Cu -> Zn -> Ga -> Ge β-decay chain using the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS) setup. The high efficiency of the detector system along with the nearly pure primary beam allowed a detailed study of the γ-ray emission from the decay chain without any member of the decay chain being dominant. The γγ and βγ gamma coincidence data obtained from the experiment was used to develop revised decay schemes in which statistical significance for each observed coincidence peak was determined quantitatively. Presented in this work are updated and expanded decay schemes with new energy levels along with new βeeding intensities and logft values for the Zn -> Ga decays. In each of the Zn decays, a number of new energy levels and transitions have been proposed to the structure of respective Ga isotopes in addition to correcting discrepancies from previous works. The 74Zn β decay now has 29 new γ rays assigned to 74Ga in addition to previous 35 transitions (Winger et al., 1989} depopulating 19 energy states, including 7 new ones. The maximum level energy is increased from previous 1086- to 1555-keV. Similarly, the updated 75Zn decay scheme has its level energy increased from previous (Ekstrom et al., 1986) 3209- to 3924-keV, with addition of 37 new energy levels and 53 new γ rays. New decay scheme for 76Zn is established up to 2603 keV, similar to previous literature (Ekstrom et al.) with addition of 4 new energy levels and total of 5 new γ-ray transitions. In case of 77Zn decay, we proposed the decay scheme up to 3948 keV with addition of 8 new energy levels and 10 new γ-ray transitions.

The National Nuclear Data Center (NNDC) contains a compilation of information on the beta decays of Gallium isotopes. In the mass range A = 74 to 77, the Germanium daughters lie close to or at the valley of stability leading us to believe the decays would have been well studied. However, closer inspection indicates significant conflict for placement of gamma rays and energy levels between different measurements, especially for upper-lying states. Detailed beta-decay studies for the 74-77Ga isotopes were performed using a high resolution four clover Hyper-Pure Germanium (HPGe) detector system with two beta scintillators in the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL) to better understand the structure of the corresponding 74-77Ge daughter nuclei. In our experiments, use of a high-resolution mass separator greatly improved the purity of the samples in comparison to previous measurements. Besides that, the efficiency of the detector system we utilized was much higher than used in previous studies. We also established a method to determine statistically significant gamma gamma coincidence relationships to add reliability to the placement of gamma rays to energy levels and avoid experimental biases. From our analysis, we have established comprehensive decay schemes for all four Germanium nuclei in this study. In most cases, we have extended the energy levels to cover more of the energy window available for beta decay. Our proposed 74Ge decay scheme contains 44 energy levels occupying up to 4.36-MeV with the placement of 99 gamma rays. Similarly, 75Ga decay scheme contains 72 gamma rays with 29 energy levels occupying up to 2.75 MeV. The 76Ga decay scheme has 49 excited states with 100 gamma rays occupying up to 4.81 MeV. And, the 77Ge decay scheme has 68 gamma rays and 34 energy levels occupying up to 3.14 MeV. Based on the expanded level schemes, betaeeding intensity and log(ft) value lower limits were calculated and attempts were made to assign the spin-parity of the observed states. The resulting level schemes were then compared with the Nushellx theoretical predictions.